A Composite Pylon Support Structure For The Jetranger Helicopter

This paper describes a program to design, fabricate, ground test, and flight test a prototype pylon support structure for the JetRanger helicopter. The structure, a single-plane truss made from unidirectional S-glass prepreg and E-glass fabric, replaces a steel forging that is 2.4 times as heavy. One part was static tested to failure at 310 percent of limit load. On two fatigue tests, benign failures occurred at the number of cycles predicted by the S-N curve for the part. A residual strength equivalent to 3.1g remained after the fatigue test. A flight test program was conducted on a helicopter in which a pair of fiberglass mounts were installed. Flight loads were comparable to those measured on the production part. The program also investigated a production-type mount structure. It weighs slightly more than the prototype, but should be competitive in cost with the present steel part.