Experimental investigation of a novel vtol thrust vectoring nozzle

Abstract

A two-dimensional corner-expansion thrust vectoring nozzle, in which thrust vectoring is achieved by rotation of a single vane, is proposed for high supersonic V/STOL aircraft. A -fa scale model of the configuration has been statically tested with most favorable results. A thrust coefficient in excess of 0.97 was demonstrated in the VTOL mode and throughout transi- tion at nozzle pressure ratios typical of turbojet engines considered for high supersonic V/ STOL applications. In addition, a thrust coefficient in excess of 0.96 was attained in the horizontal cruise mode down to a nozzle pressure ratio of 3.5. This is particularly significant when considering that the design pressure ratio of the nozzle was 21. Effective thrust vectoring was also demonstrated, with a 1:1 correspondence between vane mechanical deflection and thrust vector direction. A jet pumping effect was found to exist at very low-pressure ratios at a slightly deflected position of the thrust vectoring vane, and an alternating normal compon- ent of the total thrust vector was found to exist at low-pressure ratios in the horizontal cruise mode. studies have generally shown that thrust vectoring is a favorable scheme for high supersonic V/STOL interceptor missions, thus establishing the need for developing a simple, highly efficient, and reliable thrust vectoring nozzle; in addition to providing the basic V/STOL thrust vectoring and low-pressure ratio cruise performance for subsonic and low supersonic missions, an efficient nozzle is required for the high supersonic cruise condition in which the nozzle pressure ratio may be as high as 30. A simple and efficient thrust vectoring nozzle, fulfilling all the requirements of a high supersonic V/STOL mission, has been conceived and tested at Nor air with favorable results. The detailed results of this test are documented in Ref. 2. The basic features of the configuration, which conveniently lends itself to underbody installations, are shown in Figs. 1 and 2. In the horizontal flight position, the nozzle geometry is that of an isentropic wedge in which a two-dimensiona l free- jet corner-expansion to the local ambient pressure occurs at the nozzle lip. The upper boundary of the nozzle is denned analytically by a Prandtl-Meyer stream line at the nozzle design pressure ratio. Ideally, an isentropic expansion occurs at the design pressure ratio giving a horizontal free- jet boundary downstream of the nozzle lip, with uniform, parallel, fully expanded flow at the axial location defined by the intercept of the nozzle upper boundary with the design Mach number line emanating from the nozzle lip. At off- design pressure ratios, nozzle losses due to overexpansion and underexpansion of the exhaust gases are minimized by the ability of the lower jet boundary to adjust to the external local pressure as for a conventional plug nozzle. Side plates are provided to contain the jet in the transverse direction in the region of the flow field where jet pressures are greater than ambient. The side plates eliminate end-effect losses by maintaining a constant and maximum pressure across the width of the upper boundary, thus insuring the maximum value of axial thrust. Variable nozzle throat area in the aft position, if desired, can be conveniently provided by rotation of the nozzle lip. In the VTOL and transition modes of operation, an efficient free-jet aerodynamic-throat nozzle is formed by rotation of the thrust vectoring vane and associated extension. In these modes of operation, the flow expands around the sharp corner at the terminal point of the nozzle lip with a free-jet boundary and aerodynamic throat prevailing downstream of the nozzle lip. Ideally, the flow is expanded supersonically and uni- formly at the vane trailing edge. In principle, the internal aerodynamic operation of the nozzle in the VTOL and transi- tion modes is much like that of the horizontal cruise configura- tion, with the essential difference being that the locus of the sonic line in the former modes occurs downstream of the minimum physical internal cross section of the nozzle and, of course, the design pressure ratio is an order of magnitude lower.