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 Post subject: Wing profile
PostPosted: Wed Aug 06, 2014 10:59 pm 
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Hi,
I own a RR hydrofoil and am working on making a higher aspect ratio front wing. I've seen eppler hydrofoil profiles like E836 and E837 which look like the foil on my keel/mast. I was under the impression that a hydrofoil wing uses a foil on one side, and flat on the other. Are there popular profiles that people are using for their wings, that are only foiled on one side?
Thanks.


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 Post subject: Re: Wing profile
PostPosted: Fri Aug 15, 2014 8:55 pm 
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Location: rhode island
this guy does a pretty good job of justifying one profile vs another

http://www.tspeer.com/Hydrofoils/h105/h105.htm

http://www.tspeer.com/


i imagine even cavitating foils are not flat on the bottom.
w/o having a "grown-up" do the math, i can only assume both sides interact at some level to determine the total net flow. particularly near the nose and tail.
another consideration is your design AOA. there could be no contribution from the bottom surface without a positive angle of attack. no idea what the impact really is, but L/D will likely suffer with increasing AOA.

tom is easy to find on his web page and boats.net .
try asking him for the straight answer.

-bill


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 Post subject: Re: Wing profile
PostPosted: Sat Aug 16, 2014 7:31 pm 
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Ditto the boat design forums. There are some good discussions on foil profiles for moth sailboats. Here is an interesting paper on the moth with analysis on several foils -

http://www.moth-sailing.org/download/CSYSPaperFeb09.pdf

:o


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 Post subject: Re: Wing profile
PostPosted: Wed Sep 03, 2014 7:24 pm 
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Check out epp 817 at 90% thickness.
We and many others who have been up to making and testing wings find this flys well.
Epp 222 also seems to work well.
Just my thoughts.
Although I will make a speer 105 but thinner soon to test. :thumb:
R H


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 Post subject: Re: Wing profile
PostPosted: Wed Sep 03, 2014 7:44 pm 
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Good luck chosing, there are sooo many. I just tried one I already had. Here's a picture


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 Post subject: Re: Wing profile
PostPosted: Wed Sep 03, 2014 7:49 pm 
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revhed wrote:
Check out epp 817 at 90% thickness.
We and many others who have been up to making and testing wings find this flys well.
Epp 222 also seems to work well.
Just my thoughts.
Although I will make a speer 105 but thinner soon to test. :thumb:
R H


Sorry, you lost me there revhed ?

What do you mean by "90% thickness" ???

And the Eppler 817 is 11% thick so not just a typo zero error...

8) PF


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 Post subject: Re: Wing profile
PostPosted: Wed Sep 03, 2014 8:26 pm 
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Location: rhode island
forgive me for speaking out of turn.

I'm quite certain that Dr revhed has gone on record saying that he is scaling all of the thickness coordinates (by 90%) w/o changing the length coordinates of the profile.

pretty creative.

something like xfoil would provide calculated estimates of potential benefits or disadvantages.

i was hoping RH would offer his thoughts and opinions regarding any design goals when tweaking one profile vs another.

-bill


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 Post subject: Re: Wing profile
PostPosted: Wed Sep 03, 2014 9:16 pm 
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Hmm, maybe you are right zfennel....

But then you (we) can not "check it out", as the polars can be extremely different when you change the thickness ever so slightly, and particulary the max lift and the max lift/drag can not be predicted well.

But I get it - think you are right, it is an 817 slimmed down 10% in thickness yes, thanks :thumb:

8) PF


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 Post subject: Re: Wing profile
PostPosted: Thu Sep 04, 2014 1:12 am 
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Eppler 817 vs 818 polars.JPG
Eppler 817 vs 818 polars.JPG [ 79.17 KIB | Viewed 565 times ]


This is actually a very interesting topic. I've tried the Eppler 817 profile at about 80% and also the S7012. Both work fine, my S7012 wing came out a bit thicker than the 9% it should have. It feels a bit slower at top end than the Eppler profile, but less prone to stall, so starts a bit earlier.

Peter, the airfoil tools website gives you an option to scale thickness when you either print it or download the co-ordinates - so it's pretty easy. From playing with XFLR5 is seems like small changes in thickness don't change the lift slope much as the camber stays the same.

The interesting thing that I don't understand is that thickness doesn't seem to play much of a role? if you look at Eppler 817 at 11% and Eppler 818 at 9% the curves (lift and drag) are almost identical - if fact the thicker wing has a wider range where it works better. I'd be most grateful if someone could explain this, it's counter intuitive that a thick wing and thin wing would have the same drag.

If you eyeball the Spotz wing profile and the Sword profile, they're completely different, so obviously there is more than one successful approach.


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 Post subject: Re: Wing profile
PostPosted: Thu Sep 04, 2014 9:03 am 
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Sorry PF for not being clear but you smart guys out there already have the answer.
When we talk of wing profiles we say 90% to mean it is thinner ONLY on the thickness and we know we change the TRUE naca specs but we feel thinner should be better?
Meaning that if a given NACA is 10 thick we do 9 or sometimes even thinner.
We could be very wrong here........just seems logical that "thinner struts, fuses and wings should be more hydrodynamic? :idea:
But Tom Speer probably knows better according to the numbers concerning his 105.
As we hand make all our molds and wings we spend a lot of time on them.
Bye the way a at least for us, a nice find.........quadaxial carbon.........just seems better and each layer after vac sac comes out 1mm so we start to precut our layups for more presion and less filing and sanding.
We have looked into 3d printing and cnc milling but beyond our budget now.
BUT,
We have found a Very inexpensive solution that will be our winter project. :!:
A simple home made 3 axis mold cutter for use with hard foam to make one time use molds.
I will post findings.
On an off note,
We had the fine chance to play with the (in my and many others who know) first true foil innovator
and rode a front wing he made at 350 cm2 and stab at about 200cm2 with a most stiff strut and fuse.
What a F/&%")= PLEASURE talk about the sensation of gliss, sorry french term, shall I say slicing thru the H20!
And for the third time flew the 15m2 chrono and I absolutely, positivly would buy either that or a 12m2 for the light and up wind is unreel!
I have found nothing new as most racers already know this, just chiming in.
FOIL + FOIL!!!
Other real life flying test result.
Moustach (wing tips angled up) stabs simply work better than flat, even with vert TT style fin, and rear wing, stab AOA does play a most critical role, even half a degree can be felt.
After reading "how wings work" I am now intrested in the Coanda profiles and because the bottom is almost flat will be easyer to mold and shape.
See the Coanda 3, I have to think for "normal" foiling this should be just fine, Thoughts? :?:
R H


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