Girish Mahajan

Armstrong Siddeley ASX

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The ASX was an early axial flow jet engine built by Armstrong Siddeley that first ran in April 1943. Very little information on the engine is available, and it appears it was never put into production. A turboprop version as the ASP was somewhat more successful, and as the Armstrong Siddeley Python saw use in the Westland Wyvern.


Design and development

The ASX was unique in layout. The inlet to the 14-stage compressor was placed near the middle of the engine, the air flowing forward as it was compressed. From there it fed into 11 flame cans arranged around the outside of the compressor, flowing back past the inlet, and finally through the turbine.

This layout allowed the compressor and combustion areas to be "folded" together to make the engine shorter, although the overall reduction in the case of the ASX appears to be fairly limited. Additionally this makes it more difficult to service the compressor, although in modern designs it is the "hot section" that generally requires most servicing.

The ASX was flight tested fitted to the bomb bay of a modified Avro Lancaster, ND784, the first flight taking place on 28 September 1945.

At full power the engine ran at 8,000 rpm and developed 2,600 lbf (12 kN) of thrust at sea level. For cruise the engine ran at 7,500 rpm and developed 2,050 lbf (9.1 kN). It weighed 1,900 lb (865 kg). The ASP conversion used a second turbine stage to drive the propeller through a gearbox, producing 3,600 shp, as well as 1,100 lbf (4.9 kN) of leftover jet thrust.

Beyond this, little has been published about this engine. Armstrong Siddeley appears to have given up on the design just after the war, and took over the Metrovick F.9 Sapphire design instead.


  • Avro Lancaster (Test only)
  • Specifications (ASX)

    Data from

    General characteristics

  • Type: Axial flow turbojet
  • Length: 167 in (4,241.8 mm)
  • Diameter: 42 in (1,066.8 mm)
  • Dry weight: 1,900 lb (861.8 kg)
  • Components

  • Compressor: 14-stage axial reverse-flow compressor
  • Combustors: 11 stainless steel can combustion chambers arranged around the compressor
  • Turbine: 2-stage axial
  • Fuel type: Kerosene (R.D.E. / F / KER)
  • Oil system: pressure feed to bearings, dry sump, 80 S.U. secs (10.2 cSt) (D.E.D. 2472D) grade oil
  • Performance

  • Maximum thrust: 2,600 lbf (11.57 kN) at 8,000 rpm at sea level
  • Overall pressure ratio: 5:1
  • Turbine inlet temperature: 1,220 °F (660 °C)
  • Specific fuel consumption: 1.03 lb/(lbf h) (104.98 kg/(kN h))
  • Thrust-to-weight ratio: 1.37 lbf/lb (0.0134 kN/kg)
  • Military thrust, static: 2,600 lbf (11.57 kN) at 8,000 rpm at sea level
  • Cruising, static: 2,050 lbf (9.12 kN) at 7,500 rpm at sea level
  • Idling, static: 130 lbf (0.58 kN) at 3,000 rpm at sea level
  • References

    Armstrong Siddeley ASX Wikipedia

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