Analysis of a System to Prevent Helicopter Rotor Blade-Airframe Strikes

Rotor blade-airframe strikes are rare but they do occur. Three areas of the airframe are particularly vulnerable the tail boom, canopy and, in the case of the underslung, teetoring rotor, the rotor shaft. This latter case is known as mast bumping. This report studies a system to prevent a helicopter rotor blade from striking any part of the airframe. Essentially, the system continuously predicts ahead the rotor blade flapping in response to an input such as pilot control or an atmospheric disturbance. If a blade strike is predicted to occur then an appropriate feedback control is applied to alter the future flapping. The prediction is then begun again with the altered control. In the actual system, an enunciator might warn the pilot at the time that he is attempting a control input which could be hazardous. Two somewhat independent approaches to the design of the controller are taken. One of the programs is entirely numerical in its approach. The other uses modern control theory and considers the preliminary aspects of implementing the controller in digital hardware. Both methods indicate the feasibility of preventing excessive flapping, although the question of implementation in a dedicated microprocessor is not fully resolved. Helicopter rotor control systems.