Backyard Planes

Lisa Holland Kaminsky
September 01, 1996

Imagine an airplane in 2002. What does it look like? How does it fly? Can it land in your own backyard?

Maybe. The V-22 Osprey tiltrotor combines the vertical take-off and landing ability of a helicopter with the long range and fuel efficiency of a plane. At the tip of each wing it has a triple-bladed rotor. The blades of these rotors face forward during flight, like propellers, and rotate upward for landing and takeoff, like helicopter rotors.

boy with toy plane

But the tiltrotor still needs some work to convert it from the military Osprey (which is bulletproof and foldable, so it will fit onto a ship) into a quieter, faster, and more stable aircraft for commuter hops. Ed Smith, an assistant professor of aerospace engineering at Penn State, and doctoral student Anna Howard are currently working with NASA to improve the tiltrotor's blades. They are experimenting with composite materials that will better withstand wind pressure, which causes a condition known as whirl flutter. On a still, calm day, whirl flutter is not much of a problem. But if a gust of wind happens to come along (and it most likely will), the propellor wobbles and causes the wing to begin vibrating. The bending and twisting motions of the wing and the wobbling of the propeller—altogether known as whirl flutter—"can result in severe vibrations, ultimately damaging costly equipment and presenting a safety risk," says Smith.

The combined bending and twisting—or elastic coupling—is the focus of Howard's doctoral research. In the early 1970s, Smith explains, engineers at Boeing, where the V-22 Osprey was developed, experimented with different blade materials, but they "didn't have a complete understanding of the concept of elastic coupling in composites," Smith says. "Now we can go beyond where they stopped." Using composites of glass fibers and graphite fibers fused with epoxy, Howard is developing rotor blades that are "aeroelastically tailored": Layers of fibers are placed upon more layers in a cross-stitch type of pattern, strengthening the blade in any direction of motion. By changing the orientation of the fibers, she can control how the blades bend and twist in flight.

Although intent on making the tiltrotor available to the public, Howard has never even flown in a helicopter. "I have no interest in flying," she says, "only building." She spends four weeks a year at NASA-Langley, performing wind-tunnel tests on the tiltrotor model. A poster of a crashed airplane taped to the side of Smith's desk (the 28 other posters and the shelves full of 34 model helicopters leave little room elsewhere) makes his and Howard's philosophy clear: Consider the possible consequences if you are careless in your work.

Anna Howard is a doctoral student in aerospace engineering. Ed Smith, Ph.D., is assistant professor of aerospace engineering in the College of Engineering, 233 Hammond Bldg., University Park, PA 16802; 814-863-0966. Their research is funded by NASA and the Army Research Office.

Last Updated September 01, 1996