Reliability Based Aircraft Structural Design Optimization with Uncertainty about Probability Distributions

Probabilistic structural design is beset with a credibility problem. Uncertainties associated with errors in structural and aerodynamic modeling and quality of construction are not well characterized as statistical distributions. Therefore, many engineers are skeptical of the accuracy of failure probability predictions. We propose a probabilistic design optimization method, where the probability of failure calculation is confined to failure stresses, to take advantage of the fact that statistical characterization of failure stresses is required by FAA regulations. The stress distribution is condensed into a representative single value by utilizing inverse cumulative distribution function of the failure stress. The method is demonstrated by performing the weight and safety optimization of a representative system composed of wing, horizontal tail and vertical tail. It is found that by moving material from the heavy components to the light components corresponding to a small redistribution of the safety factor, it is possible to reduce the overall weight while maintaining the same level of safety. The proposed method is also applied to a representative wing structural design problem and similar results are obtained.