Author Topic: Surf board like blades , revisited (Read 7323 times)

willib · « **on:** January 31, 2006, 08:29:09 PM »

great news! The fiberglass polyester resin doesnt eat the the insulation in any way!!

It is called polyisocyanurate insulation and made by Dow Chemical as home insulation.

I tested the process by laminating the 1" thick insulation, on the top and bottom with some fiberglass and resin. and all i can say is , man is it strong!

and light!!

this stuff cuts like butter ,with a serrated kitchen knife ,and is sandable.

it doesnt get any better!!

but i would wear a dust mask when cutting and shaping it.

this is a link to a previus discussion on the topic.

http://Http://www.fieldlines.com/story/2005/12/19/02711/230

willib · « **Reply #1 on:** January 31, 2006, 05:56:33 PM »

As for the spars i bought some $2.99 Graphite arrows, which should work perfect.

willib · « **Reply #2 on:** January 31, 2006, 10:59:57 PM »

i got three stages done...

http://www.otherpower.com/images/scimages/2965/IM001324.JPG

http://www.otherpower.com/images/scimages/2965/IM001328.JPG

http://www.otherpower.com/images/scimages/2965/IM001330.JPG

Chagrin · « **Reply #3 on:** January 31, 2006, 11:13:02 PM »

Sailboat rudders would have a very similar construction to your windmill blades (and similar stresses), but I've never seen one designed with any internal spars to add rigidity. I don't think it's the proper way to construct the sort of thing -- compromising the even stress across the sandwiched foam might do more harm than good.

willib · « **Reply #4 on:** February 01, 2006, 12:04:54 AM »

This is what i'm shooting for..

thanks Mike from warlock.com.au

nothing to lose · « **Reply #5 on:** February 01, 2006, 04:59:27 AM »

I see what you are doing, though it's not what I first thought you meant.

So your not cutting an entire blade out of foam then laminating the blade with fiberglass? Instead it looks like your building a hollow blade with spars like an airplane wing, is that right? The Arrow and the fiberglass mat are all that's running the length of the blade then?

My thought was that you were carving the blade out of a sheet of insulation same as carving one out of wood. I will try that later.

I been wanting to build a surfboard type sail boat this way. Laminate the insulations together and cover with fiberglass. I think it would be fun to take to Canada next trip for on the Montreal river and others. I have not had time to build it though. Sort of a cross between canoe, Kayac, and sail boat. With a small trolling motor for no winds or up stream power.

Foam can be very strong itself when thick or covered, and it's very light weight.

willib · « **Reply #6 on:** February 01, 2006, 07:17:55 AM »

Origionally i was going to carve the whole blade out of one (or two)long pieces of insulation, yes , But , now i am going to use this approach..because it has some advantages over the other meathod.

one being , i can move the sections in any angle i want.since they are not fixed to the spar yet.

i can easily make as many sections as needed.

i can glue the sections together when i am happy with their position.

lastly it looks really cool. and is so simple to do..

BigBreaker · « **Reply #7 on:** February 01, 2006, 08:57:07 AM »

You could make several metal forms like a cookie cutter representing the cross section in various places.

Heat those cutters up with a torch and use them to perfect cross sections in the foam sheet.

With that techique you could use a lot more foam "ribs" on each spar and make nice skeleton for fiberglass. It would also make the construction process very repeatable.

Alternatively you could have cross sections jet cut out of aluminum and use a hot wire to cut using the sluminum as the pattern.

paradigmdesign · « **Reply #8 on:** February 01, 2006, 10:44:46 AM »

The idea behind doing the sections is to have them be solid. Try cutting out the airfoils from thin wood 1/16" or 1/8". I found it easiest to glue the printouts of your airfoil sectoins right to the wood and cut from there. Have you tried using a hot wire knife to cut the insulation? That is the way that most people have been cutting the foam in the past.

You can make the cutter from some dorbell transformers, and a dimmer switch. You have to get a special kind of wire to run, like is found inside of hair dryers, and electric heaters. Just be carefull that you get the biggest dimmer switch you can find, cause they can get overloaded easy.

Chagrin · « **Reply #9 on:** February 01, 2006, 11:46:58 AM »

Now that I see your construction I can understand the advantages of doing things this way, but in the end it's not going to work. With repetitive stress, your stiff carbon spar is going to loosen the holes in the foam due to its comparative stiffness to the fiberglass and eventually the fiberglass will crease/buckle with nothing to back it up.

Chagrin · « **Reply #10 on:** February 01, 2006, 11:49:23 AM »

"nichrome" wire is used as picture hanger wire. It can be found at just about any Kmart/Walmart/Home Depot/etc in a braided form.

Definitely superior to steel wire, though.

Experimental · « **Reply #11 on:** February 01, 2006, 03:06:23 PM »

Great Willib,

And all looking well -- those arrow shafts are really stiff and from reading your post, I see the foam is probably what we used to call "Urithane foam"..

Just have a couple of suggestions for you, and one BIG caution !!

When "glueing the stacks together -- try to keep the glue away from the outside edges -- as if the glue reaches the outside edges where you will be sanding-- it will change the consisitancy of the foam --(hard and soft spots) It,s also helpful to use a "backing"board, with your paper attached, or you wind up with big scallops in the finished product!! (hope that makes sense!)

The "BIG Caution", is -- some forms of foam can be hot wire cut, as someone suggested --BUT, if I remember correctly -- Polyurithane, forms a rather dangerous and toxic gas, when hot wired -- so be very careful, when hot wireing some types of foam!!!! It works really well, and I have used aircraft, stainless steel safety wire, for the wire -- it works well and I have used a 12 volt battery charger for the power to heat the wire -- getting the heat correct, takes some practice !!

If you need more info on that, email me.....

When glueing foam together, I thicken the resin, with glass beads -- so it dosen,t run all over (available from fiberglass suppliers or Aircraft spruce Co..)

Other than that, and as you mentioned -- wear a filter mask, as that foam dust can really cause you health problems...

Hope this is helpful, Bill H........

paradigmdesign · « **Reply #12 on:** February 01, 2006, 03:24:16 PM »

Hey, you guys can find the file that I used to design the blade that I am working on. It is in my files, it is called resin_transfer_molding.pdf

It is a large file, 180 pages or so, like 8 megs, but I learned alot from it.

willib · « **Reply #13 on:** February 01, 2006, 06:12:30 PM »

Thank you all for your sugestions. :-)

Thanks to paradigmdesign and the pic he posted in the first surfboard-like blades,i have 39 of 48 stations printed out and ready to cut.

http://www.otherpower.com/images/scimages/4937/airfoil_sections.jpg

To make a 8 foot dia. triple blade prop , i need 48 one inch stations ( the thickness of the insulation).

in the program below

http://warlock.com.au/bladecalc-abstract.htm

i have the following information,

Num.Blades=3

TSR=6

efficiency=0.4

Blade radius 3.9 Feet.

With some work i was able to take paradigmdesign's 20% airfoil and enlarge it to 18 inches long , actual size..

which is as far as i want to go,... 28 " is just too much..!

I had to put clear foil on the screen and trace it out in sections..

thats about where i am now

willib · « **Reply #14 on:** February 01, 2006, 09:51:36 PM »

i like the teardrop airfoil on the inside..

bob golding · « **Reply #15 on:** February 02, 2006, 06:23:08 AM »

hi, this is the address o the people i got my foam from.

http://www.homeblown.co.uk/technology/chemistry.php

they make there own foam so might be a better bet than dow as regards technical info. i am fairly sure it is not a good idea to try hot wire cutting. treat it more like wood. i used a block 6" x 2" x 3ft and drew the shape onto it. i then just carved away with a surform, a kind of rasp, and finished off with sandpaper. good luck.

bob golding

willib · « **Reply #16 on:** February 02, 2006, 10:31:53 PM »

I decided to make the blades 10 foot dia.

and five inches per station , 10 stations..

There is a drawback to doing it this way , its soooo tedius....

anyway i hope it turns out ok..

The five sections on the top , are half way from the root 50% of the length of the blade..

the ones closer to the camera are 60%.

the diagram is to let me know the distance between the start and end of the station,so i can make the transitions a little easier

This is a rough cut out, of the 18" chord section @ 42deg. It has to go down to 10.8" chord length ( the next station) @ 23deg , in about 5" if ya know what i mean.

i am going to carve the second blade a little differently, since the two sections that i just finished ( and the 70 to 100% ones) are thinner than the thickness of the insulation , why not carve them in a regular fashion, and save the section method for the thicker part of the blade....

ghurd · « **Reply #17 on:** February 03, 2006, 12:11:14 AM »

Not sure if this is safe or relevent, but we used to cut foam with a coat hanger twisted a few times around the base of a propane torch, then a little extra for cooling, then bent down through the flame, then a couple inches straight.

The straight part melted through the foam straight and smooth as could be.

The cooling area between the torch and flame often had a few coils, as did the part in the flame if the stock was thick.

Very detailed foam parts could be quickly and easily crafted. We used it for 'lost wax' style casting, but it should be about the same idea.

Not sure if its a good idea by todays standards.

G-

willib · « **Reply #18 on:** February 03, 2006, 02:34:07 PM »

maybe so , i dont really have to make the spar part of the blade.

willib · « **Reply #19 on:** February 03, 2006, 02:45:26 PM »

I also tried glueing two pieces together , with just the resin , it also worked great!

at this stage of the process, i think using hot wire to cut the sections ,is something i may try later on, although is a great idea .like you say though isocyanurate isnt something that i want to mess with..But maybe later on with the surfboard foam , i may try it...

willib · « **Reply #20 on:** February 03, 2006, 02:49:33 PM »

also a good idea !

with enough Al cross-sections , of the right size , that would be the way to go..

willib · « **Reply #21 on:** February 03, 2006, 02:52:56 PM »

good to know ! thanks..

isnt Nichrome what is used in heating elements?

willib · « **Reply #22 on:** February 03, 2006, 03:01:53 PM »

great link! thanks.

rather than buy a blank , or some block stock , i think i'll look around to some garage sales this weekend, being at the shore , i often see old surf-boards for sale , but never had a use for them, before now!

willib · « **Reply #23 on:** February 03, 2006, 03:05:05 PM »

Yes i agree, the fumes from isocyanurate are not something i want to be breathing.

willib · « **Reply #24 on:** February 05, 2006, 04:09:03 PM »

I havnt got to far but this is what i have ..

Great news ! 70% of the blade can be done with just a single slab of foam.

to update all of yall they are going to be 50" radius ...

With that largest section having a chord length of 18" @ a 42 degree twist..

Here i've layed out the middle of the blade

a look back tward the root

a look tward the tip,

Well thats it, so far

willib · « **Reply #25 on:** February 06, 2006, 09:57:51 PM »

paradigmdesign · « **Reply #26 on:** February 07, 2006, 12:20:37 AM »

There ya go! That is they I have been making mine, and I can see that it seems to be working for you too.

I still can't belive you are doing this all by hand (I would have gone insane). If you give me a list of the sizes and angles that you want, I could fairly easilly give you another file with more segments in it. It only takes me a few minutes.

Have you put any thouhgt into the glass you will be using for the skin, and the spar?

I would recomend 7715, a unidirectional, and 7725 a 0/45 degree fabric, and maby some chopped strand inside to blead off stress.

paradigmdesign · « **Reply #27 on:** February 07, 2006, 12:22:50 AM »

"That is they" should read, "that is the way."

willib · « **Reply #28 on:** February 07, 2006, 12:55:41 AM »

Once i finally got the ends glued on and , in the right spot, it only took about 45 min to an hour to shave that off.

That section i just did is the 50% to 60% section of the blade and there is only three degrees between the end stations, the hard part i think will be near the root because there is 23 degrees between the the first one ,18" chordlength and the the second one ,10.8" chord, but we'll see .

as for the glass , i allready have some , it seems to be a standard 90 degree weave .

the spar i am undecided at this point if or not to use one..

willib · « **Reply #29 on:** February 07, 2006, 05:33:29 PM »

this one took a lot less time to set up ,and still about an hour to carve..

the new one is on the right..

willib · « **Reply #30 on:** February 07, 2006, 11:15:37 PM »

Thanks for the offer of more stations , i think i have it <;-)(i think ?)

I've got the blade diagram pasted out on the wall.

Where do you put your spar?

because i was looking at a site recently, where the guy was using carbon fiber layed in a channel on the outside ,going the length of the blade .

What is 7715 ? and 7725.

paradigmdesign · « **Reply #31 on:** February 08, 2006, 01:46:35 PM »

is a unidirectional fiberglass fabric. <--mostly for spar
is a bi-axial fabric, 0/45 degree bias. <---mostly for skin

You can find out more about them at fiberglast.com, but if you are going to buy, I would go to fiberglasswarehouse.com

It is funny you asked, because my shipment of 7715, and 7725 just came in today, I will upload some pics later.

--------------------------------

The spar goes on the inside of the blade skin. If you look in the doc. that I uploaded about Resin Transfer Molding, they go through the whole process very well.

It is a long read, (I've read it about 10 times) but the information in it is great. The whole process that I have described to you previously, is basicially from there. They do a couple things differently, (I am not using resin transfer molding.....yet), and they went with a different x-profile that I did. Also they are building a 20k blade, and I am building a 10k.

paradigmdesign · « **Reply #32 on:** February 08, 2006, 03:04:13 PM »

on the image with the two fabrics, the one on the left is the 7725, and the one on the right is the 7715. Notice the difference in pattern of the material?

the 7715 looks like regular fiberglass cloth, but actually 95% of the fibers are oriented in one direction.

The other pic is just my 10yards of chopped strand matt

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Author Topic: Surf board like blades , revisited (Read 7323 times)