Working Area Engine and Aircraft Performance Calculation

Fig. 1: Scheme of a two-spool turbofan engine thermodynamic calculation model . Fig. 2: Balance of the forces affecting an aircraft in flight . Fig. 3: Comparison of a flight mission calculation and data recorded on-board during the flight

For calculations of characteristic engine parameters like thrust, fuel consumption and internal pressures and temperatures the section Engine operates an engine performance program. This program simulates the off-design behaviour of jet and turboprop engines of any configuration, optionally also with intercooler and recuperator, based on thermodynamic cycles and applicable loss correlations. The program is basic for type and flight mission specific emissions analyses and moreover facilitates design, examination and evaluation of new propulsion concepts. Figure 1 shows exemplary the main program parameters of a two spool turbofan engine.

To estimate fuel consumption and emissions of an aircraft in flight it is essential to know the thrust demanded by the aircraft, which has to be delivered by the engines, for any point fo the trip. An aircraft performance calculation provides this data, balancing all forces affecting the aircraft in flight (Lift, drag, thrust and weight, see figure 2). Some of these forces are dependent on the current weight of the aircraft, which in turn is dependent on the fuel consumption of the engines. As input data specific aircraft parameters and engine data -provided by the engine performance program- are needed to calculate the resulting accelerations and/or climb angles.

It is possible to recalculate given flight profiles with nearly any number of calculation points, including environmental impacts like wind or air temperature for each point of the flight mission. But even with relatively few calculation points, the approximation of a real flight mission is fairly good (Figure 3).

Related Literature

• Plohr, M., von der Bank, R., Schilling, T., Vergleich des Emissionsverhaltens effizienter Hochbypasstriebwerke mittlerer Schubgröße für den ICAO LTO-Zyklus und Flugmissionen, Deutscher Luft- und Raumfahrtkongress 2003, München, 17.-20. November 2003, DGLR, DGLR Jahrbuch 2003, DGLR, 2003

• Plohr, M., Döpelheuer, A., Lecht, M., The Gas Turbine Heat Cycle and its Influence on Fuel Efficiency and Emissions, Paper 34 in "Gas Turbine Operation and Technology for Land, Sea and Air Propulsion and Power Systems", RTO MP-34, AC/323(AVT)TP/14, 2000

• Deidewig, F., Ermittlung der Schadstoffemissionen im Unter- und Überschallflug, Institut für Antriebstechnik, DLR Forschungsbericht 98-10, 1998

Author: Martin Plohr, DLR AT