de Havilland Sprite

The Sprite was a British rocket engine built by de Havilland for use in RATO (Rocket-assisted take off) applications. For RATO use only a short burn time is required, with simplicity and light weight as major virtues. The intended market was for assisting take-off of de Havilland Comet 1 airliners (as hot and high operations in the British Empire were considered important) and also for V bombers carrying heavy nuclear weapons.^[1][2][3] 30 successful test flights were carried out by Comets, from May 1951, but gas turbine performance improved rapidly, and so RATO was not required in service.

A hydrogen peroxide monopropellant was used, decomposed into oxygen and steam over a metallic calcium catalyst. The maximum thrust was 5,000 lbf (22 kN), varying over the 16 second burn time for a total impulse of 55,000 lbf (240 kN) seconds.^[4]

Variants

• DSpr.2

silver-plated nickel-gauze catalyst, tested in Comets during April 1952

A technology update then took place with the proving of silver-plated nickel gauze packs as catalysts with the establishment of optimum loadings and flows. This practice was replicated in all future applications with the catalyst no longer consumed. In April 1952 the DSpr.2 proved this modification impressively in Comet demonstration with clean exhaust. The next stage was pursued with the Super Sprite (DSpr.4) following the ATO development precedent with 'hot' operation but now enhanced in simplicity by ability to inject kerosene fuel once chamber pressure was established by the catalysed peroxide flow. The units, flight approved in August 1953, reverted to the practice of being parachuted after firing for routine re-use in service operations with the Vickers Valiant V bomber.^[5]

Super Sprite

The Super Sprite DSpr.4 was a re-development of the Sprite application, using a significantly different 'hot' propellant technology, that of hydrogen peroxide / kerosene.^[7][8] Although the peak thrust was actually reduced, burn time was 2.5 times longer, with a proportionate increase in total impulse.

For simplicity, there were no fuel pumps and the tanks were pressurised by nitrogen from nine cylinders wrapped around the combustion chamber.^[4]

The Super Sprite was packaged as a self-contained engine in its own nacelle, jettisoned after take-off and retrieved by parachute. Inflatable air bags cushioned its impact with the ground. To obtain a clean separation from the carrier aircraft, the production engines fitted to the Vickers Valiant had a small canard vane at the nose, pitching the nacelle downwards on separation.

De Havilland regarded the 166 units manufactured as a standard production item, supported by their Service Department alongside piston and turbojet engines. It was the first rocket engine to gain formal type approval.^[9]

The Super Sprite project was cancelled in October 1960, at a reported total cost of £850,000.^[10]

References

Aviation rocket engines and rocket motors
Liquid fuel	XR-4A3 XR-4K14 XLR11 XLR99 Bristol Siddeley 605 de Havilland Spectre de Havilland Sprite Armstrong Siddeley Screamer Armstrong Siddeley Snarler Napier Scorpion Dushkin S-155 Dushkin D-1-A-1100 Walter HWK 109-509 Toku-Ro.2 (KR10)
Hybrid Propellant	RocketMotorTwo
Solid Propellant	Type 4 Mark 1 Model 20 Jetex engine
Related articles	List of aircraft engines List of rocket aircraft Rocket Assisted Take Off