The Joint Strike Fighter (JSF) is the Department of Defense's affordable next-generation strike aircraft designed to meet the needs of the Air Force (AF), Navy, Marines, and US allies. Currently in development by Lockheed Martin, the multi-mission, supersonic, JSF aircraft will provide all services with enhanced lethality and survivability and reduced vulnerability (see figure). The JSF's unique, multiple-variant design pushes the threshold of fighter technology far beyond current limitations. The AF variant of the technology takes multirole fighter performance to new levels, offering improved stealth, increased range on internal fuel, and advanced avionics. The JSF's advanced avionics, as well as its flight control, target acquisition, and other sophisticated electronic systems rely on high-performance coolants to ensure proper operation. Designers employ dielectric coolants to dissipate heat from high-energy electronic components and therefore consider these fluids critical to aircraft operation and safety.

The JSF

AFRL researchers have extensive experience in developing unique fluids and lubricants to meet demanding AF requirements and are also the custodians of the AF specification related to aircraft dielectric coolants. The MIL-PRF- 87252 specification defines the dielectric coolant properties required for effective performance in a fighter aircraft environment. Twelve dielectric coolants, manufactured by eight different companies, are on the AF's qualified products list for MIL-PRF-87252. The Aeronautical Systems Center's Air Vehicles Subsystems Branch requested that AFRL evaluate the 12 coolants on the qualified products list to determine if any of the fluids maintained thermal stability at operating temperatures higher than MIL-PRF-87252 requirements dictate. Although these dielectric coolants are not required to perform at higher operating temperatures, the scientists expected the MIL-PRF-87252-qualified fluids to demonstrate thermal stability at higher temperatures without a noticeable decrease in coolant performance.

AFRL materials scientists conducted several high-temperature stability tests that confirmed the thermal stability of the qualified MIL-PRF-87252 dielectric coolants up to 232°C—adequate evidence for permitting their use at temperatures much higher than specified in the original requirement. The results of the high-temperature testing indicated no significant change in viscosity, acidity, or weight, and no chemical breakdown in any of the 12 candidate coolants identified in the qualified products list as appropriate for use in advanced fighter aircraft systems. The team reported its findings at a joint conference with AF, Navy, and Lockheed Martin JSF engineers. The attendees concurred that the fluid will perform at both the temperatures and the operating duty cycle required by the JSF. AFRL subsequently amended the MIL-PRF-87252 specification to accommodate the new temperature range of -54°C to 200°C. Scientists will periodically sample the working dielectric fluids throughout the JSF development program to monitor long-term coolant performance.

Ms. Lois J. Gschwender and Mr. Tim Anderl (Anteon Corporation), of the Air Force Research Laboratory's Materials and Manufacturing Directorate, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at http://www.afrl.af.mil/techconn_index.asp . Reference document ML-H-05-09.