Pitcairn AC-35, 1935 - (scan-1996)

This roadable autogiro was built under contract by the Autogiro Company of America for the U.S. Bereau of Air Commerce.

Engine: Pobjoy Cascade, 90 hp (Smithsonian caption)

Developments in autogiro design of early 30s led to direct control rotor 1932. In this system, rotor could be tilted in any direction, resulting in forces that would control direction of autogiro accordingly. Next step was to provide power directly to rotor while still avoiding much more complicated helicopter transmission with all its difficulties. Power from engine spun rotor; as speed built up, pilot would declutch engine from rotor and simultaneously change pitch of rotor blades. Swiftly spinning blades would then impart lift that caused autogiro to rise. Transition to forward flight resulted from prop's thrust. These improvements led to rotor hub remarkably like that of modern helicopter. Then remained only for development of transmission systems and improvements in torque control to make helicopter possible. AC-35 won Department of Commerce competition "for an aircraft of greater utility" for the average pilot (in this case, a roadable aircraft). Later, additional testing done before donating it to NASM. Smaller in size than any previous Pitcairn design, had rotor diameter of just over 34 ft and gross weight of less than 2000 lbs. Had 2 radical features: first was foldable blades to facilitate ground transport; second was direct drive to single rear wheel so it could be driven along city streets. AC-35 went through long series of tests mainly in effort to improve somewhat sensitive stability problems. Flew very well and, after a variety of fixes, was able to fly "hands off" for relatively long periods. Also had surprisingly good road performance of 25 mph. (Despite technical success, this class of aircraft was said to have combined worst features of car and airplane.) Had a near rebirth 1961 when Skyways Engineering Company reformed. Skyways purchased rights from Pitcairn and planned to clean up design and install 135 hp Lycoming engine. Engine would have provided considerably improved performance; new rotor hub planned with hydraulic pre-rotation of blades to provide a jump start capability.

Click on the picture to get a full-screen, high-res photo!