Lightweight Exoskeleton Fuel Bladder Transition

Previous efforts demonstrated the ability to achieve a 30% weight reduction for a MIL-DTL-27422D Phase I test cube construction with Protection Level A gunfire performance, using a lightweight 2-ply exoskeleton design to replace the 4-ply construction otherwise required to meet crash impact test requirements. An additional 20% reduction in weight was projected by replacing the natural gum rubber (NGR) used in conventional fuel bladder constructions with a lightweight formulation. This paper reviews the technical efforts executed to support the transition of the lightweight exoskeleton construction to the Apache AH-64 helicopter. The fuel bladders made with the lightweight sealant were 15.5% lighter for the AH-64 FWD fuel bladder and 13.2% lighter for the AFT. Additional weight savings based on the 2-ply exoskeleton construction was not realized as the existing AH-64 fuel bladders are already relatively lightweight constructions. The final AH-64 fuel bladders demonstrated the ability to be qualified to all MIL-DTL-27422E performance requirements; however, the program concluded without demonstrating Protection Level A gunfire performance. Importantly, there did not appear to be any discernable difference in the self-sealing performance of the fuel bladders made with the lightweight sealant and the constructions based on conventional NGR sealant. While additional work may be required to address this performance deficiency, there were several issues that were noted during the Phase II gunfire testing that should be reviewed and resolved prior to additional testing.