tower pipe types...

[birdhouse]

hello all-
i've started shopping around for tower pipe.  i want my tower to be 60 foot plus tower stub.  putting a homemade 8.5 footer on top of it. 

i started by borrowing a set of engineered plans for a tower from a turbine company.  they spec four inch schedule 10 pipe for up to 80 foot.  this is for their 11.8 foot turbine.  guys every 20 foot in all four directions. 

4" sch 10 has a .12 wall thickness.  it weighs 5.6 lbs / foot
4" sch 40 has a .24 wall thickness.  it weighs 10.8 lbs / foot
3" sch 40 has a .22 wall thickness.  it weighs 7.58 lbs / foot.

the 4" schedule 10 is hard to find and spendy.  (got a quote for $20.00/foot)
the 4" schedule 40 is easy to find and way cheaper $6.79/foot
haven't priced the 3" yet. but i'll bet it's cheap.

sorry to beat all around the bush, but MY ACTUAL QUESTION-  do you think 3" sch 40 has similar strength to the 4" sch 10?  it has near double the wall thickness and is super easy to come by.  and not too heavy either. 

it seems with the larger mills, folks are leaning towards larger diameter pipe with thinner wall because it is stronger, and i know i'm going in the opposite direction. 

my gut tells me that the 3" sch 40 would be plenty, but just wanted to know what you folks think. 

thanks
birdhouse

[slopecarver]

You will want to look at http://www.engineersedge.com/column_buckling/column_ideal.htm to find the real numbers for the strength of tubing as a column. make a spreadsheet as to the costs and weights for a tower of each size then look at your safety factor. Good luck with your tower selection.

[freejuice]

Birdhouse,
 It depends on what size wind generator you are using.
 I have 4 inch sch 40  tower at 60 feet, I think it could possible handlee a 14 footer, but I'm no enginner by any means. Currently I have a 11 footer on it and it appears very rigid.
 Personally, I would think a 10 footer would be fine on 3 inch sch 40, so as you use enough guy wires and anchor it well.

I cannot give you an answer on the thinner wall but larger diameter comparison....I just dont know.
 All the best,
 Gavin

[hayfarmer]

I went with the 3.5 inch sch 40,and if you ask they should have it in 24 foot length's as well as the 21 foot.

[birdhouse]

hey all-
thanks for the info!

i went to that buckling link, and got really confused really quickly. 

i think what it boils down to is if i deviate from a stamped plan then it is all based on gut feeling, and "knowing" what looks strong enough.  i do like the sch 40    3.5 inch.  kinda like splitting the difference. 

it's for an 8.5 foot homebuilt, but would like it to hold a ten foot dans type eventually. 

birdhouse
 

[youmanskids]

for what its worth,  my 60 foot tower is all sch 40, the bottom is 3.5 inch, midsection is 3 and top 20 foot is 2.5 inch.  I have a Dans 10 footer on top.  the 2.5 inch had MUCH more flex than I thought . adding an 3rd set of guy wires helped alot but if I had to do it again, I would go with 4 inch all the way up. hope my $ 0.02 helps. Roger

[prasadbodas2000]

My first post on upgraded board   
A typ wind turbine tower that we are talking about faces more of bending load due to wind thrust as compared to downward weight load of the mill itself. And that is why a set of guy ropes at suitable length is important. Let one of the guy ropes go away and even a supposedly stronger pipe tower will bend and/or collapse beyond repairs. Now having said that guy ropes are in place, then what determines the safe pipe diameter is the unsupported length between guy rope levels, mill weight and pipe section / size. And here is where the link http://www.engineersedge.com/column_buckling/column_ideal.htm is useful.

[birdhouse]

roger-  thanks for your info on your personal tower.  that's the kinda info i'm after.  folks who have self (but not really) engineered their towers and what they have observed. 

prasad-  i checked that website and have no clue what to do with their formulas.  it's funny, i can frame some of the most complex structures without batting an eye, yet the link you give sends me into idiot land. 

the master plan is a 60' tower with NESW guys 3 each, every 20' up the tower.  3/4 yard of concrete per guy footing, footings 30' radius around tower.  1/4" cable for top, then 3/16 for middle and lower.  full 30' gin pole. 1 yard for base footing, with a burly loose hinge, like the dans like.     

i'm just not sure on the pipe.  my gut tells me 3" sch 40 would be plenty for even a 10' mill, but i guess it is all a gamble. 

i really like the idea of 3.5" sch 40.  just haven't called around yet to see if it is redily aval and chep like the 4".

working on all the other parts too.  making my mind wiz!  volts, amps, watts, batteries, it's becoming a blur that i am welcoming with open arms!

birdhouse

[Art.S]

I may have a good deal on a 44 foot aluminum sailboat mast with a 8.5 inch x 5.5 inch base that is stayed at 24ft.  It seems pretty stout, and it once supported gigantic sails.  Would it support the 10 foot or 17 foot home brew?

[dlenox]

art,

I'd be very cautious in using this mast, it is elliptical shaped and therefore stronger along the wider length of the ellipse.

A wind turbine can get wind from any direction, and the elliptical shape is weaker across the narrower section.

Others may know if it could be suitable for a smaller turbine, but myself - I wouldn't do it.

Dan Lenox

[Tink]

Birdhouse,
I lucked out on my 40' tower in that I was able to wield together multiple sections of Sch 40 pipe of different diameters that I had laying around. But as I was shopping around for alternatives I came across 40' lengths of 3" sch 80 from a well driller in the area for a mere $6.00 a foot! I couldn't find a way to get to my location but that would have made a great tower. Granted the pipe was a bit rusty but could be sanded and painted to make a very usable tower. Just a thought. Also fence companies often have short lengths of sch 40 pipe of different sizes that they cut from their standard 20 and 24' lengths that they will give you just to get rid of it.
For what it's worth,
Tink

[birdhouse]

tink-
thanks for the info.  thats really cool you were able to "scab" your tower together using stuff you already had. 

i think i'm sold on the 3.5" sch 40 pipe.  (3) 21' sticks with a tower stub will give me 68' total.  i'll be happy with that.  now it's time to buck up and buy the stuff...  i wish there was such a thing as the tower fairy.  i'd just go up to my ranch and a tower would be ready for my turbine. 

it's all coming along...  got a layer of fiberglass on my blades last week...

birdhouse

[tanner0441]

Hi

As far as a boat mast is concerned.... A mast on a boat has the load distributed down the full length putting the base under shear stresses, not trying to flex the last few feet. also as stated earlier to minimise drag the masts are oval and not very strong on from the sides.

Brian.