Tower design

[Stewart Corman]

For those like me who are terrified about climbing up a guyed tower for fear of life, and also in my case where I want ease of changing experimental parameters at a moments notice and don't want a crew and tractor to raise a telephone pole from the ground to vertical ...the ham guys were fairly smart in developing a tiltup design. My buddy Jack and I went to see a Rohn 60 foot tiltup ham tower with what was known as a "backbone" and it was quite impressive.

All the more recent models have been "crank up", but I am planning to incorporate both constructions in same unit

I have recently found a pdf file which I converted to a jpg which details a Rohn tiltup product from several years ago
http://s145.photobucket.com/albums/r203/scorman1/Wind/?action=view&current=rohntiltover.jpg
(I have a much higher resolution image upon request)

The basic concept is here:

[Mark Parsons]

Greetings Stewart,

Great info on the Rohn tilt-up free standing.

I have access to an older 64 foot free standing TV antenna tower that is missing top 2 sections so is now only 48 foot. I am considering for Wind turbine use. I suspect it is a Delhi or Channelmaster unit.

Could you direct me to a resource to determine its loading capacity so I can design a wind turbine that won't twist it over?

Thanks and regards,
Mark

[Stewart Corman]

Mark,
I have only see Rohn close up and the custom made one in my pics.
If yours is similar construction ie welded tubular, then your question is not really relevant ...in compressive load, these will hold up many hundred of pounds ...BUT they require good guying to keep them from twisting in the wind at 60 feet.

The trick on building the tiltup is to have the cantelever (boom section) very heavy ie 20 ft section of 3inch thick wall steel pipe and then hang a few hundred pounds of lead ballast on the far end. That way the entire tower + turbine is almost balanced on the support tower and the winch just handles a 100+ pounds or so to pivot it up and down.

I will use (2) 11 ft sections of the heavy 3 inch steel channel that is shown at the base of my tower photo (the gin pole) ...I have (4) 14 foot sections that I will bolt to heavy angle iron top and bottom frame to make the "base section" and bolt it to footers, and the ham tower tilts/cranks up from there.

http://i145.photobucket.com/albums/r203/scorman1/Turbine%20project/4194.jpg

If you have all the right dimensions, you should be able to tilt it down so that the turbine is 6 or 7 feet off the ground for setup and maintenance OR ..just take it down if a hurricane is coming!

The problem with fixed length ham sections which don't telescope, is that you will have a very long lever arm with a heavy weight at the end which is hard to counterbalance.

Stew Corman from sunny Endicott

[Mark Parsons]

Hi Stewart,

Another great pic. Excellent idea with the gin pole on a lattice tower. I've only seen those with steel pipe towers.

I found the Rohn website and dug this page out for their BX tower.
http://www.antennasystems.com/bxload.html

I believe my scrounged tower will be very similar to the 48' - BX-3-4-5-6-7-8 line item. Shows an allowable thrust of 360 pounds.

My location will be amongst trees on the edge of open wetland. Guying will be problematic.

Wind atlas info for my site shows a wind speed histogram (Weibull) max of 14 m/s at 30m and my tower will only bring my rotor height to 16m. For 360 pounds = 160 kg of max thrust at 18 m/s wind speed on the above tower for a safety margin. My calculator tells me that turbine rotor diameter = SQR(160kg * 24 / 18 m/s *18 m/s) = 3.4 meters.

Calculator and resource data says I should be able to fly a 10 foot diameter HAWT without guy wires and have a 50% or so safety margin.

I know what you are saying about guying to prevent twisting. Had a microburst twist up my home antenna tower a few years back. The Weibull data for my cottage site where this tower is going doesn't show the F2 Tornado that tracked 3/4 of a mile from my place last summer. Biggest wind I've ever experienced.

I will have to reasses the guy wire situation.

Thanks for making me think this through.:)

Mark

[Stewart Corman]

Mark,
I checked out that link and not exactly sure their load data from antenna is equivalent to turbine rotors ..need to jawbone more

that said ...if you are making a self supporting tower, you have to cast a monsterous base ( reads tons of concrete)

but if you can cast a base, you can cast anchors for guy wires?
I have several concepts on how to do this.
Easiest mechanism if ground is soft (reads no rocks) is to drive a five foot piece of 2 inch angle iron (whose foot is cut to a triangle point), at an angle normal to the guy wire and weld a drop forged eye bolt at the top just above ground level.

I would do the above even if it is a self standing unit and go to a tractor supply and buy hi-tensilized galv non-barb fence wire for guy wire:
http://www.mytscstore.com/detail.asp?pcID=8&paID=1043&sonID=366&page=1&productID=15542
4000 ft/$80 and use two strands twisted


Stew Corman from sunny Endicott

[Mark Parsons]

Hi Stewart,

Thanks for the reply and the link for a source for steel cable.

My tower location is next to a creek. The soil / rocks above bedrock is of varying depth (exposed to 5' deep). I was going to probe an area that I can get my little backhoe into, to dig as deep as possible for the concrete base - yes tons of concrete. The creek itself will present a problem since the tower will be located on a pennisula with the creek on 3 sides. In attached picture the penninsula is on the extreme left of photo.

Is there a rule of thumb on setback of guy anchor to height of tower? i.e. 3:1 tower height to guy anchor.

Regards,
Mark

[Stewart Corman]

Mark,
nice setting ..wish I were cross-country skiing there now

wish I had a backhoe avail to dig footers:(

first, here is another link to a tilt-up design with photos:
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=12733

second, pdf on concrete footer:
http://www.ustower.com/40fs.pdf

third, more details on galv hi-tensile wire:
http://www.kencove.com/wire.htm
note:AG 200 12½ Gauge 200,000 PSI min = 1540 lb at .099 inch
so if you use 150# load, then 3 strands would give you about 500# working limit per guy wire assm ...(simple crank handle fixture and vise at other end to twist them)

fourth, link to otherpower where they have diagram of guy placement:
http://www.otherpower.com/otherpower_wind_towers.html

http://www.otherpower.com/images/towers/drawing1.JPG


me personally like a 45 degree guy angle so a 60 ft tower needs 90 ft guys and 2 shorter ones lower down every 20 ft

other idea since your backhoe can dig a deep hole ...collect car brake rotors or old car rims, weld to bottom end of 6 ft long scrap 1" galv pipe , cross weld scrap angle iron near ground surface, leave pipe sticking 6 inches above soil level, tap top end of pipe for 5/8 shank forged ring eye "knuckle" ( usually avail as scrap from local telephone co ) ...dig 5+ ft deep hole, place brake rotor at bottom, back fill, cast small concrete pad at surface ...this will hold tons!


BTW, same technique could be used to make foundation pad w/o tons of concrete ...four of the above anchor posts 30 inches apart with 5/8 bolts sticking out of the 1 inch pipe make a larger pad then the following:

check out this small footprint:

http://otherpower.com/windfarm/pigtowerhinge.jpg

..scavenge around your local metal salvage yard ...around here they get about $0.04/lb for scrap iron ...your mileage might vary ...look especially for telephone co hardware from poles (or ask them where they dump stuff) ..they use 14 inch 5/8 bolts, knuckles, turnbuckles, cable clamps, heafty brackets, thrown away guy wire assem, etc

BTW, I have a design for a selfsupporting "portable" tower ie not even bolted into footers ...hint, uses lots of steel (which I have)

BTW, you'd never catch me putting up this jin pole !:

http://www.kgnz.com/towerpics2/images/Jin%20pole%20going%20up_JPG.jpg


Stew Corman from sunny Endicott

[Mark Parsons]

Wow!!

Thanks Stewart for the links and info.

Lots more research for me.:D

Mark