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 Post subject: Re: Building a hydrofoil
PostPosted: Sat Nov 02, 2013 8:43 pm 
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I'm Ready to start.

First up will be the pylon ; had some good ideas run past me
for this part of the build.

I'm going to order the highest density foam this link below has in stock, and
have them hot-wire out the airfoil that's 100cm long.

https://www.flyingfoam.com/content/what ... ld-i-use-0
Thanks --ronnie-- on page 2 of this topic !!

I'll build (2) wood stiffeners out of (2 X 6) and a bit of glass on both sides
to keep them straight. Next i'll contact-cement the cradles from the foam
wing to both stiffeners , and glass the concave parts with (3) layers
of 3oz , to stabilize the foam and tie them to my 2x6. This makes a Super-cheap
and Fast female mold ; just need alignment pins . The only place that will need work on the
part that comes out of the mold, will be the Leading Edge.

I'm planning on getting 20 or so low resolution parts out of this mold, so
if i screw-up the first pylon, i won't loose too much work, and a second one is
only a day's work away.

Pylon AIRFOIL
That N66-012 in the link above looks like it could be made Strong and
Stiff with little weight , because of the Thickness distribution ; i'll need to ask
around if it would work in water, or the NACA-0012 would work just fine.

I'll talk about the lay-up After i got the mold ; but the Pylon will be the
first thing i make.

The first one will have a balsa core, the second one
will have Nomex-honeycomb ; both will use Stitched 12K carbon and
pre-made carbon rod for strength.

There IS cheaper stitched than this :
http://cjcompositestechnology.com/produ ... rbon-fiber
Carbon Rod :
http://www.marskeaircraft.com/carbonrod_p2.html

Bille


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 Post subject: Re: Building a hydrofoil
PostPosted: Sat Nov 02, 2013 8:51 pm 
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Location: rhode island
plummet wrote:

Why is the tip dihedral on the front and back wings apposing?


I have no idea and appologise for any distraction away from the folks that have already made these things work.

back on page 1, Christoff offered a pretty good overview of his thoughts on the matter.
Towards the end of his blog, in the design menu.

http://kitehydrofoil.com/index.php/design/design.html

As Peter stated, opinion vary.
This offered a different perspective than Peter's
But all very interesting


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 Post subject: Re: Building a hydrofoil
PostPosted: Sat Nov 02, 2013 9:41 pm 
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Location: rhode island
Bille wrote:
I'm Ready to start.................

.Pylon AIRFOIL
That N66-012 in the link above looks like it could be made Strong and
Stiff with little weight , because of the Thickness distribution ; i'll need to ask
around if it would work in water, or the NACA-0012 would work just fine.


I like it.
The narrow LE will make it a bit more sensitive to AOA , but if pylon racers can navigate the course without falling out of the sky, who cares?

I believe the rationale for moving the location of max thickness so far back was to allow the flow to accelerate as long as possible. The resulting pressure gradient is to maximise the amount of laminar flow in the boundary layer (reduce drag). Easier in air, but tough to do in water because of all the bugs, dirt and bubbles.
Just the same, no harm in trying.

I agree that the profile does look more convenient for the addition of a central spar or other reinforcement flavors.
But, from a structural standpoint, the amount of carbon used in any central spar may provide more benefit in the skins. (even if the compromise was a hollow tube to meet any shear or buckling requirements)

good for you.


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 Post subject: Re: Building a hydrofoil
PostPosted: Sun Nov 03, 2013 2:14 am 
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Would these standard foil tubes work? http://www.cstcomposites.com/products-and-services/tubes-rods-and-components/foil-and-elliptical-tubes/

Or are they all too thick?


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 Post subject: Re: Building a hydrofoil
PostPosted: Sun Nov 03, 2013 6:56 am 
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davesails7 wrote:
...

Or are they all too thick?


Look at the stream line foil here

C-EA30015A -- Id=30.0 -- Id=12.6 -- wall=1.5 -- Streamline Foil

1.5 wall on both sides adds 3mm total to the Outside diameter.
so --30+3 = 33
and 12.6+3=15.6 , and that would make the thickness present at 47%
and i want 11% or 12%.

I'm gonna contact them on Monday, and see if they could wind a
12% thick something, even with a rounded TE, it could have
a MOD to make it sharper on the trailing edge for less drag.

Might be a Good source , if they can !!

Bille


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 Post subject: Re: Building a hydrofoil
PostPosted: Sun Nov 03, 2013 7:10 am 
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Location: Langebaan (Cape Town)
Quote:
That N66-012 in the link above looks like it could be made Strong and
Stiff with little weight , because of the Thickness distribution ; i'll need to ask
around if it would work in water, or the NACA-0012 would work just fine.


That profile looks like it will work well in water (looks like a laminar flow profile) except that it will have a limited range of angles of attach because the fattest part is so far back (I think, do I remember the theory correct?).

What that would mean (my opinion here), is that you must really get your torsional stiffness (twisting of the keel/pylon) high so that it does not twist too much and cause large angles of attack in the bottom of the keel. I do not think a hydrofoil keel sees any significant angles of attack during normal use, but if it twists then it could see some larger angles relative to the water flow at the bottom section which could cause a stall.

I believe I have this happening on my MHL foil. In certain conditions (when the water chop pattern is just right and the wind is light) I find that when I try to ride too far upwind that the hydrofoil reaches a point where it suddenly tries to throw me off. Very irritating! I believe this is caused by a stall on the side of the keel when it flexes too much and causes a too great angle of attack on the one side of the keel. I do not find the same problem on stiffer keels, but there are lots of other factors that might also influence it.

I think if you go for a laminar profile with the fattest section around 35% then you will have a bit more leeway in your design before you run into the same problem.

But that is just my opinion, I might be wrong here.


Quote:
Would these standard foil tubes work? http://www.cstcomposites.com/products-a ... cal-tubes/

Or are they all too thick?


So close I think. A keel thickness from 12 to 20mm should work, but I think for water you would need a sharper trailing edge and a longer chord so that the water flow stays laminar. But maybe it would be easy to fill the back up with some non-structural material just to get the profile more streamline?


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 Post subject: Re: Building a hydrofoil
PostPosted: Sun Nov 03, 2013 7:54 am 
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ChristoffM wrote:
...

I think if you go for a laminar profile with the fattest section around 35% then you will have a bit more leeway in your design before you run into the same problem.

But that is just my opinion, I might be wrong here.
...


Your the Second person that told me that !!
The other guy said to look at This one ; the NACA 63,A 012
it would have Way less problems with the high-point back at 35%
and still have a thickness distribution that's Easy to build Stiff and light !!

Bille


Attachments:
NACA 63,A012.jpg
NACA 63,A012.jpg [ 80.51 KIB | Viewed 336 times ]
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 Post subject: Re: Building a hydrofoil
PostPosted: Sun Nov 03, 2013 2:11 pm 
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Posts: 878
Location: rhode island
if you source a core/plug/mandrel that you like

then using a braided carbon sleeve may help you get the layup you desire
http://www.acpsales.com/Carbon-Fiber-Ta ... eeves.html

many paddle manufactures do this and some hi-tech surfboards like coil.

just a thought.


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 Post subject: Re: Building a hydrofoil
PostPosted: Sun Nov 03, 2013 8:21 pm 
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zfennell wrote:
if you source a core/plug/mandrel that you like

then using a braided carbon sleeve may help you get the layup you desire
http://www.acpsales.com/Carbon-Fiber-Ta ... eeves.html

many paddle manufactures do this and some hi-tech surfboards like coil.

just a thought.


That is an Excellent Idea ; however, if i wind myself one on a mandrel, i
would use my 50K carbon uni, and build a wet-out machine that i could
pass the Uni through a bath of epoxy then pass the wet carbon through
some adjustable pinch rollers to get rid of the excess epoxy.

Your saving the Over-lap on each turn by not using that tape you mentioned.

Bille


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 Post subject: Re: Building a hydrofoil
PostPosted: Sun Nov 03, 2013 8:43 pm 
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Here's WHY i'm building my own pylon :

http://www.fastacraft.com/
said they would build me a pylon from carbon with a cord length of 100mm
and a length of 800mm and a wall thickness of 3mm, and use that
NACA 63, A 012 airfoil. ((make it for $400 ADU)).------------------OUCH !!

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

They just E-mailed me and said they Absolutely could special-cut that
NACA 63, A 012 airfoil.

I NEED to know what cord-length is on a standard pylon, (the distance fron LE to TE) ?
The plans that --Europ2-- posted on page 1, indicate 110mm cord length, which
seams about right ; what do they measure on the production boards ?
** Also, 95-cm length on the pylon seam about correct ?

They can cut my airfoil Tomorrow ; just need that cord length.

Bille


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