Standup Zone Forum

The Foil Zone => Wingsurfing, Windfoiling, Wingfoiling, Wing SUP => Topic started by: Badger on November 19, 2021, 02:37:09 PM

Title: Wing aerodynamics question.
Post by: Badger on November 19, 2021, 02:37:09 PM
Why aren't wings more wing shaped?

I keep thinking that wings might be more efficient and have better upwind ability if there was less turbulence behind the leading edge. It seems like a substantial amount of area behind the leading edge is just going to waste and the resultant turbulence interfering with performance.

Is the underside of the wing irrelevant to performance or is it only a matter of time before someone invents a way to fill that gap allowing the air to flow more smoothly across the underside of the wing?



Title: Re: Wing aerodynamics question.
Post by: JohnnyTsunami on November 19, 2021, 02:58:55 PM
I'm curious about double skinned wings - think kitefoiling "foil" kites, but no need for the rammed air because we have an inflatable leading edge (and we need one since we have no bridles to maintain shape). It seems relatively easy to do, just put a thin canopy on the handle side of the wing as well, doesn't necessarily need to be connected at the trailing edge. Handles/boom can be where they are now, just come out through some reinforced holes the inner canopy, since it wouldn't be any further out that the main strut anyway.

Obviously would weight a bit more, but maybe you could get away with a lighter material and sill not have much flapping due to the double skins.

“ Tube-kite profile creates more lift than a Soft-kite profile in stationary flight conditions, but the drag is higher in low angles of attack.” So upwind the double skin wins, but more grunt in the single skin.
https://www.ralfgroeseldesign.com/post/tube-vs-softkite-an-epic-battle (https://www.ralfgroeseldesign.com/post/tube-vs-softkite-an-epic-battle)

America's Cup Boats use this https://youtu.be/-M54CVWotvc?t=86 (https://youtu.be/-M54CVWotvc?t=86)

Also see the IWS inflatable sailboat sail, supposedly far more efficient that a similar sized regular sail and less heeling force compared to lift.
https://youtu.be/QGJ02kEDtXI?t=8 (https://youtu.be/QGJ02kEDtXI?t=8)

AKA "wing sail" https://en.wikipedia.org/wiki/Wingsail (https://en.wikipedia.org/wiki/Wingsail)

Of course, kite foil racers use "foil" kites which are far more efficient than leading edge inflatable (LEI) kites, which are like our wings. Ozone seems to be the leader here. 

I'll give my shipping address to anyone and am happy to test!  ;D
Title: Re: Wing aerodynamics question.
Post by: Dwight (DW) on November 19, 2021, 03:57:05 PM
We’ve been through this before with Windsurfing and Hang Gliding.

Back in about 1980 or 81 a brand introduced double surface. It performed worse. Why, because hang glider design wasn’t good enough. There were way more design improvements that needed to be invented first.

Same with windsurfing. Double surface sails were not faster. Tip twist had not even been figured out yet.

Wings, way too early in the evolution of design.
Title: Re: Wing aerodynamics question.
Post by: Badger on November 20, 2021, 04:42:48 AM
All of those ideas attempt to bring the underside surface all the way to the trailing edge.

All I'm suggesting is to cover or fill the area directly behind the front tube of the wing where the air turbulence is. Beyond that, it's not needed. Then instead of being dead space, it would actually add to the usable sail area.

Foil wings have a gigantic leading edge which carries a tremendous amount of dead air behind it compared to any other type of sail.

It would be easy to take a 20-inch wide strip of cloth and attach it with adhesive velcro to cover the area of turbulence behind the tube just to see what would happen. Unfortunately, all my wings are new and I'm not ready to defile them yet

.
Title: Re: Wing aerodynamics question.
Post by: Wetstuff on November 20, 2021, 06:29:45 AM
I don't know?!  But, these guyz never seemed to have drifted far from top-only surfaces, and they've been at it a bit longer... 

You can be sure someone will come along and add to the 'exotic' ...and the price. Pretty much anyone at the premium end of a market gains stature by default.

http://www.wikidelta.com/images/pdf/Hang-Glider-Design-and-Performance.pdf

Jim
Title: Re: Wing aerodynamics question.
Post by: Dwight (DW) on November 20, 2021, 08:48:07 AM
The original GIANT leap in hang glider design was cross bar tension. It basically created massive canopy tension tip to tip.

Kind of like what Aluula is doing for winging. Holding onto more canopy tension.
Title: Re: Wing aerodynamics question.
Post by: PonoBill on November 20, 2021, 09:15:34 AM
Double skin is likely somewhere on the list of eventual improvements, but way down the page. We're more or less a little past the "it works!" stage. I don't expect any of the performance improvements we'll see over the years to be of any benefit to me except perhaps anything that makes wings lighter.
Title: Re: Wing aerodynamics question.
Post by: Badger on November 20, 2021, 10:24:17 AM
One major drawback would be the extra time it would take to dry a wing like that.

I guess I'll leave it to the experts and be satisfied with what we have. There is a lot of money at stake for better wing designs. I'm sure they are working diligently on new concepts.
Title: Re: Wing aerodynamics question.
Post by: tarquin on November 20, 2021, 12:25:21 PM
I am pretty sure kites went down the same path and they put out some with a second skin. I think too expensive and not that big a difference.
 What amazes me is its taken what, 3 generations of wings too make a big difference. I understand companies were reluctant at the start. How can companies that have been making kites for years go, oh we need a stiffer bladder. Version 2 has a stiffer bladder, version 3 has a even stiffer bladder and tighter canopy. Sounds exactly like what kites went through.
 I think some sort of carbon batten like the C tech furling batten could work. I emailed multiple companies for inflatable SUPs,kites and wings. Not one was interested. So maybe not?
 
Title: Re: Wing aerodynamics question.
Post by: tarquin on November 20, 2021, 12:27:08 PM
https://www.sailbattens.com/products/flexifurls
 Forgot to add this.
Title: Re: Wing aerodynamics question.
Post by: Badger on November 21, 2021, 06:28:08 AM
I can see full-length battens possibly being used at some point. I'm happy with the sport so far but it can't end here. There are more breakthroughs just around the corner.
Title: Re: Wing aerodynamics question.
Post by: Wingfoil2001 on November 21, 2021, 11:50:11 AM
We have been flying leading edge inflatable kites for years, very little has changed to the leading edge to canopy design. Double surface has been tried but of little benefit.
Now it’s all about weight saving, further relegating any thoughts of double surface and battens to the scrap heap.
Title: Re: Wing aerodynamics question.
Post by: JohnnyTsunami on November 22, 2021, 11:35:38 AM
Very interesting stuff. If there isn't much to be gained on double skin, then maybe the Aluula/Spectra/Dyneema material will lead to reductions in leading edge diameter and that will be the main performance gain? The smaller leading edge will result in less drag --> more efficiency?

My 6m Duotone Echo v2 goes upwind pretty poorly looking at my gps tracks. I'm a sit down sailboat racer who knows how to go upwind.
My 4.5m Duotone SLICK goes upwind much better. Maybe ~110 degrees on different tacks, hard to say without a protractor.

Do you think the difference is the smaller leading edge of the 4.5m? Or is it the wing outline or the draft or something like that?

I noticed a couple times people on a different brand 6m wing pointing higher than me - ozone I think. I was riding ART-999 and a Mike's Lab foil, so it's not what's under the water. Anyone on an Aluula wing and compare their upwind angles to a dacron wing of the same size?
Title: Re: Wing aerodynamics question.
Post by: PonoBill on November 22, 2021, 08:28:53 PM
I've quizzed a few wing designers on what makes a wing hold a better upwind angle. It's a topic that they seem unwilling to talk about--at least not to me. Mark Raaphorst has a couple of the Ocean Rodeo Alula wings. They seem quite good, I may spring for one, and they seem to go upwind very well. I've always considered my F-one Strikes to be particularly good upwind, and Mark holds a much line than I can. Part of that is undoubtedly rider, but I suspect both the extreme stiffness of the inflated bits (leading edge and strut) and the small diameter both help.

When I'm hanging off the board in strong wind going upwind as close hauled as I can, I know my Strikes get distorted--a bit taco-ed. That has to be spilling air off the wingtips if nothing else. The cloud wings (those light green and white things) seem to offer lots of power but can't seem to reach very well. the huge leading edge seems like it's gotta be a problem.
Title: Re: Wing aerodynamics question.
Post by: Vancouver_foiler on November 22, 2021, 10:32:02 PM
I've quizzed a few wing designers on what makes a wing hold a better upwind angle. It's a topic that they seem unwilling to talk about--at least not to me. Mark Raaphorst has a couple of the Ocean Rodeo Alula wings. They seem quite good, I may spring for one, and they seem to go upwind very well. I've always considered my F-one Strikes to be particularly good upwind, and Mark holds a much line than I can. Part of that is undoubtedly rider, but I suspect both the extreme stiffness of the inflated bits (leading edge and strut) and the small diameter both help.

When I'm hanging off the board in strong wind going upwind as close hauled as I can, I know my Strikes get distorted--a bit taco-ed. That has to be spilling air off the wingtips if nothing else. The cloud wings (those light green and white things) seem to offer lots of power but can't seem to reach very well. the huge leading edge seems like it's gotta be a problem.

I was talking w Richard Myerscoff a bit back(trying out his all allula wing goodness me) and he felt winging just passed the c-kite phase. These designers have major improvements and innovations around the corner  they just can't get them tested and out fast enough. production with covid oversees saw them loose almost a year all in all.

Pono, not a surprise that the Glide felt so good. Ross Harington was a hangoglider pilot and designer before doing kites for OR. He's been designing wings for like 40 years lol.
Title: Re: Wing aerodynamics question.
Post by: surfcowboy on November 25, 2021, 08:33:17 AM
Pono, thanks for the note on the BRM Cloud. I had one and never could quite dial it. (Didn't give it much time really.) But what you say tracks. My F-One wings seem to go upwind better for me. (With the taco you describe too.)
Title: Re: Wing aerodynamics question.
Post by: PonoBill on November 25, 2021, 01:03:11 PM
I don't really track kite design, or know much about it, but it seems to me that kites are not really used as wings, except maybe the ram-air versions. They are at their maximum power with an angle of attack that would stall a wing. To me, that suggests that lift as a wing is not a big part of the equation. A big leading edge probably prevents wind from escaping over the front edge of the kite and increases the power.

Hand wings surely have a kite-like aspect, especially going downwind. On a broad reach the BRM wings seem very powerful. but on a close reach, where wing lift is most important, they seem to underperform.

Looking at the most developed sailing form--the AC foil trimarans and similar boats, a great deal of research resource gets spent on making sail design more winglike. The diameter of the support mast is a big part of getting the wings to perform. From what I've read a lot of effort is spent on making the "sails" self-supporting, which permits the mast to be thinner to reduce parasitic drag. Stayless full-on two- or three-piece wings are becoming common. I doubt we'll see that--at least not in my remaining time in the sport, but even Alula is a step in that direction. The fabric is surprisingly stiff given how thin it is.
Title: Re: Wing aerodynamics question.
Post by: burchas on November 25, 2021, 01:15:54 PM
...the Ocean Rodeo Alula wings. They seem quite good, I may spring for one, and they seem to go upwind very well. I've always considered my F-one Strikes to be particularly good upwind...

Really gunning for OR 4M A series. The F-One Strike CWC 6m is my only wing since my 3.5M Swing was decommissioned. After riding few wings (Duotone slick, Armstrong A, Cabrinha X2) in overpowered conditions I have to say the F-One really holds the bar very high. I'm hoping the OR handling is similar to the F-One than the other mentioned wings, With the Added stiffness, smaller leading edge and better weight this wing sounds like a real next generation wing.
Title: Re: Wing aerodynamics question.
Post by: PonoBill on November 25, 2021, 11:38:56 PM
The 6M CWC is my favorite wing. I use it when I shouldn't, and my shoulders spend the rest of the day explaining that the 5 and 4.2 are perfectly good options.
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