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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Tue Jan 21, 2014 6:45 pm 
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Hawaiis wrote:
Yes, except"the front foil will llikely have best trim angle at 0-2 degrees.
it will also generate at bit of forward pitch moment that will tends to nose dive the board."

If there is any positive lift profile on the front wing, the positive lift will increase as speed increases. A symmetrical wing will rely solely on the angle of attack and will require a positive angle of attack to lift off, this angle will actually prevent the nose dive of the board compared to the asymmetrical foil.


hi Hawaiis, sorry got lost in this explanation

trying to visuallizing what you mean but then all i can think is that both the cambered profile and the symmetrical profile will create lift, in both cases function of angle of attack and speed, that will turn into a pitching moment regardless

can´t really see the advantages of going with a symetrical foil, basically i´m totally confused!

would you mind to explain what you mean but for dummies?
:-)


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Tue Jan 21, 2014 6:47 pm 
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Umm animals aren't necessarily optimized for speed or efficiency either, they just happened upon their evolutionary niche. They also need to carry along an "engine" in the form of muscles and a digestive system so their shape isn't just a result of hydrodynamics. That said, having a bulbous connections between the fuselage, wing and strut would probably be a good idea, just harder to execute for a small gain. Take a look at a modern international moth foil (the boat not the creature), most of them do it and they spend a lot of time looking for 1% improvements.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Tue Jan 21, 2014 7:58 pm 
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This might be some help in visualising it, although the 'aerofoil' shape is an ellipse in this case.

https://mospace.umsystem.edu/xmlui/bits ... sequence=1

If you look at page 93 of the pdf, You can see the 10% thickness ratio has a higher maximum performance but is more sensitive to the angle of attack, whereas the thicker ellipses (eg. the 16%) have a much more smooth variation in lift/drag ratio as the angle of attack varies.
Point is that some higher performance shapes may be more sensitive to angle of attack and its a lot easier to get a sudden drop in lift which pitches the nose of the board into the water.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Wed Jan 22, 2014 12:31 am 
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If you look at airplanes and submarines, the obvious difference seem to be a pointed nose on planes and bullnose on a submarine or torpedo.
The submerged fuselage is like a torpedo or submarine,therefore it should be like one.
animals have flexible body, they are not rigid bodies, so it only works at a certain postures.
Just my 2 cents.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Wed Jan 22, 2014 12:55 pm 
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Location: Kettle Point Ontario Canada
I agree with Hawaiis about the nose of a foil.. I think for the beginner foils they should be like a sub nose. That shape has been proven for over 50 years now. But the Sword is one of the fastest foils out there and it is pointed front and back. And so it the Alpine Foil it is pointed also...

I just wish the Sword and Alpine didn't cost over 1900 ero. That is almost 4000 Canadian. My wife would kill me if I brought one home LOL


Maybe one day I can sneek one in the shop and tell her I built it.

Terrie
www.jellyfishboards.com


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Wed Jan 22, 2014 3:49 pm 
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Location: rhode island
Hawaiis wrote:
If you look at airplanes and submarines, the obvious difference seem to be a pointed nose on planes and bullnose on a submarine or torpedo.
The submerged fuselage is like a torpedo or submarine,therefore it should be like one.
animals have flexible body, they are not rigid bodies, so it only works at a certain postures.
Just my 2 cents.


dont want to get too far off track
but, as ozchrisb suggested, its a good idea to be mindful of the function before you copy the form for your own purposes.

submarines and torpedos do have symmetric control surfaces, but the vast majority of their lift forces come from buoyancy. They both float.
they have blunt noses to provide ample space for the acoustic array needed to 'see' underwater. (no windows, on a sub)

airplanes dont float in air or water. IMO the biggest difference between planes and submarines are the big wings needed to keep planes from falling out of the sky.

dont take any of this to heart, as your method seems to be working just fine.
keep goin'
-bill


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Sun Jan 26, 2014 4:20 pm 
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hello guys,
New update on hydrofoil Project.
2 hours more logged. 38 hours in total i think!!
made trhe box epoxyed with carbón box and aligenment.
Welcome to my humble office! :thumb: 8)
Pedro


Attachments:
2014-01-26_12-05-55_517.jpg
2014-01-26_12-05-55_517.jpg [ 1.2 MIB | Viewed 292 times ]
2014-01-26_12-02-26_387 (1).jpg
2014-01-26_12-02-26_387 (1).jpg [ 999.36 KIB | Viewed 292 times ]
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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Sun Jan 26, 2014 4:26 pm 
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correction its 43 hours into building.
the do overs are what take the most time.
if you take out the amount of time figuring out the best way to execute the job.
You could probably make one in 20 hours.
i


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Mon Jan 27, 2014 1:39 am 
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i spent another 5 hours redoing and adjusting a new fuselaje.
48 hours logged.
Fuselage v1 the Wall thickness = 4mm
Fuselage v2 Wall thickness =15mm
Now connection to keel is solid and has no flex.
Changed grain orientation and increased overall dimmensions by 3mm.


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2014-01-26_19-33-15_982 (2).jpg
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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Mon Jan 27, 2014 1:22 pm 
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here is a pic of how the box for keel turned out.


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