Month in the Patent Office

In a helicopter having a jet engine attached to the tip of each rotor blade, each engine comprising a combustion chamber into which liquid fuel is injected, ignition is effected by low tension surface discharge sparking plugs operated by condenser discharges at voltages below 3,000 volts, and the lead‐in cables to the plugs where the cables pass through the blades are either bare or provided with a thin insulating covering such that their total diameter does not exceed 2.5 millimetres. Where bare wires are used they are attached near the rotor shaft so that they tend to straighten out under the influence of centrifugal force; insulated supports for the wires are provided in openings in partitions in the rotor blades.