Helicopters and autogyros
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An autogyro is characterised by a free-spinning rotor that turns due to passage of air upwards through the rotor. The vertical component of the total aerodynamic reaction of the rotor gives lift for the vehicle, and sustains the autogyro in the air.
Whereas a helicopter works by forcing the rotor blades through the air, pushing air downwards, the autogyro rotor blade generates lift in the same way as a glider’s wing by changing the angle of the air as it moves upwards and backwards relative to the rotor blade. The free-spinning blades turn by autorotation; the rotor blades are angled so that they not only give lift, but the angle of the blades causes the lift to accelerate the blades’ rotation rate, until the rotor turns at a stable speed with the drag and thrust forces in balance.
From wikipedia
AZ 1/48 Kayaba KA-GO (O-GO) Ka2 Japanese Imperial Observation Autogyro Aircraft Kit
The Cierva Autogyro Depicted in Flight Art Giclee Poster Print by Edward Shenton, 18×24
Betcha didn’t know helicopters were invented by a Spaniard, eh?
Military Helicopter (Over Desert) Art Poster Print – 11″ X 17″