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My maternal ancestors were involved in pioneering helicopters back in the 1920's and 30's, and here you can see an example of a design that was used during WWII for dropping spies into France and picking them up again. The vehicle is an autogyro, a precursor to the helicopter which supports itself in the air with its unpowered rotor. Modern helicopters have a muckle great engine to turn the rotors, and drive air downwards, which by Newton's 3rd law of motion causes the vehicle to remain aloft.

Autogyros rely on ingenuity to spin the rotor and hence generate the same momentum transfer. It is something to do with angles of attack, lift vectors and differential drag on the rotors. The autogyro cannot take of or land vertically, but James Weir developed a modification to achieve the first truly vertical takeoff helicopter. The Autogyro in the picture is the Weir C3. The C designation is a reference to Cierva, the Spaniard who invented rotary winged forward flight (he was an employee of the Weir Group). He thought up the idea of freely hinging the rotor blades, using only the centrifugal force and aerodynamic damping to balance the differing lift forces on the advancing and retreating blades. Until then, all helicopters rolled over in the direction of the blade rotation... and crashed. The later autogyros were usable vehicles - one of the family used to commute some 40 miles from their house near Dalrymple in Ayrshire to the factory in Cathcart on the south side of Glasgow. They used their walled garden as a landing pad, so they must have had confidence in their machinery! Nowadays autogyros kill about 10% of those who still fly in them. Thank goodness we've moved on. I fly gliders, which are a wee bit safer.