Examples of flight path optimisation using a multivariate gradient-search method.
Abstract:ESDU 93021 deals with one method of optimisation of a complete sortie, applied as an example to a subsonic transport and used to demonstrate the penalties incurred by constraints imposed by design and operational considerations. It requires an appropriate numerical optimisation technique able to solve constrained multivariate problems. That used here is RQPMIN developed at the then Royal Aircraft Establishment. The examples were to minimise block fuel for given range, maximise range for given ramp mass, minimise time for given range, and minimise direct operating costs (in this case a linear combination of time and block fuel) for given range. Each case is initially run with no constraints other than those to ensure flight is possible (for example, thrust at the appropriate rating must exceed drag). Progressive constraints are then introduced relating speed to minimum drag speed, providing a given margin to buffet onset, limiting rates of climb and descent by rates of cabin pressure change and by a maximum cabin differential pressure, and limiting cabin attitude for passenger comfort. The results are discussed. A comparison is also made of results for optimum climb paths of a transport aircraft with results obtained for the same cases in ESDU 90012 using energy height methods.
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