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Building a hydrofoil

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Bille
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Re: Building a hydrofoil

Postby Bille » Sun Oct 27, 2013 4:04 am

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


Yes, and not trying to be disrespectful but , i knew
what the fiber orientation on your foil was ----------
before i asked , as seen Here :

As i said, + - 90 does Nothing for your Twisting moment ...
and the TE needs either Sharpening, or filed Flat.

And this conversation is going No-ware, so i'll stop.

Bille
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Re: Building a hydrofoil

Postby Hawaiis » Sun Oct 27, 2013 5:48 am

It is not the twisting moment. It is the lengthwise flex that was the problem.

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Re: Building a hydrofoil

Postby don pitcher » Sun Oct 27, 2013 4:49 pm

Nice work Hawaiis. Thanks for sharing your R&D.

Have you had more time on your metal wing yet. It sounds promising. Any vibration issues yet?

With regard to building a riser/keel, I imagine an easy and low cost solution would be a hollow aluminum extrusion in a NACA shape.

The problem is finding an aluminum manufacturer that has already made such a product that we can buy without placing a large order to have it made.

I imagine something like this but with a symmetrical NACA shape and thicker wall.

http://www.bcawnings.com/?o=modules&n=alum&f=alum&idinfo=899



Here is an example of someone that previously offered a solid aluminum NACA shape.

http://www.mtmscientific.com/airfoil.html



Here is a place that claims,
Need a custom airfoil? We supply airfoils for special projects such as windmills / wind generators and OEM rotorcraft. Send us details of what you need for a price quote.

http://www.vortechinternational.com/

Maybe such a place would have some lower cost "scraps" that were not good enough for a flying machine but would be good enough for a hydrofoil?

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Re: Building a hydrofoil

Postby Hawaiis » Sun Oct 27, 2013 9:15 pm

Don:
The Titanium front wings were tested first without anhedral, they were very unstable, after adding anhedral, they are performing better than the MHL Lift wing. the frontal area is reduced to 1/3. very smooth and vibration is less than the MHL lift wing. The limitation right now is the flexing and twisting of the MHL T-Bar. I am working on a replacement T-Bar to replace the MHL lift.

I was thinking about welding two sheets of titanium to form the vertical strut of the Tbar. I need to find a welder who will weld titanium.

Helicopter Wings are subject to less force than Hydrofoils, they may not be able to cope with the stress.

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Re: Building a hydrofoil

Postby Johnny Rotten » Sun Oct 27, 2013 10:23 pm

Hawaiis wrote:Helicopter Wings are subject to less force than Hydrofoils, they may not be able to cope with the stress.


?!?
Please....explain....

surely you are not comparing a helicopter BLADE which produces a few THOUSAND pounds of lift to a simple hydrofoil which produces a lift force of at most a persons bodyweight?

Although I admire your creative mindset, craftsmanship and ability to make it work with what you've got, and try it, and tweak it until it works, your engineering in this post is somewhat misguided and you are dismissing some sound advice for unsound reasoning....

I'm not trying to discourage you, quite the opposite, if you continue down the path you are going you will eventually convince yourself that what you are trying to accomplish is impossible when infact it is much simpler than you think.

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Re: Building a hydrofoil

Postby Hawaiis » Sun Oct 27, 2013 11:41 pm

The wing loading is counted in PSI, pounds per square inch, if you divide the weight of an aircraft by its wing area, you will find it is much less than the hydrofoil.

I got the following from the internet, it might not be accurate
The UH60 has a disk loading of 9.7 lbs/ft²
The UH1D has a disk loading of 5.25 lbs/ft²
The R-22 has a disk loading of 2.75 lbs/ft²
The B-29 has a WING loading of 69 lbs/ft²
The P-51D has a WING loading of 50 lbs/ft²
The Cessna 150 has a WING loading of 10 lbs/ft²

A typical kite hydrofoil board has the foil area of approximately 1 square foot and needs to carry the load of a person plus the force generated by the kite, which can easily double the weight of the rider.

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Re: Building a hydrofoil

Postby Bille » Mon Oct 28, 2013 1:28 am

Hawaiis wrote:The wing loading is counted in PSI, pounds per square inch, if you divide the weight of an aircraft by its wing area, you will find it is much less than the hydrofoil.

I got the following from the internet, it might not be accurate
The UH60 has a disk loading of 9.7 lbs/ft²
The UH1D has a disk loading of 5.25 lbs/ft²
The R-22 has a disk loading of 2.75 lbs/ft²
The B-29 has a WING loading of 69 lbs/ft²
The P-51D has a WING loading of 50 lbs/ft²
The Cessna 150 has a WING loading of 10 lbs/ft²

A typical kite hydrofoil board has the foil area of approximately 1 square foot and needs to carry the load of a person plus the force generated by the kite, which can easily double the weight of the rider.


:?:

Are you inferring that we aren't comprehending the difference in density between
air & water ?
And
i would NOT build with less than a 5G safety margin , my
HG is good for 10G's, (i pass OUT at 8G's) !!

Baste in that EGO young man ; it wont last long. It wont last because there are a LOT of
highly intelligent users on this forum, and your acting like the GURU who's talking
to a bunch of idiots !!

Bille

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Re: Building a hydrofoil

Postby Hawaiis » Mon Oct 28, 2013 3:19 am

I am only trying to explain to the gentleman why Helicopter rotors may not be strong enough for water use. If you try to spin that rotor in the water, it will need a nuclear powered helicopter and it will surely break.

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Re: Building a hydrofoil

Postby Johnny Rotten » Mon Oct 28, 2013 4:53 am

Hawaiis wrote:The wing loading is counted in PSI, pounds per square inch, if you divide the weight of an aircraft by its wing area, you will find it is much less than the hydrofoil.

I got the following from the internet, it might not be accurate
The UH60 has a disk loading of 9.7 lbs/ft²
The UH1D has a disk loading of 5.25 lbs/ft²
The R-22 has a disk loading of 2.75 lbs/ft²
The B-29 has a WING loading of 69 lbs/ft²
The P-51D has a WING loading of 50 lbs/ft²
The Cessna 150 has a WING loading of 10 lbs/ft²

A typical kite hydrofoil board has the foil area of approximately 1 square foot and needs to carry the load of a person plus the force generated by the kite, which can easily double the weight of the rider.



Gotcha!!! You are 100% correct that it has a higher wing loading....not force...not stress...but wing loading..... the "wing loading" you are quoting is only 1 SMALL part of the stress that a wing experiences and all things considered it is somewhat irrelevant on the scale of material stress.


As an example your hydrofoil would experience a combined stress of 200lbs over 144 square inches or roughly 2psi....paper machet could handle this loading without falure (our bladders take about 8 psi.)

The stress you need to concern yourself with is bending stress. that is the lever arm that is trying to rip the blade off the rotor of the helicopter or your foil off it's attachement point to the fusi.

When comparing a helicopter blade to a hyrdrofoil you are forgetting that the helicopter blade is lifting about 1000lbs on a 2 m lever. Your hydrofoil is taking around 200 lbs at about 25cm?
the helicopter blade needs to be MUCH stronger.

http://en.wikipedia.org/wiki/Bending

However in the case of your light loading STRESS is not the target parameter cuz your fins aren't breaking they are wobbling, it is STIFFNESS.

look to the section 7.2 on cantilivered beam with uniform distributed load.
http://en.wikipedia.org/wiki/Euler-Bernoulli_beam_equation

w= wobble (at the tip)
w = qL^4/8EI
q is the wingloading
L is the wing length
E is a material property (elastic modulous)
I is a geometric property usually proportional to the thickness^3

practically speaking this means the following
your wobble is FAR more sensitive to changes in length and thickness than ANY material properties you can throw at it.....this is a problem you can more easily and cheaply fix with SHAPE than material..... make it shorter, make it thicker,

If you're trying to choose materials the one with the highest elastic modulous will be the best

Advanced materials just allow you to get a longer and narrow shape (higher aspect) which is mostly of concern when trying to go faster.

Now as to your density of water vs air. Yes water is more dense but aircraft are much faster and bigger. The property which takes both of these into account is reynolds number We did the calcs on an earlier post and the reynolds numbers for racing fins were somewhere around that of a cessna or other low perfomance air craft....you're not dealing with fighter jet loading my friend.

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Re: Building a hydrofoil

Postby Hawaiis » Mon Oct 28, 2013 7:25 am

What you are referring to is called Torque exerted on the attachment point of the rotor or wing.

Yes, you are correct, the attachment point is much stronger in a airplane or helicopter due to their weight and span.

The 1000 lbs weight is not only distributed along the 25 foot length span of the blade, it is distributed by a 25 foot circle created by the rotor during flight.
If you were to put the 1000 lbs on the tip of the rotor, it will cause some damage to the helicopter rotor.
The rotor actually gets some help from the centrifugal force from the spinning rotor for strength.
Because helicopter rotors are more relating to the well being of the pilot, they are of course over engineered for safety reasons, some may be strong enough for hydrofoil use.
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