GScholz more ont turbo props:

[artik]

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.

[GScholz]

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?

[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

[rshubert]

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.

[Angus]

Right on, HiTech.
Power does not disappear by different gearing, if you see what I mean.

[TequilaChaser]

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

[HoHun]

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)

[GScholz]

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.

[rshubert]

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

[HoHun]

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)

[rshubert]

http://science.howstuffworks.com/fpte.htm

[Nilsen]

All energy has to go somewere.

[Straiga]

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

[hitech]

Can some one describe exatly how torque is transmited to an airframe on a high bypass turbofan?

HiTech

[Tails]

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.