Aesir,
Most of the drag seen by the current recreational gyros is induced drag.
Max L/D on an autorotating rotor occurs at ~35% of peripheral tip speed. My gyro rotor spins about 340 RPM, for a tip speed of 410 fps. Max L/D is about 143 fps, or 97 mph.
Above that, profile and parasitic rotor drag starts picking up.
Unfortunately due to
my Bensen's airframe drag, I can't even touch Max L/D . I top out at about 85 mph.
More streamilined machines could likely cruise at their most efficient rotor speed though.
Andy Keech routinely cruises above 90 mph in his
Little Wing gyro.
The previously mentioned studies highlight the importance of thrustline-to-CG relationship, and gyro designs have been moving back in that direction. I say back because this was something that Cierva had figured out in the early days of autogyros, and is just being rediscovered.
My opinion on the poor safety record of the early Bensen gyros is that:
- There were no dual trainers to get instruction in. You had to teach yourself.
- Bensen did not incorporate a proper horizontal stabilizer in his design. Without a horizontal stab, the pilot can end up in a Pilot Induced Oscillation (PIO) because of the lag and overshoot inherent in a teetering rotor system, possibly unloading the rotors. Add in an offset thrustline and the machine can begin an unrecoverable tumble. The addition of a horizontal stab can tame quite a bit of thrust offset in addition to minimizing lag and overshoot.
My Bensen has one.
As for the later designs, many 'designers' just raised the mast and rotor, and slapped a Rotax on the back with it's larger diameter propeller.
Instant thrustline offset.
And usually no horizontal stabilizer was installed to counteract it, or to stabilize the airframe.
I have flown a couple of these types and
they are a handful.
But this is what I am currently building:
http://www.rotorflightdynamicsinc.com
And they fly like they're supposed to.
That's actually me in the first picture on the main page.
