The On-Condition Qualification Of The Trailing Edge Area Of The UH-1H Metal Main Rotor Blade

A program has been conducted by Bell Helicopter Textron, Inc. ( BHTI), under contract to A VSCOM engineering, to establish an on-condition replacement status for the UH-lH metal main rotor blade considering fatigue cracking along the trailing edge. Two test specimens constructed from service-returned blades were used to generate crack growth data . Innovative approaches used in the test included application of a multistep spectrum of beamwise. chord wise, and torsional loads derived from the UH-lH operational spectrum to simulate a 2-hour flight. Application of test loads included the superposition of the significant 1/rev and 7/rev chordwise loads to realistically account for the dynamic response of the blade in flight. The paper presents details of the derivation of the crack growth test load spectrum, details of the test. and the crack growth data generated that were subsequently used to establish a safe inspection interval.