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


Centaurus
15th Apr 2006, 15:35
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
15th Apr 2006, 16:24
I guess if there was not Mr Newton would feel seriously left out......

Chimbu chuckles
15th Apr 2006, 16:36
The engines are mounted at an offset angle to counteract, as much as is possible, those effects.

Centaurus
17th Apr 2006, 02:50
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
17th Apr 2006, 03:10
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 (http://www.eaa.org/homebuilders/list/Tingle%20Special_Tingle.asp) .. but the vertical fin and rudder looks not overly big for the aircraft size given the engine's 657 shp rating ...

vapilot2004
17th Apr 2006, 04:04
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
17th Apr 2006, 04:48
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
17th Apr 2006, 07:38
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
17th Apr 2006, 07:56
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
17th Apr 2006, 09:42
'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
17th Apr 2006, 12:23
(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
17th Apr 2006, 13:51
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. :8

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! :eek:

LOMCEVAK
18th Apr 2006, 11:20
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
18th Apr 2006, 12:05
Lomcevak

Thats a mighty impressive CV you have there. :cool:

barit1
18th Apr 2006, 13:36
... 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
18th Apr 2006, 16:05
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
18th Apr 2006, 17:07
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
18th Apr 2006, 17:09
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
18th Apr 2006, 17:52
...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
18th Apr 2006, 18:38
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.

flyboyike
18th Apr 2006, 21:01
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.

barit1
18th Apr 2006, 21:55
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.

SAR Bloke
18th Apr 2006, 23:47
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.

barit1
19th Apr 2006, 01:30
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.

flyboyike
19th Apr 2006, 02:33
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.


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.

Loose rivets
19th Apr 2006, 07:52
!!!!!!!!!!!!!!!!!


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

Rivet gun
19th Apr 2006, 09:35
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)

barit1
19th Apr 2006, 15:37
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.

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

LOMCEVAK
19th Apr 2006, 23:24
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.

RatherBeFlying
20th Apr 2006, 00:02
Bringing in Newton's Every action has an equal and opposite reactionany 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.

barit1
20th Apr 2006, 01:41
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...

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:

barit1
20th Apr 2006, 02:19
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.

(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

H Peacock
20th Apr 2006, 05:07
The original post:
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?

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:

chornedsnorkack
20th Apr 2006, 10:29
So, letīs 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 isnīt 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 otherīs 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.

Rivet gun
20th Apr 2006, 11:32
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.

barit1
20th Apr 2006, 13:06
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...

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)

Rivet gun
20th Apr 2006, 14:32
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.

RatherBeFlying
21st Apr 2006, 03:03
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:\

H Peacock
21st Apr 2006, 05:54
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.

Ignition Override
21st Apr 2006, 06:29
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.

Centaurus
21st Apr 2006, 09:06
HPeacock. Re the shaking and rattling that is a characteristic of a Merlin on start. I have started Merlins many times in another life (Lincolns and Mustangs) but I had never really thought about all that vibration except it was normal. I thought it was because one or more cylinders had yet to cut in and thus it was an unbalanced crankshaft rotation causing the heavy vibration - not a variation in torque? Same thing on big radials such as the R2800 on the Convair 440.