Evaluation of transient agility metrics through unmanned simulation of the X-31 post-stall aircraft
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Development of post-stall capable aircraft has enhanced the research of agility, the ability of an aircraft to quickly and precisely change from its present state to a desired new state, and its measurement. Controlled high angle of attack (AOA) flight and rapid nose-pointing are now realities with thrust vectoring. Traditional measures of merit are incapable of comprehensively describing the rapid changes in aircraft state during close-in combat. As complements to conventional performance measures of merit, agility metrics provide a more complete description of an aircraft's rapid maneuvering capabilities. A batch simulation model of the RockwelVMBB X-31A aircraft is used to evaluate recommended open-loop longitudinal, lateral, and axial agility metrics for their effectiveness in describing transient agility characteristics, maneuvering in the 1-3 second time scale, of a post-stall fighter. Comparison to Valasek and Downing's conventional fighter aircraft agility simulations is done for each axis of agility tests, and the performance improvements due to thrust vectoring are highlighted. The power loss rate and onset rate axial agility metrics are acceptable descriptors of an aircraft's ability to rapidly transition between energy levels. The power loss rate test is modified to include a rapid pitch up maneuver and evaluate the ability to create induced drag and maximize power loss rate. The post-stall axial agility metric. Longitudinal nose pointing metrics maneuver is recommended as a post-stall axial agility metric. Longitudinal nose pointing metrics effectively describe post-stall agility and performance improvements due to thrust vectoring with the maximum, minimum, and average pitch rate metrics. A new flight path agility measure, the pitch impulse metric, is developed and simulated on the X-3 IA to describe an aircraft's balance of maximum load factor generation and maintenance during a pitch maneuver. High and low AOA lateral agility tests also show improved roll performance about the velocity vector. A high AOA loaded roll metric is developed using the integral of the velocity vector roll rate as the angle of interest. Acquisition of the X-31A batch simulation Version-120 is recommended as well as incorporating the newly acquired Agile-VU visualization program with metric research and flying recommended closed-loop agility maneuvers on the fixed-base simulator for post-stall agility evaluation.
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Fischer, Shiloh Douglas (1996). Evaluation of transient agility metrics through unmanned simulation of the X-31 post-stall aircraft. Master's thesis, Texas A&M University. Available electronically from