Airframe systems power off-take modelling in more-electric large aircraft for use in trajectory optimisation

The classical approach to trajectory optimisation uses aircraft dynamics models coupled with engine performance models to optimise for different objectives such as fuel, time, noise and emissions. However, initial studies have shown that airframe systems loads and the resulting fuel penalties due to off-takes, is influenced and more importantly influences the optimum trajectories. Moreover, the need for such an enhanced approach is required to define the “more electric aircraft trajectory optimisation” problem. This paper describes the methodology which has been used to represent the airframe systems operation and the subsequent penalties in the trajectory optimisation studies conducted within the GATAC framework, under the Systems for Green Operation (SGO) work package in the Clean Sky programme. The purpose of the integrated airframe systems model is to model and interface the airframe systems power requirements or “secondary power” requirements within the optimisation framework and other models involved in the optimisation. The integrated model accumulates the requirements for the individual models and then computes the total bleed air mass flow and shaft power off-take requirements from the aircraft engine. In the case of the more electric aircraft, the off-takes are limited to shaft power offtakes since the bleed air is eliminated. This paper presents a modelling methodology which focuses on modelling airframe systems based on the power requirements with regard to design and certification standards. Also considered is computational efficiency such that the models can be incorporated in exhaustive trajectory optimisation problems without causing significant performance penalties. Preliminary trajectory optimisation results confirm that the inclusion of airframe systems influences the trajectory optimisation, especially when trajectories are optimised for minimum fuel burn. The significance is such that the penalties due to systems have to be accounted for when aircraft trajectory optimisation is studied for environmental gains. The combined effect and the enhanced approach to optimisation progresses the prediction of optimum flight trajectories for real aircraft.