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the vehicle. Hiller’s chief test pilot, Philip T Johnston, undertook the first VZ-1 test flights and the platform performed well, demon- strating an ability to automatically right itself. However, there were handling difficulties in windy conditions and the machine could not exceed a speed of about 16mph (25km/h), or move very far out of ground effect. In February 1956 the Hiller development team, which comprised Arthur Robertson, Joseph Stuart and Robert Wagner, filed a US Patent (2,953,321) for this design, calling it a VTO wingless flying platform. Nevertheless, it had many shortcomings and the team sug- gested that the next version should be fitted with a new power transmission system that would allow both engines to drive both rotors. In the event of an engine failure this would permit a hard landing as opposed to a complete loss of control. Another proposed alteration would be the introduction of four movable vanes to give yaw control. During November 1956 the US Army ordered a second prototype (56-6944) for evaluation, which was given the company designation Model 1031A. This second plat- form flew for the first time on 20th November 1957. It was a big improvement over the ear- lier design, but the platform could not move out of ground effect, stability remained a trou- blesome issue and there were kinaesthetic control problems due to the lower centre of gravity. Hiller’s engineers tried to correct the stability problem by fitting a gyro-stabilisation system linked to the yaw vanes in an arrange- ment similar to that used on the Hiller UH-12 helicopter. To address the kinaesthetic control issue it was decided to raise the pilot’s position, but the problem was never fully resolved. Unfor- tunately there was still insufficient power to lift the platform above a height of about 5ft (1.52m) and a larger 8ft (2.44m)-diameter duct was specified, enclosing two 7ft (2.13m) rotors. A third back-up engine was fitted, because high loading on the rotors meant that autorotation was not possible, although this addition came with a significant weight penalty. On the other hand, with double the rotor area, there was an immediate improve- ment to range and payload capacity, along with less downwash and a significant reduc- tion in noise. A third prototype (56-6945) followed, which was called the VZ-1E. This had a much Fans and Ducts 135 Original drawing for the Hiller VZ-1 one-man flying platform. Hiller Helicopters Cross-section drawing of the Hiller VZ-1 flying platform. Hiller Helicopters