Contact   Imprint   Advertising   Guidelines

Surf/wave wing thickness and NACA profiles

A forum dedicated to Hydrofoil riders
Europ2
Frequent Poster
Posts: 448
Joined: Wed Mar 01, 2006 7:51 pm
Brand Affiliation: None
Has thanked: 6 times
Been thanked: 2 times

Re: Surf/wave wing thickness and NACA profiles

Postby Europ2 » Mon Dec 30, 2019 4:53 pm

plummet wrote:
Mon Dec 30, 2019 1:41 am
Down loaded. I'll have a play.
The airfoiltools.com site interfaces are also very handy for the missing NACA sections or the present ones with insufficient point number:
http://airfoiltools.com/airfoil/naca4digit and http://airfoiltools.com/airfoil/naca5digit
It also allows you to thicken or slim down a given profile or set of points.

Nevertheless, the two last digits representing the max thickness, I am not sure you would feel much difference on the water between a NACA 2408 and a NACA 2409 :(
NACA 2408 and 2409.jpg
NACA 2408 and 2409.jpg (51.94 KiB) Viewed 385 times

bohme
Rare Poster
Posts: 21
Joined: Fri Apr 22, 2016 12:01 pm
Local Beach: Ringkøbing
Favorite Beaches: Hvide Sande
Style: Foiling
Gear: Worn
Brand Affiliation: DIY
Has thanked: 3 times
Been thanked: 1 time

Re: Surf/wave wing thickness and NACA profiles

Postby bohme » Mon Dec 30, 2019 6:39 pm

plummet wrote:
Mon Dec 30, 2019 12:30 am
bohme wrote:
Sun Dec 29, 2019 9:19 pm
Why e387?
The e387 has a lot of camber and a very high sweet spot Cl around 0.7 (around 10kn of foil speed)
My guess is it get unstable above 18kn (Cl below 0.4).
A NACA 4 series might be a better choice.
I used 387 as it was a recommendation on another site. I'm open to change however.

Hmmm, think 18 knots max will be a bit too slow. What do you recommend for 14 knots average 24 knots max?

PS I can't find 1409,2409,3409 on the tools website. I can find 1408,2408.
2408-2410 might be a good compromise for you speed range. It is easy to build. Soft nose for smooth riding. Wide Cl range with a good sweet spot. Suitable for foil Reynold numbers 500k to 1.5m

Many people complain that they have a hard time keeping their big foil in the water in strong winds. It is not because the foil is too big, it is because the foil has too much camber.

User avatar
Peter_Frank
Very Frequent Poster
Posts: 9627
Joined: Wed Oct 16, 2002 1:00 am
Brand Affiliation: None
Location: Denmark
Has thanked: 164 times
Been thanked: 157 times

Re: Surf/wave wing thickness and NACA profiles

Postby Peter_Frank » Mon Dec 30, 2019 8:19 pm

True, and it will also "buckle" a lot more, because the camber gives you not only lift, but also a lot more pitching moment (Cm), so more difficult to control, needs a bigger stab.

Another disadvantage about E387 is the superthin trailing edge, VERY difficult to produce and avoid damage.

It is the almost perfect profile for max lift AND low drag - really efficient.

But drag doubles when you reach Ca = 0 (high speed).
Does not mean you can not ride 18 knots only, bohme meant it has its lowest drag at a high lift coefficient corresponding to 18 knots speed approximately.

And when you go at lower angle of attacks (on the way to faster) you need more kitepower as the drag increases a lot more than less cambered wings.

The Naca 4 series are low camber and will have low drag at high speed (low Ca = low AOA) and be a lot more stable also.

So for an allround foil in waves I agree, it will work better.

The E387 will be one of the best regarding early foiling and awesome upwind angles, by far the best L/D ratio.

But too difficult for practical use probably, and too high drag at high speeds, I agree after having thought it through :roll:

8) Peter

plummet
Very Frequent Poster
Posts: 6516
Joined: Sat Aug 29, 2009 11:25 pm
Local Beach: EE
Favorite Beaches: NZ
Style: Terrain riding
Gear: Old wornout ozone.
Plummet hydrofoil and mutant
Brand Affiliation: None
Has thanked: 4 times
Been thanked: 96 times

Re: Surf/wave wing thickness and NACA profiles

Postby plummet » Mon Dec 30, 2019 9:43 pm

Thanks for the advice men I have redrawn using Naca2409.

plummet
Very Frequent Poster
Posts: 6516
Joined: Sat Aug 29, 2009 11:25 pm
Local Beach: EE
Favorite Beaches: NZ
Style: Terrain riding
Gear: Old wornout ozone.
Plummet hydrofoil and mutant
Brand Affiliation: None
Has thanked: 4 times
Been thanked: 96 times

Re: Surf/wave wing thickness and NACA profiles

Postby plummet » Tue Dec 31, 2019 6:17 pm

Ok team, next question.

I see a lot of hydrofoils, even the low aspect front wing, ones with higher aspect stabilizers.

Why?

User avatar
Peter_Frank
Very Frequent Poster
Posts: 9627
Joined: Wed Oct 16, 2002 1:00 am
Brand Affiliation: None
Location: Denmark
Has thanked: 164 times
Been thanked: 157 times

Re: Surf/wave wing thickness and NACA profiles

Postby Peter_Frank » Tue Dec 31, 2019 10:29 pm

plummet wrote:
Tue Dec 31, 2019 6:17 pm
Ok team, next question.

I see a lot of hydrofoils, even the low aspect front wing, ones with higher aspect stabilizers.

Why?

I think it is because: "Why not?"

As higher AR stabilizer will have lower drag when at lift, and the same at low or no lift.
And more lift at extreme angles.

And as the span of the stab is so short even when higher aspect, it will hardly influence turning - like the front wing where span is almost opposite proportional to turning ease.

At some point it might not work well at really low speeds maybe, if super narrow, but I dont think it is an issue at our speeds.
It will get more fragile and can easier break though :(

I personally prefer a stab with a more reasonable AR so it is not a dagger, as it operates at almost no lift most of the time, only in tight carves it gets loaded, but here the drag is probably only a fraction of the whole system.

8) Peter

PS: Are you far into 2020 now plummet?
Fun, as here we still have one and a half hour left of 2019 :naughty:
And this forum is in UTC time so still two and a half hour left.

plummet
Very Frequent Poster
Posts: 6516
Joined: Sat Aug 29, 2009 11:25 pm
Local Beach: EE
Favorite Beaches: NZ
Style: Terrain riding
Gear: Old wornout ozone.
Plummet hydrofoil and mutant
Brand Affiliation: None
Has thanked: 4 times
Been thanked: 96 times

Re: Surf/wave wing thickness and NACA profiles

Postby plummet » Wed Jan 01, 2020 5:59 pm

I'm 12hrs + get.

So the next question is this this should the naca profile on the rear be the same as the front? Or should I look at a different profile?

bohme
Rare Poster
Posts: 21
Joined: Fri Apr 22, 2016 12:01 pm
Local Beach: Ringkøbing
Favorite Beaches: Hvide Sande
Style: Foiling
Gear: Worn
Brand Affiliation: DIY
Has thanked: 3 times
Been thanked: 1 time

Re: Surf/wave wing thickness and NACA profiles

Postby bohme » Thu Jan 02, 2020 8:52 pm

plummet wrote:
Wed Jan 01, 2020 5:59 pm
I'm 12hrs + get.

So the next question is this this should the naca profile on the rear be the same as the front? Or should I look at a different profile?
The front wing operates, from take off to max speed, between stall (cl more than 1.0 or aoa 10°) and cl = 0.25.
The rear wing operates, from take off to max speed, between cl -0.4 and 0.4. The rear foil lifts up at takeoff, and pulls down at speed (depending on your setup).
The rear foil does not operate near stall, and does not need to have the nice stall characteristic and extended aoa of a low aspect wing.
At 18-24kn the rear foil probably operates around cl 0.2~0.4 (downwards), depending of your setup.
Because of the shorter chord, the rear wing operates ~30% of the Reynolds Number of the front wing, and should be a "low reynolds number" foil.
The numbers are only to put things into perspective.

The NACA 2408-2410 is a good choice for DIY.

I have made a few DIY rear foils, and my preferences are:
- high aspect 2410 rear wing for my freeride foil. The limiting factor is stiffness. Too high aspect and too thin does not work.
- slightly crescent shaped medium aspect 2408 rear wing for my wave foil. It is a smoother ride, at the expense of drag.

plummet
Very Frequent Poster
Posts: 6516
Joined: Sat Aug 29, 2009 11:25 pm
Local Beach: EE
Favorite Beaches: NZ
Style: Terrain riding
Gear: Old wornout ozone.
Plummet hydrofoil and mutant
Brand Affiliation: None
Has thanked: 4 times
Been thanked: 96 times

Re: Surf/wave wing thickness and NACA profiles

Postby plummet » Fri Jan 03, 2020 7:37 pm

Great info, thanks men.

The front wing is in the press.

User avatar
Peter_Frank
Very Frequent Poster
Posts: 9627
Joined: Wed Oct 16, 2002 1:00 am
Brand Affiliation: None
Location: Denmark
Has thanked: 164 times
Been thanked: 157 times

Re: Surf/wave wing thickness and NACA profiles

Postby Peter_Frank » Fri Jan 03, 2020 8:03 pm

A symmetrical rear wing would also work just fine, and if not, just a tad negative camber :thumb:


Return to “Hydrofoil”

Who is online

Users browsing this forum: No registered users and 3 guests