Operation and Test of Composite Horizontal Stabilizer For The Sikorsky SPIRIT Helicopter

The horizontal stabilizer for the SPIRIT helicopter is made entirely of advanced composite materials. The skins are KevlarR/epoxy over NomexR honeycomb core, with graphite/epoxy spar caps and a Kevlar epoxy torque tube. In addition to a substantial weight savings, cost savings resulting from a greatly simplified manufacturing process that reduced part count, lowered assembly cost and overall reduced factory labor hours was clearly demonstrated. To date, laboratory testing has shown the SPIRIT composite stabilizer to be a highly reliable efficient structure. Accelerated fatigue tests at four times flight loads confirms an unlimited life with high margins. Following accelerated fatigue testing, stabilizers were loaded statically to failure giving a static residual strength of 290% of limit load with failure being local core crushing under the loading pads. Beginning with the first flight of the SPIRIT on March 17, 1977, the horizontal stabilizer has performed flawlessly during flight testing and FAA flying in meeting certification requirements. Flight time to date of 1050 hours has exposed the stabilizer to the hot, humid climate of Florida at the Sikorsky Flight Test Center and the extreme cold temperatures at Inuvik, Canada during cold weather test. In meeting FAA certification requirements the stabilizer has flown at 1.11VE at all certified gross weight and center of gravity combinations. This paper will describe the test and operation experiences with the first primary airframe structure to receive FAA production certification on rotary wing aircraft.