[217] Development of a Flight Mission Model and its Application in Order to Illustrate the Influence of Variable Thrust Nozzles


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→ Tim Sauer    
→ Tim Rückel
→ Dieter Peitsch

TU Berlin, Germany

Published: Beijing, 16th-18th September 2019

DOI 10.33737/gpps19-bj-217


Future engines tend to have increasingly higher bypass ratios in order to reduce fuel consumption. This goes along with a decrease of the fan pressure ratio which may result in an unchoked nozzle. Thus the fan working line drops whereby the efficiency of the fan can be reduced. To avoid this effect variable area thrust nozzles can be utilized.

For the evaluation of the potentials of variable thrust nozzles with regard to effects on the overall system, a flight mission model of a representative narrow body aircraft is developed based on published data. On the basis of the equations of motion of each individual flight phase, the mission fuel consumption is calculated. A validation of the nominal case on the basis of EUROCONTROL data confirms the accuracy of the results. The nominal case is opposed by an engine with a variable thrust nozzle, which fixes the working line of the fan to the peak efficiency line.

It is shown that the fuel savings per flight hour are most relevant on short-haul flights. This is explained by the relatively high proportion of operating points in the part load range, i.e. those points which deviate significantly from the respective peak efficiency point. Furthermore, it is shown that the potential savings of variable thrust nozzles are reduced with increasing bypass ratio, since the reference efficiency increases as well. So the application of such a nozzle modification in future engines can indeed help to stabilize the fan’s working line, but not necessarily to operate the aircraft more cost-efficiently.


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