Abstract
A graphite/epoxy composite shaft has been successfully balanced to operate above two flexural critical speeds while subjected to a steady torsional load. This experimental investigation has been conducted as part of a research program concerning the optimal design of supercritical composite power transmission shafts for rotorcraft applications. Of particular interest is the use of composite materials in the design of tail rotor and synchronization shafts.
Rotating tests were conducted with a composite shaft that models the half length of the tail rotor drive shaft of the AH-64 helicopter. Tests were performed with magnetic and coulomb damping. It was shown in past research that an unloaded composite shaft could be balanced through and operated above two flexural critical speeds [1,2]. In this series of tests, a steady torsional load has been applied which models that of a tail rotor driveshaft. Adequate magnetic damping performance was observed up to 1000 rpm, although its effectiveness diminished at higher speeds. The remaining tests were conducted with an external coulomb damper. Results show controllable operation above two critical speeds, and smooth operation was observed at the scaled operating speed of 3500 rpm. All synchronous and nonsynchronous vibrations were easily controlled with 6% external damping applied through the entire speed range up to 5000 rpm.
