Good Wood- page 3 | How Things Work | Air & Space Magazine
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Good Wood

Wooden propellers are like Louisville Sluggers: The distance

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By 2:00 p.m., at the master carvers’ station, it is 94 degrees in the shop, and Chris Thorpe and Ben Smith are bent over, scrutinizing a tiny area on a prop. They beckon Justin Bryant, a burly apprentice carver who moonlights as a mud wrestler. Bryant bends over and puts his face about a foot away from the blade, and three close-cropped heads hover within inches of one another as they stroke the spot with their palms and fingers. “Things you don’t feel with your fingers alone you’ll notice if you use your whole hand,” Thorpe instructs Bryant. Their shirts flutter in the stiff breeze from the fan.

Thorpe turns to his workbench and picks up masking tape and a razor blade. Smith turns the fan off and Thorpe goes to work with the blade, chipping off a glue line that is an inch long and perhaps half the width of a toothpick. Smith makes a little masking tape dam and Thorpe dribbles some epoxy into the minuscule gouge in the prop.

Thorpe bends over his props in an unbroken curve from hams to head. Later he will wield an air-driven drum sander that is revolving at 1,800 rpm and sand down the epoxy patch to a .03-inch tolerance—the thickness of a piece of paper. The carvers also use the drum sanders to sand away the leading edge so that they can make another dam to fill with urethane for erosion protection on props that don’t get protective sheet metal applied to their leading edges.

By early afternoon the carvers are ankle deep in shavings from countless strokes they pull with Stanley #64 spoke shaves. “This here is the heart of the prop carving business,” Thorpe says, holding out a six-inch-long spoke shave with a two-inch blade centered between spoon-like handles. The way he holds it tells me he is not offering it for closer inspection. “Got to take care of what makes the truck payment,” he says, cradling the tool in his palms.

When the drum sander’s whine gives way to the soft scritching of overlapping spoke shave strokes at the carvers’ station, Smith and Thorpe pass the time in blurted exchanges on topics as diverse as the taste and texture of wild frog legs versus farm-raised frogs and the heartbreaking error of feeding piglets a pickup load of rotten cantaloupes. “They couldn’t digest the seeds and swelled up and croaked, but not like frogs,” Thorpe notes. They exchange recipes for soft-tailed turtles. Most of the day, however, they are busy with a tricky bit of wood grain a few inches from their eyes, and they are absorbed into the swift strokes of their spoke shaves, and with sandwiching metal templates on the front and back of the props until they meet at a perfectly carved spot along its length.

Thorpe and Smith, arguably the two best prop carvers around, don’t race each other or the clock. “The people who pay this kind of money for a propeller deserve something as nice as humanly possible,” Smith says.

What’s humanly possible, especially without the aid of computers and duplicating routers, is what Holmes Beach, Florida freelance prop carver Ed Sterba has been doing for 20 years. He is one of perhaps a dozen independent carvers in the country who advertise their non-FAA-certified propellers in the classifieds of aviation magazines.

Sterba, a lean, tanned pilot and sailor and single parent of three teenagers, also projects the contentment and pride that seems inveterate in woodworkers. Working out of a shop smaller than the Sensenich rough lumber stack, he makes three propellers per week. He keeps a library of hundreds of index cards on which he has recorded mathematical descriptions of the angles, thicknesses, curves, and pitches of hundreds of props at four to eight stations along their two blades. His power tools are a band saw, hand-held planer, drum sander, and a drill press that he built from mismatched parts and wood scraps. Working without templates, he relies on his eyes and two decades of standing over laminated-maple blanks clamped to a workbench the size of an ironing board. He balances a maple plank using a point like an old-fashioned tire balancer. Then he drills a hub into it and sketches lines along its length to guide him when he bandsaws the laminated planks into rough props. As he listens to the predictable cadences of NPR, he planes and sands away at the rough form until it looks like the propeller he wants.

Sterba regards the first Wright brothers’ propeller, the one they carved in their Ohio bicycle shop, as a stunning achievement of calculus and craftsmanship, as amazing as the airplane itself. “Their propeller was easily as great a discovery as anything they had to learn,” he says.

His tiny shop is located in a row of commercial spaces that are rented by artisans: antique restorers, a couple of jewelry makers, a potter. He regards his work as a critical trade compared to the craftsmanship of, say, furniture or musical instrument making. “Lives are at stake,” he says. “This is closer to boat building. But real artists can do things that I can’t.”

Art is amorphous by nature, and Sterba “repitches,” or slightly adjusts the blades’ angles, at no charge if they aren’t as efficient or perfectly tuned to the aircraft’s performance as possible. “That’s the nature of experimental aircraft,” he shrugs. It’s also the nature of pilots who seek the ideal fixed-pitch prop: one that takes off and climbs taking advantage of max horsepower, but doesn’t let the engine overspeed at cruise.

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