Active Valve and Pump Technology: Modelling and Control of Variable-Speed Trim Transfer Pumps in Aircraft Fuel Systems.
Lewis Boyd, 2008
The current generation of Airbus long-range civil transport aircraft actively control the centre of gravity of the aircraft by adjusting the fuel distribution between the horizontal tail surface and the forward tanks in order to minimise cruise drag. Here, it is proposed that the current on-off control method could be replaced by a variable flow rate, provided by a variable speed centrifugal pump. The impacts of this at the aircraft level in terms of cruise fuel burn reduction, valve operation cycle reduction and power consumption are investigated here using an extension to an existing fuel system simulation package and a generic aircraft fuel system definition. It is shown that using such a control system reduces fuel burn and the number of valve cycles, which could translate into a reduction in operating costs. The benefit of changing the controller to use tailplane trim angle directly rather than inferred centre of gravity position is assessed, and is shown to further reduce the fuel burn. It is suggested that such centre of gravity could provide significant benefits over the existing method.
Steady-state and dynamic models of centrifugal pumps, AC induction drives and typical aircraft fuel system pipework components are developed. These are validated against experimental data from a test rig of a representative system. Test rig simulation results are shown to agree well with those from experimentation. A new secondary noise source is developed for the dynamic analysis of the centrifugal pump, and a new acoustic experimental method is developed for the prediction of fluid inductance in pipework components. The results are compared against an existing CFD based method and show good agreement. The new method represents a much simpler experimental means of determining the effects of fluid inertia than the existing secondary source method. It is demonstrated that the dynamic behaviour of the centrifugal pump is insignificant when considering systems containing long pipes, and that steady-state pump models are sufficient for analysing their behaviour.
The pump models are generalised by non-dimensionalisation, in order to maximise their applicability to analysis of aircraft fuel systems. They are applied to a generic aircraft fuel system simulation, in order to model the behaviour of the system during a trim transfer. This is used to demonstrate the application of the proposed variable flow rate trim control system. The results of these simulations agree well with those used to demonstrate the benefits of the control system at the aircraft level. Concepts of system health monitoring tools are discussed with reference to the system simulations.