Modelling and Simulation of an Aircraft Main Landing Gear Shock Absorber
Heininen, Arttu Aleksi (2015)
2015
Konetekniikan koulutusohjelma
Teknisten tieteiden tiedekunta - Faculty of Engineering Sciences
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Hyväksymispäivämäärä
2015-12-09
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201511251803
https://urn.fi/URN:NBN:fi:tty-201511251803
Tiivistelmä
Every traditional aircraft has a shock absorber in its main landing gear. A shock absorber takes the brunt of the shock imparted to the landing gear, absorbs it and dissipates the kinetic energy. This thesis is based on the construction of a realistic analytical model of an oleo-pneumatic shock absorber for a combat aircraft. The governing equations presented here include the effects of friction, gas spring and damping, among other things.
The model was validated with a wide range of reference data, which revealed exceptionally high friction levels detected during the validation process. The reference data consists of measurements from a static test bench, a dynamic test system and an actual aircraft landing, and the corresponding simulations are presented in this thesis. The results of the simulations closely match the measured data. The effects of variations in the gas-liquid ratio and temperature on the pressure behaviour inside the shock absorber were simulated. If the gas-liquid ratio is distorted, the damping ability of the shock absorber is diminished, which may lead to faulty operation of the landing gear. Temperature variation was examined in two ways, firstly by varying the initial temperature and secondly, by heating and cooling the shock absorber. Filling the shock absorber in conditions which differ from the environment in which the aircraft will operate causes the pressure to decrease or increase, depending on whether the shock absorber is cooled or heated. The utilization of simulations as a tool in condition monitoring and fault detection is discussed, and as a result of that a new measuring instrument is proposed, whose design can be facilitated with this simulation model.
Although the model presented in this thesis is not complete, it adequately mirrors the behaviour of the gas spring and the metering bin. However, the model does not include the deformations caused by high pressures. A number of possible improvements to the model are presented and discussed. In its present form, the load-stroke behaviour of the model is close to the real shock absorber, and the model can be used to analyse the forces and pressures generated by different shocks. Future work will involve improving the model and incorporation of the model into a larger main landing gear model so that a comprehensive investigation of the dynamics of an aircraft landing can be performed.
The model was validated with a wide range of reference data, which revealed exceptionally high friction levels detected during the validation process. The reference data consists of measurements from a static test bench, a dynamic test system and an actual aircraft landing, and the corresponding simulations are presented in this thesis. The results of the simulations closely match the measured data. The effects of variations in the gas-liquid ratio and temperature on the pressure behaviour inside the shock absorber were simulated. If the gas-liquid ratio is distorted, the damping ability of the shock absorber is diminished, which may lead to faulty operation of the landing gear. Temperature variation was examined in two ways, firstly by varying the initial temperature and secondly, by heating and cooling the shock absorber. Filling the shock absorber in conditions which differ from the environment in which the aircraft will operate causes the pressure to decrease or increase, depending on whether the shock absorber is cooled or heated. The utilization of simulations as a tool in condition monitoring and fault detection is discussed, and as a result of that a new measuring instrument is proposed, whose design can be facilitated with this simulation model.
Although the model presented in this thesis is not complete, it adequately mirrors the behaviour of the gas spring and the metering bin. However, the model does not include the deformations caused by high pressures. A number of possible improvements to the model are presented and discussed. In its present form, the load-stroke behaviour of the model is close to the real shock absorber, and the model can be used to analyse the forces and pressures generated by different shocks. Future work will involve improving the model and incorporation of the model into a larger main landing gear model so that a comprehensive investigation of the dynamics of an aircraft landing can be performed.