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B-52 aircraft to use AFRL hydraulic fluids

by Tim Anderl
Air Force Research Laboratory Materials and Manufacturing Directorate

10/6/2004 - WRIGHT-PATTERSON AIR FORCE BASE, Ohio (AFPN) -- A fire-resistant hydraulic fluid Air Force Research Laboratory experts here developed will now be used in more than 90 percent of B-52 Stratofortress bomber components, increasing the aircraft's survivability and operational safety.

In the past, B-52s used a flammable, petroleum-based hydraulic fluid, said C. Ed Snyder of the materials and manufacturing directorate fluids and lubricants group. The replacement fluid has a higher flash point and reduced flammability, a key to in-flight safety. It also allows aircraft to operate at temperatures as low as minus-65 degrees, and in high-temperature environments longer.

"The hazards associated with the flammability characteristics of hydraulic fluids are well known," Mr. Snyder said. "They are required to function in high-pressure hydraulic systems in the presence of a variety of ignition sources."

Though fire-resistant fluids will burn, Mr. Snyder said they are significantly more difficult to ignite and are much less likely to spread a fire after ignition than a nonfire-resistant fluid.

Jimmy Vo, a B-52 system engineer at Oklahoma City Air Logistics Center at Tinker Air Force Base, Okla., said revisions to the B-52 technical orders, reflecting the new hydraulic fluid requirement, will be official by January. AFRL experts will also conduct tests to determine if the landing-gear struts and wingtip protection struts can be converted to the fire-resistant fluid.

Hydraulic fluids are a critical safety material for all Air Force aircraft. Hydraulically actuated mechanisms operate many aircraft functions, including flight controls, landing gears, rudder flaps and accessory doors, Mr. Vo said. Hydraulic fluids also lubricate aircraft systems and reduce heat generated during operation.

After significant research and development, two synthetic hydrocarbon-based fire-resistant hydraulic fluids were successfully developed and were compatible with the systems and design of aircraft, including the B-52, Mr. Snyder said.

A materials and development program in the 1960s and 1970s led to AFRL experts developing the new fluid so it is compatible with and an appropriate drain-and-fill replacement for the older petroleum-based product. It also did not require any type of retrofit of hydraulic system materials or components, Mr. Snyder said.

Officials initially authorized converting all Defense Department aircraft to this fluid across the board except for aircraft required to be airborne on short notice, he said. Those aircraft were not converted because the older fluid worked better at minus-65 degrees than the new product.

Mr. Snyder said aircraft using the new product were found to require longer warm-up times for the flight controls before the aircraft could take off, a phenomenon that was considered unacceptable. So, those aircraft continued to use the flammable fluid.

Subsequently, a requirement developed for a compatible, drain-and-fill replacement for the old, flammable hydraulic fluid that would have the same low temperature operational capability, but would also offer improved fire resistance.

Based on a modified synthetic material and a similar additive package, AFRL experts developed the new fluid which is an appropriate replacement for the older, flammable hydraulic fluid in all military and some small commercial aircraft. (Courtesy of Air Force Materiel Command News Service)

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