Author Topic: Tower Construction (Read 6612 times)

kittysmitty · « **on:** February 19, 2011, 09:33:14 AM »

I'm planning to install a windmill at my off grid cabin in the spring. I starting now to "aquire" what I need for a tower. I'm looking at different options, guyed lattice, tilt up pipe, etc. Let's assume a 7 foot windmill. I need to know some of the "design factors" that come into play. I have heard that under strong winds the windmill is like having a sheet of plywood at the top of the tower.
So, first some factors. 7 foot windmill, tower height, 50 feet. It's in a remote location, so would have to withstand fairly high winds. If a hurricane was comming by, the plan would be to drive to the cabin and lower it for safty. I'm sure there is more that you required for answer.
My questions, what size should my guys wires be? What would be the safe working load? The guy wires would be set in a dug hole in concrete. With concrete at about 150 pounds per cubic foot, how much concrete.
Thanks

TomW · « **Reply #1 on:** February 19, 2011, 09:55:15 AM »

This is a good place to get a start:

It is an installation manual for a similar sized tilt up Bergey:

http://production-images.webapeel.com/bergey/assets/2010/7/28/67950/XL1.Tilt.IM.4.pdf

Tom

Seekscore · « **Reply #2 on:** February 19, 2011, 10:02:26 AM »

I just recently installed a tilt up tower. I had to hire an engineer to "stamp" the design. I copied what Dan's are doing. I installed a 12ft turbine. My tower is 58ft. Here are some specifics of what I had to use.

Wind rated at 110 mph. I am sure the engineer didn't figure in furling so this is figured with the full face of the blades always in the wind.

Guy wires 8200# break strength gave a 4x strength factor. I used 5/16th aircraft cable. I am using 5/8" turnbuckles with 12" adjustment.

No soil sample engineers report (too expensive) so the footings were designed assuming worst case soil. 2ft round x 10ft deep. Anchors set 3ft deep in concrete. 3000# minimum strength concrete. I used 4000# as it only cost a few more dollars. Anchors were 5/8".

Tower pad footing was 36" deep x 24"x24". 3/4" concrete anchors.

Tubing was 8" round 11GA. All other metal was 1/4" plate.

I use my 9000# winch on my Jeep to raise and lower. Can lower it in less than 5 minutes by myself.

Of course, you may want to consult an engineer with whatever you decide to do. Lots of tricky variables come into play.

Mike

imsmooth · « **Reply #3 on:** February 19, 2011, 02:27:40 PM »

In addition to the breaking strength of the cable, you need to take into consideration the angle they make with the ground (how far from the tower they are located). The further the cables are from the tower the less tension will be felt by the cable for a given lateral force component. An 8200lb-rated cable may work at 45deg, but fail at 60deg for the same thrust.

gsw999 · « **Reply #4 on:** February 19, 2011, 02:30:32 PM »

I have just built a tower very cheaply ,only 20 foot using basic materials I will put some pictures up tomorrow. I built it so that I can raise and lower without a Gin pole but just playing around.

Volvo farmer · « **Reply #5 on:** February 19, 2011, 08:44:09 PM »

Well, I'll throw in my .02

I don't think the tower pad need to be quite as robust as Mike has built his, The main forces on these towers come from the anchors. I don't understand why the pad itself would have to be 3' deep. Mine is basically sitting on top of the soil, about 2' x 2' and I have had no problems.

Now, I'm not advocating that this will work for everyone, by my anchors are 6" arrowheads driven in about 4 feet and set in undisturbed clay soil. 1.5 years later and none of them have moved much with a 40' tower. It's pretty amazing what a 6" equilateral triangle will hold under 4 feet of undisturbed soil. The pullout force is rated in thousands of pounds.

B529 · « **Reply #6 on:** February 19, 2011, 09:21:01 PM »

Quote from: Volvo farmer on February 19, 2011, 08:44:09 PM

Well, I'll throw in my .02

I don't think the tower pad need to be quite as robust as Mike has built his, The main forces on these towers come from the anchors. I don't understand why the pad itself would have to be 3' deep.

I'm guessing Mike's engineer was taking frost line/heave into consideration. What's another yard of concrete in the whole scheme of things for good measure?

97fishmt · « **Reply #7 on:** February 19, 2011, 09:51:16 PM »

http://fieldlines.com/board/index.php/topic,127295.msg816762.html#msg816762

It was a lot of work for me but, well worth it.
65' Rohn 45g tilting base. I'm using 3/8" guys
just because I got it for free.

http://fieldlines.com/board/index.php/topic,130202.msg847114.html#msg847114

gsw999 · « **Reply #8 on:** February 20, 2011, 08:12:40 AM »

Heres the stuff I have been working on , Tower is made up of 2 x lenghts of 60mm od 3mm mild steel, with 2 x 1m 52mm OD mild steel poles connecting them and also for the turbine head to sit on , the power cables arent connected as I want them to have a good thrash make sure they are stable

Onwards and upwards

Peace

freejuice · « **Reply #9 on:** February 20, 2011, 08:42:56 AM »

Nice setup you've got! How tall is it...about 40 feet?

A few friendly suggestions: Add at least another cable clamp to the existing cable clamps. at least have two on each connection...I think most folks use three.
I think in photo 4 you have a bare cable going through a plate has a drilled hole...you might want to add a thimble there to cut down on wire chaffing.
Lastly ( I am a bit paranoid about towers) but on your shackes they are the nice screw in type...I use a piece of wire to lace through the pin and then around the "U" portion of the shackle...to keep those threaded pins from backing out....I think folks call that "Mousing the cable"

klsmurf · « **Reply #10 on:** February 20, 2011, 08:56:28 AM »

Nice "Dualie". Yes, a minimun of 2 clamps and remember, " Never saddle a dead horse".

Flux · « **Reply #11 on:** February 20, 2011, 08:57:29 AM »

For peace of mind you have to assume the prop area is a disc, that is the worst case. If it furls properly the loading will not significantly increase beyond the furling speed so your disc loading figures will be way above anything that the machine produces.

If you have to pass inspection or satisfy safety requirements you will need to do much more than is really necessary for a small machine. Also if it is a remote site do you need to go to 50ft, that depends on the local conditions. A 7ft machine at 30 ft doesn't really need a massive tower if it furls properly, the loading is much more modest than the worst case conditions you need to satisfy inspectors.

Taking it down in a storm is a nice thought but the day will come when the storm happens and you can't be there. Make it furl properly and it will survive.

Flux

Seekscore · « **Reply #12 on:** February 20, 2011, 11:38:24 AM »

GSW,

Interesting concept for twin turbines.

I can't tell for certain, but it looks as though your cable clamp is on wrong. Looking at picture 008.

Mike

gsw999 · « **Reply #13 on:** February 20, 2011, 12:01:05 PM »

thanks for the advice guys,Yes I def need to improve a few things, just wanted to have a go at getting it up , its only 20-25 feet and I want to add at least another 10-20 feet to it.

The cables are on tight but yes there are a few that need putting on better( clamps etc ) , plus they need thimbles etc.

Next tower I build im going to try and track down a load of bulk cable.

What cables do people use, I am using a mixture of 4mm 6mm and some 10mm , also I still have the winch connected , I know this is not good practice, plus I didnt use a gin pole I just used a hook in the ground.

The tower portion itself can be built at extremely low cost but obviously gonna make a few changes before I get my 10 footer flying.

Got a couple of vids up on youtube.... peace

Hardly any wind blowing in these vids, these aluminium blades sure do catch the wind

http://www.youtube.com/watch?v=I3t2VCaGR7s

http://www.youtube.com/watch?v=kaW09YJNng4

Ill get there in the end gonna keep making improvements and stop burping / heavy breathing in the videos

ghurd · « **Reply #14 on:** February 20, 2011, 01:43:18 PM »

"Never saddle a dead horse"
G-

imsmooth · « **Reply #15 on:** February 20, 2011, 02:22:14 PM »

This page talks about the anchors
http://www.mindchallenger.com/wind/wgpage11.html

The pages that follow go into some of the physics of the tower.

My tower is 42' and it is just resting on a steel pad with a pivot for the tilt-up. It has been over two years and it hasn't moved.

gsw999 · « **Reply #16 on:** February 20, 2011, 02:47:35 PM »

Will be taking it down tomorrow and will redo the anchors,for starters.

freejuice · « **Reply #17 on:** February 20, 2011, 03:06:24 PM »

Hi,
Dont know if this helps, but I use to buy my 1/4 inch cable from this guy on ebay....dont know anything about them, but they were in Virgina and use to ship it fast.....he was about the best prices I could find:
http://cgi.ebay.com/Wire-Rope-Aircraft-Cable-1-4-7x19-250-ft-Reel-/150556762510?pt=LH_DefaultDomain_0&hash=item230de1e18e
..... However, I know you are across the pond so shipping might be a bear!

gsw999 · « **Reply #18 on:** February 20, 2011, 03:50:56 PM »

That is a pretty good price but would like you say be too expensive to ship , Im keeping an eye out for the offers.

hayfarmer · « **Reply #19 on:** February 20, 2011, 10:29:06 PM »

Hi I bought my 3/8 galvanized cable from the same guy on eBay,its from china $:-\$ but what isn't,his prices were the lowest by far .25% of cost for the exact item from TSC.you may want to google lowest price wire rope and find a supply house on the left side of pond.http://cgi.eBay.com/Wire-Rope-Aircraft-Cable-1-4-7x19-250-ft-Reel-/150556762510?pt=LH_DefaultDomain_0&hash=item230de1e18e

hayfarmer

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Author Topic: Tower Construction (Read 6612 times)

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