Armstrong Siddeley Double Mamba

The Armstrong Siddeley Double Mamba is a turboprop engine design developed in the late 1940s of around 3,000–4,000 hp (2,200–3,000 kW). It was used mostly on the Fairey Gannet anti-submarine aircraft developed for the Fleet Air Arm of the Royal Navy.

Double Mamba
Preserved Double Mamba at the Imperial War Museum Duxford
Type	Turboprop
Manufacturer	Armstrong Siddeley
First run	29 September 1949 (First flight)
Major applications	Fairey Gannet
Developed from	Armstrong Siddeley Mamba

Design and development

The Double Mamba (rarely known as the Twin Mamba) was a development of the Armstrong Siddeley Mamba with two Mambas driving contra-rotating propellers through a combining gearbox.^[1]

Engine starting was by cartridge; however, forced air restart was achieved in flight. One engine could be shut down in flight to conserve fuel. Shutting down one engine also stopped one of the propellers.

Variants

Fairey Gannet flying with one half of its Double Mamba engine shut down

ASMD.1

2,950 shp (2,200 kW) (2 x ASMa.3) used on Fairey Gannet A.S. Mk.1 and Blackburn B-88

ASMD.3

3,145 shp (2,345 kW) (2 x ASMa.5) used on Fairey Gannet A.S. Mk.4

ASMD.4

3,875 hp (2,890 kW) (2 x ASMa.6) used on Fairey Gannet AEW Mk.3

ASMD.8

3,875 hp (2,890 kW) (2 x ASMa.6) used on Fairey Gannet AEW Mk.3

Applications

• Blackburn B-88
• Fairey Gannet
• Fairey Gannet AEW

The Double Mamba engine was also proposed for the Westland Westminster, a 30-seat helicopter that was later built as a prototype powered by a pair of Napier Eland E220 turboshaft engines.

Engines on display

Preserved Double Mamba engines are on public display at the:

• Australian National Aviation Museum
• Deutsches Museum Flugwerft Schleissheim
• Gatwick Aviation Museum
• South Yorkshire Aircraft Museum
• Imperial War Museum Duxford
• Midland Air Museum
• Queensland Air Museum
• East Midlands Aeropark
• Museum of Berkshire Aviation

Specifications (ASMD.3)

Cut away of a double mamba power unit at The Flambards Experience in Cornwall

Double Mamba in a non-display aircraft at the Fleet Air Arm Museum (Australia).

Double Mamba - side view in-situ.

Data from Flight^[2]

General characteristics

• Type: Turboprop engine
• Length: 102.25 in (2,597 mm)
• Diameter: 52.8 in (1,341 mm)
• Dry weight: 2,170 lb (984 kg)

Components

• Compressor: 10 stage axial (×2)
• Combustors: Six combustion chambers (×2)

Performance

• Maximum power output: 2,960 eshp (2,207 kW)
• Overall pressure ratio: 5.35:1
• Air mass flow: 18.5 lb/sec (8.4 kg/s) per single Mamba unit
• Specific fuel consumption: 1.71 lb/(lbf·h)
• Power-to-weight ratio: 1.36 eshp/lb

See also

Related development

• Armstrong Siddeley Mamba

Comparable engines

• Allison T40

Related lists

• List of aircraft engines