Snarler and Screamer

In 1946 the Ministry of Supply asked Armstrong Siddeley Motors to develop a liquid fuel rocket motor with a thrust of 2,000 lb for use as a booster unit for fighters. Initial ideas were for a hydrocarbon/liquid oxygen motor, but after talks with the RAE, the fuel was changed to a mixture of 65% methanol and 35% water. At the time, it was thought that hydrocarbon fuels were not well suited for cooling the chamber. The first test run of the motor, now named Snarler, together with a fuel pump was achieved in February 1949.

Motors designed to be installed in manned aircraft need to be safe and reliable: by May 1950, the motor had achieved 71 minutes of full thrust in testing. A Snarler motor was then installed in the tail of the Hawker P.1040
prototype (forerunner of the Sea Hawk), the new aircraft now being designated the P.1072. Flight trials began in November 1950.

Snarler was capable of being throttled – not always easy to achieve with rocket motors – and had a maximum sea level thrust of 2200 lb. The S. I. of the motor was 195, with a combustion chamber pressure of 300 lb/sq in (2 0bar).

Work on Snarler’s successor, Screamer, began in 1950. Initially intended to give 4,000 lb thrust, the specification given by the Ministry of Supply was changed to a more powerful motor of higher thrust. One of the main differences between Screamer and Snarler is that the Snarler pump was driven externally; Screamer would have its own gas generator to drive the turbines which would power the pumps.

In these early days there was very little design knowledge of gas generators, and it was decided to add water to the combustion mixture to reduce its temperature. Because water was being carried for the gas generator, it was decided to use its excellent cooling properties for the combustion chamber jacket, the heated water then being injected into the combustion chamber itself. Unusually, the combustion chamber had no throat, being a simple cylinder followed by the usual expansion cone.

By 1954, the complete motor was ready for testing, and by September, thrust ratings of 8,000 lb had been achieved. The motor was later installed in the underside of a Meteor for flight testing, but with the cancellation of the Avro 720 rocket interceptor in favour of the Saunders Roe SR53, and the decision to use only HTP in manned vehicles, Screamer was not developed further.