Editing Napier Nomad (section)

== Design and development ==
[[File:Napier Nomad Model E. 145 Diesel Engine.jpg|thumb|At the [[Steven F. Udvar-Hazy Center]]]]
[[File:Napier Nomad I East fortune front.jpg|thumb|Napier Nomad 1]]
In 1945 the [[Air Ministry]] asked for proposals for a new {{cvt|6000|hp|MW}} class engine with good fuel 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 [[gasoline|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 [[Napier Sabre|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 engine|H-block]] similar to the Sabre, resulting in a massive 75&nbsp;litre design. Markets for an engine of this size seemed limited, however, so instead they reverted to the original Sabre-like [[Flat engine|horizontally opposed]] 12 [[Cylinder (engine)|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 <math>1 - T_e/T_p</math>, where ''T''{{sub|e}} is the exhaust temperature in [[kelvin]]s<!-- pluralized – see Kelvin#Usage conventions --> and ''T''{{sub|p}} is the peak combustion temperature. Jet engines have relatively low-temperature combustion systems which produce a ''T''{{sub|p}} of no more than about 1,000&nbsp;K, much less than the typical 5,000&nbsp;K 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 {{cvt|4000|hp|MW}}, 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.

===Nomad I===
[[File:NomadSchematic 185kBpng360kB.png|thumb|right|Schematic drawing of Napier Nomad I and II.]]
The initial Nomad design (E.125) or Nomad 1 was incredibly complex, almost two engines in one. One was a [[Twincharger|turbo-supercharged]] two-stroke diesel, having some resemblance to half of a [[Napier Sabre|Napier Sabre's]] [[H engine|H-24]]. Mounted below this were the rotating parts of a [[turboprop]] engine, based on the [[Napier Naiad|Naiad]] design, the output of which drove the front propeller of a contra-rotating pair. To achieve higher boost, the crankshaft drove a centrifugal supercharger, which also provided the scavenging needed for starting the engine from rest. During take-off additional fuel was injected into the rear [[turbine]] stage for more power, and turned off once the aircraft was cruising.{{sfnp|Lumsden|2003|page=170}}

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.{{sfnp|Lumsden|2003|page=172}} 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 {{cvt|3000|hp|MW}} and {{convert|320|lbf|kN|abbr=on}} thrust. It had a [[specific fuel consumption (shaft engine)|specific fuel consumption]] (sfc) of {{convert|0.36|lb/hph|g/kWh|abbr=on}}.

The prototype Nomad I is on display at the [[National Museum of Flight]] at [[East Fortune|East Fortune Airfield]] in [[Scotland]].

===Nomad II===
[[File:Napier Nomad ¾ front view.jpg|thumb|Front three-quarter view of a Nomad II]]
[[File:Napier Nomad Plan view.jpg|thumb|Topside view]] 
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 stage was added to the axial compressor/supercharger, eliminating the separate centrifugal part and the intercooler. The turbine (which also received an additional stage) was now only used to drive the compressor, and feed back any excess power to the main shaft using a [[Beier variable-ratio gear]];{{sfnp|''Flight'' (30 April 1954)|page=549}} the separate propeller from the turbine was deleted, just as the whole of the "[[afterburner]]" system with its valves etc. So the system was now like a combination of a mechanical [[supercharger]], and a [[turbocharger]] without any need for bypass. The result was smaller and considerably simpler: a single engine driving a single propeller.{{sfnp|Lumsden|2003|page=171}} Overall weight reduction was {{convert|1000|lb|abbr=on}}. The [[wet liner]]s of the cylinders of the Nomad I were changed for [[dry liner]]s.{{sfnp|''Flight'' (30 April 1954)|page=550}}

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.

On an equivalent power basis, the Nomad II had an SFC of {{cvt|0.327|lb/hph|g/kWh}} at {{cvt|25000|ft}} cruise altitude.<ref name="DP195409">{{cite magazine |issn=1040-8878 |magazine=Diesel Progress |title=What's going on in England: Napier Nomad |url=https://archive.org/details/sim_diesel-progress_1954-09_20/page/56 |pages=56, 58 |publication-date=September 1954 |given=Hamish |surname=Ferguson}}</ref>

A further development, the Nomad Nm.7, of {{cvt|3500|shp|MW}} was announced in 1953.<ref name="FI19531106">{{cite magazine |url=http://www.flightglobal.com/pdfarchive/view/1953/1953%20-%201456.html |magazine=[[Flight International|Flight]] |title=Here and there |publication-date=November 6, 1953 |page=610 |url-status=dead |archive-date=April 13, 2016 |archive-url=https://web.archive.org/web/20160413032333/https://www.flightglobal.com/FlightPDFArchive/1953/1953%20-%201456.PDF}}</ref>

By 1954 interest in the Nomad was waning, and after the only project, the [[Avro Shackleton|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. The design was also considered for the [[Canadair Argus]], a similar [[maritime patrol aircraft]] being designed for the [[Royal Canadian Air Force]]. This design turned to the [[Wright R-3350 Duplex-Cyclone|Wright R-3350]], the design the Nomad was intending to best.

A Nomad II is on display at the [[Steven F. Udvar-Hazy Center]] in [[Virginia]].<ref>[https://airandspace.si.edu/collection-objects/napier-nomad-model-e-145-horizontally-opposed-diesel-engine/nasm_A19640017000 Steven F. Udvar-Hazy Center - Napier Nomad] Retrieved: 7 April 2020</ref>