Ready, Set, Flap! | Flight Today | Air & Space Magazine
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Ready, Set, Flap!

Birds do it, bees do it. Can two weird aircraft make aviation history doing it?

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THIS IS A STORY ABOUT TWO GUYS named Jim. Both were born in the 1940s, both grew up in the same neighborhood of Park Forest, a town on the south edge of Chicago, and both attended the same church, but neither knew about the other until one of those one-in-a-billion coincidences. They became acquainted through a seminar at the 1999 Experimental Aircraft Association fly-in at Oshkosh, Wisconsin, and discovered they were probably the two people in the world closest to achieving an aeronautical dream that has eluded humans since the dawn of time.

This morning I'm standing next to one of them, just outside a hangar at the decommissioned Royal Canadian Air Force Downsview base in Toronto. He's tall and straight, his name is James DeLaurier, and he is a professor at the University of Toronto's Institute for Aerospace Studies. Poised beside us is a little aircraft that may one day soon realize the dream of the tow Jims, a craft affectionately known as Big Flapper. It is intended to fly not with propellers, not with jets, but with flapping wings.

For centuries, attempts at building airplanes were, naturally enough, based on the way birds fly. But coming up with the perfect wing proved extraordinarily complex. Now, with the help of microcomputers and composite materials, the dream of bird-like flights is being revisited.

This morning's run is a taxi test to feel out a redesigned undercarriage. Test pilot Patricia Jones-Bowman arrives at the hangar in a beat-up Buick. She has chestnut-red hair and wears wraparound sunglasses and a blue flying suit. An ex-bush pilot, she volunteered for the project after hearing about it from her dentist, a talented woodworker who had built jigs for the Flapper's wing spars. Craning her neck, she eyes Flapper's wings, which are poised in the up position, like the wings of a hummingbird in a strobe photo.

There's not a breath of wind in the gray dawn as she takes a few complicated minutes to settle her tiny frame into the cockpit. One of the crew chiefs, Derek Bilyk, signals "All clear," and she hits the start button. The tranquil air is cracked by a dirt-bike-exhaust note, which is backed by a whining, something like that produced by the windshield wipers of an old school-bus: rr-RR rr-RR rr-RR. Big Flapper has awakened. It flaps its 41-foot wingspan like a giant rooster about to crow at the dawn. Its 24-horsepower two-stroke ultralight engine is coupled directly to the wings through a mechanical drive unit. A sprocket-and-chain mechanism drives two pylons, located just behind the pilot, up and down, raising and lowering the center sections of the three-section wings. At top engine performance, 3,800 rpm, the wings flap 1.3 times a second. But that's not achieved until the craft is on the runway. For this runup, 0.94 per second is about the maximum at which the bucking beast can be held down.

Big Flapper was built in 1996 but is the culmination of over three decades of research. DeLaurier's partner, Jerry Harris, who conceived Flapper and paid for its construction, recounts: "I first considered flapping flight in 1968, as an application for the mechanical power amplifier I was analyzing for my master's thesis at Ohio State University." He began collaborating with DeLaurier in their spare time while both were working at Battelle Memorial Institute in Columbus, Ohio, in 1973. "Natural or flapping flight was one of the few areas still open to fundamental investigation and engineering analysis," says Harris. "Fundamental" is the critical word here; as far as practical applications go, there is little at present—a fact that appears to bother none of the team members.

When DeLaurier accepted a position teaching aeronautical engineering at the University of Toronto in 1974, flapping-wing research did produce one practical offshoot of sorts: It gave some of DeLaurier's students a focus for study. Around a dozen of senior and master's theses, as well as a doctoral dissertation, have helped design Big Flapper. And one student, Theresa Robinson, is doing a master's thesis on the use of ornithopters to explore in thin atmospheres like that of Mars. But theory and models can predict only so much. Flapping-wing flight today is akin to supersonic flight in the 1940s—an unknown regime where stability and control are only educated guesses. To find out what happens, you have to do it for real.

"By far the biggest design challenge was the wing," shouts DeLaurier over the din. "I would say this wing is the most technologically complex wing in history—it's the first that has had to provide both thrust and lift." Early on, DeLaurier and Harris studied film clips of bird flight in slow motion. "There were just too many different motions happening at once," DeLaurier recalls. "The thought of modeling it was intimidating." In designing Flapper, DeLaurier figured that it would be enough to produce a careful combination of flapping and twisting to generate lift and thrust. On the upstroke, the wing twists to a positive angle relative to the fuselage, and on the downstroke, it twists to a negative one. This provides the thrust necessary for forward flight. But achieving the optimum twist was no cakewalk. Either too much twist or too little would produce inadequate lift. In fact, too much twist would take energy out of the airstream and produce negative thrust—drag.

And while the wing is twisting, it also needs to maintain the right degree of bending rigidity. DeLaurier explains the concept by asking me to imagine holding the ends of a cardboard tube. "Try and twist it," he says, "and it remains rigid. But slit it down the length of one side and overlap the edges and you can twist it while it remains stiff." DeLaurier and Harris pulled off a similar innovation by conceiving a shear-flexing design. Each wing is composed of two flexing sections of polyester; during flapping the sections slide over the wing ribs. The sections are attached to what is essentially a double trailing edge: One section slides over the other, like two edges of the cardboard tube.

Harris and DeLaurier first tested the concept with a 10-foot-span radio-controlled model the named "Mr. Bill" (after the misfortune-prone "Saturday Night Live" creation). It took years of research, they say before Mr. Bill was able to fly with their shear-flexing design and demonstrate their method of three-axis control, which they later used in Big Flapper.

In the full-size ornithopter, the pilot controls pitch by manipulating the horizontal stabilizer. But the third function of a flapping wing, lateral control, hasn't been included on Flapper's wing. The shear-flexing wing design precludes the use of standard ailerons for direct roll control. So Flapper is designed to turn solely by rudder. The pilot will bank by a technique known as yaw-roll coupling. Lateral stick input deflects the rudder, yawing the aircraft. The windward wing experiences an increase in angle of attack and airspeed and therefore enhanced life, which rolls the aircraft in the direction of the turn.

Flapper has yet to demonstrate that it can actually do any of this. During a test in November 1998, as Flapper exceeded 50 mph, it started to lift off the runway, then smacked down on the ground so hard that the nose gear failed. To keep the craft on the runway while the speed increased, the team shortened the nose gear so Flapper had a nose-down angle. That suppressed lift buildup. "What we hadn't accounted for," says DeLaurier, "was that the new down force from the wings was imposing compressive loads in our vertical struts beyond the design limit." During another test, this one in October 1999, Jones-Bowman reached 56 mph—just short of Flapper's predicted 57-mpg takeoff speed—when one of the vertical struts buckled. The team reinforced the struts.

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