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Hydrofoil evolution challenge #2: surface piercing foil

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lobodomar
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Re: Hydrofoil evolution challenge #2: surface piercing foil

Postby lobodomar » Wed Nov 12, 2014 5:24 am

JS wrote:
lobodomar wrote:
JS wrote: 2. The AoA can never be greater than the downwind (glide) angle (and could only be equal to it if L/D was infinite). If you don't know why, get educated in the law of conservation of energy as it relates to aerodynamics. (Really educated, not just a bit Googled).
Of course it can. All you need to do is pull-in the backlines through the control bar. No conservation of energy, you use your muscles. :thumb:
The only way that kite will experience AoA greater than the downwind angle is during the early stage of backstall. If not corrected by sheeting out (to 4 degree AoA or less), it'll crash.

You can pump the bar in and out, of course, cycling between backstall and recovery. Not efficient, but you can do it.
No need to pump. There’s no reason you can’t set any given AoA at or bellow the stall AoA of the profile through the backlines.

For the example above, if you set an AoA of 18dg, standing still, kite at 12 oclock, all your “downwind angle” means is that the angle between the vertical and the line connecting the harness to the center of pressure of the kite is almost 9dg (not taking the weight of the kite and lines into consideration).

And come on, with your “actual” stall AoA of 4dg and considering that at that AoA the L/D is already starting to drecrease exponentially, it’s actual operational AoA range would be ridiculous.

But you don’t have to believe me. Just fly a perfectly trimmed kite in a steady breeze,12 oclock, standing still, at the threshold of stall. Sheet out a little (EDIT: or even a lot, since most properly designed control bar “depower travels” do not allow AoAs lower than that of optimum L/D to be reached – strutless inflatables being the most evident exception to this general rule), and see what happens with the “downwind angle”.
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Re: Hydrofoil evolution challenge #2: surface piercing foil

Postby JS » Wed Nov 12, 2014 10:32 am

lobodomar wrote:But you don’t have to believe me.
Noted.

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Re: Hydrofoil evolution challenge #2: surface piercing foil

Postby revhed » Wed Nov 12, 2014 3:19 pm

Hello,
I wrote sincerely " directly on topic" 3 pages ago and no replys or thoughts?
Yes JS, it seems that the photos I posted show way to much foil surface area as compaired to what we fly now.
So the easy fix would be thinner wings and strutwings in this case.

As I drifted off last night a super simple concept was understood, sorry again to be back to the herring history.

Seems evident that when you apply a fore weight change on your KBHF to pitch down, dive the wing
this will increase the drag (more vertical surface area) therefore slowing down, and of course the same for rear weight change.
At least for me explaining well this,

To quote JS again,
"A) AoA changes can be induced by the following means:

1. SPEED: by pitching the board upward or downward

B) Pitching the board is done with fore and aft weight changes"

So I will boldly make the following statement, using JS`s words from above.

AoA changes can be induced by speed changes by pitching the board upward or downward which is done by fore and aft weight changes.

Simple enough! :thumb:

And then as I was still awake it hit me.
If I were tasked with designing and building a SP KBHF I would do the following.

As I know that most all of our current design and builds use about 600 cm2 front wing Surface area, I would design a flat center horizontal always fully submirged wing with 300 cm2.
Say 10 cm X 30 cm with a EPP817 profile.
I would then attach the speed lifting foil wings (2) to the ends of this angled up and out at 45° to connect with the board rails about 1 meter long.
Again 10 cm wide and using same EPP817.
Design problem using this geometry the board connection width would be 1.3 m proably to wide!
So without using any foil sim soft ware of formulas I would guess that to get to 600cm2 S A it would lift up leaving about 30cm of vert submirged. Again super fast and rough ideas.
Disclaimer..... this is only super simplistic idea
I would connect the always fully submirged fuse to the center if the F wing and make it about 60 cm long.
I would make a a again always fully submirged R wing very similar to what we use now.

As I make some rough drawings I see that one would have to study well what the successful hydro boat guys have done but use only for the front. And mix our teck for the rear.
JUST FIRST THOUGHTS!

So in closing as I have standard KBHF design and build work to do.
I wish this post all the best, and will check in and read from time to time, but I have WAY to many other things to attend to now.
:bye: R H

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Re: Hydrofoil evolution challenge #2: surface piercing foil

Postby JS » Thu Nov 13, 2014 5:30 am

revhed wrote:So the easy fix would be thinner wings and strutwings in this case.
Yes, smaller, more efficient wings. Submerged struts, though, could almost disappear. It's possible to orient a single foil, or pair, so that almost all lifting surface acts in an optimal direction to balance kite and gravitational forces.
revhed wrote:Seems evident... pitch down, dive the wing this will increase the drag (more vertical surface area)...
Yes, a conventional foil board has more drag when more of its strut is submerged. At low speed it's not as much of a factor as at high speeds though, because the strut merely creates "form" drag whereas the wing creates both form and "induced" drag. Form drag increases as a roughly squared function of speed, whereas induced drag subsides with increasing speed. (Good Google/Wiki explanations are probably available.)
revhed wrote:As I know that most all of our current design and builds use about 600 cm2 front wing Surface area, I would design a flat center horizontal always fully submirged wing with 300 cm2.
Say 10 cm X 30 cm with a EPP817 profile.
I would then attach the speed lifting foil wings (2) to the ends of this angled up and out at 45° to connect with the board rails about 1 meter long.
Again 10 cm wide and using same EPP817.
Design problem using this geometry the board connection width would be 1.3 m proably to wide!
So without using any foil sim soft ware of formulas I would guess that to get to 600cm2 S A it would lift up leaving about 30cm of vert submirged. Again super fast and rough ideas.
Disclaimer..... this is only super simplistic idea
I would connect the always fully submirged fuse to the center if the F wing and make it about 60 cm long.
I would make a a again always fully submirged R wing very similar to what we use now.
I haven't had time to reflect on your numbers, but I will say that I don't think dihedral is fundamentally advantageous for a foil board. Keep in mind a flat foil becomes angled when it's edged.

Best regards,
James

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Re: Hydrofoil evolution challenge #2: surface piercing foil

Postby Europ2 » Thu Nov 13, 2014 10:34 am

JS wrote:
Europ2 wrote:Maybe will you find some inspiration from...
Thanks; interesting info.

Foil boards have an interesting advantage over other hydrofoil applications because lateral forces allow the altitude-modulation mechanism of a "v" without actually requiring a "v", along with its inherent inefficiency (related to partially opposing force vectors).
C foil inspiration that just flies fine.
Let's imagine what follows with a kite, the catamaran becoming a catafoil -
Not easy to figure out with the lateral traction of a kite. => Don Montague next challenge.
A tripod maybe would suit KBHF better (2 C foils + 1 T )

Slovenian design: www.quadrofoil.com,
https://www.facebook.com/Quadrofoil, https://twitter.com/Quadrofoil,
https://www.linkedin.com/company/quadrofoil-d-o-o-
Quadrofoil dual view.jpg
Yes, surface piercing
Surface Piercing.jpg

Interested ?
Technical Data
100kg, 22500 EUR for 21knots (March 2015), 15500 EUR for 16knots (May/June 2015) :o
info@quadrofoil.com

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Re: Hydrofoil evolution challenge #2: surface piercing foil

Postby revhed » Thu Nov 13, 2014 1:55 pm

Interesting how RADICALLY they changed wing design from many years ago.
The small ridges on the new one I assume are to stop, try to reduce ventilation?
And the vertical wing tips?
quadrofoil-radical-hydrofoil-electric-watercraft-2.JPG
quadrofoil-radical-hydrofoil-electric-watercraft-16.JPG
Thanx E 2 for the picts, I like the head on.
R H

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Re: Hydrofoil evolution challenge #2: surface piercing foil

Postby tomatkins » Thu Nov 13, 2014 9:12 pm

Good observation:

"Interesting how RADICALLY they changed wing design from many years ago.
The small ridges on the new one I assume are to stop, try to reduce ventilation?
And the vertical wing tips?”

I would like to see a time-line sequence of the design process which led up to the product, as it is now pictured. It looks like the original design of the foils resulted from a lot of care put into the features geared toward the prevention of the inefficient parasitic losses from “vorticity shedding” using the winglets and bars... I wonder if the recent design, where none of those things are incorporated, came about as a result of a problem of some kind of induced “flutter” due to some kind of undampened, forced, harmonic vibration?

Would a scalloped, saw-toothed leading aid in dampening a “vibration” in the “leggy” (and therefore less-than-rigid) “C” foils?

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Re: Hydrofoil evolution challenge #2: surface piercing foil

Postby zfennell » Sun Nov 16, 2014 1:44 pm

The "golf cart" with wings has pretty much signaled the end of this thread.
Moving on. ..maybe.
Conceptually, a T foil heeled does look like a V foil.
So, is it possible that developing a surface piercing foil is more related to a change in technique than hardware?
Heave stability would be achieved via similar mechanism.
I guess the design issues would be control of relative levels of ventilation and submerged for lifting surfaces.
-bill

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Re: Hydrofoil evolution challenge #2: surface piercing foil

Postby JS » Sun Nov 16, 2014 10:45 pm

zfennell wrote:The "golf cart" with wings has pretty much signaled the end of this thread.
Oh.
zfennell wrote:Conceptually, a T foil heeled does look like a V foil.
Exactly. But unlike a "V", a "heeled T" doesn't have two foil planes with components of lift that oppose each other, and associated parasitic drag.
zfennell wrote:So, is it possible that developing a surface piercing foil is more related to a change in technique than hardware?
It's both, I believe, although I don't think currently-popular foil board geometry is suitable for ventilated riding.
zfennell wrote:Heave stability would be achieved via similar mechanism.
I guess the design issues would be control of relative levels of ventilation and submerged for lifting surfaces.
Among other considerations, fore and aft foils should probably both be oriented to gradually ventilate in unison, for stable progression as speed increases. This is simple to achieve, but not with the current fuselage-mounted-tail approach.

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Re: Hydrofoil evolution challenge #2: surface piercing foil

Postby Rabidric » Mon Nov 17, 2014 10:52 am

Hi

Haven't we discussed this stuff before JS? with chemosavi and the like, about 6-7 years ago?

In 2007 I built a fore+aft bidirectional fully ventilated foilboard using aluminium plates. I ground down the topside leading and trailing edges to get knife edge almost. Dangerous, but it was a technical demonstration for my own curiosity. The idea was to force flow separation and full ventilation on the entire topside from the get go. Peak L/D is obviously compromised compared to conventional foils, but the low Cl regime is improved of course. Fundamentally this is what a kiteboard already is, as you have already stated. I just reconfigured the concept from one very low aspect board to two moderate aspect plates.
I could have tried a bit of camber but that would have compromised the bidirectional capability by reducing the practical range of operating AoA considering that incidence is fixed for each foil wit respect to the board. I don't think it was really necessary.

When riding on tow I was able to achieve unprecedented drag angles off to the side of the boat, literally tens of degrees better than any wakeboard or waterski or even a standard foilboard. Especially at higher speeds(25knots+). So far so good , as this is what my father and I predicted from our calculations.

The problem came when kiting in fun conditions. Once the wind is up to 20kt and above the surface conditions become "dynamic" shall we say! Control and comfort became a real problem with the surface piercing foils in these conditions. Tripping was very common. So i gave up on bidirectional capability and adjusted angle of incidence to the ideal 6 degrees for both foils going one way. This helped quite a lot obviously, but the fun was lost completely i found. A regular twintip with a bit of constant radius rocker was so much lighter, faster, controllable and capable of jumps/pops that I just accepted that the evolution of kiteboarding has done a pretty good job at arriving at the best all-round solution for speed and fun in high winds.

Regards

Rabid

Image

Looking sideways at me from the powerboat. Driver commented he had to do everything possible to stop me pulling the stern around! The lift angle here is around 60-70deg to flow direction. I did better though when I used greater heel angle, but then the loads went right up and I couldn't sustain it..


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