Development of the JS-2 landing gear system

Abstract

The aim of this study was to review literature for the most suitable landing gear components used in modern gliders in order to develop a landing gear system that will adhere to the geometrical constraints of the JS-2 fuselage as well as the safety and structural requirements of the EASA CS-22. The JS-2 glider is a high performance glider designed to be more efficient and smaller than the previous models. Compared to the JS-1, the JS-2 fuselage is 50 [mm] narrower at the widest point. This has made it necessary to develop a new landing gear system that is able to fit within the narrower fuselage and still be able to reduce the landing acceleration to a level lower than 4.5 G’s [-], when landing with a maximum all up mass of 600 [Kg] at a descent velocity of 1.77 [m/s]. A literature review was done on the different landing gear components that were able to be used within modern gliders. It was found based on the research and the JS-1 landing gear design that the most applicable landing gear components to be used in a modern glider with a single main wheel landing gear arrangement that is mechanically retracted were the compact hydraulic brake and a rubber shock absorber. During the investigation it was found that the key component within the JS-2 landing gear system was the rubber shock absorber that directed the study towards rubber behaviour during compression. Due the complex nonlinear behaviour of rubber materials, it was decided to investigate and derive an constitutive hyperelastic material model that was able to describe the nonlinear behaviour of the polyurethane rubber, in order to be able to develop an efficient and compact shock absorber for the JS-2 landing gear. The material model that was selected from a list of several different material models was the Yeoh model. This decision was based on the model’s ability to predict accurately the behaviour of large strain applications in different deformation modes and its availability in commercial FEA codes. In order to use the selected model within a FEA code, its coefficients had to be derived and validated. The coefficients were derived from a single uniaxial compression test that was validated by modelling the JS-1 rubber shock absorber in the FEA code PATRAN, and by analysing it in FEA codes MARC and NASTRAN. The numerical deflection results obtained from the FEA codes were then compared with the actual compression deflection results of the JS-1 shock absorber. A satisfactory correlation between the experimental and numerical results was obtained. This concluded that it was possible to use the Yeoh material model for complex geometries that are subjected to compression load, where the material coefficients were determined by a single uniaxial compression test. Having validated that the polyurethane rubber was modelled correctly with the Yeoh material model, it was decided to use this model to partially develop the JS-2 shock absorbing system. This included the development of the shock absorber rubber elements and the selection of the wheel and the tyre that had an influence on the shock absorber properties. The developed shock absorbing system of the JS-2 consisted of a single Michelin 5.00-5”tyre and two rubber shock absorbers situated on both sides of the shock strut arm. Each shock absorber consisted of three rubber elements with a hardness of 50 [Shore A] and a Young’s modulus of 7.5 [MPa]. It was then analytically and numerically proven that the developed shock absorption system adhered to the CS-22 certification specifications, with a limit landing gear load factor (𝑛𝐿𝐺 𝐿𝐼𝑀) of 2.794[-] and an ultimate landing gear load factor (𝑛𝐿𝐺 𝑈𝐿𝑇 ) of 3.484 [-]. These load factors with the developed JS-2 rubber shock absorber were then used to develop the JS-2 landing gear structure with FEA code NX NASTRAN. The JS-2 landing gear structure was developed to be able to withstand loads calculated with a limit landing gear load factor of 𝑛𝐿𝐺 𝐿𝐼𝑀 = 3 [-] and a maximum design weight of 𝑚𝑚 = 600 [Kg]. The loads derived from these two variables were used within the FEA code NX NASTRAN to analyse the landing gear structure for two loading conditions required by the CS-22 certification specifications. The two conditions included a level and side landing condition. The JS-2 landing gear structure was then analysed with the FEA code to investigate the stresses that the structure experienced for both load cases. The numerical stress results were then used to develop the landing gear structure to be able to accommodate the selected landing gear components and to be able to obtain a minimum safety factor equal to, or higher than 1.5 [-]. It was found by analysing each component of the final landing gear structure that the structure adheres to the CS-22 requirements with a minimum load safety factor of 1.57 [-]. The stress results that were obtained from the FEA code NX NASTRAN were then compared to a stress result that was analytically calculated in order to establish if the results of the numerical calculations were accurate. The results of the two different calculation methods correlated satisfactorily with each other. This verified that the JS-2 landing gear structure was modelled accurately and that the numerical results are reliable and accurate enough to be used to prove that the JS-2 landing gear system adheres to the CS-22 safety requirements.