Optimal Materials for a Robotic Bat/Bird Hybrid Wing

Athilesh Thanigai
Thomas Jefferson High School for Science and Technology

This article was originally included in the 2019 print publication of the Teknos Science Journal.

The wonder of animal flight is the epitome of the animal kingdom’s magic. Though we humans became airborne over a century ago, our heavy, cumbersome machines are only crude imitations of nature’s gift. Flapping flight had been majorly unexplored or unsuccessful until the past decade, with small machines now able to perform primitive flight [2]. Flapping wing vehicles (FWVs) are currently on the border between fiction and reality now that several universities and private-sector groups have developed varying degrees of successful designs. The need for FWVs relates mainly to military and surveillance purposes, but if research continues well into the future, this technology may largely impact the transportation industry itself [3]. Some examples that could soon become a reality include sports cameras, mail delivery drones, and racing sports. To understand why an FWV would be useful, it is necessary to understand how traditional flying vehicles work.

The basic principles of fluid mechanics can be easily understood. Since air is a compressible fluid, the laws of pressure dictate that air velocity and pressure are inversely related.. This means that a plane wing will be kept aloft as long as the air above the wing moves sufficiently faster than the air under the wing. This principle requires the design of the vehicle to focus on achieving and maintaining high speed, because, like a bicycle, if the vehicle is too slow, it will stall and fall. On the other hand, FWVs can stay aloft with a flapping rate of roughly 1-10 Hz (flaps per second), which is relatively slow [8]. This is useful because it is a much lower rate of energy consumption. Another benefit is that while standard vehicles lose maneuverability at such high speeds, FWVs can effortlessly about-face in midair due to a slower speed and more organic structure.

I am currently working on building my own FWV through the Engineering Design senior research lab with guidance from lab director Mr. Michael Piccione. My project seeks to identify and test materials to make a light but strong model of flapping animal flight that can generate enough power to lift its own weight, and the resources of this lab include the software and hardware necessary to produce a functioning FWV. The models that have been reasonably successful thus far have been incredibly expensive to build and not necessarily durable, open to public use, or commercially available [6]. However, through my research, I hope to lead the way towards changing these drawbacks.

Bird wings and bat wings work in largely different ways, but I plan on developing a bat/bird hybrid model to incorporate the unique advantages of both species into my design. While bird wings mainly achieve lift with the use of large and powerful wings, their key benefit comes from the use of feathers, which are simply biological check valves [7]. Though I look to integrate the concept of a large and powerful wing with a slow wing, it is unlikely that I will have the resources to develop artificial feathers. On the other hand, the structure of bat wings is more similar to a human hand than a forearm. The individual fingers are long and spindly. They are each able to move independently, which creates a smooth, cohesive scooping motion to achieve efficient and agile flight. The focus on the mobility of these joints is crucial to developing the proper flight patterns and allows for more efficient flight [4]. It will be difficult to figure out the optimal combination of characteristics of the two to create a successful product, but my plan is to develop a hybrid wing. A characteristic which both species share is an extended wing on the downstroke and a “collapsed” wing on the upstroke to reduce surface area. For my project, the main components to break down are wing geometry, flexibility, and motion, motion being the one I will dedicate most of my efforts to [1]. This is what Mr. Piccione recommended when trying to reduce stress on the wing joints: “Making the wing collapsible might help reduce the overall stresses on the upstroke if you can accurately control the collapsing with the timing of the strokes, but it could add complexity if you can’t make it sturdy enough” (M. Piccione, personal correspondence, Feb. 13, 2019).

This project mainly requires the use of computer-aided design, 3D printers, and other technological tools and procedures. First, I will design a model for the skeletal structure of the wing, incorporating the finger joints of the bat wing with the rigidity of a bird wing. After making the model, complete with separate pieces for each part and joints to connect them together, I will 3D print and assemble these materials. To test these pieces, I plan on using our in-lab wind tunnel to “test the cross-sections of [my] wing at various angles and in the collapsed state [to get] an indication as to where failure points might happen” (Piccione). Once I demonstrate the joints can move smoothly and have sufficient flexibility, I will wire up the electronics component. This will most likely require one of two methods. I can use a motor and gears to choreograph the entire motion, which is what most of the current models do. However, this method requires extensive resources and knowledge. The other method involves an ingenious creation aptly named “muscle wire,” which flexes and relaxes when a current is passed through the wire. Muscle wire has been used before on a smaller scale in an FWV, replicating the wings of a beetle [5]. Finally, when the electronics can move the physical model properly, I will develop a fabric for the wing cover that will act as the actual skin to push and pull the air around it.

I have been working on this project for several months now, and after finishing a review of literature, I have also finalized the model joints along with the 3D printer and material I will be using. I will begin the electronics component planning and combine several rough wing skeletons to create the final design. Though I hope to end up with a pair of flapping wings attached to a stationary body that will succeed in flying, my more realistic and relevant goal is approximating the flight motion of a hypothetical bat/bird hybrid as accurately as possible. I will focus on finding the optimal material for parts, such as the type of sheet to use for the wing’s “skin,” plastic for 3D printing the “bones,” etc.

Modern planes fly twenty times as fast as the Wright Brothers did in 1903, and sufficient research into building an FWV that can independently support its own weight will lead to similar advances in the future.

References

[1] Altenbuchner, C., & Hubbard, J. E., Jr. (2018). Modern flexible multi-body dynamics modeling methodology for flapping wing vehicles. https://doi.org/10.1016/B978-0-12-814136-6.01001-5

[2] Dvorak, R. (2016). Aerodynamics of bird flight. EPJ Web of Conferences, 114(01001). http://doi.org/10.1051/epjconf/201611401001

[3] Jankauski, M., Guo, Z., & Shen, I. Y. (2018). The effect of structural deformation on flapping wing energetics. Journal of Sound and Vibration, 429, 176-192. https://doi.org/10.1016/j.jsv.2018.05.005

[4] Li, G., Law, Y. Z., & Jaiman, R. K. (2018). A novel 3D variational aeroelastic framework for flexible multibody dynamics: Application to bat-like flapping dynamics. Computers & Fluids. https://doi.org/10.1016/j.compfluid.2018.11.013

[5] Muhammad, A., Nguyen, Q. V., Park, H. C., Hwang, D. Y., Byun, D., & Goo, N. S. (2010). Improvement of artificial foldable wing models by mimicking the unfolding/folding mechanism of a beetle hind wing. Journal of Bionic Engineering, 7(2), 134-141. https://doi.org/10.1016/S1672-6529(09)60185-2

[6] Robotics; advanced robotic bat's flight characteristics simulates the real thing. (2017, February 19). Retrieved from ProQuest Databases.

[7] SmarterEveryDay. (2012, October 6). How bird wings work (compared to airplane wings) - Smarter Every Day 62 [Video file]. Retrieved from https://youtu.be/4jKokxPRtck

[8] Yu, Y., & Guan, Z. (2015). Learning from bat: Aerodynamics of actively morphing wing. Theoretical and Applied Mechanics Letters, 5(1), 13-15. https://doi.org/10.1016/j.taml.2015.01.009