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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Sat Jan 18, 2014 2:10 am 
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Location: Chile/Brasil
second vaccum lamination
not perfect but almost there!
some air bubles


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Sat Jan 18, 2014 5:03 pm 
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Question:
Front wing benefits from having assymetrical foil to increase lift and reduce drag.
Does the rear wing benefit from being assymetrical ?
Wouldnt make more sense to be symetrical?
anyone?


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Sat Jan 18, 2014 9:55 pm 
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I believe in symmetry. And rely on only the angle of attack to adjust the pitch. A wing with positive lift likes to pop you out of the water and stalls. That makes it harder to ride.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Mon Jan 20, 2014 3:50 pm 
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Quote:
I believe in symmetry. And rely on only the angle of attack to adjust the pitch. A wing with positive lift likes to pop you out of the water and stalls. That makes it harder to ride.


I could use some clarification from Hawaiis,..
but i think he is saying that the back foil is typically used to help control the pitch angle of the front foil.

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.

placing the aft foil a good distance behind the main foil will allow it to resist any pitching moment from the front.
a bit of negative lift in the back will rotate the front to its desired sweet spot.
any deviation from that should help return the front to its desired equilibrium.

symmetric or asymmetric will both do the job, but symmetric will have the same efficiency when controlling pitch in both directions.

as a pitch control mechanism, the aft foil does not benefit from extra surface area if everything is trimmed properly. but im sure its provides extra stability (and drag) when things get out of control.

yes/no?


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Mon Jan 20, 2014 10:14 pm 
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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.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Mon Jan 20, 2014 10:43 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.


interesting...
so you prefer both wings to be symmetric.
did you also mention that both front and back wings have same relative pitch angle?
thanks


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Mon Jan 20, 2014 10:51 pm 
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Yes, all my wings are horizontal with no angles. That is why I am able to use a flat plank for a board.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Tue Jan 21, 2014 3:07 pm 
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Location: Chile/Brasil
after taking everything ito consideration and making some observations i have questions again!!!
after observing kitefoils and comparing it to sea creatures these are my questionss:
dolphins and cousinlike sea creatures have a bulbous frontal área,
1.wouldnt a boulbous frontal wing or fuselage be a greater advantage in hydrodynamics?
2. most dolphins and whales have a flat section on the bottom belly part.
Does this create aditional lift surface without increasing greater drag?
by that i mean that wings could deacrease in size and gain in more speed?
3.Most dolphins ,whales and sharks have a eliptical shape shaft before the aft wing .
isnt this.more hydrodynamic efficient than a square rear shaft.
4 since foils simulate same movements as dolphins and whales in a up and down motion to modify pitch do we really nead a shark like fin or rudder on the tail of the foil?
wouldnt this créate more drag?
wouldnt a wider oval fuselaje do the trick without adding drag?
thanks for everyones input. this Project has been an awesome leaarning tool!
Pedro


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Tue Jan 21, 2014 3:30 pm 
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Phocoenoides dalli is the fastest mammal of the sea. very close to an orca in shape.
capable of 33mph.
nothing alike with the foils fuselage ive seen.


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 Post subject: Re: DIY Home Made wooden Hydrofoil fins
PostPosted: Tue Jan 21, 2014 4:03 pm 
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But mammals constantly change shape as they move, so do most fish. Hydrofoils don't!
At the least, hydrofoils should be more like a tuna tail, a stiff propeller, than a dolphin or whale tail.
Hawaiis info is very interesting to consider!


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