ARCHIVED - Flight science gets close to nature
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May 08, 2008— Ottawa, Ontario
Years ago, NRC researcher Dr. Mahmood Khalid was fascinated by the flight of a bird he spotted on his way back to the lab after lunch. "It flew over the roof of the building, made a tiny figure eight, and then flew back and landed on the edge of the roof," he says. "When I saw that, I thought: no aircraft in the world can do something like that."
Today, NRC is helping to investigate a design for a tiny winged device that could come one step closer to the bird Dr. Khalid saw that day. The device, called a nano-air vehicle (NAV), is the size of a hummingbird, and would be quiet and agile enough to discreetly investigate confined spaces such as buildings, stairwells, shafts and tunnels, sending images back to a human operator. Acting as a miniature reconnaissance robot, the NAV could provide airborne surveillance during anti-terrorist activities and other high-risk operations.
While many countries are investigating nano-air vehicles, the Canadian team of NRC, Defence R&D Canada (DRDC) and Advanced Subsonics Inc. of Toronto is one of the few looking at a flapping-wing concept. "Elsewhere, people are using a simplified version of the wing that doesn't flap – we're trying to mimic nature a little more closely," says Dr. Khalid.
The NAV's two sets of wings would be made of a thin airfoil and move in a "clap and release" pattern, similar to a hummingbird's wings. The device has a wingspan of 7.5 centimetres, and is based on a larger mechanical dragonfly – the world's first hovering flapping-wing drone – created by Advanced Subsonics in 2002.
|Photo credit: Advanced Subsonics Inc.|
For small vehicles, the use of flapping wings should be more efficient than traditional propellers, and the constant thrust provided by the flapping motion would allow the vehicle to hover and manoeuvre much like a bird. Unlike some designs that are based on a scaled-down helicopter, the NAV should also be nearly silent – an important consideration for military operations.
NRC and its partners are studying the NAV's aerodynamics through computer simulation and physical modelling. NRC has created a sophisticated computer model of one of the vehicle's four wings, and will also test a physical model of the wing in a water tank at its facilities in Ottawa. The model will be able to execute the yawing, pitching and rolling motions required of the wing in flight. These results will be compared with the computer models to create a better understanding of the aerodynamics of flapping-winged flight.
The biggest challenge for researchers is computing the complex aerodynamics of flapping wings, since these are not yet fully understood. "Birds adjust the shape of their wings almost continuously to produce the optimum flight for the current conditions," says Dr. Khalid. Although the NAV will use a simpler motion based on movement at the root of the wing rather than throughout the wing, the aerodynamics are still complicated due to the complexity of airflow over a moving wing. "Our computational modelling is among the best in the world, and the computational power now available for computers allows us to probe the physics more deeply."
The fixed-wing aircraft that people have flown since the Wright brothers made their historic flight in 1903 represent just a "frozen instant" of a bird's complete capabilities, says Dr. Khalid. "Our air flight is very simplified, like a baby walking in contrast to what an athlete can do with a vault pole." With the move from a fixed wing to a moving wing, the NAV could take our understanding of bird flight one step further. "We are taking small steps towards the complete and comprehensive capabilities of what nature can do."
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