Wanted: Plug builder of 4ft wing

[anui]

Hi all,

I'm looking for someone local (SoCal) to build me a symmetrical tapered wing I intend on using for a sailboat rudder. This will be used on a 27ft Corsair Formula-27 trimaran. I need a stable male plug I can build a suitable female mold from. The foil section (considering 63-012) span is less than 4ft with the root chord length about 12in and the tip about 6in.

I know hotwiring can yield a straight tapered section. Is it possible to easily make a subtle elliptical planform?

Thanks!
Dan

[sporter]

How much does a new one cost?

Sean

[wyowindworks]

Is it possible to easily make a subtle elliptical planform?

Thanks!
Dan

Is it possible? Yes. But you can't put the word "easily" into that sentence :D .

If you want elliptical and maintain airfoil fidelity it will be a lot of work. The part would have to be CADed then cross sectioned to make the 20+ templates to gage the airfoil contours as it was shaped. Cutting it with a CNC router would be best.

If it was straight it could be made with a lot less work.

Sean, asked the right question though. You'll be spending a bit dough to get this done.

Adam

[anui]

I really don't know what the cost is yet; there isn't a production one I'm aware of for this boat. I think it would have to be custon built. I'm perfectly capable of making a mold from the plug; where I would like this to end up. Just not too confident in making a proper foil.

I am doing this of course to minimize costs. I have toyed with the idea of hotwiring it myself. But it's something I've not done before. I'm concerned about the nearly 4ft span and the learning curve needed to get it right. Small spans seem pretty easy.

Some of what I've read on the net indicate the best, and fastest way is to just have an MDF female mold CNC'd. That would make a lot of sense based on what Wyowindworks has said about the elliptical shape.

Can anyone recommend any local CNC cutters capable of this? Any guesses at the cost?

Are the elliptical foils possible for a beginner in something like Rhino or Autocad?

[wyowindworks]

It's a piece of cake in Rhino using the sweep 2 rails method, but then you have to prep it all for your cutter. I would find someone who is able to do the CNC cutting and ask them how much software work they are willing to do.

I wouldn't do an MDF female mold. I'd have them mill a MDF male plug in halves and then make your mold from them.

It's definately going to cost you thousands to get it CNC cut.

If you willing to wait 4 months, I could CNC hotwire some foam cores for you.

Adam

[wyowindworks]

Is this what you envision? It's 48" long and 12" at the root. These are generated and rendered with Rhino 4.0.

[anui]

Thanks for the effort Wyowindworks, I guess I didn't make it too clear. This is ultimately what I have in mind...

[wyowindworks]

Can you get those plans scaled 1:1? All the cutting guides are there. That would be a pretty easy hand shaping job. It could be shaped by hand faster than a CNC could mill both halves. You should give it a go. You'd be surprised what the eye and hand can do.

Adam

[anui]

Adam,

My thoughts about the female CNC'd MDF mold is that it would be more stable, as I could make it a few layers thick by bonding multiple MDF sheets. Shipping would be $$$--need someone local for that. And less chance of damage; the foil section is less than 2" thick (<1" thick for one half). Plus, from it I can build my plug for the permanent fiberglass mold and be assured of exact foil dimensions without worrying about the thickness and perfection of the layup.

Dan

[wyowindworks]

You could still have the male halves milled form MDF. These male halves would be sanded, resin coated, and prepared to a smooth finish. These would then be used to directly make the mold halves without the need for a traditional plug and parting board.

Adam

[wyowindworks]

Check out this thread for a comprehensive explanation of the CNC mold making process using MDF.

CNC MDF Mold Making (http://www.rcgroups.com/forums/showthread.php?t=784313)

[wyowindworks]

...Shipping would be $$$--need someone local for that.

You could ship that to the other side of the world for less than one hour of CNC time.

Adam

[anui]

Adam,

That is the best copy and the only copy I've seen of this foil.

I'm trying to get the template data. It's from a larger, strict class boat, and the templates are supposed to be available so the foils can be checked against the rule. It's been over a week and no response.

How would you suggest building the foil by hand?

I have some woodworking tools; tablesaw, bandsaw, 13" planer, 6" jointer, router. I've thought about running the router on a narrow sled that would work somewhat like a hotwire, making equal "percentage runs" from the larger root to the smaller tip. Just grooves that match the depth of the male templates. And will later be planed down. No elliptical shape though.

The other thought was to rough out a bunch of short cross-sections on the bandsaw, finish with a router equipped with a template guide against the proper template for that cross section. There would have to be a "registration hole" down the center of the foil for alignment place on each cross-section. That's a lot of little pieces, but the LE would be easier to get perfect and the shape could easily be made elliptical.

That's the kind of stuff I've been thinking about before I drift off to sleep.
...arrggh.

[kak8]

Another idea to make a plug is to cut a lot of airfoils with different cords, join them and smoth them out with some filler and sand them, paint,polish..........wax........

Another Adam

[sporter]

I would not take the mold route unless you want to make numerous parts.

Why not shape or wire-cut the foam, place your reinforcing points, like blocks for pivot points and a spar, then glass/carbon cloth over this? Make some templates to check the hydrofoil at various pints along the span. Then you could paint it.

Or, pull a rudder from another boat.

Sean

[anui]

kak8,

Is that how you guys do elliptical shapes? Shouldn't be too hard using a hotwire. A lot of templates though.

How about reshaping a somewhat oversized hotwired straight taper into the elliptical shape I'd like.

Sporter,

I'd like to make a mold so I get a second chance at it if I break it. I want to make it as light as possible; weight savings on a performance multihull is very important and especially getting the weight out of the stern, particularly on this boat is a big plus. Besides, my guess is that I may have some interest from others with the same model.

[kak8]

You could also cut a long, straight section with a hotwire, cut it in small sections (with a sharp "razor blade") and make an elliptical shape, but its a lot of work to get a smoth finish. And your TE will also be elliptical.

Foam plugs are very sesitive to high temperature when you make an epoxy mould and epoxy gets hot where the layer is thick.
So, thin glass fabric/ epoxy layers on foam plugs and let them cure for a few hours before the next layer or just don`t let it get hot.

Adam

[SteveC68]

The hot wire cnc cutting program GMFC has an elliptical planform cutting tool. I have not used it, but from what I understand you enter the profiles and chord lengths and cut the wing in sections. Glue the sections together along with their beds. The program even determines the heights of the various sections so when you glue the beds together there aren't any steps.

[miniphase]

perhaps try it this way, ply frame as sanding guide with blue foam sections
between sanded down to level of the ply templates, then glassed sanded
and waxed

[anui]

hey miniphase, that's brilliant! and I like your illustration! since I want to get to a female mold your idea can be my method of building a couple female half molds.

here's my thinking so far... please chime in if you notice some flaws... anybody.

cutout two planforms on 1/8" ply and bond (double stick tape?) each of them (one flipped for L/R sides) to an oversized piece of melomine covered MDF; about an inch oversize offset from the 1/8" planform. the melomine will act as my parting board for one half.

make the small section tempate guides an 1/8" shy at their base to compensate for the planform base. of course, these will be made in pairs for symmetry. lay them out and bond them to the planform base.

block the foam in. now, I have a question... wouldn't it be posssibe to get a smoother and quicker shape by using a hotwire over the top of the templates to cut the foam? at this point it seems that the HW bow would just be cutting freeform but still limited to the templates.

repeat for the other half and carefully fill, sand, polish, pva and glass.

I think after the first complete layup on the fist half, I would pull the melamine away from the first layup that gave me the first flange. leave the part in the mold and bond the second half (already filled, faired, and polished) to the first. bond some male registration keys of some type to the flange that was layed up against the melomine, spray some pva on everything and layup over the part and flange.

I think that's how its done, or maybe I'm over complicating this.

comments welcome!

BTW, what's the best way to generate NACA section shapes that can be printed on a laser printer.

thanks all for the great ideas!

[miniphase]

you could take the bulk of the foam off with a hot wire, but sanding will get you the
curves you are after, blue/pink foam sands really easily

I would strongly recommend you make a male plug and take female moulds from it

I'll post some links to threads that may help...

[miniphase]

heres a couple of threads that may help, the first is a mold for a fuzlage the second is
a tail plane which may be more appropriate

http://www.rcgroups.com/forums/showthread.php?t=303670&page=14

http://www.rcgroups.com/forums/showthread.php?t=823681&page=7

pictures are worth a thousand words, making a female mold without a plug
would be very difficult imho

for the sections, I would get a jpeg copy and just enlarge or reduce it in photoshop to the required sizes- you can do the same thing with a photocopier as well