Scaled Composites LLC used finite-element analysis to analyze buckling and optimize the weight of its SpaceShipOne. Analysis was complicated because the structure is mostly bidirectional carbon cloth. Still, several feature in Cosmos FEA from SolidWorks' Los Angeles division (srac.com) simplified the tasks.
"Weight optimization, for instance, requires the tracking of three basic composite parameters strength, deflection, and stability," says Scaled Composites Structural Analyst Dan Kreigh. "Each has independent limits that are balanced for the best structure. Furthermore, we weren't sure we could make the required 328,084-ft altitude because every extra pound of structural weight subtracts more than 100 ft of altitude. So we examined areas where weight could be trimmed and found six to eight unnecessary pounds," he says.
The software models spar caps as beam elements with different cross sections depending on their location in a wing. Each beam element must be assigned a set of constants that defines the spar's cross section, root, and tip properties.
The large amount of data required by a complex composite structure can be a bookkeeper's nightmare. So Kreigh created a spreadsheet to organize the constants. "The spreadsheet calculates the constants between the root and tip. This text data is then easily read into the FEA software. Though it takes a day or two to create the spreadsheet, it saves time in the long run because as new load cases occur, or as the vehicle changes weight, the software quickly resizes the spar caps," he explains.
Structural Research & Analysis Corp., (310) 309-2800, srac.com
Image courtesy of Scaled Composites LLC