Control of Impact Loads on Aircraft Landing Gears Using Magnetorheological Fluid Dampers

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Control of Impact Loads on Aircraft Landing Gears Using Magnetorheological Fluid Dampers: Shock absorbers in aircraft landing gears are required to absorb and dissipate the impact kinetic energy during landing so as to reduce the vibrations transmitted to the main aircraft body and to the passengers. The objectives of the proposed research are to study the performance of the landing gear system by using a magentorheological fluid damper in the system. The basic function of the shock absorber in aircraft landing gears is to absorb and dissipate the impact kinetic energy of the aircraft body frame during landing so as to reduce the vibrations transmitted to the main body of the aircraft to a tolerable level. Normally, oleo struts, which are essentially shock absorbers that have a fluid spring with gas and oil are used. Oleo-pneumatic shock absorber system is currently one of the most common in medium to large aircrafts, as it provides shock absorption as well as effective damping during landing and taxiing. During the compression process, the oil and gas either remain separated or are mixed depending on the type of design. After the initial impact, energy is dissipated as the air pressure forces the oil back into its chamber through recoil orifices. Most designs have a metering pin extending through the fluid flow orifice, which can vary the orifice area. This variation is adjusted by shaping the metering pin so that the strut load is fairly constant under dynamic loading. Once the metering pin is designed, the damping varies as a prescribed function of time to meet different loading conditions. However, it would be ideal if the damping could be varied according to the load and approach requirements such as for different weight of the aircraft or when the aircraft has different sink rate at the time of touchdown. During aircraft landing, the landing gears touch the runway with very little of the suspended mass of the aircraft transmitted to the runway because the aircraft wings still carry the bulk of the aircraft weight with the lift force. As the lift is slowly reduced after touch down, the apparent mass experienced by the landing gears changes as a function of time. The objective is to optimize the progressive reduction in the lift such that the aircraft experiences a constant deceleration in the vertical direction in order to ensure the structural integrity and ride comfort to the passengers. The scientific approaches for the above studies are (i) Analytical solutions to the equations of motion which is a system with time varying mass and damping properties, (ii) numerical simulation of the landing gear dynamics including the magnetorheological fluid dampers. Novelty and expected significance of the work to the aircraft industry: Magnetorheological fluid dampers change their damping property very rapidly by the application of a magnetic field across the MR fluid. The technology has been very successfully applied in vehicle suspensions in order to control the vehicle vibrations in a semi-active fashion. A similar vibration reduction can be achieved in aircraft structures also. The industries involved with the landing gears, such as Heroux Devtec Canada, Noramtec - Montréal, QC, Messier-Bugatti-Dowty, will benefit the most with the outcome of this research.