When the Air Force upgraded the engines for its KC-135 aerial refueling tanker, it was able to achieve energy savings in a way it didn’t originally envision.
Robert Guerrero, the Air Force’s new deputy assistant secretary for energy, said Wednesday the increased efficiency of the CFM-56 turbofan engines allowed the KC-135 to increase its landing weight. Guerrero said the landing weight restriction for KC-135s was not based off the landing gear or brakes, but off the “controllability” of the aircraft on approach.
The Air Force, Guerrero said, had a problem when KC-135 missions changed mid-flight and the tankers were required to dump fuel to land. The increased efficiency of the CFM-56 engines, Guerrero said, increased the landing weight of the KC-135 by about 35,000 pounds, allowing the tankers to land without dumping fuel.
“That’s another area that was a new technology that had a second or third order effect on the mission that wasn’t realized initially,” Guerrero told an audience at an Air Force Association (AFA) breakfast in Arlington, Va. “By implementing these new procedures, we’re looking at about a $4 million savings per year, just in that one airframe, in those situations where they (previously had) to dump fuel.”
Of the original KC-135As, more than 415 have been modified with new CFM-56 engines produced by CFM International, according to the Air Force. The re-engined tanker, designated either the KC-135R or the KC-135T, is 25 percent more fuel efficient and costs 25 percent less to operate than the original KC-135A, which featured Pratt & Whitney’s TF33 engine.
Between 1982 and 2001, the Air Force re-engined 444 KC-135s, according to prime contractor Boeing [BA]. The Air Force has 167 KC-135As in active duty, 180 with the Air National Guard and 67 with the Air Force Reserve.
Guerrero replaced Kevin Geiss in August as the Air Force’s energy czar. Geiss is now director of the human effectiveness directorate, 711th Human Performance Wing, of the Air Force Research Laboratory (AFRL) at Wright-Patterson AFB, Ohio. Guerrero was previously staff director for Headquarters Air Force Reserve Command at Robins AFB, Ga. His roots are in naval aviation.
Guerrero said the Air Force won’t be purchasing alternative fuels for use in its aircraft in the near future until they meet a satisfactory price point. The Air Force spent a substantial amount of money over the years developing alternative fuels and biofuels that can be “dropped-in,” or used in any Air Force jet, without modifying engines for use.
The service ended alternative fuel certification efforts in mid-2013 after affirming that the Alcohol-to-Jet (ATJ) biofuel was a viable alternative to power the service’s aircraft. ATJ, developed by Gevo [GEVO], is cellulosic-based fuel derived from material like wood, paper or grass. The Defense Logistics Agency (DLA) in December 2012 bought 45,000 gallons of ATJ at a price of $59/gallon. Traditional jet fuel, known as JP-8, costs $3.70/gallon, DLA said Wednesday.
“We’re a consumer…our expertise is…not in the producing of alternate and biofuels,” Guerrero said. “Once they meet the price point where it is equivalent to the other things we can get in the market, we’ll be actively involved in it.”
The Air Force had a goal of being ready to use an alternate fuel blend by 2016 (Defense Daily; Oct. 24, 2013).