Armstrong Siddeley Viper
Bristol Siddeley Viper
Rolls-Royce Viper

The Viper turbojet engine was developed and produced by Armstrong Siddeley and then by its successor companies Bristol Siddeley and Rolls-Royce Limited. First run in April 1951 it entered service in 1953 and remained in use with the Royal Air Force, powering its Dominie T1 navigation training aircraft until January 2011.
The design originally featured a seven-stage compressor based on their Adder engine — the Viper is in effect a large-scale Adder.
The Viper was developed as an expendable engine for powering production versions of the Jindivik target drone, but the limited-life materials and total-loss oil systems were replaced with standard systems for use in manned aircraft.
Because it was initially developed as an expendable engine, the Viper was subject to many recurring maintenance issues. This led to the development of the first Power by the Hour program in which operators would pay a fixed hourly rate to Bristol Siddeley for the continual maintenance of the engines.
A production Armstrong Siddeley Viper ASV.5 turbojet, of the type specified for the Percival P.84 trainer, was to undergo high-altitude trials mounted on the tip of one wing of Armstrong Siddeley's Sapphire - Canberra WD933 in 1954. The other wing-tip can either carry a similar turbo-jet or, as in the case of the Canberra, a counterbalancing weight. The Canberra should be able to test the Viper at altitudes up to about 50,000 ft.

Variants:
Viper 8
(Mk.102 / Mk.104): Engines for the Hunting-Percival Jet Provost TMk.3 (Mk.102} and GAF Jindivik Mk.102B target drone (Mk.104).
Viper 9
(Mk.103): Powered the Bell X-14 and Handley Page HP 115 among others.
Viper 11
(Mk.200): Powered the Hunting-Percival Jet Provost TMk.4 and GAF Jindivik Mk.3 among others.
Viper 20
(Mk.500 series): Powered the Hawker Siddeley HS.125 and Piaggio-Douglas PD.808 among others.
Viper 22
Built under licence by Piaggio for the Aermacchi MB.326
Mk.102
Mk.103
Mk.104
Mk.200
Mk.201
Mk.301
Mk.500 series
Mk.520
Mk.601

Applications:
Aermacchi MB-339
Aermacchi MB-326
Atlas Aircraft Impala
Avro Shackleton
BAC Jet Provost
BAC Strikemaster
Bell X-14
Dassault M.D.550 Mystere-Delta
Embraer AT-26 Xavante
Folland Midge
GAF Jindivik
Hawker Siddeley Dominie
Handley Page HP.115
IAR 99
Piaggio PD.808
Saunders-Roe SR.53
Soko J-22 Orao/IAR-93
Soko G-2 Galeb
Soko G-4 Super Galeb

Specifications:

Viper ASV.12
Type: Turbojet
Length: 64.0 in (1,625 mm)
Diameter: 24.55 in (624 mm)
Dry weight: 549 lb (249 kg)
Compressor: Seven stage axial
Combustors: Annular, 24 burners
Turbine: Single stage
Fuel type: AVTUR, AVTAG
Oil system: scavenge, metered
Maximum thrust: 2,700 lb (12 kN) at 13,800 rpm
Overall pressure ratio: 4.3:1
Specific fuel consumption: 1.09 lb/hr/lb oil consumption=1.25 pints/hr (0.7l/h)
Thrust-to-weight ratio: 4.9:1