Side-Force Amplification on an Aerodynamically Thrust-Vectored Aerospike Nozzle

Results from cold-flow experiments on aerodynamic thrust vectoring of a small-scale annular aerospike thruster are presented. Thrust vectoring is produced by injection of a secondary fluid into the primary flowfield normal to the nozzle axis. The experimental aerospike nozzle is truncated at 57% of its full theoretical length. For these tests, carbon dioxide is the working fluid. Injection points near the end of the truncated spike produced the highest force amplification factors. Explanations are given for this phenomenon. For secondary injection near the end of the aerospike, side-force amplification factors up to 1.4, and side-force-specific impulses up to 55s were demonstrated. By comparison, the main flow-specific impulse averaged approximately 38s. Secondary side-injection pulses were observed to crisply reproduce side forces with a high degree of fidelity. Side-force levels approach 2.7% of the total thrust level at maximum efficiency. Higher side forces of 4.1% axial thrust were also achieved at reduced efficiency. The side-force amplification factors were independent of operating nozzle pressure ratio for the range of chamber pressures evaluated in this test series.