Report presenting an examination of the effects of variations in efficiency parameters, including engine economy, aerodynamic efficiency, and structural efficiency, on airplane performance. Efficiency parameters were found to be extremely ineffective in adjusting the airplane performance to its tactical mission as compared to primary parameters like altitude, power, gross weight, and wing area.

Report presenting testing of a scale model of a twin-engine pursuit airplane in order to investigate the possibility of high-speed diving difficulties and to find remedies for them. Most of the data were obtained in force tests, although some pressure-distribution measurements, elevator hinge moments, and wake surveys were also made. The tests showed that the airplane will experience serious diving moments above lift coefficients of 0.5 at a Mach number of 0.65, and 0.1 at a Mach number of 0.725.

Report presenting an investigation of the Supermarine Spitfire airplane equipped with exhaust stacks designed according to the jet-propulsion exhaust-stack system developed by the NACA. An increase in the high speed of the airplane of 6 mph was obtained as compared with the airplane equipped with the Rolls Royce exhaust system. Results regarding performance and exhaust-flame visibility are provided.