Bob Thompson was biking past the Bevo Mill in St. Louis on a Sunday afternoon earlier this year when he noticed something strange about the Dutch-style windmill.
鈥淚t鈥檚 going in the wrong direction,鈥� said Thompson, a flight instructor and retired airline pilot who lives in University City. 鈥淚 just kind of laughed inside, like, has anyone noticed this before?鈥�
The more he thought about it, the more Thompson wondered why the iconic St. Louis landmark was spinning backward 鈥� so he decided to ask our Curious Louis series to investigate.
But first, which way is a windmill supposed to turn anyway? And why does it matter?
The whole point of a windmill, said Ray LeBeau, professor of aerospace engineering at St. Louis University, is to take wind energy and convert it to mechanical power.
鈥淭he way it does that is by generating a pressure difference across the blades,鈥� LeBeau said. 鈥淵ou have higher pressure on one side, lower pressure on the other. That creates a force and that force causes the blade to move.鈥�
Like aircraft wings, windmill blades often have a thicker edge that gradually becomes thinner toward the rear, which creates more lift force.
This wider edge of the blade should 鈥渉it the wind first,鈥� LeBeau said.
Old-fashioned Dutch windmills, similar to the style of the Bevo Mill, have crisscrossed latticework that juts out behind the thick edge and is usually covered with cloth to catch the wind, like the sails on a ship.
As Thompson suspected, the Bevo Mill is turning in the opposite direction, with the latticework cutting into the wind first and the thick edge trailing behind.
Technically, this is the wrong way if you were trying to generate electricity 鈥� but LeBeau points out an interesting wrinkle: The Bevo Mill is powered by an engine, not the wind.
鈥淚f you're mechanically driving the windmill, rather than having the wind drive the windmill, then there is a logic to doing it in the opposite direction,鈥� he said. 鈥淭here probably is a reduction in the drag, and therefore it takes less power to turn the windmill."
In other words, it might be cheaper to power a windmill that runs on electricity if it鈥檚 turning backward.
The question is: Was this intentional? Not likely, said co-owner Pat Schuchard.
The Bevo Mill, which has passed through the hands of several owners since its construction in 1917, has been electric-powered for decades.
At the top of the windmill, a humming engine turns a shaft, which slowly rotates the blades.
鈥淚t's been operating in this way for years and years, probably back to the 鈥�50s,鈥� said Schuchard, who purchased the property with his wife, Carol Schuchard, in 2016. 鈥淢aybe they hooked it up, turned it on and said, 鈥極h, I'm late for dinner,鈥� and it stayed that way.鈥�
If it鈥檚 running in the right direction, Schuchard said and chuckled, it鈥檚 probably 鈥渏ust dumb luck.鈥�
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