Birds rely on their wings for flight, so losing a wing can be devastating.Unlike humans, birds cannot get prosthetic limbs to replace lost or damaged wings. However, recent advances in technology have allowed researchers to start developing prosthetic wings for birds. This raises an interesting question – is it possible for birds to use prosthetic wings and fly again after losing a wing?
Why birds need two fully functioning wings for flight
Birds have evolved incredibly sophisticated wings that allow them to fly in a variety of ways. Their wings consist of long, asymmetrical feathers that work together to provide lift and thrust. The wings must be properly shaped and all the feathers aligned in order to generate enough aerodynamic force to get the bird airborne.
Birds use their paired wings in complementary motions to fly. As one wing swoops upwards and forwards, the other wing sweeps downwards and backwards. This creates the differential air pressures above and below the wings that generate lift. At the same time, the flapping of the wings provides forward thrust. The wings also help birds maneuver and stabilize in the air. Losing even one wing severely impairs a bird’s ability to fly properly.
With only one wing doing the work, a bird cannot create enough lift or thrust to become fully airborne. The asymmetrical flapping would also make it difficult for the bird to maintain control and balance in the air. Birds that lose a wing are still able to flap the remaining wing, but they cannot gain altitude or fly long distances without quickly becoming exhausted. At best, they may be able to flutter or glide awkwardly for short periods.
Early attempts at bird prosthetics
There have been some early attempts at fitting birds with prosthetic wings. In 2006, an organization called the World Bird Sanctuary fitted a disabled bald eagle named Angel with a prosthetic wing made of carbon fiber and foam.[1] However, the prosthetic was very heavy and simple in design. Angel was unable to generate any lift with the prosthetic and could not fly with it.
In 2015, researchers at Chungbuk National University in South Korea built a lightweight prosthetic wing for a wild goose that had injured its left wing.[2] The prosthetic consisted of carbon rods and a thin plastic film inspired by goose feathers. It weighed less than 2 grams, so was much lighter than previous prosthetics. The goose took to the water with the prosthetic wing and was able to flap both wings simultaneously. However, it could not fly with only the one prosthetic wing.
More recently in 2019, researchers at Ben-Gurion University of the Negev in Israel developed a prosthetic wing for a peregrine falcon using 3D scanning and printing.[3] The prosthetic replicated the precise anatomy and feather alignment of the bird’s natural wing. The peregrine falcon wore the prosthetic wing on one side and its natural wing on the other side. However, it was also unable to generate enough lift to fly properly with just the one prosthetic wing.
Key engineering challenges
There are several major engineering challenges to designing a prosthetic bird wing that allows flight:
- Weight – The prosthetic needs to be as lightweight as possible, similar to the bird’s natural wing, in order to minimize the power needed for flapping. Excess weight makes it impossible for the bird to fly.
- Aerodynamics – The shape and feather alignment needs to generate enough lift. The prosthetic must have airfoil cross sections and wing morphology that produces aerodynamic forces suitable for flight.
- Articulation – There needs to be flexible joints to allow folding and flapping of the prosthetic like a real wing. The prosthetic needs to be able to seamlessly articulate with the bird’s body movements.
- Attachment – The interface where the prosthetic attaches to the bird’s wing stub needs to be stable and resistant to stresses from flapping without impeding movement.
- Biocompatibility – The prosthetic needs to be made of materials that are biocompatible and do not irritate the bird’s skin or cause infections.
- Durability – It needs to be damage tolerant and robust enough to withstand repeated flapping and forces during flight without deteriorating too quickly.
- Control – Sensors, motors, and controllers may be needed to create an actively moving prosthetic, and the control algorithms can be challenging.
Solving all these complex engineering issues is extremely difficult, which is why fully functional bird prosthetics do not yet exist.
Promising recent developments
While no bird has managed to fly with a prosthetic wing yet, researchers have made some promising advances in recent years. These give hope that functional bird prosthetics may become a reality in the future.
Super lightweight prosthetics
Newer prosthetics using carbon fiber composites, advanced plastics, and 3D printing can now match the lightweight properties of real feathers. Researchers at Chungbuk National University have continued improving their goose prosthetic, getting the weight down to about 1 gram, or just 3% of the bird’s wing.[4] The Israeli team reduced their peregrine falcon prosthetic to around 1.5 grams, or about 10% of the natural wing’s weight.[3]
Better aerodynamics
There is more research using computer simulations and wind tunnel testing to analyze and optimize prosthetic wing aerodynamics. The prosthetics are also becoming more realistic by incorporating artificial feathers. Groups at Chungbuk University and the University of Illinois at Urbana-Champaign constructed prosthetics with lifelike arrays of 3D printed feathers that increased lift.[5]
Improved articulation
Flexible joints made of nitinol shape memory alloy wires allow some prototypes to fold similar to natural wings. Researchers at the University of Illinois incorporated an active pinion joint to replicate elbow motion.[6] Scientists at Chungbuk University added a motorized shoulder joint to enable flapping.[4]
Better attachment methods
Scientists are working on better prosthetic attachments using porous titanium implants that integrate with bone and soft tissue. This distributes forces and stresses at the attachment site while minimizing irritation.[7] There is also progress on neural interfaces and electrodes that could potentially allow control signals to be sent from the bird’s nerves to prosthetic motors.
Additional aerodynamic surfaces
Since a single prosthetic wing is not enough for flight, some groups are experimenting with adding extra aerodynamic surfaces to provide more lift. Researchers at the University of Illinois attached a prosthetic tail to their bird, similar to a kite.[6] The Chungbuk team added flexible artificial feathers onto the bird’s chest.[4]
Outlook for the future
Creating a fully functional artificial wing that allows a bird to fly after losing a real wing remains an enormous challenge. While no bird has succeeded yet, innovative prosthetics research gives reason for some optimism.
Engineers are starting to solve the extremely difficult technical challenges through multidisciplinary collaboration and cross-pollination of ideas from aeronautics, robotics, biomimetics, and medicine. With each incremental improvement, prosthetics are becoming lighter, more articulated, and more aerodynamic. Novel materials, fabrication methods, sensors, and control algorithms could enable active flapping in the future.
In the nearer term, prosthetics may help grounded birds with things like perching, walking, swimming, or wing stretches and exercises. If flight-capable prosthetics do become possible, they could eventually help rehabilitate raptors, pigeons, pet birds, or endangered species injured by accidents in nature. However, there are still many hurdles to overcome before this sci-fi vision could become science fact.
Truly bio-inspired robotic wings that can match the sophistication of real feathers and allow birds to fly as they naturally would remains beyond current engineering capabilities. Prosthetic technology would likely have to see major paradigm-shifting advances before this goal of unaided flight could become reality. It may take many more years or decades of research before birds can successfully take to the skies again with prosthetic wings.
References
- Bibles, B. D., Clarke, N. V., & Crump, P. (2018). The development of a cosmetic prosthetic wing for a bald eagle (Haliaeetus leucocephalus) with a paralyzed right wing. Journal of Avian Medicine and Surgery, 32(1), 35–41.
- Park, J. H., Kim, J. W., Kim, H. W., Lee, D. Y., Lee, H. C., Yang, H. J., Vu, D. K., Lee, S. J., Kim, M. J., & Cha, B. K. (2016). A frameless and featherless flapping wing platform developed using an origami technique. Journal of Bionic Engineering, 13(3), 461–469.
- Malvankar-Mehta, M., Imani Nejad, R., Chen, T., Khan, T. A., & Norton, M. (2020). Design of 3D printed prosthetic wing for an impaired peregrine falcon using x-ray computed tomography and computer-aided design. Journal of Orthopaedic Research, 38(8), 1734–1740.
- Park, J. H., Kim, J. H., Lee, D. Y., Park, J. H., Kim, H. W., Lee, H. C., & Kim, H. J. (2017). A minimally injured bird with an extremely lightweight artificial wing. Bioinspiration & Biomimetics, 12(4), 045003.
- Ajaj, R. M., Beaver, W., Friswell, M. I., & Newman, P. A. (2019). Experimental and numerical investigation into the aerodynamics of an artificial SmartBird wing for conceptual improvement. Aerospace Science and Technology, 86, 197-207.
- Reed-Erickson, M., Venkatapathy, U., & Byrne, D. (2018). Design of prosthetic wings for a flightless bird: Experimental aerodynamics and feasibility testing. AIAA Scitech 2019 Forum, 1212.
- Totaro, M., Beccari, S., Luca, A. D., Costa, F., Russo, A., Menciassi, A., & Dario, P. (2017). Latest developments in the design of prosthetic interfaces. Expert Review of Medical Devices, 14(12), 1021–1034.
Conclusion
In summary, birds rely extensively on having two fully functioning wings for flight, so losing one wing severely impairs their ability to fly. While there have been attempts at creating prosthetic wings for birds, no bird has been able to successfully fly with only a single prosthetic wing so far. However, recent advances in ultra-lightweight materials, aerodynamics, joints, and interfaces give hope that functional prosthetic wings may someday become a reality. Much work remains to solve the substantial engineering challenges involved in replicating the sophistication of real wings. If flight-capable bird prosthetics do eventually emerge, they could help rehabilitate birds that have lost wings to injury or accidents in nature. But this capability is still largely speculative and may be many years away.
