Improved Analytical Design Technique for Low-Power-Loss Engine Inlets

An improved computerized analytical method for the optimization of VTOL engine-inlet contours to minimize power loss has been developed and proven experimentally. This computerized analytical technique, used to develop the inlet contours for the Boeing Vertol Model 179 helicopter, makes use of a two-dimensional and axisymmetric potential-flow technique developed at the Wichita Division of The Boeing Company. With the use of this program, the inlet designer can compute a flow-field solution for any flight condition from hover to level-flight speeds. Once the potential-flow field has converged, flow properties on the specified stream-line contours can be calculated using the appropriate gas dynamic equations. This permits the evaluation of the flow at any point outside or within an inlet. Additional programming added recently makes automatic plotting of the output possible. This analytical tool has also been used successfully in several other areas; e.g., to assist in determining the power requirements for anti-icing inlet surfaces and to locate the nacelle cooling-air inlet slots. Pressure recovery calculated in this manner was found to agree with flight-test results within 1/4 percent. Furthermore, the use of this program reduced the development time and cost of the final product.