1 More power is not always the answer
Unmanned aerial vehicles (UAVs) have become increasingly capable systems. Modern drones can hover, navigate autonomously, inspect infrastructure, collect environmental data, and operate in environments that would be difficult or dangerous for humans (Ahmed et al. 2022). However, extending endurance, increasing payload capacity, and improving flight performance often place greater demands on onboard energy storage and propulsion systems. More demanding missions may therefore require greater battery capacity and propulsive capability, potentially increasing vehicle mass and structural requirements (Ahmed et al. 2022; Ariante and Del Core 2025).
This approach is effective, but it also involves important trade-offs. For a given battery technology, increasing battery capacity generally increases vehicle mass, which can in turn increase the power required to sustain flight. Therefore, energy availability and flight endurance remain important limitations for small aerial vehicles (Ahmed et al. 2022; Ariante and Del Core 2025).
Biological flight suggests that another approach is possible. Rather than producing every required force through continuous mechanical power, natural systems often exploit morphology, elasticity, gravity, and interactions with the surrounding fluid. Bioinspired flight research seeks to translate such biological principles into engineered aerial systems (Han et al. 2021). Bioinspiration therefore raises a different engineering question: how much of the desired behaviour can be obtained from the physical design of the vehicle before additional power and control are introduced?
Gliding mammals provide an interesting example of this principle. Extant gliding mammals can be broadly organized into four major groups: flying squirrels, colugos, marsupial gliders, and scaly-tailed squirrels (Jackson and Schouten 2012; Byrnes and Spence 2011). These groups comprise several distinct evolutionary lineages in which gliding evolved independently multiple times (Byrnes and Spence 2011). Despite their separate evolutionary origins, they have converged on specialized anatomical structures, most notably deployable skin membranes known as patagia, which transform their bodies into controllable aerodynamic surfaces. Representative examples of the four groups are shown in Figure 1. Their solutions are not miniature versions of conventional aircraft wings. Instead, the body, limbs, membranes, tail, and supporting structures operate together as an integrated flight system.
The aerodynamic function of these membranes depends not only on their surface area but also on their ability to change shape during flight. Extension of the limbs deploys and tensions the patagium, increasing the effective lifting area, while adjustments in limb position and body posture modify membrane geometry and therefore the aerodynamic forces acting on the animal. Experimental studies of flying squirrels have shown that the deployed patagium generates substantial aerodynamic forces and that changes in body configuration can contribute to pitch control (Bahlman et al. 2013; Zhao et al. 2019).
The analogy with aircraft should nevertheless be considered carefully. Biological gliding is not energetically ``free’’, since animals generally need to gain altitude before initiating a glide, and the energetic benefit varies with species, body size, locomotor strategy, and ecological context. Northern flying squirrels, for example, have been estimated to achieve substantial energetic savings compared with quadrupedal terrestrial locomotion, whereas the energetic balance can differ in larger gliding mammals (Flaherty et al. 2010; Byrnes and Spence 2011). The engineering lesson is therefore not that gliding eliminates energy consumption, but rather that passive aerodynamic phases can reduce the duration for which active propulsion is required.
2 What can engineers learn from gliding mammals?
The most useful form of biomimicry is not necessarily literal imitation. A UAV does not need to resemble a flying squirrel visually in order to learn from one. What matters is identifying functional principles and determining whether they solve an engineering problem.
One such principle is deployability. The aerodynamic surface of a gliding mammal becomes effective when the limbs extend and tension the patagium. A technological analogue could be a UAV whose lifting area changes between compact and deployed configurations. Such a vehicle might remain compact during storage, launch, or powered manoeuvres and deploy a larger lifting surface when entering an efficient gliding phase.
A second principle is compliance. Biological membranes are flexible structures rather than perfectly rigid wings. Their geometry can respond to aerodynamic loading, while local skeletal or cartilaginous elements provide support and tension. Flying squirrels, for example, possess specialized structures near the wrist that support the outer region of the patagium (Jackson and Schouten 2012). Rather than reproducing this anatomy directly, engineers can ask whether flexible membranes combined with strategically placed stiffening elements could offer useful combinations of low mass, deployability, and aerodynamic adaptability.
A third principle is morphological control. Animals can alter aerodynamic behaviour by changing limb configuration, membrane tension, body orientation, or tail position. Existing flying-squirrel-inspired robots already illustrate how such concepts may be translated into technology (Figure 2). Researchers have developed multimodal robots using flexible membranes and articulated structures (Shin et al. 2019), flying-squirrel-inspired UAVs with controllable foldable wings (Lee et al. 2025b), and, more recently, the SquirrelDrone, which uses coordinated forelimb, hindlimb, and tail actuation together with a compliant membrane to achieve whole-body morphing (Zheng et al. 2026). These prototypes demonstrate that biological inspiration can influence not only external shape but also the architecture of actuation and control.
3 From biological specimens to engineering models
Identifying an interesting biological mechanism is only the beginning of biomimetic design. Engineers must transform a complex organism into measurable quantities, geometries, models, and ultimately design rules. This translation is particularly challenging for gliding mammals because their aerodynamic performance depends on membrane geometry, limb positions, and the interactions among these structures during flight (Zhao et al. 2019; Zheng et al. 2026).
As a first step in this research, we sought to reconstruct the three-dimensional geometry of different gliding-mammal species in order to characterize their morphology and study it quantitatively. Natural-history collections can play an important role in this process, as museum specimens preserve biological diversity that may be difficult to observe or measure directly in living animals. However, a preserved specimen is not immediately suitable as an aerodynamic model. Taxidermy preservation frequently resulted in partially retracted membranes and limb orientations that did not correspond to natural gliding postures (Thorington and Heaney 1981).
We therefore explored the use of non-invasive photogrammetry using specimens from the collections of the Muséum national d’Histoire naturelle (MNHN) in Paris, as an intermediate step between biological observation and engineering analysis. Each specimen was photographed from multiple viewpoints and digitally reconstructed as a three-dimensional surface. The resulting geometry was then cleaned and dimensionally calibrated before being further processed using digital rigging to approximate a natural gliding posture and reconstruct retracted membrane regions. The overall workflow is illustrated in Figure 3. At the current stage of the research, these three-dimensional models are being used as geometric inputs for aerodynamic analysis and computational fluid dynamics (CFD).
This approach illustrates a broader opportunity for interaction between natural history and engineering. Biological collections need not be considered only as archives of the past; with appropriate digital methods, they can also become sources of quantitative information for the development of future bioinspired technologies.
4 Conclusion: from copying forms to learning strategies
The promise of passive flight naturally connects biomimicry with discussions of energy-efficient technology. A UAV capable of alternating between powered and unpowered flight could, for suitable missions, reduce the use of active propulsion during portions of the flight. Unpowered gliding phases could also reduce propulsion-related noise, which may be advantageous for environmental observation or operation near noise-sensitive areas. Low-speed manoeuvrability and deployable surfaces could be valuable in forests, rugged terrain, or other cluttered environments where conventional fixed-wing aircraft are less appropriate.
Gliding mammals demonstrate that controlled aerial locomotion can emerge from a strong coupling between morphology and aerodynamics. Their deployable membranes, compliant structures, limb-mediated shape changes, and integrated control strategies offer a design space that remains relatively unexplored in aerial robotics.
The objective of biomimetic engineering should not be to construct mechanical replicas of animals. It should be to understand why a biological structure works, identify the physical principle behind it, and determine whether that principle can be translated responsibly into technology.
For future UAVs, this perspective suggests complementing the traditional question; how much power is required to achieve the desired performance?, with another: how much of that performance can first be achieved through morphology?
The answer may lead not only to new deployable-wing aircraft, but also to a broader way of thinking about engineering systems in which structure, aerodynamics, and control are designed together rather than treated as separate problems.
References
Citation
@online{yassir_laalej2026,
author = {Yassir Laalej, Mohamed},
title = {Learning from {Gliding} {Mammals:} {Toward} {Quieter} and
{More} {Energy-Efficient} {Aerial} {Robotics}},
date = {2026-05-13},
url = {https://www.cytopia.fr/cycles/2026/bio/conferences/bio-1/topics/learning_gliding_mammals/article.html},
langid = {en-US}
}