High altitude operations with piston engines power plant design optimization: Nozzle design and ramjet general considerations

In stratospheric flights with piston powered aircrafts, the cooling system takes part to the vehicle design optimization process. An integrated design of the cooling duct(s) is strictly necessary. At high altitudes, the cooling air is taken from high-pressure areas into a subsonic ramjet: the Meredith cooling duct. A diffuser reduces the airspeed and increases the pressure of the cooling air. Then a group of high performance finned radiators rejects the heat from coolant, air charge and lubricant. A variable geometry nozzle transforms the added enthalpy into speed and thrust. The nozzle is positioned in a low pressure, high turbulence area. The nozzle design and the duct thrust are discussed in this paper. At first the results from Parts I to IV are summarized and discussed. The resulting data are also exposed and summarized. The pressure recovery and heat rejection are evaluated in function of aircraft speed for a 1-m2vertical-radiator circular duct. The nozzle is then optimized and the total thrust is evaluated.