Towards trajectory prediction and optimisation for energy efficiency of an aircraft with electrical and hydraulic actuation systems

As part of the CleanSky programme, this paper investigates the power consumption characteristics of standard hydraulic actuation systems against the two main power by wire alternatives; electro-hydrostatic and electromechanical actuators. Mathematical models are constructed for each technology which simulates the position response and power consumption of the actuators. The models are dynamic and designed with execution speed as a primary concern. The difficulty with aircraft primary flight control actuator simulation is obtaining input command and load force data. One solution is to record the data from flight tests but this is costly, another solution is to use a 6 degree of freedom (6-DOF) aircraft dynamics model (ADM). This technique is much more accessible and with today's high performance computers it is easily achievable; the computing power of modern desktop PC's already accommodates the concurrent simulation of a 6-DOF aircraft with high fidelity models of subsystems. The actuator models are integrated with a 6-DOF flight dynamic model of a medium range, single aisle 150 seat transport aircraft to generate control surface demands during manoeuvres. The outputs of the actuator models, in turn, generate surface responses which affect the motion of the aircraft. The aerodynamic force is estimated using textbook methods for two dimensional aerofoils, programmed into a series of lookup tables that run continuously with the 6-DOF and actuator models. The aero load estimator generates hinge moments as a function of aircraft speed, angle of attack, altitude and surface deflection as well as static wing geometry data. This allows the aircraft to fly a predetermined route using an autopilot and facilitates the analysis of the power consumed by the actuation systems during that route. By tuning the manoeuvre parameters such as bank angle and rate, it is hypothesized that a reduction in energy consumption can be achieved by executing manoeuvres in such a way that the actuators operate in their most efficient states more regularly. Whilst the magnitude of the savings may not be large, it will be simple to implement and of some value.