Tower legs, 3 or 4

[Windmill Farmer]

Anyone know of a good write-up of the virtues of 3 versus 4 leg towers.

c

[JBarker]

Letter

[billcobb]

From wreckage I've seen, the foundation elements are the weak point. Ground irons pull out and lower leg sections bend to allow ground angle irons to pull straight up. A sturdy bottom section is a benefit as well as the pullout mechanism. If the fan is facing into the wind, a larger moment is created which further aggravates the likely-hood of toppling.

Last one I saw had the tower base welded to to the ground irons. Welds fractured from vibration, age, corrosion and fatigue cycles. But, it did get me a nice Aermotor cheap!

[Kansas Rust Buzzard]

Every old timer I ever talked to said a 3 leg was stronger than a 4 leg but you couldn't sell them. When I was a kid, almost every tower around in a pasture was wood, still a lot of them but the center pivots got rid of most of the grassland. I would like to know how the engineering data would work for wind load when when you figure a 40 foot 4x4 tower with all the sheathing on it. When you think about it, the structure alone catches a lot of wind. I have dug some anchor posts out on the old wood towers, normally they took a big hedge post and bolted two deadmen on the bottom and must have tamped them in good with moist soil as I have never seen a hedge post pull out yet. Now I have seen a lot of concrete pull out on steel towers, some amazing chunks in sand.

[Ron Stauffer]

This was often discussed in the old forum. This is the most documented info that I have ever found, I had posted this on the prior forum, from the 1901 Aermotor catalog

3 vs 4 p1.jpg

3 vs 4 p2.jpg

Ron Stauffer
Montrose CO

[windybob]

The discussion still goes on. I thought the whole world knew by now that 4 legged is stronger than 3. lol

You get one triangle with a 3 legged tower, draw a line diagonal across 2 legs of a 4 legged tower. Voila'! now you have 2 three legged towers in one, plus 1 more anchor in the ground with each 3 legged setup..
Seems to me 4 legged is always stronger. Of course, 1 less leg, reduced cost, and much advertising can get a company through a depression when times are hard.

[Kansas Rust Buzzard]

What is this about a 3 or 4 legged milking stool? I never had anything like that, just one post you had to balance on? Gee, rich people......

[Wayne]

I don't know I've read the 3 legged is stronger. Look at what most radio towers of today are. Triangles are stronger than squares. The stories I've read you were thought to be cheap or too poor to buy a real tower is why you went with a 3 legged. So no one wanted to be labeled as cheap so the 3 legged was a tough sale.

[windybob]

I'm just tweakin' the folks. lol Not twerkin', tweakin. lol

[63markB]

Interesting for sure! When did aermotor quit offering the three legged tower? Or do they still?