M.L. Aviation Rotabuggy / Rotajeep
Raoul Hafner, an Austrian expatriate engineer, was working for the British Airborne Forces Research Establishment when he developed the idea of using free-wheeling rotors to deliver airborne personnel into enemy territory. Having proved that his Rotochute could support a combat ready soldier, Hafner suggested that much heavier loads might also be delivered by rotor; a jeep, perhaps, or a truck, possibly a tank.
The scheme had a naive simplicity; take a vehicle, add a suitably sized rotor and tail surfaces, tow it to altitude behind an aircraft, then cast it free at the planned landing point for landing. M.L. Aviation at White Waltharn airfield in Berkshire, were awarded a development contract for the first Rotabuggy to Specification 10/42, which appeared in 1943. The basic vehicle was a US Army jeep, to which was attached a fuselage extension with a twin-finned tailplane (no rudders), and a 14-m (46 ft 8 in) diameter rotor. The jeep was equipped with a rotor control column which hung from the roof, a rotor tachometer, and a rudimentary set of flight instruments, but was otherwise quite standard. Preliminary tests were conducted with the Rotabuggy, or Rotajeep as it was otherwise known, ballasted with concrete to 1430 kg (3150 lb) and dropped from a height of about 2.1 m (7 ft) to test its impact absorption.
This demonstrated that the standard model could absorb impacts of 1lg without damage, and a two-blade rotor with a diameter of 46 ft 8in (12.4 m) was then fitted.
Camouflaged in the wartime fashion and sporting a prototype "P" and RAF roundels, a 4½ -litre super-charged Bentley sports car was hitched to the jeep and towed the combination at speeds up to 105 kph (65 mph). The Rotabuggy becoming airborne for the first time on 16 November 1943. These trials took place at Sherburn-in-Elmet, near Leeds.
By November 1943 the Rotajeep was ready for air-testing from Sherburn-in-Elmet air-field towed by a Whitley bomber. Seven flights were made, one flight crashed nearly killing the pilot. The combination made one very short circuit on the final flight.
Mary de Bunsen with the Air Transport Auxiliary witnessed one of the flights: "We all stood and watched while an old Whitley taxied out on to the runway and took off, with a jeep in tow. They made a very short circuit, and when the Whitley touched down, the jeep, which had not cast loose, remained airborne for some seconds a few feet above the runway. It was at this juncture that we realized that the occupants were unhappy. The pilot held the control column, which was directly connected with the rotor and was suspended from the roof. The driver sat beside him and held the steering wheel. Up and down, up and down, it wandered, white we all stood and prayed that it would stall on a "down" rather than an “up". This it fortunately did, landing plop on all four wheels, and the motor driver took over and steered it down the track like Stirling Moss. When it stopped, nobody got out for a while, and then the pilot was assisted out and laid down flat beside the runway to recover. Apparently the joystick had whipped round and round in circles all the time they were in the air and only sheer strength had kept the jeep under control, so the poor man was completely exhausted."
Not all the flights were as nerve shattering as this had apparently been. The handling and flying qualities of the Rotabuggy have been described officially as "highly satisfactory", especially after larger fins had been fitted and greater blade articulation provided. However, the development of the Horsa and Hamilcar vehicle carrying gliders made further development of the idea unnecessary, before a 47.25-m (155-ft) rotor could be tested on a Valentine tank.
Rotor diameter: 12.40m
Gross weight: 1411kg / 3,110 lb
Empty weight – Jeep: 964kg
Weight - rotor unit and tail: 249kg / 550 lb
Design max speed: 241kph / 150 mph
Rates of descent – est: 4.9 - 10m/s / 960-1,980 fpm
Minimum take-off and landing speed: 58kph
Basic rotor speed: 230 rpm
Max rotor speed: 260 rpm