Wooden propellers are like Louisville Sluggers: The distance.
- By Tom Harpole
- Air & Space magazine, July 2003
(Page 3 of 5)
At each station where the props are taken through another stage of development, there’s a fan and a boom box. The ambient noise in the gymnasium-size building never lets up, a gnashing din of whines, grinding, chipping, and hammering that competes with rock, salsa, rap, bluegrass, and oldies blaring at the various workstations.
Props follow a spiral path around the factory floor, starting at the center of the building, where rough-sawed yellow birch planks, all one inch thick and random widths and lengths, are stacked on carts that crowd an area the size of a parking space.
Here at the center, inspector Charlie Brown sorts through the birch boards, which are harvested from New England tree farms. Before Brown begins making a stack, he has a specific propeller in mind. He balances each board on the edge of his hand, culling nearly half of them as he stacks up as many as 16 laminations, swapping ends so that heavy sides alternate. (A stack of five 0.75-inch-thick laminations is stronger than a solid 3.5-inch-thick piece of wood.)
The shop, near the Plant City airport, resembles an industrial museum, with tools that haven’t changed in 75 years. Not even the glue has been improved in decades. Resorcinol has been the only adhesive used by Sensenich since “somewhere back in World War II,” Rowell says. “We’ve never had a glue failure. If we tried to use some new glue we’d have to go through recertification. Way too expensive to replace something that has worked flawlessly for 50 years.”
The purplish glue coats nearly every surface in a far corner of the factory where Jose Mendez and Wayne Allen are making up a blank for a 98-inch Stearman prop. The set-up time of the resorcinol, at 90 degrees, allows them less than an hour to apply the glue to each surface of the eight laminations and get the blank clamped. “It’s no big deal,” Mendez says. “We’ll get it in 25 minutes.” Twenty-two minutes later, the two have applied 112 C-clamps to the laminations. There is nowhere on the prop that they can insert a fist between clamps. Resorcinol drips down the terraced edges of the big blank in one-inch intervals. After the initial machine carving, the glue lines along the laminations of yellow birch will define the prop’s curve from root to tip and provide guidelines for the master carvers to follow.
After letting the glue set for up to 24 hours, the workers rough-shape the blanks in a computer-controlled carving machine, or on the duplicating router, a 70-year-old machine designed by Martin Sensenich that rough-cuts laminated wood blanks into propellers. Like a three-dimensional key-cutting machine, the big router, modeled after a gunstock-duplicating machine, tracks the shape of a pattern prop and transfers the profile to the blank. When the blanks are rough-cut they are within 3/16 of an inch of their final shape. A worker carries the rough-cut blanks to a drill press, where a large hole is milled out of the hub, then a drill press is used to bore the bolt holes. The hub hole doubles as the fastening point for vises that are designed to allow the carvers to set the props at any angle they wish.
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.