Rolls-Royce Gem

The Rolls-Royce Gem is a turboshaft engine developed specifically for the Westland Lynx helicopter in the 1970s. The design started off at de Havilland (hence the name starting with "G") and was passed to Bristol Siddeley as the BS.360. When Rolls-Royce bought out the latter in 1966, it became the RS.360.[1]

Rolls-Royce Gem at The Helicopter Museum (Weston)
Type Turboshaft
National origin United Kingdom
Manufacturer Rolls-Royce Limited
Major applications Westland Lynx

Design and development

The Gem's three-shaft engine configuration is rather unusual for turboshaft/turboprop engines. Basic arrangement is a four-stage axial LP (Low Pressure) compressor, driven by a single stage LP turbine, supercharging a centrifugal HP (High Pressure) compressor, driven by a single stage HP turbine. Power is delivered to the load via a third shaft, connected to a two-stage free (power) turbine. A reverse flow combustor is featured.[2]

The Gem 42 develops 1,000 shp (750 kW) at Take-off, Sea Level Static, ISA, but the Maximum Contingency Rating (MCR) is 1,120 shp (840 kW).

Until recently all versions of the Lynx have been Gem powered. However, now that Rolls-Royce own Allison, they have been marketing the more modern LHTEC T800, developed jointly with Honeywell.


Engines on display

Specifications (Gem 42)

Data from Rolls-Royce[3]

General characteristics

  • Type: Triple-shaft two-spool turboshaft
  • Length: 43.4 in (1090 mm)
  • Diameter: 23.5 in (590 mm)
  • Dry weight: 414 lb (187 kg)


  • Compressor: 4-stage axial LP, single-stage centrifugal HP
  • Turbine: 2-stage power turbine, single-stage LP, single-stage HP


See also

Comparable engines

Related lists



  1. Gunston 1989, p. 155.
  2. Rolls-Royce Gem product page
  3. Rolls-Royce Gem 42 factsheet Archived 17 December 2010 at the Wayback Machine Retrieved: 16 July 2009


  • Gunston, Bill. World Encyclopedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9
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