New Composite Material Skins the HTE Competition

  • Published
  • By Heyward Burnette
  • Materials and Manufacturing
WRIGHT-PATTERSON AIR FORCE BASE, Ohio --  Through its implementation of a new hot trailing edge skin composed of the composite material AFR-PE-4, AFRL expects to virtually eliminate field repairs, reduce downtime, and achieve higher mission capability rates for B-2 aircraft. The successfully demonstrated skin confirms AFR-PE-4's viability as a more durable, higher-performing material in addressing the sustainment challenges related to the B-2's current HTE. The positive outcome also showcases the coordinated efforts of personnel from Air Force Research Laboratory; Hill Air Force Base, Utah; and the University of Dayton Research Institute and further boosts B-2 Program Office confidence regarding plans initiated for an on-aircraft demonstration.

Located behind the exhaust nozzles on the aircraft's upper surface, the B-2 HTE experiences repeated thermal and vibro-acoustic stress. The polyimide material presently used for HTEs degrades quickly in this operational environment; as the incessant exposure to heat and engine exhaust exceeds its capabilities, the material cracks and the resin disintegrates. Recognizing the need for a more resilient material, AFRL commenced its design of a new application based on AFR PE 4, the maturation of which culminates work started in the late 1990s towards a new composite material. The successful demonstration of this AFR-PE-4-based design prompted the technology's transition from the lab to a production environment, thanks to the combined efforts of AFRL, Hill AFB, and UDRI.

In order to determine the composite's suitability as an appropriate alternative to the conventional material, scientists initiated performance testing. Accordingly, they subjected AFR-PE-4 purchased from three separate vendors to several types of durability tests, including both long-term (1,000 hr) exposures and high-temperature exposures (in a burner rig at the National Aeronautics and Space Administration's Glenn Research Center and in a combustion chamber at AFRL). The team also conducted mechanical characterization, with the associated tension and compression tests enabling determinations regarding the material's shelf life; leveraged Advanced Manufacturing Propulsion Initiative activities to develop cure cycles and identify cost drivers for the material; demonstrated material repairability (with the help of B-2 maintainers and Northrop Grumman personnel); and fabricated demonstration (2' x 2') panels in a laboratory environment before investigating a production facility build. Since HTE production currently occurs at Hill AFB, the team implemented a plan to cure numerous panels in the Air Logistics Center's large, 15' x 30' autoclave. Personnel first fabricated 12" x 12" coupons and then proceeded to build 2' x 2' panels. Based on bagging schedule and cure cycle refinements, the researchers next constructed a large, 32" x 73" panel in preparation for the full HTE skin, with their final demonstration employing the representative production tooling for that complete product.

Future AFRL activities include preparation of the demonstrated materials for flight evaluation by the B-2 Program Office. These activities will entail the evaluation of tooling, as well as the comprehensive mechanical testing of AFR-PE-4 material batches.