Buzzing like a giant bee and frantically beating its five-foot wings like some great mad stork, the creature brought forth by Jeremy Harris and James DeLaurier set a world record last fall. While the two men watched in awe and delight, their comical beast--made of wood, Kevlar, carbon, and glue and powered by a one-horsepower engine--became the world’s first successful engine-driven aircraft with flapping wings. It’s not going to become the next Boeing jumbo jet, but it’s the closest man has ever come to flying like the birds.
In all plane designs from the Wright brothers on, wings have stayed put, providing lift while a propeller or jet engine supplies forward thrust. But in Harris and DeLaurier’s ornithopter (ornitho from the Latin for bird, pter from the Greek for wing), the flapping wings lift the craft into the air and move it forward at the same time.
The wingspan is made up of three connected sections: a right and a left wing attached by hinges to a center panel directly above the plane’s fuselage. The panel is bolted to a boxlike wooden structure that is shoved in and out of the fuselage by the engine; as the box is moved up and down, the wings move along with it. Each wing has a pivot joint near its center, where it’s attached to a strut coming out from the fuselage, and the wing pivots over this joint like a seesaw.
Harris, an engineer at Battelle Memorial Institute in Columbus, Ohio, began work on this flapping mechanism in the late 1960s when, for his master’s thesis, he was developing a mechanical amplifier--a device to exaggerate small movements mechanically. He started to wonder if such a contraption could deliver energy from arm movements to wings that would beat even more powerfully. Wouldn’t it be neat if I could become a bird, he mused, and flap some wings myself?
In the early 1970s he met DeLaurier, an aerospace engineer now at the University of Toronto, and hooked him on this fanciful problem. It became a hobby that con- sumed the duo’s spare time during the next 20 years. Like a couple of smart young en- gineers, we thought we could knock this one off real easily, but we couldn’t, DeLaurier recalls. It turned out to be the most difficult airplane design project I have ever engaged in.
Once the two engineers came up with a flapping mechanism that wouldn’t shake the craft apart--not an easy task in itself and one that had stumped many other would-be ornithopterists--they needed wings. To make a flapping wing that lifts and thrusts at the same time requires a great deal of analysis, DeLaurier says. What looks intuitively like a perfectly reasonable wing could, in fact, be horrible.
They started out with a thin, flexible wing because they wanted it to twist slightly into the wind when hit by oncoming air. For proper lift and thrust, it’s best that air hits a wing on the chin, DeLaurier says, coming from just beneath and slightly ahead of it. Some of this air then makes a U-turn around the wing’s leading edge to flow over the wing top. The airflow speeds up as it does this, and what it gains in speed it loses in pressure. That low-pressure area just in front of the wing creates a vacuumlike pull that sucks the wing forward.
However, a thin wing also has a thin leading edge, and that created a problem. The edge was too sharp, and air couldn’t flow around it. It’s like trying to make a turn in your car, DeLaurier says. If you make the turn too tight, you skid. It took the engineers a long time to devise a thicker wing that could still twist in the breeze.
There were many setbacks and crashed ornithopters before that cool September day when the craft was launched. I was holding my breath, DeLaurier says, and waiting for Murphy to step in and do his usual thing. But even Murphy’s Law had run out of surprises. Instead of crashing, the ornithopter climbed and turned and flew. It was great! DeLaurier says. I got so excited I forgot to turn off the stopwatch. A videotape of the event later revealed the flight lasted a minute and 46 seconds. It also revealed the two inventors whooping and hollering. Flapping flight touches something inside, DeLaurier explains, which says ‘Yeah, that’s what we really had in mind.’