Towards a stochastic in-flight thrust determination process 2007-01-2542
Traditionally jet engines in-flight thrust determination is a deterministic process that starting from the fan and core measured pressures and temperatures calculates, by many different ways, the intermediate turbomachine parameters up to the exhaust nozzle pressure and temperature while iteratively search for the engine mass flow, attending simultaneously energy, mass and momentum conservation. With this data and the previously determined nozzle coefficients, the engine installed thrust is calculated. These methods are industry standards that are well documented on SAE reports AIR 1703A and AIR 5450. A new approach is proposed in this work, a more stochastic approach, which in fact estimates the engine fan and core pressures and temperatures from initial air mass flow and gross thrust values. Using the Output-Error Method the values of gross thrust and air mass flow are iteratively updated by a modified Newton-Raphson algorithm minimizing the error between the fan and core calculated and measured air pressures and temperatures. The new technique solves in fact, by optimization, the inverse formulation of the in-flight thrust determination problem. The advantages of the new technique over the traditional one is that it has stochastic properties allowing to process the noisy flight test data samples without previous averaging. This paper presents the new technique and demonstrates its application to a set of engine Deck data transformed to sampled data by application of noise.