Otto,

While a coaxial contra-rotating design theoretically provides aircraft stability as the differential lift of the advancing and retreating blade pairs cancel each other out, it seems to me that each advancing blade will still be trying to flex upwards while each retreating blade will still be trying to flex downwards. Therefore, I would think that a flapping hinge (ala Bensen's teeter bar) would still be necessary in order to minimize the bending forces at the (rigid) hubs as the blades naturally try to rise and fall during each 360 deg of rotation. Of course, having two coaxial sets of flapping blades rotating in opposite directions is just asking for a blade collision and a big mess unless the blades are stacked a ridiculous distance apart. On the other hand, adding a helicopter's cyclic system to automatically increase and decrease each blade's pitch as they rotate would keep the advancing and retreating blades from rising and falling but this would increase the complexity of the system. Your thoughts?


Norfolk,

The absence of torque in an autogyro's rotor doesn't really justify a need for contrarotating coaxial rotors or the extra complexity and weight to add them. Aerodynamically, such a system isn't necessary. However, if you're just looking to build/experiment with something unique, by all means give it a try. Experimenting with "non-mainstream" ideas such as yours has been a big part of what made full scale aviation so successful over the past 100 years. Good luck and let us know what you come up with.

Harvey