Engineers Develop Nature-Inspired Drones with Four Wings That Flap

Engineers from the University of South Australia have successfully developed four-winged bird-like drones, called ornithopters. The engineers were able to make these drones take off and fly with the agility of hummingbirds and insects by reverse engineering the aerodynamics and biomechanics of the two creatures.

Ornithopters are flying robots inspired by birds. They operate by flapping their wings to generate forward thrust, unlike existing drone configurations that rely on propellers and static wings. The engineers said that their invention could outperform and outmaneuver these existing drones.

The relationship between the way birds flap their wings and aerodynamics allows them to fly and move in ways that are impossible for conventional drones.

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What can ornithopters do?

Unlike the existing drones, ornithopters can glide, hover, and perform aerobatics. By flying like an airplane or by hovering, ornithopters can save their energy. They can land safely in tight space but can quickly soar upwards to perch like a bird.

Existing multirotor drones can also hover but use a considerable amount of energy. They use even more energy in forward flight, which disables them from traveling far. At the same time, fixed-wing drones may not hover without compromising the entire design, although they can travel efficiently at high speeds.

Moreover, hybrid concepts of drones that are usually equipped with wings and rotors perform poorly with hovering and cruising because of its additional weight from having more parts than other drones.

The engineers thought that flapping wings are nature's answer to the limitations of most drones. It will allow the drones to fly at a desired rate and execute a perfect takeoff and landing. For birds and insects, every part of them is used for hovering and cruising, without any redundant or unnecessary components.

It seems that existing fixed-wing and rotor-wing drones have come to their limit. Any additional features will only come at a cost to its performance.

The engineers said that their invention, ornithopters, are capable of complex missions impossible for conventional aircraft, like flying from distances, hovering, and maneuvering in tight spaces.

Additionally, ornithopters are less noisy and are safer to use because they have a large wing area with slow wing beats.

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The Mechanism Behind the Ornithopter

The ornithopter developed by Australian engineers is not the first flapping drones invented. However, most of those are slow-flying drones and cannot increase its speed and power required for vertical flying or sustained hovering.

The design made by these engineers differ from those as the wings of the ornithopters can "clap and fling." The two pairs of wings clap as they meet, making enough forward thrust for takeoff.

They also improved its efficiency by tuning the wing and body hinge to store and recover energy when the wings move in a different direction. To avoid any loss of energy, the engineers added minute bearings and rearranging shafts in the transmission to maintain the space of the gears.

The ornithopters' tails comprise a rudder and elevator that creates a lot of turning force, allowing the aggressive aerobatic maneuvers. This drone is designed to be able to pitch-up, which rapidly increases its angle of attack wherein the wing does not generate lift, an event called "dynamic stall."

Dynamic stall is undesirable in many drones as it creates a lot of drag in turning the wing into a parachute. But its ability to enter this state and quickly recovers adds to its unique maneuverability, which can be useful in cluttered surroundings or landing on a perch.

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