Electrostatic discharge clearance for Eurofighter typhoon air to air refuelling

Whenever an aircraft flies through the air an electrostatic charge is built up on that aircraft. The size of this charge is dependant upon several factors including aircraft size and speed. In an air to air refuelling operation two aircraft, each with a different amount of static charge, are connected together via an electrically conductive refuelling pipe. When this connection is first made an electrical pulse flows along this refuelling pipe, as the amount of charge on the two aircraft is redistributed. This electrostatic discharge pulse causes currents to be induced on the wiring of the two aircraft. This induced current could cause damage or malfunction of flight safety critical systems on the aircraft, if the systems and airframe are not designed to protect against this threat. It is a requirement that before air to air refuelling operations can take place a clearance against the electrostatic discharge threat is obtained for the Eurofighter aircraft. This paper will describe how a transmission line matrix (TLM) code with an incorporated multi-core wire solver has been used, as part of an advanced computational electromagnetic modelling facility, to provide the electrostatic discharge clearance for Eurofighter development aircraft.