C-17 conducts flight tests with biofuel

Published Sept. 4, 2010
By Kenji Thuloweit
95th Air Base Wing Public Affairs

EDWARDS AIR FORCE BASE, Calif. -- The Air Force's ongoing alternative fuels certification efforts reached a new milestone Aug. 27, 2010, when a C-17 Globemaster III from here flew on all engines using jet fuel blended with a combination of traditional petroleum-based fuel, or JP-8, biofuel derived in part from animal fat, and synthetic fuel derived from coal.

The 418th Flight Test Squadron at Edwards conducted the flight tests Aug. 23 to 27. The flight was a first for any Department of Defense aircraft where a 50 percent mix of traditional petroleum-based JP-8 was blended with 25 percent renewable biofuel and 25 percent fuel derived from the Fischer-Tropsch process, essentially liquified coal or natural gas. It was also the first time an aircraft from Edwards had used fuel derived from beef tallow, essentially waste animal fat.

"The C-17 fleet is the biggest Air Force consumer of jet fuel annually," said Lt. Gen. Mark Shackelford, Military Deputy, Assistant Secretary of the Air Force (Acquisition). "This is a big step forward in achieving the Air Force's energy goal of increasing the available supply of fuel by acquiring half of the Air Force's domestic jet fuel requirement from domestically derived, environmentally friendly alternatives sources by 2016."

For several years the Air Force has been looking at alternate sources of fuel to support their operations, said James Holther, 418 FLTS project engineer for biofuel testing.

"The first thing the Air Force did was look at Fischer-Tropsch fuels that use natural gas or coal as the feedstock and this is just a continuation of that ongoing effort," he said. "The fuel we're testing this time around is a biofuel manufactured with biomass as the feedstock."

The hydro-treated renewable jet fuel used by the C-17 contains biomass that can be made from either animal fats or plant extracts such as camelina, a weed-like plant not used for food. The HRJ is blended with regular JP-8 jet fuel for the testing to gather data to support Air Force transport aircraft certification on alternative fuels from various feedstocks.

The Air Force Fuels Certification Office at Wright-Patterson Air Force Base, Ohio, has certified more than 85 percent of all Air Force aircraft to use Fischer-Tropsch derived fuels and is now focusing efforts on certifying aircraft to fly on HRJ biofuel blends.

"When the certification effort is completed, it won't matter what feedstock or process was used to make the fuel, we will simply call it 'JP-8,'" said Jeff Braun, director of the Air Force Fuel Certification Office.

Mr. Braun added that his office tests and manages certification of 'drop-in' alternative fuel blends that will require no modification to aircraft or ground equipment. It also would necessarily provide the desired performance and burn as clean or cleaner than current JP-8, as demonstrated during the ground engine emission evaluation conducted as part of the C-17 test program.

"We want maintainers, aircrews and fuels handlers to be able to say they can perceive absolutely no difference between traditional JP-8 and the alternative blends," Mr. Braun said.

The testing process featured the C-17 flying with different combinations of HRJ and JP-8.

Mr. Holther said the testing required the Globemaster III to perform several maneuvers at different altitudes such as decelerating and then accelerating to see how the plane responds with the HRJ mixed in.

The 418 FLTS took precautionary measures to build up to the final test day.

"On Monday three engines had JP-8 and one engine had a blend of 50-50 biofuel and the JP-8 -- it's part of a safety build-up," said Mr. Holther. "We'll build up to putting the fuel in all four engines by verifying the performance differences are insignificant between the blended fuel engine and the regular fuel engines."

On Aug. 24, the test team expanded the evaluation by utilizing the HRJ blended fuel in all four engines, flying the aircraft on 50 percent biofuel.

A successful test is signified when the C-17 performs with little or no difference between the blended fuel and JP-8.

The flight testing culminated Aug. 27 with the C-17 using a blend of 25 percent HRJ, 50 percent JP-8 and 25 percent Fischer-Tropsch fuel mixture.

The potential use of alternative fuel could provide the Air Force with more options and greater flexibility in the future.

"This is an opportunity for us to investigate the possible use of clean, renewable fuel sources," said Lt. Col. Clifton Janney, 418 FLTS commander. "If successful, it can broaden the spectrum of fuels that we can use Air Force-wide."

Mr. Holther said successful testing of the HRJ with the C-17 will be used by the AFCO to support certification of the biofuel in military and commercial transport aircraft.

"This test we are doing with the C-17 and biofuel is considered a 'pathfinder' effort, which means similar aircraft, like the C-5, might be qualified to use this fuel based on the test results we get with the C-17," said Mr. Holther.

Mr. Braun said lessons learned from certifying individual airframes on Fischer-Tropsch fuels has been applied to the HRJ alternative fuel certification process, which will enable accelerated certification using pathfinder aircraft, then certifying other systems by similarity. The F-22 is the planned pathfinder for certifying the fighter fleet, and Global Hawk is being explored for platforms which operate at high-altitude.