De Havilland Spectre 4 Assistant Take-Off (ATO) Unit: 1957

Note: some panels of the ATO are raised to show the internal arrangement.

As in the case of the earlier de Havilland Super Sprite ATO Units for the Vickers Valiant bomber, the Spectres for the Handley Page Victor and the Avro Vulcan were carried in two jettisonable and recoverable nacelles (pods) under the aircraft s wings between its jet engines. The Spectre and the nacelle were designed to withstand very high 'g' loads and rough handling. Each nacelle houses a Spectre complete with tanks for oxidant and fuel. The nacelle structure is of riveted light-alloy construction There is a basic floor above which are mounted the tanks, engine and recovery parachute while below is contained the air-bag used for cushioning impact with the ground after jettisoning.
Immediately behind the spun nose -cap of the nacelle is the large oxidant tank compartment. The bay has an inner metal skin to provide smooth boundaries for the polythene bag-tank containing the HTP (hydrogen peroxide) oxidant This tank is filled via the removable nose-cap, and a polythene supply pipe passes through the bulkhead at the rear to feed the engine. Aft of this bay is strapped the small kerosene tank (the ratio of HTP to kerosene used is about 9:1) and four nitrogen bottles which pressurise both kerosene and HTP tanks, thus supplying inlet pressure to the propellant pumps.

Above the kerosene tank is the parachute compartment which houses a glass-fibre pack containing a 36ft diameter parachute (designed to give a rate of descent of 25ft per sec), a 4 ft diameter pilot canopy and an extractor gun. The Spectre is canted down at an angle and exhausts through an orifice in the rear of the nacelle. Below the floor in a central compartment is the air-bag which is enclosed by plywood doors coated with Nutracote, a finish compatible with HTP. As the nacelle is nose -light when the propellants are exhausted, stub wings are fitted on each side of the nose so that the nacelle is pushed down on jettisoning.
Nacelle Dimensions: Length 162in: Width 65m: Height 49m

The nacelle could be released from as low as 1,000ft and at speeds up to 290mph.

Spectre 4 Engine
The main cylindrical structure contains the turbine for driving the propellant pumps, the catalyst pack and the combustion chamber. Ahead of this integral assembly is the gearbox, on which are mounted the centrifugal-type propellant pumps and under the gearbox is the oil sump. On the engine's sides are various control valves and associated linkage systems, the starter unit and fuel-cooled oil cooler. A small high-speed turbine energised by a separate supply of HTP is employed for driving the pumps and the associated decomposition products from this unit are subsequently directed through the combustion chamber. The high flow of HTP is able to cool the nozzle before it is injected into the engine (known as regenerative cooling)
Dimensions: Length 59in; Width 37in; Height 38in

Applications
One reason for using extra power at take-off was that either more fuel or a heavier weapon could be carried. Alternatively, the extra power could be used to permit operation from high-level airfields in high ambient temperatures, or taking-off within the standard Bomber Command runway length when carrying the stand-off bomb. (Blue Steel)

Historical Note
Although the nacelle and engine went into limited production, circumstances changed with requirements for V-bomber operation limited to UK bases and only one single trial take-off was undertaken with a Victor.