The beetle rhinoceros beetle is commonly known as the "one-horned fairy". It possesses two pairs of wings – a pair of thick elytra, which serve as forewings; and a pair of film-like hindwings that can be folded like origami.
Beetles have the most complex flapping and retraction mechanisms of any insect.
On the evening of July 31, Beijing time, a new study published online in the international academic journal Nature (Nature) unraveled the mystery of the beetle "unicorn" rhino beetle, and inspired people to improve the ornithopter.
Compared with fixed-wing or rotary-wing aircraft, ornithopters have the advantages of higher flight efficiency, strong concealment, strong maneuverability and strong adaptability. The wings of an ornithopter flutter up and down like the wings of a bird or an insect, allowing them to be adjusted at the right time.
Over the past decade, scientists have developed a variety of flapping wing robots that mimic insects, but none of them have been able to retract their wings in the same way that insects do—to retract their soft, strong wings when they collide or rest. These robots all use fully extended, flapping wings.
00:11
A beetle with flapping wings. (00:11)
Hoang-Vu Phan, a researcher from the Ecole Polytechnique Fédérale de Lausanne in Switzerland, and his colleagues used a high-speed camera to film and analyze the process of flapping and retracting the wings of the rhino turtle.
They applied their latest findings to the design of a miniature ornithopter, which achieved rapid wing closure in 100 milliseconds, while allowing it to release the wing in a single flapping cycle at various frequencies.
Hoang-Vu Phan told The Paper that the tiny flapping wing robot can be used in small spaces that humans can't access, such as carrying out search and rescue missions in collapsed buildings. In this case, the flapping wing robot can fold and store its fragile wings on the body after flight, which facilitates movement in tight spaces and also reduces the risk of damage. It can also help biologists study the flight mechanics of insects and explore the wild behavior of insects in forests. This is not possible with conventional rotary-wing UAVs.
A miniature ornithopter that can quickly close the wings.
Birds and bats have well-developed pectoral muscles and other flying muscles, so they can stretch their wings and wings when flying, and when they are resting, they retract their wings and wings so that they attach to their bodies. Although insects can also flap and retract their wings in this way, the details of their mechanism have always been mysterious.
When the beetle flies, it needs to raise its elytra first, and then unfold its relatively "bulky" hindwings, and mainly rely on flapping its hindwings to provide flight power and achieve flight actions such as taking off and hovering. When stopped, one of its hind wings is able to fold and hide under its elytra.
Hoang-Vu Phan and colleagues found that the beetle goes through two processes to unfold its wings, in which muscle control is required to complete its hindwing movements.
They found that the release and unfolding of the beetle's hind wings were passive, as was its folding and retracting. In the absence of elytra, its hindwings remain elevated. Thus, at the first stage, when the beetle opens its elytra, its hindwings become, like springs, partially pop open, exhibiting the characteristics of an under-damped spring-mass system.
The researchers found that the beetle's hind wings only unfold when they start flapping. That is, in the second stage, while the beetle flapps its hindwings, the base of the hindwings is raised, the wingtips are expanded, and it enters the state of flight.
Whereas, the beetle retracts its hind wings and needs the push of its elytra to push one leading edge against the other. To verify this, Hoang-Vu Phan and colleagues removed one of the beetle's elytra and found that the beetle could not retract its hindwings without elytra.
Until now, little was known about how the beetle's hindwings were raised to a flying position and folded again. It has been suggested that the beetle's thoracic muscles drive the movement of the base of its hindwings, but experimental evidence to support this theory is lacking. Newly published evidence suggests that the release of its hindwings is related to elytra, whose folding is driven by elytra.
Inspired by these observations, researchers such as Hoang-Vu Phan created a microrobot that mimicked the passive unfolding and retracting of a beetle's wings, and the robot successfully took off and maintained flight.
Hoang-Vu Phan said in an interview with The Paper that the "armpits" of the microrobot's wings are equipped with elastic tendons that replace the elytra of the beetle to facilitate its rapid closure of the wing within 100 milliseconds. Not only does this make the robots more like insects, but it also allows them to passively spread their wings during takeoff, hover steadily, and quickly retract their wings on landing or in the event of a collision in flight, without the need for additional devices.