Investigation of Translating-Double-Cone Axisymmetric Inlets With Cowl Projected Areas 40 and 20 Percent of Maximum at Mach Numbers From 3.0 to 2.0

The performance of two translating-double-cone inlets with contrasting rates of turning on the spike shoulder and corresponding cowl projected frontal areas of 40 and 20 percent of maximum was compared over the Mach number range from 3.0 to 2.0. Pressure recoveries were about the same for both configurations) the 20-percent-cowl inlet falling 0.01 to 0.03 lower than the 40-percent-cowl inlet over the entire range of Mach number and angle of attack up to 15°. At Mach 3.01, the 20-percent-cowl inlet had a recovery of 0.625 compared with 0.635 for the 40-percent-cowl inlet. At this same Mach number, the cowl pressure-drag coefficient for the 20-percent cowl (0.103 based on max. projected model frontal area) was 45 percent less than that for the 40-percent cowl (0.187). On a propulsive-thrust basis) the 20-percent-cowl inlet was superior over the entire range of Mach number.

Total and component drags were obtained at Mach numbers 3.01, 2.73, 2.44, and 1.97. In order to match the airflow requirements of a hypothetical turbojet engine, the second oblique shock was located at the cowl lip at each Mach number. Total drag coefficients during supercritical inlet operation increased with decreasing Mach number, primarily because of the increasing additive drags. Distortions at zero angle of attack were low, about 0.02 at Mach 3.01 and about 0.12 at Mach 1.97.

With the 40-percent-cowl inlet, retracting the spike slightly from its design position at Mach 3.01 resulted in a stable subcritical range of mass-flow ratio from 1.0 to 0.6. This result did not occur with the 20-percent-cowl inlet.