Wind-tunnel evaluation of mid-airframe installed turbojet engines

Abstract

A series of power-on wind-tunnel tests have been conducted to evaluate the installed performance of midairframe mounted tactical-missile turbojet sustainers. Two low-cost, expendable turbojet engine designs were installed in a high-fidelity wind-tunnel model of a specific tactical missile. To accommodate the unique installation requirements, each engine design incorporated bifurcated pitot inlets and side-exhausting bifurcated exhaust ducts. Each installed engine was fully functional and was intended to closely replicate the in-flight operational response. Power-on wind-tunnel evaluations were conducted for each engine model that encompassed a wide range of sea level, steady-state flight conditions. The test condition variables evaluated were Mach number, pitch angle, yaw angle, engine throttle setting, and control fin deflection. Missile axial force data were acquired to determine installed, delivered engine net thrust. In addition, extensive thermal instrumentation was installed on the model to evaluate the influence of the turbojet exhaust plume on the aft section of the missile. A detailed description of the test program is provided. Detailed descriptions of the hard ware configuration and test variables are presented. Presented are discussions of theoretical engine performance models, experimental installed performance results, projections of overall missile performance, and evaluations of the effect of pitch on engine performance. A detailed evaluation of the thermal impact of turbojet operation is provided. Discussions of the thermal impact of pitch, yaw, and fin deflection angles are presented. The results presented demonstrate that both sustainer configurations, successfully operated in an installed configuration under in-flight conditions, delivered adequate installed performance to satisfy missile system requirements, and had minimal adverse thermal impact on the airframe. The results of the evaluation fully verify the viability of employing turbojet engines in a mid-airframe installation. Nomenclaturê4jet = J et nozzle area, in. 2 F = net thrust, corrected, Ibf F ax = missile axial force, corrected, Ibf I p = optimization index of performance, Ibf 2 M = Mach number N = engine speed, corrected, krpm P -pressure, psia R = range per fuel weight, km/lbm S/N = engine serial number SFC = specific fuel consumption, corrected, Ibm/h-lbf T = temperature, °F V = flight speed W f = fuel flow rate, Ibm/h a = pitch angle, deg )8 = yaw angle, deg A = difference 8 = pressure correction factor 6 = temperature correction factor Subscripts a = ambient max = maximum possible min = minimum possible or measured