Nonlinear Aircraft Loads in Severe Atmospheric Turbulence

The problem of predicting loads due to turbulence for aircraft with nonlinear flight-control systems is reviewed, and related recent research in this area is described. Two alternative approaches to the problem, stochastic simulation and worst-case analysis, are compared and problem areas associated with each are identified. It is concluded that the latter method, which involves a search over a specified family of gust patterns to find the pattern that causes maximum load, is appropriate for investigating a limited number of critical cases, but that a preliminary simplified method of estimation is called for by computational considerations as a means of identifying such critical cases. A new genetic algorithm is described and proposed as the most reliable method of performing the search. It is illustrated how this search algorithm can be simplified computationally by introducing a weighting factor that penalizes the more complex gust patterns, a step that is supported by measurements of the amplitudes of gust patterns in severe turbulence.