When tip–mounted engines are employed on a helicopter rotor, such as lightweight turbines, ram-jets or pulse-jets, the action of the fuel flowing along the blade gives rise to a power loss. For a ramjet helicopter this is of the order of 6 per cent, of the total power requirement of the rotor system. In addition, if the fuel injection nozzles in the combustion chamber face upstream this leads to an additional power loss of 1-6 per cent, of the total power, and it is evident that these effects should be allowed for in helicopter performance calculations. It is shown for a ramjet helicopter that the total spraying and centrifugal pumping loss is of the same order as the total transmission and tail–rotor power loss for a conventional shaft-driven helicopter. The same effect can be demonstrated for pressure-jet rotors, where it has an even greater magnitude.