For propellers, as the airspeed increases thrust decreases. Is the airspeed component taken as a vector quantity perpendicular to the propeller? If that's true, then it's quite easy to visualize in the case of airplanes.

However, for quadcopters can the forward component of the thrust vector of a quadcopter type rotor be expressed as:

$$ V_q\cdot{sin}\theta_t $$


  • $V_q$ is the forward airspeed of the quadcopter, and
  • $\theta_t$ is the angle of rotor tilt

Is this an accurate expression of the thrust vector?

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    $\begingroup$ Welcome to Aviation.SE could you please clarify what you are asking for? $\endgroup$ Mar 30, 2016 at 16:10
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    $\begingroup$ Note for a tilting helicopter (and I guess a quad too), tilting forward produces forward motion, and this generally increases lift too. So it's a lot more complex than just taking the cosine of the tilt angle. Also, you might want to edit and rephrase your question as it's not 100% clear what you mean. $\endgroup$
    – Andy
    Mar 30, 2016 at 16:21
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    $\begingroup$ I think this question should stay open, but the OP really needs to clean up the formatting so it's easier to follow...please? $\endgroup$
    – Jae Carr
    Mar 30, 2016 at 17:54
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    $\begingroup$ I have attempted to clarify the formatting and wording. If my edit is too presumptive it should be rolled back. $\endgroup$
    – J W
    Mar 30, 2016 at 18:48

1 Answer 1


The term $$V_q\cdot{sin}\theta_t$$ is a speed, not a force, so it cannot be an accurate expression of the thrust vector.

Propellers accelerate the air flowing through the propeller disc in the direction of the propeller axis (or perpendicular to the propeller disc), so the force is only parallel to the propeller axis when the airspeed is aligned with the propeller axis. If the airspeed is at an angle to the propeller axis, the thrust vector is tilted towards the airspeed vector. The magnitude of this tilt depends on the speed increase of the propeller stream relative to airspeed.


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