Bristol Siddeley BS.360
Rolls-Royce RS.360 / Gem

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.

The Gem is a three-shaft configuration turboshaft/turboprop engine. Basic arrangement is a four-stage axial compressor, driven by a single stage IP (Intermediate Pressure) 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.

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).


Agusta A129 Mangusta
Westland Lynx


Gem 42
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
Maximum power output: 1,000 shp (746 kW)
Overall pressure ratio: 12:1