Spitfire, Mustang and the 'Meredith Effect'

By the mid-1930s the obstacles to high speed that aircraft designers faced included the question of cooling the engine. This was a big challenge that those working on the new fast airplanes entering service as the war clouds gathered over Europe had to consider, as the drag from the system increased as a square of the speed. Ducted systems were designed which lowered drag, but these were based on the assumption that the system was cold. This ignored the potential energy from the air, heated by the radiator, for liquid-cooled aircraft, and from the discharged engine exhaust gases.

It took a profoundly lateral thinker to harness the possibilities of the paradox that heat could cut the cost of cooling. That thinker was the British engineer Frederick William Meredith. A researcher at the Royal Aircraft Establishment at Farnborough until 1938, F.W. Meredith a key player in the UK’s development of the autopilot and remote-controlled aircraft. His contribution to Allied success in the Second World War was enormous – but, incredibly, he was also a known Soviet agent.

Few would doubt that the Supermarine Spitfire was a pioneering airplane – not because it was an all metal, monoplane with retractable undercarriage and enclosed cockpit as these were not unique – but because it was the first to incorporate a Meredith designed ducted cooling system. This was intended from the beginning to use heat to create ‘negative drag’. In practice the Spitfire’s design was flawed, as Meredith himself pointed out, and did not fully use what became known as the ‘Meredith Effect’.

Meredith also made entirely overlooked but extremely important contributions to resolving the problem of how to induce air smoothly into cooling ducts at high speeds without which, as the Spitfire demonstrated, ducted cooling systems worked sub-optimally.

The first airplane properly to exploit the ‘Meredith Effect’ was the North American P-51 Mustang, this being a very significant factor as to why it was 30mph faster than the Spitfire when both had the same Rolls-Royce Merlin engine.

This book by Peters Spring examines the life of the remarkable, and controversial, F.W. Meredith, an individual who has largely been forgotten by history despite the brilliant advances he made – advances which helped the Allies win the war against Hitler’s Third Reich.