The Napier Oryx was a British gas-turbine engine designed and built by Napier. The engine was developed by the Aero Gas Turbine Division of Napier in conjunction with Percival. Funding came from the Ministry of Supply.
Its sole application was the unsuccessful Percival P.74. The P.74 was a design for a tipjet-powered helicopter. The jet power to be supplied from engines within the helicopter and piped to the rotor tips.
The output gas temperature from the engines had to be below 400°C for the helicopter's stainless steel rotor ducts, so a bypass design was used. This also blew "cold" air from the compressor, rather than purely hot turbine exhaust. Rather than using an over-sized compressor with a bypass around the turbine (as commonly used in the turbofan engine), the Oryx used an auxiliary compressor in addition. This was mounted behind the turbine, with its gas flow in the opposite direction to the main engine core. The two air streams were deflected through 90° in a collector chamber, then exited vertically upwards. Gas flow through this collector was arranged so that each stream remained separate, the cold air from the auxiliary compressor passing through a bifurcated duct, so as to wrap around the hotter turbine outlet. By this means, the duct was further protected from the hot exhaust. Separator plates inside each duct split the stream into a number of flows and deflected each one separately, thus preserving the flows approximately constant across the whole duct. When the flows finally merged, they were flowing parallel and at approximately the same velocity, thus reducing turbulence and energy loss.
A Corliss non-throttling valve could divert individual engine output to the outside of the aircraft through a butterfly valve (closed in flight), permitting full running with the rotor stationary for starting and ground running. In the P.74 the two Oryx engines fed their outputs to a common duct that took the thrust to the rotor head.
Rotax electric starters were used but alternate methods could have been used.
First run in November 1953, the Oryx and the P.74 tip jet powered helicopter project, were later cancelled.
The Oryx was expected to be used for the planned commercial P.105 development of the P.74. In the P.105 the two engines would have been fitted back to front on either side of the rotor mast, feeding their outputs to the rotor hub. It was anticipated that 900 "gas horsepower" could be produced in its developed form.