Taking their cues from the birds, Airbus engineers have flown a scale-model airplane that incorporates flapping wing-tips. Based on the structure of the albatross wing, the remote-controlled AlbatrossOne uses a "semi-aeroelastic hinge" concept that reacts to turbulence and wind gusts to minimize their effects and reduce stress on the airframe.
If you watch old newsreels online, sooner or later you're bound to come across clips of some inventor showing off an ornithopter – an airplane that flies by flapping its wings like a bird. What makes these grainy, black and white films so funny is that as the machine gyrates like a demented crow trying to take off, it remains stuck firmly to the ground until it shakes itself to bits.
But imitating the birds isn't that daft an idea. Leonardo Da Vinci's early plans for a flying machine were based on his observations of the birds, and modern engineers are still very interested in taking some tips from our feathered friends.
For example, the Airbus semi-aeroelastic hinge takes its inspiration not from the wild flapping of the crow, but the graceful soaring of the sea albatross, which can fly for thousands of miles without flapping its wings. The albatross doesn't get tired because it can lock its wing bones in place and then unlock them when it runs into a wind gust or wants to do come maneuvering.
The semi-automatic hinge does something similar. Airbus says the folding wing is nothing new – aircraft carriers are full of aircraft equipped with them – but the Airbus demonstrator has freely-flapping wings that can lock and unlock in flight as air conditions change.
The demonstrator is a scaled down version of an Airbus A31 aircraft that's made out of carbon composites and glass-reinforced resins. It was developed over a 20-month period at Filton, South Gloucestershire, England, the home of the famous Concorde SST and is billed as the "first Filton aircraft since Concorde."
According to Airbus engineer Tom Wilson, the flapping section extends along a third of the length of the wing and is designed to react autonomously to in-flight turbulence and lessen the load on the wing at its base. This is a great weight savings because it means that the airframe doesn't need the heavily reinforced wing boxes that prevent the wings from being too stressed where they meet the fuselage.
The first test flights that concluded in February 2019 took place with the wings fully locked or unlocked from takeoff to landing. The next phase will involve unlocking the wings in flight to study the transition.
"[This is] how nature can inspire us," says Jean-Brice Dumont, Airbus' Executive Vice-President of Engineering. "When there is a wind gust or turbulence, the wing of a conventional aircraft transmits huge loads to the fuselage, so the base of the wing must be heavily strengthened, adding weight to the aircraft. Allowing the wing-tips to react and flex to gusts reduces the loads and allows us to make lighter and longer wings – the longer the wing, the less drag it creates up to an optimum, so there are potentially more fuel efficiencies to exploit."
The project results were presented last week at the International Forum on Aeroelasticity and Structural Dynamics conference in Savannah, Georgia.
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