Building light weight tail

[windy]

 I am trying to build a light weight tail for my 17 foot  diameter generator and would like some suggestions before I proceed. The tail I am using now is made out of aluminum, but it is too heavy. The entire tail assembly weighs about 35 lbs with the tail alone weighing 15 lbs. I can't go any thinner on the tail without it getting flimsy.
 The offset is 9 inches, the tail boom is 10 feet, and the tail area is 14 square feet. I also made the tail angle adjustable, but can't adjust it anywhere near to 20 degrees. It will not furl if I set it at 20 degrees and if I set it at a lower angle, it furls to soon. It's too hard to adjust with the tail that heavy.
 I would like to keep the tail weight under 7 lbs but am not sure what kind of material to use. I looked into using thin plywood but it would still weigh around 1 lbs per square foot. i also looked into using laminate bulkers but by the time I add the resin and a few layers of fiberglass, I still get over 10 lbs.
 Has anyone tried laying up multiple layers of fiberglass to make a light weight tail? I could easily stay around 7 lbs if this would work.
 Any suggest or comments would be greatly appreciated.

windy

[spottrouble]

Are you rolling beads into the sheet metal to stiffen it? Flat aluminum sheeting has no stiffness, with beads rolled into it it can become quite a bit stiffer, both in the horizontal and vertical axis. Talk to a sheet metal man.

Kristi

[Mary B]

Carbon fiber? http://www.dragonplate.com/ecart/categories.asp?cID=35 yes I know relly expensive 

[breezyears]

You can make your own "foam core" tail using carbon fiber.
  A much more economical choice over buying it already laminated.
http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=10720

[fabricator]

There are lots of tails out there that are made out of Dacron sail cloth, make a frame out of thin wall conduit and have a canvass shop make you a sail with grommets to fit inside the conduit, then simply zip tie it in place, you want to make sure you use the zip ties that are UV proof though.
Your 14 sq ft sail would weigh 54.6 ounces using the typical 3.9 oz Dacron sail cloth.

[windy]

Thanks for the replies.
 I looked at different carbon fibers. You're right. TOO expensive.

 Fabricator, I like your idea of using Dacron sail cloth. Twenty five dollars for the sail cloth and conduit is cheaper than anything I could think of and I can choose from different colors. I have the tools for installing grommets, so I can do that myself.
 The tail will not be square. It will be 60 inches tall in the back, 50 inches long and 40 inches tall in the front.
 Could you recommend what size of conduit to use and what would be a good spacing on the grommets. I'm thinking 3/4 inch ID conduit with 6 inch grommet spacings.

windy

[nekit]

I built mine out of 1/4" foam core and two layer of fiberglass cloth on each side. You'll want to put hard spots where it mounts and along the edges.  I build Carbon fiber racing parts for a living, and it's probably over kill for this application.  Fiberglass should be fine.  Not sure how much lighter this will be than aluminum. I never weighed mine.  I also used some left over chromemoly tubing for the tail structure to save weight.  I have areas at the tip of the tail that I can fill with lead shot to adjust the weight.

Hope this helps.

[taylorp035]

Well.... if you want to save weight on both parts, doing a carbon fiber frame to hold your tail could save a bunch of weight and not too hard to make with pre-made joints and carbon fiber tubes.  As for the sail, carbon fiber isn't going to save you a ton of weight when compared to aluminum unless you make it half the thickness of the aluminum.  I would think a frame of C.F. to hold the cloth material suggested before me might be a good idea.

I have also heard that it might be necessary to have something to protect the glue from breaking down from the sun rays... maybe Nekit might have something to say about this or a little research.

From my experience, 2 layers of 3k thick C.F. would just fine IMO, but you will still see small holes between the fibers after you are done.  3 layers of 3k would block 99% of the holes.  Or you could do 2 layers of a heavier material like 12k would do the trick too.  Stiffness at 3 layers of 3k or 2 layers of 12k would be a little less stiff than 0.032" aluminum sheet metal.  But as long as you had a frame, 1 layer would probably do it (our seat for our supermileage car is only 1 layer thick, so it support at least 200 lbs).  But from a $$$ standpoint, using C.F. for the sail isn't a great idea.  I'm guessing you would be looking at about $100 or so.

I didn't realize the C.F. sandwhich pre-made material was so expensive....  I would make my own with some foam and two layers of C.F. fabric... and you could jump on it like a trampoline when you are done.


Here is a pic of a ~1"x6" beam with a foam core (house insulation).

[spottrouble]

Dacron is a pretty good idea, thats the same stuff used for covering fabric aircraft. Get some Poly-Tak (Aircraft Spruce and supply Co. I have no affiliation), you glue Dacron to the tubing with the poly-tac, then run a hot iron over the dacron  to shrink it, then paint it with silver roof paint to block the UV's and seal the dacron. Its super easy to work with, but I'd recommend trying it on a 1' square frame if you just want to get a feel for it first.

Kristi

[scoraigwind]

20 degrees is a pretty big angle for a tail hinge on a 17 foot machine.  I imagine there is a way to solve this using a lightweight tail, but the easy way to solve it is to reduce the hinge angle to about 7 degrees.  The important thing then is to be sure your yaw bearing is truly vertical or you will get different furling behaviour in a west wind from an east wind.

[fabricator]

Thanks for the replies.
 I looked at different carbon fibers. You're right. TOO expensive.

 Fabricator, I like your idea of using Dacron sail cloth. Twenty five dollars for the sail cloth and conduit is cheaper than anything I could think of and I can choose from different colors. I have the tools for installing grommets, so I can do that myself.
 The tail will not be square. It will be 60 inches tall in the back, 50 inches long and 40 inches tall in the front.
 Could you recommend what size of conduit to use and what would be a good spacing on the grommets. I'm thinking 3/4 inch ID conduit with 6 inch grommet spacings.

windy

Sounds good to me, but so does Hughs suggestion.

[windy]

scoraigwind,

 Thanks for the reply.
  I built the generator using the book, "Homebrew Wind Power" by Dan Bartmann and Dan Fink. They used a 20 degree tail angle,so that is what I used. But I made my tail angle adjustable.
 I don't know what angle I have it set at now, maybe 7 to 10 degrees, but when it furls, I hardly notice the tail raising. In gusty winds, I have seen it go over 80 amps at 55 volts, so I am reluctant to increase the tail angle.
 In the 15 to 20 MPH wind speed range, it furls and watts drop to around 800 to 1000. I would like to start furling just above 20 MPH which should generate around 3000 watts. That is why I would like a lighter tail so I can increase the tail angle. It doesn't seem like there is enough adjustment with this heavy tail.

windy

[scoraigwind]

One thing to be aware of is that the tail can't be expected to control the output when the wind changes rapidly.  A big machine like that takes a wee while to yaw out of the wind and would damage itself if it tried to do it faster anyway.  So there will be surges of current on turbulent sites even where the tail is working perfectly.  You may need to include sufficient dumping capacity to absorb these surges of current so as to prevent overload of the system.  Sustained high currents can be addressed by adjusting the tail but brief gusts will tend to cause brief surges.

[fabricator]

That sounds pretty close to the setup I have on my 17' machine, but mine is wired for 24 volts, I'm kind of curious, if you have a good dump control setup you should never see much over what you have your max set point set at.

[windy]

fabricator,

 I use two Morningstar TS-60 controllers with independent 5000 watt dump loads. One dump load is used to heat water and the other is in my forced air furnace.  If the first controller gets to 3000 watts, battery voltage starts to increase and the second controller starts to dump into the furnace. With this setup I should be able to peak 6000 watts. Each controller handles 3000 watts.
 Another question. How did you make your tail and how many square feet?

scoraigwind,

 With my adjustable tail angle, it is tough to know where it was set after I release the bolts. I will have to put an adjusting bolt to raise or lower the tail angle. Maybe I need to set it a degree at a time and see how it runs.
 I was thinking that with a heavy tail, when it unfurls, it continues to rotate the entire generator out of the wind. At least that is what it looks like it does. The blade almost stops rotating before swinging back into the wind. I have seen it go from 80 amps to 20 amps in a few seconds and back up to 50 or 60 amps. It's all over the place. The yaw tube is mounted on a bearing so there is no drag on  the yaw tube. Maybe I'll have to post a video.
 I was thinking that it may be turbulence, but if I apply the brake, the tail hardly moves from side to side.

windy

[fabricator]

My tail is pretty heavy, it's made out of 1/8" plastic sheet. about 12 sq ft

[just-doug]

i would double check the smoothness of the tail hinge.