Is there engine "torque" on take off in a turbo-prop single engine aircraft?

[Centaurus]

With a turbo-prop single engine aircraft is there any engine torque on take off like there is on a piston engine powered type? There is propeller effect (down going blade etc) that causes a yaw - but engine torque? I recall on high powered wartime aircraft such as the Mustang, Spitfire and Typhoon, engine torque caused one wheel to dig harder into the runway creating drag and requiring rudder to correct. Does that also apply to a turbo-prop aircraft?

[John Farley]

I guess if there was not Mr Newton would feel seriously left out......

[Chimbu chuckles]

The engines are mounted at an offset angle to counteract, as much as is possible, those effects.

[Centaurus]

Ok - so I gather there is torque. In the turbo-prop home-builts then the power (torque?) developed at take off power must be tremendous relative to aircraft weight and size. It follows (?) the take off swing must be really hard and it would be all too easy to swing off a narrow say 45 ft wide airstrip due to insufficient rudder authority?

What this is all about is an accident in USA where a homebuilt called a Tingle Special powered with a Walter turbo-prop was seen by witnesses to veer off a 45 ft runway during the take off run and one wheel went into sandy surface. NTSB Report LAX 06LA041 with Occurrence Date 19th November 2005 refers. Seems the pilot went to high power and tried to pull the aircraft off the ground but after getting airborne probably flicked, stalled and went in.

The discussion came up seperately that maybe he had experienced a deflated tyre during the early part of the take off run, causing the aircraft to swing off the runway. My guess is that something distracted the pilot from keeping straight and the aircraft simply veered from the centre line of the narrow runway and the drag from the sandy surface on one wheel caused things to go from bad to worse. An abort would have fixed the nproblem but the pilot decided otherwise (fatally).

My question therefore on these Pprune pages was to ask the really clued up among readers if an overpowered light aircraft of this sort could swing on take off due perhaps too rapid application of take off power in the turbo prop?
Certainly it could happen in a P51 Mustang (from personal experience - and I don't mean a minature Mustang but the real thing), but then playing amateur investigator I found myself all mixed up between engine torque and asymmetric blade effect.

[john_tullamarine]

One probably needs to consider at least the following contributors to handling problems ..

(a) torque due to and in the opposite sense of engine rotation ... I've never really been comfortable with the thesis that this causes a significant problem on the ground .. once the aircraft has lifted off .. different matter

(b) whatever might arise from the action of the prop slipstream on the particular aircraft's surfaces.

(c) gyroscopic precession of the rotating mass as the aircraft pitches .. especially a consideration on a high powered tailwheel machine as the flying attitude is assumed at low speed and high thrust

(d) asymmetric thrust distribution over the prop disk when there is a significant pitch attitude leading to a yawing moment. Possibly a similar effect is contributory to control loss in the event of a significant yaw angle being allowed to develop .. which might cause some pitching moment anxieties ...

(e) normal prop disk force at high pitch attitude and high thrust (especially a problem during missed approach and the usual reason for SAS gear on turboprop conversions). For those who might not be familiar with the concept, it results in a significant nose up pitching moment and a major problem with the pilot's perception of longitudinal stability.

I have no familiarity with the aircraft concerned .. but the vertical fin and rudder looks not overly big for the aircraft size given the engine's 657 shp rating ...

[vapilot2004]

With a turbo-prop single engine aircraft is there any engine torque on take off like there is on a piston engine powered type?

I believe the torque-steer is attributed to the action of the prop. and with that much oomph up front there....(600shp !!), I would say the p-factor would be pretty darn high.

[gas-chamber]

Chimbu, surely the offset thrust line would be aimed to minimise the torque at a particular power setting - cruise for best economy? By reducing the amount of rudder/aileron trim at that setting? At takeoff and climb, I expect that torque would still need to be trimmed out for pilot comfort at least, and that at idle the trim would have to go in the opposite sense. I am just curious how these single engine turboprops handle, never having flown one.

[Feather #3]

Flick this to the Mil forum; those who've flown the Tucano and PC-9 will be able to answer.
Anecdotally, a thru-jet mate went to fly the PC-9 and on a touch'n'go nearly went sideways as he slammed on full throttle. He HAD asked if there was any torque effect and suffered an inadequate briefing [IMHO!]
G'day

[john_tullamarine]

Think I might leave it here .. but a good idea to ask our TP/FTE colleagues over the way if they might fancy having a look at the thread ...

[On-MarkBob]

'P' Factor

'P' factor relates to the angle of attack of the aircraft Vs. the angle of attack of the prop. At high aircraft angles of attack, ie. low speed flight, the down going blade of the propeller will be at a higher angle of attack relative to its own airflow. Thus the thrust line will move outboard from centre towards the down going blade. This also produces a swing and thus requires rudder to compensate in the climb. Most of the effects of the airflow over the fuselage are already compensated for by the manufacturer or designer by way of offsetting the direction of the fin and installing the engine 'on-the-piss'. If you measure the tips of the prop to the leading edge of the wing on either side you may well find a difference, and if you look carefully at the fin you may well find it doesn't point in the direction of flight.
The 'P' Factor is responsible for twin engine aircraft having what is known as a 'critical engine inoperative' (shortend to 'critical engine' but technically incorrect!) The 'Critical Engine Inoperative' will be the engine that has the down going blade inboard towards the fuselage. If you loose this engine, then the thrust line of the other engine in now well outboard of centerline of the aircraft and thus the asymmetric problem is the most critical.

Bob

[RatherBeFlying]

(b) whatever might arise from the action of the prop slipstream on the particular aircraft's surfaces.

The more power, the more slipstream -- doesn't matter whether it's piston or turboprop.

From a standing start, accelerate the Legend to flying speed in about 5 seconds. After liftoff, the steady push on your back continues as you retract the gear and flaps. Pitch up for the best rate of climb air speed and note climb rates of five thousand feet per minute, and more.

There are a number of WWII fighters that would roll uncontrollably if full power was applied at low speed.

Likely this a/c has engine and fin offset as it was designed around the powerplant, but the approach speed of 85 kt. is a hint that full power below that speed may be a bootfull.

http://www.legendaircraft.net

[barit1]

Originally Posted by RatherBeFlying

The more power, the more slipstream -- doesn't matter whether it's piston or turboprop.There are a number of WWII fighters that would roll uncontrollably if full power was applied at low speed.
Likely this a/c has engine and fin offset as it was designed around the powerplant, but the approach speed of 85 kt. is a hint that full power below that speed may be a bootfull.
http://www.legendaircraft.net

In my library is an interesting series of articles by George Collinge - "Is It Really Torque?" published in Sport Aviation in early 1969. In these articles, he examines unbalanced engine torque, "P" factor, gyroscopic moment, etc. and concludes that the rotating slipstream from the prop, striking the fin at an angle, is the major culprit. However, the unbalanced torque of a Merlin prop shaft is several thousand pound-feet and not to be disregarded.

My dad when instructing always insisted the student become familiar with applying power quickly just above Vs. The airplane's response is often an eye-opener!

[LOMCEVAK]

Torque is a very misused word in propeller driven aircraft. In a piston engined aircraft the engine produces power to rotate of the crankshaft. This power is normally dissipated via the propeller to the airflow and produces thrust. However, if all of the power cannot be transferred thus, it will rotate the engine, and thus the aircraft, in the opposite direction; basic Newtonian physics. Hence, with a powerful piston engined aircraft at low forward speed and high power, a rolling moment may occur; this is the basis of a torque roll in aerobatics. Also, due to torque a Spitfire needs about 1/3 to 1/2 aileron at the start of the take-off roll to maintain wings level. However, with a turboprop there is no mechanical connection between the turbine/propeller and the engine/airframe and so, neglecting friction, there can be no true torque effect in a turboprop.

However, there are rolling moments generated by the propeller in a single turboprop, partly due to the propwash giving different downwash angles at each wing root. This is what generates some the aileron requirement to maintain wings level in flight at high power and low speed, although some of it also comes from the fact that with the slip ball central there will be sideslip and thus a rolling moment due to lateral stability.

What really muddies the waters is the fact that the word "torque" is often used incorrectly as the cause for yawing moments in single propeller driven aircraft. Many of the causes of this yaw such as 'p' factor have been well described above. The moral is be very careful when using the word torque!

[issi noho]

Lomcevak

Thats a mighty impressive CV you have there.

[barit1]

Originally Posted by LOMCEVAK

... due to torque a Spitfire needs about 1/3 to 1/2 aileron at the start of the take-off roll to maintain wings level.

Really? How effective are the ailerons at zero IAS???

...
However, with a turboprop there is no mechanical connection between the turbine/propeller and the engine/airframe and so, neglecting friction, there can be no true torque effect in a turboprop.

Newton's laws still apply to a turboprop. The torque generated by the power turbine is relatively low, but it is multiplied in the prop gearbox (typically 13 or 15 to 1). In concept, it is no different from a geared piston engine (e.g. Merlin): The torque delivered to the propeller must be reacted by the engine mounts, transferring directly to the airframe.

PS - it would be no different if the driver were an electric or hydraulic motor - had you ever held a small electric motor in your hand when it starts?

[barit1]

Let's think about P-factor for a moment. The texts tell you that at high AOA, the downward-moving prop blade has a bigger "bite" than the blade on the other side. Very well, for a taildragger on the ground this might contribute to a left yaw on a right-hand rotation prop. But for a tri-gear single, the AOA is near zero on the ground, so P-factor is about nil.

In multi-engine aircraft (except for those with counterrotation such as the PA-39), it's likely that P-factor is a contributor to the yaw on takeoff; On one side, the downward-moving blade is farther outboard from the fuselage centerline (i.e. longer arm) than the other side. The engine with the shorter arm is thus the critical engine for OEI.

[Loose rivets]

Forgive if my quick scan through has missed something on this interesting thread...will read again later. But for the moment.

If an aircraft was suspended on a string in a total vacuum, but magically made to run for the purpose of measuring torque, what would be the effect of the forces then?

Clearly, we would only be considering accelerating masses, but this may serve to clarify some of the basics.

On the subject of props being driven by the gas-flow only, surely, all one is doing is changing the coupling from molecules of steel to those of gasses.

[Rivet gun]

Originally Posted by LOMCEVAK

However, with a turboprop there is no mechanical connection between the turbine/propeller and the engine/airframe and so, neglecting friction, there can be no true torque effect in a turboprop.

Like issi noho said, a mighty impressive cv . Which makes the above misunderstanding all the more interesting.

All turboprops I have flown had a cockpit gauge labelled "torque"; and a turbine powered helicopter still needs a tail rotor!

Torque can be thought of as the reaction to the angular momentum imparted to the airflow. Any propeller or rotor blade will develop torque, whatever sort of engine drives it.

[barit1]

Originally Posted by Loose rivets

...On the subject of props being driven by the gas-flow only, surely, all one is doing is changing the coupling from molecules of steel to those of gasses.

Seems to me this applies to ANY internal combustion engine, piston or turbine.

[H Peacock]

As a few have pointed out already, LOMCEVAK is incorrect in his statement regarding lack of torque effect from a turbo-prop. Furthermore, there appear to be some misunderstands about 'torque effect'.
Any engine driving a propeller will be subject to a torque reaction. The harder the propeller 'bites' into the air, the greater the torque. A change of torque will only occur if you alter the power delivered by the engine, or alter the load on the propeller. A further complication is that most turbo-props run at a constant rpm. With a piston engine you are usually not in a constant rpm band until the aircraft is already moving/airborne. Therefore a change in rpm will put an additional torque load on the engine as it tries to increase or decrease the propellers angular momentum. A big (heavy) prop accelerated from a low idle rpm to full speed will have a considerable torque effect (roll) on the airframe, and this is in addition to any of the gyroscopic or aerodynamic effects. Try the same on a Tucano say, with over 1000shp available, and you don't have the addition torque loading (roll) induced by the change in angular momentum of the constant speed, but still heavy, propeller.