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If the engine(s) on one side of a multiengine airplane are set to a higher throttle setting than those on the other side, the airplane (all else being equal) will yaw towards the lower-throttle side; this is best known as a technique for controlling airplanes that have suffered a partial or complete failure of their primary flight control system(s).

Are there any airplanes that make use of throttle steering during normal operation?

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    $\begingroup$ I doubt any aircraft uses this as a normal method of control since it really is a poor way of doing things. Asymmetric thrust doesn't just affect yaw, one wing will drop and is difficult to get level again if it degrades too much. It also becomes a problem if one of the engines happen to fail. $\endgroup$
    – Ron Beyer
    Aug 9, 2018 at 1:37
  • $\begingroup$ I take it my small cheap styrofoam dual channel RC aircraft isn’t what you’re after, although it technically qualifies, the way the question is worded. $\endgroup$
    – Cpt Reynolds
    Aug 9, 2018 at 3:59
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    $\begingroup$ Aircraft do not steer by yawing, but by banking. The rudder is needed to compensate for the adverse yaw of entering the bank, but in a steady turn on most aircraft it is deflected very little. Differential thrust would not help anything. $\endgroup$
    – Jan Hudec
    Aug 9, 2018 at 5:39
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    $\begingroup$ Nearly all quadcopters! (“drones”) $\endgroup$
    – szulat
    Aug 9, 2018 at 8:11
  • $\begingroup$ @Sean, please clarify your question, do you mean aircraft as in anything that takes to the skies, or airplanes, which is much more specific. Also, do you mean manned or unmanned craft. $\endgroup$
    – GdD
    Aug 9, 2018 at 8:18

2 Answers 2

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Yes, The Northrop Grumman B-2 Spirit Stealth Bomber.

The leading edge of the wing has an internal structure that helps it absorb radar energy. The outermost wing segment features a "rudderon" or "deceleron", a vertically-split airbrake / rudder that simultaneously opens up and down. To act as an airbrake, both the decelerons are opened, while to act as a rudder only one is. This clever gimmick goes back to the original Northrop flying wings. There is an elevon inboard of the deceleron on the outermost segment of each wing, and then two elevons further inboard, on the next segment. Finally, there is a single control surface for pitch control on the "beavertail" at the center end of the aircraft, giving a total of nine control surfaces.

The decelerons have to be opened about five degrees before they are effective, and in normal cruising flight they are left slightly open. However, this undermines stealth, so when the bomber is in hostile airspace, it uses differential engine thrust for yaw control.

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    $\begingroup$ "Yaw control" would normally just mean keeping the airplane aligned with the airflow. If we are talking about turning, then we are talking about banking as Jan Hudec mentioned. So is the B-2 using engine induced yaw to skid the plane, thereby inducing a bank, and getting a turn that way? Or are the elevons inboard still doing the job of banking the plane and it's just differential thrust being used keep the turn coordinated? I would tend to think it's the latter. $\endgroup$
    – John K
    Aug 9, 2018 at 21:39
  • $\begingroup$ This does not qualify as throttle steering because yaw is not about steering, it's about compensating for other forces during steering, $\endgroup$
    – Juan Jimenez
    Aug 10, 2018 at 8:08
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Another aircraft is the AeroVironment Helios, which was solar powered and flew with ten or fourteen electric motors. The torque of an electric motor can be controlled very rapidly and precisely, far faster than gas turbines.

To turn the aircraft in flight, yaw control is applied by applying differential power on the motors — speeding up the motors on one outer wing panel while slowing down motors on the other outer panel.

In fact, in this flying wing design, differential thrust also provides pitch control:

A major test during the initial flight series was the evaluation of differential motor power as a means of pitch control. During normal cruise the outer wing panels of Helios are arched upward and give the aircraft the shape of a shallow crescent when viewed from the front or rear. This configuration places the motors on the outer wing panels higher than the motors on the center panels. Speeding up the outer-panel motors caused the aircraft to pitch down and begin a descent. Conversely, applying additional power to the motors in the center panels caused Helios to pitch up and begin climbing.

Had the aircraft not crashed, the eventual plan was to remove the elevators, the only control surface, and fly completely by differential thrust.

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  • $\begingroup$ Maybe we should specify that it should be aircraft that successfully used differential power for this. In reality, it was not yaw control that gave them steering, but the fact that a drop in power on one side and an increase in the other would cause one wing to generate more lift than the other, inducing a bank. That is what provided the steering control. But in the end, it was a poorly designed aircraft. $\endgroup$
    – Juan Jimenez
    Aug 10, 2018 at 8:14

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