Rapid composite bonded repair for helicopter tail drive shafts

Helicopter tail drive shafts (TDS) are safe-life items with strict limits on allowable damage. Typically, shafts with scratches as small as several thousandths of an inch may require replacement. Despite these severe tolerances on damage, TDSs are designed with relatively large ballistic damage tolerance. In battle damage scenarios, repair for damage to TDS caused by small arms fire is required to enable the helicopter to continue its mission or return safely to base. This paper describes a novel repair technique using composite bonded patches to restore the strength of damaged TDSs. Analytical approaches are provided for the design of the repair. An experimental testing program was conducted to validate the theoretical results. It has been demonstrated in this study that the proposed composite bonded repair possessed sufficient static and fatigue strength to restore the structural integrity of the TDS even with minimal surface treatment.