scope:

Description of Driving Event:

Photoanalysis of the STS-28 (OV-102, Columbia) flight showed larger body flap deflections than were calculated. The flaps are in a turbulent flow field, which creates a hinge moment spectrum greater than that used in the structural fatigue analysis. The loads are all within the structural limits, but the fatigue analysis shows a reduction of allowable flights from 100 to 77.

After the higher hinge moments were observed, additional ground tests were conducted using recalibrated strain gages on the body flap actuator as well as additional instrumentation on the rotors and stators. Three types of loads were applied. It was discovered that an additional load path existed back through the driving gear to the supporting structure. The original equations assumed only four load paths at the actuators. With a fifth load path, it is necessary to develop a new set of equations. It also was discovered that the actuators were more flexible than originally assumed and that the OV- 102 (Columbia) actuators were more flexible than those on OV-103 (Discovery) and OV-104 (Atlantis). This is attributable to increased tooth width on the OV-103 and OV-104 actuators. Additional tests are planned to further evaluate the body flap structure.