The fatigue life of a nose landing gear is assessed to increase the fatigue life computing efficiency in the structural optimization cycles. The metamodels of the structural fatigue life have been researched systemically. Three kinds of metamodels were compared: the polynomial response surface model, the kriging model, and the radial basis function model constructed by the central composite design and the Latin hypercube design. It is found that the radial basis function model constructed by the Latin hypercube has the highest fitting precision and higher fitting efficiency. The research results offer a guidance for selection and construction of the metamodel of structural fatigue life. Improved particle swarm optimization algorithm is implemented. As an example, the forward strut of one aircraft's nose landing gear is optimized by using the improved particle swarm optimization algorithm.

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A drop-test rig is developed for the landing gear of a light multifunctional amphibious airplane based on its drop-test specifications. Several key technologies (including the schematic design of the light-aircraft drop test, the control-system design for the drop test, the high-speed turn of the wheel, the accurate lifting of the drop system, design of the measuring platform, and the imitation of the runway) are studied. Simultaneously, the system can realize accurate measurement and conduct the light-aircraft drop test with high-speed belt turn. Based on a drop test under initial parameters to get the friction between the tire and platform, and the elastic parameters of the wheel to simulate the interactions of components, the simulation models are repeatedly modified by analyzing the results of comparisons between drop test and simulation. Thus, an accurate model is established with optimal parameters, which verifies that the shock-absorbing properties of the landing gear with the optimal parameters meet the requirements of airworthiness rules, and the properties are greatly improved. According to the requirement of China Civil Aviation Regulations Order No. 132 (CCAR-23-R3) and the application of virtual prototype technology for the light multifunctional amphibious airplane, the adjusting-parameter drop test, the limited drop test, and the reserve-energy absorption drop test of the nose landing gear are accomplished. The limited load measured in the test is less than the design load, and the landing gear can bear the reserve-energy absorption drop test. The study shows that the adjusting-parameter drop test for establishing a simulation model is an available and reliable way to optimize the shock-absorbing properties of an amphibious-aircraft landing gear. The test system can be applied for the landing-gear drop-test of other light airplanes. Moreover, the test results can be used as the certification of the airworthiness for this airplane.Nomenclature A a = area where the piston rod squeezes out the air (except for the oil-hole area) A h = area where the piston rod squeezes out the oil (except for the oil-hole area) A 0 = sectional area of oil hole a t = acceleration of hanging basket C d = flow coefficient of the oil hole C = vertical damping coefficient of the wheel d m = diameter of the main oil hole d s = diameter of one-way oil hole F m t = total friction force between platform and the four supported pillars F x = horizontal load acting on the wheel F Y t = vertical load of the wheel F z = vertical load acting on the wheel K = vertical deformation coefficient of the wheel k va = calibration value of vertical acceleration sensor fixed on platform. k vg = calibration value of vertical load sensor M 1 = mass of platform N = number of wheel N Y t = inertia force of platform n n = inertial overload coefficient P S = atmospheric pressure P y t = resultant force measured by four sensors P 0 = initial pressure of buffer pt = tension-compression load of platform in the drop test S = stroke of buffer S max = maxi...

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