Flight Tests of NACA Jet-Propulsion Exhaust Stacks on the Supermarine Spitfire Airplane

Airplane was equipped with exhaust stacks designed according to the NACA system. An increase in speed of the airplane of 6 mph at constant propeller thrust hp was obtained as compared to the airplane equipped with the Rolls Royce exhaust system. No differentiation between effects of reduced drag and increased exhaust jet thrust was possible. The exhaust flame produced with the NACA exhaust stacks was greater than that produced with the Rolls-Royce stacks under some conditions. Neither system is believed to be satisfactory in regard to flame damping.