AER 615 Lecture Notes - Lecture 26: Thrust Specific Fuel Consumption, True Airspeed, Propulsive Efficiency
15 Oct 2017
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Recall that for minimum fuel consumption in cruise in going from a to b, one would fly at maximum specific air range if no wind present (and maximum specific ground range. Up to now, we"ve assumed in our analyses that properties like tsfc, 0pr and bsfc are relatively constant, but in fact they do vary as a function of airspeed or flight mach number. To illustrate the importance of allowing for property variation in optimization, consider the following example for a jet aircraft. Assume that tsfc varies with true airspeed as follows: For convenient algebra, it is better in this case to work in terms of minimizing sar-1 : One can thus solve iteratively for the best cl for maximum air range. When coefficient a2 is zero, the solution reduces to the well-known result for a jet aircraft"s cl,mr . As a2 gets higher in value, it will force the optimal airspeed down to keep the fuel consumption reasonable.
