Forums > Windsurfing Foiling

DIY Foils - Which NACA?

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Created by Slim Jim 1 month ago, 8 Jun 2018
Slim Jim
SA, 177 posts
8 Jun 2018 9:39PM
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There are many airfoils to choose from airfoiltools.com/ with lots of good data.
I'm interested in which foil profiles are used on the commercially available foils
I'm about 90% complete building my own using Rob Rock's Instructions.
This has NACA0010 (half) for main wing and spoiler (spoiler- thrust down 2 degrees).
I've been modelling up the NACA0010 half foil section as 6409 9% not being able to find any data on NACA0010 half.
Some interesting charts of below make me think about experimenting with symmetrical NACA0010 spoiler.
Later after I try this construction out - hopefully I can make it fly!
















Paducah
78 posts
9 Jun 2018 3:16AM
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Interesting project. Couple of questions: Did you go with 2 degrees because of Rob Rock suggested it or another reason? Do you have an easy way to change that?
How long is your mast?

Slim Jim
SA, 177 posts
10 Jun 2018 8:28AM
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1. Mast length 45 cm - shorter mast meant to be better for beginners. I see Slingshot offering 38, 61, 76, 90 cm to this end. Also there are sand banks where I sail!
2. -2 degrees per the instructions. I think it is to put the main wing at a nice angle to generate lift and balance mast foot down force around the main wing up force fulcrum point. Achieved by hardwood wedge. I guess you could make a series of wedges or pack the bolts with varying numbers of washers to get some adjustment?

i think this is an older (superseded?) design. Are the commercial products converging on a similar 'optimum' design?

Are speed sailors designing foils for speed - can sailboarder start going significantly faster than wind speed like Paul Larson's Sailrocket = 65.45 in 27 knots wind. According to Zara Davis in Windsurf mag two years ago the top guys were hitting 52 in 60 knots wind. Last year she clocked 46.49 in 45 knots. Interesting times!

azuli
QLD, 117 posts
10 Jun 2018 10:45AM
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Slim Jim said..
Are speed sailors designing foils for speed - can sailboarder start going significantly faster than wind speed like Paul Larson's Sailrocket = 65.45 in 27 knots wind. According to Zara Davis in Windsurf mag two years ago the top guys were hitting 52 in 60 knots wind. Last year she clocked 46.49 in 45 knots. Interesting times!


see mauiultrafins.com/technology/how-fast-can-we-go/

Apparently foil drag limits the application of foils for high-speed windsurfing, currently foiling is working very well at speeds below 30 kts. For higher speed, the foiling area must be reduced which shift the lifting speed to higher values. For very high speeds, the foil area has to be drag optimized for the required speed, for 50 kts e.g. it means about 100 cm2 in area. Such a small wing would lift the board out of the water, not before 20 kts.

Paducah
78 posts
11 Jun 2018 4:22AM
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Slim Jim said..
1. Mast length 45 cm - shorter mast meant to be better for beginners. I see Slingshot offering 38, 61, 76, 90 cm to this end. Also there are sand banks where I sail!
2. -2 degrees per the instructions. I think it is to put the main wing at a nice angle to generate lift and balance mast foot down force around the main wing up force fulcrum point. Achieved by hardwood wedge. I guess you could make a series of wedges or pack the bolts with varying numbers of washers to get some adjustment?

i think this is an older (superseded?) design. Are the commercial products converging on a similar 'optimum' design?

Are speed sailors designing foils for speed - can sailboarder start going significantly faster than wind speed like Paul Larson's Sailrocket = 65.45 in 27 knots wind. According to Zara Davis in Windsurf mag two years ago the top guys were hitting 52 in 60 knots wind. Last year she clocked 46.49 in 45 knots. Interesting times!


The Slingshot works because the masts are easily interchangeable and come from a kiting background where a long mast is a bigger challenge when starting out. For your first couple of flights, you think, "why do they make masts so long?" Then, you realize that getting the foils to the surface is as big or bigger problem. The wings ventilate, stall and the board drops straight down. Not good. It's even worse if there's any sort of chop which can suddenly get the wings close to the surface in the troughs.

Understand about the sandbanks. You may end up at a happy medium around 60-75 cm. Hitting the bottom is no fun and potentially damaging. You may have to be more selective about your venues. I vacation at a very good windsurfing spot that is pretty much impossible for foils. I didn't even get mine out of the car for the week.

re: angle. 2 degrees is a fair amount. The amount you need varies by a number of factors including how the board balances out - your foot position vs the fin box and where the mast foot is as well as your size. The better balanced everything is, the less stab angle you'll probably require. Also, going faster tends to require less angle. Glad you have it adjustable and not "hard-wired".

For rec riding, 20 kts is plenty fast. Things go by in a blur when you are 50 cm off the water. If you are going to push the envelope - (afaik) currently in the low 30s, you'll probably want to at least ride a commercial wing to see what others have done before you. With planing boards so efficient at higher speeds and much more "pitch stable", foils aren't seen yet as straight line speed weapons. Their efficiency at lower wind and board speeds, though, makes them ideal for light wind competition.

There isn't really "a" design. Different foils address different objectives. Slingshot is intended as a stable free-ride platform, which they do well.

I enjoy Rob Rocks' videos a lot. Glad others are getting inspiration from them.

Te Hau
324 posts
Saturday , 14 Jul 2018 6:09AM
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Slim Jim said..
1. Mast length 45 cm - shorter mast meant to be better for beginners. I see Slingshot offering 38, 61, 76, 90 cm to this end. Also there are sand banks where I sail!
2. -2 degrees per the instructions. I think it is to put the main wing at a nice angle to generate lift and balance mast foot down force around the main wing up force fulcrum point. Achieved by hardwood wedge. I guess you could make a series of wedges or pack the bolts with varying numbers of washers to get some adjustment?

i think this is an older (superseded?) design. Are the commercial products converging on a similar 'optimum' design?

Are speed sailors designing foils for speed - can sailboarder start going significantly faster than wind speed like Paul Larson's Sailrocket = 65.45 in 27 knots wind. According to Zara Davis in Windsurf mag two years ago the top guys were hitting 52 in 60 knots wind. Last year she clocked 46.49 in 45 knots. Interesting times!


Re.......Are the commercial products converging on a similar 'optimum' design?
I've just been on Maui for a month. The shops have all sorts of foils for sale and there is a huge variety of foil section types and sizes. Looks to be a long way from any 'optimum design' yet.
Talked to a home builder who was using MH32 for the front (8.7% x 2.3% camber) and NACA 2408 (8%x 2% camber) upside down for the stabiliser.



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"DIY Foils - Which NACA?" started by Slim Jim