The Goshawk was developed from the
Kestrel IV prototype engine, to use
evaporative (also known as "steam") cooling. Rather than keep the cooling liquid below its boiling point in the cooling system, the coolant was allowed to boil; the phase change from liquid to vapour takes more heat from the engine, so less weight of coolant is needed. However, the radiator had to be bulkier to accommodate coolant in its gas phase, which increased drag. Twenty engines were built, and flew only in prototypes as a few manufacturers' private ventures and "one-offs". Powers for individual installations are quoted between 650 and . Problems with coolant leaks, coolant pumping and the realisation that large wing-mounted condensing radiators would be vulnerable to combat damage caused the project to be cancelled, although valuable lessons had been learned and were put to good use with development of the later
Merlin. ==Variants==