We have developed four-winged bird-like robots, called ornithopters, that can fly with the agility of swans, sparrows and insects. We did the aerodynamics and biomechanics of these creatures by reverse engineering them.
Our ornithopters have the ability to outperform and outmaneuver existing drone configurations with stationary wings or propellers.
What are ornithopters?
Ornithopter are flying machines based on the design of birds. Current drone configurations depend on propellant and stationary wings. The ornithopters flap their wings and generate them forward. The complex relationship between aerodynamics and feather movements allows birds and insects to fly in ways that are impossible for conventional drones.
Why do we want ornithopters?
Ornithopters fly differently to traditional drones. They can glide, hover, and perform aerobatics. In various situations, they can either save energy by flying like a regular airplane or choose to hover. They can descend and descend slowly in tight places, yet quickly move upward like a bird.
Current multirotor drones hover very well, but use even more energy than the hover in forward flight, so they can’t really travel very far. Fixed wing drones can travel efficiently at high speeds, but hovering is not normally possible without compromising the overall design. There are usually hybrid concepts with wings and rotor. Hybrid aircraft perform poorly as compared to other designs due to the extra load and hover and drag from more parts.
The flapping wings are the basic solution to nature that needs to fly both quickly and slowly, as well as landing and taking off from anywhere. For a bird or insect, each part of the system is used for hovering and cruising flight, without carrying haphazard thrusters or extra wings.
Existing fixed-wing and rotary-wing drones are well understood that the designs are now near the limit of how efficient they can be. Adding anything new comes at the expense of other aspects of performance.
In theory, ornithopters are capable of more complex missions than conventional aircraft, such as long-range flight, hovering several times, and maneuvering in tight locations. Ornithopters are less noisy and safer to use around humans, due to their larger wing area and slower wing beats.
How do we make a working bird?
An ornithopter is a highly complex system. Until now, flapping wing drones have been flying at a slow speed and have not been able to achieve the speed and power required for vertical aerobatics or continuous hovering.
Some commercially available ornithopters are designed for forward flight. They climb slowly like a slow airplane, and cannot climb or climb steeply.
Our design is different in many ways.
One difference is that our ornithopters use the “clap and fling” effect. The two pairs of wings flutter such that they meet, as they clap. It gives enough extra thrust to lift its body weight while hovering.
When changing the direction of the wings and changing the direction like a spring, we improved efficiency for grooming the wing / body hinge. We also discovered that most of the energy loss occurred because the gears flexed under the load of the driving wing. We solved this by placing the gears correctly by rearranging the shaft with the gear bearings and in the transmission.
The large tail, which includes a hull and lift, creates a lot of turning force. This allows for aggressive aerobatic maneuvers and rapid switching from horizontal to vertical flight.
The system was designed to be able to pitch from the nose, rapidly increasing its angle of attack to a point where the wing does not generate lift, a phenomenon known as a “dynamic stall”.
The dynamic stall creates a lot of drag, turning the wing into a parachute to slow the plane down. This would be undesirable in many drones, but the ability to enter this state and recover quickly increases mobility. This is useful when working in a clotted environment or on a perch.
Catch up with evolution
One of the major findings of our work was that a practical ornithopter could achieve the same efficiency as a propeller-driven aircraft. Several behaviors became possible for the ornithopter once some additional power was freed.
It has actually been revealed that optimization of the flight mechanism is important to make these new aircraft designs feasible. We are now working to use wing designs copied from nature. We expect equally big reforms.
In some ways, achieving such great efficiency from design changes in these new systems should not be surprising. Wing organisms have been adapted by evolution over hundreds of millions of years. We humans have been on it for less than 200 years.
Javan Chahal, Joint Chairman of DST Group Sensor Systems, University of South Australia.
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