Flight Test of Advanced-Geometry Boron Blades
Final technical rept.
BOEING VERTOL CO PHILADELPHIA PA
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This report presents the results of an exploratory flight test program conducted on a CH-47C Army helicopter for the purpose of investigating the structural performance of boron-reinforced epoxy aft rotor blades and the associated effects on the helicopter system. The boron-reinforced epoxy aft rotor blades were developed. The forward rotor was equipped with S-glass- reinforced epoxy rotor blades and are the same aerodynamic configuration as the boron blades. On-board instrumentation was used to provide real- time telemetric monitoring and magnetic tape recording of 132 data parameters on the CH- 47C. Data were obtained at nominal gross weights of 33,000, 40,000, 46,000, and 50, 000 pounds gross weight at altitudes from sea level through 15,000 feet density altitude and were recorded on level-flight airspeed sweeps, rpm sweeps, climbs, turns, autorotation, partial-power descent, and mild flare maneuvers. This program has demonstrated the flightworthiness of boron- reinforced epoxy main rotor blades in the demanding environment of the aft rotor on a tandem-rotor helicopter. No structural problems were encountered. There were no restrictive 3rev vibrations despite a first-elastic-mode, flap-bending natural frequency of 3.21 times rotor speed. Track adjustments were required on the forward rotor throughout the program S-glass blades. The increase in torsional stiffness of the boron blade over the glass blade provided excellent blade-to-blade track conformance throughout the program after minimal initial adjustment.