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Tom's Wind Turbine -- Building the Tower

Since I could find no current "tilt style" wind generator towers over 80' to copy, I elected to expand on the design Prairie Turbines uses for the smaller towers and add common sense modifications to it. The tower is fabricated out of 3 - 42' lengths of 12" x 3/16" wall pipe with a 12' length of 8 1/2" x 3/16" wall pipe for the final extension. The center truss is located just over 60' up the tower, which is fabricated out of 2 1/2" thin wall pipe. This truss is supported by 45 degree angle supports to the tower as well, as the 5/8" truss cables place a tremendous amount of strain on the center truss when tightened by the turnbuckles on the bottom to straighten the tower.

The four other tower trusses are made from the same material and sized appropriately to scale so the cable runs straight over the center to the top and bottom attach points. If I was to build another tower, I would size the four smaller trusses larger so the cable placed a little more inward pressure on the tower (even when perfectly straight). All trusses have pipes welded on the end of them (guide tubes) to secure and route the cable as it runs past each truss. The center truss "guide tubes" were cut from a piece of 90 degree x 2 1/2" hard galvanized conduit normally used for the entrance conduit for an electrical service. I cut 4 pieces at about 22.5 degrees so I could compensate for the angle at the center truss and not damage the cables when they transitioned this bend. An added benefit of these guides is they closed off the end of the truss tubes. We cut and sized everything at my shop (I own a truck dealership and fabrication shop), and hauled it to my home at the time we were ready to assemble the tower.

Tower with truss work added.  Note the temporary supports for the tower.
Tom is recovering the sand used sandblast the pipe before painting.

When the cement work was done, it was time to transport and assemble the tower. We hauled the pipe out with a large truck and trailer, unloading it with my front end loader (although a small tractor with a front bucket would have served fine too). Once we had two of the 42' lengths of pipe welded together, it was evident this would need supports every 25' or so. The supports were not an issue at first, but once we started installing the truss piping, we realized the end of the pipe (at 140') would need to be quite a ways off the ground to clear the center truss. We made tower supports out of 2x10's, with a vertical support, two side supports at a 45 degree angle going from the tower to the ground, and a bottom support that tied all the boards together. These were leveled as well (my ground was slightly pitched where the tower lies in the down position). We were able to straighten the tower with the ground supports. It was surprising how much the pipe would bend over it's length before the truss and cable portion was finished and tensioned up. At this stage I was truly getting nervous. It seemed like the scope of the project may have gotten larger than my engineering abilities. The tower looked HUGE.

We welded the gin pole sections together and supported it for the truss work. This would have a tremendous amount of stress on it during the initial part of the tower raising. 20,000 lbs of force trying to compress this would likely collapse the pole without some "truss like" support. Using the same scale Prairie Turbines used for their "standard" 60' tower, I installed a truss on the gin pole made mostly with 3/4" re-rod, and 1 1/4" Schedule 80 pipe on the center truss. Re-rod was used for the tension part of the truss system as well, with the pole hung various ways to "tension" the re-rod while welding to the pole.

I was able to "borrow" a large capacity compressor and portable sand blaster to blast and paint the project. The sand blaster held about 300 lbs. of sand and the compressor had a 6 cylinder flat head gasoline engine powering it. I recycled most of the sand by laying two large tarps down, but still purchased 1500 lbs to complete the project. Since the project was so big, we had to break the blasting and painting into 4 segments. Any freshly blasted metal could not be left overnight or it would rust, so painting had to be competed the same day as the blasting. The gin pole was finished on one day (about 8 hours). The main pole was broken into 3 days (or partial days) of blasting and painting. We used a special Sherwin Williams industrial epoxy paint that did not require primer and rolled it on with small rollers. This was one stage my wife Beth really helped a lot; timing was critical to get the fast drying paint on before it set (and it got dark outside). As you can see from the pictures, my 8' and 12' step ladder got a workout for a lot of the painting.

Closer view of the tower truss work.
 

Tom

October 20, 2008