Catching the Wind
The Aermotor Model 502 windmill
Restoring old windmills is sometimes more exciting and adventurous than it sounds. One day a while back, a neighbor bought an old Aermotor Model 502 windmill at auction. The only hitch was that it was still standing on the same farm where it was erected in the 1930s, and it was up to us to catch it, restore it and then release the windmill back into the wilds of South Dakota.
Actually, I didn't know it was an Aermotor windmill until I climbed up 45 feet past the bees and grapevines to its perch high above the old farm site. My helper stood on the ground, frantically waving a board at a swarm of mosquitoes. Above the tree line, a stiff breeze took away the insects, and the last 30 feet was easier to climb. I instantly realized that the windmill's tail was different when I got a better look at the top, because corrugated steel was installed to stiffen the design. When I finally turned the mill's motor around, I discovered it was a rare Model 502.
Before work on the windmill could start, we cleared a path through the grove of trees to make room for the long trailer and crane we needed to move the windmill. We attached a bridle high enough so the mill sat upright after we torched off the legs. As the crane lifted the mill, it overbalanced and the tail just barely missed the crane's boom. Mike, the crane's driver, lowered the unit, and we carefully removed the tail. Next, we laid the tower on the trailer, wired the tail to the top and collected all the fan sections and brace rods that had been piled by one of the towers. It was amazing to imagine that those parts had sat undisturbed beside the mill since the 1930s when electricity arrived at the farm and the windmill was decommissioned.
The man who'd bought all the iron on site for $25 offered to sell us another open-geared Aermotor head, fan and tail he discovered on the property for $50. It was difficult to pass up, because that mill originally sat on the tower we'd just moved. As luck would have it, the farm was owned by the same family for more than 100 years, and all that remained were the windmills in the grove. Sometimes, dumb luck plays a big part in collecting.
The 502 was the first attempt at a self-oiler made by Aermotor. The model is fragile and tends to bend. Worse yet, the mechanism didn't oil the guide roller and upper yoke, which caused premature failure. Aermotor only built the 502 in 1915, followed by the better-manufactured 602 for 16 years. The Model 702 is still in production, while the 802 is a recent addition to the line. Several shops around the United States build and rebuild mills; we get our work done at Dakota Windmill and Supply, in Hurley, S.D.
Very early mills used a direct stroke for each revolution of the fan, with an up-and-down stroke in the pump rod. The design worked well in a good breeze, although the rods could get a bit jerky as the mechanism aged from wear. All early mills had open-faced gears. Ideally, the gears were greased weekly, but that didn't usually happen until the mill stopped spinning. Later, open back-geared mills came out, which featured smaller gears on the fan shaft and a larger set of gears on the pumping shaft, generally in a three-to-one ratio. This design enabled the mills to pump water with lighter breezes and smoother operation.
Self-oiling mills were available in the early 1900s, which replaced frequent greasing with one-time annual maintenance. To service the self-oiling mills, first the oil was drained. Then the settlings were cleaned out in the motor bowl and a quart or two of very light non-detergent oil added. For some reason, that same variety of oil is used in windmills today, and contaminants still settle to the bottom and grind up bearings and gears through time.
From early on, windmill governors were a big problem. Some farmers tried to change the pitch on the blades in response to wind speed, while other farmers used counter weights. Still others used a small tail tightly mounted to force the fan out of the wind. Finally, farmers discovered that setting the mill offset from the pivot point was the easiest fix. This technique allows the wind to push the fan blades out of the wind's direct force, and solved the speed problem.
In most windmills made after 1900, a spring from the tailbone to the motor acts as the governor. Holes in the tail-bone stretched the spring tight and kept the fan facing more directly into the wind. Conversely, lighter tension allowed the fan to run at a better angle to the wind. This simple method works, and if the spring breaks, the fan nearly turns to a right angle to the wind direction, either motoring slowly or shutting off with no damage. Some common mills that utilize this feature include Dempster, Baker, Fairbury and Aermotor varieties. The results are amazing, and the Aermotor Model 602, with its 6-foot fan, can run at 125 rpm and 40 strokes per minute.
Catching and restoring windmills may be difficult, but it's easy to release an old mill back into the sky. We simply assembled it on the ground, then we picked it up with the crane and bridle so the mill hung almost vertically above the holes we dug for its legs. Then we bolted anchor sections to the tower's legs, and set it in place so that the tower is leveled and earth is tamped back solidly over the four holes above each anchor plate. Finally, the restored windmill is again ready to work in the wind.
- Jim and his wife, Joan, operate Little Village Farm at 47582 240th St., Dell Rapids, SD 57022. Contact them at (605) 428-5979.