As someone who regularly flies a Piper Meridian (PA46-500TP), I can tell you that there doesn't seem to be much of a torque problem. P-factor, however, is significant enough that the "before takeoff" checklist calls for 2deg right rudder trim.

Aha! Hard data from the SE turboprop community! :cool:

Tell us this: Is the fin LE offset to the left a few degrees? This is the common way of providing some relief to the right boot.

Not sure if we are talking torque or P-factor but the Tucano requires huge bootfulls of rudder early on in the take off run to stop it careering off the side of the runway. The power output of the engine is measured on a torque gauge.

I also fly turbine helicopters and guarantee that even though the engine is not physically connected to the rotors/propellor there is a HUGE amount of torque.

As I said a few posts ago, if AOA is near zero (i.e. prop axis aligned with incident airflow) then P-factor must by definition be near zero. Torque (unbalanced torque reaction transmitted by engine mounts) might increase the normal load on the LH main gear, but the relative friction increase is negligible.

So that leaves the slipstream rotation - and on pusher aircraft where there's no flat surfaces in the slipstream, I'm told there's no "torque" to be countered with the rudder. Also, if most of the fin & rudder are below the prop axis, the "torque" reaction is opposite that of a more conventional layout.

It doesn't appear to be, at least not on the schematic drawings I have, nor on the actual airplane. That may be part of why our checklist says what it does.

Ah Rivet gun, twas only a matter of time before we got together:}

Give me a 2 lb bucking bar and I'll put perfect shop heads on your AN470s without a smile in sight!

(off topic, sorry)

So - the fin must be optimized for cruise; makes sense to me, since that's the airplane's mission. A good healthy rudder trim on TO does the job, though. :8

My previous post was made somewhat hastily, and I had made an invalid oversimplification. I had just considered the mechanics of a propeller connected directly to the turbine by a single shaft. In that arrangement, there would be no more torque reaction causing the aircraft to roll than in a turbofan. The torque referred to in other posts is the torque on the propeller shaft, which is essentially what is measured on a turbo-prop torque gauge. This would not cause a rolling moment on the aircraft if connected directly to the turbine. However, having thought it through more carefully, I agree that torque is transmitted to the airframe but due to the reduction gearing. The gear box is attached to the airframe, and the reaction between the gears, which are usually offset from the propeller shaft axis, is what then generates a rolling moment. Any roll due to torque is not produced by the turbine directly, but by the torque on the shaft connecting the turbine to the gearbox. Hence, the torque effect in a turbo-prop is all down to the gearbox design.

Barit 1, obviously ailerons are not affective at zero airspeed, but in the Spitfire they are effective at a very low speed (with the ASI on the bottom stop so I cannot quote a number) so the aileron input is made before the take-off roll commences and this levels the wings very quickly. If you increase power slowly enough, by the time the torque effect occurs, they are effective.

Bringing in Newton's any torque measured about a propeller (or jet core for that matter) is matched by another one.

In the piston case, it's applied by the crankshaft and resolved through the crankcase and engine mounts into the airframe.

With turbine engines, the propeller/fan receives torque from the turbine and there is no transmission of torque forces to the airframe (excepting bearing friction).

In both cases, thrust bearings carry that force to the airframe.

So yes, turboprop engines do not transmit torque to the airframe; however, slipstream effects as noted by many are quite significant and generally have a linear relationship to torque.

I have to disagree with you here too, because of the essential difference between a turboprop and turbofan. No, not the shroud, but the fan stator vanes just downstream of the rotor.

Turboprop: The accelerated airflow leaving the prop blades does not travel straight aft, but is rather is a swirl or vortex centered on the prop axis. The rotation of this airflow means some of its energy does not contribute to thrust. But it's an acceptable compromise for the usual turboprop (or piston) application. The corollary Newtonian reaction in the engine mounts equals the torque on the prop shaft. PS - it makes no difference if the gearbox is planetary or offset spur gears; It's the output torque that counts.

Turbofan: The accelerated airflow leaving the fan rotor blades does not travel straight aft, but is rather is a swirl or vortex centered on the fan axis. BUT just downstream is the fan stator row, which a) stops the vortex rotation, and b) is a diffuser to lower the velocity and raise static pressure. In stopping the vortex, it is the Newtonian reactive torque that otherwise would show up in the engine mounts. So, if the fan stators are properly designed, there is no torque resolved in the engine mounts in normal operation.

OK? :ok:

(For LOMCEVAK too...)

I'm afraid you don't understand the aerodynamics of a turbine very well; you seem to be neglecting the function of turbine stator a.k.a. nozzle guide vanes or turbine diaphragm.

Gases exiting the combustor are traveling straight aft. The turbine nozzle turns this flow in the desired direction of rotation, so that it is caught by the turbine rotor blades to create (you guessed it) torque! But the nozzle vanes, in turning that gasflow, create an equal and opposite (you guessed it) torque!
This latter torque is indeed reacted in the engine cases, but it is a small fraction of the output torque of the gearbox, and besides the turbine case is bolted right to the gearbox, so the turbine torque doesn't get transmitted directly to the mounts.

Let me give you some sample numbers:
Power Turbine rpm = 20000; PT torque=500 lb-ft

Shaft hp = rpm x torque/5252 = 1904 shp (see note)

Prop reduction ratio = 15:1

Prop rpm = 20000/15 = 1333 rpm

Prop torque = 500 x 15 = 7500 lb-ft

By the same formula, the prop is absorbing 1904 shp.

Note the constant 5252 applies to any rotating machine where the units are rpm and lb-ft. :8

The original post:
Clearly caused a mixed spread of views, but some of you have got it very wrong (LOMCEVAK & RatherBeFlying). As already mentioned, if you have a shaft sticking out of an aeroplane with a propeller attached to it, there will be a torque on said shaft to drive the propeller. This torque is, for given conditions, the same regardless of engine type (piston, turbine, electric, steam, hydraulic). Any 'machine' with a spinning output shaft will be subject to an equal and opposite torque to that applied to the shaft by the load (prop). (Have you seen Wallace & Grommit building the rocket in A Grand Day Out, when the drill bit jam's in the wood being drilled?)

As mentioned earlier, any propeller aircraft is subject to various forces as it takes off: be it prop slipsteam, assymetric thrust etc. But the only torque effect is produced by the action and reaction to the torque driving the propeller. Watch a car engine when accelerated (in neutral) and you'll see it rock in it's mounts due to the change of torque needed to accelerate and decelerate the moving parts. The engines flywheel is the biggest cause of this.

So back to our aeroplane and the original question; yes there is a torque effect - the engine type is irrelevant (ish). The one caveat being, as I mentioned in an ealier post, the torque needed to accelerate the propeller from idle to full power is not needed if it is already running at a constant speed, like most turbo-prop aircraft. If you watch a big piston start (BBMF Lanc is a good example) you'll see each engine rock in its mounts as it accelerates the big heavy prop to groung idle. The fine pitch and low rpm put almost no aerodynamic load on the prop. It's a TORQUE action/reaction as the engine accelerates the props which are only acting as a flywheel. :ok:

So, let´s have a look at it this way:

If you have a propeller which is being rotated then it is an airfoil which necessarily creates lift (thrust) as well as drag. It pushes the air backwards but also causes the air to swirl. One effect is that by law of action and reaction, the torque has to be transmitted to the engine powering the propeller. Another effect is that unless the propeller is a pusher (and the vortex is left in free air touching no aerodynamic part of plane again) there would be some aerodynamic forces where the slipstream hits plane.

If you have a propeller which isn´t rotated, but is stuck, and it is subject to airflow, it creates drag. But if the propeller is a spiral (not pitched to be feathered) it also creates swirling airflow. This means that there has to be a torque transmitted to the engine wherever the engine mountings are stuck to prevent the propeller from rotating - and there also would be a slipstream creating aerodynamic forces if and when it meets aerodynamic surfaces.

If you have a plane with 2 propellers distant from each other, on different axes, and both are rotating in opposite directions, then there are 2 slipstream swirling vortices separate from each other. Both engines would create torques - but those torques would cancel out over the airframe if they are exactly equal.

Now, some planes have pairs of counterrotating propellers close to each other on the same axis They would tend to create swirl in opposite directions - and those swirls would tend to cancel. But if the propellers are coaxial (and close in diameter) then unlike propellers on separate axes, the swirl would be eliminated much more thoroughly (and the energy of the swirling movement recovered!).

It follows that a powered propeller and an unpowered spiral that are on the same axis might also cancel out each other´s slipstream swirl. Wonder why it is not common on exposed propellers...

In any case, turbofans normally use stator vanes (inside) to keep the swirl of the exiting jet blast minimal.

Now, flywheels are a different effect. A propeller in airflow creates torque when it is rotating at a steady rate, or when it is not rotating and causing airflow to rotate.

But anything with mass, whether a propeller or internal engine parts, create additional torque effects when the speed of rotation is changing - like speeding up or slowing down engines.

But this happens only when the speed changes. If a propeller and the engine behind change the speed of rotation, this changes thrust, slipstream torque et cetera, and also causes torque while the change is going on.

Whereas if a propeller changes pitch while the rotational speed of propeller and engine behind is kept exactly constant, the thrust changes, the slipstream torque changes - but since the rotation speed is constant, there is no extra temporary torque.

I was about to write a post about turbine stators, but barit 1 got in first with an excellent explanation. As barit's example shows, most of the torque in a turboprop is generated in the gearbox (and it is this that the torque gauge measures) but the turbine stator torque still contributes to the total.

We are all familiar with the idea that thrust is equal to the rate at which linear momentum is imparted to the air. By the same token, torque is equal to the rate at which angular momentum is imparted. As chornedsnorkack points out, the only way to eliminate torque is to elimnate the net angular momentum of the slipstream.

Actually, it doesn't make any difference where you measure the torque, so long as you know what the correct value should be be at the point it's measured.

For example - GE T64 and CT7 and Allison T56 turboprops measure torque delivered from the PT to the gearbox, by sensing the torsion in the coupling shaft. It's rather clever if you ask me. The big recips had a hydraulic torquemeter in the mounting of the stationary ring gear of the planetary set. (Perhaps some engines still use this system today)

Yes, that's the kind of torque gauge I had in mind, I think from the RR Dart. As you say it does not matter where you measure it since the the pilot is only interested in percentage anyway.

I do stand ably corrected with respect to the stators:\

Now if we consider the PT6, we do see that the gas generator produces torque about the casing -- lots of stators there.

But I suspect that the gas flow in the propeller turbine only swirls against the exhaust -- don't think there are any stators in that area -- until corrected:\

You may well be correct about there being no stators after the propeller (output) turbine, but if the engine makes the turbine spin, and you absorb this torque in the propeller (or any load), then the opposite torque must be applied to the engine mounts, less a fraction for the swirl still left in the exhaust gases.

As interesting as this is, it is moving away from the original post about torque affects on the airframe from a single turbo-prop as opposed to a single piston.

Centaurus: my once said that he almost got rolled over when pushing up the throttle to quickly during a go-around in an (P) F-51 in the mid-50s. but

I can easily imagine such problems with a single-engine turboprop, especially as almost all have constant-speed props (?) and the engines are not as complex as with recips, allowing faster throttle movements. Anything with a single Garrett or Allison (i.e. similar to the T-56 in P-3s, C-130s etc) might be extra demanding.

A Pilatus single-engine would be fun, not to mention a classic, twin-engine Bandit Emb-110.