Napier Nomad
Encyclopedia
The Napier Nomad was a complex British
compression-ignition aircraft engine
designed and built by Napier & Son
in 1949. Two versions were flight tested:
asked for proposals for a new 6000 hp class engine with good economy. Curtiss-Wright
was designing an engine of this sort of power known as the Turbo-compound engine
, but Sir Harry Ricardo
, one of Britain's great engine designers, suggested that the most economical combination would be a similar design using a diesel two-stroke in place of the Curtiss's petrol
engine.
Before World War II
Napier had licensed the Junkers Jumo 204
diesel design to set up production in the UK as the Napier Culverin
, but the onset of the war made the Sabre
all-important and work on the Culverin was stopped. In response to the Air Ministry's 1945 requirements Napier dusted off this work, combining two enlarged Culverins into an H-block
similar to the Sabre, resulting in a massive 75-litre design. Markets for an engine of this size seemed limited, however, so instead they reverted to the original Sabre-like horizontally opposed
12 cylinder design, and the result was the Nomad.
The objective of the design was to produce a civilian power plant with far superior fuel efficiency to the emerging jet engine. Thermal efficiency is given by 1-(Tx/Tp), where Tx is the exhaust temperature (any absolute scale) and Tp is the peak combustion temperature. Jet engines always have a Tp of no more than about 1000 Kelvin, much less than the typical 5000 Kelvin of a reciprocating engine, and so jets have very poor thermal efficiency. The Nomad design focused on replacing the low temperature combustion chambers of the jet engine with highly efficient Diesel combustion chambers. In practice, it was much too difficult to couple the Diesel power output back into the turbine cycle. The maximum practical power of the Nomad was 4000 hp, and it was much heavier than a pure jet of the same power. By this time civilian jets such as the Boeing 707
were nearing completion, and the Nomad was never seriously considered by any aircraft manufacturer.
diesel similar to the upper half of a Napier Sabre. Mounted below this was a complete turboprop
engine, based on their Naiad
design, the output of which was geared to a shaft driving the front propeller of a contra-rotating pair, as well as the axial compressor
. To achieve higher boost, a centrifugal supercharger was used. This was driven by the crankshaft, which also provided the scavenging needed for starting this two-stroke engine from rest, before the turbine section was up to speed. As if that were not enough complexity, during takeoff additional fuel was injected into the rear turbine
stage for more power, and turned off once the aircraft was cruising.
The compressor and turbine assemblies of the Nomad were tested during 1948, and the complete unit was run in October 1949. The prototype was installed in the nose of an Avro Lincoln
heavy bomber
for testing: it first flew in 1950 and appeared at the Farnborough Air Display on 10 September 1951. In total the Nomad I ran for just over 1,000 hours, and proved to be rather temperamental, but when running properly it could produce 3000 hp and 320 lbf (1.4 kN) thrust. It had a specific fuel consumption (sfc) of 0.36 lb/(hp·h) (0.22 kg/(kW·h)).
The prototype Nomad I is on display at the National Museum of Flight at East Fortune Airfield
in Scotland
.
and the compressed air for the Diesel was no longer "robbing" power for the turboprop. In addition the propeller shaft from the turbine was eliminated, and geared using a hydraulic clutch
into the main shaft. The result was smaller and considerably simpler: a single engine driving a single propeller.Lumsden 2003 p171 Overall about 1000 lb (453.6 kg) was taken off the weight. The wet liners of the cylinders of the Nomad I were changed for dry liners.Flight 1954 p550
While the Nomad II was undergoing testing, a prototype Avro Shackleton
was lent to Napier as a testbed. The engine proved bulky, like the Nomad I before it, and in the meantime several dummy engines were used on the Shackleton for various tests.
A further development, the Nomad Nm.7, of 3500 shp was announced in 1953.Flight Nov 1953 p 610
By 1954 interest in the Nomad was waning, and after the only other project, the Avro Type 719 Shackleton IV
, based on it was cancelled, work on the engine was ended in April 1955, after an expenditure of £5.1 million.
A Nomad II is on display at the Steven F. Udvar-Hazy Center
in Virginia
.
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
compression-ignition aircraft engine
Aircraft engine
An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...
designed and built by Napier & Son
Napier & Son
D. Napier & Son Limited was a British engine and pre-Great War automobile manufacturer and one of the most important aircraft engine manufacturers in the early to mid-20th century...
in 1949. Two versions were flight tested:
- The Nomad I diesel engineDiesel engineA diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...
drove one of a pair of contra-rotating propellers with the Napier NaiadNapier Naiad|-See also:-Bibliography:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:*...
based turbine driving the other propeller as a turbopropTurbopropA turboprop engine is a type of turbine engine which drives an aircraft propeller using a reduction gear.The gas turbine is designed specifically for this application, with almost all of its output being used to drive the propeller...
and also superchargingSuperchargerA supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...
the diesel unit.
- The later Nomad II used the turbine to boost the manifold pressure of the diesel unit and was also coupled to the crankshaftCrankshaftThe crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...
, this version drove one propeller only. The resulting unit set the lowest specific fuel consumption figures seen up to that time, despite this the project was cancelled in 1955 after interest in the project had passed and £5.1 million had been spent on development.
Design and development
In 1945 the Air MinistryAir Ministry
The Air Ministry was a department of the British Government with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964...
asked for proposals for a new 6000 hp class engine with good economy. Curtiss-Wright
Curtiss-Wright
The Curtiss-Wright Corporation was the largest aircraft manufacturer in the United States at the end of World War II, but has evolved to largely become a component manufacturer, specializing in actuators, aircraft controls, valves, and metalworking....
was designing an engine of this sort of power known as the Turbo-compound engine
Turbo-compound engine
A turbo-compound engine is a reciprocating engine that employs a blowdown turbine to recover energy from the exhaust gases. The turbine is usually mechanically connected to the crankshaft but electric and hydraulic systems have been investigated as well. The turbine increases the output of the...
, but Sir Harry Ricardo
Harry Ricardo
Sir Harry Ricardo was one of the foremost engine designers and researchers in the early years of the development of the internal combustion engine....
, one of Britain's great engine designers, suggested that the most economical combination would be a similar design using a diesel two-stroke in place of the Curtiss's petrol
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...
engine.
Before World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
Napier had licensed the Junkers Jumo 204
Junkers Jumo 204
-Bibliography:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9* Jane's Fighting Aircraft of World War II. London. Studio Editions Ltd, 1989. ISBN 0-517-67964-7-External links:*...
diesel design to set up production in the UK as the Napier Culverin
Napier Culverin
-Bibliography:* Lumsden, Alec. British Piston Engines and their Aircraft. Marlborough, Wiltshire: Airlife Publishing, 2003. ISBN 1-85310-294-6.-External links:*...
, but the onset of the war made the Sabre
Napier Sabre
The Napier Sabre was a British H-24-cylinder, liquid cooled, sleeve valve, piston aero engine, designed by Major Frank Halford and built by Napier & Son during WWII...
all-important and work on the Culverin was stopped. In response to the Air Ministry's 1945 requirements Napier dusted off this work, combining two enlarged Culverins into an H-block
H engine
An H engine is an engine configuration in which the cylinders are aligned so that if viewed from the front, they appear to be in a vertical or horizontal letter H....
similar to the Sabre, resulting in a massive 75-litre design. Markets for an engine of this size seemed limited, however, so instead they reverted to the original Sabre-like horizontally opposed
Flat engine
A flat engine is an internal combustion engine with multiple pistons that move in a horizontal plane. Typically, the layout has cylinders arranged in two banks on either side of a single crankshaft and is sometimes known as the boxer, or horizontally opposed engine. The concept was patented in 1896...
12 cylinder design, and the result was the Nomad.
The objective of the design was to produce a civilian power plant with far superior fuel efficiency to the emerging jet engine. Thermal efficiency is given by 1-(Tx/Tp), where Tx is the exhaust temperature (any absolute scale) and Tp is the peak combustion temperature. Jet engines always have a Tp of no more than about 1000 Kelvin, much less than the typical 5000 Kelvin of a reciprocating engine, and so jets have very poor thermal efficiency. The Nomad design focused on replacing the low temperature combustion chambers of the jet engine with highly efficient Diesel combustion chambers. In practice, it was much too difficult to couple the Diesel power output back into the turbine cycle. The maximum practical power of the Nomad was 4000 hp, and it was much heavier than a pure jet of the same power. By this time civilian jets such as the Boeing 707
Boeing 707
The Boeing 707 is a four-engine narrow-body commercial passenger jet airliner developed by Boeing in the early 1950s. Its name is most commonly pronounced as "Seven Oh Seven". The first airline to operate the 707 was Pan American World Airways, inaugurating the type's first commercial flight on...
were nearing completion, and the Nomad was never seriously considered by any aircraft manufacturer.
Nomad I
The initial Nomad design (E.125) or Nomad 3 was incredibly complex, essentially two engines in one. One was a turbo-superchargedSupercharger
A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...
diesel similar to the upper half of a Napier Sabre. Mounted below this was a complete turboprop
Turboprop
A turboprop engine is a type of turbine engine which drives an aircraft propeller using a reduction gear.The gas turbine is designed specifically for this application, with almost all of its output being used to drive the propeller...
engine, based on their Naiad
Napier Naiad
|-See also:-Bibliography:* Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9-External links:*...
design, the output of which was geared to a shaft driving the front propeller of a contra-rotating pair, as well as the axial compressor
Axial compressor
Axial compressors are rotating, airfoil-based compressors in which the working fluid principally flows parallel to the axis of rotation. This is in contrast with other rotating compressors such as centrifugal, axi-centrifugal and mixed-flow compressors where the air may enter axially but will have...
. To achieve higher boost, a centrifugal supercharger was used. This was driven by the crankshaft, which also provided the scavenging needed for starting this two-stroke engine from rest, before the turbine section was up to speed. As if that were not enough complexity, during takeoff additional fuel was injected into the rear turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
stage for more power, and turned off once the aircraft was cruising.
The compressor and turbine assemblies of the Nomad were tested during 1948, and the complete unit was run in October 1949. The prototype was installed in the nose of an Avro Lincoln
Avro Lincoln
The Avro Type 694, better known as the Avro Lincoln, was a British four-engined heavy bomber, which first flew on 9 June 1944. Developed from the Avro Lancaster, the first Lincoln variants were known initially as the Lancaster IV and V, but were renamed Lincoln I and II...
heavy bomber
Heavy bomber
A heavy bomber is a bomber aircraft of the largest size and load carrying capacity, and usually the longest range.In New START, the term "heavy bomber" is used for two types of bombers:*one with a range greater than 8,000 kilometers...
for testing: it first flew in 1950 and appeared at the Farnborough Air Display on 10 September 1951. In total the Nomad I ran for just over 1,000 hours, and proved to be rather temperamental, but when running properly it could produce 3000 hp and 320 lbf (1.4 kN) thrust. It had a specific fuel consumption (sfc) of 0.36 lb/(hp·h) (0.22 kg/(kW·h)).
The prototype Nomad I is on display at the National Museum of Flight at East Fortune Airfield
East Fortune
East Fortune is a village in East Lothian, Scotland, located 2 miles north west of East Linton. The area is known for its airfield which was constructed in 1915 to help protect Britain from attack by German Zeppelin airships during the First World War. The RNAS airship station also included an...
in Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
.
Nomad II
Even before the Nomad I was running, its successor, the Nomad II (E.145) Nomad 6, had already been designed. In this version an extra compressor stage was added, replacing the original supercharger. This stage was driven by an additional stage in the turbine, so the system was now more like a turbochargerTurbocharger
A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...
and the compressed air for the Diesel was no longer "robbing" power for the turboprop. In addition the propeller shaft from the turbine was eliminated, and geared using a hydraulic clutch
Clutch
A clutch is a mechanical device which provides for the transmission of power from one component to another...
into the main shaft. The result was smaller and considerably simpler: a single engine driving a single propeller.Lumsden 2003 p171 Overall about 1000 lb (453.6 kg) was taken off the weight. The wet liners of the cylinders of the Nomad I were changed for dry liners.Flight 1954 p550
While the Nomad II was undergoing testing, a prototype Avro Shackleton
Avro Shackleton
The Avro Shackleton was a British long-range maritime patrol aircraft for use by the Royal Air Force. It was developed by Avro from the Avro Lincoln bomber with a new fuselage...
was lent to Napier as a testbed. The engine proved bulky, like the Nomad I before it, and in the meantime several dummy engines were used on the Shackleton for various tests.
A further development, the Nomad Nm.7, of 3500 shp was announced in 1953.Flight Nov 1953 p 610
By 1954 interest in the Nomad was waning, and after the only other project, the Avro Type 719 Shackleton IV
Avro Shackleton
The Avro Shackleton was a British long-range maritime patrol aircraft for use by the Royal Air Force. It was developed by Avro from the Avro Lincoln bomber with a new fuselage...
, based on it was cancelled, work on the engine was ended in April 1955, after an expenditure of £5.1 million.
A Nomad II is on display at the Steven F. Udvar-Hazy Center
Steven F. Udvar-Hazy Center
The Steven F. Udvar-Hazy Center is the Smithsonian National Air and Space Museum 's annex at Washington Dulles International Airport in the Chantilly area of Fairfax County, Virginia, United States....
in Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
.
