USAF C-17s engage in ‘vortex surfing’ tests
Traveling in formation to take advantage of the vortex effect is not just for Tour de France riders or migrating birds. Soon USAF “birds” might also be flying in formation to take advantage of the same “vortex surfing” benefits, but in this case, it’s fuel savings on transoceanic flights resulting from the dragging effects provided.
“The concept, formally known as Surfing Aircraft Vortices for Energy, or $AVE, involves two or more aircraft flying together for a reduced drag effect like what you see with a flock of geese,” reported Air Mobility Command Chief Scientist Dr. Donald Erbschloe.
Recent vortex surfing flight tests involving one pair of C-17 aircraft at a time were conducted at Edwards AFB, last month and again earlier this month.
During the flight test series, the second of the two aircraft situated itself in the lead plane’s updraft, which provided extra lift to the trailing aircraft without requiring extra fuel burning. The aircraft in the test flights flew at longitudinal separations of at least 4,000, and modified C-17 formation flight software enabled autothrottle and autopilot systems to keep the trailing aircraft in the correct flight position “without active assistance from pilots.”
“The autopilot held the position extremely well – even close to the vortex,” according to Capt. Zachary Schaffer, who participated in a test flight. “The flight conditions were very safe; this was as hands-off as any current formation flying we do.”
Not all pilots had the same ride quality experience during the test flights, though, and some thought certain flight test points could be challenging when undertaking long-endurance flights.
“The key will be finding the right balance of quality for improving fuel efficiency and ride,” remarked Maj. Eric Bippert, who participated in a flight test.
Though savings in fuel consumption could reach an estimated level of up to 10 percent, the savings for Air Mobility Command’s 80,000 flights per year could be millions of dollars.
The flight tests are the result of collaborative efforts of NASA Dryden Flight Research Center, the AFRL, the Air Force Life Cycle Management Center, Air Mobility Command, The Boeing Company, DARPA, and the 412th Test Wing.