USAF Details Broad-Based Fleet Fuel Savings Initiatives

C-17 engine pylon drag reductions could save more than $3 million per year across the fleet in lower fuel costs.

Credit: USAF

LONDON—The U.S. Air Force plans to conduct additional test flights of drag reduction modifications to its Boeing C-17, KC-135 and Lockheed Martin C-130 aircraft as part of an accelerating initiative to reduce fuel burn and maximize combat capability across its main transport and tanker fleets.

Updating the Air Force Operational Energy (OE) program, Roberto Guerrero, deputy assistant secretary of the air force for operational energy, says in wartime the fuel burn reduction goal “allows us to deliver more combat airpower. In peacetime that allows us to save money to put back in the mission.”

With the Air Force consuming around 2 billion gal. of aviation fuel per year, Guerrero adds that the initiative also will have a secondary effect of reducing greenhouse gas emissions. “But our focus is how do we get more bang for the buck out of the platforms that we have right now,” he says.

Speaking at the Global Air and Space Chiefs Conference here, Guerrero says following earlier flight tests of a set of drag-reducing microvanes on a C-17, additional tests are expected in September and October to “ensure the performance of those aircraft with these modifications to them.” The vanes, which are attached to the sides of the aft body between the base of the vertical tail and ventral strakes on either side of the cargo ramp, are the final elements of a wide-ranging set of aerodynamic modifications tested with varying degrees of success since 2016. Developed by Lockheed Martin in collaboration with the Air Force, microvanes are already available for the C-130 and have been installed on some Canadian Armed Forces aircraft.

Targeting a 1% reduction in the aft body upsweep drag around the ramp, the Air Force effort is expected to generate fuel cost savings worth around $10.7 million per year across the fleet. “By next year we’re going to be doing some pylon fairing modifications. That’s about another half percent and that’ll be complete by the end of next year,” Guerrero adds. The engine pylon change is expected to reduce fleet fuel costs by an additional $3.2 million per year.

Similar aft body drag-reduction projects are slated for the C-130 and KC-135. These “should be done with flight testing by the end of next fiscal year—so around September 2024,” Guerrero adds. The C-130 fleet will be equipped with strake-like devices dubbed “finlets” around the aft fuselage near the intersection of the cargo ramp with horizontal stabilizer, while the KC-135 “air contour system” is envisioned as a set of six small fairings to be attached around the empennage. The Air Force recently issued a “sources sought” document for the potential procurement of the drag-reduction kit for up to 325 KC-135s.

Air Force planners estimate the C-130 finlet package will cut drag by up to 6% resulting in fuel savings of around $5.4 million per year, while even the relatively modest 1% drag cut from the air contour package on the KC-135 will save around $6.3 million a year. “The big thing for these [upgrades] is that as we work on sustainment issues, we have to understand that the application has to be fairly simple to apply. It must require no maintenance and it has to have some kind of benefit to the mission,” Guerrero says. An additional fuel saving initiative under study for the KC-135 covers replacement of the existing windshield wipers with a vertical wiper. The resulting 1% drag cut could save $6.3 million more in fuel per year across the fleet, he adds.

The Air Force also is looking to re-rig control surfaces across its entire air mobility fleet as part of a broader effort that could see fuel savings worth around $11 million per year. “When you collect the data, you realize that most of the aircraft will look just like the computational fluid dynamics is telling you with respect to performance, but some of them don’t. And that’s because we have old aircraft—some of them are bent and need to be re-rigged,” Guerrero says.

Beyond aerodynamic improvements, the Operational Energy program includes engine optimization initiatives such as engine washes, upgraded compressor blade coatings and new fan ducts for the CFM56-powered KC-135s, as well as operational changes and longer-term plans for the adoption of sustainable aviation fuel. Operational changes include the Mission Execution Excellence Program (MEEP), which encourages crews to optimize fuel use by more precise planning and best practices. 

Referencing MEEP, Guerrero says “we’re spending some time looking at incentivizing our crews to think differently about fuel use. We’ve seen a pretty good reduction in a couple of test squadrons that we’ve looked at—and seen about 10,000 lb. of fuel reduction per flight. For two locations where this has been tested, this ends up being about $4 million in fuel use that was reduced just by thinking about fuel differently. On the front end this is providing cash incentives to those wings to think differently. But on the long end it’s actually aimed at changing the culture to have everyone realize that—unlike previous recent air wars that we’ve had—fuel saving means somebody else has more fuel to conduct missions that we couldn’t have done otherwise.”

Guy Norris

Guy is a Senior Editor for Aviation Week, covering technology and propulsion. He is based in Colorado Springs.