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Could an aircraft have a spinning wing as a helicopter rotor at low speeds which stops spinning at high speeds to act like an airplane wing? The tail-rotor would turn 90 degrees and become a pusher propeller when this happens.

This is different than tilt-rotors or tilt-wings because in my case the rotors/wing switches from vertical thrust to vertical lift instead of switching from vertical thrust to horizontal thrust.

There must be some serious flaw with my design, and stopping the rotor fast enough to avoid retreating blade stall may be a problem. Maybe we could set the collective to almost zero and have a short period of low-g while we transform (but not negative g which would be bad)?

Helicopter blades have shorter chord than airplane wings which may force us to get a not-so-good compromise.

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  • $\begingroup$ Is this design going to have an aerofoil moving backward at some point? Unsure if there is an wing form that works efficiently with reversed flow. $\endgroup$ Commented Jul 7, 2022 at 8:16
  • $\begingroup$ I invite you to investigate the Sikorsky X2 before you consider this further. $\endgroup$ Commented Jul 8, 2022 at 19:44
  • $\begingroup$ @KorvinStarmast what exactly do you mean by that? Because of alternate loading of the wing blades or because you think that the coaxial main-rotor with pusher propeller configuration is superior? $\endgroup$
    – U_flow
    Commented Jul 19, 2022 at 12:17
  • $\begingroup$ @U_flow Because they demonstrated how to make it work, and because it doesn't include the rube goldberg feature of trying to change the tail rotor in to a thrust producing feature. The tail-rotor would turn 90 degrees and become a pusher propeller when this happens This is a great idea if you want to kill people, but not if you want to design a new generation of rotary wing aircraft. The 'stacked" blade discs have been around for a while, to include the Russian Hormone/Helix aircraft, and now the X2, S-97, and Defiant. Granted, they are still works in progress. (I do not work for SAC). $\endgroup$ Commented Jul 19, 2022 at 12:27

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Yes that is possible and also has been demonstrated a couple of times:

The sikorsky S-72

The concept is a special case of a convertiplane, sometimes called a stoprotor or Heliplane. Sikorsky tried to demonstrate it, even an X-Plane, the X-50 was built for demonstration purposes. However none of these full-size demonstrators sucessfully transitioned to forward flight. The X-50 was even cancelled, because both demonstrators crashed. Nowadays there are UAV concepts which have a similar concepts in mind.

The problems you mention do exist, unfortunately I could not find a reference how exactly the demonstrators solved all these problems. From what I can see: One of the wings will be experiencing reverse flow, it looks like the Sikorsky simply used very thick wings to overcome this problem. However retreating blade stall is not an issue, simply because by stopping the rotor you get less retreating blade stall.

I have not (yet?) seen your concept that the tail rotor swivels in order to create forward thrust. But I think that is not essential for the grander idea of stopping the rotor in mid-flight in order for it to act like a wing.

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  • $\begingroup$ "However retreating blade stall is not an issue, simply because by stopping the rotor you get less retreating blade stall." Maybe I should phrase it as "retreating blade transient loss of lift" since the airfoil does not necessarily stall as the zero airspeed point passes through it. $\endgroup$ Commented Jul 9, 2022 at 5:20
  • $\begingroup$ You will get a transient in Lift, meaning that in Rotorcraft flight mode, retreating blade stall will be experienced at the retreating blades while more lift is experienced at the advancing blades. When you stop the rotor, this unbalance of lift will diminish until the rotor is stopped and normal flight is achieved. $\endgroup$
    – U_flow
    Commented Jul 9, 2022 at 9:59

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