PISTON ENGINE COOLING: AN EVERGREEN PROBLEM

Immediately before Wold War II (WWII), piston engine cooling has become a resource instead of a problem. The Meredith paper defined a static engine that converted the heat dissipated by the engine into thrust. Some solutions (see the De Havilland Mosquito, Messerschmidt BF 109F, Supermarine Spitfire…) used hot air also to improve the efficiency of flaps. In any case the Meredith effect proved to be effective even at the relatively low speed of F1 racing cars. The main problem proved to be a design. In recent times turbodiesel piston common rail engines are coming back into the aircraft field. However the experience coming from the racing car field cannot be directly applied to the flying machines for many different reasons. First of all racing rules usually ban moving flaps and variable geometry intake and exhausts, that are commonplace in aircraft (see for example supersonic air intakes). Moreover racing cars are relatively “dirty” reversed wing air machines, very different from the slender and elegant aircrafts. Then the cooling system arrangement should be adapted to the necessity of the diesel engines and of the high altitudes. This paper starts from the existing historical and new solutions and demonstrates that many improvements are still possible to improve the overall propulsion efficiency of new flying machines.