Ornithopter: The plane that flaps its wings like a bird
Last Updated Oct. 24, 2006
Canadian aeronautical engineer and University of Toronto professor emeritus James DeLaurier with the Flapper, the first ornithopter to achieve sustained flight.
Birds make flying look simple, but taking to the sky on flapping wings is no easy feat.
In normal fixed-wing aircraft, the powerful thrust of the engines causes massive airflow over the surface of the wings as the plane moves forward, which in turn is used to produce lift. Panels on the wings are angled during the flight to alter the airflow, causing the aircraft to ascend, descend or cruise in a straight line.
In birds, bats and man-made ornithopters, however, the flapping of the wings must generate both lift and thrust.
An ornithopter’s thrust results primarily from a low-pressure region created around the front edge of the wings as they flap, which provides a force known as leading-edge suction. This draws the aircraft forward, and the resulting speed provides sufficient airflow over the wings to generate lift.
In comparison, there is little leading-edge suction in a fixed-wing craft and the propellers or jet engines provide the push to get the plane moving.
An ornithopter is also literally lifted into the air partly by the flapping motion of the wings, which produces an oscillating vertical force of several hundred pounds.
Ornithopter design began more than five centuries ago, with Leonardo da Vinci’s 1490 human-powered model. Over the centuries, many gliding models and fully motorized ornithopters have been built by inventors around the world, but none were able to fly for any appreciable time or distance. Then in July 2006 in Canada, James DeLaurier — an aeronautics engineer and professor emeritus at the University of Toronto — achieved the first sustained pilot-controlled jet-boosted ornithopter flight. DeLaurier worked the problem exhaustively for three decades, collaborating in the early years with American engineer Jeremy Harris.
In DeLaurier’s ornithopter, affectionately known as the Flapper, the wings are attached to a central section along the fuselage that is moved vertically by the drivetrain of a 24-horsepower Koenig engine, a model often used in ultralight aircraft. The wings have three panels (a design patented by Harris); the middle panel of each wing, supported by an outboard vertical link, is moved up and down by the motion of each innermost panel, and in turn, drives each outer panel vertically.
The wings of the Canadian ornithopter also passively twist in response to the flapping because of their unique structure, which DeLaurier calls “torsionally compliant in just the right amount … Too little twisting would cause massive stalling, and too much twisting could cause the wing to act in a ‘windmilling’ mode, actually taking energy from the flow.”
Although the ornithopter’s wings appear similar to those of a normal aircraft, they are actually built much stronger because of the far greater stresses that must be withstood during flight. To achieve this level of strength while minimizing weight, DeLaurier had the wings constructed of a lightweight but very strong composite of carbon fibre and Kevlar.
The designers of the Flapper had to overcome two major problems before they finally got airborne. Even though the 345 kilogram craft could accelerate by flapping along on flat ground to reach liftoff speed (82 km/h) at about one flap per second, it couldn’t leave the ground. This was partially because the distance to achieve liftoff speed was greater than that provided by a conventional runway, which is about two kilometers.
Additionally, as the ornithopter accelerated, the flapping produced a strong vertical force that caused the aircraft to rise off the ground during the wing’s down-stroke and come back down during the upstroke. The bouncing was a very serious problem that both pushed the craft’s structural limits and dampened the acceleration.
For several years, DeLaurier’s team grappled with the problem of successful takeoff while they conducted further tests, made structural modifications and overcame electronic challenges. The eventual addition of a mini jet engine lent an extra boost of thrust that allowed the Flapper to overcome the bouncing problem.
The craft left Canadian ground for a short but sustained flight on July 8, 2006. It flew about one metre above the ground for 14 seconds for a distance of roughly 300 metres, beating by two seconds the first flight of the Wright brothers’ powered plane in 1903.
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