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(Source) Rudder twist on a Saab 91 Safir.

What are the design methods used to balance a propeller aircraft for left turning tendencies? I think it matters more the more powerful the engine(s) is.

A rudder twist seems to be one, not-so-detailed sources mention an offset engine, a slightly longer-, or differently balanced wing.

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There are several ways, and the most effective vary their own yawing moment contribution with engine thrust:

  • A trim tab on the rudder which forces it into a correcting deflection. This trim tab can either be adjusted in flight or only on the ground. The flight-adjustable trim tab is set according to flight speed and is used on airplanes with a wide speed range.
  • Mounting the engine at a slight angle to the airplane centerline. This places the propeller at an offset which produces its own yawing moment.
  • Camber on the vertical tail. Since the tail is in the propeller slipstream, it experiences a relatively higher dynamic pressure at low speed and high engine settings, just when the p-factor is biggest.
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Rudder twist seems like an exotic and expensive means to solve the problem. Most light aircraft use a pre-set rudder trim tab set during flight test at the factory, like this on a CE-172.

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    $\begingroup$ Set at the factory and adjusted by the operator according to need. $\endgroup$
    – J W
    Commented Mar 17, 2017 at 1:27

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