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Getting most power out of a foil kite

For all foil kite riders
RomeUtah
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Getting most power out of a foil kite

Postby RomeUtah » Thu Feb 27, 2020 11:28 pm

I was talking to some fellow kiters about foil kites, as I am trying to figure the kite i got, and they mentioned that you get the most power out of the foil when it is sheeted out. Power, according to the guys, or at least how i understood it, is at most when you have the bar fully out not in. I fly a soul and have not had the same experience. Can anyone explain what these guys are talking about, or did I completely misunderstand what they said. I fly a soul, and it definitely has the most hang time when gliding when i am almost fully sheeted in, same thing on jumps. After i get ripped off the ground, i am the floatiest when sheeted in.

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Re: Getting most power out of a foil kite

Postby tkaraszewski » Fri Feb 28, 2020 1:23 am

You are conflating "float" and "power".

Take your Soul and downloop it. Do it once with it all the way sheeted out, and another time with it all the way sheeted in. See which pulls harder. In fact, with the kite sheeted all the way in, it may barely even complete the loop, stalling halfway through. Do you think it pulls harder through the loop sheeted in or out?

Basically it makes more power when it's moving faster, and it's moving faster when it's not oversheeted.

Also, watch this part of this video (from 5:15):

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Re: Getting most power out of a foil kite

Postby Trent hink » Fri Feb 28, 2020 2:40 am

Foil kites can backstall. Some are designed to do it, others you just don't have your bar and lines set up correctly.

Backstall is a funny thing, sometimes it feels like the kite is pulling more, but if you are back stalling the kite then it cannot accelerate and generate more lift.

In the hands of a really competent kiter, backstall can be useful. For most average kiters it is not.

If you don't want backstall, adjust your trim strap, your line attachments or tune your kite to make it go away.

Maybe you could just be careful not to sheet in so hard that the kite starts backstalling, because just a bit before it does is when the kite is lifting the most.

Where that point is can change depending on the wind strength and the amount of load you are putting on the lines.

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Re: Getting most power out of a foil kite

Postby joriws » Fri Feb 28, 2020 9:44 am

In simple words. Kite pull is squared to kite forward flying speed. By allowing kite to fly fast forward it pulls more than suffocating kite by oversheeting via bar getting more AoA but slower flying speed. Your task as a rider is to find optimum forward flying speed and sheeting of bar to get the most out what you want to achieve.

If you look airfoil typical speedpolar (quoted picture is more about wing loading how it affects polar but every airfoil has similar shaped polar, kite or A380 wing) you can see to top point of polar, IMO anything in the left side of it is a waste of energy, so try to fly always at peak L/D speed or right side of speed range. That's how I've reasoned it.
Image

If kite cannot be backstalled it cannot be relaunched. LEI single line pull is backstalling that side of kite to lift it up in the wind. Foils do the same, depending on canopy AR you can single line or dual line backstall to relaunch leading edge down situations. Usually foil & bar travel is tuned so that in light winds fully sheeting in the kite might start backstalling. Just push a bar forward to let kite fly forward as fast as possible and fly via speedy arcs and you get the most power out from foil kite.

You can kite with 15m foil kite when 17+m LEI does not want to fly properly or to turn from edge towards zenith. This video is from pre-hydrofoil-era (2014), me and my 110kg using first time Spleene monster door twintip with 15m Speed4 Lotus kite. As you can see I am not fully sheeting in with bar but trying to get enough power me to glide and kite to fly until apparent wind kicks enough and kite can be parked. Depower is at max power, some people pull depower to eliminate too much sheeting in.
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Re: Getting most power out of a foil kite

Postby foilholio » Fri Feb 28, 2020 3:05 pm

Faster kite more power. Sheet just a little and fly it fast. It is the same on any kite.

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Re: Getting most power out of a foil kite

Postby grigorib » Fri Feb 28, 2020 3:17 pm

When people say "use trimmer to depower" or "depower the kite by sheeting out", the depower in first case is only relevant to limiting maximum AoA and to reducing AoA as the kite flies. Both will reduce kite pull in strong winds but there's more kite power sources than this - apparent speed power, looping power, "not stalling the kite in lightwind" power". For last three you need kite to fly fast and at low AoA. You want kite to move around and not choke it and that's why in lightest winds you trim-in/depower the kite to ride, or depower the kite to get it further to the edge of the window and get more upwind.

Basically choking kite is not giving you more power and that why you trim in or depower. Our kites are meant to fly and fly rather fast, not stall

My advice - practice without board, and play with trimmer/depower somewhere on a soccer field to get good feeling of how it behaves at different settings and that practice is priceless.

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Re: Getting most power out of a foil kite

Postby jakemoore » Tue Mar 03, 2020 7:42 pm

Both trimmer and bar movement have the same effect but yes the whole idea is not to choke the kite. It needs to fly fast at low AOA.

It may be easier to pull the bar trimmer if the kiter does not have the feeling for the sweet spot or needs to push the bar out uncomfortably far to get the kite moving. Also, I think the limiting factor for the single skin e.g. Peak/Marabou performance is the fact they go from flapping with no forward speed or power to choked in only a few cm of bar travel. Its very hard to feel the sweet spot in this kind of kite and in that case I would definitely trim so that there is no way to choke it with the bar. Because our instinct is to pull the bar for power, using the trimmer is an easy way to defeat this bad habit.

My big kites are 9 and 13. Somewhere between those two kites I find I need to depower at the trim strap because my hands are naturally in the wrong position during water start and I tend to choke it.

Sometimes it helps to have a little choke in the bar to make a fast turn. Also you can get a short e.g. 1/2 second boost by pulling the bar before the kite slows down e.g. maybe the critical moment to get out of the water and get some board speed. Finally there is an alternative to moving the kite up and down in a sine wave to increase power and speed that was a trick with old foil kites where we flew the kite with the bar on the trimmer knot with a short depower. That is to pull the bar in so the kite moves deeper and then push the bar away so it flies faster, in essence pumping both sides of the kite rather than one at a time.

With the 13 I will often power the trimmer back up after water start in lightest winds to have the full range of kite movement.

Finally, realize that rear lines shrink more than fronts so tune the bar.

Grigorib advice to practice in light wind and get to know the kite is a top tip. There is no substitute for flight time.

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Re: Getting most power out of a foil kite

Postby edt » Tue Mar 03, 2020 8:34 pm

lots of good answers. this is actually a pretty complicated issue dependent on the wing, angle to the wind, wind speed, drag, lift, so when someone tells you they get "more power when it is sheeted out" that is no way that the statement is right because it simplifies the issues too much. I think if you can understand the diagram that joriws has then you'll have it figured out.

But if that graph is too complicated, well, don't worry what others say. If you get more power when you pull in, keep pulling in. Maybe they are racing at a high upwind angle and need to sheet out who knows. You need to adjust the angle of attack for your kite according to the type of riding you do not for the riding that someone else does.

The soul is by far my favorite foil kite. It's incredibly forgiving and and you can fly it in ways where another foil kite would just crumple up in a ball.

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Re: Getting most power out of a foil kite

Postby windrider1 » Tue Mar 03, 2020 11:22 pm

Its very simple , just practice to sheet a foil kite a little bit out on the upstroke. so dive the kite dwn and as it starts to move back up ease up on the bar a little bit and that's the secret to a foil kite. This allows the kite to accelerate . With experience u will feel how the kite behaves when its stalling which translates to loss of some power and speed and when to sheet out to fix it . An experienced rider usually has it trimmed with a just a little stall with bar pulled all the way in but then only rides with bar 3/4 to 1/2 until ready to jump and so on.


RomeUtah wrote:
Thu Feb 27, 2020 11:28 pm
I was talking to some fellow kiters about foil kites, as I am trying to figure the kite i got, and they mentioned that you get the most power out of the foil when it is sheeted out. Power, according to the guys, or at least how i understood it, is at most when you have the bar fully out not in. I fly a soul and have not had the same experience. Can anyone explain what these guys are talking about, or did I completely misunderstand what they said. I fly a soul, and it definitely has the most hang time when gliding when i am almost fully sheeted in, same thing on jumps. After i get ripped off the ground, i am the floatiest when sheeted in.

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Re: Getting most power out of a foil kite

Postby TomW » Fri Mar 06, 2020 7:50 pm

First, I'm no expert.
But windrider put it simply.
If your foil kite is moving, and you need some grunt to get up, sheet out. It's counter intuitive if you are used to lei kites.
My Sonic 2 13m was extreme in that behaviour with my limited experience. If you can adjust your technique, then the kite performance is excellent.
But I found my Hyperlinks much more forgiving in this, they have the ability to sheet in and get grunt, but also power up if you sheet out. They are much closer to lei behaviour, but offer the full stall and helicopter or depower with power and no flapping that foil kites offer.


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