Live Fire Testing A Legacy System - Assessing Dry Bay Fire Potential in the New C-5M Engine Pylon

The new C-5M engine pylon was subjected to live fire testing as part of the overall C-5 RERP Live Fire Test and Evaluation (LFT&E) program. The pylon was designed, as much as possible, to physically separate the flammable fluid carrying lines from the ignition sources. This was done by routing the flammable fluid carrying lines through the structural box while the ignition sources are routed from the engine core compartment to the wing/pylon interface through the pylon leading edge. Designed into the pylon are fire resistant materials for structure, hydraulics, fuel, and bleed air lines. The pylon also provides fluid drain lines for potential flammable fluid line fitting leaks, and ventilation in flammable fluid areas. Twelve ballistic shots were performed on this unique, orthogrid construction engine pylon. The objective was to determine the ignition and sustained fire potential by impacting two dry bays within the engine pylon. The bays of interest are Zone 2 – “Wing Interface Compartment (Fire Zone)” and Zone 3 – “Structural Box Compartment (Flammable Fluids Zone)”. Zone 2, enclosed by Aluminum 2219-T81 skin, contains fuel and hydraulic lines, an ECS duct, wire bundles, fire resistant bulkhead seals, a 5-min – 2000 F fire-resistant bulkhead, and drainage. Zone 3, enclosed by Aluminum orthogrid skin, contains a fan bleed-air duct, multiple hydraulic lines, a fuel line, a hydraulic accumulator, 15-min – 2000 F firewalls, fire resistant bulkhead seals and side skins, an engine fire extinguisher line, and drainage. For this ballistic test, the ultimate targets in each of these two zones were fuel and hydraulic lines. Pretest ballistic testing was performed on the Zone 2 and Zone 3 skin material. Ballistic impacts on the Al 2219-T81 material was conducted to determine the ability of the aluminum to cause the threat to react upon penetration. Threat impacts on the orthogrid material were accomplished to determine any trajectory deflections, caused by the thick, orthogrid material when the threats passed through at the required impact velocity. Simulated airflow, from engine bypass air, was blown over the test article at 250 knots to better simulate airflow and flight conditions. The twelve shots on the engine pylon test article resulted in 10 sustained fires and 2 ignited, self extinguishing fires. The damage, due to both ballistics and fire, was repaired by a BDR team after each test event to preserve the integrity of the engine pylon for the following test. The data provides insight to the fire potential of combat threats that impact the RERP engine pylon. This effort exhibits the value of risk reduction pretests performed prior to live fire test events and that such activities are critical to reaching the end goals of live fire testing. 50th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference 17th 4 7 May 2009, Palm Springs, California AIAA 2009-2360