A little spark will go a long way...
Some helicopters are designed so that the static buildup on the rotor blades is carried directly to the airframe bypassing the transmission. On some helicopters that have elastomeric teeter bearings the charge can not get to the airframe nor can it pass through the transmission. This is true for the Cobra models like the AH1-J and the Bell 214. On these helicopters the static charge forms a torroidal magnetic field around the rotor disc with this field centered on the main mast. This causes magnetization of the mast and the steel parts on the rotorhead. This can also happen on the Bell 412. The level of magnetization is far in excess of that allowed in the Bell overhaul manuals when a part is Magnafluxed and then degaussed. This can result in minute electrical charges flowing across gears and bearings in the transmission causing spark discharge erosion. This also happens on those helicopters where the static charge is drained to the fuselage through the transmission.
Last edited by Lu Zuckerman; 10th May 2004 at 03:14.