Electrostatic Voltage Sensors for Helicopter Dischargers

Abstract : To maintain hovering helicopters at safe energy levels, a noncontacting electrostatic sensor is required to accurately determine the voltage on the aircraft relative to ground and provide proper control data to an active discharger for neutralizing hazardous charging conditions. Analytical model studies of a sphere suspended between two electrified ground planes and surrounded by space charge resulted in a theoretical relationship showing how charge density, excess surface charge, and external electric fields affect the voltage on the sphere. The electrostatic trends predicted from the theoretical analysis were sufficiently verified through independent large-scale laboratory experiments using empirical analysis techniques. From the theoretical and empirical analyses, helicopter charge equilibrium conditions were specified, together with a methodology for determining the electrostatic coefficients of full-scale hovering helicopters. The implications of the investigative program are that active electrostatic discharger systems are now feasible for helicopter applications. (Author)