U-M Aerospace Engineering PhD candidate Christina Harvey investigates how gliding birds stack up to UAVs

Researchers have been studying gliding birds and designing fixed-wing aircraft for over a century, but little has been done to directly compare the two, resulting in some misconceptions. A new comprehensive review is the first to draw together and analyze data from various studies about the efficiency of gliding birds compared to those of Unmanned Aerial Vehicles (UAVs) and has revealed some surprising results. The article accepted for publication in Bioinspiration & Biomimetics surveyed all theoretical and experimental estimates of avian aerodynamic efficiency and investigated the uncertainty associated with each estimation method to allow for a better like-for-like comparison. Remarkably, the researchers discovered that there is no evidence that birds are more efficient gliders than current UAVs.

“Birds have inspired many aircraft designs since the beginning of aviation,” says Harvey. “However, we are improving our ability to quantify how good of fliers birds actually are. The goal of this paper was to establish if gliding birds are actually more aerodynamically efficient than our comparable small aircraft or if our manmade techniques have actually been able to keep up or even improve on the birds’. The thing that I found the most surprising is that, within the academic literature there currently isn’t any evidence that large gliding birds are more efficient than comparable UAVs. Especially since there is a pervasive belief in the general public that birds are superior gliders.”

The researchers stressed that this is not an indication that there is no bird that could outperform the best modern UAVs while gliding but, if so, the efficiency of such a bird has not yet been quantitatively documented in the academic literature. “We found that further experimental or improved theoretical and numerical studies will be necessary to document the efficiency of some birds expected to be highly efficient, such as an albatross.” 

But, the study did find an alternative way that some birds outperform UAVs. “Interestingly there are very few UAVs that are on the same scale as a small bird like a swift or jackdaw,” says Harvey.

I believe these smaller birds could inspire future UAV designs that might extend the capabilities of our manmade aircraft to operate on a smaller scale.

Christina Harvey

“Our study highlights how important it is for those who pursue bio-inspired designs to consider the findings and advancements from both biological and aeronautical studies.”

Harvey is the recipient of the Alexander Graham Bell Canada Graduate Scholarship and the Francois Xavier-Bagnoud Fellowship. She is a member of the American Institute of Aeronautics and Astronautics (AIAA) and the Society for Integrative and Comparative Biology (SICB).

The paper will be published in 2021.