Foils

[Wilee]

Thought I share my winter project...
No clue if it will work. Just alot of guess work and eyeballing, no real science yet. If anyone has any input that would be rad, foil design ect. Im am thinking of casting an RC uni-wing plane for the front foil, again just looks about right.

[juandesooka]

I get the sense that it's not as technical as you might think to have something that works. Needs to be more refined to be super fast, but just to zip around, a rough n ready DIY one will work.

Here's my winter project....just the wings. I am going to carve a 2nd set to play with canard style, like zeeko spitfire

http://www.kiteforum.com/viewtopic.php? ... &hilit=g10

[Wilee]

That build looks great. sleek foils.

[Windsurfish]

I bet after the Maui visit this will happen faster. Can't wait to test it out!

[AJSpencer]

Just wanted input from other foilers regarding design as I had an experience which has made me wonder ever since which is the lightest-wind take-off/sustainable flight foil design.
I was trailing Bobson last year at IV in some light wind, was close enough that the wind on the sails was likely the same pressure, about 10-12 knots. Bobson and I are probably similar in weight, but I had a 7.0 sail and I believe he had a 6.0 sail, both Flyers. The boards were fairly different but both bigger boards so maybe not a huge factor. But the big difference was our foil designs:
Bobson had a higher aspect and lower surface area foil (starboard)
I had a lower aspect and higher surface area foil (slingshot hoverglide 84)
Now one other important factor is skill/technique which I am also much less experienced. But, when a 12 knot gust hit or so, Bobson was able to get up and keep going. Whereas I could not and never really felt there was enough pressure/speed to get much lift at all. If I recall, the few times I could get up in the lighter wind that day, it was as if I would have had to continuously pump to keep going on the foil, otherwise I would be back down onto the board.
Being less experienced, I was possibly stalling the foil, making drag, but being conscious of that and trying to keep the foil "level" didn't seem to make much difference and more weight forward was just off the foil sooner.

So what I'm wondering is, are the high aspect race foil designs much more efficient and earlier take-off?
Alternatively, even bigger than my 84cm hoverglide foil is a 99cm, and that seems popular in some youtube vids on the light-wind windfoil experience, like sub 10knot even for a heavier guy.
So for light wind, would a very wide high aspect foil fly earlier than a narrower low aspect of the same surface area?

I know air and water with foils are different, but I guess there's a reason most planes have high aspect wing design and not low aspect like a space shuttle. But, is that for lift, stability, speed, efficiency, or?, and would that principle apply to a foil in water?

[winddoctor]

My caveman understanding of foils:

High aspect foils: Usually thinner profile, require higher speed to get up and flying, but once there will have higher top speed/less drag, higher stall speed threshold (gotta keep 'em movin'), more instability at lower speeds, less ability to roll/change direction quickly.

Low aspect foils: fatter profile, lift early, carvey, less top end speed, easier to ride, can ride ride slower with less chance of stalling.

Most of what people call "high aspect" foils are closer to medium-high at best, though the Starboard foils that Tweezer and Bobson ride for wind foiling seem more high aspect.

Lots of other factors could be in play as to why Bobson got up and foiling earlier, but likely it was experience/technique. As you improve in technique/efficiency, your foiling threshold drops substantially, allowing much smaller sails/foils to get up in a given amount of breeze. Foil-mast position has a huge effect as does tail shimming and mast foot position. Lots of variables!

[AJSpencer]

Thanks WindDoc. Pretty good for a caveman! Got up in the 12-13kt range the other day for first time so yes prob technique is a bigger factor in that scenario that I wanted to admit.
Maybe I’ll get the 99 foil soon to try in the light wind days and see how that goes.
Wanted: 74cm and 99cm hoverglide foils.

[more force 4]

So for light wind, would a very wide high aspect foil fly earlier than a narrower low aspect of the same surface area?

I know wind design is crazy complicated but I think yes in principal a very high aspect will fly much earlier compared to a low aspect delta of the same area. There is a reason sailplanes have such enormously long, high aspect wings and they are the ultimate for low power takeoff (even big bungie cords and power winches) and have exceptional low glide angles/soaring ability.

[more force 4]

So for light wind, would a very wide high aspect foil fly earlier than a narrower low aspect of the same surface area?

I know wind design is crazy complicated but I think yes in principal a very high aspect will fly much earlier compared to a low aspect delta of the same area. There is a reason sailplanes have such enormously long, high aspect wings and they are the ultimate for low power takeoff (even big bungie cords and power winches) and have exceptional low glide angles/soaring ability.

As for DIY wings, may as well play around with them! THe consequences are so much less than when airborne! Maui early kiters were known for getting things like cafeteria trays working as kite boards, thats a bit different but 'put a foil on it' as Tweezer would say.

[Bobson]

I’m going with ‘pumping’. I remember that day and I was pumping my a$$ off. Once on the foil you need much less wind to continue foiling. I have a lot of pumping experience from sailing formula gear for the last 15+ years. Similar technique, not exactly but similar. Almost every session I’m pumping to get going. Usually only 1-3 pumps but sometimes in marginal conditions it’s more like 8-10 pumps. 2-3 sail flicks, then 2-3 full body pumps, then front foot in then 2-3 more body pumps then back foot in.

[BigD]

What a visual Bobson! Can't wait to witness your patented pumping technique in person this summer! Whhooooohoooo

[AJSpencer]

Got a taste of the pump benefit last session. Will work on it.
Tomorrow looking good!

[grantmac]

Hands close together, body low, mast upright, push forward with the toes.

Foiling efficiency is all about the pump. I was going in 12-14kits with a 5.2 today no problem.

[AJSpencer]

Bobson - then, do you do the hokey pokey?
GMac - that's efficient! I wonder what wind range a 7.0 flyer with a 99cm slingshot foil could do. Sub 10 for the more experienced I would guess. A lot of 10 knot winds these days which is why I'm pondering how to unlock for the future.

[grantmac]

The large foils don't seem to benefit much from bigger sails.

Better idea is a more efficient foil and higher volume board.