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Air Force saves $7M on fuel for KC-135 by turning windshield wipers vertical

The KC-135 Stratotanker's primary mission is to refuel long-range bombers. It also provides aerial refueling support to Air Force, Navy, Marine Corps and allied aircraft. Depending on fuel storage configuration, the KC-135 can carry up to 83,000 pounds of cargo. Photo by Master Sgt. Dave Nolan/U.S. Air Force
The KC-135 Stratotanker's primary mission is to refuel long-range bombers. It also provides aerial refueling support to Air Force, Navy, Marine Corps and allied aircraft. Depending on fuel storage configuration, the KC-135 can carry up to 83,000 pounds of cargo. Photo by Master Sgt. Dave Nolan/U.S. Air Force

April 20 (UPI) -- Windshield wiper blades mounted vertically on a KC-135 Stratotanker's windshield can save about $7 million in annual fuel costs, a U.S. Air Force test concluded.

Aerodynamic drag is reduced by about 1 percent, under cruise conditions, when the wipers are left upright on the windshield, the Air Force said in a statement on Monday. It could potentially save $7 million annually in fuel costs for the 398 KC-135 planes in the Air Force fleet.

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"While one percent efficiency may not seem like a lot, it equates to millions of dollars in fuel savings each year, which can then be re-invested into other programs," Daniel Pike, acquisition manager and chief of future operations for Air Force Operational Energy, said in a press release. "When you combine the results of optimization efforts across multiple aircraft, you start to understand how much of an impact this could have."

First introduced in 1956, the Boeing-built plane serves as a military aerial refueling aircraft, and was the first jet-powered refueling tanker in the Air Force.

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It has since been built in 14 variants. The militaries of Chile, France and Turkey use the plane, and the United States has 156 in active duty, 70 in the Air Force Reserves and 172 in the Air Force National Guard.

The Air Force fleet of KC-135s consumed 14 percent of total Air Force aviation fuel use, or over 260 million gallons, according to the Air Force.

The windshield wiper blades have remained positioned horizontally since the plane's debut, but the Advanced Power and Technology Office of the Air Force Research Laboratory at Wright-Patterson AFB, Ohio, identified it as a candidate for analysis and modification.

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In tests performed by the U.S. Air Force Advanced Power and Technology Office, a horizontally-positioned KC-135 Strtotanker windshield wiper blade, shown at left, had more aerodynamic drag than one left vertically, at right, on the windshield. Photo by U.S. Air Force

Using planes at Rickenbacker Air National Guard Base in Ohio, computational fluid dynamics tests indicated that less drag was evident if the wiper blades remained to the side, and not below, the windshields. Data indicated a drag reduction of 0.8 percent on planes with repositioned wiper blades, and another 0.2 percent with a newly designed, slimmer wiper design.

"This is a significant milestone for us," said Ed Clark of the APTO program. "Over several months, we performed thousands of flight configurations during CFD testing to prove efficiency gains on the KC-135."

Another phase of design refinement is planned for the summer of 2020, and the APTO team has partnered with Delta Airlines to assess the possibility of vertical wipers on Delta's fleet of Boeing 767 planes.

RELATED Transportation Command head questions Air Force's plan for refueler upgrades

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