Building a hydrofoil

[TPink]

As regards building, using a cnc high density polystyrene core and laying up over it with epoxy resin would be one way to go.

This company supplies HD polystyrene.
You can see that they supply in Dow Surfboard foam at density 2.2 lb/ cu ft

https://www.flyingfoam.com/content/choosing-right-foam

You could choose a symmetrical foil and have the taper you chose, to make the top thicker - for the mast.

There are a range of aerofoils to choose from and you could make the wings tapered, but they only make them as straight tapers.

You can specify wing length, chord and thickness.

https://www.flyingfoam.com/content/what ... ld-i-use-0

https://www.flyingfoam.com/content/quic ... ps-cores-0

Thats a great site, I just pumped in some quick spec's for a mast and it came back w $14. That's an awesome deal.

Question, on the forward foil, are the high AR foils running w flat bottoms or semi-symmetrical?

[Hawaiis]

If you want to build one with foam core, it will have more twist and wobble than a solid core.
It may work for low wind cruising. At 15mph or above it will wobble and shake. If you do high speed racing or jumping, Solid Core Carbon Fiber is the way to go.

[Bille]

If you want to build one with foam core, it will have more twist and wobble than a solid core.
...

You Can stabilize the foam-core, (cradle) with ply on the flat side and 3oz glass on the airfoil
side ; then use it as you would use a female mold.
OR
Stabilize the airfoil itself with 3oz glass , then make a female mold of That , to do
the lay-up in.

PFP molds are the easiest for testing, but a conventional mold of glass & epoxy , with
an epoxy surface-coat, is the best way to learn mold-making.

You can get Reasonable accuracy with Both these methods.

Seriously, if i was a Despicable Low-life, it would be EASY to mold a (state of the art)
hydrofoil, then build a copy from the mold. I got a cold Beer that says the ONLY
person here that could tell My copy from the real thing, would be the manufacturer
himself. The resolution would be a dead give-away, but i would spray the mold
with a clear-coat First, then do the lay-up and come back and shine the finish to
near perfection.

The point is :
"Ya do NOT need a $20,000 mold, to make Good parts out of" !!

Bille

[Hawaiis]

On my high AR wood front fin the span was 25 inches long, it was flexing too much, so I fiberglassed it and sand and fiberglass and sand and it still flexes. Fiberglass does not seem to work in high stress environment in hydrofoils. My titanium high AR front wing was showing better speed than the factory carbon wings. My GPS clocked 15 knot top speed with 7 knot winds while the factory wing only did 13 knots. A 1/3 frontal area really helps.

[Bille]

On my high AR wood front fin the span was 25 inches long, it was flexing too much, so I fiberglassed it ...

I've Never built a hydrofoil , (Yet) ; but i know about how stress goes through
a frame from building Rigid-Wing hang gliders, where the wing is fully cantilevered,
and needs No wire or strut support.

This is important :
What was your Fiber orientation with the glass" ?
What weight glass ?
and WHY did you choose Glass to begin with ?

The glass skin would have worked , with the addition of some strategically
located carbon-Tow.

Bille

Ps :
and --Hawaiis-- , you need to start researching on , (How to build Molds) .

[Hawaiis]

Water is hundred times more dense than air, the stress a hydrofoil faces is much more than hangliders

[Bille]

Water is hundred times more dense than air, the stress a hydrofoil faces is much more than hangliders

I realize that water as a Bunch denser, and it's why i asked how you wrapped
your wood core foil ?

The stress goes through your foil, the same way it goes through a glider
wing, (just More of it in water) . If you wrapped it + - 90deg to the span-wise , you
did essentially Nothing to take care of the twisting moment. You Did say it
still bends !!

The forum is suppose to be a learning tool ; hope your Not getting pissed
because i'm gathering as Much info as i can here.

Bille

[Hawaiis]

I lay the fiberglass 90 degrees. The vibration creates a loud low frequency noise. Any vibration will create more drag than a rigid wing. In the French forum, they are talking about using prepreg high modulus carbon fiber to make the foil more rigid.

[Bille]

I lay the fiberglass 90 degrees. The vibration creates a loud low frequency noise. Any vibration will create more drag than a rigid wing. In the French forum, they are talking about using prepreg high modulus carbon fiber to make the foil more rigid.

Got a cold Beer, that says i Know where that resident-frequency is coming from ;
stress & the lack of addressing it.

Did you know that Ya can make that Pre-preg stuff, ((Yourself)) ?
but even with the use of (Pre-Preg) ; unless the fibers are going in
the correct direction, Ya -- (("Still" got nothing )) !!

Bille

[Hawaiis]

Wood has its limitations, no matter how many horses you put in a Toyata, it is still not a Ferrari.