Results 1 to 10 of 10

Thread: Small Wind Tower Deflection

  1. #1
    Associate Engineer
    Join Date
    Nov 2012
    Posts
    4

    Small Wind Tower Deflection

    Hello,

    I want to build a tower to support a 75kg turbine.
    I have access to some 8/5/8" pipe with a wall thickness of .25".
    What I would like to do is embed about 8 ft of the pipe in concrete and have 27ft of the pipe sticking above the ground.

    My question is what kind of deflection would I see @ 40 mph,90 mph, and 125mph?

    The other information I have is the lateral thrust of the turbine which is 800N @ 27 mph and 8600N @ 90mph.

    Thanks!

  2. #2
    Lead Engineer RWOLFEJR's Avatar
    Join Date
    Mar 2011
    Location
    Rochester Pennsylvania
    Posts
    396
    Hi pechan and welcome to the forum.

    I made a couple assumptions... low carbon steel pipe... and babies and puppies playing directly below this... and sorry to say... The pipe you selected won't handle your load. I didn't go full out calculating this because I can be a little lazy sometimes. I just took a quick look at the stress and deflection with just the turbine thrust load you gave, and your tube or pipe doesn't come close to cutting it. Add to that the tower weight and drag etc. and the numbers will only get worse.

    You should contact the manufacturer of your turbine and tell them how how high you need to go and have them tell you how much tower or post you're going to need. Better check with your local building codes to be sure you're even going to be allowed to put the thing up. A lot of places frown on them?

    Good Luck,
    Bob

  3. #3
    Technical Fellow
    Join Date
    Feb 2011
    Posts
    1,043
    Welcome to the forum. Having spent some time with wind and solar power systems there is more to this than just deflection. Also you have fallen short on providing enough information. What are the lateral thrusts at speeds higher than 90mph? It would be unwise to consider it as linear and just extrapolate from the 27 and 90 figures.

    Soil compaction and stability for the embedded end would need some looking at too.

    Can the slewing bearings and supports handle the thrust at 125mph or local-Code-max + safety factor?

    Have you considered making the support in two halves hinged in the middle so the head can be lowered for maintenance without hiring a 50' crane? How structurally sound is that mechanism if it exists?

    What is the local Code for snow-load and wind-speed? At 125mph, you may be being conservative if something fails and the head cannot be dragged (yawed) out of the wind.

    How close to buildings and people will this be?

  4. #4
    Associate Engineer
    Join Date
    Nov 2012
    Posts
    4
    Thanks for checking the out for me RowlfJr,
    I am out in the country so permits/ neighbors will not be an issue.
    The soil is clay, and I was planning on drilling a 3' diameter hole and concreting the pipe in.
    Sounds like I need to go in another direction since this pipe will not handle the load.
    PinkertonD,
    The turbines I have are the Kestrel 300i 1000 watt units.
    The blades furl under high winds to reduce the rpm/ load on the unit.
    I have thought about making a tilt down tower, and it would be preferred for easy of install etc.
    This would be installed about 100 feet from my house, in a rural Wyoming.
    Does anyone here have a design for a tilt down tower they would like to share?
    I do not know how to do the calculations to know what would hold up in high winds.
    I might have to just use guy wires, something I was hoping to avoid for aesthetic reasons/ just being in the way.

  5. #5
    Technical Fellow
    Join Date
    Feb 2011
    Posts
    1,043
    Hi Pechan,
    A 3' diameter hole x 8' deep is a lot of concrete and probably overkill. I would talk to a local Engineer as with local-knowledge he may be able to reduce that diameter significantly. What you save on concrete will pay the Engineer.

    Guy wires generally, add stability not strength. They are there more to prevent failure than to support an actual load. Look at them more as a safety net than a full structural member. They will reduce the cost of materials greatly though.

    Having helped some neighbors by insisting on the folding down system, you will appreciate the value, the very first time you need to pull the head down to fix a loose wire or some chafed wire-insulation. I would suggest the fold-down be a mandatory part of your design.

    You would probably be better advised to find a local Engineer to design the mast system. There are too many variables that depend on locality and weather conditions. Local solar/wind installers will probably have masts that are over-kill and overly costly whereas an Engineer may well be able to provide you with a safe design you can build yourself for a third the cost of commercial units.

    I would be very cautious of any designs offered by the faceless "experts" of the Internet, myself included. You are going to have a lot of bucks spinning on top of that mast and I doubt mast-failure will be an insurance cover item.

  6. #6
    Lead Engineer RWOLFEJR's Avatar
    Join Date
    Mar 2011
    Location
    Rochester Pennsylvania
    Posts
    396
    I'd be inclined to go with something built like what you see every day where you're at. (See attached picture of my buddy our first day in Lusk Wyoming) Sturdy and they look really cool...

    Copy the design using steel... Big pins at the base so you can lay it down.

  7. #7
    Associate Engineer
    Join Date
    Nov 2012
    Posts
    4
    I have seen many of those windmills throughout the west. Built in the 30's and 40's and still running!

    Well I hate to ask again, but I went down to the scrap yard today and found a hexagon shaped piece of steel 5 inches across from one flat side to the opposing one, this steel is about 1.25 inches thick and 35 ft long.
    would this do any better?

    thanks!

  8. #8
    Lead Engineer RWOLFEJR's Avatar
    Join Date
    Mar 2011
    Location
    Rochester Pennsylvania
    Posts
    396
    Hi,
    Believe it or not that heavy bugger would actually be worse. You need to get the diameter up to reduce deflection. It can be light wall (relatively speaking) if the diameter gets much-much bigger. Problem is the single stick with a big load wagging around way up there. There can be a tremendous amount of gain in rigidity with tower designs.

    I'm sure you understand that the higher you go the worse it gets... and the bigger the load same thing. You will have some amount over a ton pushing on the top of the post in a 90 mph wind trying to bend the thing 27 feet away. That's a lot of leverage. If it were a huge cheater bar on a wrench you'd be producing something over 54,000 ft. lbs. of torque.

    I took a quick look on the manufacturers site and looks like they only offer up to 12 foot and that was guyed. They're also only rated for the 90 mph with your unit on it so anything over 90 might void the warranty?

    So things to consider... Can you reduce the height or get it up on top a nearby hill? (wire is relatively cheap) Maybe clear some tress that are in the way? (wood burner?) Or are you O.K. with spending maybe as much as you did for the unit for a stick of BIG tube? Or maybe you can do a search for folks making tapered poles and find something for a little less that'll get you up there and work? You might possibly save a little building it in reduced section sizes but I doubt it for one post. Or maybe live with the guyed wires?

    Or maybe build a really cool looking tower?

    Bob

  9. #9
    Technical Fellow
    Join Date
    Feb 2011
    Posts
    1,043
    Quote Originally Posted by RWOLFEJR View Post
    I took a quick look on the manufacturers site and looks like they only offer up to 12 foot and that was guyed. They're also only rated for the 90 mph with your unit on it so anything over 90 might void the warranty?
    ...or worse, overload the pitch-control mechanism and prevent blade-furling over 90mph. We could look for the OP's video on YouTube.

  10. #10
    Associate Engineer
    Join Date
    Nov 2012
    Posts
    4
    Quote Originally Posted by RWOLFEJR View Post
    Hi,


    I took a quick look on the manufacturers site and looks like they only offer up to 12 foot and that was guyed

    Bob
    That is 12 meters.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •