The Global Observer is an unmanned aircraft with the wingspan of a Boeing 767 but less than 10% of the weight designed to provide communications and sensing for flights lasting up to one week at up to 65,000 feet. With a maximum wing loading of only 3.5 pounds per square feet, the wingtip deflects greater than 22 feet at its design limit load.
MSC Nastran was utilized to develop nonlinear stress, structural dynamic and aeroelastic finite element models. The structural dynamics model was correlated to a ground vibration test, both of which had to accommodate the apparent mass of the air, which is atypical. The ultimate test of the nonlinear stress model was correlation with the static wing load test, performed last summer. “Correlation with static load testing was so good that at first I did not believe it,” said D.J. Taylor, Principal Engineer for AeroVironment, the company developing the Global Observer. “All of the NASTRAN models have proven valuable for addressing the various modifications and design changes inherent in a proof of concept /prototype effort and will be even more useful in optimizing a production version.”