Wingbox
Complete failure of the wingbox occurred at the root interface in the bolt connecting the wingbox to the test equipment. There was also visible signs of buckling in the skin panel although the damage was minimal compared to the 3 in maximum deflection for a 16 in span. Signs of bearing yield in the top spar cap root interface were also observed.
My contribution to this project consisted of analyzing and predicting the failure load of the wingbox, manufacturing the wingbox, and contributing to the design of the wingbox. Throughout this project, I learned how to perform a thorough analysis of a wingbox structure and methods for designing a wingbox. I also improved my manufacturing skills, particularly with sheet metal processes.
There are several changes that I would make if I were to restart this project. One change is that I would drill the spar cap root connections together after assembly instead of individually before assembly. One of the reasons for the bolt failure was due to improper alignment of the spar cap connections.
Another change is that I would target a higher strength-to-weight ratio as well as a lower overall failure load. While my team had a high strenght-to-weight ratio and a very high failure load, the wingbox was comparatively heavy. As weight is extremely important in aviation, it would be more preferable to have a lighter wingbox with lower but sufficient strength than a very sturdy wingbox that is heavy. Some methods in which this could be done is to decrease the number of rivets and to remove or change the horizontal rib. The spacing between rivets was less than what was necessary. The horizontal rib provided stiffness against buckling, but the amount of load experienced for the length of the spar did not warrant a need for it and removal of the rib would lighten the wingbox and remove unnecessary rivets. This would also ease the manufacturing process. If the horizontal rib was determined to be necessary, punching holes in the rib would effectively decrease weight without significantly affecting maximum load.
Future iterations of this project could involve aerodynamic considerations in design.