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Foil theory 101
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Post new topic   Reply to topic    Northwest Kiteboarding -> Gorge / Portland / Oregon Coast
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J.P.

Since 10 Mar 2005
638 Posts

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PostFri Apr 10, 15 8:55 am     Reply with quote

Pepi wrote:
stringy wrote:
this thread has way too much text...
and let's stop the pissing contest before it starts


Agreed. Excess tech talk is best left to beach discussions or one on one off of the forum.

Foiling is fun, that's all I have to say.



Gentlemen, no one is pissing here.

I understand that point of view, here's mine , I want it to be more fun quicker!

It's my sincere hope that some tech discussion will help the designers and manufacturers hit my mark and what I have to is believe many others requirements.

An agile, turnie, yet stable foil that excels in surf.

Looking at aircraft as a point of comparison, my desire is a foil that preforms like a P-51 or British spitfire, 2 aircraft that go down in history as very effective “Dog fighters” ("quick turners")

Interestingly, both of those air planes had thin systemically foiled wing and horizontal stabilizers...

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Last edited by J.P. on Fri Apr 10, 15 9:07 am; edited 2 times in total

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J.P.

Since 10 Mar 2005
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PostFri Apr 10, 15 8:56 am     Reply with quote

Spotz v1 has both a rear stabilizer shaped to create neagtive lift and 1-2 degree down ward AOA.
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UPWIND LAUNCH OF A SPORT

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Gator

Since 15 Sep 2012
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Portland
 



PostFri Apr 10, 15 10:02 am     Reply with quote

Nak, from a physics standpoint both AOA and a curved surface affect the pressure below vs the pressure above causing lift so I don't think there are any descriptions that are wrong out there. I think your original point was that when you need significant lift it typically comes from adjusting AOA. You would not want to design a plane with a flat wing because it would need too much AOA at cruising speeds and be very inefficient (too much drag)...as well as a number of other reasons.

Good description (describes how camber can give 2-3x the same coefficiant of lift at the same AOA)
http://code7700.com/angle_of_attack.html

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Nak

Since 19 May 2005
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Camas
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PostFri Apr 10, 15 10:50 am     Reply with quote

Gator wrote:
Nak, from a physics standpoint both AOA and a curved surface affect the pressure below vs the pressure above causing lift so I don't think there are any descriptions that are wrong out there. I think your original point was that when you need significant lift it typically comes from adjusting AOA. You would not want to design a plane with a flat wing because it would need too much AOA at cruising speeds and be very inefficient (too much drag)...as well as a number of other reasons.

Good description (describes how camber can give 2-3x the same coefficiant of lift at the same AOA)
http://code7700.com/angle_of_attack.html


PM Sent.

Your link is an interesting, quite the blast from the past. I taught from the reference materials footnoted.

Last edited by Nak on Fri Apr 10, 15 10:53 am; edited 1 time in total

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Kmun

Since 05 Jul 2009
250 Posts

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PostFri Apr 10, 15 10:50 am    Try Cheerleading or Basket weaving instead... Reply with quote

Pepi wrote:
stringy wrote:
this thread has way too much text...
and let's stop the pissing contest before it starts


Agreed. Excess tech talk is best left to beach discussions or one on one off of the forum.

Foiling is fun, that's all I have to say.


Check yourself! Interjecting lofty critical judgment may be inappropriate.

Just to remind you: The Subject of this forum is "Foil theory 101".
To many of us it is an excellent discussion constrained to the SUBJECT. The intent was meant to "raise all ships". That is, until you sniped-in from the shadows. Interrupting and suppressing a communities exposure to education or controversy ends technical progress and evolution.

Furthermore, if "technical discussions" were only meant "for the beach" then there is no reason for this forum.

This is an OPEN community venue. If you can't handle the "Subject" or intellectual banter simply "step away from the keyboard..."

"Better to remain silent and be thought a fool than to speak out and remove all doubt." - Abraham Lincoln

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J.P.

Since 10 Mar 2005
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PostFri Apr 10, 15 11:26 am     Reply with quote

Gator wrote:
Nak, from a physics standpoint both AOA and a curved surface affect the pressure below vs the pressure above causing lift


Given the significant difference in weight and density of water to that of our atmosphere , does the foils thickness and curvatures really need to be that significant to make a performance difference that be felt by the rider?

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Nak

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PostFri Apr 10, 15 1:42 pm     Reply with quote

No, not at all. The foil shape certainly can make a difference in feel and efficiency; I have no doubt of that. My point would be that given the thickness--or thinness--of the foils, camber alone won't be able to make a difference in positive or negative lift. I think that the pitch demanded instinctively by the rider will be in excess off the negative chord on the stabilizer, resulting in positive lift. If that is in fact the case, then the negative camber on the stabilizer will be inefficient and result in excess drag. Of course, it may be that excess drag that is creating the stability the rider feels. If the stabilizer is pitched nose down by other means than just camber, then it definitely could result in negative lift. Whether that would be good or bad could only be determined by test flights/rides.

My considered opinion--and it is opinion only--is that raising the stabilizer an extra couple of inches might make a pretty big difference. There is a lot of turbulence coming off of a lifting surface. It tends to move down, but we're talking a pretty short distance here... Anyways, that's why you see high stabilizers on certain aircraft. The turbulence will have negative effects on the stabilizer. Moving the stabilizer up and out of the turbulence eliminates the negatives. It all depends on the wing where that turbulence is when it gets back to the stabilizer. Since tunnel work would be prohibitively expensive, experimentation is the only way to advance. Good shapers are always going to win this game over theorists. But a good shaper with good theory...

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Dern

Since 11 Jul 2010
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Vancouver, WA
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PostFri Apr 10, 15 4:54 pm     Reply with quote

Quote:
My considered opinion--and it is opinion only--is that raising the stabilizer an extra couple of inches might make a pretty big difference. There is a lot of turbulence coming off of a lifting surface. It tends to move down, but we're talking a pretty short distance here...


I'd say do this, or increase the distance between the front and rear foils. But that distance is much more subject to the speed of the foil than is is the height of the boundary layer, so it's probably much easier to raise or lower the stabilizing foil.

I'd also wager that you wouldn't really want a cambered foil for water use, to take advantage of the larger range of angle of attack available to a symmetrical foil. I imagine that "stalling" the foil board would effectively throw the rider over the front of the board. I haven't ridden a foil yet myself, however, so I can't speak for how easy it is to manipulate the angle of the board while riding.

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J.P.

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PostSat Apr 11, 15 7:33 am     Reply with quote

Nak wrote:
My considered opinion--and it is opinion only--is that raising the stabilizer an extra couple of inches might make a pretty big difference. There is a lot of turbulence coming off of a lifting surface.


I concur on that point and by observation it appears the StringyFoil & Sword2, do as well.

Regarding AoA & it’s trim, some see it as a feature on there entry model. Very Happy


   manta_Stab.jpg 

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Kmun

Since 05 Jul 2009
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PostSat Apr 11, 15 9:19 am    Foil theory 101 Reply with quote

This is a GREAT discussion! Thanks for the clarification Nak. The first theory presented had me spun-out due to conflict of what I learned in physics classes. Every contributor’s time invested is appreciated. IMO; Nak’s level of diplomacy in contradiction and correction seemed plenty graceful enough.

The NASA link was a good refresher. It is fascinating to know that despite many years of applying a wrong theory still did not stop the advancement of aviation. It is great example of how being “right” may be fleeting as evolution crawls, marches and sails forward.

The North’s solution seems to represent an interesting point in the continuum. The safety features seem wise for a portion of the market segment. Their approach to the management of loading equilibrium is an interesting study. One would think a glide phase with unloaded kite tension would test the performance of the fin box fulcrum.

I am grateful you did not yield to suppressive interruptions (Trolls) i.e. “this thread has way too much text, let's stop the pissing contest before it starts, Excess tech talk is best left to beach discussions”. A thoughtful read of the healthy banter is in fact a constructive, creative, thread stitching together many yet to be seen design solutions. Keep up the awesome and reckless creativity!

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J.P.

Since 10 Mar 2005
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PostSun Apr 12, 15 7:24 am    Re: Foil theory 101 Reply with quote

Kmun wrote:
The first theory presented had me spun-out due to conflict of what I learned in physics classes. !


After looking at the many offerings commercially available globally and the approach, some of which appear to be aware of the the body of thought call Physics, and those who appear to be in vacuum on it, posting a theory 101 that provokes thought and discussion, not a nap on the key board was the goal. I sincerely, that continues

I strongly believe as the riding community's understanding increases on "all things foils", more will come to it.... Very much like kiting itself experienced in the late 90's

The opportunity to crowd source: fixes, new design, ways to make them 'funner' faster, remains to be seen.

Thanks to all forcontributing.

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UPWIND LAUNCH OF A SPORT

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J.P.

Since 10 Mar 2005
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PostMon Apr 13, 15 8:16 am    Re: Foil theory 101 Reply with quote

Kmun wrote:
I am grateful you did not yield to suppressive interruptions (Trolls) i.e. “this thread has way too much text, let's stop the pissing contest before it starts, Excess tech talk is best left to beach discussions”. A thoughtful read of the healthy banter is in fact a constructive, creative, thread stitching together many yet to be seen design solutions. Keep up the awesome and reckless creativity!


Kmun, Thanks for the support!




Link



Hey, Gman, got any video9s) of your coastal endeavors?

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John

UPWIND LAUNCH OF A SPORT

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registered

Since 12 Jul 2005
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tsunami
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PostMon Apr 13, 15 8:21 am     Reply with quote

Yesterday as the violent ocean stole my board I was reflecting as I walked miles down the beach looking for my ride.

I was wondering how far would a foil have gone.... and if in all the surge and crazy currents with sets breaking 1/4 mile past the jetty would have been a place where a foil could even be enjoyed.

Or if it more of a yard care implement.

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Aeolus

Since 20 Apr 2010
354 Posts
Gold Beach, OR
OR-SoCo-Aficionado



PostMon Apr 13, 15 8:58 pm     Reply with quote

Is this the place where I can request a foil with an oversized mast so I can get to the outside on thursday? Very Happy
(so sorry to degrade the thread..I'm trying to control my fear through humor) The fellow in the Tuto seems to know what's up.


   highRoad.jpg 

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Gman

Since 11 Feb 2006
4907 Posts
Portland
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PostTue Apr 14, 15 12:16 am    Re: Foil theory 101 Reply with quote

J.P. wrote:
Kmun wrote:
I am grateful you did not yield to suppressive interruptions (Trolls) i.e. “this thread has way too much text, let's stop the pissing contest before it starts, Excess tech talk is best left to beach discussions”. A thoughtful read of the healthy banter is in fact a constructive, creative, thread stitching together many yet to be seen design solutions. Keep up the awesome and reckless creativity!


Kmun, Thanks for the support!




Link



Hey, Gman, got any video9s) of your coastal endeavors?


That Horue guy is badass Thumb's Up

No videos yet - Aeolus is funny as was thinking about a taller mast at Arlington Sunday - some neck adjusting wipeouts in the 45 mph windswell on the stringy foil and 4.5 rpm but some magic bombing runs and with selective amnesia may keep at it

Yo regi glad you gots it Sunday! Yeah the foil can go into full "harvester" mode in pitching waves and head high whitewater is hard to body drag thru bear huggin the lopper - does offer some crack induced highs when all comes together...

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https://m.youtube.com/watch?v=eu2pBpQolKE

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C Johnson

Since 17 Apr 2009
853 Posts
Seattle
Opinionated



PostTue Apr 14, 15 11:56 am     Reply with quote

its going to be interesting to see foil evolution over the next few years. It seems many people who are building these boards still don't understand that even though bernoulli was brilliant, he was wrong.

I also think there is still a lot to be learned about intelligent flex in foils and using flex to make the ride more forgiving. It seems right now everyone is focused on making everything as ridgid as possible to help with control. I think flex and proper loading in the right areas could be a really good thing for stability.



A perfect example of this is to all the people who are riding super stiff carbon bamboo hex core fins out there on your surfboards in the choppy water, I welcome you to try some nice cheapo molded resin fins. You may actually like the forgiveness the flexible resin offers in choppy conditions.

Plus I know from personal experience that when you fall on a resin fin it tends to break off instead of stabbing you. I feel pretty grateful for that feature Very Happy

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C Johnson

Since 17 Apr 2009
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PostTue Apr 14, 15 12:03 pm     Reply with quote

Nak wrote:
I'm curious, has anyone tried raising or lowering the stabilizer? Without tunnel work, it's impossible to know how turbulence from the foil is affecting the stabilizer. Putting the stabilizer on a different plane from the foil might have pretty drastic results. No way of knowing without either experimentation or tunnel work.


if you raise the stabilizer you are reducing your margin before the stabilizer breaches the surface. if you lower it then you are requiring more clearance from the bottom.

Because of this I'm guessing lowering the stabilizer would be the way to go unless you are restricted by your riding location to a certain depth.

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