Shipborne helicopters are widely used, but their takeoffs and landings are very dangerous. For improving the security, a stabilized platform system, which is connected with ship body by hydraulic cylinders and has the function of ship motion compensation, is proposed. When the system works, the platform rises up to the deck and gets the general effect of ship movements (i.e. rolling, pitching and heaving) compensation by the way of each cylinder performing heave compensation of the corresponding point of the deck of ship. Laboratory experimental observations on the behavior of the system are reported and control performance researches are described.
Shipborne helicopters possess a wide variety of operational use, but their takeoffs and landings are very dangerous. For the sake of safety, shipborne helicopters usually stop flying and training when the sea conditions are severer than third degree or when the ship's rolling exceeds ±5°, pitching exceeds ±2°, heaving exceeds 2 m and wind velocity is bigger than 15 m/s. According to statistics (Mu, 2000; Newman, 2004), the accident rate of shipborne helicopters is 5 times to that of spacecrafts, 10 times to that of bombers and 54 times to that of civil airplanes. There were 300 shipborne helicopters of American navy which fell into the sea from 1963 to 1983 and 380 people died. And about 50% of the accidents occurred during takeoffs and landings. In addition, there were 14 accidents of helicopters falling into sea in the infrequent sea works and training of CAAC in the lately 30 years. The present approach for improving the takeoff and landing security of shipborne helicopter is to predict their takeoff and landing opportunity by using prediction technologies of frequency domain and time domain (Cai et al., 2003; Yang et al., 2008).
