Volume 1. Performance Phase. Chapter 11. Cruise Performance Theory
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Published: 1993
Total Pages: 69
ISBN-13:
DOWNLOAD EBOOKThis chapter examines the theory and flight tests required to determine cruise data presented in aircraft flight manuals. Aircraft cruise performance is dependent upon the combination of airplane aerodynamics and engine characteristics. Basic aerodynamic and engine theory applied to cruise testing are covered. Aerodynamic forces acting on the aircraft, i.e., lift and drag, and engine thrust and fuel flow are presented as functions of easily measured parameters. Engine and aerodynamic functions are then combined to complete the analysis. The end result provides a method by which engine and airplane cruise performance characteristics may be determined with minimum flight testing. The data obtained from the flight tests are used to determine cruise performance charts and tables presented in the flight manual, and to determine cruise specification compliance and military utility. The basic assumption of cruise theory is that during cruise the aircraft maintains level, unaccelerated flight. When the aircraft is in level, unaccelerated flight, the sum of the forces acting upon it equals zero. Assuming the thrust acts along the direction of flight (or differences in direction of thrust due to engine installation angle and aircraft angle of attack are negligible), the lift force, L, is equal to the aircraft weight, W, and the net thrust, Fn, is equal to the aircraft drag, D.
