Riveted patch repairs for helicopter tail drive shafts with battle damage

Abstract

AbstractThe ability to repair battle damage in a helicopter tail drive shaft (TDS) caused by small arms fire is a very important capability. A successful repair will enable the helicopter to continue its mission or at least allow it to return safely to base. This paper describes assessment of conventional and novel repair techniques using riveted metallic patches to restore the balance and strength of a damaged TDS. Analytical approaches are provided for the design of the repair. Modal analyses indicated that the effect of repair on change of the natural frequency of the TDS was negligible. An experimental testing program was conducted to validate the proposed repair methods. It has been demonstrated that the proposed repair methods achieved sufficient balance restoration by a defined repair procedure, assuming the unbalance could not be measured during a repair in the field. The conventional thin, single aluminium sheet, riveted repair significantly restored static strength. However, it only gave a fatigue life of 15hrs, and thus the repaired shaft may only be used for limited time for a military mission. The improved thick, two-half aluminium shell, riveted repair had sufficient static strength and met the 100-hour fatigue requirement.