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Forum Index : Windmills : Thinking about styrofoam for hawt blades
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| Throgdor Newbie  Joined: 26/01/2012 Location: United StatesPosts: 22 |
I'm seriously thinking about making styrofoam blades for a hawt. I've never used a hot wire foam cutter or even made one. The blades would be very close to the wood blades I have come up with (2 wood blades finished, but not as straight as I want. Length would be close to 4 feet per blade, 5.5 inches wide at the hub and 4.5 inches wide at the tip. If anyone has any tips on making a hot wire foam cutter, I would like to see what you have come up with. Cutting through 4 feet of foam is a concern I have. I do have the airfoil shape for the hub and tip area figured out. Just need find material to cut it out. Either aluminum or formica. I've also done several searches for images of styrofoam blades and the only ones I seem to find are a few vawt types.... My first foam blades would have the fiber embedded strapping tape applied to minimize flexing/bending. (The first radio control plane I had many years ago had foam wings that had the same type of tape applied to the bottom of the wing. The tape made a huge improvement in strength. |
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| VK4AYQ Guru  Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Throgdor The blade length you propose would give a diameter of approx 9 feet and would stress the Styrofoam severely during furling and directional changes I feel it would require a wood spar to provide some rigidity and a skin of fine glass matt with epoxy resin to reduce erosion into the blades to get a useful service life from them. There are a lot more stresses in a VAWT blade than a light model plane wing. All the best Bob Foolin Around |
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| Throgdor Newbie Joined: 26/01/2012 Location: United StatesPosts: 22 |
The blade would be a hawt blade, not a vawt (Just to clear that up). Vawt styrofoam blades are the only ones I can find images of so far, other than RC wings. It kind of would be nice to see how they look and how it was done. (Any HAWT foam blades that is!) Nice to have reference material. As far as reinforcing, that may be needed, but my initial challenge is coming up with a hot wire foam cutter/ making one. However those "light" RC planes can pull many more G's than a real plane, so they do go through more stress than one might think. I still think applying fiber embedded strapping tape over the (whole) blade might be a good initial start, one I learn how to hot wire cut the foam. |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
I agree with Bob, there is a lot of force on a turbine blade, much more than a typical wing. A 4 foot blade will have many kg pressing on it during normal winds, and this can rise to 10's of kg in strong wind gusts or storm conditions. It's the reason a light plane has wings made of fine timber spars and fabric, but a propeller made of solid laminated timber or aluminium. A coating of fibreglass will strengthen a foam blade many times, without adding much to the overall weight. Might be an idea? Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| karvik Newbie Joined: 10/06/2012 Location: EstoniaPosts: 3 |
rc planes must handle 20-30G forces. If 4 foot plane weight is up to 1kg then the wing must deal with the force and they are strengthened only wood or some fiber. i have made one set 1,2m Piggotts blades from styrofoam and they work. i strengthened the face with glass fiber. i used hacksaw, knife, file and sandpaper. it took 2 hours for set of 3 blades. to cut foam i use old 200W PC power supply and 0,8mm welding wire around 1-1,2m length. if wire is too short the wire gets too hot and its not good. http://www.daswindrad.de/forum/viewtopic.php?f=17&t=958 this forum is in german but pictures are same in every language. sorry for poor english |
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norcold Guru Joined: 06/02/2011 Location: AustraliaPosts: 670 |
Feel there would be some advantages using styrofoam, you could cut tapered blades altering the airfoil from a low speed on inner to a high speed airfoil on the outer, probably have a steel tube for strength inserted up a distance. The steel tube would allow an easy fitting to the PMA with the added advantage of allowing the angle of attack to be easily altered. My experience with foam wings on RC planes is they take a lot of punishment especially when covered with glass cloth and epoxy(although a little heavy) . Just make a bow up to tension the wire suspend it from the ceiling with pulley and counterweight to balance, with a variable DC voltage power supply to get the temp right. Cut two airfoil templates with equal number of graduations,pin them on each end of the foam blank than draw the hot wire through the foam ensuring the graduations are reached at each end simultaneously(two people required) As Karvik has noted you`ll have to play around a little to get the temp right, but the results will give you blades that are probably closer to dead equal than any other method and with practice very quickly. Just google search to obtain airfoils(100`s) We come from the land downunder. Vic |
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| Throgdor Newbie Joined: 26/01/2012 Location: United StatesPosts: 22 |
Thank you for this reply, which is the first on trying to describe what to use for power. (Which is what I asked for in my first post on this thread.) I still have no idea what wires from a PC power supply would be my live wires, or even how to rig that up. |
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| Throgdor Newbie Joined: 26/01/2012 Location: United StatesPosts: 22 |
I have the desired airfoils already. However I have no idea what Voltage or amperage I need, plus the wire type would also impact the volts/amps. 12 volts 2 amps? 19 volts 3.5 amps? Yes, I would need 2 people or a weight system to pull both ends of the bow, I agree. I also think the styrofoam blades could be more uniform and consistent if done properly. I have found some info on powering up the wire at http://hotwirefoamcutterinfo.com/Hot_Wire_Foam_Cutter_Info/H ot_Wire_Foam_Cutter_Info.html I emailed this guy (above site owner) and he even wrote back. I still don't have all the info I need, but am on a better direction. A side note: The raw materials cost. For the 48 inch long blades out of pine or spruce cost is $1.50 per blade. Blades made from the blue styrofoam would cost $1.75 per blade. Not including mishaps of course. Also not including finishing materials such a fiber tape, or fiberglass, or paint. Thank you to everyone who has made some input on this. For the near future I'm going to finish up the 9 wood blades I have first before I attempt any of this styrofoam cutting. |
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| Xmaswiz Regular Member  Joined: 14/04/2011 Location: United StatesPosts: 69 |
if you look at this post, you may get some of what you are looking for my new blades Santa Maria, CA. Noel |
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| Throgdor Newbie Joined: 26/01/2012 Location: United StatesPosts: 22 |
That is interesting, but after doing a search for STYRODUR I could find nothing about it in the USA where I am. Also my first most important question (to me anyway) on this thread was How to make a Hot Wire Foam Cutter. For me to be able to cut 48 inch long foam blades is the First step, which I am a long ways from still. So far I haven't seen any members detailed images or descriptions on how or what they used to hot wire cut foam blades..... |
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| Xmaswiz Regular Member Joined: 14/04/2011 Location: United StatesPosts: 69 |
do a search for his posts, I know he had one of how he made his Blades.  Santa Maria, CA. Noel |
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| windtinker Newbie Joined: 16/01/2012 Location: New ZealandPosts: 38 |
Hi Throgdor, You could buy nicochrome wire from a electrical store, its the same stuff in a toaster. 1mm wire about 60cm could get powered from a car battery for about 2mins shorted. You could probable by a 240volt/110volt 1amp transformer socket which might power about (12v*50am=600,110*1=110) 6-10cm wire. Thinner wire heats up more with less power... |
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| karvik Newbie Joined: 10/06/2012 Location: EstoniaPosts: 3 |
in mi experience thinner wire is not good because it cools down in the in the middle and heats up in the ends. if you use CNC then its a different story. if i remember correctly, 0.8mm cheap welding wire uses around 4amp in 1.2m(47,25inch) length at 12v. heats up enough to cut and does not stretch. you can change the amps and heat of the wire by changing the length of wire. thin and long wire bends easily and the cut is not straight. with shorter cutter you can use thinner wire. i made mi cutter like antique bow saw. if you have old type of pc power supply (AT) then is easier to use it, but with newer power supplies(ATX) you have to google how to turn it on and some of them had some problems when you use only part of it (only 5v or only 12v). 100-150w variable power supply is perfect. sorry for poor english |
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| Throgdor Newbie Joined: 26/01/2012 Location: United StatesPosts: 22 |
I found this on http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-t o-a-Lab-Power-Supply . Thought it might help others who are following this thread. It is fairly descriptive and does have a video as well if you scroll down. Time for my morning coffee. |
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| Xmaswiz Regular Member Joined: 14/04/2011 Location: United StatesPosts: 69 |
thanks for the link, looks pretty easy, if you do a search there for power supply, you can also find a diy for a veriable output from ATX unit, only slightly harder, and a few more bits to get, but then you have some very fine control for your cutter. also if you have an old heating pad that doesn't work anymore you can take it apart for the nichrome wire to practice with. it is usually 26g, wound around a non conductor. just have to be careful while stripping the outer jacket and sleave. Santa Maria, CA. Noel |
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TEA20 Newbie Joined: 10/06/2011 Location: AustraliaPosts: 7 |
Hi guys, I have made a foam cutter from the nichrome wire removed from an old hair dryer and a small gel battery, to get the shape on the wings i made some end profiles out of MDF pinned them to the ends of the foam. I used a pair of metal rings on the ends of the wire to pull it tight over the two MDF ends, worked great Muchea W.A. |
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MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Throgdor Coroflute Blades are pretty easy to build and if you put a hollow T-6 aluminum (aircraft grade) pipe up the center, it'll stand up to ginormous forces. I buy the Coroflute (called Coroplast in the States) from a sign maker in Orange, CA. I use 2 mm and get it in 4' x 8' sheets for about $12 a sheet; pretty cheap. Hope this helps you out some. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| TEA20 Newbie Joined: 10/06/2011 Location: AustraliaPosts: 7 |
These where going to be the tail sections for the mod plane I mentioned, its still in the unfinnished projects area  Muchea W.A. |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
A simple hotwire cutter i have made that works reasonably well for how simple it is follows below. You need a transformer of around 2 amp output capacity (or greater), the output voltage is not 100% important but think mine was about 24 volt. A standard household light globe is fitted in series with one of the mains supply wires, this works as a current limiter to the transformer to prevent it burning up, because the secondary side of the transformer has a dead short across it being the hot wire. The light globe can be changed to adjust the wire temperature..... a 25 watt globe will give a hotter wire than a 100 watt globe will. The hot wire is connected as a dead short across the output of the transformer. (secondary side) I used some 0.6 mig welding wire, but piano wire would work better, you need a wire with some strength or you will snap it frequently. Also the wire needs to be left long and coiled up one end for spare replacement, as it will break, then you can just slide a few inches through, lock it in place and back to work. I would do the wire as a bench mounted frame and feed the foam through it like a bandsaw, as opposed to a hand held bowsaw arrangement. All said i think you would be foolish to try to fly foam blades without a fiberglass skin over them. That causes problem number 2, the type of foam you use, as not all foams are suitable to fiberglass. 
Pete. Sometimes it just works |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Not trying to be picky but putting a higher wattage bulb in series increase temperature as it is a lower resistance. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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