Experimental study of a static discharger for aircraft with special reference to helicopters

Abstract Flying aircraft often develop a strong electrification due to friction with airborne particulate matter. Charging currents in the range 1–10 μA are commonplace, and values up to 1000 μA have been recorded. Because of the perfect insulation of the aircraft body, very high potentials are reached, and the electric balance is restored by corona discharges from protruding parts, causing strong interference with navigational aids. In the case of fixed-wing aircraft, this can be remedied by “passive dischargers”, i.e. discharge points trailing in the wake of the plane with a damping resistor inserted. The problem is much more difficult and intricate in the case of helicopters. The mere fact that the potential of the helicopter is not zero can cause serious hazard to ground personnel. Besides, the ions generated by a passive discharger will linger and create a space charge cloud since the speed of the aircraft relative to the air is smaller than their drift velocity. The present paper concerns the “active” type of discharger, and takes advantage of previous work carried out at the University of Southampton, U.K., by a research group under the guidance of the late Professor A.W. Bright. In this type of discharger, charge generation can be controlled by a closed loop system actuated by a field sensor in order to keep the potential of the craft to a negligible level. Moreover, the charge carriers ejected have a very low mobility and can be carried away by the rotor wind, thus ensuring an effective charge transport to the ground. The device studied is very similar to the supersonic air blast electrostatic generators extensively studied in the 1960's, and the problems encountered are discussed in the light of generator technology.