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72 That Thing Up Front Here is a truth about my flying history. My first flight lesson never happened . The instructor, a man way too tall to fit into the ancient and glorious 152 we were about to use, walked me out to the airplane and began to talk about the preflight inspection. I checked the fuel and the oil. I checked the ailerons and flaps, the air pressure in the tires, and the amount of travel in the front strut. I was ready to fly. When I got to the prop, I ran my hand down the length of each blade. I remember feeling the subtle twist in the shape. And I remember the way the blade curved back at the end, like a winglet. “Wait,” my instructor said. “That’s not what it should be.” A mechanic was called. He frowned; then we all frowned. Someone had run something into the end of the propeller. It would have to be removed and fixed. “That propeller,” he said, “would shake the engine right out of the plane.” Unhappy, but safe, we all went back inside. Yet there is something about the feel of that shape in my hand I have never forgotten. Even now, when I preflight an airplane, I begin at the nose, with my hand running the length and curve of a propeller. If there is magic in an airplane, I think, it resides in the prop. —————————————————— Archimedes, the mathematician from ancient Greece, is generally credited with inventing the first propeller-like tool—the screw. And while the screw may not look very much like an airplane prop, the basic principle is the same. What’s changed are just the math and the materials. Jeremy Kinney, curator for aircraft propulsion at the Smithsonian National Air and Space Museum, oversees aircraft propulsion in general, and in partic- That Thing Up Front 73 ular aerial propeller development. “Propellers have their own story,” he says, “and it’s just as dynamic as you can imagine.” There are 527 propellers in the museum, many of them representing new ideas in design or materials. Walk in the main entrance on Independence Avenue, and one of the first things you see is the Rutan Voyager, the first plane to circumnavigate the globe without stopping or refueling, and the Hartzell constant-speed props crucial to its long-distance performance. A prop from the Enola Gay is here. Whereas the prop from the original Wright Flyer is in a case near the Flyer (the airplane was overturned on the ground in a gust of wind, and the prop was damaged), the Spirit of St. Louis boasts its original propeller. “Lindbergh insisted on a metal propeller,” says Kinney. “His was the first well-known use of the ground adjustable-pitch idea.” I ask him what are some of the most significant props in the collection. “Our newest prop—the Dowty R391—is from a C-130 transport,” he said. “Six blades. Composite. Hydraulically actuated. It really is the latest, most up-to-date prop there is. But to me, the most important propellers are the Hamilton Standard props of the 1920s, ’30s, and ’40s. These became the standard, especially the Hydromatic constant-speed propeller. Every DC-3 had these Hydromatic props. Every B-17. Just about every Allied airplane had Hydromatic props. They are the basic core of what all modern propellers are.” —————————————————— To be accurate, a propeller is a rotating wing in a helical path. Because it’s a wing, pitch and angle of attack are the problems that keep engineers awake at night. The Wright brothers introduced the twist in the blade, but every inch of a blade should be maximally efficient. Remember calculus class? Change one variable, such as the engine or airframe behind the prop, and you have a whole new set of efficiency goals. At Sensenich, Steve Boser, vice president, says, “We make somewhere between seventy-five and a hundred fixed-pitch propeller models. About twentyfive of those are what you could call our most popular. Well over one hundred different airplane models fly with our props.” Sensenich divides its products roughly into 50 percent aircraft, 35 percent airboat, and 15 percent UAV for the military. “We also service the antique market,” he says. “A lot of our wooden props are made to order. J-3 props are popular, as are Stearman, Fairchild, Stinson props. There are some really obscure ones, too, like the Funk B or Bird BK. Every one...

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