I saw this double foil on Horue site. It seems to increase the surface area with the second foil under the main foil. Did anyone try this foil for light wind on windsurf board.

I had thought I saw a video somewhere of a windfoil using a bi-wing config. Don't remember it had any advantages. Although this seems like a gimmick to me, I'm not sure the advantages would be. Looks expensive vs. simply having a larger wing.

It appears to have an adapter for the second foil, that could provide a larger surface area to enhance lifting. But this needs to be proven by foilers!

You can buy the adapter from horue. The idea is that for a small price compared to a wing you get a lot more surface area. They say it gives a lot more lift, similar to a wing of the combined area, but also gives a lot more drag, more than a single wing of the same area would.

adapter for a biplane I have long noticed. since I bought the wing xxlw hands did not reach to make a biplane. I made on different I took I took hydrofoil horue h10 and added from below wing xlw. but take off did not work as the lower wing xlw protrudes forward. Chief horue Philip said move the lower wing back and then get. I haven't had time to do that this season. I bought a square tube of stainless steel 25 by 25 mm as the fuselage Foyle h10. I want to make a long fuselage 1200 mm and try to make a biplane. But the idea is good having two wings on a strong and medium wind can not buy a third expensive wing xxlw.

With the wings as close together as shown, there will be a lot of interaction in the water flow. That's even true for tri-fin and quad windsurf boards, where the distance between fins is a lot larger.

I'd love to see a dual foil board where the two foils are further apart, with the upper one much closer to the board. The upper wing could provide lift for early starts, but then be above the water to reduce resistance and allow more speed.

Greetings from your old Mate who use to windsurf on Botany Bay from 1997 till September 2000 where my avatar comes from.
For last 19 years I have been living in "VSn VM". Gee it is hard to write up side down "WA USA" Seattle Area where WA stand for Washington State.
OK, we have this frequent challenge as we do not have enough strong steady wind in Seattle Area and the Columbia Gorge takes somewhere between 4 to 11h to drive. Yes my last trip took me 11h to get back home.
My personal challenge is also that Foil Manufacturers are not really thinking about "Heavy Dudes" like myself at 100kg (220LB).
I wrote about it in our Pacific NW Windtalk blog:
"Heavy Dude Windsurf Foiling around Seattle & Exocet RF91 + e.g. Slingshot foil match challenges"
groups.io/g/nw-windtalk/topic/31693545

So what is the solution?

1) snap on your windsurf foil board a trolling motor and you can enjoy TOW (time on water) when wind dies out.
Details you can read at:
"How to quickly convert your Windsurf Foil Board into Electric Foil Board for around $1500 - DIY - Methodology behind"
groups.io/g/nw-windtalk/topic/32817001

2) add the second foil into "bi-plane" mode
Details you can read at:
"WWII Sinking the battleship Bismarck - Inspired by British Torpedo Bombers - What does it have to do with Slingshot Hydrofoil ?"
groups.io/g/nw-windtalk/topic/wwii_sinking_the_battleship/34412719

From this update you can see that "bi-plane mod" does work generating more lift at the cost of speed comparing to otherwise single foil without second bolted on. This also is tested in so called "controlled environment" because with trolling motor I do not rely on changing wind conditions.
I am still to test it with the sail though. Right now if not enough wind I go work on my "Windfoil e-foil convert" project and when get ! enough steady wind forecast for 5 to 10 mph (9knots) I will continue windfoil (windsurf foil) bi-plane mod testing.







This way I am achieving 50% more surface area for the front wing than the largest Slingshot wing Infinity 99 (i99).
BTW: i99 is considered huge by many but my "bi-plane mod" gives me more flexibility to add i76 foil under i84 foil only when I want to with just two bolts. The i76 foil has been sitting idle in my car as a spare but now I can quickly put it into use only when I want to.

When the Hydrofoil Industry does not listen to your needs then you can either whine about it or do something about it.

Happy Mods !

Marek S

Guys you don't have enough shovels infinity 84? I'm on the wing Horue xlw take off with the wind 8 knots and this wing span 920 mm and an area of 971 cm2, and with the wing XXLW span 1200 mm and an area of 1349 cm2 take off with the wind 6-7 knots. And with a biplane if you take the wing 800 and 970 only 1760 and this should be enough.

Just to clarify the Slingshot foil surface numbers.
I have already done that in out NW Windtalk Blog under:
"I99 test"
groups.io/g/nw-windtalk/topic/34414532
So the numbers are like this:
Wing Surface size %
i99 2371cm2 - 100%

i84 2066 cm2
i76 1534 cm2
sum: 3600 cm2 - 152% of the i99 wing when using i84+i99 in bi-plane mode

That obviously only calculates frond wings. 420cm & 480cm stabilizers not included.

Sure, if you live in Sydney with steady stronger winds (as I did) you do not have to get creative to enjoy your TOW when average day is 0 to 5 mph (up to 4 knots) and gusts only 10 mph (up to 9 knots).
Also if you get to 100kg (220lb) weight, as I am, then you will see skinny kids flying in conditions you can only dream of.
Again, you can whine about it or do something about it.
Come to Seattle for a while where Olympic Mountains are blocking westerly flow and creating CZ (Convergence Zone) just around Seattle then you would understand our challenges. you may have one moment dead calm 0mph next moment 30mph.

Happy Mods!

Marek S

Select to expand quote

mareks360 said..
Just to clarify the Slingshot foil surface numbers.
I have already done that in out NW Windtalk Blog under:
"I99 test"
groups.io/g/nw-windtalk/topic/34414532
So the numbers are like this:
Wing Surface size %
i99 2371cm2 - 100%

i84 2066 cm2
i76 1534 cm2
sum: 3600 cm2 - 152% of the i99 wing when using i84+i99 in bi-plane mode

That obviously only calculates frond wings. 420cm & 480cm stabilizers not included.

Sure, if you live in Sydney with steady stronger winds (as I did) you do not have to get creative to enjoy your TOW when average day is 0 to 5 mph (up to 4 knots) and gusts only 10 mph (up to 9 knots).
Also if you get to 100kg (220lb) weight, as I am, then you will see skinny kids flying in conditions you can only dream of.
Again, you can whine about it or do something about it.
Come to Seattle for a while where Olympic Mountains are blocking westerly flow and creating CZ (Convergence Zone) just around Seattle then you would understand our challenges. you may have one moment dead calm 0mph next moment 30mph.

Happy Mods!

Marek S

So the French are right. The main thing is the wingspan, not the super shovel and area. But a large wingspan of 1200 mm must be done very durable fuselage.

"Biplanes suffer aerodynamic interference between the two planes. This means that a biplane does not in practice obtain twice the lift of the similarly-sized monoplane. The farther apart the wings are spaced the less the interference, but the spacing struts must be longer."

according to wiki

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MrA said..
"Biplanes suffer aerodynamic interference between the two planes. This means that a biplane does not in practice obtain twice the lift of the similarly-sized monoplane. The farther apart the wings are spaced the less the interference, but the spacing struts must be longer."

according to wiki

Horue recognized this and did their best to optimize the strut to minimize the effects. They also soon after came out with the XXLW wing. Much wider. Not as much total area but their preferred solution to very light wind windsurfing.

Biplanes can have a lot of area in a confined wing span but, ultimately, outside of very specific uses, the higher drag meant that monoplanes tend to be the preferred solution. Which is why, I guess, one doesn't see many biplane gliders.

Mareks360, have you tried your biplane with only one stab?

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Paducah said..

Mareks360, have you tried your biplane with only one stab?

No, I have not tried to use single stabilizer. Do you think it would have much difference ?
In the meantime I focused on optimizing some hydrodynamics as the force of resistance goes in square of speed therefore eliminating any excessive drag is my first priority:
I still need to bevel the aluminum edges but here is updated mod:






By the way Mates, the Fall / Autumn has just arrived in Seattle and that white thing is not "an icing on the cake". That is bloody frost. Its bonkers to get it so early.
Gee I miss Sydney !

Love that you are willing to have a go. i see you have staggered the wings. staggering the wings apparently reduces the interference between the wings Staggered by a chord apparently gets best results.
citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.726.9922&rep=rep1&type=pdf
biplanes generally only have one tail plane and given you are effectively increasing the fuselage length, one stab may be enough for pitch control especially on the rear most fuselage and will reduce drag by eliminating one stab wing following your progress with interest.

Here is another setup to address concern that in bi-plane mode the wings might be interfering with each other.
Because I did not use the same propeller I can not confirm 100% but all felt the same and i was getting similar speeds with similar propeller bi-plane on my custom design adapter and all Slingshot HW here with short Taxi 15" mast addition.

More details at our NW Windtalk Forum:
"WWII Sinking the battleship Bismarck - Inspired by British Torpedo Bombers - What does it have to do with Slingshot Hydrofoil ? "
groups.io/g/nw-windtalk/message/63670

You guys know that surface area is not everything??! My largest racing wing is 900mm wide amd 872cm2, and I can keep flying and even jibe it in the air in 4-6 knots. Ofcourse I use a big sail in these kind of conditions, but it works, and you are dreaming if you think you can use smaller than a 9.0 to get going in that kind of wind if you're similar weight as me (88Kg).

I recently tried some bigger wings to windsurf with. A 2200 and an 1800 (The 2200 has a 1100mm wingspan!). And completely did not like it. The acceleration of the kit is so little and the drag so big that in the jibes I felt I had less time to flip my rig etc. (The "no power" period in the jibe). Also I compared it directly to my high aspect 900cm2 freeride wing, and takeoff was similar, just needed a little more technique! In the air the 900cm2 wing was so much better than the 2200cm2 wing though. More acceleration, way less drag, to me easier to jibe because it kept more speed, and better gliding through the lulls. The only real plus of the 2200 was that pumping in the air was more effective, but it was also necessary to get through the lulls..

The 2200 did take less rider input to get going, it went on its own, although pumping didnt really matter much for the power needed to takeoff. It did feel more reassuring, so for a beginner it is definately an option. However, for more advanced riders who are not aiming to ride on waves I would not use such a big wing, smaller ones offer very similar low end, more high end, more speed and a better glide. Also, I wouldnt put a sail much over 6m on the big wings, allthough the more high aspect designs can handle them with ease, in the end unlocking even more low end performance.

All that being said. Taking off below 6 knots is a fad, I've never seen it, and I dont think anyone will of off sail power alone, maybe if you are a very good pumper with an 1800 for example, but than you wouldnt really need the sail anyway.. I have never really seen a low aspect wing break the 9-10 knot takeoff threshold. The only people who really manage that are racers. Keeping flying a little below that is something else entirely ofcourse.

I'll take some comparative pictures of the setups tomorrow!

P.s. I had a wonderfull session with 10.0 Phantom Iris SF, Lokefoil Race L (872cm2) and my formula board today. The chart of the wind below. I was out only for an hour between about 13:40 and 14:40, wouldnt dare imply I can fly in 2 knots of wind, but 4 kts is enough to keep going (I think there was a knot or so more than the chart shows). Once I'm up I never really loose flight (except by user error).

Select to expand quote

mareks360 said..
Here is another setup to address concern that in bi-plane mode the wings might be interfering with each other.
Because I did not use the same propeller I can not confirm 100% but all felt the same and i was getting similar speeds with similar propeller bi-plane on my custom design adapter and all Slingshot HW here with short Taxi 15" mast addition.

More details at our NW Windtalk Forum:
"WWII Sinking the battleship Bismarck - Inspired by British Torpedo Bombers - What does it have to do with Slingshot Hydrofoil ? "
groups.io/g/nw-windtalk/message/63670

A biplane is an interesting idea. And here is when many wings this already bust and foolish