The Napier Oryx was a British gas-turbine engine designed and built by Napier in the early 1950s for the

Percival P.74 The Percival P.74 (later Hunting Percival P.74) was a British experimental helicopter designed in the 1950s that was based on the use of tip-jet powered rotors. Although innovative, the tip-rotor concept literally failed to get off the ground ...

tip jet A tip jet is a jet nozzle at the tip of some helicopter rotor blades, used to spin the rotor, much like a Catherine wheel firework. Tip jets replace the normal shaft drive and have the advantage of placing no torque on the airframe, thus not r ...

-powered helicopter project. The P.74 was unsuccessful and it and the Oryx were cancelled.

Design and development

The engine was developed by the Aero Gas Turbine Division of Napier in conjunction with

Percival Percival (, also spelled Perceval, Parzival), alternatively called Peredur (), was one of King Arthur's legendary Knights of the Round Table. First mentioned by the French author Chrétien de Troyes in the tale ''Perceval, the Story of the G ...

, later Hunting Percival. Funding came from the

Ministry of Supply The Ministry of Supply (MoS) was a department of the UK government formed in 1939 to co-ordinate the supply of equipment to all three British armed forces, headed by the Minister of Supply. A separate ministry, however, was responsible for aircr ...

. The

was a design for a

tipjet A tip jet is a jet nozzle at the tip of some helicopter rotor blades, used to spin the rotor, much like a Catherine wheel firework. Tip jets replace the normal shaft drive and have the advantage of placing no torque on the airframe, thus not re ...

-powered helicopter. The jet power was to be supplied from engines within the helicopter and piped to the rotor tips. Napier developed the Oryx specifically to power the P.74. 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 gas. In order to give a compact installation, rather than using an oversized compressor with a bypass around the turbine (as commonly used in the

turbofan engine The turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft propulsion. The word "turbofan" is a portmanteau of "turbine" and "fan": the ''turbo'' portion refers to a gas turbine engine which achieves mechanic ...

), the Oryx used an auxiliary compressor coupled to the turbine. This was mounted behind the turbine, with its gas flow in the opposite direction to the main engine core. The two gas 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 starting valve, consisting of a Corliss non-throttling rotating valve in combination with a butterfly valve (closed in flight),A typical "butterfly" valve restricts flow somewhat, even when completely open could divert individual engine output to the outside of the aircraft, permitting engine starting and ground running with the rotor stationary. Without the valve,

back pressure Back pressure (or backpressure) is a resistance or force opposing the desired flow of fluid through pipes, leading to friction loss and pressure drop. The term ''back pressure'' is a misnomer, as pressure is a scalar quantity, so it has a magnitu ...

in the duct and rotor system would prevent the starting of the engine. In the P.74 the two Oryx engines fed their outputs to a common duct that took the thrust to the rotor head. Development of the engine began in 1951. The engine was designed with a 12-stage axial flow compressor less than nine inches (19 cm) in diameter and a set of nine tie rods around the periphery of the compressor discs linking them together. Air from the compressor was fed to an array of five tubular combustion chambers, with the resulting hot gas driving a two-stage turbine connected to the four-stage auxiliary compressor via geared couplings. The first Oryx prototype engine was started for the first time in November 1953 and about 1,400 hours of test running had been achieved by the end of July 1955. 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. Percival p-74

Variants

;E.146 Oryx: Company designation. ;NOr.1:

(MoS) designation for the first variant. ;NOr.5: MoS designation for the fifth variant; gas hp at 22,600 rpm for take-off at sea level.

Engines on display

A preserved Napier Oryx is on display at the

Science Museum (London) The Science Museum is a major museum on Exhibition Road in South Kensington, London. It was founded in 1857 and is one of the city's major tourist attractions, attracting 3.3 million visitors annually in 2019. Like other publicly funded ...

Specifications (Oryx N.Or.1)

Notes

References

{{Napier aeroengines

Oryx ''Oryx'' is a genus consisting of four large antelope species called oryxes. Their pelage is pale with contrasting dark markings in the face and on the legs, and their long horns are almost straight. The exception is the scimitar oryx, which l ...