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I can understand coaxial rotors cancelling the need for a tail rotor, however, I am curious as to if the second rotor is needed to actually maintain the same pitch or could be just used to offload the primary disk in a powered auto-rotate capacity? That would just create more drag I assume.

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You could use the second rotor to provide anti-torque function only, as Arthur Young did when developing his helicopter test models at Bell during WW2. In that case the upper rotor did all the lifting and the lower one had blades that were at 90 degrees and just made drag to generate a cancelling torque.

But that is really inefficient, and Young quickly moved on to using an anti-torque tail rotor (with a decently long arm to minimize the thrust it had to make), not wanting to go the whole-hog coaxial route, with all its mechanical complexity.

So if you want to have a coax machine to do away with a tail rotor, you might as well design it so both rotors are lifting (to realize the efficiency you are seeking by going with co-ax in the first place) and you can easily get yaw control by using a mixing system operated by the anti-torque pedals that adds collective pitch to one rotor and decreases collective pitch to the other rotor equally, in a way that the total lift is unchanged but a yawing torque can be created and varied. And there you go.

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  • $\begingroup$ Thank you for this lead, I can see this.... So coaxial with collective on both... Gain altitude and engage a lateral drive to a point of speed allowing auto-rotation and disengaging rotor power...... Autogyro may live after all :) $\endgroup$ – Skyhawg Jan 21 at 1:51
  • $\begingroup$ Well they all glide fine when you take the power off because you pitch the blades down so they can glide forward. An auto-rotating rotor is just like two gliders that pass each other going opposite directions and lock wingtips so they are forced to glide in a little circle. One rotor, two rotors going coaxially, or two rotors in tandem, it's all the same. $\endgroup$ – John K Jan 21 at 1:56
  • $\begingroup$ Yep, however, autogyro going VTOL is what I am after..... No rocket tips or Carter "Jumps"..... Once vertical and moving lateral disengage power and fly lateral at speed then re- engage to go vertical again to land... We got this! $\endgroup$ – Skyhawg Jan 21 at 2:10
  • $\begingroup$ Electric is the key and batteries suck $\endgroup$ – Skyhawg Jan 21 at 2:11
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    $\begingroup$ @Skyhawg I'll nudge you one step further: hydrogen storage is the bottleneck, because the tanks are so heavy. There have been several good tech demonstrators in the past decades, but they all were weighted down (literally) by the terrible energy density once you add the H2 tank into the calculation. $\endgroup$ – AEhere supports Monica Jan 21 at 9:39

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