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How fast can a rotocraft go, relative to the air, if it is flying towards its tail?

Tiltrotor and powered lift aircraft do not count. Helicopters and gyroplanes do. The aircraft must have a readily visible tail end, so the Jerome-de Bothezat Flying Octopus for example is excluded. This is about level flight with zero yaw.

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  • $\begingroup$ aviation.stackexchange.com/questions/15853/… $\endgroup$
    – Anonymous Physicist
    Commented Aug 14 at 1:55
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    $\begingroup$ Would a Chinook be indifferent about flying cockpit-forward or ramp-forward? $\endgroup$
    – Ralph J ♦
    Commented Aug 14 at 3:33
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    $\begingroup$ @MichaelHall Flying forward and then yawing 180 degrees does not count as flying backwards. $\endgroup$
    – Anonymous Physicist
    Commented Aug 14 at 19:33
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    $\begingroup$ African or European? $\endgroup$
    – Jon Custer
    Commented Aug 16 at 19:50
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    $\begingroup$ @JonCuster You have to know these things when you're a king. $\endgroup$
    – Anonymous Physicist
    Commented Aug 16 at 22:04

4 Answers 4

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Inspired by Jpe61's answer I checked the flight manual of the Chinook, and it mentions

"Maximum airspeed in rearward flight is 45 knots" (23.15 m/s)

This value is rather close to the upper bound of Jpe61's estimate.

enter image description here

Of course, this does not mean it's the maximum speed achieved, but I think the Chinook is a helicopter whose setup is quite well suited to flying backward, and this will be close to the maximum speed achieved.

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  • $\begingroup$ What? A helicopter can go backwards faster than 10 knots or 5 m/s $\endgroup$
    – U_flow
    Commented Aug 14 at 8:44
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    $\begingroup$ I thought so too, but I can't find any measured numbers/sources confirming it, so I'm putting this as a lower bound. $\endgroup$
    – ROIMaison
    Commented Aug 14 at 10:59
  • $\begingroup$ Since the video i linked to is from an airshow, it makes sense they are not using the full envelope to have safety margins 👍 $\endgroup$
    – Jpe61
    Commented Aug 15 at 9:54
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This video: Chinook CH-47 Roll and flying backwards amazing to see at RIAT 2017 shows a Chinook taxiing backwards and the proceeding to take off at the same backwards speed. I estimated it travelled its length in about 1.5 to 2 seconds, and knowing the length being 30 meters, that would give it a speed of approximately 15 to 20m/s, which would be about 30 to 39kts.

Chinook is, of course, not your garden variety helicopter, its tail end is clearly distinctive though.

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  • $\begingroup$ chinook is also the only helicopter where flying backwards makes sense, turning around it's vertical axis is trivial for other helicopters. $\endgroup$
    – paul23
    Commented Aug 16 at 15:53
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For the maximum reverse speed of a conventional helicopter I have found one example, the Bell AH-1F Cobra.

The "Technical manual operators manual for army model AH-1F attack helicopter" sets the rearward flight speed limit as 30 kts.

This is lower than the sideways limit which is 35 knots, and I agree with Sophit in that the tail becomes destabilizing factor in rearward flight, restricting the envelope.

(Section V. airspeed limits, page 163) snippet of section V.

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I don't have hard numbers (although the maximum backward speed should be readily available in the flight manual of any helicopter) but if you consider helicopters with tails then some 20 kt should be a maximum limit. A tailplane is added to give the aircraft stability and download the rotors... when flying forward! Flying backward the tailplane becomes destabilising and the rotors now need to provide additional stability as well, more and more the faster they fly backwards.

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