Liquid colled engine installations in general aviation aircraft : design consideration and analysis of collant heat exchangers and their installation

Rising fuel costs, operating costs, and the trend to operate general aviation aircraft at altitudes above twenty thousand feet have shown deficiencies in the present air-cooled engine installations. Alternate engines and engine installations with better specific fuel consumption and lower cooling drag are needed. Liquid cooled installations could provide a more efficient general aviation aircraft.

A literature search reveals that this problem has been investigated in considerable detail by NACA and others in the 1940's. This data, however, has not been applied to general aviation aircraft. Design data and design guidelines were extracted from this data and are discussed in relation to the efficient integration of a liquid cooled engine installation in a general aviation aircraft. Design methods are developed and computerized to allow rapid sizing and evaluation of liquid cooled installations.

Results show that sharp intake lips should be avoided. The intake should be located within the propeller slipstream to take advantage of the increased dynamic pressure. The installation of the heat exchanger will be easier to accommodate in the fuselage than in the wing, although the wing location is more efficient aerodynamically. Diffusers can be designed to operate with relatively large divergence angles without separation by proper location of the heat exchanger core. An outlet flap should be provided to regulate the exit area and to provide a reduced static pressure at low speeds.

Liquid cooled installations are shown that have been designed to fit in typical general aviation aircraft space envelopes. Analysis of these installations indicate that adequate engine cooling can be achieved for 2 percent or less of the engine shaft horsepower.