Birds are the undisputed masters of aerodynamics.
The airborne cacophony of a huge flock of geese, honking away while flying in a perfect “V” formation, is a wonder to see and hear.
Those formations have also provided the inspiration for researchers at Airbus UpNext, the aircraft manufacturer’s future-flight demonstration and technology incubator.
Initial flight testing with two A350s began in March 2020.
The program will be expanded next year to include the involvement of Frenchbee and SAS airlines, along with air traffic control and air navigation service providers from France, the UK, and Europe.
“It’s very, very different from what the military would call formation flight, it’s really nothing to do with close formation,” Dr Sandra Schaeffer, CEO of Airbus UpNext, said.
An aircraft in flight sheds a core of rotating air from the end of its wings, known as a “wingtip vortex.”
Extremely powerful vortices, especially those generated by a large aircraft, have been known to flip smaller planes that have encountered the horizontal tornado of air streaming behind.
“Pilots are trained to not fly into the vortex of a preceding aircraft,” Ms Schaeffer said.
“They will be 1.5 to 2 nautical miles (2.8 to 3.7 kilometres) away from the leading aircraft, and slightly offset, which means they are on the side of the vortex.
“It’s no longer the vortex, it’s the smooth current of rotating air which is next to the vortex, and we use the updraft of this air.”
Taking advantage of the free lift in this updraft of air is called “wake-energy retrieval.”
Ms Schaeffer says that upcoming flight trials using two A350s could prove that on long-haul flights, fuel savings of between 5 and 10 per cent may be achieved.
“This is the reason why we want to accelerate it. It is not a product today, but it is something we strongly believe in,” she said.
While it may seem simple to just watch a flock of birds to figure out the aerodynamics of their energy-saving flight, it really isn’t.
However, Dr Bishop cited a landmark 2001 paper in weekly international journal Nature by Henri Weimerskirch, where the researcher and his team had access to tame pelicans, known in the birding community as the best at formation flight, even better than geese or swans.
“Their study is technically the only one that shows direct evidence of energetic advantage rather than theoretical calculations in aerodynamics.”
Mr Weimerskirch was able to put heart rate monitors on the birds, and according to Dr Bishop, the trailing pelicans in the formation clearly saved energy.
“They had a 14 per cent drop in heart rate, and they also glided more. They were finding it easy [to fly] with this aerodynamic advantage.”
Just like the pelicans, the pilots of the trailing A350 in the fello’fly test will position the aircraft to optimise the effect of the upwash, but that points to one of the challenges facing the research team.
“You can’t see the wake, so you just can’t say ‘Ah, I’m in the right spot,'” Ms Schaeffer said.
“We need to provide assistance to the pilot to position the aircraft properly.”
Once in the upwash, auto flight systems will be required to maintain the correct position, reducing the workload on the pilots and ensuring a smooth ride for passengers by avoiding the more turbulent components of the wake.
Procedures to enable the two aircraft to coordinate their position will be tested much like during an aerial refuelling mission.
“We need to make sure we can do the joining safely. We will have no compromise on safety, whatsoever,” Ms Schaeffer said.
Once the wake energy retrieval concept is proven out, operational and financial considerations will still have to be solved.
According to Ms Schaeffer, air traffic service providers and government aviation agencies will need to be convinced to change regulations to allow for much closer aircraft separation standards than what are currently in place.
And a process to share the savings in fuel costs amongst airlines will be a priority.
“We know there are questions. Our aim as a demonstrator is to find answers to those questions.”