1
$\begingroup$

In different flight sims I've experienced the same effect on certain planes: when accelerating on the runway, the plane drifts to the left as if the rudder was set to yaw left. You can counter this by actually yawing right to somehow remain on the runway. When you're in the air the plane is rolling to the left as if the ailerons were set to roll left, and you have to counter this by actually rolling right. If you kill rotation, the plane would start to roll left again.

An example anyone can see is the SR-22 Cirrus in Google Earth's flight simulator (the F-16 doesn't do that). But interestingly I've seen the very same effect in other ones. What's the reason behind that strange behavior? Ailerons and rudders are set to 0 (no roll/yaw), so they obviously aren't or shouldn't be causing that.

$\endgroup$
1
  • 12
    $\begingroup$ let me guess, it is only with single engine prop aircraft $\endgroup$
    – Federico
    Commented Feb 5, 2022 at 11:37

1 Answer 1

11
$\begingroup$

The simulator behaves just like the real thing.

Propeller powered aircraft with a prop that rotates clockwise will drift left during the takeoff roll if not corrected. This is caused by a left turning tendency due to four distinct effects: P-factor, torque, spiral slipstream and gyroscopic precession. Of these effects, torque and spiral slipstream cause the most left turning tendency during a takeoff roll.

Engine torque creates additional loads on the left main landing gear which, in turn, increases the force of friction on the left main wheel(s). Consequently, this creates a yawing moment to the left during a high speed taxi or takeoff ground roll.

Spiral slipstream or ‘corkscrewing effect’ is a result of propwash rotating in a clockwise spiral along the airplane’s long axis. This impinges on the left side of the vertical fin and tail boom, creating a yawing moment to the left as well.

This combined yawing moment should be counteracted with right nosewheel steering and/or differential braking and right rudder as the speeds increase and aerodynamic control surfaces become more effective.

On tailwheel airplanes doing three point takeoffs, P-Factor will enter in to the left turning tendency, but only as speed increases and a nose high attitude maintained. P-Factor’s effect will largely depend on the airspeed and angle between the propeller shaft and the relative wind.

If the airplane is equipped with an engine and propeller that rotates counterclockwise, these effects are reversed and a right turning tendency happens during the takeoff roll. One famous example were the Supermarine Spitfire and Seafire variants powered by the Rolls Royce Griffon engines, which could be temperamental during the takeoff roll for this reason.

Twin engine airplanes equipped with counter rotating propellers and single engine airplanes equipped with contra rotating propellers can largely negate much of this left turning tendency as such systems counteract the torque produced on the airframe, eliminate P-Factor and gyroscopic precession effects, and reduce the spiral slipstream effect to a greater degree. The downside is that these systems increase the weight, complexity, and costs of the propeller and power plants used, and this generally deters their integration into light airplanes by the manufacturers.

$\endgroup$
12
  • $\begingroup$ Thank you. So pilots actually yaw to the right on the runway to correct that. Pretty dangerous. But shouldn't planes whose propellers rotate counterclockwise then drift right? $\endgroup$ Commented Feb 5, 2022 at 12:35
  • 1
    $\begingroup$ You will apply right rudder during the takeoff roll to counteract the effect of torque and track the A/C on centerline $\endgroup$ Commented Feb 5, 2022 at 12:44
  • 1
    $\begingroup$ The only time precession is really noticeable is when you raise the tail early in the takeoff run of a taildragger. If you force the tail up sharply, early, you will get quite a hard swing left from precession, depending on the weight of the propeller relative to the airframe. $\endgroup$
    – John K
    Commented Feb 5, 2022 at 18:02
  • 1
    $\begingroup$ No airplanes don't normally turn by yawing; it's mostly P factor and torque from the high power & mass of the propeller relative to the airframe. P factor offsets the thrust line to the right any time the propeller isn't perpendicular to the airflow, which is most of the time, to some extent. You normally apply rudder trim as required to stop the pull. On takeoff the Mustang requires a specific rudder trim setting as part of its checklist. Torque and yaw reactions to engine power complicated aerial gunnery, since every time you moved the throttle the nose would move and throw your aim off. $\endgroup$
    – John K
    Commented Feb 6, 2022 at 13:50
  • 1
    $\begingroup$ @Better not tell. No, that’s just symptomatic of a poorly trimmed airplane. Larger more powerful airplanes like that will require trimming after every power change in order to neutralize control pressures in all three axes. $\endgroup$ Commented Feb 6, 2022 at 13:51

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .