Is it possible to have dual contra-rotating rotors on a gyrocopter or gyroplane? Are there disadvantages that would outweigh the extra lift?
You can get additional lift with a larger rotor, without going to the extra complication of having two of them. Present-day autogyros are very light machines that have more than enough with one rotor. Besides, in the case of the coaxial configuration, the centre of mass of the machine will be much higher, a very undesirable thing for landings, as any gyro pilot would attest...