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Permalink Reply by Andrew Rabbitt on February 11, 2012 at 6:31pm

But then you'll have a pitch-yaw coupling or a roll-yaw coupling (depending on which way you orient your reference coordinate system) that you don't necessarily have on multiple independently powered rotors.

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DeveloperPermalink Reply by R_Lefebvre on February 11, 2012 at 6:56pm

I'm a big fan of Helis and don't have any quads, so you might think I'd be a proponent of this idea.  But I'm not.

There are a number of things going on here.

1. Lifting efficiency.  Is it better to use flat helicopter blades or propellers?  If you use relatively long rotors spinning at a low speed, you will gain efficiency.  But, most helicopter blades on the market are made for 3D, and are thus less efficient at lifting than a single-direction profile.  I think that propellers will get back some efficiency advantage because the blade angles along it's length to maintain a true pitch value.

2. Complexity.  Obviously it's more complex.  It's more complex than a quad, and probably more complex than a heli.  Depending on how you do it, it could be much more complex than a heli.  So what really is the point?  If you are OK with the complexity of a heli, why not just fly a heli, and benefit from the longer flight time and payload resulting from the massive rotorspan?

3. Stability.  The servo system will have slop.  Period.  I think any benefit you get from quickness of response will be lost in servo mechanics.  Plus, I've seen quads so stable you could probably balance a ball on their nose.  I've also seen quads incredibly responsive and acrobatic.  I really don't see room for improvement?

I'd be much more interested in seeing somebody work on a tandem helicopter or tilt-rotor airframe instead.  Both of those offer significant advantages and are worth pursuing.

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