Preliminary Thermodynamic Analysis of Power System Impact on Tactical Aircraft Performance

A computerized thermodynamic analytical program is being developed to help investigate the impact of power system requirements on aircraft performance. The Visual Basic for Applications (VBA) program has a user interface that operates in MS-EXCEL, linking several subsystem analysis programs for execution and data transfer in the power systems analysis. The program presently includes an encoded propulsion engine cycle code, which allows the inspection of power extraction effects on engine performance. To validate the results of the encoded engine program, a study was conducted to investigate the separate effects of shaft power extraction and pneumatic bleed. The selected engine cycle was that for a standard tactical fighter, with a flight condition of varied altitude (sea level to 40k-ft.) and constant Mach Number(0.9). As expected, the resultant data showed that the engine performance was more sensitive to pneumatic bleed than to shaft power extraction. Fuel inventory comparisons for a given mission were made for three different secondary power system configurations. The lower fuel consumption of the more-electric secondary power system succinctly reflects the sensitivity of the engine performance to shaft power extraction or bleed air power extraction.