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 Question in english?

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dwb

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MessageSujet: Question in english?   Mer 5 Fév 2014 - 14:06

Hello everyone ,sorry again for posting on the french side in english, but it seems that if I post on english side I will not get a reply? Sad 
I have thought about this for awhile and was hoping to figure it out myself, have not, maybe someone out there really knows? Question 
As we know that the front wing is pushing water down because of positive A O A, How far down? And causes "washout"
I have read or heard that jumbo jets washout, turbulence can extend for miles, kilometers!
So what about h2o?
I ask because I would think that we do not want the rear wing (stab) flying in the front wings washout.
As most of you have probably experienced after riding thru a boats wake, of even another foilers, or in wave white water, the foils flight is perturbed!
So, Is the rear wing (stab) flying in the washout of the front wing?
I know others have sought to address this in their design and builds.
By mounting the front wing on top of the fuse (short for fuselage,r c  largo) and the stab under the fuse thinking that because of the angle of flight, front wing considerably higher than stab, that washout passes ABOVE the stab?
OR,
By mounting front wing under fuse, (Making much more mechanical sense) and stab above fuse, that front wing washout passes under stab?

Would someone please explain their thoughts on this, heck the more the better!

And because it is raining hard here (no bike, walk,rc heli) and I finished my foil mastic finish for the day,
I throw out a random thought:
When we kiteboardhydrofoil we are piloting (flying) objects in 2 different states of matter, air and water.
Flying the kite with our hands and arms, and flying the foil with mostly our legs and feet,  Is it just me or is this cool or what? Or am I way out there? bounce 
I can`t think of any other system that does this?
I must say that for years I have double flown a lot, but have not for 3 months and am in withdraw big time! I  am having trouble finding the nearest kiteboardhydrofoil anonymous meeting!
I wanted to know just the wing loading of our toys so just did simple calculations. I was surprised by results.
I still think in lbs per inch 2, but also need grams per centimeter 2.
Front wing only as I wonder just how much the stab adds lift, another question for you smart guys out there, % of lift front wing vs stab?
Anyway, If you have a front wing that is 600 cm square and a 75 k rider on a 5 k board and foil,
wing loading is only 1.8 lbs/inch2 or 133 grams/cm2.
I find this to not be so much!
Time to work on a kite launch and land safety post.
dwb
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franckite24

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MessageSujet: Re: Question in english?   Mer 5 Fév 2014 - 20:44

hello david!good questions,
First question:i tried all positions  ,up or down,and i only felt a real difference of réactions with the stab of SWORD that it needs a different position( not inline with the front wing)
For all my personnel foils i am sure there is not influence from the front wing to the rear one
I think it dépends the shape of the front wing;the stream is different with a EPPLER 817 or a reflex profil
Second question:to many parametres for me to answer
Depends the shape ,the speed ,the programm,the level of the rider etcccc
I hate calculating i préfer the feeling Very Happy Very Happy Very Happy 
Sorry for my short and simple answer DAVID
See you in Leucate as soon as possible
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chris_middleton

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MessageSujet: Re: Question in english?   Jeu 6 Fév 2014 - 0:24

Hi David,

it's good that you post in English on the French side of the forum I can post my reply in good old mother tongue blighty ;-)
In my opinion there's zero risk of the front foil wash disturbing the rear wing performance because - maybe its easier if just I post you a simple diagram :
There are foils around today that have their wings mounted on the same plane and they work perfectly, regardless of the wing profile shapes.
Super efficient foils will utilise up to 3 or 4 different profiles along the length of the wing span.



For the second question - ooh la la Reynolds No's formula not enough time to go into that - it's too late in the evening for me on that one.

Cheers for chivers and see you soon Smile
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Laurent Ness

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MessageSujet: Re: Question in english?   Jeu 6 Fév 2014 - 8:09

by the way, the rear stab has negative lift
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samdam

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MessageSujet: Re: Question in english?   Jeu 6 Fév 2014 - 12:53

I suppose on hydrofoils too, there is a vortex at the tips, like on planes (can be reduced with winglets)


I think it's not a problem if the stab is much shorter than the main wing, but maybe if the stab is very long, the tips can be perturbed by the vortex starting at the tips of the main wing?
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samdam

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MessageSujet: Re: Question in english?   Jeu 6 Fév 2014 - 12:58

by the way, tip vortex could be a more serious problem with "canard" configuration (small stab in front of the main wing)
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dwb

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MessageSujet: Thanx for the replys!   Jeu 6 Fév 2014 - 20:20

Chris, or anyone else....
As you have studied foils a lot if  I understand from all your work and in looking at your drawing, can we assume that the "pushed down"  H2o will ALWAYS pass BELOW  the stab?
And what do you think about tubercled wings?
I am having fun reading all my google searches concerning this but it would seem that if it really was that great we would see it everywhere??
Over 10 % lift to drag reduction, that works for me.
Is it market hype or reality? Have some fun and read a little about this if you have not already.
Now the HUGE QUESTION?
Car makers and airplane designers can compute the drag coefficients of their designs, HOW CAN WE?
If you go to wiki and search drag coefficients you see simple shapes, how can we measure our foils or am I DREAMING??
I have always wanted to see a foil in a water tunnel and add coloring to see what happens, is your built and working yet so I can stop by on my way back down to see?
dwb
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samdam

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MessageSujet: Re: Question in english?   Jeu 6 Fév 2014 - 20:33

dwb a écrit:

Car makers and airplane designers can compute the drag coefficients of their designs, HOW CAN WE?

one of my colleague is trying to simulate the flux around a hydrofoil (thanks Chris  Wink ). seems to be a very difficult job to get some serious results! I hope he will have more time next summer to work on this simulation. 
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dwb

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MessageSujet: Thanx samdam!   Jeu 6 Fév 2014 - 21:04

I am most interested to see what you find out, please keep us posted!  cheers 
Just for those interested in some simple shape drag coefficients see wikipedia.
dwb
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yan34

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MessageSujet: Re: Question in english?   Jeu 6 Fév 2014 - 23:55

麦克风 秀 酷伊妹儿拜拜 阿司匹林 比基尼巴士克隆 黑客 幽默 卡通 雪茄 法西斯 吉他 jí 贝司吉他 ?
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nico34

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MessageSujet: Re: Question in english?   Ven 7 Fév 2014 - 1:52

searching about tubercles wings I found that, maybe you read it already?
http://hidrofoilsurf.wordpress.com/blog/
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nico34

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MessageSujet: Re: Question in english?   Ven 7 Fév 2014 - 2:09

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Mic29s

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MessageSujet: Not a goof idea   Ven 7 Fév 2014 - 8:44

nico34 a écrit:
searching about tubercles wings I found that, maybe you read it already?
http://hidrofoilsurf.wordpress.com/blog/

Yes, here is the post... in 2011 with 8000 readings and counting

http://kitefoil.forumactif.org/t777-whale-fins-for-foils

pointing towards http://kitefoil.forumactif.org/t665p75-le-foil-venu-du-desert

The lace work from Renaud Barbier... filled up with much relief immediately after tests because more drawbacks than advantages ....

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dwb

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MessageSujet: Thanx Nico34 and mic29   Ven 7 Fév 2014 - 10:06

I had seen photo of "surfoil" years back even, funny that he has posted no new news?
But I see he and Renaud used FLAT wings and who knows if they respected the profiles of both the wing cord AND tubercles.
When I checked up on whalepower.com there seems to also be nothing happening?
I agree that it was mainly thought that it would benefit most at higher angles of attack and not stall, but it claims to reduce drag coefficient even at low a o a as well?
This concept is being used by company called "quadrofoil" and again seems like there is hype then nothing?
So strange, it seems that their foils are completely wrong? It looks like the curved, rounded, convex section of the wing profile is correct on the top close to the boat, but then it
curves around and is on the bottom side of the submerged part?
Any way .....maybe just all b s
Sorry for being so far behind the info on this forum as many of you already know all of this for a long time now!  Embarassed 
dwb
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Laurent Ness

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MessageSujet: Re: Question in english?   Ven 7 Fév 2014 - 10:22

I have visited Quadrofoil site, nice foil shape (tubercles) to grab sea weeds to me...
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dwb

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MessageSujet: Laurent   Ven 7 Fév 2014 - 10:36

Nice sense of humor Laughing 
dwb
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Laurent Ness

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MessageSujet: Re: Question in english?   Ven 7 Fév 2014 - 10:41

it wasn't humor at all ! Therefore no smiley.

Just imagine garbing some seasweeds? They are already difficult to get rid off when your foil has a straight leading edge, with those tubercles, I bet they would stay stuck as long as you don't evacuate them yourself with your hands !
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dwb

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MessageSujet: Sorry Laurent I saw it another way!   Ven 7 Fév 2014 - 17:32

Really I laughed so hard seeing the quadrofoils foils looking crabish and grabbing weeds to eat!  Laughing 
But you are correct, we have etanges that sometimes have floating weeds that are no fun to foil in!
But thanx for the image anyway, I would have not laughed had you not brought it up.
dwb
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