Surf/wave wing thickness and NACA profiles

[Jyoder]

PF, An interesting concept I learned flying hang gliders is that the angle of attack of a glider wing for maximum lift and slowest descent isn’t the same as the angle of attack for best glide distance (ie. efficiency).
Beyond adjusting the thickness, camber, and aspect ratio of a hydrofoil wing, I imagine adjusting angle of attack of wing/stab ratio with shims can make a foil more or less tuned toward glide vs lift. For wave foiling, I imagine you want high AoA when on wave face but a more efficient AoA when carving and bleeding off the energy you gained from the wave. Unfortunately, we have yet to see a foil that you can change wing/stab AoA relation on the fly. What if we had a foot switch that adjusted stabilizer or wing AoA between “slow-lift” and “fast-glide” settings.
Another variable geometry solution is changing aspect ratio of the wing, such as hang glider VG setting, or the military fighter jets with this ability. Doubt that would be easy to manage on a submersed foil wing, however. Food for thought.

[plummet]

i have contemplated an auto-adjusting stab. Put a pivot on the front of the stab, Then 3d print a sectional rubber packer than can compress with additional pressure. More speed = more pressure which would squish the packer and allow a shallower aoa, less lift/more speed.

[Peter_Frank]

PF, An interesting concept I learned flying hang gliders is that the angle of attack of a glider wing for maximum lift and slowest descent isn’t the same as the angle of attack for best glide distance (ie. efficiency).
Beyond adjusting the thickness, camber, and aspect ratio of a hydrofoil wing, I imagine adjusting angle of attack of wing/stab ratio with shims can make a foil more or less tuned toward glide vs lift. For wave foiling, I imagine you want high AoA when on wave face but a more efficient AoA when carving and bleeding off the energy you gained from the wave. Unfortunately, we have yet to see a foil that you can change wing/stab AoA relation on the fly. What if we had a foot switch that adjusted stabilizer or wing AoA between “slow-lift” and “fast-glide” settings.
Another variable geometry solution is changing aspect ratio of the wing, such as hang glider VG setting, or the military fighter jets with this ability. Doubt that would be easy to manage on a submersed foil wing, however. Food for thought.

You are correct, the max lift, well actually not max lift but lowest "sinkrate" is at a higher AOA than where you got the best glide ratio, quite far apart on very cambered wings in fact.

But this difference doesnt matter at all for us freeride and wave hydrofoilers IMO, unless you race where you want max glide angle upwind of course, and will often use different wing profiles where these two points will be closer.

Also bear in mind, many misunderstand this (quite understandingly), that the angle between the wing and stab got absolutely nothing to do with the AOA the wing rides - you can still ride at max or zero or for a moment negative AOA on the front wing - thats why we can ride with a fixed stab and hydrofoiling pitch/speed is so clean and simple, when learned.

For a hangglider this is natural, as we change AOA in exactly the same way, changing weight forward or rear, and stability is obtained by slightly swept wings and washout, so the tips works exactly like a stab, and we avoid instability. Or reflex profile can be used.


For a hydrofoil nowadays where many of use use extremely small stabs, the relative AOA between the wings will just contribute to a very small amount of drag from the stab when not going extreme, and thats it - you can still ride any front wing at ANY angle of attack

PF

[plummet]

I had a look at some wings the other day with the other lone foiler at my area. Sup wings are pretty darn thick. Like 40mm profile. The surd wing for small waves was around 30mm. The wing hw liked the most for larger waves was an adapted hover glide wing around 22mm thick and maybe 650 cm3. My wing max profile thickness is 17mm thick which explains the fast acceleration and difficulty shedding speed on the bigger waves.


I'm thinking i need to get up to 22mm max thickness then role a hydrofoil profile with some anhedral and some token winglets In the 600-700 cm3 range.


Care to measure the max profile thickness of some of your wings Peter?

[Peter_Frank]

I had a look at some wings the other day with the other lone foiler at my area. Sup wings are pretty darn thick. Like 40mm profile. The surd wing for small waves was around 30mm. The wing hw liked the most for larger waves was an adapted hover glide wing around 22mm thick and maybe 650 cm3. My wing max profile thickness is 17mm thick which explains the fast acceleration and difficulty shedding speed on the bigger waves.


I'm thinking i need to get up to 22mm max thickness then role a hydrofoil profile with some anhedral and some token winglets In the 600-700 cm3 range.


Care to measure the max profile thickness of some of your wings Peter?

I certainly can plummet, but as your wing is not wide in chord, it seems pretty thick, so the lack of area is IMO the cause for what you describe.

Measuring up to 5 cm "out" from the center of the fuselage, to avoid having errors from the fuselage/wing junction or taper effects, and it is still pretty much across the max width of the wings.
A manual measurement but probably still max 0.1 or 0.2 % error.


Some Ketos wings

570 cm2 wave wing: 7.5 % thickness (9.8 mm on 130 mm chord)
790 cm2 wave wing: 7.9 % thickness (12.2 mm on 155 mm chord)
1200 cm2 wave wing: 8.1 % thickness (17.5 mm on 215 mm chord)

An older smalk fast racewing I use for jumping in light wind was 6.9 %

The absolute thickness itself is not relevant for the overall drag, it is only the percentage of the chord that matters, and total surface area.

Havent measured if it tapers differently towards the tips (they usually dont), but not that important as the most area is in the center

Peter

[bohme]

My wave foil "Uni foil 175":
12% thickness (26.6mm on 220mm chord), It is close to a NACA 2412 (pretty plat pressure side).

I believe a NACA 6412 has way too much camber. A bigger area it better at giving you the slow speed lift you need.
A thinner foil has less drag and perhaps a more direct feel to it, but lower CL max (stall speed).

I have also made some "auto-adjusting" stab experiments. I did not like it. You loose feel at slow speed, and stability at speed. I am now using a slightly crescent shaped stab, which softens the ride a bit. Otherwise my experience is that everything else should be as rigid at possible.

I might be wrong.

On the topic of men, I think that foils made in female moulds are the best

Jacob

[plummet]

Good discussion men. Thanks for the input. Peter your profiles seem very thin compared to the current wave foil standards. Do you have an idea what naca profile your wings are?

Bohme, I think i agree 6412 will probably have too much camber. I like the 2412 profile and that thinking fits in with my research also. Interesting to hear about your auto adjusting stab experiment. My thought experiment suggested to me that it probably was not practical.


PS My current design is 10% of chord. I'm thinking naca 2412 12% chord might be worth a trial.

[Peter_Frank]

What ARE other wave foils in thickness???

Coming from "flight" design, I never wanted to use thick profiles, and I think the same goes for hydrofoils.

If they are thinner and more cambered, you can have more lift and less drag, but more limited upper end at some point.
If you want "range", you make them thicker yes, but they will still be more draggy, just over a wider range.

Using a reasonably cambered not too thick (but thicker than race wings) profile, will give you the best of everything IMO, and then you can use area for "how low you wanna go", and still maintain good glide and speed if needed

"Draggy" wings in itself (really thick) is never a goal IMO, that does not make any sense whatsoever.

Better use more area, and sell a bit of low-drag by using lower AR if they gotta turn on a dime

We need some more measurements of thickness on current wave wings - eventhough they are so new that we dont know what works the best, and it will probably, like most things, be individual liking.

As I have no idea/experience about where the sweetspot for most riders on wavefoils is, 7 - 8 - 10 - 12 - 15% thickness, or?

Peter

[jumptheshark]

Stingy's new wing is around 1200cm. Plenty of surface area, but it has a very thin profile (under 1cm max depth) and a pretty sharp leading edge. Thinner than both my stock Zeeko wings and they are also pretty slick.

[Breze]

The new 2019 Ketos V2 1200 KOOL has now 21.8 chord and about 16.5mm thickness 7.6%