simultaneously. Large elevators on the tailplane help control the fuselage attitude and provide reaction to pitching moments from the wing and variation on rotor disc angle. The control system is complex due to the sheer size of the aircraft and the need to compensate for aeroelastic deformation of the structure, as well as the very large friction loads of the control rods, levers etc. To keep the control forces felt by the pilots to a minimum, the control system has three distinct stages. Stage one is the direct mechanical control from pilot input forces which are fed into a second stage, intermediate powered control system with low-powered hydraulic boosters transferring commands to stage three, the high-powered rapid action control actuators at the main gearboxes operating the swashplates directly. Operational history Construction of the first prototype was completed in 1968. A first flight on 27 June 1967 ended prematurely due to oscillations caused by control problems; one set of main wheels contacted the ground hard bursting a tyre and bending a wheel hub. The cause of the oscillations proved to be a harmonic amplification of vibrations in the cockpit floor feeding back into the control column when a roll demand was input into the cyclic stick. It was widely but erroneously reported in the Western press that the aircraft had been destroyed. The first prototype, given the registration SSSR-21142, made its first flight on 10 July 1968 from the Mil factory pad in Panki to the Mil OKB test flight facility in Lyubertsy. In February 1969, the first prototype lifted a record payload to . On 6 August 1969, the V-12 lifted to a height of , also a world record. The second prototype was also assembled at the Mil experimental production facility in Panki but sat in the workshop for a full year awaiting engines, flying for the first time in March 1973 from Panki to the flight test facilities in Lyubertsy. Curiously the second prototype was also registered SSSR-21142. The prototype V-12s outperformed their design specifications, setting numerous world records which still stand today, and brought its designers numerous awards such as the prestigious Sikorsky Prize awarded by the American Helicopter Society for outstanding achievements in helicopter technology. The V-12 design was patented in the United States, United Kingdom, and other countries. Despite all of these achievements the Soviet Air Force refused to accept the helicopter for state acceptance