Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Straiga on January 04, 2005, 03:51:14 AM
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Is it me or does the B-24 have to roll aileron in on takeoff I guess to conter prop torque. 4 engines null the torque in the airframe.
All 4 engines are off the longitudnal center of the airframe torque is not a factor. I cant see 4 engines trying to roll over an airplane, maybe P-factor or Yaw but not torque. But P-factor is Yaw what am I saying.
Do you see my point.
OK hornets have at it.
Straiga
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Multiple engines do not counter torque. Some of the torque is absorbed by the airframe, but not all.
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Hey GScholz, do you have any idea why the controls show right aileron on takeoff and show right aileron in straight and level flight. Is this a glitch or more AH physics.
Hey did you read my post for real pilots?
Straiga
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Yes I did, and I held similar views some time ago. I was however proven wrong. I suggest you read the following threads before continuing yours.
http://www.hitechcreations.com/forums/showthread.php?s=&threadid=95026
http://www.hitechcreations.com/forums/showthread.php?s=&threadid=95079
As for the B-24 FM ... I have not yet had the pleasure of flying that plane since I've been on "vacation" from AH for some time now. However I think you will find that all multiengine aircraft in AH does suffer from the effects of torque ... with the notable exception of the P-38, which had counter-rotating props and cranks.
Also AFAIK modern turbo-props do not generate torque like piston engines do since they do not "push" on the engine block to turn the prop like pistons do, but simply blow air through a set of turbines. The props still generate prop wash though.
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GScholz. I dont see anywhere or any post that proved you wrong.
I total agree with your opion. Did you read the tail plane icing sight.
Straiga
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No I did not read it. I only have time for a short post before I must go.
The tail plane can create lift and still keep the plane stable. The NACA (or was it NASA) documents HiTech showed me in one of those threads proved that.
It then becomes quite clear that if the tail plane is removed the nose will pitch up unless all the weight the tail plane supported also is removed. These planes were "ass heavy", and you can easily see that if you take a closer look at some of these planes. The P-39 series is a prime example. It even had the engine mounted behind the wing. Clearly (or at least intuitively) one can see that the tails of these aircraft had to carry some weight.
(http://www.realtime.net/centex/MissConnieCopyright.jpg)
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Looks to me like the engine sits in the mid range CG and is mounted low also. I guess the gas in the wings and nose also. I dont think it is to much tail heavy either.
Straiga
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Is it me or does the B-24 have to roll aileron in on takeoff I guess to conter prop torque. 4 engines null the torque in the airframe.
All 4 engines are off the longitudnal center of the airframe torque is not a factor. I cant see 4 engines trying to roll over an airplane, maybe P-factor or Yaw but not torque. But P-factor is Yaw what am I saying.
Yep I see your point, you have never had a physics class.
Because absolutly everything you state about torque in this post is incorect.
Moving the engine out on the wing has absolutly no effect on the torque aplied to the plane. It dosn't change even 1 foot/lb.
HiTech
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OOOHHH TESTY!
Yes your right I have never had an AHII physics class Im not into fiction.
Im in a physics class every day flying for a living.
So explain why right aileron is used on take off in a four engine bomber when you dont need to. Explain youself I would like to hear this.
I guess you dont have a multi-engine rating either.
Straiga
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If, in four engined plane, two propellers rotate clockwise and other two counterclockwise, then torque is cancelled and aileron input should be not needed. If all props rotate in the same direction, then the total torque is four times the torque of one engine. That the engines are offset from the center axis of the plane is irrelevant.
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Lets start at the Number 1 engine. The engine sits on the pilots side all the way out on the wing. Prop rotation clockwise the helical prop downwash hits the top and right side of the wing and under the wing on the left side. Prop torque rolling moment to the right the resultant torque moment to the left.
Rolling moment is reduced to a yaw-wise torque since the engine does not lie in the center line rolling axes. This is the same for all the engines.
Plus on takeoff using differential power you dont even to need rudder on takeoff.
The B-17 time I have, did not require ailerons on takeoff or climb out.
I bet you guys will say also that if you lose 1 out of 4 engines you only lose a 1/4 of your total power output or in a twin engine you would lose half your power. WRONG!
Straiga
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In real life, none of the 4 engines had exactly the same rpm. Imperfections in the prop and the airframe also influenced yaw and roll.
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Originally posted by Straiga
I bet you guys will say also that if you lose 1 out of 4 engines you only lose a 1/4 of your total power output or in a twin engine you would lose half your power. WRONG!
Straiga
80% loss in a twin. I've never seen the power/speed ratings for a quad, so can't comment.
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You got it Jigsaw
4 engines you lose two its about 70 to 80% loss
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Lancaster pilots had to use full right rudder on an overloaded takeoff to counter torque.
That's got four engines...
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Originally posted by Seeker
Lancaster pilots had to use full right rudder on an overloaded takeoff to counter torque.
That's got four engines...
B-24 was famous for requiring a lot of right alieron. There's a cartoon somewhere showing a B-24 pilot with huge biceps - on his left arm only.
- oldman
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The B24 pilots had to hold the yoke with their left arm whilst working throttles etc with their right.
It was known as a heavy aircraft to fly (no power assistance) and required constant trim adjustments.
Therefore the inflated left bicep was due to the left arm doing a lot of work just to fly the plane.
Pilot Comments:
"You could always tell a Liberator pilot by the bulging biceps muscle in his left arm, from hauling on that yoke for 14 hours at a stretch."
"Where the B-17 was an airplane, the B-24 was a truck."
"The airplane has inherent directional stability which may be maintained for long periods of time by slight adjustments in trim. However, the controls are normally heavy, as they should be in a heavy airplane, and the pilot who fails to maintain proper trim is in for an exhausting workout." (From the B-24 Training Manual)
TAKEOFF
* Cowl Flaps: 1/3 Open
* Flaps: 1/4 (10 degrees) down
* Mixture: Aircraft equipped with auto-mixture control. Set to full rich.
* Elevator trim: +1-2 degrees (nose-up)
* Rudder trim: +2-3 degrees (right)
* Aileron trim: Neutral
* Power: 49" Hg/2700 rpm
* Liftoff speed: 120-130 mph IAS
Apply power smoothly and gradually, walking the throttles forward evenly until reaching full takeoff power in the first 1/3 of the runway. The aircraft will have a moderate tendency to pull to the left; use right rudder or differential throttle to correct. Good rudder control is achieved by 80 mph IAS. At 90 mph IAS, pull back on the yoke to lighten the nosewheel and assist in raising the nose. Hold the nose up and allow the aircraft to fly itself off the runway at about 120-130 mph, depending on gross weight. Retract gear as soon as a positive rate of climb is established. After reaching 140 mph IAS reduce power to rated power (46" Hg and 2550 rpm). Retract flaps before reaching 150 mph IAS. Hold the aircraft in a very shallow climb until an indicated airspeed of 155 mph is achieved.
Taken from http://www.shockwaveproductions.com/wingsofpower/manual/b24.htm
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Great post 214th Cavalier Thanks
I have time in a b-17G sounds like what how the 17 was on takeoff and real heavy on controls too. Trim baby!
HMM but no aileron for prop torque and no aileron trim for takeoff especialy in a heavy airplane like this, interesting. It may be I might know something.
I was just wandering why in AHII the B-24 rolls right aileron in on auto takeoff and has right aileron in cruise flight. But I dont see any major rudder input either. In auto takeoff it should reflect the same control inputs as you decribed.
Seems like all the planes in auto takeoff are the same way. I know when flying any single fighter that when you look back in a climb the rudder should be deflected right quite a bit but its is just centered. I just dont understand. In the real plane its definatly way to the right. You have to hold rudder for P-factor and slip stream to point the nose.
Straiga
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Straiga, instead of looking at the control surfaces look at the trim gauges. Auto-pilot in AH only control trim AFAIK
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I know but when you look at the surfaces they dont reflect needing rudder in the climb, its 0. At least some rudder should be used right. When you trim the controls it should be deflected. The trim tab goes one way while the control surface is deflected in the oposit direction.
Heres what it should be for a P-51 on takeoff. Power increases as right rudder is applied and should show about 6 degrees right rudder trim too. Elevator full up and elevator trim 2 degrees up. No aileron or aileron trim, it should be 0 anyway. Release some elevator to let the tail fly. Get the plane flying and set power for climb. You still need right rudder and very little elevator set the trim and no aileron for a straight out climb. Im still trying to figure what AHII is doing but its not this.
Straiga
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Straiga: How about you first explain how torque is removed just by moving engnines out on the wing.
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Originally posted by Oldman731
B-24 was famous for requiring a lot of right alieron. There's a cartoon somewhere showing a B-24 pilot with huge biceps - on his left arm only.
- oldman
Always keep me working oldman :)
Dan/Slack
note bottom left
(http://www.onpoi.net/ah/pics/users/169_1104995120_24s.jpg)
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I may be recalling this wrong, but it is my impression that all four engines on this plane rotated in the SAME direction. Why it was designed that way is beyond me.
-Blogs
Originally posted by Straiga
OOOHHH TESTY!
Yes your right I have never had an AHII physics class Im not into fiction.
Im in a physics class every day flying for a living.
So explain why right aileron is used on take off in a four engine bomber when you dont need to. Explain youself I would like to hear this.
I guess you dont have a multi-engine rating either.
Straiga
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Cuppy35 I dont see were its says he has a big arm due to ailerons on takeoff. YOU DO NOT NEED AILERON ON TAKE IN A B-24, B-17, and AVRO LANCASTER, B-26, B-29. But rudder you need alot. If anybody tells you different they dont know what there talking about, period.
Torque in these four engine bombers produce a yaw torque not a roll torque. Torque is there but not in a roll moment, to need aileron use for takeoff or in cruise flight. If you had some flight experience of any kind in a multi-engine you would agree.
These are some of the multi's I have flown C-310, Piper Seminole BE-55 TC, C-421, C-414,E-90, B-200, B-300,B-350, DHC-6-300, DHC-8, DHC -7 this is a big four engine turbo prop, B-17G, L-1011, DC-9-50, B-717, DC-10-10 &-30, B-767-300ER. None of these require any kind of airleon or trim on takeoff. WHAT MULTI'S HAVE YOU FLOWN?
Read what 214thCaviliar wrote about takeoff from a pilot describing a takeoff. Hmm no aileron and no aileron trim.
When are you going to believe it. I guess never. Thats sad
I have B-17G time, its funny that I have flown a four engine bomber but someone who has not , knows more about flying the thing than I do. No experience and no clue. So whats it take to believe in something and admit your wrong. I guess when it hit between your eyes or maybe not.
So how much four engine bomber time do you have, or do you even have a basic multi-engine liscence. Like I said no experience.
Straiga
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I don't think turbo-props and jets produce torque.
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Turbo props due to the prop torque itself, and turbines will if the N1 and N2 stages turn in the same direction. Some N1 and N2 stages are counter rotating.
Straiga
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Granted it's 1:15am now but I have been reading and rereading straigas posts and can't find where he said moving the engines outboard on a wing removes torque. Or at least didn't interpret the info that way.
I know if you move the engines outboard on the wings, you've got a bigger arm between that engine and the CG so if you lose an engine the other one has just that much more leverage to upend the airplane on a twin (Vmc).
I too have noticed the B-24 likes to torque left (much like a single would, if rudders were left unattended) on takeoff. It doesn't have counter-rotating propellers so P-factor/Torque/natural left turning tendencies could have to do with this. Multiply by 4 and I see how this could be a fairly big issue. In other airplanes, smooth application of power yields no real turning tendencies one way or the other. I don't normally think much about the 24's little wobble, but this week I've found myself taking off of small airfields loaded with bombs and a mountain on either side of the runway. Made me really pay attention to technique so I didn't wind up decorating the hillsides with virtual airplane parts.
My only explanation for the phenomenon would be the natural left turning tendencies associated with a clockwise rotating engine times four.
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When you take four engines and mount them on the wing you do not cancel torque from the engines or the props you just transform it into a yaw torque moment. Be it four times more than a single fighter would be, they are mounted to a much bigger airplane.
There is now more mass to move, and know there is a longer arm distance from the engines datum to the logitudinal center of the gravity. The natural twisting moment of prop or the engine torque on the airframe, like in a single engine fighter, is not the same for a four engine airplane. Because of the larger arm the engines cant not roll the airframe.
But as torque is trying to force a roll moment which it cant, it transfers it into a yawing moment torque to the left. So the yaw is the only force thats going to effect the airplane at this time on takeoff and a large amount of rudder is needed for directional control. Now as we rotate the airplane we now get two other forces that come into play.
Gyro procession will affect the plane to the right because of the pitch up moment or raising the nose gear off the ground, and the resultent moment acts 90 degrees later in the prop rotation and the force pulls the plane to the right.
P-factor the downward right rotating prop has a higher angle of attack to the relative wind, then the oposit upward rotating prop. This yaws the airplane to the left as turning force.
When you lose two engines on the same side, say the left side engines 1 & 2 then this makes the 3 & 4 engines the critical engines. Meaning that the P-factor on the 3 & 4 engines have a larger arm away from logitudinal center line. With the 1 & 2 engines feathered the drag from dead engines pull the plane to the left. The two good engines are pushing the nose to the left in a yaw torque moment.
But if the 1 & 2 engines were the ones that were running the yaw moment from the p-factor would not be as great or less critical being closer to the Logitudinal center of gravity.
We add right rudder to prevent this yawing moment. We call this dead foot dead engine, or good foot, good engine, this is a good clue to tell during the engine failure which engine or engines have failed due to yaw and rudder application. We also verify, identify and feather the dead engines and do a clean up after airplane is under control.
Just because we have right rudder in the plane it still does not want to fly straight or cordinated. In training we tape a string to the windscreen and when this string is straight on the windscreen you are flying straight. But we also have to roll the left wing 5 degrees into the good engines to help keep the plane straight, and to help counter the yawing moment.
When you fly a multi-engine the worst thing you can do is get the plane slow below effect flight control airspeed. We call this VMCA (minimum controlable airspeed)this is the minimum airspeed at which you will lose directional control of the airplane. Not enough airspeed across the flight controls to counter the force on the airplane. If you were to go below VMCA with the 3 & 4 engines yawing to the left with no aileron, elevator or rudder, effectiveness, the airplane will drop the left wing and the yawing moment will increase and will continue to drop the left wing. Then the airplane will roll inverted and be uncontrolable.
To get out of this situation, if you had the altitude, is to pull off the power on the running engines, point the nose down and level the wings. While increaseing the airspeed above VMCA and then slowly reintroduce power and maintain blue line (VYSE) or (VYME) best single or multi-engine rate of climb speed. Then hope you can get it home.
Straiga
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Originally posted by Straiga
Turbo props due to the prop torque itself, and turbines will if the N1 and N2 stages turn in the same direction. Some N1 and N2 stages are counter rotating.
Straiga
Really? How do these fans and props generate torque on the airframe when they are not mechanically connected to it? The expanding air deflects the fan blades in one clock direction while it self being deflected in the other. The structure should be unaffected. Almost like having a prop driven by a windmill.
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The B-24 Pilot's training manual (1945) indicates that all 4 propellers rotate in the same direction.
Manual recommends rudder & elevator trim for takeoff.
-Blogs
Originally posted by joeblogs
I may be recalling this wrong, but it is my impression that all four engines on this plane rotated in the SAME direction. Why it was designed that way is beyond me.
-Blogs
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Golfer:
All 4 engines are off the longitudnal center of the airframe torque is not a factor. I cant see 4 engines trying to roll over an airplane, maybe P-factor or Yaw but not torque. But P-factor is Yaw what am I saying.
Unless I miss read this,It states moving the engs off center line makes torque not a factor.
GScholz: Every action requires equal and oposit reaction.
Obviously there is torque at the prop shaft turning the prop one way . The plane has to have the same torque rolling it the oppist way of the prop.
Now there might be a small amout of torque generated the oppisit way by the gas spining as it exits from the turbin, but I have never looked into it that effect.
HiTech
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Originally posted by hitech
GScholz: Every action requires equal and oposit reaction.
Obviously there is torque at the prop shaft turning the prop one way . The plane has to have the same torque rolling it the oppist way of the prop.
Yes, every action has an equal and opposite reaction. A piston engine is like a rifle firing a piston that turns a crank (thereby generating torque). A jet turbine is like a recoilless rifle blowing an expanding gas out one end to push something in the other direction. The way I picture it, the plane structure is simply "holding" the propeller/fan shaft with a propeller spinning in one end and turbines spinning in the other end, being spun up by an expanding gas blowing through the turbines. The expanding gas leaving the exhaust pipe is the equal and opposite reaction to the turning of the shaft. Of course if you then channel this force through gears that use the plane as leverage it will produce torque on the plane structure.
That's how I understand it.
Another way of creating propulsion without torque is having a small jet engine on each prop/rotor blade.
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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.
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double post
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Originally posted by hitech
Golfer:
Unless I miss read this,It states moving the engs off center line makes torque not a factor.
HiTech
Thx for the snip Hitech,
The way I viewed that was it takes away the rolling moment of torque, which it does because it is not on the longitudinal axis anymore. Think of it this way, your RV on climbout will want to not only yaw to the left, but roll too because the engine produces the torque to make it want to roll left. In a twin, this isn't really a factor because that torque is moved away from the longitudinal axis and doesn't cut through the Center of Gravity anymore...no more rolling due to torque.
The yawing tendency is still there due to Pfactor and so on, but engine torque will not make the airplane require aileron trim. Back to your RV on departure, you hold some right rudder to center up the ball and maybe a little right aileron to keep the wings level in a level climb. If you had a twin RV8 (hmm...maybe I'll start designing, turbodiesels!) with conventional engine installations, you'd have a left yaw tendency but no left roll tendency.
What this picture is supposed to show is the "O"as the CG, the Prop ahead of the fuselage and the logitudinal axis of the airplane. This is a single:
__^__
. l I l
. l I l
. l I l
. l I l
. l O l
Now, In a twin, you do not have engines producing torque to make the airplane roll because the torque just doesn't have any way to twist the whole airframe anymore, due to it not being lined up with the CG
Masterpiece of lines and dots:
Dots symbolize thrust line, l's show fuselage and logitudinal axis.
__^__ __^__
. . l l l .
. . l l l .
. . l l l .
. . l l l .
. . l O l .
Doh! wonder why these pictures aren't lining up?
-Put in another row of dots all the way at left, disregard them.
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GScholz: I agree with you water assement, but somthing is different in the turbin engine. In the water experment the torque or force is transmited to the slowing or changing direction of the water.
So lets change this experment slightly. Same setup but this time you are standing on the platform with the bearing and holding the hose. Now there would be a torque transmited from the water exiting the hose.
Where is it transmited to when burrning the fuel? Im scratching my head on this one trying to see where all the forces are going.
And btw turbo props do go have gear boxes between the turbin and the prop.
HiTech
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Originally posted by Golfer
Now, In a twin, you do not have engines producing torque to make the airplane roll because the torque just doesn't have any way to twist the whole airframe anymore, due to it not being lined up with the CG
Have you ever held a pen or pencil between two fingers (like a cigarette) and wiggled it back and forth (creating a pleasant feeling of torque between your fingers to distract you from a boring lecture)? If you moved the pen off centre were you then unable to wiggle it?
Of course not.
A wing mounted engine will twist the airframe around the engine's crankshaft just like a fuselage mounted engine. Multiple engine will try and bend the structure between them. This will absorb some energy (since the structure will bend somewhat), but it will hardly cancel out the engine torque.
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Have you ever held a pen or pencil between two fingers (like a cigarette) and wiggled it back and forth (creating a pleasant feeling of torque between your fingers to distract you from a boring lecture)? If you moved the pen off centre were you then unable to wiggle it?
Shifting to practical experience:
My conventional twin time includes a majority of time spent in PA-23 series airplanes, though some King Air B100 time.
Since i've been a mere decoration in the cockpit of the B100 and have no formal training, its not being used in the example.
As far as the PA-23 (apache and aztec) go, I don't touch the aileron trim tab. I use the rudder trim regularly, but that big black handle above my head never gets touched.
In theory, in zero gravity and no other forces acting on the airframe, the engine torque would be able to roll the airplane. In practical application, it just doesn't happen when airspeed and gravity are factored in. When on the ground, the weight (gravity) of the airplane keep the engines from torquing left...because they just don't produce enough oomph to torque a 4000lb airplane. In flight, airspeed which is a stabilizing force, won't let them either.
In space...in theory. We're not in space.
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Golfer: That is incorect, moving the engines off center line or making 2 of them, does not change torque in the roll axis.
Torque is torque no mater what point it is applied to an object.
Your description of flight experience that not much action is required to correct for the torque can be accurate. But it dosn't change the fact that it is not because the engines are out board.
The torque is exactly the same as if they were both on center line.
HiTech
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Originally posted by hitech
GScholz: I agree with you water assement, but somthing is different in the turbin engine. In the water experment the torque or force is transmited to the slowing or changing direction of the water.
So lets change this experment slightly. Same setup but this time you are standing on the platform with the bearing and holding the hose. Now there would be a torque transmited from the water exiting the hose.
Where is it transmited to when burrning the fuel? Im scratching my head on this one trying to see where all the forces are going.
In a jet turbine the torque/force is transmitted to the slowing or changing direction of the air moving trough the turbine. Just like with the water hose, when burning fuel the force (expanding gas) is directed aft (giving additional thrust) through the exhaust pipe of the jet engine. Since a jet-turbine is rotating and balanced no other unchecked force is created, except for gyroscopic forces.
Originally posted by hitech
And btw turbo props do go have gear boxes between the turbin and the prop.
If these gears use the aircraft as leverage it naturally will create torque on the aircraft (like on helicopters). I'd have to see how it's set up to get an idea of where the forces would go.
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Maybe I'm being stupid, but why isn't this just a response to unequal lift across the wings?
I know that if I take an overloaded F6f off a CV and don't get fast enough off the deck, that plane is going to roll left unless I counter.
I always assumed one wing was stalling before the other, especially because it doesn't happen until after you gain some altitude, even if it is just a few feet.
This is less likely if I use rudder trim. Perhaps it's the yaw that determines the wing drop in a partial stall?
-Blogs
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GScholz: I assume we aggree that you can not change a linear force to a torque with out there being somthing taking the same torque in the oposit direction?
For there to be no torque on the airframe it would have to be accounted for in the mass of the spinning air as it exit's the engine. Now im not postive this isn't the case but if it was wouldn't jets have torque?
HiTech
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Originally posted by joeblogs
Maybe I'm being stupid, but why isn't this just a response to unequal lift across the wings.
I know that if I take an overloaded F6f off a CV and don't get fast enough off the deck, that plane is going to roll left unless I counter.
I always assumed one wing was stalling before the other, especially because it doesn't happen until after you gain some altitude, even if it is just a few feet.
-Blogs
The left roll you will see is due to all the left turning tendencies inherent with a conventional airplane. A major player in this case is Engine torque. You're heavy, low, slow with a high angle of attack, engine torque is at its worst here and thats why you need to counter with aileron and rudder. F4U's have particulary nasty torque and more than a few have become red marks on the back of a carrier.
I'm also not saying that Torque isn't there anymore, it just won't roll the airplane with regards to multiengine airplanes because it doesnt have the leverage to do anything with its torque.
When the engine is moved from the longitudinal axis...i.e. a twin. This just makes the engine unable to produce a roll movement with torque. It won't do it. Torque is still there, but it won't roll the airplane. Its there in yaw, but not roll.
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When the engine is moved from the longitudinal axis...i.e. a twin. This just makes the engine unable to produce a roll movement with torque. It won't do it. Torque is still there, but it won't roll the airplane. Its there in yaw, but not roll.
Gofer this satement is inacurate, Not sure how to convince you the roll torque generated does not change based on where the engine is. It realy is just a physics 101 question.
HiTech
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Originally posted by hitech
GScholz: I assume we aggree that you can not change a linear force to a torque with out there being somthing taking the same torque in the oposit direction?
For there to be no torque on the airframe it would have to be accounted for in the mass of the spinning air as it exit's the engine. Now im not postive this isn't the case but if it was wouldn't jets have torque?
HiTech
Yes I think we agree on this one Sir. To my knowledge jet-turbine engines do not produce torque on the engine/airframe.
Edit: Turbine spinning in one direction, air in the other. The forces that create these motions cancel each other out.
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Originally posted by hitech
The torque is exactly the same as if they were both on center line.
Torque still exists and still has a rolling moment. The difference is how it affects flight.
In a conventional plane if you lose the critical (left) engine, you're going to get a larger rolling effect from the right engine. This is due to torque rolling into the centerline, and the shorter arm to the end of the right wing being easier to lift.
Losing the right engine will create a lesser effect, as torque from the left engine is now in the opposite direction of centerline and has to lift most of the left wing, fuselage, and all of the right wing. However, it does help with Vmc because it wants to help "raise the dead" engine.
With counterrotating props, it's a moot point.
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jigsaw: Your asesment of why is incorect. Loosing left or right eng makes no difference in the torque do to the engines. Both effect the plane exactly the same with respect to torque. Belive this first then continue to ask why your example happens, becaue the resone you stated is not why.
Now this is not saying in anyway that loosing left or right engine it is the same. The prop slip streams flow over the wing produces lift hence more lift one wing, hence more roll. Loosing one engine obviously produce a yaw do to off center line thrust. This yaw with any dihedral in the wing also produces roll.
But you realy must belive that torque effects with respect to roll are exatly the same no matter where you place the engine.
HiTech
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GScholz:
Turbine spinning in one direction, air in the other. The forces that create these motions cancel each other out.
This would be true on a free flow of air, But what is spining the turbin to accelerate the air? If the torques match with the air spin and the turbin spin, We still need some torque to turn that turbin that would be transmited to the air frame. Im reasonable certain jets do not produce much if any torque. Therfore the air spin can not be equal torque on the turbin.
Therfore turbo props must produce torque.
btw GScholz: Im also trying to convince myslef of this.
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Originally posted by hitech
jigsaw: Your asesment of why is incorect.
I'll give you that my explanation is more detailed than what you'll typically hear, but if you think it incorrect, then do these things;
Grab a book: Multiengine Flying: Second Edition. Page 33. Read the first item listed under "What changes the airplane's minimum control speed."
Next time you're at the airport, ask around for a DE or MEI. Ask them to explain the P.A.S.T. acronym.
P: P-Factor
A: Accelerated slipstream
S: Spiraling slipstream
T: Torque
Let me know what they say.
Just for grins, here's a diagram.
(http://home.earthlink.net/~revolution/x/torque.jpg)
edit-fixed link
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Originally posted by hitech
GScholz:
This would be true on a free flow of air, But what is spining the turbin to accelerate the air? If the torques match with the air spin and the turbin spin, We still need some torque to turn that turbin that would be transmited to the air frame. Im reasonable certain jets do not produce much if any torque. Therfore the air spin can not be equal torque on the turbin.
Therfore turbo props must produce torque.
btw GScholz: Im also trying to convince myslef of this.
I think I see where you're getting it wrong. The turbines do not accelerate the air. They bleed energy from the air. The air is accelerated by overpressure in the combustion chamber of the jet engine. The only reason there are turbines in a jet engine is that it needs to draw in air at the front; leaching energy from the rear turbines to operate the front turbines that feed the engine with air.
A ram-jet is theoretically identical to a turbo-jet, but does not have any moving parts at all. However it needs to be propelled up to speed before operating independently so the ram effect is feeding it with sufficient amounts of air. In all simplicity a turbo-jet engine is an air-breathing rocket that blows on a windmilling set of fans that helps it breathe.
A turbo-prop leeches energy from the turbines to turn the prop. In modern turbo-jets/props there is usually a large set of counter rotating turbines that incrementally slow the jet exhaust down by deflecting it with the turbine-blades. This generates an enormous amount of torque on the turbines to power either a big fan (turbo-fan) or a prop.
... ... ... at least that how I understand it works.
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there's more to it than that, GS.
The compressors are there to compress air, these are some of the turbine blades. They work just like the engine in your car...
Suck Squeeze Boom Blow
Air enters engine inlet...suck
Compressors mush the air into combustion chamber...squeeze
Ignition takes place in combustion chamber...boom
Burning fuel/air mixture expands and goes out the back of engine...blow
Turboprops don't leech energy from the turbines to turn the prop, they're connected via a gearbox. So the turbine speed is controlled by the throttles, the prop speeds are controlled by prop levers and there are also condition levers that regulate fuel flow into the turbine.
The turbine engines on turboprops aren't really big enough to power anything, they're essentially little APU motors.
Here is a short halfassed paper done on the Garrett engines for a B100 turboprop that I had to do to pass my 'Turbine Transition" ground course. It's a short overview done well enough to only pass but it may help.
AVSC 4200
King Air B100 Powerplants
The B100 uses Garrett TPE-331-6 Engines (everyone knows the –10’s an a 441 Conquest just ooze testosterone, but since I left my Conquest in my other pants I will stay on subject), which produce 715 Shaft horsepower each. There are five primary fuel injector nozzles, along with ten secondary nozzles for startup. 100% N1 in the B100 is equal to 41,730 turbine rpm and 2000 prop rpm…that in anyone’s book is a whole lot of spinning. The gearbox on the engine drives the Starter/Generator, fuel pumps, flow control unit, oil & scavenge pumps, tach generator and the propeller governor.
A power and engine speed lever located between the two pilots controls the engines. The power lever basically regulates how much fuel is going to the engine in order to produce the desired amount of power. The engine speed lever sets the governors. When the governors are engaged, they limit the power to a 65% minimum to a 97% maximum. When they are in “propeller governing mode” the prop governor controls the engine speed. This will keep engine speed within the 95-100% range.
The fuel cutoff and feather levers do just that. When selected, they shut off the fuel flow to the engine and feather the prop in case of an emergency. Friction locks are standard and enable the levers to be secured in any position desired.
Engine instruments on the panel include the ITT, Torque, Tach, Fuel Flow, and Oil temp & pressure gauges. These instruments are powered by 28 volts of DC power with the exception of the Tach (N1 Gauge), which is self-generating.
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Originally posted by Golfer
AVSC 4200
UVSC?
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Originally posted by Golfer
there's more to it than that, GS.
Unquestionably. I'm just trying to work out the basics.
Originally posted by Golfer
The compressors are there to compress air, these are some of the turbine blades. They work just like the engine in your car...
Suck Squeeze Boom Blow
Air enters engine inlet...suck
Compressors mush the air into combustion chamber...squeeze
Ignition takes place in combustion chamber...boom
Burning fuel/air mixture expands and goes out the back of engine...blow
= "air-breathing rocket that blows on a windmilling set of fans that helps it breathe." (just keeping it simple)
Edit: btw. unlike in a piston engine the "suck, squeeze, boom, blow" is not separate actions or "strokes". A jet is constantly sucking, squeezing, booming and blowing. If fact I would call it "burning" rather than "blowing". Burning like a rocket.
Originally posted by Golfer
Turboprops don't leech energy from the turbines to turn the prop, they're connected via a gearbox. So the turbine speed is controlled by the throttles, the prop speeds are controlled by prop levers and there are also condition levers that regulate fuel flow into the turbine.
Umm ... if the props are connected to the turbines via a gearbox then ... they do leech energy from the turbines. Also, unless there is some sort of variable gearing the prop and turbine speeds are linked at a fixed ratio, so both changing prop pitch and fuel flow will affect prop/turbine speed.
Originally posted by Golfer
The turbine engines on turboprops aren't really big enough to power anything, they're essentially little APU motors.
Well, they better be big enough to power the prop. ;)
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Umm ... if the props are connected to the turbines via a gearbox then ... they do leech energy from the turbines. Also, unless there is some sort of variable gearing the prop and turbine speeds are linked at a fixed ratio, so both changing prop pitch and fuel flow will affect prop/turbine speed.
I'd been going about this conversation under the assumption that there was a basic working knowledge of jet engines.
When you said "leeching power" from the turbines, it seemed as though you were trying to define Bleed Air, where air is taken from the compressor section to power airplane systems such as anti-ice and environmental systems.
"Leeching power" and "directly connected" seemed to clash as definitions in my mind.
Well, they better be big enough to power the prop.
I meant if they were mounted as straight turbojet motors...they can spin a prop but they don't produce enough thrust to get my car fast enough to get a speeding ticket.
Umm ... if the props are connected to the turbines via a gearbox then ... they do leech energy from the turbines. Also, unless there is some sort of variable gearing the prop and turbine speeds are linked at a fixed ratio, so both changing prop pitch and fuel flow will affect prop/turbine speed.
Nope. The prop pitch is controlled by a prop governer which regulates pitch of the blades and thus RPM. So you move the throttle to create as much power as you want, and move the prop levers to the desired setting for noise reduction, better cruise ect ect.
This is the same as the airplanes in game. You have throttle which controls Manifold Pressure, the prop control regulates prop rpm (+/-) keys. The propellers use a governer to pump oil into the hub, and based on the position of flyweights, the settings of the set spring and a number of other things, the props regulate themselves to maintain a constant RPM.
In turboprops, if you have the prop lever full forward (max rpm) and pull the power levers back to idle, the prop turns into a big drag inducing disc because the pitch flattens out to maintain RPM and its just a big airbreak.
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jigsaw: Read item 1 in the none counter rotating props. That is what I am describing. Torque does not change with engines on wings instead of center line.
Also in statments 2 and 3 it sais when the engine is lost the plane will tend to roll. What is causing this roll? because in the same statement they are saying torque is either working with or against that roll. Therefore it isn't the torque which has always been there but somthing else.
Once again that is exactly what I am describing about lift generated by slip stream.
So I am in complete agreement with that page.
HiTech
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Originally posted by Golfer
I'd been going about this conversation under the assumption that there was a basic working knowledge of jet engines.
Umm... will "I think so" do? ;)
I'm basically trying to work out where all the forces of a turbo-prop go, so I can figure out if it creates torque.
Originally posted by Golfer
"Leeching power" and "directly connected" seemed to clash as definitions in my mind.
I meant "leeching" as in "stealing" power from the turbines. Power that the turbines otherwise would use to do more sucking and squeezing.
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HiTech: I think I see where we're both having some confusion. Hopefully I can clear it up. I've been discussing this from the standpoint of having only one engine working, which is probably the root of confusion.
Torque itself, indeed does not change. But, because the engines are no longer on the longitudinal axis, if you lose an engine, torque now wants to rotate about the CG.
What causes the roll is a combination of "A" and "T" in PAST. "P" and "S" are yaw. The diagram is discussing only how torque is contributing. I've got diagrams for the other three as well. This is why I suggested talking to a MEI. Vmc is much easier to explain in person.
Let me know if this makes sense.
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Originally posted by Golfer
The turbine engines on turboprops aren't really big enough to power anything, they're essentially little APU motors.
The 4 Allison T56-A-15 turboprops @ 4,300 horsepower in the C-130 are a bit large for use as CPUs, would you not say?
(http://www.aircraftenginedesign.com/pictures/T56.gif)
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The 4 Allison T56-A-15 turboprops @ 4,300 horsepower in the C-130 are a bit large for use as CPUs, would you not say?
Gack, I need a lawyer to approve all my posts from now on to ensure no loopholes in what I'm saying.
The turboprops I've been using as examples all have smaller (1015 or less SHP) and those engines aren't very big at all.
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jigsaw: Realy no need to talk to an MEI, I do understand the terms and there function.
But torque always rotates about the CG no mater that the torque is applied on a wing or center line. Acctual when 1 engine stops there is less torque on the plane being caused by the "T". It just that the "A" now has a differential between the wings.
HiTech
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Originally posted by jigsaw
HiTech: I think I see where we're both having some confusion. Hopefully I can clear it up. I've been discussing this from the standpoint of having only one engine working, which is probably the root of confusion.
Torque itself, indeed does not change. But, because the engines are no longer on the longitudinal axis, if you lose an engine, torque now wants to rotate about the CG.
What causes the roll is a combination of "A" and "T" in PAST. "P" and "S" are yaw. The diagram is discussing only how torque is contributing. I've got diagrams for the other three as well. This is why I suggested talking to a MEI. Vmc is much easier to explain in person.
Let me know if this makes sense.
The important (and obvioux and boring) thing is that you agree that a piston engine turning a propeller will have an opposite and equal effect to the propeller (i.e. torque; I do hope no one's made a gear box where the prop spins opposite to the engine; we'd never finish this...)
The interesting point is that once you agree that the #4 engine on a Lanc produces just as much torque as any other Merlin does in a Spit or Stang;where is that torque manifested?
I don't pretend to understand the physics; but I do know that pilots felt the effect; citing take off's that had the whole four engine bomber being a helpless victim to torque; albiet manifested in an unfamiliar way.
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Im back good post guys.
Torque is always present from the prop and engine.
If you have the right engine running and the left engine dead. There is torque present but the combonation of the engine, prop torque and the aerodynamics effects on the airframe fight each other. Aerodynamics wont alow the engine, prop torque to prevail into a rolling moment. So best it can do is a yawing torque moment. When you lose the aerodynamic force namely rudder and airleron control is when the torque still present get stronger against the airframe to be dominate again. This starts the left wing to drop and the right wing to climb in the rolling axis. But as rudder is getting less effective it is still trying to over come torque. This start a left turning force in yaw first then translating into a roll force.
These are the way multi-engines fly. I have never had to use airleron or airleron trim on a multi-engine airplane to counter prop, engine torque. Rudder is the dominate flight control on a multi-engine for directional control.
Turbines
Would you say that any rotating mass has torque assosiated with.
Turbo jets, the main thing you want to do for more efficience turbo jet is to get the air in the intake as straight as possible and get the air out as straight as possible.
If the air in not channeled straight into the air intake this air it will be turbulent and can cause a compressor stall at the N1 stage. The air enters the N1 compressor and rotates as it is drawn into the different stages of the compressor, even though the compressor stage blades counter rotate. also the air is heated by the friction of the compression. This air then vunneled out to the outer section the the compressor to enter the combustian cannister. At this stage you can take "P" air of the turbine also known as Bleed air.
As the air enters the cannisters its air flow in turned 180 degrees in direction before the air and fuel is mixed. The air and fuel is mixed and fired off by the ignitors. As the explosive gas expands this gas is rotated another 180 degrees in flow and is exhausted on to the N2 stage turbine blades. Now these blades do not counter rotate, there is a series of stators and turbine blades. When the gas flow, flows across the turbine and stator blades this inturns (through a shaft) turns the N1 compressor blade section. Now as this gas flow is directed to harness all the available energy across the turbine section it is also straighted out to exhaust as straight as possible.
There is torque in the N1 stage, N2 stage on the compressor shaft. Plus the acceleration of the rotating mass as a hole there is torque present. Suck squeese burn and blow.
Yes jet airplanes do have torque that can pull an airplane to the left or right. It depends on the turbine being used also. It acks like a gyro effect. On engine spool up the B767 pulls to the left.
As for torbo props, the same goes as in the above discription applies. Its still is a jet engine but with a prop connected to it. You also get a jet thrust from the exhaust from the turbo prop. The exhaust on some turbos have the exhaust coming out forward from the engine through exhaust headers and the air intake is at front of the cowling but air enters at the back of the turbine. The engine is turned backward. The allisons on the C-130 the air enters at the front and exhausted to the back of the turbine.
The props are either attached to a gear box or not.
The torque comes mainly from the prop airstream.
Straiga