By Kathleen Bangs
Geese Inspire New Airbus Formation Flying Technology
Few aerial sights are as majestic as a V-formation of Canadian geese honking overhead against a blazing autumn sunset.
The last time geese and Airbus made airline history together was when the big migratory birds got sucked into Captain Sully’s Airbus A320 engines over New York City, 208 seconds before his famed landing on the Hudson. That was 2009.
Coincidentally that same year, a group of doctoral Stanford University students entered an Airbus “Fly Your Ideas” contest, an international competition searching new concepts to make commercial aviation more environmentally responsible.
The Stanford team’s pitch was simplicity gleaned from nature: if airlines mimicked the V-formation flying technique of geese, they could save fuel. And beyond reducing fuel costs, also decrease carbon emissions. Decades earlier, scientists learned that birds flying in formation exerted less energy. Similar to humans trudging through snow, the person breaking trail has to use substantially more energy than the followers in their footsteps. Heart monitors strapped to migrating birds showed those flying at the back of the V had slower heart rates than those at the front, and flapped their wings less often, using up less critical energy on long migrations.
Although Stanford’s team didn’t win the contest, Airbus liked their geese idea. So much that eventually, Airbus launched the fello‘fly demonstrator program, hosted within UpNext, their innovation subsidiary created to fast-track future technological breakthroughs.
On Nov. 9, Airbus departed two state-of-the-art Airbus A350s test jets from Toulouse, France. Once airborne the duo commenced a rendezvous, then maneuvered into a tandem position and crossed the Atlantic in formation flight, before landing in Montreal. The event was the first long-haul demonstration of formation flight in regulated transatlantic airspace. The two airliners, flying approximately 1.5 nautical miles apart, were called leader MSN1 and follower MSN59.
So, how does formation flight for airliners work? Geese conserve energy by “surfing” the invisible upwash of smooth air from the flapping wings of the birds ahead. A technique known as wake energy retrieval (WER) allows a trailing aircraft to take advantage of the rotating vortices left behind a lead jet’s wing and retrieve its lost kinetic energy by surfing the invisible air upwash. This upwash enables the following aircraft to benefit from a little free lift.
WER commences once the two jets are separated longitudinally by 1.5-2 nautical miles, and 1,000 feet in altitude. The magnitude of the effect from the updraft varies with the lead aircraft’s weight and wingspan, so aircraft selection plays a significant role. To remain in level flight, the trailing aircraft flies at a pitch-down attitude, descending relative to the upward moving air, tilting the normally vertical lift vector slightly forward. The reduction in drag translates to a reduction in fuel burn.
What did the Airbus trans-oceanic demonstration flights prove? That the long-haul formation concept was feasible, safe, and as predicted – reduced fuel burn and carbon emissions from the trailing jet. Over 6 tons of CO2 emissions were saved on the trip, confirming the potential for more than a 5% fuel savings. Formations are still viable even if the aircraft depart from separate airports, as long as they are within 50 nautical miles of each other.
Yet to many, the very idea of flying in or near vortexes sounds counterintuitive. Or dangerous. Pilots view wingtip vortices and wake turbulence as hazards to avoid, and with good reason.
In 2017 a Bombardier Challenger 604 business jet over the Arabian Sea encountered the wake of an Emirates Airlines Airbus 380, flying overhead in the opposite direction. The two jets were separated vertically by 1,000 ft. As the Challenger got caught in the wake, the business jet rolled to the left multiple times, plummeting 9,000 ft., and pulling a minus 3.2 negative G load in the chaos. Two passengers were badly injured, and the aircraft was later written off as a loss. At the time of the wake encounter, the two aircraft were estimated to already be fifteen miles apart.
To enable close in-trail flight, Airbus developed a flight control system that positions the follower aircraft safely in the wake updraft of the leader and keeps the two jets connected and communicating. A ‘sweet spot’ lateral distance must also be maintained as the updraft intensity diminishes the further the trailing jet moves sideways away from the vortices.
Daniel Percy, fello’fly Product Development Director, told Airline Geeks that Airbus test pilots relied on the autoflight system to perform the tasks required for a safe tandem flight. “The two demonstration flights we completed recently have shown that this new technology is capable of doing everything, from preparing the rendezvous, to identifying and then tracking the wake updraft, and also to keeping the aircraft safely positioned in the updraft no matter the weather conditions or leader behavior.”
The visionary project will require strict protocols to assure the airlines and their passengers that the formation flights can be conducted safely. Initially, there could be pushback from industry organizations ranging from flight crew unions to passenger groups, but every great aerospace leap forward has had its detractors. From the first passenger flight to the moon landing. It will be exciting to experience V-flight technology if in the future it becomes mainstream.
To earn the eventual trust of the traveling public, perhaps cargo carriers could be the first adopters of the new technology. But Airbus’ Percy reports that a fully automated formation flight is designed to ensure no impact on comfort, adding that “the findings from our test flights so far have been that there is no difference compared to the cruise phase of a normal flight.” If widely adopted, Airbus predicts fello’fly could eliminate at least 3.5 million tons of CO2 emissions annually. Next steps are to gain widespread industry support so that the new operational concept can be certified.
Bird flight research showed that flying in formation isn’t just about staying in the right place. It also involves wing movements at just the right time, as each trailing bird adjusts their own flapping to stay within the moving zone of free lift. Makes one wonder if someday beyond two jets in tandem, we’ll see entire fleets in formation like flocks of geese, conserving energy for their long-haul journeys across the sky.