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Old 03-10-2012, 04:23 AM   #18  
Cubdriver's Avatar
Joined APC: May 2006
Position: ATP, CFI etc.
Posts: 5,988

Originally Posted by JamesNoBrakes View Post
Isn't torque only an issue due to bearing friction (and that's compensated for with engine mounting usually) and when accelerating/decelerating the prop? I know the size of the prop and the power behind it can have a big effect obviously. Maybe it's just me, but when I took off in conventional twins by going full power, then brake release, it never seemed to take off to the left nearly as much as if I went full power while rolling.
I would think bearing friction is a trivial quantity. You can turn an engine with your bare hands, compression and all- there isn't a lot of friction there.

Torque is not dependent on rate of RPM change like gyroscopic precession is. P-51s and other high displacement engines may produce a lot of torque, but it is constant for a given RPM, disc load etc.

PHAK (Pilots Handbook of Aeronautical knowledge) mentions that since airplane wheels are small and often a bit low on air, high torque engines compress the left wheel on takeoff roll (conventional twins, single engines) making ground friction on the left a significant left turning factor.

In cruise torque shows up as a constant roll force, which is as you mention is countered by engine angle and aerodynamic design tweaks. High torque engines on slow airplanes produce a lot of residual roll. Roll of course is a turning function in airplanes. Stand in front of Caravan for example, and notice the angle of the engine is noticeably to the right.

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