Propeller Torque and P-Factor with twins engine planes

1st Official Post

    I had my first flights with Dash 8 Q400 and one thing which annoy me was the strong rotation around the roll axis and the turn to left during takeoff and climbing. I know the effects propeller torque and p-factor from single engine props planes, but I didn't expect it from twin engine planes.

    I tested all available twin engine planes of FS2. All jets fly straight ahead, but all props turn either to left or to right. I looked into the internet and have learned, propeller torque and p-factor effect exist too for twin engine planes, if both engines rotate in the same direction. I expected that both engines rotate in the opposite direction, but this isn't true of all planes, the Dash 8 Q400 too. Both engines of the Dash 8 Q400 rotate clockwise (with view to front).

    This means the pilot has to stop the turn by applying aileron and rudder to right, manual or to trim. So it isn't a mistake in FS2. I ask myself are these effects really so strong in the real?

    May be I have found a mistake. If both engines rotate to right (clockwise) the plane turn to left. The engines of Baron 58 rotate to right (see youtube videos), so the Baron has to turn left on takeoff, but it turn to right!?

    The left engine of P-38 rotate to left (counterclockwise) and the right engine to right. Here I expect no propeller torque and p-factor effects, but P-38 turn to right. What the reason?

    • Official Post

    The propeller in piston engines are actively creating a counter moment on the fuselage, so it directly rolls the fuselage.

    On top of that the propeller slip stream has a certain rotation to it. This rotating air hits surfaces like the wing or tail at an angle and creates asymmetric effects.

    The amount of the propeller rotation is a bit too high in the Q400 I think, but this might be readjusted in the future. Some roll tendency would be expected they are still quite huge blades cutting through the air and throwing the wash onto the wing and flaps in an asymmetric fashion.

    I'll look into the Baron 58 more closely, could you please send me the youtube link of the video(s) in question? Thanks

    The P38 should stay straight since the effects of the both engines should cancel each other out. I'm going to check if the P38 does turn to the side for me as well. Maybe this is just the bank angle instability, once you increase your bank it never returns to center but gradually increases. (This would mean if you put it in a left turn this left turn becomes steeper and if you put it in a right turn this right turn tightens up as well)

    Regards,

    Jan

    This is actually very well modeled IMO.

    All "torque" effects - engine/prop torque, p-factor ( not so important in the Q-400, unless at a high AoA (+ or -), or in sideslips ) and spiraling slipstream effects are all responsible for this "turning tendendencies".

    The real Q-400 requires rudder trim to be set before takeoff, and during every high power / high AoA or power reduction ( for descent ).

    It Works very plausibly in AEFS2.

    Another good effect is asymmetric thrust, which we can model in the Q-400 by assigning diferente keys / axis to the two "condition levers" and then using it to kill one of the engines and fight the resulting asymmetric thrust, even if the prop is auto-feather.

    Limited by Main Thread...

    Edited 2 times, last by jcomm (July 31, 2017 at 12:13 AM).

    It's mostly yaw-induced roll, in the Q-400, if one does not correct the sideslip... and very far from what we had in XP when Austin decided to finally introduce torque effects along XP9... ( well, I had thought they were already modelled by that time, just as the propwsh effects he's now fine tuning for 11.10... it is certainly not as bad as the torque bug in XP... ).

    It looks plausible to me the way it is, and AEFS2 can be fine tuned regarding the propwash effects, even on the fuselage, so, I believe we can end up we very satisfactory models...

    Limited by Main Thread...

    Quote

    I'll look into the Baron 58 more closely, could you please send me the youtube link of the video(s) in question?

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    I searched for "Baron 58 startup" or "Baron 58 starting engine".

    That are small harmless mistakes (if one) and can be fix later. :)

    I have assigned keyboard keys to aileron and ruder trim for using, but I tested also the trim knob in the cockpit of Q-400. Difficult to use during the flight and not using VR, but working. :thumbup::thumbup::thumbup::thumbup::thumbup:Great! Thanks!

    Remember that singles vertical stabiliser offset is optomised for the cruise. The plane is slower and the slipstream is from full engine power in the climb. Twin climb power set after about 400 feet is subject to variations in throttle and propeller lever positions and some accessories might not be present on both engines so it is natural to expect some power imballance. Rudder force or trim is applied to centre the ball and blue levers adjusted to remove beat noise.

    A six lever engine control and three axis trim would make the home sim' more authentic as would switches for cowling flaps and other complex aeroplane controls. Turboprop propellor speed is subject to less variation than in piston planes, it might have a single fixed speed change after take off which is maintained all the way to landing. There can be minor performance differences in multi engine aircraft which can cause asymetric power at times.

    No Aerofly drift in yaw and roll would be less authentic.