What is this?

March 11, 2012 6:26 PM

What are these giant fans/propellers I sometime see in farm fields?

There is a picture of one here. Sometimes I also see smaller ducted ones, maybe 5 feet in diameter. This one is I. A field of ornamental bushes, but I can also remember seeing them in vineyards and other places (around northern and central California at least).

What are they? What is their purpose?

posted by tylerkaraszewski to Technology (5 answers total)

Best answer: They are frost fans. They blow air across the crop to keep it from freezing in some conditions. Here is an example manufacturer.
posted by ChrisHartley at 6:29 PM on March 11, 2012 [3 favorites]

I asked a farmer the same question. What ChrisHartley said.
posted by zippy at 6:51 PM on March 11, 2012

They are the sensible alternative to this.

Cold air is denser than warm air, so it literally flows (like a fluid) downhill into valleys and low spots. Mixing air from just a few meters above can make the difference between saving the harvest and a hard frost that's a total loss.
posted by wnissen at 7:49 PM on March 11, 2012

And they make for a terrible night's sleep. Those suckers are LOUD.
posted by Cortes at 7:50 PM on March 11, 2012

Here in southern Oregon the fans are used a lot to protect pear orchards from frost, together with water spraying to put a thin layer of ice over the trees to protect from lower temperatures. These are a vast improvement over the smudge pots that were used which burned oil to create the slightly higher temperatures needed. They also created horrible smoke and smog conditions.

The fans often come on very early in the morning as temperatures reach the lowest points and sound like a huge invasion of helicopters.
posted by uncaken at 8:17 PM on March 11, 2012 [1 favorite]