The Rolls-Royce Gnome is a British turboshaft engine originally developed by the de Havilland Engine Company as a licence-built General Electric T58, an American mid-1950s design. The Gnome came to Rolls-Royce after their takeover of Bristol Siddeley in 1968, Bristol having absorbed de Havilland Engines Limited in 1961. A licence to manufacture the T58 was purchased in 1958. The T58 had begun bench testing in 1955 and by 1958 had already been used in helicopters and de Havilland were able to test their first engines in a Westland Whirlwind and Wasp helicopters in August 1959. A free-turbine turboshaft, it was used in helicopters such as the Westland Sea King and Westland Whirlwind. The design was sub-licensed to Alfa-Romeo. There were two series produced: the "H" turboshaft for helicopter use, and the "P" turboprop for fixed-wing aircraft.
Design and development
A single-stage turbine drives the 10 stage all-axial compressor, whilst a two-stage free power turbine drives the load. The combustor is annular. The Gnome differed from the T-58 in having a British developed fuel control system. Because an all-axial design is employed, the final stage compressor rotor blades are amongst the smallest ever manufactured. Normally, a small engine such as this would feature an axial/centrifugal or even a double centrifugal compressor. The engine was the first developed with a full authority analogue computer, de Havilland's own, as part of the fuel control system, specifically to anticipate helicopter power demand from pilot control inputs and to limit fuel flow during acceleration to prevent engine surge from occurring. The system developed relieved the helicopter pilot of the need to control rotor speed directly and in this way was the analogue forerunner of all subsequent FADEC systems worldwide.
Variants
;H.1000: 1,050 shp, first production version for use on later marks of Westland Whirlwind ;H.1200: 1,250 shp, the Westland Wessex uses two H.1200, as the Coupled Gnome, with a coupled gearbox with a power limited to 1,550 shp at the rotor. ;H.1400: 1,400 shp for the Westland Sea King HAS.1 ;H.1400-1: 1,535 shp, uprated from the 1400 by increasing the gas-generator speed and using improved blades that can operate at higher temperatures for the Westland Sea King HAS.2. ;H.1400-1T:For the Westland Commando HC.4 ;H.1400-2: 1,660 shp for the Westland Sea King HAS.5. ;H.1400-3: 1,720 shp with new two-stage power turbine. ;H.1600: 11-stage compressor with 2-stage free power turbine ;P.1000:Turboprop version of the H.1000 ;P.1200:Turboprop version of the H.1200 ;P.1400-3: Turboprop version of the H.1400-3 rated at 1,700 shp. ;Gnome Mk.101: ;Gnome Mk.110: Handed H.1200 engines for Coupled Gnome units used in Westland Wessex helicopters. ;Gnome Mk.111: Handed H.1200 engines for Coupled Gnome units used in Westland Wessex helicopters. ;Gnome Mk.112: Handed H.1200 engines for Coupled Gnome units used in Westland Wessex HU.5 helicopters. ;Gnome Mk.113: Handed H.1200 engines for Coupled Gnome units used in Westland Wessex HU.5 helicopters. ;Gnome Mk.501:Civilianised H.1000. ;Gnome Mk.510:Civilianised H.1000. ;Gnome Mk.610:Civilianised H.1200. ;Gnome Mk.640:Civilianised H.1200. ;Gnome Mk.640A:Civilianised H.1200. ;Gnome Mk 660: Used in the civilian Westland Wessex 60 helicopter ;Coupled Gnome:Twin engines driving through a common gearbox to a single output.
