PLT243: Torque and Left-Turning Tendencies
What code PLT243 covers, why the FAA tests it, and how to study Torque and Left-Turning Tendencies before your checkride.
Recall forces acting on aircraft - propeller / torque
What this means for your checkride
A spinning propeller and engine create the four left-turning tendencies: torque reaction, spiraling slipstream, gyroscopic precession, and P-factor. They are strongest at high power and low airspeed, which is why right rudder is needed on takeoff and climb.
These tendencies explain why the airplane yaws left when you add power, so the FAA tests each cause and when it dominates.
Pilots credit all the left yaw to torque. Torque is only one of four effects; P-factor and spiraling slipstream often matter more at climb attitudes.
Where to study it
Oral checkride defense
A code on your report is an area the examiner can revisit. Here is how an examiner might probe it, and how to explain it out loud.
Name the left-turning tendencies and why the airplane yaws left on takeoff.
Torque reaction rolls the airplane opposite the prop rotation; P-factor at high angle of attack moves the descending blade's thrust right of center, yawing left; the spiraling slipstream strikes the tail; and gyroscopic precession acts when pitch changes. On a full-power, high-AOA climb they combine to yaw left, so I add right rudder.
What is gyroscopic precession and when do you feel it?
A force applied to a spinning propeller takes effect 90 degrees ahead in the direction of rotation. You feel it most when the pitch attitude changes quickly, such as raising the tail on a tailwheel takeoff, which yaws the nose left.
A code on your test report is an area of deficiency. An authorized instructor must review it with you and endorse that review before you take the practical test, and the examiner may revisit it during the oral. Study it until you can explain it out loud, not just recognize the answer.