I have no knowledge about aviation or mechanics or something. Recently I started a computer game 'besiege', a kind of sandbox-like game with bunch of parts to make all kinds of machinery.

And I'm trying to make a single-propeller airplane. What I'm concerned about is that it might roll over. I made a simple helicopter once before, which rotated to the other direction of the way propeller(of course facing up) did when only one prop is attached. I know this is why another small prop is at the tail.

So, is my airplane going to stay in balance with single propeller? I considered putting one on another rotating to the opposite direction in the same speed too, but that isn't the way I am planning to. Thanks in advance.


2 Answers 2


When it is slow, the two or three wheels should keep it from flipping over.

Once it is fast enough to fly, the wing will provide what we engineers call roll damping: Any tendency to roll† will cause an opposing moment which will stop the motion quickly. The rest is done by a differential deflection of the ailerons, so the wing creates an equal and opposite rolling moment to that of the propeller.

What is roll damping: Once the wing starts to roll, one side will go up while the other goes down. This will cause a change in local angle of attack and, consequently, local lift. The down-moving wing will see a higher angle of attack and a local lift increase, and the opposite happens on the other side. Total lift will remain unchanged, but now the change in the spanwise lift distribution will lift the down-moving wing back up and vice versa. The movement stops before it could pick up any speed.

With powerful engines, engine torque is a real problem and needs to be canceled with a few tricks:

  • Camber on the vertical tail: The vertical tail will create a side force and rolling moment which depends on the speed of the air flowing over the vertical. This helps to make the correction depend on the power setting of the engine. Just make sure that the vertical is in the slipstream of the propeller.
  • With contra-rotating propellers you can cancel the rolling moment of each propeller with that of the other. This needs a more complex gearbox, however.
  • In operation, apply power changes only slowly. With its narrow undercarriage, the Me-109 would become uncontrollable if the pilot went from idle to full power on the ground too quickly.
  • Watch the gyro forces of a spinning propeller: In taildraggers, the aircraft will yaw due to gyro forces once the tail is lifted during the ground run or the pitch attitude is changed in flight. Also, yawing (rotation around the vertical axis) will create a pitch moment (which acts around the spanwise axis).

† Roll: Movement around the longitudinal axis.

  • 3
    $\begingroup$ "The Me-109 would become uncontrollable if the pilot went from idle to full power on the ground too quickly" - I love the use of the word uncontrollable to describe being upside down and on fire :p $\endgroup$
    – Jon Story
    Dec 3, 2015 at 11:43
  • $\begingroup$ Plenty of WWII-era aircraft, especially the late war ones tended to have such massive torque that go-arounds on short final were discouraged due to loss-of-control risks. $\endgroup$
    – habu
    Dec 3, 2015 at 13:04
  • $\begingroup$ @JonStory: Upside down and on fire would be a rather extreme outcome. Normally what happened was that the aircraft yawed left and went into whatever happened to be there. If the take-off was on a wide open field (remember, many airfields were round grassy patches back then), the normal result was less spectacular. $\endgroup$ Dec 3, 2015 at 21:43

An aircraft has control surfaces for controlling its attitude: elevators for pitch, ailerons for roll and rudder for yaw.

At flying speed, the ailerons can provide much more torque than the propeller and the rudder can provide more torque than the p-factor and the effect of the rotating slipstream, so the aircraft simply flies straight with ailerons and rudder slightly deflected, with the amount of deflection depending on the engine power.

On the ground, wheel steering or asymmetrical braking is used to compensate the yaw below the speed at which rudder becomes effective and roll stability is ensured simply by the main gear track width.


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