Tech Briefs

B-52/Missile Sustainment Group adopts AFRL-developed hydraulic fluid.

AFRL nonstructural materials experts have dedicated significant research and development effort to preventing hydraulic fluid hazards. Though fireresistant fluids will burn, they are significantly more difficult to ignite than non-fire-resistant fluids and/or they exhibit a lower propensity to propagate a fire after ignition. Thus, earlier researchers eventually developed two hydrocarbon-based fire-resistant hydraulic fluids to meet B-52 requirements, and these synthetic fluids were also compatible with the systems of other aircraft using the flammable, MILPRF- 5606 fluid. Ultimately, a materials development program instituted in the 1960s and extending through the 70s led to development of MIL-PRF-83282, a hydraulic fluid compatible with, and an appropriate drain-and-fill replacement for, MIL-PRF-5606. Another advantage of the newer, MIL-PRF-83282 fluid was that it did not require any retrofit of hydraulic system materials or components.

Air Force (AF) officials subsequently converted all aircraft—except those required to be airborne on short notice—to MIL-PRF-83282. They did not convert aircraft meeting the shortnotice criteria because the MIL-PRF- 83282 fluid exhibits a higher viscosity at -65°F than does MIL-PRF-5606 at the same temperature; therefore, aircraft operating in these extreme temperatures require longer warm-up times prior to takeoff. Since military planners considered the longer time-to-takeoff unacceptable, these short-notice aircraft continued to use the more flammable, MIL-PRF-5606 fluid.