Napier Nomad I, E125 NM.3 Engine



Pre Restoration - Overview

Restoration I

Restoration II

Restoration Complete


Restoration Description

In July 1999 the engine was in rather a sad state - paint, what remained, rather shabby with much having lost the will to cling on thus exposing areas of reaction to our coastal atmosphere. The various metallic components all reacting differently to the cause. Rust / discolouration / verdigris / corrosion / ageing (of rubber) / bloom of stainless of chrome finished parts. Certain light aluminium heat shields had sustained deformation damage, origin unknown, all had a dusty and grime coating since the complex build defied appearance maintenance. The twin props free to rotate had been chocked in the interest of H&S.

This was to be a learning as you go experience - no design or maintenance information was available on site at the time. The first task was to reduce the mass for transport to the workshop was the removal of the prop assembly. By trial and error the front item was separated. The rear set eventually had to be taken away together with the gearbox closure plate after removal of the wiring harness to gain access. It was decided here - in line with good practice, to retain all securing items in matched sets and / or patterns, a labour that paid off as things progressed.

The gearbox exposition revealed no innards other than the remains of an attempt at immobilising the props. Further inspection suggested that the cam shaft - conrods & pistons might also be missing making the transport to the workshop that much easier. This proved to be so and with time and systematic stripping it was confirmed that the internal components of the engine were missing.

With the engine reduced to components or manageable sub assemblies the process of cleaning to bare metal began in early October 1999. Activities included cataloguing of parts and dismantling order, scraping / chipping / wire brushing and shot blasting where appropriate. The processes leading to restoration included burnishing / degreasing / priming / undercoat / finishing coat all hand brush applied before polishing. Aluminium was polished and lacquer coated, stainless steel and chrome surfaces were crystalline wax coated. Internal surfaces were mist oiled and bearings greased or oiled.

We are indebted to the Napier Power Heritage Trust for providing source and colour of the main finish.

The disassembly, recovery and preparation of parts took from late 1999 to 2001 and rebuilding work was completed in July 2002. This was a three year effort by two volunteers spending one day a week on the task. The total effort amounted to some 1200 hours which saved the museum about 30,000 in professional fees.


At the end of the 39-45 war the focus of piston engine design started to move towards fuel economy using novel architectures. Consumption was normally measured in how many pounds of fuel per horsepower per hour the engine consumed and it appeared that this was an area where piston engines could outperform jet engines. The company D. Napier & Sons of Acton, (founded by the Scottish engineer David Napier in 1808), took up an aircraft ministry requirement for an economical engine of 6000 hp. To put this in context the famous Merlin engine achieved approximately one third of this power in its final developments, a typical car engine develops one sixtieth of this power.

The initial Napier response was to design a 75 litre 24 cylinder diesel engine using experience from the Sabre engine as well as earlier diesel engines. The limited commercial opportunities caused the design to be abandoned and the Napier E. 125 (Nm.3 Nomad 1) was developed as a 3000 ehp flat 12 cylinder two stroke diesel with a large supercharger, twin turbocharger and contra rotating props. For technical details of this remarkable engine click on the diagram.


The compressor and turbine assemblies were tested during 1948 and in October 1949 the prototype engine was run as a complete unit. The engine was installed in the nose of Lincoln SX973 which flew with the Nomad 1 in 1950. In total the Nomad 1 ran for 860 hours on the test rig, 270 hours driving test propellers and 120 hours in flight. When running properly it could produce 3000 shp plus 320lb thrust with a specific fuel consumption of 0.36 lb/ehp/hr. It was temperamental however, often the exhaust was a jet of flames as if it had a reheat fitted.

In parallel with the flight tests the chief engineer E.E.Chatterton was redesigning the engine to improve gas flow and simplify it, this engine was named the E145 Nomad 2, an engine significantly more different than the simple name change implies. Again this was flight tested but the commercial opportunities failed to materialize. It was proposed that a world record endurance flight be made using a heavily modified Lincoln with only two Nomad engines, anticipating a range of 13,300 nm at 30,000 ft altitude. This would have been daunting for the crew of an non pressurised aircraft since it meant a flight time of over 60 hours.

When the Griffon engine was adopted for the Shackleton aircraft the fate of the Nomad was sealed, the higher speed of jet passenger aircraft left no market for the Nomad. It had also been targeted at the Beverly transport where the power increase would have been very beneficial but again this did not happen. The technology did not die totally, Napier switched to Deltic diesel engines for trains, another of their exercises in byzantine engineering.

The East Fortune Nomad I is the only known remaining example of this mark. There are at least two examples of Nomad II engines remaining, one in the Science Museum at Wroughton and one at the Smithsonian in the USA.




The APSS is a registered charity in Scotland, charity No. SC033307
A member of the British Aviation Preservation Council