de Havilland Sprite DSpr.2 / Super Sprite DSpr.4
The Sprite was a British rocket engine built by de Havilland for use in RATO 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. 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. Propellant capacity was 39 gallons. The dry weight was 350 lbs.
The DSpr.2 used a 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.
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. Although the peak thrust was actually reduced (4,200 lbf / 18.7kN), burn time was 2.5 times longer (40 seconds), with a proportionate increase in total impulse (120,000 lbf seconds). Propellant capacity was 60 gallons (approx.).
For simplicity, there were no fuel pumps and the tanks were pressurised by nitrogen from nine cylinders wrapped around the combustion chamber.
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.