Session: Research Posters

Paper Number: 163704

Prediction of the Landing Gear Performance Considering Uncertainty in Servicing Conditions 

The main role of a landing gear is to absorb the impact energy and alleviate the ground reaction during touchdown. There are many types of shock absorbers used for this purpose. The majority of aircraft landing gears adopt an oleo-pneumatic type, which basically consists of an oil damper and a gas spring.  For this type of landing gear, the servicing parameters that have a significant effect on shock absorbing performance can have a certain amount of uncertainty in field operations. For example, the servicing conditions such as gas inflation pressure, oil volume and tire pressure may deviate from the nominal values. Additionally, variations in ambient temperature could be considered another source of uncertainty. 

Regarding shock absorbing operations, understanding the impact of those uncertainties is important for ensuring safety margins. Because extreme conditions resulting from the combination of uncertain parameters could cause excessive reaction loads or unexpected stroke bottoming in the shock strut.  The performance of each possible case could be studied through drop tests, but it would be unrealistic to do so considering the time and cost involved. Thus, modeling uncertainty and incorporating it into performance prediction in an efficient way is necessary during the development stage.

In this paper, Response Surface Methodology (RSM) and Convex Modeling are used to study the shock absorbing response considering uncertainty in the prescribed factors. The RSM is a collection of statistical and mathematical techniques used for analyzing responses with respect to multiple input factors. The design of experiment (DoE) technique is introduced to derive the response surface function, in which the simulations are performed by considering combinations of uncertain parameters at different levels of variability. For this, the second-order polynomial response function and the central composite designs (CCD) are utilized for building the mathematical model. Then, the shock absorbing performances under the uncertain circumstance are evaluated using the obtained response function. This surrogate model enables prediction of the effect of uncertain parameters without performing a full-model analysis for each case.
In the convex modeling method, only the information for the bounds of uncertain parameters is required for analysis. The convex sets enclosing the hypervolume, determined by boundary of uncertain variables, are constructed and the response function is linearized with respect to those variables. In this condition, the minimum and maximum values of the function occur on the boundary of the convex set due to the linearity of the response function, thus the extremum case can be easily searched with computational efficiency.

The numerical results, considering the uncertainty, show that the performance of shock absorber could be worse than expected under normal operating conditions. The landing load factor and shock absorber stroke are considerably increased in some cases, which might threaten the safe operation of the landing gear. Therefore, it is crucial to consider the possible uncertainties in the analysis and the proposed methodology can be used as an efficient tool for evaluating the effect of such uncertainties.
 

Presenting Author: Tae-Uk Kim Korea Aerospace Research Institute

Presenting Author Biography: I received my Ph.D. degree in computational mechanics from the Seoul National University. I have been working at Korea Aerospace Research Institute since 2000, and my research interests include the structural optimization and reliability analysis of aircraft structures and subsystems.

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