Use of Aileron trim on twin prop/turboprop aircraft...

[jcomm]

First of all I have to state that the only License I own for RL flying is a glider pilot licence (ICAO ) obtainned in 1980 here in Portugal.

I've flown gliders only, all my life, but I am a simulator fan, now involved with a new toy, after having used ELITE for quite a while.

Well, I never really understood if it is acceptable to find considerable bank from torque effects on a prop aircraft, specially a twin with non counter-rotating props, like a Baron58, a Beech C90, a Kingair, etc...

All have aileron and rudder trim, but I wonder if these are particularly set away from neutral for takeoff, full power climbs to overcome slipstream & / or torque effects from their engines, or if those effects are indeed noticeable, making the pilot input right yoke to counteract or use aileron/rudder trim.

The simulator (PC-based) I am now using exhibits a huge amount of left bank on it's Baron58 and C90 models. I have asked the designers if this is realistic and of course was told IT IS!

I do not have any fellow pilots operating such aircraft. At my local airclub I have flown in the right seat of DR-400 and SOCATA 180GT glider tugs, and all I remember is the need for rudder to counteract slipstream assymetric hitt of the tail, probably helped by a yaw moment due to torque roll (?), but I really can't recall (when I was given the chance to fly those aircraft) any noticeable need to use right stick to counter any torque from the engine/prop...

Comments from Baron, C90, Kingair, whatever... pilots are really welcome. Is bank a factor when climbing at full power on such aircraft? Do you use right yoke or aileron trim to counter it or just rudder because yaw and not bank is what is felt?

Ah! Another noticeable effect is right bank when the throttles are brought back during descent, this time requiring either left yoke or left aileron trim. I could understand this if the trims were used before, of course, or if fixed trim tabs are set to compensate for cruise, but I believe those aircraft (Baron58, C90, Kingair, etc...) do not have fixed trim tabs set on ground only but rather trims, either manual or electric, actuated from the yoke, control column, etc...

Thanks in advance for any help / insight on this subject ...

[1jz]

Well short story... Yes , even in larger turbo props or twin piston props u need to trim all three main control surface in order to fly hands off. The torque reaction does however cause bank changes in climb or descent a bit so, u need to trim the aileron too n if some 1 disagrees then I won't quarrel over it but, this is applied practically flying aircraft on 300- 500 nm sectors without autopilot n that even kinda handsoff trim.
FLYING IS A SCIENCE N TRIMMING IS AN ART.

[jcomm]

1jz, thank you very much for your prompt and informative reply :-)

Looking forward for even more hints on this trim "art" :-)

[AerocatS2A]

Aileron trim is generally a set and forget type thing. You might tweak one way or another to get it flying nicely after take-off but it doesn't need anything after that, and as long as it is not reset on the ground it won't need changing for a subsequent flight. Rudder trim, on the other hand, needs constant attention. Any change in power requires a change in rudder trim. It is not necessary to set anything other than neutral for take-off though. I'd suspect that someone who is changing aileron trim a lot should probably be adjusting the rudder trim instead.

Many twins don't even have an aileron trim.

[mad_jock]

Thats only on some types.

Others as the airframe gets older and more bent you have to retrim it every time you change speed and or power setting or configuration

normal for me its rough elevator trim, then trim rudder, then aileron, then fine trim elevator. Once in the cruise and power set rudder trim for max ground speed off the gps, aileron trim, finally the elevator. After which you can fly hands off for extended periods in still conditions.

As soon as you start to decend your back on it again.

It sounds all very labour intensive but quite quickly it becomes second nature like changing gear in the car and your hands just do it without commiting much brain power.

The trimming art is what makes a pilot on a manual twin. Once you crack it the work load drops off and you can leave the aircraft to do the flying and you only have to point it in the right direction and not annoy it which would then take it out of trim and mean you would have to fly it.

[Tu.114]

On the DH8-400, all three trims find much use in case of a power change. Rudder trim will obviously be required due to the tremendous P-factor; Elevator trim is needed because of the prop wash induced changes in lift, requiring a readjustment in pitch. And while the banking moment caused by torque changes is small, it is definitely noticeable and requires a bit of aileron trim adjustment as well. On some of our -400s, reducing power for descent might even cause a MISTRIM - TRIM LEFT WING DOWN message when the autopilot is engaged - with the aircraft trimmed for cruise power, the always present banking moment to the left is countered, but when one reduces the power, the engine-induced banking moment is reduced as well. This seems to result in a load on the autopilot servos sufficient to cause the above mentioned message on a few planes in the fleet.

[Clandestino]

Darn... it gets worse with wear and tear. As the oldest Q400 I fly is barely 4 years old, aileron trim doesn't get much use. However, rudder trim is constantly tweaked and switch gets quickly worn. On ATR-42-300, we would fine tune the ball in the middle using rudder trim in cruise on the first flight in the morning and than forget about either rudder or aileron trim for the rest of the day.

So it is type, series and individual airframe specific.

FLYING IS A SCIENCE N TRIMMING IS AN ART. Typing all caps and using textspeak is neither.

[jcomm]

Well,

I keep following this thread with great expectation and interest. All of your comments are being very important and have already contributed to some judgement regarding the real need for aileron (and not only rudder) trim on prop / turboprop aircraft operations, single or twin (with non counter-rotating props), and under normal situations (no asymmetry due to differential thrust/engine failure, fuel imbalance, etc...).

A few pilots I was meanwhile able to talk to, mentioned that only rudder trim is used, because yaw and not bank is the main / perceptible effect of the "family" of prop effects (torque (engine inertia + airflow drag), p-factor, slipstream asimmetrically hitting various aircraft surfaces, gyroscopic effects). Other pilots acknowledge the need to use aileron trim under various phases of flight to be able to "fly hands off"...

On the particular source I am using, unfortunately not real life experience but rather a PC-based simulator, the bank from torque is very considerable, most probably because the asymmetric hit of the wings & tail surfaces is not fully modeled, which could account for some forces to counter the torque effects - spiraling slipstream hitting the left wing from bellow, thus tending to counter the left roll tendency assuming clockwise running props...

I look forward for even more posts :-)

Thank you very much you all :-)

[mad_jock]

There is a big difference between those that fly autopilot with a yaw dampener and those that fly manual. Also those with a critical engine and those that have counter rotating props.

[jcomm]

True mad_jock,

I meant to ask about hand flying twins with a critical engine, or singles with a powerfull engine where torque can become a factor...

[AerocatS2A]

My experience is flying Dash 8 200 and 300 series, some nearly 20 years old. Rudder trim only was required. If the autopilot was engaged and it was out of balance, the aeroplane would fly one wing low because the autopilot didn't have rudder control aside from the yaw damper and it would try to stop the heading wander caused by insufficient rudder trim by banking. However, although this showed up as flying with some bank, it was fixed by using rudder trim. We hand flew them a fair bit as well and I never had a need to trim aileron other than just after take-off. Obviously other's experiences are different, but I think the rudder trim is a far more important tool.