Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: hitech on January 10, 2005, 04:58:13 PM
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Start with the assumption like you stated that no torque is produced by jet engines: If they do, it would just go into more torque for the turbo prop, so lets assume they do not.
Lets say that the shaft is spinning at 10000rpm and 100 ft/lbs torque at the front compressor turbin.
Now when that is sent to the gear box with about a 10 to 1 speed reduction the shaft at the prop would have 1000 ft/lbs torque. This change in torque i.e. 900 ft/lbs would be transmited to the airframe thew the gear box mounts.
Do you agree?
HiTech
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No torque would be transmitted to the airframe. Gyroscopic progression would still have an effect though.
g00b
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yes a turboprop Produceses torque on the mounts and airframe but only when the Prop pitch is increased . they have a Torque staft w/ a mag pickup between the eng and gearbox that measures the torque .
i would say that most of the torque is transmitted to the shaft and turbine wheel that drives the gearbox and not as much on the mounts or airframe.
Remember a turbo shaft /prop engine only uses the last 1-2 stages of Turbine to drive the shaft and gearbox . the rest of the jet engine is basically a seperate enity
for a normal Jet engine very little torque is applied on the airframe . (thats why alot of the engines are hung w/ only 3 bolts )
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A propeller powered by a turbine produces the same torque on an airframe as a propeller powered by a reciprocating engine of the same power. The propeller does not know if it's being powered by a turbine or a recip.
In the aircraft I normally fly the actual torque produced by the propeller is used to indicate the amount of power the engine is producing (PT6-27 and PT6- 6X). The -27 redlines at 1500 pounds feet and the -60 I think @ 3200 pounds feet.
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Ok with the gearbox in mind I think I see how torque could be transmitted to the airframe. If there was no gearbox there would be no torque, correct?
g00b
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Originally posted by hitech
Start with the assumption like you stated that no torque is produced by jet engines: If they do, it would just go into more torque for the turbo prop, so lets assume they do not.
Lets say that the shaft is spinning at 10000rpm and 100 ft/lbs torque at the front compressor turbin.
Now when that is sent to the gear box with about a 10 to 1 speed reduction the shaft at the prop would have 1000 ft/lbs torque. This change in torque i.e. 900 ft/lbs would be transmited to the airframe thew the gear box mounts.
Do you agree?
HiTech
Umm ... no. Only the power lost in the gearbox would be applied to the airframe. All the torque transferred to the prop from the gearbox is not ... I think. So if the gearbox power loss is 20%, up to 20% of the torque will be transferred to the airframe.
I found this document:
http://www.swedflight.com/addons/guide_to_turboprop_aircraft.pdf
"The Gas Generator
is a jet engine that produces a high speed gas stream aimed to the Power Turbine which will then rotate and transfer this power to the Power Generator.
The two parts are not physically connected which makes it possible to start the engine with still standing propellers – actually you can hold the propeller still with bare hands for a while at start-up if you like too.
The Power Generator
is connected to the Propellers via a Propeller Gearbox – necessary as the Gas Turbine spins with a whopping 44.000 RPM and it would be a bit unhealthy to put out the generated power directly to the propeller to say the least."
Since the jet engine is simply blowing air on a windmilling turbine (like my garden hose was) I do not see how any torque is generated.
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(http://www.aerospaceweb.org/question/propulsion/jet/turboprop.jpg)
(http://www.aerospaceweb.org/question/propulsion/jet/turboshaft2.jpg)
Come to think of it; a conventional Sikorsky helicopter layout does not spend 50% of its power countering torque with the tail rotor. Obviously most of the engine's power is transferred directly to the main rotor, and the only torque transferred to the airframe is from the power loss in the gearbox.
Does this make sense?
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So Hitech are we getting the Westland Wyvern?
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Power = RPM x 2 x pi x Torque
A spinning prop has RPM, there is power, so there is torque.
In a turbo jet, the spinning spool has a torque associated with it, the compressor section aerodynamic forces all wrapping around the rotor in a like direction. The compressor stators all need to wrap the torsional force around the casing the opposite direction.
In the turbine section, as the combustion products force the rotors to spin, the torque wraps the rotor opposite to the wrap of the compressor. The turbine stators wrap opposite of the compressor stators. When the rotor achieves a constant speed, the torsional forces largely balance, leaving pure thrust.
In a fanjet where a few compressor stages act as a ducted fan, I would believe that torque would remain to be absorbed by the engine mounting.
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Pistin engines with prop: propeller torque.
Jet engines = very very little torque.
Turboprop = propeller torque.
Helicopters: Stop of tail rotor: You're dead, whooping around the main rotor. Stop the main rotor, you're also dead.
Autogyro with a pusher propeller = some torque. Hell, I tried hopping in a thingie like this.
Right?
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Originally posted by Holden McGroin
Power = RPM x 2 x pi x Torque
A spinning prop has RPM, there is power, so there is torque.
In a turbo jet, the spinning spool has a torque associated with it, the compressor section aerodynamic forces all wrapping around the rotor in a like direction. The compressor stators all need to wrap the torsional force around the casing the opposite direction.
In the turbine section, as the combustion products force the rotors to spin, the torque wraps the rotor opposite to the wrap of the compressor. The turbine stators wrap opposite of the compressor stators. When the rotor achieves a constant speed, the torsional forces largely balance, leaving pure thrust.
In a fanjet where a few compressor stages act as a ducted fan, I would believe that torque would remain to be absorbed by the engine mounting.
How does the torque get transfered to the engine mounting if there is no physical connection?
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Helicopters: Stop of tail rotor: You're dead, whooping around the main rotor
Well thats wrong. I have lost two tail rotors on two different helicopters and brought them back no problem.
The first was a S-76B, I was about 3 miles just off the number 21 oil rigg and sheared a tail rotor shaft I flew it back to the base and did a run on landing with no tail rotor. The other was a Huey 212 it also ended in a run on landing.
I can tell you that Jets and turbo props have torque assosiated with them. Jets- acceleration of mass and gyro scopic processionial torque. Turbo props-Prop torque, acceleration of mass, and gyro procession.
If there was no gearbox there would be no torque, correct?
Gear box or not there is torque.
High bypass fan jet have a rotational airflow from the bypass section and this rotational airflow creates a rotational torque.
for a normal Jet engine very little torque is applied on the airframe . (thats why alot of the engines are hung w/ only 3 bolts )
How about jet trust on the airframe is this not torque. when a engine hangs from a pylon with jet thrust present that pylon has a large torque force applied to it. Have you seen how big these bolts are? On a Be-200 there are 4 bolts an F-14 there are 12 bolts per engine. This thing about bolts doesnt wash.
Straiga
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Holy cow, rotorless lander!
Did you autorotate? Wasn't there some turning?
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http://www.mcasco.com/p1rdy.html
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Originally posted by GScholz
How does the torque get transfered to the engine mounting if there is no physical connection?
There is a physical connection. It is thru the gas going thru the engine. The stators in the engine are connected to the engine mount, rotors are connected to the engine shaft. Both the stators and rotors have aerodynamic forces associated with them.
The gas being forced thru the engine aerodynamically reacts with the stators. The stators transfer the force to the engine mount.
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Originally posted by hitech
Start with the assumption like you stated that no torque is produced by jet engines
What about the torque that caused by changing the direction of the flight?
Jet engine turbine is huge gyroscope and when the changes its pitch or yaw it should add torque in the perpendicular axis. You you change pitch gyro-effect will add yaw and same for yaw - changing direction will add torque effect on pitch.
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Originally posted by Holden McGroin
There is a physical connection. It is thru the gas going thru the engine. The stators in the engine are connected to the engine mount, rotors are connected to the engine shaft. Both the stators and rotors have aerodynamic forces associated with them.
The gas being forced thru the engine aerodynamically reacts with the stators. The stators transfer the force to the engine mount.
Are the stator vanes only in the compressor, or are they also in the generator and power turbine stages?
Stator vanes in the generator/power stage would create torque, however the stator vanes in the compressor would counter act it (at least to some degree).
Or am I wrong?
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GScholz:
I belive you are incorect about the torque change effect of a gear box.
Picture a simple gear down arange ment. I.E. One big gear driven by a small one. When the small gear drives the big gear the small one is also creating a side force picked up by the bearing of the small drive gear. This force is transmited to its mounting. Now this force will be equal to the torque at the primary shaft. Hence how the prop drag is transmited to the air frame.
HiTech
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Originally posted by GScholz
Are the stator vanes only in the compressor, or are they also in the generator and power turbine stages?
Stator vanes in the generator/power stage would create torque, however the stator vanes in the compressor would counter act it (at least to some degree).
Or am I wrong?
Gscholtz, the simplest way to look at this is through Newton's Laws. Remember, for every action there is an equal and opposite reaction. The prop turns with a force of X. The plane tries to spin in the opposite direction with exactly the same force.
If this weren't true, turbine powered helicopters would not need tail rotors.
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Right on, HiTech.
Power does not disappear by different gearing, if you see what I mean.
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from my personal experience, in regards to TF34 turbojets( I mistyped turbojet when I actually meant Turbo-fan) on the S3 viking(Navy), when we changed out an engine then powered them up for low & high turn qual, they indeed transfered torque/stress to the mounts/airframe......what percentage I am unsure of
anyhow, you could visually see the plane act like it wanted to twist in the Turn Qual area ( where we had aircraft tied down with bunch Tie-Down chains and had a JBD behind the AC) as we ramped up the throttle to 80% Military Power
when I say twist try to invision the way a beefed up muscle car will twist the front end when you romp on the pedal.....just not as violent, the torque is very minimal yet noticeable when the plane can not move
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Hi Straiga,
>High bypass fan jet have a rotational airflow from the bypass section and this rotational airflow creates a rotational torque.
Excellent explanation :-)
This leaves us with:
Propeller/piston engine: Rotational propeller slipstream -> torque
Propeller/turbine engine: Rotational propeller slipstream -> torque
(exhaust gases could counteract that if ducted properly, but I'd say they'll never get up to equal but opposite torque. Tip jets excluded! :-)
High bypass fan/jet turbine: Rotational airstream -> torque
(That one was new to me, but it makes sense)
Low bypass fan/jet turbine: hardly any rotational component -> hardly any torque
(At least, that's what I suspect.)
Regards,
Henning (HoHun)
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Originally posted by hitech
GScholz:
I belive you are incorect about the torque change effect of a gear box.
Picture a simple gear down arange ment. I.E. One big gear driven by a small one. When the small gear drives the big gear the small one is also creating a side force picked up by the bearing of the small drive gear. This force is transmited to its mounting. Now this force will be equal to the torque at the primary shaft. Hence how the prop drag is transmited to the air frame.
HiTech
Of course. Thanks, my brain was starting to hurt. ;)
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AHHHHHHHHHHHHHHHHHHHHHHHHHH.. .
Study some physics, guys.
Torque is force. FORCE IS GOVERNED BY NEWTON'S LAWS.
If you want an airplane to move forward, you must apply a force backwards. All that MUST somehow be transmitted to the airframe if the plane is to move. BASIC NEWTONIAN PHYSICS.
Trust me, I am an electrical engineer. When I design a system that has an electrical motor (torque machine) driving anything (like a pump) I need to account for the counter-torque of the motor. Yes, Virginia, the motor tries to spin in the opposite direction of the rotor motion.
Every time.
No exceptions for torque converters (we call them fluid drives), belts, direct gearing, suspension by magnetic field, force field
mounts, or welding the rotary power source directly to the frame. Again, there are
NO EXCEPTIONS.NO EXCEPTIONS
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Hi Rshubert,
>Torque is force. FORCE IS GOVERNED BY NEWTON'S LAWS.
>If you want an airplane to move forward, you must apply a force backwards. All that MUST somehow be transmitted to the airframe if the plane is to move. BASIC NEWTONIAN PHYSICS.
Good points :-)
Since you've posted that after I talked about turbojets for which I claimed "hardly any" torque, let me clarify that Newton's laws are just what leads to this conclusion:
Jet exhaust: gases without any rotational component -> no torque
Since there is no rotational force exerted on the airframe, the spinning turbine inside makes no difference for the system, and no torque is exerted on the airframe.
So "no exceptions" is true, but that doesn't mean that all engines with spinning components exert torque on the airframe.
Regards,
Henning (HoHun)
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http://science.howstuffworks.com/fpte.htm
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All energy has to go somewere.
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One big gear driven by a small one. When the small gear drives the big gear the small one is also creating a side force picked up by the bearing of the small drive gear.
In a turbo prop there is a planetary gear box. One big gear rotating around 4-6 smaller gears that set inside the big gear and attached to the turbine shaft, but not to a stationary point or mount. This is in the forward part of the engine.
HoHun, Rshubert, good points all.
One important point when you add power to a turbine the RPM as it increase from, say 5,000 rpm to 45,000 rpm during an engine spool up, torque is also present. Acceleration of a rotational mass. In the DC-10 and B-767 as power is increased the aircraft pulls to the left on spool up.
Also when the jet thrust exits in one direction, the torque leverage is excerted on the airframe in the oposite direction, as in an engine hanging on a wing pylon. For every action theres an oposite and egual reaction.
Straiga
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Can some one describe exatly how torque is transmited to an airframe on a high bypass turbofan?
HiTech
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Originally posted by hitech
Can some one describe exatly how torque is transmited to an airframe on a high bypass turbofan?
HiTech
Speaking as an aircraft mechanic that Uncle Sucker stuck in the wrong job...
A bypassing fan, or even a turbojet, will impart torque onto the turbine case (and the engine it's attached to) by forces acting on the stators within the turbine. The stators redirect the airflow into the turbine rotors to spin them, but naturally the process of deflecting airflow causes a force to be applied to the stators.
Result: Torque (just not an incredible amount of it)
Something related to this is something I heard from a pilot with the Russian Knights (combat and demonstration team, flying Su-27 Flankers). In some of their maneuvers they have to apply a small amount of rudder to counter the torque created by the Sukhoi's fans, which rotate complementory, and would roll the plane in an undesired fashion if uncorrected.
EDIT: Before anyone tries to bring up the topic of fly-by-wire on Suhkoi's, the '27 did not have it. The '33 might, and the '35 and anything newer based on the Flanker design (Berkut included) does.
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Originally posted by hitech
Can some one describe exatly how torque is transmited to an airframe on a high bypass turbofan?
HiTech
via the hot section of the engine. The torque produced there is transmitted to the engine mounts, and to the airframe.
Think of it like this: The hot section pushes power to the cold section via whatever coupling is used, right? Thus the POWER used by the fan is equal to the POWER generated in the hot section.
Torque of a rotating object is this:
HP * 5250/RPM
IF we hold horsepower constant, then Torque is inversely proportional to RPM. In other words, as speed goes up, torque goes down. This is true in any constant-horsepower application of a rotating machine, such as a turbine or electric motor.
Obviously, in a constant HP situation (power) such as the turbofan we're talking about, the torque at the hot section (rotating very fast) is lower than the torque in the fan (rotating much more slowly). Remember, the power is the SAME.
So, it becomes obvious that while the power transmitted from the fan throught the thrust bearing is the same as the power transmitted through the coupling to the fan, the torque transmitted to the airframe from the hot section is much lower than the torque transmitted by an equal horsepower--but much slower running--piston engine. The same is true for a turboprop or a turbojet, by the way. High HP produced with high rotational speed produces less torque than the same HP produced with low rotational speed.
Remember, it's the ENGINE that transfers the torque, not the prop. Forget all the propellor torque calculations--they only work for engine torque when there is no gear reduction of any kind. Any other time, you have to think in terms of POWER, and find the engine torque. That is the torque that is transmitted to the airframe.
shubie
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My 1st mis-conception was this.
IF you had a direct-drive turbofan, with no intermediate gearbox between the compressor and the propellor there would be no torque applied to the airframe, with the exception of stator induced torque and mechanical losses in bearings and such.
Correct?
Now you place a gearbox between the compressor and propellor. In order for the gearbox to do it's job it must apply a torque to the airframe to turn high-RPMs and low-torque into high-torque and low-RPMs.
Correct?
I visualize it like this.
Direct Drive: apply a rotational force to the compressor blades, measure at the propellor, should be 100% minus any frictional losses.
10:1 Geared Drive : apply a rotational force to the compressor blades, measure at the propellor, should have 10 times the torque at 1/10 the RPM. 90% of the torque is going to have to be balanced by the airframe. If you were to spin the compressor while holding the propellor, the plane is going to spin around. i.e. torque.
So... it's really the gearbox that applies the torque to the airframe. There is of course some effect from the stators and compressor blades as well as propwash and various mechanical losses but all those are probably pretty minor compares to whatever mechanical advantage you are getting out of the gearbox.
g00b
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By jove, I think he's got it!
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Originally posted by g00b
My 1st mis-conception was this.
IF you had a direct-drive turbofan, with no intermediate gearbox between the compressor and the propellor there would be no torque applied to the airframe, with the exception of stator induced torque and mechanical losses in bearings and such.
Correct?
Now you place a gearbox between the compressor and propellor. In order for the gearbox to do it's job it must apply a torque to the airframe to turn high-RPMs and low-torque into high-torque and low-RPMs.
Correct?
I visualize it like this.
Direct Drive: apply a rotational force to the compressor blades, measure at the propellor, should be 100% minus any frictional losses.
10:1 Geared Drive : apply a rotational force to the compressor blades, measure at the propellor, should have 10 times the torque at 1/10 the RPM. 90% of the torque is going to have to be balanced by the airframe. If you were to spin the compressor while holding the propellor, the plane is going to spin around. i.e. torque.
So... it's really the gearbox that applies the torque to the airframe. There is of course some effect from the stators and compressor blades as well as propwash and various mechanical losses but all those are probably pretty minor compares to whatever mechanical advantage you are getting out of the gearbox.
g00b
NOOOOOnononononononononononon ono!
There is ALWAYS torque applied to the airframe. ALWAYS. It is equal to the torque produced by the engine. NOT THE PROPELLOR or fan section or whatever. See my post above that explains it.
Take a plane, such as a P-47. Put a 2000 HP P&W radial on it. Turn said engine at 2700 rpm, and go 400 mph. Can we agree that the torque is 2000*5250/2700, or 3889 ft.lbs?
Same plane, same weight, same aerodynamics. Replace the engine with an Allison turboprop engine, hot section RPM 16000 rpm, producing 2000 HP, and the plane is going the same speed.
Now, the torque is 2000*5250/16000, or 657 ft.lbs of torque.
The propellor torque (assuming we used the same prop and the same prop RPM) is the same in both cases. Remember, the prime mover--not the power absorbing device--is what transmits torque to the mount. The propellor is beating on the AIR. The engine is beating on the PLANE.
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hrmmm, I don't see how a direct drive turbofan could produce torque. Nor do I see how the same propellor driven at the same speed could apply a different amount of torque to the airframe no matter what the power source is.
HiTech said it right from the beginning, it just didn't sink in right away.
g00b
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When you slice away all the fancy names, a high bypassing fan is really nothing more than a ducted turboprop with a LOT more blades on the 'propeller'. Direct drive or no, if a turbine engine is turning something, including itself, it is going to make torque, with one exception:
Multiple compressor/turbine sections that contra-rotate. To brake it down into something a pilot can understand, if your N1 (low-pressure compressor /w associated turbine disc) turns one way, and the N2 (high pressure compressor, /w associated turbine disc) turns in the other, the toque forces counter and the engine transfers no torque to the air frame.
This is assuming a perfect world of course. Now I just need to dig into my books and see which engines actually do this, I know there's a few....
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Originally posted by g00b
hrmmm, I don't see how a direct drive turbofan could produce torque. Nor do I see how the same propellor driven at the same speed could apply a different amount of torque to the airframe no matter what the power source is.
HiTech said it right from the beginning, it just didn't sink in right away.
g00b
Remember, it's not the PROP that transmits torque, it's the ENGINE. Big difference, man. That's a very important concept, here. Goob, you are hung up on one issue. You think "torque" is power. It isn't. Power is power, torque is force. They are different.
Another issue I see here is a lack of a gut level understanding of Newton's Laws. I'm sure you studied them in school, everybody does, but applying them is sometimes not so obvious. Remember this: For every action, there is an equal and opposite reaction. If you believe and understand that law, the rest becomes apparent. Newton's Laws are immutable constants--that's why they aren't called "Newton's suggestions" or Newton's recommendations".
Don't feel bad about this lecture, and don't feel like I am flaming you or anybody else--remember that this stuff is not obvious, and can be difficult to grasp, since it can't be tasted, felt, or smelled. I suggest you follow the link below, and get a good handle on the basic physics involved here. Then, you will see the light!
http://science.howstuffworks.com/fpte.htm
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Originally posted by Tails
When you slice away all the fancy names, a high bypassing fan is really nothing more than a ducted turboprop with a LOT more blades on the 'propeller'. Direct drive or no, if a turbine engine is turning something, including itself, it is going to make torque, with one exception:
Multiple compressor/turbine sections that contra-rotate. To brake it down into something a pilot can understand, if your N1 (low-pressure compressor /w associated turbine disc) turns one way, and the N2 (high pressure compressor, /w associated turbine disc) turns in the other, the toque forces counter and the engine transfers no torque to the air frame.
This is assuming a perfect world of course. Now I just need to dig into my books and see which engines actually do this, I know there's a few....
You're partially right. In the case above, the engine itself absorbs the torque loads. I'll bet there are some serious thrust bearings on those compressor sections.
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Turbo fan or piston engine there is somewhere a spinning shaft that is geared up/down to a rotor.................
Given the same rotor and the same footlbs at its tip then the opposing force applied to the mounting system is the same.
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Will this never end?
1. Propellers do not create torque, crankshafts and pistons do.
2. An engine does not need to apply torque on the airframe to produce thrust ... rocket engines don't.
3. If the engine produces thrust by balancing torque forces, no torque is applied to the airframe (which is what I believed turboprops did ... now I don't know what to believe).
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Torque is an element of spinning power. Rockets do not spin, hence no torque. Turbines spin, hence torque is present in the turbine.
In a turbojet, the turbine powers the compressor and all the compressor gas goes thru the turbine. The torque of the compressor can balance the torque of the turbine, so the net torque to the airframe can be near zero. (Though spinning the same way, the turbine torque is the opposite direction of compressor torque because the turbine is removing power from the airstream and the compressor is adding power to the airstream)
The power is from expanding combustion gasses and the turbine takes a bit of that power and spins the compressor to keep the brayton combustion cycle giong.
In a turboprop, the power of the engine spins a prop which imparts power to the airstream. That requires that there be rpm and torque at the prop, and that torque must be counteracted in the engine mount.
A turbo fan works much the same way as a turboprop, the horsepower of the bypass airstream is imparted by a spinning rotor disk; hence rpm and torque.
Turbine and compressors work with spinning blade disks (rotors) and static blade disks (stators) which could be analogus to pistons and cylinders. The moving piston (rotor) reacts with the static cylinder (stator) to react with expanding or compressing gas to create torque and rotational speed.
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Originally posted by Holden McGroin
In a turbojet, the turbine powers the compressor and all the compressor gas goes thru the turbine. The torque of the compressor can balance the torque of the turbine, so the net torque to the airframe can be near zero. (Though spinning the same way, the turbine torque is the opposite direction of compressor torque because the turbine is removing power from the airstream and the compressor is adding power to the airstream)
In a turboprop, the power of the engine spins a prop which imparts power to the airstream. That requires that there be rpm and torque at the prop, and that torque must be counteracted in the engine mount.
How does the propeller transfer the torque to the engine mount if there is no mechanical connection?
Originally posted by GScholz
I thought up a simple home experiment for those fortunate enough to not live in the arctic. Take a shaft (wood pole etc.) and attach a bearing to it with a handle on it ... so that you can hold the shaft while turning it.
You should now have a handle with a bearing on it with a shaft running through it.
On one end of the shaft you mount a small propeller. On the other end you mount a small fan/turbine.
Now take your garden hose and mount it on the handle/bearing so that the nozzle points in the direction of the fan/turbine (actually you should use at least two nozzles to ensure a balanced application of force on the turbine, but what the heck). You now have a very primitive jet turbine powered by tap water rather than expanding air.
Turn on the water and hold this construction by the handle.
The water will deflect off the turbine blades and make the turbine rotate in the opposite direction. Since the turbine is mounted on the shaft it will turn the shaft, and since the propeller is mounted on the other end the propeller with turn also.
You now have a turning propeller creating power, but not torque, since your hand is not mechanically connected to any moving parts at all ... except you are holding around the shaft. The only torque I can see this will create is from friction in the bearing.
See? Turning prop, forward propulsion, no imparted torque on the structure. The torque is countered (and created) by the deflection of the water.
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Originally posted by GScholz
How does the propeller transfer the torque to the engine mount if there is no mechanical connection?
(http://www.wpafb.af.mil/museum/engines/eng47.jpg)
What are those tubes from the gear case attached to?
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How does it work w/o connection? same way a cylinder head pushes a piston down with force but with no mechanical connection. Expanding gasses shove against a static cylinder head, and a moving piston.
The airfoils which are the stators in the turbine have a fluid dynamic differential pressure associated with the hot gas flowing past them.
One side it high pressure due to Newtonian ram effect, the other side is low pressure due to Bernolli's equation.
This differential pressure on the stator ring is connected to the turbine casing. The casing then has a force (torque) that needs to be countered in the aircraft structure.
In your water turbine, you will put into the engine a certian amount of thrust, associated with the impulse of the tap water nozzle against the turbine. You will get the same amount of thrust minus the mechanical inefficiency of the prop, turbine, and bearings. You still need to absorb the impulse of the water jet in the structure of the boat, so your action has a reaction.
If the turbine you use is a pelton wheel which would be appropriate, the nozzles would be pushing 90 degrees to the shaft at the pelton wheels radius, and the force of the water impulse at a radius is torque.
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Hitech is correct.
The sum of all forces must be zero, the sum of all moments must be zero. Always. Even in acceleration where you have to deal with virtual forces by the "heavy" mass (F = m*a)
So when there´s an imbalance of moments ( prop´s moment being higher due to reduction gearbox compared to the turbine shaft moment), where´s the difference gone that makes the sum zero? It´s the imbalance on the gear wheel, axis distance in the gear box comes into the game and so on. At the end it will result in an moment to the frame.
niklas
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Originally posted by Tilt
Turbo fan or piston engine there is somewhere a spinning shaft that is geared up/down to a rotor.................
Given the same rotor and the same footlbs at its tip then the opposing force applied to the mounting system is the same.
ahh, but remember, it depends on WHICH rotating member is actually imparting the torque to the mount. The prime mover does it, not the output device. An important point, but one that is getting lost in the discussions of propellor torque. Drop the concept that it is the prop that transfers the torque, and you, too will see the light.
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rshubert:
In your prat & witney example, the torque you calculated would be between the crank shaft and the gear box housing. There would be aprox. a 2 - 1 reduction in prop speed. Hence to the motor mount and air frame, it would be (3889 * 2) ft/lbs.
Except for the stator vane example: I havn't seen enyone describe how a hi bypass engine transmits torque to the mounts.
The problem I trying to solve in my head, and it is a close example to a turbo fan, is a very simple pinwheel childs toy.
Hold said pinwheel and blow on it. Asumption no torque is transmited to the handle (excpet for minor friction)
My assumption the air down wind of the pin wheel will be rotating in 2 directions.
They way I see what is happening to balance things out is that the slip stream behind the pin wheel would be rotating the oposit
the direction of the pin wheel. (air stricking angled blade goes one way pin wheel other) Once the pin wheel has reached a steady Vel the blades are also pushing air out do to drag rotating in the oposit direction of the slip stream.
Hence no torque on handle but we we have 2 masses of air rotation different directions.
HiTech
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Originally posted by Holden McGroin
How does it work w/o connection? same way a cylinder head pushes a piston down with force but with no mechanical connection. Expanding gasses shove against a static cylinder head, and a moving piston.
Nonsense. In a piston engine the pistons operate 90 degrees on the shaft and are literarily cranking the shaft. That's a rather substantial mechanical connection between shaft and engine frame. In a turbine engine the only mechanical connection would be in the bearings (with the noted exception of reduction gearing being used).
Originally posted by Holden McGroin
The airfoils which are the stators in the turbine have a fluid dynamic differential pressure associated with the hot gas flowing past them.
One side it high pressure due to Newtonian ram effect, the other side is low pressure due to Bernolli's equation.
This differential pressure on the stator ring is connected to the turbine casing. The casing then has a force (torque) that needs to be countered in the aircraft structure.
This torque would then be produced by all jet engines of similar construction, and as such has nothing to do with torque specific of turboprops. If all jet engines produce torque then naturally all machinery powered by a jet engine will also have torque (unless otherwise countered).
Originally posted by Holden McGroin
In your water turbine, you will put into the engine a certian amount of thrust, associated with the impulse of the tap water nozzle against the turbine. You will get the same amount of thrust minus the mechanical inefficiency of the prop, turbine, and bearings. You still need to absorb the impulse of the water jet in the structure of the boat, so your action has a reaction.
If the turbine you use is a pelton wheel which would be appropriate, the nozzles would be pushing 90 degrees to the shaft at the pelton wheels radius, and the force of the water impulse at a radius is torque.
No, the water nozzles are (just like in a turboprop) vectored aft and literally blowing on a windmilling fan. This fan is directly connected to a prop via a shaft that runs parallel to the direction of water thrust.
The source of power is the water hose. The nozzles themselves create linear forward force by ejecting water aft. The water hits the fan and creates two new forces. 1: an aft linear force, which counteracts some of the force created by the nozzles, and 2: a rotational force on the fan. The fan turns the propeller via a direct mechanical connection.
(http://www.onpoi.net/ah/pics/users/245_1105546653_gscholz-jet.jpg)
Voilà! Propeller driven propulsion without applied torque on me! (not going to go very fast though ;))
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With the exception of torque forces created by friction losses in the bearings, and a -rearward- force on the whole thing from those nifty water jets. Now, add a gear-box with changes in direction of rotation or ratio, and you get torque on that thing.
And if that example of yours had stator vanes attached, those would cause torque forces too.
(And lucky for you guys, I go back to work in a half hour, so I wont be able to argue again until I get back ;) )
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This is an interesting discussion. While reading it I'm starting to feel like Brian Fellows on SNL.
Of course a propeller powered by a turbine produces a torque. The source of power does not matter, it can be reciprocating, turbine, rubber band, or sitting in the wing in a rubber space suit shooting a pelton wheel with a firehose. The propeller and whatever its source of motive power is affixed to the airframe.
I stated above and I will restate here that torque is one of the primary power indicating instruments on smaller PT-6 engines (the other being ITT). It senses the actual torque that is being imparted to the airframe by the prop.
To run the rough numbers:
Torque = hp * 5252 / rpm
For a -27 flat rated to 680 shp that would be:
Torque = 680 * 5252 / 33,000 = 108.2 pounds feet.
The prop spins at 2200 rpm at takeoff so assuming a 10% loss though the gearbox (just a guess) the prop produces:
Torque = 612 * 5252 / 2200 = 1451 pounds feet of torque.
The gauge that I'm looking at redlines at 1500 pounds feet so we know we're in the ballpark.
If you use a propeller to power an airplane it will produce a torque on the airframe. The exception: contra rotating props, like the Tupolev T-95 Bear Bomber.
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Nonsense. In a piston engine the pistons operate 90 degrees on the shaft and are literarily cranking the shaft. That's a rather substantial mechanical connection between shaft and engine frame. In a turbine engine the only mechanical connection would be in the bearings (with the noted exception of reduction gearing being used).
The same goes for the turbine and stator blades they are also 90 degrees and connected to the turbine shaft. So whats the difference. The mechanical connection in a piston engine is the same as a turbine they both have bearings.
Tails, Rshubert, Milo Morai and Holden Mcgroin have it correct.
In a helicopter you have a turbine engine turning a hydralic pump to a transmission then to the rotors. The only mechanical connection in this instance is the hydralic fluid in the pump. So why do you still need a tail rotor on a helicopter. It the same as a turbo prop. Blade drag torque.
High bypass fan jet have a rotational airflow from the bypass section and this rotational airflow creates a rotational torque.
A high bypass stage fan is a hughe 70 blade ducted propeller turning at a great RPM and produces about 70 percent of the total thrust of the engine. As this fan turns and blows air around the turbine case the air flow rotates as its exited the nacell. This creates a torque from the airflow.
When you power up an electric drill the torque is felt from the increase in rotation. The only mechanical connection is the motor with magnets around it but it still porduces a torque. The drill case that holds all the motor and magnets and drill shaft and while being held in your hand, can be the same as the engine case connected to the motor mount. This is the same a turbine as its increasing its rotation and torquing on an airframe.
A prop moves a large mass of air and accelerates it in a small amount, a jet engines moves a relative small mass or air and accelerates it in a large amount, a high bypass turbine moves a large mass of air and accelerates it in a large amount.
Straiga
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wel cant resist , remember time HT send me to hel cose i told there is no torque , btw abotu discusion , some 1 in RL teling me until u not get ride of all transmision element , example even liqid or air viscosity or even in vacum there is a theoretical distance barier where even a 2 mases close to each other can be create or react on action reaction , and stop whinign about my typing HT do not type beter like me ( who care abotu spel check ? ) :D
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Originally posted by Casca
Of course a propeller powered by a turbine produces a torque. The source of power does not matter, it can be reciprocating, turbine, rubber band, or sitting in the wing in a rubber space suit shooting a pelton wheel with a firehose. The propeller and whatever its source of motive power is affixed to the airframe.
...
If you use a propeller to power an airplane it will produce a torque on the airframe.
This is a fallacy. The propeller never create or impart torque to the airframe. Whether or not torque is applied ALWAYS depend on where the power is created and where and how the forces are directed. If you mechanically separate the power source and the airframe no torque is transferred.
(http://www.nasm.si.edu/research/aero/aircraft/images/hiller_hoe-1.t.jpg)
This helicopter's rotor does not transfer any torque to the airframe, because its power source (rotor-tip jets) is not mechanically connected to the airframe. You will however notice that the rotor is in fact still connected to the airframe.
Originally posted by Straiga
The same goes for the turbine and stator blades they are also 90 degrees and connected to the turbine shaft. So whats the difference. The mechanical connection in a piston engine is the same as a turbine they both have bearings.
I'm sorry, this is completely false. If you can't see the difference between ...
... this ...
(http://www.greatbigstuff.com/prodpics/wrench.jpg)
... and this ...
(http://wings.avkids.com/Book/Sports/Images/pinwheel.gif)
... then I don't think you will ever understand.
Originally posted by Straiga
When you power up an electric drill the torque is felt from the increase in rotation. The only mechanical connection is the motor with magnets around it but it still porduces a torque. The drill case that holds all the motor and magnets and drill shaft and while being held in your hand, can be the same as the engine case connected to the motor mount. This is the same a turbine as its increasing its rotation and torquing on an airframe.
A jet-turbine is nothing like an electrical motor. Do you have any idea of what you are talking about? I don't think so.
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then I don't think you will ever understand.
I understand so much that I actually fly jets, turbo props, and helicopters. Also I instruct people how to fly them too.
Keep reading from people who know, like jet engine mechanics, pilots. I think you will understand eventually.
What you have to look at is that there is a power source turning a prop in one way and a force acting in another. Meaning that if you had an any engine (recip, turbine, electric) in the airframe turning a rotor, the oposite reation would be the airframe turning oposite the rotor.
This is just like your wrench, its is a torque leverage. The pin wheel on the other hand has no torque leverage associated with it at all like your little jet tip rotor.
Your little jet tip rotor is not the same princyple except for the jets tips, for every action there is an oposite and equal reaction, because of jet thrust.
This helicopter's rotor does not transfer any torque to the airframe, because its power source (rotor-tip jets) is not mechanically connected to the airframe. You will however notice that the rotor is in fact still connected to the airframe.
How can a rotor that rotates and that is attached to the helicopter, not be mechanicaly connected to the airframe. UUHHHH!
Straiga
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I'm dumbfounded. I post in another thread about moving engines off-axis of the CG and talk about how the left turning tendency of torque is reduced. I thought I made a good point saying I never touch the rudder trim once the ball is centered up no matter what phase of flight or power setting. That degenerated into talk about Vmc which has nothing to do with anything when you've got 2 working engines.
(http://www.onpoi.net/ah/pics/users/621_1105581640_bonanzacgpic.jpg)
(http://www.onpoi.net/ah/pics/users/621_1105582839_apachecgpic.jpg)
THERE IS TORQUE its effect on a multi engine airplane is just not seen significantly during flight.
Ok, now that that is out of the way.
There is torque because you've got something spinning. Whatever force is causing that to spin, there must be something reacting against it and that causes an opposite direction spinning motion.
In a helicopter (Please correct me if I am wrong Straiga, using a Bell 206 Jetranger as an example)
The blades rotate clockwise when looking DOWN from above at the helicopter. Because of this, there is a significant torque effect causing the helicopter want to torque to the right.
The tail rotor is mounted on the left side of the tail boom, producing left yaw movement to counter the right yaw movement created by the torque of the main rotor blades.
If there were no torque, no need for a tail rotor. (Or the notar system, which simply blows air to the left, still producing a left yaw movement when viewed from the cockpit)
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If your looking down its counter clockwise or from the right side pilots seat the rotation is from right to left. With left anti-torque pedal. Your close! LOL
Straiga
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Originally posted by GScholz
Nonsense. In a piston engine the pistons operate 90 degrees on the shaft and are literarily cranking the shaft. That's a rather substantial mechanical connection between shaft and engine frame. In a turbine engine the only mechanical connection would be in the bearings (with the noted exception of reduction gearing being used).
I am referring to the cylinder head and the top of the piston. What shoves a piston down is expanding gas. What shoves the turbine rotor around is expanding gas. Same principal... expanding hot gas is indeed a mechanical connection.
This torque would then be produced by all jet engines of similar construction, and as such has nothing to do with torque specific of turboprops. If all jet engines produce torque then naturally all machinery powered by a jet engine will also have torque (unless otherwise countered).
Correct to a point. A turbojet puts its main force to the atmosphere by the expansion of hot exhaust gas. The compressor and turbine are there just to support combustion. Torques are present on the rotor shaft and the casing, but turbine and compressor torques wrap aroung the engine in opposite directions, cancelling each other within the engine system.
No, the water nozzles are (just like in a turboprop) vectored aft and literally blowing on a windmilling fan. This fan is directly connected to a prop via a shaft that runs parallel to the direction of water thrust.
The source of power is the water hose. The nozzles themselves create linear forward force by ejecting water aft. The water hits the fan and creates two new forces. 1: an aft linear force, which counteracts some of the force created by the nozzles, and 2: a rotational force on the fan. The fan turns the propeller via a direct mechanical connection.
(http://www.onpoi.net/ah/pics/users/245_1105546653_gscholz-jet.jpg)
Voilà! Propeller driven propulsion without applied torque on me! (not going to go very fast though ;)) [/B]
But you will have less thrust than if you just squirted the water nozzle out the back in the first place. Your turbine is just mechanical loss and wasted money, and can do no work.
The fact that horsepower is being put to the atmosphere through a rotating fan or prop necessarily requires that rpm and torque exist. The torque is absorbed by the engine mounting though fluid dynamic related differential pressures in the turbine section, which is a mechanical system, just like pneumatics and hydraulics. Newton's equal and opposite law applies to rotational motion.
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Originally posted by Holden McGroin
Correct to a point. A turbojet puts its main force to the atmosphere by the expansion of hot exhaust gas. The compressor and turbine are there just to support combustion. Torques are present on the rotor shaft and the casing, but turbine and compressor torques wrap aroung the engine in opposite directions, cancelling each other within the engine system..
False statement on torque. Yes, while the torques created in the compressor and turbine sections of a jet engine are opposed, the turbine section creates a considerable ammount more torque in comparison to what the compressor creates. The same holds true for turbines with seperate high and low pressure compressor setups that rotate complementory.
A turbojet or bypassing fan engine with N1 and N2 spinning the same way will make torque, and most of it originates from the hot section.
EDIT: And after thinking a couple minutes, you proved yourself wrong. A turbojet does work on priciple of compressed hot air expanding in the comparitivly cooler ambient air. HOWEVER, if all the energy produced by the combustion section was absorbed by the turbine section (in the form of torque imparted on the compressor/turbine shaft from the turbine wheels) to offset the power loss (torque loading, opposed to torque created by power source) from driving the compressor, you would have hot, but uncompressed, air squirting out the back of your turbojet, with little available thrust due to all the energy losses internally.
End result: A really expensive hair dryer
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End result: A really expensive hair dryer
More like a Toaster.
Or one of those boot dryers I use, Same thing as a toaster but you put your boots on them and they come out nice, dry and toasty the next morning.
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Open-air convection oven, maybe?
Now that I think about it, there is one example of a turbine engine that DOES use all its energy driving the turbines, with little if any jet thrust...
Turboshafts, turboprops, they use all that energy driving the power turbine (or the main turbine section, in the case of direct drive turboshaft, as opposed to free-turbine), that the poundage of leftover jet thrust is in the double digits.
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Originally posted by Tails
False statement on torque. Yes, while the torques created in the compressor and turbine sections of a jet engine are opposed, the turbine section creates a considerable ammount more torque in comparison to what the compressor creates.
In a Pratt and Whitney FT-8, (the power generator version of the A/C turbine powering 737s, DC-9s and numerous other A/C) The high speed turbine powers the high speed compressor, and the same with the LST / LSC.
As the HSC and HST are on the same shaft, running the same speed, (after all they are the same shaft) where does the extra torque come from? The shaft between the HSC and HST only has one torque.
The LS shaft runs independantly from the HS shaft.
As the compressor is powered by the turbine, and they are running the same speed, the compressor at a constant rpm, the torque must balance.
In a turbo-prop the turbine does over power the compressor, and the extra hp (torque as we are at constant rpm) goes into the prop. In a turbofan the turbine provides hp over and above the needs of the compressor so hp can spin the bypass fan.
But in a turbojet, the turbine and compressor sections precisely balance torque. There is nowhere for extra torque to go.
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Again, if the torque, or power, created in the hot section of a turbojet was equal to the torque load of the compressor section, then all the energy created in the combustion section would be used up just driving the turbines, and you would get no resulting thrust. The torque created in the turbine section will ALWAYS be greater than the load in the compressor in a turbojet, thus a torque force, opposed to the torque imparted on the turbine shaft, will be present trying to turn the engine case.
Now, will it be a whole heck of alot? No. But it will be there. The only turbines that have a chance to create zero torque to the engine case are designs that have the high speed and low speed compressors contrarotating, and even that is in a perfect-world scenario.
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Energy is not created in the compressor.
The compressor spins to support combustion.
Power is used in the compressor.
The combustor creates the power.
A portion of the power from the combustor is harnessed in the turbine.
The turbine uses its portion of the power to spin the compressor.
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Im with Holden McGroin on this one: Still looking how a Hi Bipass fan can transmit substantial torque to the airframe other than.
1. Air friction of the air travling in the engine.
2. Bearing friction.
3. Stators (this might be a substantial force)
Just as he describes torque must be equal between compressor and turbin. In a Bypass system compressor + bypass = turbin.
Apears to me all torque (other than resons listed) are oposit directions and accounted for my airflow deflection. I.E nothing to the airframe.
Also
But you will have less thrust than if you just squirted the water nozzle out the back in the first place. Your turbine is just mechanical loss and wasted money, and can do no work
Belive this is not quite accurate. You will have less power. Total thrust could be increased at slow speed.
Edit:
On 2nd thought not sure Im correct on this , is it posible to create more thrust with out lowering rpm?
HiTech
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anything thats driven from the midlle of the object has torque
seen a helicopter from wich the main rotor was driven by jet (exhaust) from the end of the blade tip.
it didn't need a tail rotor because the was no torque.
i can imagine where as the heli tailrotor failures.
the pilot only has to drive his main rotor just to keep speed slowly turning slower at a point not accelerating and no steady rpm
but he certainly has to land
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I believe this thread is spent. Its purpose was to figure out if turboprops applied torque on the airframe. I believe HiTech answered that with the clarification of how the reduction gearing would create torque.
However before I eject, I have a few parting comments:
Originally posted by Holden McGroin
I am referring to the cylinder head and the top of the piston. What shoves a piston down is expanding gas. What shoves the turbine rotor around is expanding gas. Same principal... expanding hot gas is indeed a mechanical connection.
Yes same principle, but different application of force. A cannon and a recoilless rifle work on the very same principle too, but I think you will agree that one creates recoil, but the other does not. Different application of force; one is balanced, the other is not.
Originally posted by Holden McGroin
But you will have less thrust than if you just squirted the water nozzle out the back in the first place. Your turbine is just mechanical loss and wasted money, and can do no work
Utter nonsense. You never get more energy out of a machine then what you put in, and the GScholz-jet is no exception. Just like a turboprop it just converts linear force into rotational force. In fact, exchange the water nozzles with a jet engine and you have a turboprop.
Your thinking is like saying "Why have electricity when we have steam power? Your steam-turbine generator is just mechanical loss and wasted money".
Originally posted by Tails
Again, if the torque, or power, created in the hot section of a turbojet was equal to the torque load of the compressor section, then all the energy created in the combustion section would be used up just driving the turbines, and you would get no resulting thrust. The torque created in the turbine section will ALWAYS be greater than the load in the compressor in a turbojet, thus a torque force, opposed to the torque imparted on the turbine shaft, will be present trying to turn the engine case.
No. All the turbines are connected to the same shaft, and so they must all have the same torque applied to them (unless there is some sort of gearing involved). There is only one force created by the combustion and that is a linear force of moving/expanding gas. However the turbines converts some of this linear force into rotational force. That "some" is equal to the force spent in the compressor stage at the other end of the shaft.
Originally posted by Straiga
I understand so much that I actually fly jets, turbo props, and helicopters. Also I instruct people how to fly them too.
Oh I'm sure you are quite capable of piloting an aircraft ... just don't try to build one. As it has been pointed out in numerous threads you (like I used to) have some misconceptions about how airplanes actually work. If you don't trust me, ask HiTech ... he's a pilot too.
Oh and if you're afraid there's still a few people that don't know you're a pilot, you could start a thread in the O' Club or General Forum with the title "I AM TEH PI3LIT!!!". That way everybody will know you're a busdr ... pilot, and the importance of everything you say.
Just some friendly advice.
(http://www.onpoi.net/ah/pics/users/245_1105566001_threadeject.jpg)
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I'm getting a headache through all of this, so I'm gonna take a break, and study my FAA AC 65-9 and my power plant text-books and get back to you all.
Peace :D
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Well, that was quick (caffinee is a wonderful creation).
I dont know where my head was, but it seems things were rattling around too much in my head, so I say we start from the beginning. First, turbojets:
A turbojet gains thrust from the interaction of hot, compressed exhaust air with cool ambient air. This air is comressed by the compressor section of the engine, then superheated in the combustion section wherwe it tries to expand away. It cant go back the way it came under normal situations (and when it does, you get a 'compressor stall' with a loud bang and flames shooting out both ends), so the expanding exhaust air follows the path of least resistance and goes out the back of the engine, into the turbine section.
The stators in the turbine section deflect the expanding gasses to impact at a more usable angle on the turbine blades, which forces them to move and turn the wheel they're attached to. The turbine blades themselves are also curved, partly to gain a little more energy from deflection forces, and partly to help direct the air into the next stage of stators. Wash, rinse, repeat, until you run out of turbine stages. Now, as Sir Newton teaches us, with every action, in this case the air being deflected by the stators, there is a reaction, the turbine case (and the engine it is attached to) trying to rotate in the direction opposite the direction the air is deflected in. There's your torque.
Now, for some reason I said that the comressor creates torque forces as it's compressiing, agreeing with someone else here. This is FALSE. The compressor creates a torque load, which is overcome by the compressor shaft, which is spun by the turbine wheels. The more load, the more force is required to over come it, simple mechanics there. And with more force being created to spin the turbine, more force is acting on the stators, and thus more torque is created. All this time, the force is coming from that hot air from the combustion section expanding and trying to get out of the damned engine!
Now, if you use up all of your energy just keeping the compressor turning, then the air will of completely expanded as it exits the turbine, and you get no jet thrust and little airflow. This is what happens with turboshaft designs, as they draw out the maximum ammount of power from the expanding gases with the power turbine (or the hot-section's turbine, in the case of a direct-drive turboshaft).
Ok, next lesson, bypassing fans. Hitech is correct in his statement of sources of torque from a bypassing fan. The torque forces are created from the hot section overcoming the load of the high and low speed compressors, by blasting more hot air through the turbine, which creates more force on the turbine blades to spin things, and creates more force on the stators to direct the air to spin things.
Still here? Ok...
Next, turbo props. A direct-drive, non-reduced turboprop with no gear-box between the engine and the prop would generate torque in the same way as a bypassing fan or turbojet. It would also self-destruct the prop from the gee forces, so we stick a reduction gear on it. This now adds a new load, as well as another kink in the torque problem. We now have something mechanical, bolted to the air frame, that is trying to spin a propeller. And with the load the propeller is creating, we have a reaction trying to spin the gear-box it's attached to. That's torque, folks.
Dont beleive me? Then tell me what would happen if you hung a 182 with the Power Pak STC performed (thats a little turboprop, Allison A250 model) by it's prop and fired it up? If you try to tell me the aircraft wouldn't end up spinning around, then you need to take what you're smoking and share it with the rest of the class.
PS: And if anyone here questions anyone's certifications, I know how to get to the FAA's Airmen Inquiry site. I'll happily give anyone that requests it my real name to look up my A-P ticket :D
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Tails: Thanks for a precice explination.
Btw any idea on the scale of torque created by the stators?
HiTech
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Originally posted by Straiga
In a turbo prop there is a planetary gear box. One big gear rotating around 4-6 smaller gears that set inside the big gear and attached to the turbine shaft, but not to a stationary point or mount. This is in the forward part of the engine.
HoHun, Rshubert, good points all.
One important point when you add power to a turbine the RPM as it increase from, say 5,000 rpm to 45,000 rpm during an engine spool up, torque is also present. Acceleration of a rotational mass. In the DC-10 and B-767 as power is increased the aircraft pulls to the left on spool up.
Also when the jet thrust exits in one direction, the torque leverage is excerted on the airframe in the oposite direction, as in an engine hanging on a wing pylon. For every action theres an oposite and egual reaction.
Straiga
I could not have said it better. In fact on the C-130 (which I have 4000+ hours on) we measure the amount of power that an engine is producing by torque. We have a limit of 19,600 inch pounds. The aircraft will create a bunch more. I have seen upto 25,000inlbs which is not good. The aircraft was grounded for a month to do massive over-torque inspections. The C-130 suffers from the P factor (rollling motion created my engine torque) and we really have some issues when we have #1 prop or engine failures... Just my .02
Skip
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The C-130 suffers from the P factor (rollling motion created my engine torque)
You sure thats what P factor is?
And with all this torque discusion, want to give the diffenition.
Torque is when you wake up in the morning with an erection. Go to take a Pee, push it down, and your feet fly off the floor.
HiTech
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HT did I miss a previous discussion? Was it ever stated that a turboprop would have no torque effects on plane?
I'm not a physics/math type by nature but to my layman's view it seems logical that any powered rotating device would impart torque forces to the structure its attached to.
Is that a correct assumption?
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Ok Hitech, You made me go talk to my Stan-eval Flight Engineer and Pilot. Here is the definition we came up with on the P factor (C-130)
It is the tendency of an aircraft to roll due to force/torque applied from the engine/prop. In the C-130 (the only aircraft I know) all of the props spin in the same direction. So.. when power is applied the aircraft has a tendency to roll toward the #1 engine. All of our told data is based off of the #1 engine wind milling in NTS. (Negative torque system) the P-fator increases as the amount of power (measured by torque in the C-130) is applied. This is the short answer Dale, but I am going to have to stick to my guns here. This is the way I was taught and this is what I know to be true in the Herk world. I may be off base here, and I am sorry if I stuck my nose into a topic that is well beyond my knowledge, but this is the answer I am sticking with. DALE, feel free to slam me. (S)
Skipz
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Originally posted by hitech
Torque is when you wake up in the morning with an erection. Go to take a Pee, push it down, and your feet fly off the floor.
HiTech
CLASSIC!!! Thanks for the word that i was looking for LOL (S)
Skipz
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T1Loady, all the effects you describe I 100% agree with.
But check this page out.
http://www.mindspring.com/~cramskill/propefct.htm
From that page.
P-Factor. Asymmetrical thrust is most apparent with taildraggers because it's mostly a function of the prop not being perpendicular to the oncoming airflow - but that can also happen with any plane when at a high angle of attack, like right AFTER takeoff. When the air is coming into the prop at an angle instead of square to it, one side of the prop operates at a higher angle of attack than the other, and the resultant thrust is no longer acting on the planes' centerline, but off to one side. And that makes the plane want to turn. See fig. 3. The usual case, nose high, gives us a left turn.
Torque. Our props have a certain amount of drag - and the torque (twisting force) the engine exerts on the air is, in opposite fashion, also exerted through the engine mount to the airplane. Since all our props turn to the right, that means there is a force trying to twist (roll) the airplane to the left. Note that this force is about the ROLL axis - the torque forces do not by themselves TURN or yaw the plane as do the previous two effects. We automatically take care of this with ailerons in keeping the wings level, and it really doesn't take much force from the ailerons to do it. On the ground, all torque forces are countered by the wheels.
So im curious does the military define the term P-factor differently?
Or is it called Power Factor?
HiTech
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Originally posted by hitech
You sure thats what P factor is?
And with all this torque discusion, want to give the diffenition.
Torque is when you wake up in the morning with an erection. Go to take a Pee, push it down, and your feet fly off the floor.
HiTech
Heh, actually that would be jet-thrust. :rofl
Semi-seriously, this is how octipie get around. They suck in a bunch of water, point themselves in the direction they wanna go, and letterrip!
EDIT: And Hitech, in responce to your question about the scale of jet engine torque: I have no clue. How ever, it is significant enough to need to be compensated for in a hydraulicly boosted, non-flybywire fighter. Like in the Su-27 I mentioned earlier, where when doing very low speed maneuvers they have to apply a little rudder to compensate for the torque, and in any manuever where the aircraft is supported entirely by engine thrust (IE A tail-slide in a Su-27, or the MiG-29's 'hovering trick') they have to throttle one engine back a little, so that asymetric thrust helps to compensate for the torque. So it's there and noticable.
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Originally posted by hitech
Torque is when you wake up in the morning with an erection. Go to take a Pee, push it down, and your feet fly off the floor.
i FINALLY understand something in this thread!!!!
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We automatically take care of this with ailerons in keeping the wings level, and it really doesn't take much force from the ailerons to do it. On the ground, all torque forces are countered by the wheels.
Hitech with all due respect this is absolutley wrong Im sorry. Someone had a post about a B-24 on takeoff and this B-24 pilot said he used no aileron or aileron trim for takoff just rudder. How come you cant see that this is how a 4 engine airplane actually flys and that your use of aileron is wrong in takeoff or in cruise flight.
Torque is pronounce at the first onset of power output. You would be in the ditch, before you could counter torque with effective aileron on takeoff. Think about that.
Hey T1loady ask your C-130 driver if he has ever had to use aileron for takeoff to counter torque roll. I bet he only uses aileron for cross wind takeoffs. Torque roll on the ground is a yawing torque and countered by RUDDER not aileron.
T1loady have him discribe exactlly to us all what happens to a C-130 on takeoff and what controlls and trim settings are used in takeoff and how the plane flys in cruise. May be we can all learn something here. I will be waiting for your post.
Tails that is a very good explanation of torque in turbines and turbo props. So I guess torque does affect an airplanes airframe.
But GScholz still wont believe what you say. Because you have actual experience on the subject. I guess having real experience either working on them or flying them, I guess we dont know what we are talking about. Its interesting that someone who has never flown a jet or multi-engine turbo prop really believes they are right reading from a book, and that these planes should fly like they think, but if they actually flew these airplanes they would be shocked, that what they think of how it will fly, just doesnt happen. Its really sad.
When you go for a pilots liscence who do want to listen to teach you how to fly and can get your ticket, maybe someone with a flight instructors certiticate and thousands of flying hours or a computer pilot flying a flight sim who he think he knows it all.
GScholz thats a good picture, it proves my point that you have an extensive knowledge of not knowing how to properly fly an airplane or how it works. Did your chute work the way you thought it would or do you need someone to explain it to you? Oh! your not going to listen anyway.
GScholz, when I say Im a pilot and have flown for many years, this is not to bragg, I could care less if your Impressed or not. Im just saying that I have been there, and done that. I dont think that other people think Im bragging and I dont think I have come across like that either. Im just letting everbody know where Im coming from with my experiences. If this offends you to make snide remarks so be it.
If you had actual experience in something that I have not had I would listen or read the information. I could learn from that and say wow I didnt know that. I have learned something new. But Im not going to listen to any flight sim pilot trying to tell me how a real airplane flys or what makes it work. Im sorry they just dont know.
You may think I dont want to listen because I think I know it all. Thats far from it, but I cant agree with someone who thinks they know how, without experience how a certain type of airplane will fly.
When I interviewed with the airline Im at now I was competing against over 40,000 applacants for the same job. Whats the odds, so why did I get the job and the others didnt. It just may be I had more experience than the others. Its probably like getting into pro sports.
I have been told that experience dosent give you knowledge about a subject, you will know more by reading a book. Would you enjoy sex more by reading a book or by actually doing it. What do you think?
Being a single engine pilot does not give you experience in knowing how to fly a multi-engine airplane. Flying a jet is different than flying a piston airplane. You think you might know but until you flown them, then and only then is when you will know the differences on how they fly.
Straiga
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Straiga I think you're just not using the correct vocables/words.
If we apply full power to a B24 without propeller , torque will still be present.
Agree ?
Now will this force be enought to make the B24 turn on place ?
I don't think so.
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Straiga: Are you saying T1loady's definition of P-factor is correct?
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HiTech's definition of P Factor from the Ramskill article is correct.
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If you had actual experience in something that I have not had I would listen or read the information. I could learn from that and say wow I didnt know that. I have learned something new. But Im not going to listen to any flight sim pilot trying to tell me how a real airplane flys or what makes it work. Im sorry they just dont know.
This is what you are totaly incorect about. I have no doubt that when you tell me such and such a plane does this on a take off roll. That your are correct. But if you wish to talk experience you want to count your flying experience toward your expertiese in physics. You could just as will say your flying makes you an expert in sex. Because flying is not physics, it is flying. Your analagy is the same as saying that having sex 5 times a day, for 20 years makes you a PHD in the humun repoductive system. You might know how to use it. But that in no ways equates to knowing what makes it work.
Belive it or not some of us have a much greater knowledge of the physics of flight than you. Also some of us like to debate to gain a greater understanding of how things work. This turbin/ turbo prop discusion was one of those. You tend to just always state this is the way it is, and then when you try post why, your arguments tend to be incorect. So you can state that your experience tells you a Hybass fan has torque. But when you stated why, your analisis was totaly incorect. You also stated another one that when you spun up a turbin from 5000rpm to 30k it had torque. Now once again, I do not debate that it does. You have done it, and seen it. But your resone given is not accurate. You stated it was because you were accelerateing the turbing, that acceleration caused the plane to rotate the other way. This again is not entirely accurate. We could analize exatly why it is. But quite frankly I am tired of your wanting to sight your expertise as to why you are correct. Wrather than looking deaper into a problem and solving it. Or be able to precisly argue why something is. Of course you never need to look deaper, because you already know absolutly every thing about planes.
HiTech
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Straiga: Are you saying T1loady's definition of P-factor is correct?
No this is not correct. P-factor is the unequal lift produced on the prop disk oposing relative wind.
Since all our props turn to the right, that means there is a force trying to twist (roll) the airplane to the left. Note that this force is about the ROLL axis - the torque forces do not by themselves TURN or yaw the plane as do the previous two effects. We automatically take care of this with ailerons in keeping the wings level, and it really doesn't take much force from the ailerons to do it. On the ground, all torque forces are countered by the wheels.
This is also incorrect about a 4 engine aiplane. Knowing physics I dont think so or this statement would be true.
I may not explain myself very well when it comes to physics. A lot of times in very early in the morning is when I post. My last physics class was over 25 years ago. But in the end, I have said what was right was right. Wouldnt you agree.
So everybody tell me what degree you have in aerodynamics, any kind of aerodynamics. You to hitech. I have told you about me, now what about you.
1.
2.
3.
4.
Anybody!
Im I the only one with and aeronautical engineering degree here.
Also tell me when you last flew a multi-engine and when did you get your liscence. I have told you my experiences, how about you lets here.
1.
2.
3.
4.
Anybody!
Im I the only one here with a multi-engine certificate and have actual 4 engine flight experience, also 3 engine flight experience and 2 engine.
If you cant respond because you dont hold a multi-engine certificate. This will inform me that you have no formal experience in the subject matter. Physics on paper is one thing flying the plane is different. Statements like the above quote proves this fact.
According to physics bumble bees cant fly either.
Straiga
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quote:
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Since all our props turn to the right, that means there is a force trying to twist (roll) the airplane to the left. Note that this force is about the ROLL axis - the torque forces do not by themselves TURN or yaw the plane as do the previous two effects. We automatically take care of this with ailerons in keeping the wings level, and it really doesn't take much force from the ailerons to do it. On the ground, all torque forces are countered by the wheels.
--------------------------------------------------------------------------------
This is also incorrect about a 4 engine aiplane. Knowing physics I dont think so or this statement would be true.
_____________________________ ________________
Ok please explain one topic. How does adding or moving engines change the Torque effect. Please do not speak to P-factor/slip stream or preccesion. Just about Torque. I.E. a rolling moment created only by the force of the engine.
Because I view that statement about engine torque to be 100% accurate.
Because you could put those 4 engines in a straight line all behind each other, or out on the wings. And the roll force on the the air frame do to engine torque will be exatly the same.
If you do not agree with this, please explain presicly why.
As to my credentials. They are irrelavent. I never use my credentials to prove or disprove a point. Either the argement can be shown to be true or not.
HiTech
And just so you know
According to physics bumble bees cant fly either
Is an old myth. Was shown how they fly many years ago.
http://www.wolfson.ox.ac.uk/~ben/zetie1.htm
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Allow me to summarize.
The compressor creates some torque.
The spinning mass of air dragging on the stators, combustion chamber walls/thrust tube/exhaust also create some torque.
But most of the torque comes from the gearbox.
Agreed?
Some wrong theories.
A turbo-prop is NOT like any other motor. Not an electric one, not a reciprocating internal combustion, etc...
HiTech "Because you could put those 4 engines in a straight line all behind each other, or out on the wings. And the roll force on the the air frame do to engine torque will be exatly the same."
Um... the toque applied the airframe will be the same, however the moment arm to the center of mass will change, which changes the force from a rotory one to a linear one... I think. Which means engines on the tips of the wings would apply less of a rolling force to the aircraft... I think.
Straiga, I have a huge respect for your wealth of experience. But be aware some of us may have a fair amount of knowledge on the subjects at hand as well.
Since you asked, I don't hold a degree but I do design record setting streamlined Human Powered Vehicles, the most aero-efficient vehicles on the planet.
(http://www.easyracers.com/images/011_9.jpg)
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Hi Straiga,
Seeing we had good success with tackling the single-engine torque question by looking at the interacting forces, I'd like to suggest to try the same approach for the multi-engine problem.
For example, we could have a look at a multi-engine propeller-driven aircraft in slow flight on a stable, level flight path.
I'm confident that Hitech is correct that the engine torque is acting on the airframe. I'm also confident that you are right that use of rudder is the correct piloting technique for ensuring the stable, level flight path.
So the question is now, what would happen if
a) we held the rudder centered and fed in aileron to compensate for the engine torque?
b) we held ailerons neutral and fed in rudder to compensate for the engine torque?
c) We held all controls centered? (Probably not necessary because we all seem to agree that we have some kind of asymmetry in the system, but included for the sake of completeness.)
Maybe that's a better approach than looking at a complex situation as we have at the take-off where all parameters change dynamically :-)
Regards,
Henning (HoHun)
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Um... the toque applied the airframe will be the same, however the moment arm to the center of mass will change, which changes the force from a rotory one to a linear one... I think. Which means engines on the tips of the wings would apply less of a rolling force to the aircraft... I think.
Nope torque dosn't have a moment arm.
moment arm * force = torque.
In the engine case we are not appling a force , just a torque.
A force would be adding the thrust to the airplane, if that thrust is off center it will create torque in some axis.
When adding torque to a system, there is no need to know where that torque is applied when computing the total systems torque.
HiTech
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a) we held the rudder centered and fed in aileron to compensate for the engine torque?
You'd keep rolling left, take out some runway lights, dig in your left main gear and get stuck in the mud. Hopefully it would still be on its legs.
b) we held ailerons neutral and fed in rudder to compensate for the engine torque?
This is what you're supposed to do in a no-wind situation. Ailerons control the roll of the aircraft, so if there is a yaw movement in the airplane, you're swatting at a fly with a hollow tennis racket.
c) We held all controls centered? (Probably not necessary because we all seem to agree that we have some kind of asymmetry in the system, but included for the sake of completeness.)
Same as using only aileron. Rolling left, take out some more runway lights, hit the same ditch you made earlier and this time rip off your left main landing gear.
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And Straiga, I have flown 'Texas Raiders'
B-17G. Not typed, no LOA and no formal school. But I moved the yoke around.
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Hi Golfer,
Argh, remember that we're already flying way above the runway, and that I'm not a native speaker :-) No idea what I'm supposed to do with a tennis racket! "There is no body checking in golf!" ;-)
Regards,
Henning (HoHun)
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g00b:
Is there a link with some more information about the vehicle in the picture?
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remember that we're already flying way above the runway
Ah...I didn't get that the first time around but you did mention 'Straight and level flight' so I shall restate.
a) we held the rudder centered and fed in aileron to compensate for the engine torque?
Engine torque really isn't a big issue at altitude and when flying Straight and level. But, just sayin the word 'torque' and using the prop as well here we go...
Due torque, the airplane would yaw left, the vertical component of lift would cause the aircraft to roll. While this is not directly due to torque, it is a byproduct. If you used aileron only to correct the problem, you'd have a level attitude though the ball would not be centered. The ball would be to the right, because we need to hold right aileron to keep level (Due to the yawing moment being converted to roll by vertical lift component built into the wings due to dyhedral, NOT because torque rolls an airplane) and that would cause the nose to want to go left.
b) we held ailerons neutral and fed in rudder to compensate for the engine torque?
This is still what you're supposed to do. As mentioned before, I never touched aileron trim when flying in a conventional twin (Piper Apache as an example). I used the red rudder trim a lot, but never EVER touched aileron. All the rudder trim is used for is to keep that ball centered.
(DOH!) I think something is hitting me, its not aileron trim in the Apache, its elevator trim that is the black ball. Still, no matter I never used it. It's the King Airs with aileron trim.
c) We held all controls centered?
the airplane would slowly yaw to the left, and because of the vertical component of lift it would start to roll. This would be cause the airplane to nose over and you would be providing someone a hole of significant size to plane a redwood.
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a) we held the rudder centered and fed in aileron to compensate for the engine torque?
The plane would yaw left because of assemetric aileron in the direction of the torque. You would not have any directional control in flight. But on takeoff ailerons are not effective until about 45 -60 MPH so now how can you use aileron on takeoff to counter torque at a low airspeed when torque is at its most prominate state.
we held ailerons neutral and fed in rudder to compensate for the engine torque?
This is the correct way to counter torque in a 4 engine airplane and the use of rudder gives you directional control.
Straiga, I have a huge respect for your wealth of experience. But be aware some of us may have a fair amount of knowledge on the subjects at hand as well.
Goob, its nice to know where your coming from. I now know what experience you might have. Thats all, I hope I did not affend you if I did Im sorry. Do you live in Las Vegas it looks like the area behind my house?
As to my credentials. They are irrelavent. I never use my credentials to prove or disprove a point. Either the argement can be shown to be true or not.
You mean you cant tell us where you get your vast aeronautical experience from. We all would like to know.
Ok please explain one topic. How does adding or moving engines change the Torque effect. Please do not speak to P-factor/slip stream or preccesion. Just about Torque. I.E. a rolling moment created only by the force of the engine.
Because I view that statement about engine torque to be 100% accurate.
Because you could put those 4 engines in a straight line all behind each other, or out on the wings. And the roll force on the the air frame do to engine torque will be exatly the same.
If you do not agree with this, please explain presicly why.
I have in other posts and have given actual flying experiences about this. You can not understand because you dont have any kind of Multi-Engine time. You do not want to believe when I have real flight experiences for some reason you except to say that I have no knowledge of physics.
So you explain why in detail, about torque of four engines affecting an airframe so we can all see were you are flawed in your thinking.
So dont believe me go ask any multi-engine rated pilot to tell you that your wrong in your thinking. I dont have a problem understanding the physics about a four engine airplane but you do so please go ask someone who also knows about this subject.
All I have done is mention that I have seen some flaws in AHII aerodynamics. I have heard that this is the most accurate flight sim out there. Even to the point were Pyro has to get it right about how a spent shell casing is either discharged over board or remains in a box in the airplane. Who cares. It is probably so minute' that it woundnt be a factor anyway. But you go for it pyro lets get it right.
We had a discussion about losing the tail plane in a fight and which way will the nose point afterwards and found that the CG is not even modeled while this happens. So it just makes you wondered what else is not modeled correctly in AHII. But when you try to tell someone about this with real experiences they dont believe you.
Straiga
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I'd like to chime in, but I'm still trying to work out complex torque interactions to the airframe in multi-engine craft...and this is WITHOUT a physics degree :confused:
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Originally posted by Casca
g00b:
Is there a link with some more information about the vehicle in the picture?
http://www.easyracers.com
Check out the racing page
http://www.easyracers.com/racing
And the Virtual Rush page
http://www.easyracers.com/virtual_rush.htm
A video produced by Ford:
http://www.easyracers.com/videos/VR_Ford.wmv
Our Junior Rider setting a new world record:
http://www.easyracers.com/videos/BM2003_Macky_Thurs.wmv
Check out the multimedia page for other cool videos too:
http://www.easyracers.com/multimedia.htm
g00b
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Originally posted by Straiga
This is the correct way to counter torque in a 4 engine airplane and the use of rudder gives you directional control.
In wich conditions ? be more explicit please.
Is it on the ground ,during rotation , on cruise ?
And please read my previous post , if there is no propeller on the plane will torque change or not ? (at full power obviously)
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On the ground and in the air, Straffo.
Also, if you didn't have props, you'd just have a big noisy thing that sat on the runway. No matter how much torque or power the engines are putting out, with no prop (way to convert all that torque into movement of air) then you sit there.
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Hey Golfer you also have B-17G time too Cool. Tell me did you have to use any aileron in the flight except to turn or use them for a crosswind. I dont think anybody will beleive you, you have actual flight experience. LOL
Straiga
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Thank Golfer, you agree the torque force produced by the engine is still here.
So it's not the torque ,it's another force.
Perhaps one is the "souffle hélicoïdal de l'hélice" I'll translate by "Helical propwash"
plus the "précession gyroscopique" ...
The only think I remember for sure is it's the sum of 4 forces
I will dig in my "Mécanique du vol" books but I guess it can be found in an English book aswell.
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I'm not shallow enough to say I have time in one. I don't have any training whatsoever. I sat in the right seat and moved the yoke around while keeping the HSI of my GPS pointed at Lancaster, OH.
It was a real neat experience, I didn't land (I have 50hrs tailwheel time but no friggin endorsement...I need to amend that) nor did I start the engines, taxi or takeoff. Climbing through about 1500' AGL (about 2400' MSL) I took the controls for the 30 minute flight.
It was a fall afternoon and not a breath of wind here in Ohio...just like Aces High. Clear 'n a million. Windsock limp. (Unlike >15kts wind which I refer to as 'Boner Conditions')
I got to imagine a P-51 off my wing taking me into Germany. I got to think of what it would be like to have 10's and 100's of luftwaffe fighters coming in with only one purpose...killing me.
What an experience. (Also, was not multi rated at the time nor was the pilot a current CFI so no logbook time for this. I'd burn my logbooks to do it again)
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Hi Golfer,
>Due torque, the airplane would yaw left, the vertical component of lift would cause the aircraft to roll. While this is not directly due to torque, it is a byproduct. If you used aileron only to correct the problem, you'd have a level attitude though the ball would not be centered. The ball would be to the right, because we need to hold right aileron to keep level (Due to the yawing moment being converted to roll by vertical lift component built into the wings due to dyhedral, NOT because torque rolls an airplane) and that would cause the nose to want to go left.
OK, I agree with the flight status :-)
However, as the sum of all moments around each axis as well as the sum of all forces parallel to each axis have to be zero for an equilibrium, I'd say that the aileron-induced right roll moment counters the engine-torque induced left roll. The yaw in my opinion is aileron-induced.
I believe that while we still disagree, we have now exactly identified where we do :-) Roger on this being the critical spot?
>the airplane would slowly yaw to the left, and because of the vertical component of lift it would start to roll. This would be cause the airplane to nose over and you would be providing someone a hole of significant size to plane a redwood.
OK, again I agree with the flight status (and the depth of the hole as well :-)
But again, I'd say that the roll would be torque-induced, and the yaw roll-induced, for the same reason as above, so (as already expected) we can conveniently treat point c) as part of point a).
Regards,
Henning (HoHun)
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It's very very very important we are talking about the same type of airplane. What airplane are you using in your mind as an example.
Then I'll show you mine :)
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Hi Golfer,
>It's very very very important we are talking about the same type of airplane. What airplane are you using in your mind as an example.
>Then I'll show you mine :)
Actually, my mental image is sort of an animated threeview line drawing with plenty of vector arrows :-)
But if you need a type, how about a He 219?
Regards,
Henning (HoHun)
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not to be a stickler for details...but what is that?
Tell me :
Single or Multi Engine, High/low wing. Or just pick a common GA airplane like a C-172 or C-310
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Hi Golfer,
>not to be a stickler for details...but what is that?
The Heinkel He 219 (http://en.wikipedia.org/wiki/Heinkel_He_219) is a heavy, high-powered WW2 night fighter in twin-engine, mid-wing, twin-fin configuration.
Regards,
Henning (HoHun)
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To be honest I was hoping that you picked an airplane you had some experience with. Its not in-game its not something anyone can go out and fly.
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Hi Golfer,
>To be honest I was hoping that you picked an airplane you had some experience with. Its not in-game its not something anyone can go out and fly.
Well, suggest any other, I'll just follow your lead :-)
Regards,
Henning (HoHun)
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http://142.26.194.131/aerodynamics1/Multi/Page3.html
In this photo it shows a yawing monent not a rolling monent.
Straiga
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Hi Straiga,
>In this photo it shows a yawing monent not a rolling monent.
Hm, that could mean that the influence of the P factor is larger than the influence of torque. (A certain amount of rolling moment due to torque should be there in any case.)
Of course, it becomes even more complicated because angle of attack can vary (and the orientation of the engines' thrust line, too).
To simplify things, could we assume for the moment that the straight and level flight situation of our example aircraft has the thrust line aligned so that there is no P factor?
That would bring us to the situation I suggested:
>>a) we held the rudder centered and fed in aileron to compensate for the engine torque?
>The plane would yaw left because of assemetric aileron in the direction of the torque.
I believe we agree that the yaw (in the no P factor case) is the by-product of aileron application?
>>b) we held ailerons neutral and fed in rudder to compensate for the engine torque?
>This is the correct way to counter torque in a 4 engine airplane and the use of rudder gives you directional control.
What would the stabilized flight situation look like in terms of yaw and bank? This is difficult to visualize for a non-pilot :-)
Regards,
Henning (HoHun)
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I believe we agree that the yaw (in the no P factor case) is the by-product of aileron application?
I can't.
There is something called Adverse yaw. This is the tendency of the nose to yaw opposite the direction of turn in the application of aileron movement. This is why you need to use rudder in the direction of turn to maintain a coordinated turn. Coordinated meaning you keep the ball centered.
This is typically not in any excessive amount (with most modern nosewheel trainers) but it is worth noting because it will require correction.
I'm confused slightly (I understand all the principals you're referring to) about how you might mean to interpret when you say aligning the thrust line and P-factor. I know how to answer the question, I just want to make sure you asked it this way on purpose.
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To simplify things, could we assume for the moment that the straight and level flight situation of our example aircraft has the thrust line aligned so that there is no P factor?
Hi HoHun, This is true in straight and level flight you do not have any P-Factor only until you change the angle of attack. Then P-Factor is a yawing monent in flight.
I believe we agree that the yaw (in the no P factor case) is the by-product of aileron application?
This is also true the when the right aileron is deflected up this decreases Lift, decreases Drag, and so the wing moves forward.
The left aileron is deflected down the Lift increases, drag increases, and the wing moves aft. This is with no rudder appilcation.
So if you were to counter torque roll by only aileron it would yaw the airplane into the direction of the torque. This would create more problems. An airplane yawing to the left, turning left and rolling to left so how can fly in the direction you want to go in. Only by using rudder and no aileron can you effectivly counter torque roll and maintain directional control too. Plus have less drag on the airframe. No assemetric drag from the ailerons. Remember that in flight at cruise speed rudder is very effective to counter torque roll. You can also turn a airplane by rudder alone.
When you move the engines out toward the wing tip the torque force is still present but the force it applies is in the form of yaw moment to the airframe not a roll moment. When flying a multi-engine you can see this very clearly, and by doing so it makes this very simple to understand.
What would the stabilized flight situation look like in terms of yaw and bank? This is difficult to visualize for a non-pilot :-)
Stabilized flight at cruise airspeed would be this:
Single Engine Airplane: Right rudder or right rudder trim to the right.
Multi-Engine Airplane: both props same rotation to the right (same as for the single engine airplane).
MEA: counter rotational props, nuetral rudder
SEA: aileron nuetral, Aileron trim nuetral.
MEA: Airleron nuetral, Aileron trim nuetral (same rotation props and counter rotational props)
SEA: Elevator nuetral or nose down, elevator trim nuetral or nose down.
MEA: same as in the SEA (same rotation props and counter rotational props)
You have a good understanding so far. HoHun good points.
Straiga
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Hi Golfer,
>There is something called Adverse yaw.
Yes, I should have said "adverse yaw".
Then the situation would be: Clockwise turning propeller, anti-clockwise (left) torque-induced roll, we feed in right aileron in order to keep the wings level, producing adverse (left) yaw. So we end up wings level, ailerons deflected, rudders neutral, in a left yaw.
Does that sound plausible?
>I'm confused slightly (I understand all the principals you're referring to) about how you might mean to interpret when you say aligning the thrust line and P-factor.
Let's say that in our cruise situation, the free airstream hits the propeller disk perpendicularly so that the propeller blade angle of attack is symmetrical and we have no P factor effects.
(Thinking about it, P factor would also induce a left yaw for the situation described above, so we seem to have two factors adding up.)
Regards,
Henning (HoHun)
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Hi Straiga,
>Stabilized flight at cruise airspeed would be this:
>Single Engine Airplane: Right rudder or right rudder trim to the right.
>Multi-Engine Airplane: both props same rotation to the right (same as for the single engine airplane).
The thing I haven't fully understood yet: If you're flying with a slight right yaw, does that mean you have the left wing down a bit?
In any case, the left wing gets a bit more lift due to the dihedral effects Golfer mentioned, compensating the (as I assumed, rolling) torque without the necessity for an aileron deflection?
I assume the slight right yaw trim is preferable above the wings-level, left yaw, ailerons deflected situation described in my post above?
If I manage to score 2 out of 3 here that probably means I'm getting real close ;-)
Regards,
Henning (HoHun)
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The thing I haven't fully understood yet: If you're flying with a slight right yaw, does that mean you have the left wing down a bit?
When your flying straight and level with rudder input to the right th ball is centered wings level. No right yaw at all.
The vertical stabilizer is set at an angle of attack to the left of the center line of the airplane. Also the left wing sets a higher angle of incidence then the right wing this is rigged to counter torque roll as the vertical stabilizer is.
Angle of incidence is the fixed angle of attack position of the wing to the fuselage.
In any case, the left wing gets a bit more lift due to the dihedral effects Golfer mentioned, compensating the (as I assumed, rolling) torque without the necessity for an aileron deflection?
Dihedral is set into both wings as the plane rolls in one way the lowest wing is at a greater angle of attack and will create more lift then the other wing and will roll the plane level again.
Then the situation would be: Clockwise turning propeller, anti-clockwise (left) torque-induced roll, we feed in right aileron in order to keep the wings level, producing adverse (left) yaw. So we end up wings level, ailerons deflected, rudders neutral, in a left yaw
Yes exactly.
Let's say that in our cruise situation, the free airstream hits the propeller disk perpendicularly so that the propeller blade angle of attack is symmetrical and we have no P factor effects.
When the relative wind is perpendicular to the prop disk the prop has equal lift through out the prop disk. But when you change angle of attack of the main wing up the prop disk on the right is at a higher angle of attack the left side of the prop disk yawing the plane to the left. Now when the airplane is nose down the left side prop disk is now at a higher angle of attack and yaws the plane to the right.
There are two types of wind that affects the airplane. 1 the wind that blows around the trees and 2. relative wind which is the oposing wind which is oposite to the flight path of the airplane. It is not oposite to the way the airplane is pointing but the direction its is traveling. ie nose high but moving forward.
Straiga
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The vertical stabilizer is set at an angle of attack to the left of the center line of the airplane. Also the left wing sets a higher angle of incidence then the right wing this is rigged to counter torque roll as the vertical stabilizer is.
Straga: Do we agree that the left wing greater AOA is simply to counter the engine torque. I.E. preforming the same functions as ailarons.
Also:
Dihedral is set into both wings as the plane rolls in one way the lowest wing is at a greater angle of attack and will create more lift then the other wing and will roll the plane level again.
Can you describe how the low wing, in a stead state bank with dihedral creates more lift than the other?
If your just talking about the yaw produced in the bank , and that yaw producing oposit roll then no need to describe the dynamics.
Also: If you do not except that moving engines outboard does not effect there torque on the plane. We are realy going to have a hard time totaling up the forces for stable flight.
HiTech
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Hi Straiga,
>Also the left wing sets a higher angle of incidence then the right wing this is rigged to counter torque roll as the vertical stabilizer is.
OK, let's assume a simplified symmetrical airframe.
In that case, the higher lift required from the left wing would be the result of more favourable aerodynamics on the left wind due to the right yaw?
(Fuselage blanketing the right wing and lots of complex stuff - I guess this is why Golfer asked for a specific aircraft type :-)
Regards,
Henning (HoHun)
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Straga: Do we agree that the left wing greater AOA is simply to counter the engine torque. I.E. preforming the same functions as ailarons.
Yes I agree this is why no aileron is nessasary only in a single engine airplane.
Can you describe how the low wing, in a stead state bank with dihedral creates more lift than the other?
Think of a dutch roll.
If you do not except that moving engines outboard does not effect there torque on the plane.
Torgue does not change true but how it affects the airframe in a multi-engine airplane yes it does change to a yaw moment.
Go ask somebody else if you dont believe me thats all.
Straiga
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Originally posted by hitech
Straga: Do we agree that the left wing greater AOA is simply to counter the engine torque. I.E. preforming the same functions as ailarons.
Also:
Can you describe how the low wing, in a stead state bank with dihedral creates more lift than the other?
HiTech
It doesn't, actually. BUT the more horizontal wing has a higher component of it's lift vector pointed straight down. One thing to remeber is that in ground school, they always talk as if the wing lift vector in stable cruise flight is straight down. Actually, it isn't in a plane that has wing dihedral. It's off vertical by the amount of dihedral, and some lift is lost in a horizontal direction. Not much, but it is there.
In a plane with dihedral, when a wing drops, the downmoving wing becomes more horizontal, and the upmoving wing less horizontal. Without dihedral, the falling wing becomes less horizontal at the same rate in the opposite direction as the rising wing.
Back to the plane with dihedral. As the dropping wing rotates past horizontal, it still has a smaller angle to the horizon as the rising wing, and still has a larger lift vector straight down. The net effect of this is that when a wing drops, aerodynamic forces tend to right the plane about the longitudinal axis.
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A wing does not generate more lift because it is oriented horizontally. The reason dihedral works is that when the wing drops it induces a slip that moves the relative wind to a greater AoA on the decending wing.
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Casca: That has always been my understanding.
Straiga:
Torgue does not change true but how it affects the airframe in a multi-engine airplane yes it does change to a yaw moment.
You keep stating that engine torque is changed to a yaw. But never describe how.
Unless I missed it some where.
Now if your just describing that torque is counter by extra AOA in the one wing, or by ailaron, then because of the extra AOA more inducuded drag, hence that needs to be countered with rudder.
Then im in agreement.
But the fact still remains that moving the engines out board did not in any way change the engine torque in the roll axis. Nore how those forces affected the airframe. They were just compensated for in the rigging of the plane.
Straga: Also wondering if you have ever done power off and power on stalls in a twin. And noted the difference in stall speeds? Haven't done the calcs but curious how much speed difference in a light twin.
HiTech
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Originally posted by Casca
A wing does not generate more lift because it is oriented horizontally. The reason dihedral works is that when the wing drops it induces a slip that moves the relative wind to a greater AoA on the decending wing.
EDITED FOR CONTENT I guess that DURING the initial roll motion, the aoa changes. However, neither of our statements is completely accurate. According to the NASA web site, there is sideslip involved. But they also show the vector info I have been talking about.
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Hi Hitech,
>You keep stating that engine torque is changed to a yaw. But never describe how.
I think from the discussion above, I could summarize that the yaw is generated due to engine torque as soon as the pilot generates a rolling moment to counter engine torque.
The pilot could either use aileron, which would lead to a strong yaw with ailerons deflected, or rudder, which would lead to an insignificant yaw with ailerons centered.
So I believe both the concept of torque causing a rolling moment and the concept of rudder input being the proper piloting technique because the pilot will be dealing with yaw if the engines produce torque have turned out to be correct :-)
Regards,
Henning (HoHun)
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Not quite sure I agree with that. First in normal flight the ailaron force would be very very small.
2nd if the ball is already centered and only a slight roll is occuring.
You would have to have a non centered ball to maintain level flight. You would just percieve this as a slightly heavy wing and correct it with ailaron and fuel tanks.
Btw, can't say I have ever consiously felt torque on any plane i've flown. Pfactor and slip stream far out weigh it's scale.
On a real smoth day been wanting to do some hands off test of climb and level flight with ball centered to see how much roll is affected. Wish I had ailaron trim to test with.
Also: In a departure condition, or at very slow flight, if a wing droped do to torque I 100% agree proper action would be to correct with rudder. Ailaron would be a very very bad thing at that point.
HiTech
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Hi Hitech,
>Not quite sure I agree with that.
Well, we made a number of simplifying assumptions in order to isolate the effect.
For example, if you're flying an asymmetrical aircraft, it does some of the compensating by itself.
Additionally, the pilot mainly tends to perceive changes in forces or moments, and the engine torque is constant in cruise.
Only when making rapid power changes, the equilibrium is upset and an impression of the order of magnitude of the rolling moment is conveyed.
I'd imagine this is the kind of rapid power change one would prefer a simulator to try it out :-)
Regards,
Hennign (HoHun)
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Straga: Also wondering if you have ever done power off and power on stalls in a twin. And noted the difference in stall speeds? Haven't done the calcs but curious how much speed difference in a light twin.
I have done stalls lately in a King Air 200 twin turbo prop 12,500 gross wieght, my books are out in the truck right now, so to get the exact stall number but give me time I will get them for you. The big difference in stalls is in the power on stalls you will have a higher angle of attack. With full power, its stalls about 47 degrees nose up and I think at about 79 kts but let me check for shure. Power off we hold a set altitude bleed the power off maintaining altitude and its stall about 64 kts. Then applie full power a lot of rudder and still hold the pitch angle and blow the stall off with full power prop wash. Its is a instant stall recovery.
Ok guys there are two types of planes generaly single and multi-engine. Now in a single engine the prop sits in the roll axis or logitudnal center line. So the plane has been built to counter torque roll efects by increasing the angle of incidence of the left wing and the vertical stabilizer, its angle of incidence is set to the left of center line to also counters torque effect and prop slipstream. So at cruise aileron is really not used to counter torque roll effects at max cruise speed. Rudder can be applied to counter torque roll better then aileron because of averse yaw do to the aileron. There is more drag on the airframe with aileron adverse yaw so more rudder is nesissary to counter the adverse yaw but also torque roll.
At a slow cruise with a power increase just use rudder. Match power increase and rudder at the same time, there is no torque effect. If you counter torque with aileron you will get an averse yaw and rudder will still have to be applied for directional control.
Do you guys understand? Yes , No ?
Now for a multi-engine there still is a roll axis is in the center line of the longitudnal center line of the airframe. If we had a twin engine or a four engine airplane. We can see that the engines do not sit in the longitudnal center line of the airframe. The engine now sit away mounted to a wing not the fuselage. The engine acks as a lever on the airframe. You may think that the airplane can still torque roll as in a single engine airplane, but because of the distance of the engine from the longitudnal center line and the leverage its exerts on the airframe it can no longer roll the airframe due to the aerodynamic force in play and the mass of a heavier airframe, so all it can force the airframe to do is yaw the airframe not roll it. The center of torque roll axis on the multi-engine is in the center line of the engine thats is mounted to a wing not the longitudnal center line or roll axis of the airframe. This distance between the two also contributes to a yawing moment.
Take a length of wing say 30 ft long and mount a engine in the center and think of it as a single engine airplane with each wing being 15 ft long. Now the plane will torque roll to the left with the engine at the roll center axis. Now with this same wing mount a fuselage on the left wing tip, now you would think that the plane will still roll left, but we have a horizontal stibilizer and elevator and also a vertivcal staibilizer with rudder on this fuselage preventing this. Now add another 30 ft wing with engine in the center to the other side of the fuselage and that wing trying to roll left, it cant because of the elevator and rudder. So can you see why it has no roll effect just yaw. The wings of a multi-engine have no angle of incidence in them because there is no torque roll to counter. I have tryed looking for something to show what happens in this situation with some kind of math but I have had no luck. I hope this explains what happens, but with my multi-engine flight experience please believe me this is what happens. I not trying to blow smoke, this is just the way multis fly. Can you see what Im trying to explain here. Please say yes. LOL
2nd if the ball is already centered and only a slight roll is occuring.
Im assuming this situation is level unexcellerated flight, if so, when the wing rolls the ball will be oposit the roll correct. If the ball is centered with rudder the wing should be level with no aileron input to counter the roll. I dont think you can have a slight roll with the ball centered. If anything any roll, use rudder and the ball will be centered.
Also: In a departure condition, or at very slow flight, if a wing droped do to torque I 100% agree proper action would be to correct with rudder. Ailaron would be a very very bad thing at that point.
Yes I agree, plus at slow airspeeds there is very little aileron effectiveness.
Later Straiga
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I am a failure. I even drew a friggin picture. I am quitting aviation and am going to be a...I dunno.
This is infinately easier to explain in person using fun hand gestures but look at the pictures and read what straiga just said. pleeeeease.
Straiga, I was sifting through my Spam folder and caught an email you wrote (Thanks AOL!) but it didn't have any data. Remember anything about it?
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Golfer I think it was about a BE-350 manual. Read my post again its been updated.
Straiga
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Ah yes, I was going to be a good little boy and study up on the 350. As it is now, that job dried up. The pay wasn't there which really disappointed me with the company doing the hiring. They were looking for a PIC/SIC and the requirements were not all that high so a friend told me.
I faxed a resume with a letter and heard back. When salary was mentioned (I didn't pull any NBAA numbers) I really lowballed it considering it was a corporate part 91 full time job. When they said they wouldn't pay me (the figure was in the 20's) and made a counter offer. This was in the low teens. Given the projected use of the aircraft, which was 400-600 hours a year, that was decidedly unacceptable.
The way it was structured was the F/O would be not only a full time pilot, but also act as dispatcher and scheduler. I don't have a problem doing any of those jobs, but I couldn't justify working my tail off for a wage that was at the poverty level.
I asked about second year salary (I was intent on conceeding training costs for the first year low wage, as they'd be sending me to SimCom) in hopes that they'd actually make good, and this was also laughable.
I'm still the part time traffic guy and playing geetar once a week at a local 'pub' which keeps me solvent. It's amazing how aviation dried up around here lately. There aren't even any line jobs to be had. GRR!!! I love this industry.
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Why moveing engines out board has no effect the torque on the airframe created by the engines.
Below is two cases.
Case 1. One eng with 100 ft/lb of torqe.
Case 2. Twin engine with 50 ft/lb of torque each.
(http://www.hitechcreations.com/hitech/twintorque.jpg)
Also notice changing the 11 ft center line of the engines to anything else will have the exact same 100 ft/lbs result. Even if the engines are different distances on each side.
If you still do not belive that moving engines outbord has no effect on the total torque to the airframe, not much I can do to convince you.
Also.
http://www.aerospaceweb.org/question/dynamics/q0015a.shtml
And I happened to discover this sight which is one of the best I have seen in describing all forces. Including all those we have been discussing.
http://www.av8n.com/how/htm/roll.html
HiTech
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Hitech, Lets take a look at this picture. The right wing and engine is trying to roll the left wing tip down that is mounted to the right side of the fuselage. True! The left wing and engine is trying to roll the right wing tip up and away from the left side of the fuselage. The fuselage sits between both rolling moments one side rolling up one side rolling down. Both rolling moments are fighting each other with the fuselage in the middle. This is why there is no rolling moment just yaw.
I see you still dont believe me would you like a number to call a multi-engine rated CFI to help explain this.
Straiga
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Straga: This sample would be the correct rolling moment about the fuselage:
rolling moments one side rolling up one side rolling down
If one is up, one is down, wouldn't that be both helping eachother?
If you belive my diagram is incorrect show me how to calculate the moments about the fuse useing the same example.
HiTEch
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Hi Straiga,
>Match power increase and rudder at the same time, there is no torque effect.
I'd say it gets fully compensated for, but that probably means we're in agreement.
>Do you guys understand? Yes , No ?
Yes :-)
>... and the mass of a heavier airframe ...
Hm, I'd say that (along with the outward position of the engines) means a higher rotational inertia so that the rolling moment due to torque doesn't result in the quick roll acceleration we get for single-engined aircraft.
>Please say yes. LOL
I'm afraid I have to say no :-) From a formal physics point of view, it's easy - the sum of all moments in the system has to be zero for an equilibrium. Moving the engines out to the wing leaves the moments unchanged.
Regards,
Henning (HoHun)
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And a warm thank you goes out to Flying Magazine editor Peter Garrison for this month's "Technicalities" article. Feb 2005
Peter Garrison has designed from a blank sheet of paper and scratch built two airplanes. Melmoth and Melmoth 2. It just so happens that this month, his column is entitled "P Factor, Torque and the Critical Engine"
How fitting.
I am going to quote some small snippits from the article.
Logically P factor must exist, I was beginning to think, but is it really significant? And if P Factor is not the real reason for needing right rudder in a climb, what is? It must be something that closely mimics the behavior that we ascribe to P factor. Torque and slipstream rotation are the usual suspects; an often unindicated co-conspirator is propeller side force.
To clarify what torque means, imagine a single-engine airplane parked in a level attitude and running up at high power. If there were a scale under each main wheel, the one under the left wheel would indicate a higher load than the one under the right wheel, though their sum would still be the same as with the engine off. The scales would be measuring the drag of the spinning propeller blades, which is ecactly equal, by definition, to the torque of the engine. But these forces are "couples"--pure twisting forces about theaxis of the crankshaft, like the pure twisting force you use to spin a top without pushing it over--and they have no component that would pull the nose of the airplane up or down or to the side. Torque, in short, is innocent
That leaves us with propller side force and slipstream rotation
Another little snippit...
The cylindrical slipstreams of a twin's propellers pass on either side of the vertical fin. If the airplane has counter-rotating engines, as many do, there is no yaw on takeoff and climb. If it doesn't, then a low horizontal stabilizer tends to concentrate the momentum of the descending side of the left engine's slipstream on the left side of the fin while shielding the fin from the ascending side of the right engine's slipstream; the result is a left yaw, just as in a single.
There you have it sports fans, if you want to question a guy who has lived, breathed and made his life on aerodynamics go right ahead. Torque doesn't have an effect in a twin.
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Hi Golfer,
>There you have it sports fans, if you want to question a guy who has lived, breathed and made his life on aerodynamics go right ahead. Torque doesn't have an effect in a twin.
Well, that's not exactly what he said :-)
The same scale example he provides for a single-engined aircraft would also work for a twin:
"The scales would be measuring the drag of the spinning propeller blades, which is ecactly equal, by definition, to the torque of the engine."
Two engines, two times the drag of the spinning propeller, two times the torque.
Regards,
Henning (HoHun)
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Peter Garrison is a friend of mine. I'll shoot him an e-mail pointing to this thread and see if he's got some input. I 1st saw the Melmoth2 like 20 years ago :) The first one got chopped up by a DC-3 if I recall correctly, with Peter still in the cockpit!
g00b
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I've gone out of my way to pull a lot of back issues of Flying (I've only subscribed since July 2001) and I believe it was a 210 that mashed up his airplane while he was holding short.
That would be great if you could get some insight.
HoHun---the point is it doesn't matter how much torque there is. Double, Triple, Quadruple, Infin-it-oople It won't cause any effects to the flight characteristics of the conventional multiengine airplane with engines on the wings.
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Hi Golfer,
>HoHun---the point is it doesn't matter how much torque there is. Double, Triple, Quadruple, Infin-it-oople It won't cause any effects to the flight characteristics of the conventional multiengine airplane with engines on the wings.
Hm, not sure what you mean by "no effects on the flight characteristics", but it sure creates a rolling moment the pilot has to arrest somehow.
Engine torque that does not cause a rolling moment is transferred to Westminster Abbey instead, making Newton spin in his grave ;-)
Regards,
Henning (HoHun)
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based on what you said, the drag of the spinning props takes care of the engine torque.
With regards to multiengine airplanes only...ONLY. Thats all I've ever been referring to, torque doesn't do anything to the airplane. For the 35th time, without the engine on the longitudnal axis going through the CG, there just isn't any way that engine torque alone can cause a rolling tendency in the airplane. It will not happen. ever.
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Golfer: Look at my diagram again in detail. You should see how torque in a multie engine plane is transfered to a rolling moment about the CG.
And the article you post completly supports what I have been saying. Just as there would be different wieght on the wheels on the ground. Somthing in the air will have to compensate for the difference in the force on wheels when flying.
HiTech
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Straiga: When you have a heavy wing do to fuel. How do you correct for it?
HiTech
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The middle paragraph relates to the definition of torque. We all understand what it is. It also is talking about a SINGLE ENGINE aircraft. Torque is a factor due to th fact the engine is mounted in the middle of the airplane and the torque twists right along the longitudnal axis going through the CG. This gives it the leverage it needs to cause the airplane to roll. The column also goes on to conclude that torque is innocent, provide yourself with a copy of the magazine if you need further detail. Feb 2005 issue.
In a traditional twin, Torque doesn't to anything to roll the airplane. Nada. Zip. Zero.
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And the article you post completly supports what I have been saying. Just as there would be different wieght on the wheels on the ground. Somthing in the air will have to compensate for the difference in the force on wheels when flying.
This is referring to a single engine not a multi-engine.
Golfer: Look at my diagram again in detail. You should see how torque in a multie engine plane is transfered to a rolling moment about the CG.
I do not see this at all if anything its show two indipentent wings wanting to roll left but cant because of the fuselage with elevators and rudder attached. I see lots of YAW though.
Straiga: When you have a heavy wing do to fuel. How do you correct for it?
By fuel transfer or a little bit of rudder trim. If it is a large inbalance a little bit of rudder and airleron trim just a little. I know were your coming from, a large wieght in the wing has a roll moment but it is not that great at all. I have had 5000 LBS fuel inbalance in a DC-10 with out using trim. We found out the other day that one of the King Air 200s had the left AUX tank full of gas but we did not know it because of an inop fuel transfer system that was 637 Lbs of fuel we had no idea it was there or did we have to use anykind of trim either.
Multi-engines still YAW.
Thanks again Golfer
Straiga
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Ok I give, newton was incorect and forces do not require a = and oposit reaction.
Btw to put the engine torque into a scale I can relate to and to know what it feels like.
My RV is 200 HP at 2700 rpm. So that equates to 390 ft/lb torque.
If a fuel tank is 5 gallons less than the other it would create between 100 to 200 ft/lb of torque. Didn't actualy messure the moment arm of the tanks.
Now in reality the fuel isn't creating a torque, but wrather moving the CG lmoving left or right, And the lift being greater on one side or other of the CG is creating the torque. For this example It dosn't make any difference.
I.E. It is hardly notisable.
And I rest my case why pilots are not always the best at describing all the forces involved in making a plane fly.
HiTech
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And I rest my case why pilots are not always the best at describing all the forces involved in making a plane fly.
I've taken and scored well (B or better) in 3 different (2 advanced) aerodynamics courses.
Not to mention have flown all 3 basic types of twin engine airplanes. Conventional, ex. PA-23. Counter-Rotating, ex. BE-76. Centerline Thrust, ex. C-337.
I know what controls I use to do what with the airplane. With two engines operating in normal conditions on traditional twins with the engines on the wings...aileron trim isn't one of them.
That's a simple fact. Wouldn't you agree if no trim is necessary, then there isn't a force being generated that needs to be countered? If there was something there, holding in a control pressure for the entire flight would be fatiguing, uncomfortable not to mention annoying.
Hitech, you're right when it comes to single engine aerodynamics, torque is a factor. NOT in multis that are non-centerline thrust.
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Straiga:
What plane. The ones I tested all show the speed of the CV. Unless you were facing backwards?
HiTech
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Golfer: Just because you are not triming for the force, does not meen that it hasn't already been riged into the air plane.
Btw care to make a wager on my claim that torque is the same on multi Vs not? In fact Im willing to wager HTC on it.
And can even give you a simple experiment you can do at home to find out.
HiTech
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Wouldn't take that bet......
What would you do if you had Pyro, Skuzzy and everyone else sitting around your house all day?
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Hi Straiga,
>Multi-engines still YAW.
Yes, but it's not torque that causes the yaw.
The engine torque causes a roll moment.
The pilot causes the yaw moment :-)
This is in fact only a matter of perception. You're looking at the entire system and considering the bottom line. Hitech as an engineer considers all the individual sums, and it seems to me he arrives at the same bottom line, just a bit slower - and while accounting for everything :-)
Regards,
Henning (HoHun)
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Hi Golfer,
>based on what you said, the drag of the spinning props takes care of the engine torque.
Not at all. The drag of the spinning propeller IS the engine torque.
Drag is air pushing against the propeller against its direction of travel. That force is transferred directly to the engine mount, where it's actually measured on some aircraft, as BMEP with the big radials of old or as, well, torque on turbines. Something has to oppose this torque, or the aircraft will be spinning like a top in no time at all.
And whatever it is that opposes torque, it has to do so in the form of a rolling moment because by definition, everything else is not opposition.
Regards,
Henning (HoHun)
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The amount of torque being exerted on a twin is actually double. You've got two engines producing torque.
I.E. a Baron has 2x the torque of a Bonanza.
The effects torque has on the airplane in flight are different.
While the rotating propeller, engine torque, p factor and whatever else in a single require holding of right rudder (gasp! a correction for yaw) in a twin things are different.
Use a Beech Duchess as an example, counter rotating props.
No rudder necessary for takeoff/climbout flying a constant heading. Nada. Zip. Zilch. None. Zero.
In a Piper Apache, thanks to the spiraling slipstream and propeller side force you may need to hold some right rudder, just like a single. This is not due to engine torque, rather I will cite Peter Garrison again "The cylindrical slipstreams of a twin's propellers pass on either side of the vertical fin..."
"If it doesn't [have counter-rotating props], as many do, then a low horizontal stabilizer tends to concentrate the momentum of the descending side of the left engine's slipstream on the left side of the fin while shielding the fin from the ascending side of the right engine's slipstream; the result is a left yaw, just as in a single."
The reason torque isn't having an effect is because with the weight of the airplane, air passing over it or just 'because' there is no leverage for the torque to cause the airplane to roll. This is because the torque does not have the same advantage as a single (rotating around the CG) instead the entire torque and rotation of the propeller is outside the long axis of the CG.
The 160hp engines of the Apache may as well be Cox engines if you're trying to get the airplane to roll due to engine torque.
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Use a Beech Duchess as an example, counter rotating props.
Off course counter rotating props cancle eachother out with torque, but that isn't the question at hand. Why do you think they make them counter rotating?
This is because the torque does not have the same advantage as a single (rotating around the CG) instead the entire torque and rotation of the propeller is outside the long axis of the CG.
Everything you stated is correct with the exception of this quote.
It realy dosn't work like you think it does. Moving them off CG has absoltly no effect to the roll moment i.e. torque of the airplane.
HiTech
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Btw care to make a wager on my claim that torque is the same on multi Vs not? In fact Im willing to wager HTC on it.
You can keep HTC its not much to me plus my retirement is already paid for. But I bet you will not go get some multi-engine time, you will see the light.
It realy dosn't work like you think it does. Moving them off CG has absoltly no effect to the roll moment i.e. torque of the airplane.
I beg to differ.
Off course counter rotating props cancle eachother out with torque, but that isn't the question at hand. Why do you think they make them counter rotating?
To not have a critical engine thats why. If you had any multi-engine experience you would know that.
Straiga
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Hi Golfer,
>While the rotating propeller, engine torque, p factor and whatever else in a single require holding of right rudder (gasp! a correction for yaw) in a twin things are different.
Due to Newton's axioms, the torque-induced roll moment and the opposing roll moment have just the same in a (conventional) twin-engined aircraft as in a single-engined aircraft.
However, I'm ready to believe that due to the different layout the effects on piloting technique are very small or even unnoticable.
You have pointed out that torque is not the only effect, so it might simply be hidden by other, stronger effects. Add the radically higher rotational inertia of a twin and consider that a pilot perceives the forces disturbing the equilibrium, but not the forces in equilibrium, and I'm only mildly suprised there is no perception of this rolling moment and that it is irrelevant for piloting technique as a result.
That's not the same as as saying the rolling moment does not exist, though :-)
Regards,
Henning (HoHun)
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What happens in a three engine plane if all the motors are counter-rotating?
is the torque counter-balanced?
;)
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To not have a critical engine thats why.
In most cases this would be one of the resones why. But it is not the only resone.Take a look at the p38. The props do not rotate the direction you think they would to remove a critical engine. It acctualy has 2 critcal engines.
HiTech
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Please forgive my directness, but only the mathematics matters.
Attempts to describe perceived effects, forces or torques applied must be supported by the total system (including aircraft rigging) vector analysis - which will always sum to 0 in equilibrium.
Can we see the mathematics proving the theory that wing-mounted engines apply a rolling moment and torque on an aircraft differently to a single-engine configuration?
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It acctualy has 2 critcal engines.
You can't have two critical engines. Only one can 'most adversely' affect the flight characteristics.
If they counter-rotate then there isn't one, unless on one powers some sort of system (whether its vaccum, hydraulic, electrical) that will go down that the other engine doesn't have.
And the downward blade on a P-38 is on the outside. This had to do with the tail's design and so there would be a way, and I may be wrong, to get rid of severe buffeting during certain phases of flight.
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In most cases this would be one of the resones why. But it is not the only resone.Take a look at the p38. The props do not rotate the direction you think they would to remove a critical engine. It acctualy has 2 critcal engines.
Thats aircraft designers, they had no clue untill later.
Until you get some experience in the matter no one here is going to change your mind regardless of you trying to pawn off HTC to us. If you cant afford it I will pay for some time for you we can also probably pass a hat around.
You can't have two critical engines. Only one can 'most adversely' affect the flight characteristics.
You just cant beat flight experience if you did hitech I would be listening and we would be talking about something different know.
Later
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Hi Straiga,
>> It acctualy has 2 critcal engines.
>You just cant beat flight experience if you did hitech I would be listening and we would be talking about something different know.
LOL! I'd say you didn't get the joke :-)
Look at a P-38 with counter-rotating engines with one engine failed.
Then compare it to a P-38 with two equal-handed engines (right or left-handed doesn't matter) with the non-critical engine failed.
What you have is two absolutely identical aircraft. You can tell apart which one is flying on the critical engine and which one has no critical engine only from the memory which way the standing engine turned when it was still turning, but not from any physical reality.
If that doesn't seem funny to you, don't worry, engineer humour admittedly has shortcomings :-)
Regards,
Henning (HoHun)
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Originally posted by Straiga
To not have a critical engine thats why. If you had any multi-engine experience you would know that.
Wrong ,if both have the same impact they are equally critical.
It's just pure logic not physic or in-flight experience.
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Wrong ,if both have the same impact they are equally critical.
What do you think I just got through saying.
Off course counter rotating props cancle eachother out with torque, but that isn't the question at hand. Why do you think they make them counter rotating?
Not to have a critical engine. But in P-38 they got it wrong. Twins with counter rotating props that both rotate toward the fuselage do not have critical engine. The P-38 does its prop rotate away from the fuselage. Bad design.
It's just pure logic not physic or in-flight experience.
Ok Spock! You been mind melding to much with that jello bowl. Stop that.
>> It acctualy has 2 critcal engines.
Well I didnt say this and I do get the joke I have been laughing this hole thread long.
Its funny that Golfer and I have multi-engine experience and everybody who oposes us doesnt, get the point. If you do not have multi time you have no clue, truely you dont. So go get some then will talk.
Straiga
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We all know being a pilot makes you an expert in physics. So much an expert you get to change the rules.
And the downward blade on a P-38 is on the outside. This had to do with the tail's design and so there would be a way, and I may be wrong, to get rid of severe buffeting during certain phases of flight.
And at least golfer knows why it wasn't a bad design.
What does get under my skin is you will continue to believe and posibly teaching an incrorect physics principle that moments change based on where they are aplied to an object.
HiTech
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Hi Straiga,
>Its funny that Golfer and I have multi-engine experience and everybody who oposes us doesnt, get the point. If you do not have multi time you have no clue, truely you dont. So go get some then will talk.
Unfortunately, it's not very likely that Newton was wrong and you are right :-)
Considering your professional background, I'd certainly not hesitate to put my life into your hands by flying as a passenger in any aircraft you might control.
However, considering your posts on this board, I feel to obliged to offer some friendly advice: Read up physics 101. Just as Rolex pointed out, mathematics DO matter.
I'm confident that after just a short look at the chapter "forces in equilibrium", everything will come back (and I'm certain you really forgot more about flying than I ever knew :-), and you'll be able to explain your points in a way that actually makes sense even to narrow-minded engineers :-)
Regards,
Henning (HoHun)
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We all know being a pilot makes you an expert in physics. So much an expert you get to change the rules.
No I dont get to change them I just can understand them more by having that experience in flight. Im sorry you dont or wont. Dont get mad because I wont listen to you, Im just laughing that you will find out what were saying if you just go get some multi-engine time. I dont have to prove your wrong. I know whats right but you cant prove me wrong were is your physics, I dont see it, nor your experiences either.
So why dont you get some twin training. Why dont you?
What does get under my skin is you will continue to believe and posibly teaching an incrorect physics principle that moments change based on where they are aplied to an object.
I love getting under peoples skin especialy when Im right. They just get more mad when they find out there wrong. Thats even better.
All the people that I have ever taught how to fly have real experiences and praticality of flight. They dont have armchair certificates in physics. So show me Im wrong with your physics, show me, and when your wrong throughin your RV-8 along with HTC in the bet. You can keep Pyro.
I have to go fly and get more multi-engine time. Stepping on rudder to counter YAW with aileron trim in nuetral. You just have to be there.
HoHun Im not going to try to get Hitech to listen to me. I already know whats right, I fly twins every day, it his turn to prove us wrong. Which he cant do.
Straiga
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Hi Straiga,
>I already know whats right, I fly twins every day, it his turn to prove us wrong. Which he cant do.
He already did.
It's just that you need to brush up your physics in order to notice.
Regards,
Henning (HoHun)
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Straiga: Realy want you to bet on this. You name the stakes.
HiTech
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Hello all.
A humble question.
Do contra-rots have the same pitch for the inboard and outboard propeller?
Pilots note that the contra rots create no torque, or rather that one does not have to keep trimming the rudder to counter it any more.
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Well its looks like everybodys waiting on me to respond. I have dug out some info from some old texts but I dont know how to get it from this book onto this post. I can scan it but from there Im lost, Any suggestion? I have good information on Yawing moment coefficients and formulas. So if you can help me get this info on this post I would appreciate it.
Straiga
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Scan it: Email it to dalea@hitechcreations.com Ill post them for you.
HiTech
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Do contra-rots have the same pitch for the inboard and outboard propeller?
Props on any airplane very in pitch from the inboard to the tip as much as 20 degrees.
All engines will have the same props.
Thanks Hitech let me gather all this stuff I will get it to you as soon as I can. I have a lot on my plate right know so give me some time. I will probable just send you charts and figures I will type in the rest.
Straiga
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This Thread looks a bit clutterd.
1. hitech did say P38 has the props the wrong way round, making for two critical engines.
2. someone else says there are no two critical engines.
3. Straiga says that there are 2 crit engines and hitec is wrong on this one... i dont get it... misunderstanding?
4. torque on twin engined...the overall torque on the plane is around the center of gravity or?
In the famous drawing it is assumed that it is around the longitudinal axis, but that only works if there is such axis, as in a fixed mount and ther is not in a plane....
i think it is around the center of gravity, not around an axis, and when you apply it around that POINT twin engined get a diffrent momentum than one engined.
5. On top of this it is opposed by the stabilizing wings and tail, which makes the inflight behaviour eaven more complicated than just generating a torque around the CoG.
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3. Straiga says that there are 2 crit engines and hitec is wrong on this one... i dont get it... misunderstanding?
Hey Schutt, Misunderstanding, I didnt say that a twin like a P-38 had two critical engines. I just said the P-38 rotation outward is a bad design. Frankly you can have only one critical engine at a time. Now for a four engine airplane this statement is true. The reason why some multi-engine airplanes have counter rotating props is to get rid of the effects when the critical engine dies.
I sent Hitech pages of info thats he is going to post for me so stay tuned. I sending more info also.
Later Straiga
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Hi Schutt,
>3. Straiga says that there are 2 crit engines and hitec is wrong on this one... i dont get it... misunderstanding?
I think we all agree on the physical facts, the disagreement is actually just a question of nomenclature. Straiga of course is right that no engine is called "critical" when they are contra-rotating, and Hitech of course is right when the effect of the P-38's engines' sense of rotation is the same as being left with the critical engine on a twin with co-rotating engines.
>4. torque on twin engined...the overall torque on the plane is around the center of gravity or?
Ah, that question aims right at the core of the misunderstanding :-) Torque is not calculated around any certain point, it just adds up. You only have to consider an axis when you convert forces into moments.
>5. On top of this it is opposed by the stabilizing wings and tail, which makes the inflight behaviour eaven more complicated than just generating a torque around the CoG.
I'd say that while the entire system is complicated, the situation with regard to torque is very simple :-) The engines produce torque, something else generates an opposite moment. The side-effects of "something else" account for all the effects the pilots here describe (as I'm confident) absolutely correctly.
I'd suggest that the situation for the twin-engined aircraft is exactly the same as for the single-engined aircraft (on which we all seem to agree), except that due to higher rotational inertia, longer aileron moment arms etc. the rolling moment is much smaller than for the single so that it's submerged in the larger "side-effects" :-)
Regards,
Henning (HoHun)
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This whole thread has been a talk of not just torque exisiting (it does) or a twin having more torque than a single (it does, double in fact of a single with the same engine).
It's been about what's the torque do. Does it have an effect on flight? The answer is still no, for the reasons described above...there is no leverage for the torque to do anything to the airplanes with regards to creating a rolling moment. It all gets thrown into Yaw.
Anyway...I had an idea. I talked to a buddy of mine, we did our multi ratings together and I am going to make a short video. Aircraft will be a PA-23 Apache that we have access to. It's going to be a multi-engine flying for dummies video tape but its going to show exactly what control inputs are used and when.
Now, if anyone has any idea how to get those little sony handicam 8mm videotapes magically transformed into an Mpeg, I am all ears. We need to have that step figured out before we go burn a couple hundred bucks making the video.
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It's been about what's the torque do. Does it have an effect on flight? The answer is still no, for the reasons described above...there is no leverage for the torque to do anything to the airplanes with regards to creating a rolling moment. It all gets thrown into Yaw.
This is our basic disagreement.
It's been about what's the torque do. Does it have an effect on flight?
How it effects flight we realy do not disagree on.
there is no leverage for the torque to do anything to the airplanes with regards to creating a rolling moment
It is this statment that I say is totaly inacurate.
HiTech
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It is this statment that I say is totaly inacurate.
Well at least we made it through of 4 pages of garbage to wind up where we stood originally and have everyone sticking to their guns.
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Originally posted by Golfer
Well at least we made it through of 4 pages of garbage to wind up where we stood originally and have everyone sticking to their guns.
That's why I ejected earlier. Turned into a circular conversation.:D
edit- Regarding the video. King Schools has one. Easiest way to make a digital version of your own would be one of the Dazzle (http://www.pinnaclesys.com/Category.asp?Category_ID=1&Family=24&OpenFamily=24&Langue_ID=7) products.
I used it to make my class project video for AVSC 1010.
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Originally posted by Straiga
I just said the P-38 rotation outward is a bad design.
Ever since I first noticed the 38 was built that way I've wondered why. The only hypothesis I've come up with would be that it gets more lift from accelerated slipstream that way. Otherwise, I'm at a loss.
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Hi Jigsaw,
>Ever since I first noticed the 38 was built that way I've wondered why.
The XP-38 actually had conventionally-handed counter-rotating engines, but it was found that the slipstream over the centre-wing section disturbed the airflow and lead to elevator buffeting, so from the YP-38 aircraft onwards the direction was reversed.
Regards,
Henning (HoHun)
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Hohun, I'd thought about interference drag with the nacelles and cabin destroying lift, but hadn't thought about tail buffet. Thanks for the info.
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Golfer:
Study this drawing:
(http://www.hitechcreations.com/hitech/twintorque.jpg)
It realy is showing how to convert torques to forces and forces back to torque. And why the torque about the CG is just the sum of all torques.
HiTech
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Hitech did you get all that paper work I sent you. If you didnt get it I will fax it to you. Then we can have a better discussion about torgue not being a factor and Im sending more.
The XP-38 actually had conventionally-handed counter-rotating engines, but it was found that the slipstream over the centre-wing section disturbed the airflow and lead to elevator buffeting, so from the YP-38 aircraft onwards the direction was reversed.
HoHun where is this info your talking about.
Straiga
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Lets look at hitechs picture a second. Put the landing gear down when the airplane is sitting on the ground and if you started the right engine and went to full power torque is present and the right wing that mounted to the fuselage will tip down oposit torque do we all agree at this point. Now when this wing moves down it will tend to raise the left landing gear of the ground.
Now if we just started the left engine only the left wing that is mounted to the fuselage will move up. This will tend to lift the right landing gear of the ground.
With a multi-engine with both props turning in the same direction each wing will roll in the same direction, But when you mount a fuselage to both wings this rotation is stopped. This roll moment is then translated into a yaw moment.
If the right engine is running and release the brakes the plane will turn to the left. If the left engine is running only it will have a harder time trying to turn to the left. But either way its a yawing moment. So why doesnt a airplane roll over on its back when sitting on the ground holding the brakes with both engines running a full power. It doesnt does it.
There are other forces at work, the length of the wing, engine horse power, how big of a rudder and vert stab. How big of a horizontal stab and elevators, gross wieght of the airplane, airspeed, desinty altitude where the engines are mounted to the wing, and also how far they are from the CG and what ind of leverage they produce. All of this comes together to make airplane and will determine how it will fly.
Ok you would think in a single engine airplane that using aileron to counter torque would be the same for a multi-engine but its not. Especially when you have an engine failure, using a lot of aileron only pronounces the problem (MAKES IT WORSE) so what about this. When you have an engine out, the wing with the good engine has prop wash crossing that wing, while the other is just getting relative wind. If the plane slows where the left wing stalls the right wing with the good engine because of assmetric lift will roll the plane to the left. So by adding more aileron to counter this roll it will stall the wing faster. But not from torque roll effects. Just from an unequal lift between the two wings. One wing stalls the other does not so what happens next a spin. Whats a spin a yawing moment about an axis. This is what happens. Torque if any has little to do with this.
Straiga
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Something that I don't get about HT's drawing that one of ya'll might be able to explain;
What are the -10 and -12 representing?
If you're measuring the arm, shouldn't that still be a positive number?
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Hi Straiga,
>HoHun where is this info your talking about.
It's from "P-38 Lightning in action" by Larry Davis.
Regards,
Henning (HoHun)
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Hi Straiga,
>Put the landing gear down when the airplane is sitting on the ground and if you started the right engine and went to full power torque is present and the right wing that mounted to the fuselage will tip down oposit torque do we all agree at this point.
Hm, actually I'd say revving up the right engine on the ground will try to force the left wing to go down, loading up the left landing gear leg.
>Now if we just started the left engine only the left wing that is mounted to the fuselage will move up. This will tend to lift the right landing gear of the ground.
Revving up the left engine will give the same result as revving up the right engine.
>With a multi-engine with both props turning in the same direction each wing will roll in the same direction, But when you mount a fuselage to both wings this rotation is stopped. This roll moment is then translated into a yaw moment.
Hm, I disagree on the fuselage bit. A flying wing would behave just the same with regard to torque.
>If the right engine is running and release the brakes the plane will turn to the left. If the left engine is running only it will have a harder time trying to turn to the left. But either way its a yawing moment.
But that's the result of thrust, not of torque.
>So why doesnt a airplane roll over on its back when sitting on the ground holding the brakes with both engines running a full power. It doesnt does it.
In Hitech's picture 2, it will try to roll over onto the back. If you add landing gear legs (say at 5 ft out from the centreline), you'd find that the left landing gear gets loaded up with an extra 20 lb(f) with both engines revving at full power. (Puny engines Hitech gave us! ;-)
>But not from torque roll effects. Just from an unequal lift between the two wings.
Ah, good point - I hadn't thought about that :-) But that's with one engine out - with both engines running there is a torque-induced roll tendency in a twin just as for a single, or even for a twin when one engine is out (though aileron obviously is not the way to compensate for it :-)
Regards,
Henning (HoHun)
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Hi Jigsaw,
>What are the -10 and -12 representing?
>If you're measuring the arm, shouldn't that still be a positive number?
That's just a convenient way of representing the direction of the arm. Obviously, pushing down the left wing or pushing down the right wing will have the opposite effect, so an arm to the left of our reference point given a negative length to represent that.
Regards,
Henning (HoHun)
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Ah, good point - I hadn't thought about that :-) But that's with one engine out - with both engines running there is a torque-induced roll tendency in a twin just as for a single, or even for a twin when one engine is out (though aileron obviously is not the way to compensate for it :-)
Hmm so would you say rudder is the primary flight control used to countering this effect?
The other points I still disagree with you though, But we will get you to see the light.
When you fly any single and multi-engine in AHII with auto pilot on you see aileron trim set to the right but no rudder trim is used at all. This is a adverse aileron yaw situation why is rudder not used to counter this yaw. Also If you let a plane takeoff in auto pilot and go eat and come back a half hour later the plane has made a 90 degree left turn in course heading. I believe this is also due to adverse aileron yaw with no rudder. I would think that the plane would track straight out from takeoff with a no wind condition if rudder was used to control direction. Remember that anytime aileron is used so must rudder.
Im still insist that in flying multies I have not used aileron to counter any torque or have experienced any torque roll tendincies.
Straiga
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Havn't recieved the images yet. Sent you our fax number.
And to brush up on your physics:
Scanned from Tipler Physics (colage physics book): Pages 322 & 323
Key piece is in the description of Figure 12-25.
The couple exerts the same torque FD about ANY point in space.
(http://www.hitechcreations.com/hitech/page1.jpg)
(http://www.hitechcreations.com/hitech/page2.jpg)
Hitech
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Hitech I re e-mailed you that paper work and sent it to others they got it did you?
Straiga
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Hi Straiga,
>Hmm so would you say rudder is the primary flight control used to countering this effect?
Yes, certainly. Ailerons have unwelcome side effects, as discussed for the single-engine engine.
>The other points I still disagree with you though, But we will get you to see the light.
Thanks for the confidence :-) This thread has already been quite instructive for me because it's difficult for a non-pilot to see the three-dimensional chain of reactions around the different axes of an aircraft as clearly as a pilot does.
Maybe I should emphasize here that the torque I'm expecting from a multi-engine aircraft doesn't really mean that the pilot is struggling with large roll moments, but rather that torque is one of several forces that are in balance when the aircraft in smoothly flown while the pilot only perceives the necessity for a yaw.
Torque is not so much noticable in its direct, but in its indirect effects. That's why I consider the yaw pilot-induced, though a pilot might see it as inevitable result of the torque - which of course is true since the other option would be to let the plane roll out of control and crash.
>Im still insist that in flying multies I have not used aileron to counter any torque or have experienced any torque roll tendincies.
Hm, maybe the P-factor effects requires rudder input anyhow so that you automatically counter the torque roll in the same action? I figure smooth flying might make the torque virtually unnoticable because it's only one factor in an equilibrium.
Regards,
Henning (HoHun)
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HoHun, Logical thinking your getting there. Most twins in flight use very little rudder trim in stable unexcelerated flight. Aileron trim just sits there collecting dust. I have sent hitech a lot of paper work. I hope he gets it, its some good reading, and I will send more when he post what I have sent him.
Maybe I should emphasize here that the torque I'm expecting from a multi-engine aircraft doesn't really mean that the pilot is struggling with large roll moments, but rather that torque is one of several forces that are in balance when the aircraft in smoothly flown while the pilot only perceives the necessity for a yaw.
You would be supprized how little trim is needed in a multi-engine they are that stable until you lose a engine and thats when the fun starts. But even when this happens prop slipstream and P-factor far outway what torque does to the airframe. I have never felt any roll moment tendencies do to torque in any multi.
Torque is not so much noticable in its direct, but in its indirect effects. That's why I consider the yaw pilot-induced, though a pilot might see it as inevitable result of the torque - which of course is true since the other option would be to let the plane roll out of control and crash.
The only roll situation would be because of a single engine failure and the lost of lift on one wing while the prop wash is present across the other wing so the plane rolls due to assimetric wing lift. Any plane will roll even a glider (NO ENGINE, NO TORQUE) with this unequal lift happening. This is the first step to a spin.
Hm, maybe the P-factor effects requires rudder input anyhow so that you automatically counter the torque roll in the same action? I figure smooth flying might make the torque virtually unnoticable because it's only one factor in an equilibrium.
Ok Hitechs thinking is that a single engine airplane will roll left due to torque, and that a multi-engine has twice the amount of torque so it will roll twice as much. I havent seen this at all if anything Id say its less torque than even in a single engine airplane, effecting the airframe in a multi.
I will let the blood pressure rise on some people, and will be back to continue.
Later Straiga
HoHun I will get you out of that dark room yet!
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Ok Hitechs thinking is that a single engine airplane will roll left due to torque, and that a multi-engine has twice the amount of torque so it will roll twice as much. I havent seen this at all if anything Id say its less torque than even in a single engine airplane, effecting the airframe in a multi.
HiTech thinks no such thing. We are talking torque created in the roll axis, we are not talking how much the plane roles. How much a plane rolles is effected by many other forces that counter the torque created by the engine.
These forces are primarly .
1. Slip stream over the wing. AOA higher on one side of the prop then the other.
2. Incindence greater on one wing than other.
3. One wing having more area then other.
4. Ailron riging.
5. Flap rigging.
But what I do know is that 2 engines the same size create twice as much torque about the CG as 1 enging does no mater where you place them.
HiTech
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Hi Straiga,
>I have never felt any roll moment tendencies do to torque in any multi.
Hm, that might be because the rotational inertia grows quicker than the torque.
The P-51D weighing 6356 lbs empty according to NACA TN No. 1629 has a rotational inertia of 4486 slug ft^2 in the roll axis.
If we make us a Twin Mustang from two of these by joining them with a distance of 15 ft between the two fuselages, that will give as an aircraft with a rotational inertia of a stunning 53000 slug ft^2 (2883 kg empty, 4.572 m space, 6198 kgm^2 Single Mustang, 72661 kgm^2 Twin Mustang).
This increase of rotational inertia by a factor of almost 12 easily outweighs the increase in torque by a factor of 2.
(In normal twins, you don't actually move the entire mass out of the centre line but only the engines, but these usually a bit farther than on the P-51, in relation to the propeller diameter.)
This calculation shows us that twins with off-centreline engines should be much less susceptible to roll accelerations than singles. Accordingly, despite the increased torque, the torque would be much less noticable and probably completely buried by P-factor and slipstream effects.
>Ok Hitechs thinking is that a single engine airplane will roll left due to torque, and that a multi-engine has twice the amount of torque so it will roll twice as much. I havent seen this at all if anything Id say its less torque than even in a single engine airplane, effecting the airframe in a multi.
Maybe my Twin Mustang example has contributed to resolve this apparent contradiction. I still think the pilot mostly notices torque changes and not so much the constant torque, so the high roll inertia of a multi really seems to be a reasonable explanation for your experience.
>HoHun I will get you out of that dark room yet!
I can already see the tunnel at the end of the light ;-)
Regards,
Henning (HoHun)
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HoHun read the post that says straiga heres your multi-engine pictures.
Straiga
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Hi Straiga,
>HoHun read the post that says straiga heres your multi-engine pictures.
Roger, I already did! Great read, highly instructive. Shortly afterwards, I came across a picture from the Tupolev Tu-2 manual recommending a 15° bank in an engine-out situation - which scared me badly! ;-)
But I agree with Hitech that engine torque wasn't mentioned at all. Of course, that might have been your point :-)
Regards,
Henning (HoHun)
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C'mon this thread shouldn't be this long. First day of high school physics. Equal and Opposite Reaction.
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I sent Hitech more paper work He should have it post later.
But I agree with Hitech that engine torque wasn't mentioned at all. Of course, that might have been your point :-)
My point exactly. Torque is so minor, but prop slipstream and P-Factor far out weigh what torque has on the airframe. If torque plays any part in the way multies fly you would think that at least it would be mentioned.
C'mon this thread shouldn't be this long. First day of high school physics. Equal and Opposite Reaction.
I guess you never flown a multi-engine airplane then.
Hey what happen to all the multi-engine paper work.
Straiga
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Hi Straiga,
>My point exactly. Torque is so minor, but prop slipstream and P-Factor far out weigh what torque has on the airframe. If torque plays any part in the way multies fly you would think that at least it would be mentioned.
Hm, now if you say torque as a rolling moment is there, but it's not a major factor, we're actually getting closer. As I have pointed out, it should be less noticable on multi-engined aircraft than on singles due to the higher rotational inertia of the multis, but it has to be balanced the same. Also, if you're losing an engine in a twin, torque halves while other problems multiply, so I'm not suprised it's not mentioned in the engine out articles :-)
>I guess you never flown a multi-engine airplane then.
Well, Funked has hit the nail on the head anyway :-) The rolling moment has to be there, and for stable flight, it has to be balanced by an equal and opposite rolling moment. The only question is, where does that come from?
Regards,
Henning (HoHun)
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Hohun let me get to work and i will post back on 31st.
Later Straiga
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Originally posted by HoHun
Well, Funked has hit the nail on the head anyway :-) The rolling moment has to be there, and for stable flight, it has to be balanced by an equal and opposite rolling moment. The only question is, where does that come from?
The fuel tanks. Fuel is pumped into the engine combustion chambers where it is burned. The burning causes the gas to expand, and this causes the turbine rotors to spin. The turbine stators act like a cylinder head does to a piston, confining the gas so that it can only expand by spinning the rotor.*
The stators in the engine have forces on them due to their associated differential pressures, those forces are transferred to the engine case, then to the mounts, and ultimately to the airframe.
As turboprops are constant rpm engines, the only way to change the HP is to change the torque setting.
On a typical demonstration flight at 10,000 feet, with 3 to 5 people on board and full fuel, prospective Comp Air 7 Turbine builders will observe cruise speeds of about 220 mph indicated airspeed (IAS) at 100 lbs. torque, or about 205 to 210 mph at a typical economy cruise power setting of 80 lbs. torque. At this power setting (about 95% N1)
*simplified but pretty much the idea. Actually the stators redirect the gas flow rather than confine it.
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Originally posted by Straiga I guess you never flown a multi-engine airplane then.
Yes, Newton was wrong, he didn't have enough multiengine experience. Multiengine experience clearly trumps the physical laws of the universe. Silly me!
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Straiga: Can you also send the next page of the first group of documents.
The Section is labled Four factors that make the left engine critical (American Engines) But then it only List 2 of them P-factor and spiraling slip stream.
HiTech
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Here's a link to an article that talks about flying multi-engine planes on one engine.
http://www.avweb.com/news/airman/184438-1.html
Seemed to explain some things nicely.
Snak
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Yes, Newton was wrong, he didn't have enough multiengine experience. Multiengine experience clearly trumps the physical laws of the universe. Silly me!
Your still wrong, Newton didnt have any multi-engine experience at all so your in good company. Newtons law still applies though not do to torque, but to Yaw do to asymmetric thrust. Read the post (Straiga your multi-engine images). Newtons at work.
The Section is labled Four factors that make the left engine critical (American Engines) But then it only List 2 of them P-factor and spiraling slip stream.
No prob hitech Im at work right now I will be back on the 15th and I will send them out to you. But I think the other two are low airspeed and high power conditions. So what do you think so far?
Snak good artical too.
Straiga
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I know the F-4 Phantom's engines could produce enough torque to roll a parked plane if the throttles were punched from idle to full power.
That little fact backs up everything Holden McGroin has been saying.
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As turboprops are constant rpm engines, the only way to change the HP is to change the torque setting.
So all along that pesky N1 gauge just produces a number out of thin air? I hate being lied to by aircraft flight manuals :( They all told me it measured tubrine RPM which was portrayed on the gauge in percentage format. Damn engineers.
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Perhaps I was being too simplistic as this thread was started to explain how or if a turboprop transfers torque to an airframe, but I should have used the term "relatively" when saying that a turboprop engine was a constant rpm engine.
The prop has a maximum rpm. It cannot have a tip speed past Mach 1. Prop speed governers keep the rpm from climbing higher.
On a PT-6 once 100% prop speed is reached, you can still alter horsepower, and that is done by altering the torque. The prop pitch is altered accordingly.
Horsepower is changed at a constant rpm by changing torque.
Obviously the rpm changes when the engine ramps up and shuts down, and for those phases of operation like decent that require a "relatively" small percentage of engine power.
(https://engineering.purdue.edu/ECO/wrap2/themes/default/aa/bannerHead.gif)
Purdue explains it "A turboprop engine bears a functional similarity to a turbofan, in that the shaft of the engine is used to drive another system. The other system is in this case a gearbox and a propeller, rather than a ducted fan. The core engine is designed much more in focus on creating torque, rather than providing thrust. The core should account for less than 10% of the engine's total thrust."
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I know the F-4 Phantom's engines could produce enough torque to roll a parked plane if the throttles were punched from idle to full power.
Well I just spoke to my dad about this he just laughed. Hes a retired Major General USAF with 1200 hrs F-4 time 106 mission in the F-105 and F-4 over N. Vietnam. He told me on rdy alert they used to start the engines and put the throttles in full burner. After the engines would spool all the way up they would go into burner and release the brakes and get it air. He did the same thing in an F-111.
But to have enough torque to roll a plane on the ramp no thats not possible. If you shoved the throttles full forward you would spike the temps first, and probably would have a great bang due to compressor stall. Turbines engines are never cramed full throttle while sitting on the runway with no airflow across the airframe. Power is advanced slowly until the temps stabilize then you can advance the throttles briskly all the way into burner. As for starting in burner it is one steady increase in rpm with no temp spikes. When your in the air it is a different ball game but you can still compressor the engine, with rapid throttle management.
Straiga
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The more rice you feed the hamster the faster it goes!
:D
The less rice the slower it goes!
:rolleyes:
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The more rice you feed the hamster the faster it goes!
OK!
The less rice the slower it goes!
OK! again
So whats that got to do with anything.
Straiga
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No offense Straiga but your full of bs with this statement.
If you shoved the throttles full forward you would spike the temps first, and probably would have a great bang due to compressor stall. Turbines engines are never cramed full throttle while sitting on the runway with no airflow across the airframe.
Especially considering we do throttle snaps in the hush house from idle to burner on the F-15s with Pratt & Whitney F-100-PW-100 motors to ensure the EEC is properly trimmed. We do the checks step by step per the technical orders for trimming the motor. Last time I checked these are turbine engines with the throttles being crammed to burner. Granted we do each engine seperately but that's purely due to the fact the hold back tool and arresting hook can't handle both engines in AB at the same time.
If a motor isn't trimmed properly then yes it will have a compressor stall when snapping from idle to burner. That's why we do these checks to ensure the motors won't stall if the engines are slammed from idle to mil or burner in any situation. I know our aircrews also walk up purely so that if in the event of a compressor stall during take off it will happen early and not during the red zone of take off. If the plane were to have a compressor stall in this zone the aircraft would come smashing back down to the runway.
Simple fact is if you have a compressor stall because of snapping the motor from idle to burner it's due to an improperly trimmed motor or a faulty Electronic Engine Control. Newer turbine engines like the Pratt & Whitney F-100-PW-220 or 229 don't have many issues with this due to the Digital Electronic Engine Control and the PS2 probe that monitors airflow down the intake. These motors can auto trim the motor through the DEEC which drops the compressor stall incidents to a minimum. Typically you'll see stall stagnations which majority of the time are pilot induced failures. They'll yank and bank and forget to input throttles and stall the motor in the process.
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In the late '70s I had a turn-up license for the GE J-79 for my squadron's F-4s. Once the engine is started, oil pressure and temp stable, there weren't limitations that I recall on how fast you move the throttles, or how far while on the ground, as far as the engine itself was concerned. Also, runups to 90 percent were standard max on the flightline for maintenance. And the pilots would hold mil at the end of the runway, release brakes and go to burner immediately, before there was any significant airspeed.
--- Maintenance war story alert ----
Once electric shop needed fuel tanks completely empty to recal the fuel gauges. The jet mech was burning off the bird's remaining fuel on the flight line, chocks on the main wheels and ONE tie down chain at an angle on the nose wheel. The jet mech got impatient and went beyond 90 percent, (they said he was nibbling burner), the plane was already light from practically no fuel. The plane jumps chocks, the tie down chain on the nose swings the nose around long enough to keep it from crashing into the hangar, then breaks, and the plane "taxies" at 100 percent several dozen yards across turf till it sinks enough to stop it. The jet mech would-be pilot was passed out in the seat. Dang, plane went hard down for a long time till they magnifluxed the LG.
Another strange maintenance story to make you marvel. Hyd leak somewhere inside the extremely long intake throat of an F-8 Crusader. Hyd shop couldn't find the leak on the outside, whether the plane was turning or not, or on the inside when not turning. So, they asked for a volunteer to "dive the intake" while the bird was turning. They tied a rope on the guy, taped his aural protectors on his head and sent him down the intake of the turning bird. And, he found the leak. Crazy Marines.