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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.

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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, 2019 at 19:22
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    $\begingroup$ @edgerunner Right. $\endgroup$
    – Koyovis
    Aug 26, 2019 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? $\endgroup$ Aug 26, 2019 at 20:20

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