A pressure-fed liquid oxygen/petrol rocket motor was first tested in Britain as early as 1941. It could provide a thrust of 2,000 lb and was intended as an assisted take-off device. The motor was also used in the early LOP/GAP and the later RTV-1. Hydrocarbons have a high flame temperature and cooling proved to be a problem – the solution was found by changing from petrol to a water – methanol mixture as in Snarler. This led to a prejudice against the combination that persisted through the early 1950s.

In the early 1950s, RPE began taking an interest in larger rocket motors, and a design for a liquid oxygen/liquid ammonia motor was drawn up, notable mainly for its spherical combustion chamber2. Discussions were held with ICI at Teeside concerning the availability and supply of liquid ammonia, but visits to America by members of the technical staff at Westcott re-awakened their interest in kerosene as a fuel. The idea of lox/kerosene motors moved back up the agenda, and the ammonia design was dropped. These new designs were named Delta, following the Alpha/Beta/Gamma sequence.



Thrust (lb)

Delta 1



Delta 2



Delta 3



Delta 5



Delta 7



Delta 3 is the most interesting in that it would have been the starting point for a ballistic missile. Indeed, reasonably detailed sketches were made for a design of such a missile.3

Once Rolls Royce had licenced the North American S3 design and developed it into the RZ 2, there was little point in continuing with the work on the larger Delta chambers, and work on them ceased in 1957. Firings of the smaller Delta 5 and 7 continued until 1966.

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