Sine wave spar wakesurf board internals

Are you still rolling your eyes, after that title? We know it’s way out there, but what that we do here at Flyboy Wakesurf Boards, isn’t way out there? Don’t answer that! It was rhetorical! We want to show you a picture, so that we can continue the discussion on the same page.  This is NOT a wakesurf board.

Is that cool or what?! Now that is the cut away of a carbon fiber wing panel from a remote control glider. It’s go a super long wing span, in order to capture as much of the thermal updraft as possible, yet the wings in total only weight 36 ounces. If you look at the cross section, the wings are hollow, but also, doesn’t that look like it could be the cross-section of a hollow wakesurf board?

That wavy piece that attaches the top and bottom skin of the wing is referred to as a sine wave spar and it was originally develop by the Boeing company for use in it’s F-22 Raptor fighter aircraft. The conceptualization offered a few benefits, one being lower weight, but another was a reduction in heat transfer in the wings. We don’t really have that issue, mostly likely none of us is ripping so hard as to develop any significant heat.

Trying to find the definition of a sine wave or for that matter remember from your high school physics class is impossible. Principally, for our purposes, it’s just a repeating wave formation. Each trough is the exact inverse of each peak and all of the peaks and troughs are the same across the length. That may or may not be optimal, but it’s certainly easy to replicate, develop a tool for shaping and it can be repeated in foam or some other material. What that structure will do is absorb some energy and disperse it down the length of the sine wave spar. This is not dissimilar to a foam core or even our composite sandwich wakesurf board construction, but it completely eliminates foam within the construction. AND all of the component parts can be molded, so that when assembled, each production unit would behave identically and be identical. It also resolves several issues with hollow construction. The resulting structure is still principally hollow, but with significantly more struture.

You’ll have to forgive this picture, we hit the wrong button and everything is distorted! But what we want to show is that we created a rough shape in EPS foam that could be used to create a carbon fiber sine wave

Next we cut 3 layers of 6 oz carbon fiber, one of them on a bias close to 45 degrees.

Next we cut two layers of 3 oz kevlar, that will be interleaved between the 3 layers of carbon fiber. Carbon is very stiff, but doesn’t manage impacts all that well, whereas Kevlar has greater impact resistance. The intent here is to impart both properties to the sine wave spar.

Ok so we did a REAL crappy job of documenting this. But we’ve laid down a piece of plastic to act as a wet out table and also that we can transfer over to the wave form tool, so that we don’t stick the whole mess together! We then layered the laminate stack with the bias cut carbon fiber strip in the middle and interleaving carbon fiber and kevlar. Next we cover the whole thing with another piece of plastic so that we can vacuum it and not have it stick to the vacuum bag. It also demonstrates that we could use peel ply, bleeder or whatever to develop a specific resin content or external texture.

Next we place the whole thing in the bag and pull a vacuum. You can see that we have a basic wave form shape, although it would appear not a true sine wave. The shaping of the tool will need some help, but it’s fairly straight forward.  Even the original wing cutaway isn’t a true sine wave, as the peaks and troughs have a slight flat’ish spot where they attach to the skins.

As a spoiler, we did pull the project out of the bag and it retains the shape and properties that we’d expect from the tool we develop and the materials used. So that process is very easy. If the sine wave spar can be used to minimize skin thickness or allow the use of a lower density reinforcement, they it could prove to be a great design for use in wakesurf board construction. Certainly a very novel approach and something we’d like to pursue in a hollow carbon fiber wake surf board.

Thanks again for following along, we appreciate it!

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