Investigation into an alternative electrically actuated braking system for aircraft

• Main Author: Simpson, Nick
• Published: University of Bristol 2014
• Subjects: 629.134
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.659106

Modern commercial aircraft predominantly employ hydraulically actuated multi-disk wheel-brakes on their main landing gears which are used to control the velocity of the aircraft during landing and ground operations. In recent years, investigations into the electrical actuation of the wheel-brakes have shown a number of advantages ranging from better energy efficiency to improved reliability and maintainability. Electrically actuated braking systems tend to employ a plurality of electric brake actuators featuring a high-speed brushless dc motor coupled to a ball/roller-screw through a reduction gear. This arrangement exhibits a high force-density and long stroke, however, the three-phase power inverter, filter and power conductor requirements of each actuator results in a considerable overall system mass when compared to a hydraulic counterpart whose components and operating pressure have been optimised over many years of in-flight service. This thesis investigates the feasibility of an alternative electric braking system which has the potential to reduce the overall braking system mass through the use of a direct drive non-commutated electric brake actuator topology. A permanent magnet tubular linear actuator topology is identified as an attractive candidate. Due to the short-duty and high force-density requirements of the electric brake actuator it is desirable to take account of the electromagnetic and thermal aspects of the design simultaneously. Therefore, a coupled electromagnetic and transient thermal design methodology is developed. It is found that a compromise exists between the accuracy and the computation time of the electromagnetic and thermal analyses. A procedure for efficiently constructing and analysing finite element models is developed to minimise the computational cost of the electromagnetic analysis. A method of automatically constructing and parameterising lumped parameter thermal equivalent circuits with nodes arranged in a regular mesh pattern is proposed which maintains low computation times while allowing superior thermal field resolution and more accurate identification of hot-spots and their location. A method of estimating the equivalent thermal properties of impregnated electrical windings is proposed in order to parameterise the thermal model. The coupled design methodology is employed to study the achievable short-duty performance of the tubular linear actuator topology and establish the feasibility of the alternative electric braking system. A prototype actuator is constructed and tested under short-duty conditions in order to validate the modelling and thermal property estimation methods.