Better Flying Through Chemistry

courtesy of ted windecker2007_4_17

Leo Windecker was a successful dentist and inventor when he took a turbulent demo ride in an all-aluminum Cessna 172 in 1956. “He was startled by at how flimsy it was,” says his son Ted, an Austin aerospace engineer. “He kept saying, ‘There must be a better way.’”

Windecker had long been intrigued by the superior strength-to-weight properties of bone, with its ultralight cellular interior and rigid outer shell. In his Lake Jackson, Texas, practice, many of his patients were scientists researching FRP (fiberglass-reinforced plastic) at the nearby Dow Chemical Laboratories. “One afternoon it hit me,” he recounts 50 years later. “Why not a plastic airplane?”

In his garage, Leo built quarter-scale composite wings by coating Styrofoam with polyester resin and fiberglass cloth. When that combination misbehaved, Leo’s Dow connections upgraded him to epoxy resins and urethane foam. By 1959 he was enrolled in aerodynamics courses at the University of Houston and sufficiently distracted by his experiments to take a break from his dental practice. Dow executives gave him a $50,000 research grant, later bought the company, and eventually invested nearly a million dollars in the project. Windecker never got back to dentistry.

In 1959 Leo installed his first full-scale plastic wing on a 1930s Monocoupe racing plane. It was static-tested to more than 11 positive g’s of stress; the standard for light planes is 3.8 g’s. Flight tests delivered a significantly higher cruise speed and lower stall speed than the Monocoupe’s original wood-and-fabric wing.

In a warehouse in tiny Hondo, Texas, plastic planes became a Windecker family affair. Leo’s wife, Fairfax, also a dentist, was his primary research assistant. Ted engineered structures, while his brothers handled fabrication. Seeking alternatives to common crisscross-weave fiberglass cloth, Leo tried a new nonwoven, unidirectional glass fiber, manufactured by the Ferro Fiber Glass Corporation, that was superior in load-bearing capacity. These experiments culminated in Windecker’s trademarked Fibaloy, which combines unidirectional cloth with a high-performance resin. It’s one of 22 composite patents in his name. The Fibaloy wing proved more than twice as strong as aluminum—and while aluminum accumulates fatigue, Fibaloy actually strengthens with age, as molecular bonding continues for years after the resin has cured.

By 1962 the Windeckers were ready to concentrate on a production passenger plane modeled after Beechcraft’s successful Bonanza. In a new factory in Midland, Texas, the wings were molded as integral units—electrical wiring, fuel lines, and plastic fuel tanks included—while the fuselage popped out in halves, to be glued together like a model plane. The only metal components bigger than a breadbox were a 290-hp Lycoming engine, the landing gear, and the propeller. In October 1967 the prototype Windecker Eagle took to the West Texas skies.

The Eagle was an objet d’art of compound curves and slick, rivet-free surfaces. Color pigment, registration numbers, and even antennas were permanently molded into its glossy fuselage. But its beauty was much more than skin-deep. An all-metal Bonanza contained around 50,000 individual parts, the Eagle only 5,000. And it blew the wings off comparable Beechcrafts, Cessnas, and Bellancas.

A second prototype was submitted for certification by the Federal Aviation Administration. “They treated us very nicely,” Leo says, denying a long-standing rumor of plastic-phobic feds. But prototype two failed to recover during a spin trial, and after its test pilot bailed out, it plunged 8,000 feet to the ground. Analysis of the surprisingly intact plane attributed the mishap to its tail-heavy weight distribution. A redesigned prototype recovered from more than 250 spins in one of the most extensive spin-testing programs ever conducted. On December 18, 1969, the Windecker Eagle became the world’s first FAA-certified all-plastic aircraft.

The second, Beechcraft’s Starship, came nearly 20 years later.

“Technologically, the Eagle was a brilliant success,” Ted Windecker maintains. The fact that only nine were built says more about the perils of general-aviation start-ups than the merits of plastic planes. The early 1970s saw the beginnings of a long slump in general aviation, with even mainstays like Beech and Cessna floundering, and Windecker’s new financial backers, a consortium of oil millionaires, were aviation greenhorns. “They grossly undercapitalized the company,” says Ted. After rebuffing a well-funded bailout, company directors pulled the plug in 1975.

Leo knew his plane would have a low radar signature. With so little metal to reflect the waves, it would show up as a speck amidst the swarming blips on air-traffic control screens. As a safety measure, he specified metal for an assortment of small, nonstructural components. But radar shyness could also be a virtue. In 1973 the U.S. Air Force ordered an Eagle without added metal parts and with a plastic propeller. It was flown against a variety of radar devices in classified military tests for seven years. Today the composites in Lockheed’s F-117 stealth fighter are thought to be mostly Windecker-patented.

For all the manifest virtues of composites, however, aluminum still predominates in aircraft by a considerable ratio. “Starting over from scratch with something new like composites presented huge financial obstacles for manufacturers,” says an industry executive. It didn’t pay to introduce them into existing plane designs, partly because the planes would have needed extensive modification and partly because “per pound, composite prices were much higher than aluminum to begin with.” This was particularly true since by the end of the 1970s, when Beechcraft began development of its composite plane, carbon reinforcement fibers had been substituted for fiberglass to provide greater strength. Carbon fibers remained in limited supply until demand from applications outside the aviation industry boosted production.

Clean-slate start-ups like Cirrus and Columbia built all-plastic light planes cost-effectively from day one, but among established firms, only Boeing and Airbus have been able to get very far with composites. Even with their deep pockets, the expenditures needed to retool were daunting. But the payoff looms large. Boeing estimates that its 50 percent composite 787 Dreamliner will yield 20 percent improved fuel efficiency over comparable metal aircraft.

Still, the hoped-for weight savings have not come easily. The new Airbus A400M military transport, which has the world’s largest composite wing, is now undergoing a redesign to slim down. Boeing has struggled with similar issues in the 787. The first half-dozen are expected to roll out about 5,000 pounds too heavy before the Dreamliner can be adjusted to its target weight.

Another consideration is that from skin to skeleton, the health and fatigue state of aluminum airframes are easier to evaluate by visual inspection. Potential fatigue could lie hidden within a composite’s molded “sandwich” of plastics, caused by moisture absorption over time or delamination of layers from seemingly innocuous impacts. Still other areas of concern include ease of field repair, lightning protection, tolerance of ultraviolet rays, and recyclability.

Things were different back in the 1930s, when the aircraft industry shifted its main structural material from wood to aluminum alloys over a period of about five years. That was possible for a number of reasons: The industry was much smaller than it is today, with less investment in the prevailing technology. Its history stretched back only about 20 years, so the spirit of experiment and improvisation was still strong. Safety expectations were lower, and the old wooden designs were not all that safe or sturdy to begin with. Most of all, aluminum was so much easier than plywood to mold into complex shapes, and so clearly superior in strength, flexibility, durability, and reliability, that its advantages were undeniable.

“It’s fair to say that the chief engineers of aircraft companies are probably the most conservative engineers in the world,” says Dr. Mark Shuart, chairman of the Materials Technical Committee of the American Institute of Aeronautics and Astronautics. Yet the 40-year record of composites reveals very few catastrophic failures. In his former position as director of structures and materials at NASA’s Langley Research Center, Shuart evaluated airframe failures. He says, “I can’t point to the failure of any large civil aircraft structure and say composites were at fault. If you understand the way they behave and design accordingly, you just don’t run into a problem where they break.” Boeing believes its flawless experience with highly stressed composites in the horizontal and vertical stabilizers of more than 600 of its 777s, as well as advances in ultrasound inspection, now leave no safety concerns unanswered.

“Composites are riding a crest right now,” says an observer. “They’re depicted as sexy and futuristic.” The chain reaction of research and development, initiated when Windecker molded that first wing in his garage in 1957, is now reaching a critical mass of profitability and public acceptance. “Ultimately, the decision always gets away from the technical guys,” Mark Shuart says. “Engineers are confident in their designs, manufacturers now believe they can make money selling composite planes, and the public is comfortable with them. We’re inevitably going to see an increasing number of composites replacing aluminum very soon.” H