I know that regular main+tail rotor helicopters stall at higher speeds as the relative airspeed of the retreating blade approaches zero.

I'm curious if coaxial or intermeshing dual-rotor helicopters are affected by the same or a similar problem.

I'm aware that other factors may dominate and impose speed limits on them as well, but I'd like to know if a retreating blade stall is a problem that can be overcome with dual rotors.


Dual and intermeshing rotors also suffer from retreating blade stall at high forward velocity. But the effect of this is much less dramatic than with a single rotor.

Retreating blade stall causes a loss of lift on one side of the rotor: the single rotor helicopter will start to roll. A helicopter with two rotors that counter-rotate doesn’t experience this rolling moment, only an increase in drag.

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    $\begingroup$ So as I understand it, it can keep flying safely even if its efficiency suffers. Right? $\endgroup$ – edgerunner Aug 26 '19 at 19:22
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    $\begingroup$ @edgerunner Right. $\endgroup$ – Koyovis Aug 26 '19 at 19:33
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    $\begingroup$ Is it worth mentioning that in coaxials, the faster you go the upper retreating blade rises less while the lower advancing blade rises more, eventually leading to a very exciting intersection of the rotor cones? $\endgroup$ – Carl Kevinson Aug 26 '19 at 20:20

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