ALTHOUGH the first Merlin engine was developed only a little over 10 years ago, its design was based on the Rolls-Royce engines that had already been successfully built, including the widely used Kestrel engine - the present-day Merlin being a direct scale-up of this engine.
Improvements during these years have taken the form of such changes as: alternate supercharger and airscrew reduction gear ratios; stepping up power ratings and supercharger performance; and improved cylinder cooling by changing over from pure glycol to pressure cooling systems.
The battle of Britain was responsible for some of the improvements in supercharger performance. Increased supercharger pressure raised the sea level power of the Merlin by 40%, giving the pilots of the Spitfires the advantages over the German flyers.
Further developments of the engine, many of them discussed here by Mr. Ellor, have made it possible for the RAF to retain this superiority.