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The Napier Nomad Engine


We've carried some pieces from David Taylor about his racing exploits. For many years his "day job" was with the Napier Engines division of English Electric, working mainly on the Deltic, about which more later. This piece, which we freely admit is nothing to do with car racing, is about one of the great might-have-beens of post war aero engines, the glorious, inventive Napier Nomad.

D.NAPIER & SONS had a good reputation for designing and producing high quality Aero engines of outstanding performance. In 1917 they had designed and produced the Lion Aero engine which was a 12 cylinder broad arrow section (often referrred to as W) with four valve cylinder heads, twin camshafts, and in 1922 added a turbo charger, which would be advanced by today’s standards a century later. This was so far ahead of any other engine that it soon became a world leader and used in a great number of aircraft types. It was also used in world speed record breakers on land, water and in the air. It can still be seen in action at Vintage race meetings in The Napier Railton and the Napier Bentley.

The mighty Napier Sabre aero engine was designed and produced just before the outbreak of WW2 and used in the Typhoon and Tempest, amongst the fastest fighters of their time. They were the only aircraft capable of catching the V1 flying bomb and destroying them. The Sabre was an H section with 24 cylinders, sleeve valves, and a two stage supercharger. It was capable of producing 5,500 BHP but down rated to 3,200 BHP for use in flight.

In 1945 the Ministry of Aircraft Production issued a requirement for an engine of up to 6000 BHP with great fuel economy to power transport and military aircraft. D.Napier&Sons had been taken over by The English Electric group in 1942 and part of a large corporation with substantial recourses capable of designing and producing such an engine so were awarded a contract to produce six test engines.

 

Nomad engine. Based on the sound of 2 stroke Commer lorries of the 1960's plus turbine roar and whistle, the sound of the Nomad must have been glorious

CONCEPT

The Jet engine / gas turbine was showing great promise for aircraft propulsion in 1945 but was in its infancy with very high fuel consumption so was unsuitable for long range flight. The thermal efficiency or fuel consumption of an engine is governed by its compression ratio, and the early Jet engines worked on low compression ratios of about 5:1.showing thermal efficiency of only about 17%. The most efficient engine was and still is the diesel which operates on compression ratios of about 20:1.shows thermal efficiency of about 40%. The engine designers at Napiers had the vision to see that a gas turbine coupled to a diesel engine would show very good thermal efficiency.However these engines have very different characteristics and difficult to mate up.

The Nomad uses a gas turbine where the axial compressor has a compression ratio of 5.5:1 feeding the compressed air at about 90 PSI into a Diesel engine creating an overall compression ratio of 32:1. The fuel is burnt in the Diesel engine at very high temperature. The gas expands producing power delivered by the crankshaft and then is exhausted at very high speed.driving a three stage exhaust turbine. Most of the power produced by the exhaust turbine is used by the compressor with the excess power transmitted to the crank shaft which drives the propeller. The final recovery of power from the hot gas is achieved by the thrust of the exhaust from the turbine.

 

 

DESIGN

The first attempt to design the Nomad was a flat 12 Diesel engine with a gas turbine fitted under as shown on the cross section below. The Nomad 1 design was over complicated as the compressed air from the 12 stage axial compressor was fed through an intercooler then through a radial compressor then to the two stroke diesel engine. The exhaust gas from the diesel engine was fed to a three stage axial turbine. For take off power part of the exhaust gas was diverted to a combustion chamber where compressed air was added and fuel burnt to enhance the power of the turbine. A gear drive from the gas turbine was connected to a counter rotating propeller. Hence it was a two-stroke, horizontally opposed, turbocharged, supercharged, afterburning, turbo-compound flat 12 engine.

Despite all these un-necessary complications one engine was constructed and tested to show promising results, and was fitted in the nose of a Avro Lincoln for flight tests in 1950. An interesting "party piece" that the Lincoln performed was to shut down its 4 1,635hp RR Merlins and fly solely on the Nomad.

NOMAD 2

The basic layout was the same with the flat 12 diesel engine with a gas turbine mounted below. The air from the 12 stage axial compressor was fed direct to the diesel engine. The exhaust from the diesel engine was fed to the three stage axial turbine which powered the compressor with the surplus power geared to the engine crankshaft via a Beier variable speed gearbox. The output shaft drove a 13 ft four blade Rotol propellor.

SPECIFICATION

The flat 12 two stroke diesel engine had inlet and exhaust ports controlled by the piston. and was liquid cooled .
Bore 6 ins X Stroke 7.375 ins.
Displacement 41.1 Litres.
Max power 3125 BHP at 89 PSI boost. Plus thrust from the turbine exhaust of 320 lbs.
Crankshaft RPM 2025, Turbine RPM 18200.
Power to weight 0.88 BHP per LB.
Specific fuel consumption 0.345 LB/BHP/HR. which was excellent at the time.
Length 119 ins width 56.25 ins height 40 ins. Dry weight 3580 lbs.
Five engines were built and two cleared for flight test but never flown.
By the early 1950’s the Jet engine and turbo prop engines had been vastly improved and were the way forward for aircraft propulsion, and interest in the Nomad waned, the project being cancelled in 1955

CONCLUSION

The Nomad showed excellent fuel consumption and adequate power for use in certain types of aircraft such as the Shackleton , but it was a new concept without the reliable history of the 37 litre Rolls Royce V12 Griffon.

I worked for Napier’s at their Liverpool works in the 1960’s on the Napier Deltic. Some of my colleagues had worked on the Nomad and fitted two flight cleared Nomads in to the prototype Shackleton at Luton in 1954 but it was never flown as the project was cancelled by the ministry, a great waste of effort.

D.R. TAYLOR.

Post script This very British engine still exists - surprisingly in the Smithsonian Musuem of Air and Space in the USA.

Disclaimer: The above represents only the unofficial view of the writer and not of the Monoposto Racing Club in any way whatsover. Subheadlines and captions are not originated from the named author. We are unable to reproduce results due to copyright reasons. If any pictures are copyright and the owner wishes them removed please email us.

 

Napier Lion Arrow 12. Up to 1350hp in short life "racing" trim, generally around 5-600hp

Sea Lion engine in use in Napier Bentley racing car

Hawker Tempest 5 with Sabre.

Avro Lincoln with Nomad in the nose. Flew on just the Nomad.

Flight Magazine in 1955 showed a fuzzy pucture of a Shackleton with a Nomad installed on the wing

Possible application: the Blackburn Beverley freighter.

Another possible application: Shackleton long range maritime reconnaissance aircraft.

 

Pictures: Internet, Wikipaedia, Flight Global