Diy sup foil

[PonoBill]

Most of the wing construction I've seen, including my own, leaves a lot to be desired in terms of rigidity, weight, strength and cost to produce. I'm reluctant to take on another project, but I have some ideas, expanding on the conversation in the "Safer Foils" thread to potentially improve those factors and make the parts safer to use at the same time. I guess I'll build a couple of prototypes in Hood River. The ideas are too seductive to let lie.

I've been reading up on molding polyurethane. I've done silicone molds before to make suspension bushings for race cars. The materials available have increased dramatically in sophistication. Combining 3D printing to make the plugs and choosing the right materials could yield semi-production parts quickly and cheaply. I"m thinking standardized two-piece core for both wings and mast with plug-in attachment and fuselage and mounting system (plate or Tuttle) and replaceable leading and trailing edges of cast urethane.

For the wing it's a core with the upper and lower surfaces curved to good foil shape, modified by attachable leading and trailing edges. The core can be made with a modest lateral curve to start the anhedral with plug-in wingtips cast in stiff urethane to finish the curve. The surface area of the foil can be added to with wider leading and trailing edges. The stiffness of the trailing edge can be set to provide a decrease in lift and drag with higher speeds. The trailing edge can be cambered to increase lift and then the camber decreases at higher speed by flexing flatter. The Shore value of poured urethane is highly variable and parts can be cast that are stiff in one place and flexible in another.

It's more parts, which usually means more expense, but they are much simpler parts that are very easy to make with precision.

[surfcowboy]

Pono, there are a ton of different durometers of 3D printable materials now too for prototypes. You could test the theory by printing up a few leading and trailing edge pieces. That way you can experiment without having to make molds.

Check some of the new TPU's.

[PonoBill]

I plan to print the prototype molded parts (leading and trailing edges for wing and mast), but I'll probably use them to make the molds rather than try to print them in the resilience I want. The wingtips will be printed I suspect, though I might have better choices for molded than printed. Certainly, polycarbonate would be strong enough but I can do glass or carbon filled parts in molding.

There's certainly a lot of choices for printing--nothing like the old PLA or nothing that the early printers supported. Actually, none of my current printers will do Polycarb. In theory, I could update the printheads, in practice, I bought too early.

[SUPeter]

I,ve made a few SUP foils so far and I would guess most of us wish to find the fastest, easiest and least expensive method to keep experimentation going.  I’ll share some pictures if all goes well with this forum thing since I am new to this whole deal.   From what I’ve read it is also very important to make strong wings that are of very precise dimensions with regards to maintaining the same foil shape from root to tip.   
Using 24K (x2) carbon fiber tow( can be found for $30 for 3-4 lbs on eBay)an endoskeleton is created between 3mm plywood wing profiles.  These ply wing profiles are hot glued onto a mold of desired anhedral.  This keeps them in place while “lacing the wing with these twisted and epoxy infused carbon fiber cords(36 cords per wing,approx)  This skeleton comes out perfect every time to exact specifications.  Once cured the spaces between the ply wing profiles can then be filled with 2 part foam , microspheres with epoxy,  or any other filler which offers the appropriate strength and lightness..  I use 3 different densities depending upon location.  Most is ultralight 2 part polyurethane expanding foam. 
Once all is filled and faired out with microballoons and epoxy the wing is already strong enough to surf.  Sounds hard but compared to many other methods it is accomplished in very little time .  Once wrapped in a layer or two of glass, it is more than strong enough.  So now we have both an endoskeleton and an exoskeleton.  The single layer of carbon cloth I finally wrap or just use alone without the glass is mostly cosmetic.  I just finished 2 wings that took me less time than 1 wing by my previous method.(carved plywood).  I will attempt to post pictures but don’t hold your breath, I’m an idiot when it comes to this stuff.

It all seemed so easy until I tried to attach pictures.  If anyone has any advice, I’d appreciate it.  My files are too large, even for one photo.  I’ll just post my description for now and hope I can post pics later.

[SUPeter]

Here is a photo of laced wing.

[SUPeter]

another photo

[SUPeter]

One more

[SUPeter]

Ahh! One more

[SUPeter]

I'm getting good at this now

[SUPeter]

Las one, I promise

[surfcowboy]

Ingenuity, I love it. I'm not sure how you came up with this, but I'm impressed.

Can you speak to the start of the process? I'm not sure how you would keep the ribs standing up or how the ends are anchored or is the tow already cured in resin when you put them in? Are they wet with unfurled resin or cured, like sticks?

This would be a great video. Grab a phone or a GoPro (or grab some young person to do it for you) and get this out there. It's really cool man.

[SUPeter]

     Well, to start you need a form which will follow the anhedral of the bottom side of the wing.  Each wing segment is scroll  sawed from 3mm ply based upon the airfoil shape you require.   The pattern of 1/8 inch holes is then drilled into each plywood wing segment.  Once done, these wing segments are hot glued, bottom down, to the anhedral shaped form.  This holds them in place for the next process.
I use one 24K piece of carbon fiber tow, folded in half and long enough to thread through entire width of wing.  Tie a knot at the folded end.   At the other end  use a tightly wrapped layer of scotch tape to make the cord ends easy to thread through holes in wing segmnets.  Like the hard ends on shoelaces.  Before threading the cord, it must be wet out with epoxy resin.   Slow cure resin helps since lacing the wing will take 3 hrs or so.  Wet out one at a time, thread it through first hole,  then twist the cord 10-15 times before threading through the other holes.  The knot will keep one end in place.  Small clamps, small clothspins or i use surgical instruments kold the other end.  Do it again, until you are done.   So you are threading a very flexible, damp, twisted piece of carbon fiber. Once cured, the entire wing can then be removed from the anhedral form.  be sure not to use too much hot glue.  Just enough to hold them in place.
     With the laced wing removed I then turn it over, bottom side up and loosely lay a piece of wet out 6 oz fiberglass.  It helps to let this glass layer drape down between the wing segments so it rest on the carbon laces. let it cure in this upside down position.
     Once cured,  I then cut out the space in the wing center where I will need to insert the square carbon tube that the fuselage will fit into.  Making sure its square to wing and of proper angle of attack(1-3 degrees) I use a very dense filler(milled fibers, wood flour) to attach cut carbon cords to inserted piece.  Let cure.
     Placing wing back onto anhedral form, I then fill the segments.  The very ends I fill with a high strength filler.  Around the fuselage insert, I use a lighter mix of microballoons and milled fiber,  the rest is 2 part expanding polyurethabe.  It ends up being pretty light since most strength is gained from internal skeleton.
     Sand or file to shape than recoat with microballoons. Keep sanding. You will be amazed at how strong this wing is even without its glass skin or carbon cloth. 
      I then vacuum bag a layer of 6oz fiberglass before adding 1 layer of 3K carbon twill.  Sometimes i omit the fiberglass and just go with the carbon cloth.
      As with all my wings, they tend to be overbuilt and with some experimenting one could build more flex into the system and make them even lighter. 
     Hope this helps!
     

[opie]

I think you win the prize for coolest construction method.

Are you happy with the square carbon tube connection method?  Is your fuselage tapered or do you get a tight enough fit without taper? Thanks.

[SUPeter]

     Non tapered so that I can adjust the distance between the mast and the wing.  Forward wing  position for pumping, back position for increased stability.  Its too bad all this lacing must be covered up with filler and carbon.  It looks real cool as it is.

[808sup]

Great work Peter! I enjoy the pictures and the description of each. When I first saw the lacing my thinking was “ how long did that take? “ 3 hrs is some work! However the results look amazing.
What is the finished weight of a wing that size?