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What makes one foil kite have more lift then another besides the size and aspect ratio

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billiq
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What makes one foil kite have more lift then another besides the size and aspect ratio

Postby billiq » Wed Jan 10, 2024 11:48 am

When looking at different foil kites some say good for buggy very little lift and others say they have lots of lift. What makes one foil kite have more lift then another besides the size and aspect ratio :?:

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Re: What makes one foil kite have more lift then another besides the size and aspect ratio

Postby Herman » Wed Jan 10, 2024 2:01 pm

Speed accross the window, ability to fly to edge of window. Personally I think saying good for Buggy, very little lift is a bit of a red herring but perhaps understandable. Slower or less spikey kites will probably make life easier for the inexperienced but once experienced with a buggy higher performance kites are probably more fun IMHO. In fact slow grunty kites may even start to feel uncomfortable because they take a long time to get where you want them. Working a smaller high performance kite, once you have acquired the necessary skills, may actually feel safer as well as being more fun. Difficult to describe but I hope this helps.
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Re: What makes one foil kite have more lift then another besides the size and aspect ratio

Postby Peter_Frank » Wed Jan 10, 2024 11:06 pm

Herman is right, but maybe you are asking more basic about HOW this is obtained?

A thicker foilkite has more lift, but also quite some more drag.

A more cambered foilkite has more lift, a bit more drag, but usually less lift/drag meaning not the same upwind performance.

And reverse, thinner and/or less cambered foils has less lift and less drag, and if not too flat also better lift/drag ratio.


So the lifty ones has "grunt" and starts early, but as more drag they do not accelerate nor go as far to the edge, so can not be flown or sinused actively to more lift the same way.

Thinner less grunty/lifty foilkites are good for buggy or ice because of the high lift/drag, which is needed as you have more riding speed compared to windspeed.

Whereas many wants more grunty/lifty foilkites for kitefoil or kitesurf.
Depending on personal liking, as some prefer faster foilkites which needs to be bigger or flown actively now and then.
Others prefer a more powerful small foilkite which can be parked.

Just the basics.

8) Peter
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Re: What makes one foil kite have more lift then another besides the size and aspect ratio

Postby Trent hink » Wed Jan 10, 2024 11:59 pm

I concur with my esteemed virtual associates. 😜

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Re: What makes one foil kite have more lift then another besides the size and aspect ratio

Postby grigorib » Thu Jan 11, 2024 12:04 am

- Projected area matters quite a lot.
- insyfficient depowerability will feel like being pulled by a truck.

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Re: What makes one foil kite have more lift then another besides the size and aspect ratio

Postby kitexpert » Thu Jan 11, 2024 2:00 pm

Peter_Frank wrote:
Wed Jan 10, 2024 11:06 pm
Herman is right, but maybe you are asking more basic about HOW this is obtained?

A thicker foilkite has more lift, but also quite some more drag.

A more cambered foilkite has more lift, a bit more drag, but usually less lift/drag meaning not the same upwind performance.

And reverse, thinner and/or less cambered foils has less lift and less drag, and if not too flat also better lift/drag ratio.


So the lifty ones has "grunt" and starts early, but as more drag they do not accelerate nor go as far to the edge, so can not be flown or sinused actively to more lift the same way.

Thinner less grunty/lifty foilkites are good for buggy or ice because of the high lift/drag, which is needed as you have more riding speed compared to windspeed.

Whereas many wants more grunty/lifty foilkites for kitefoil or kitesurf.
Depending on personal liking, as some prefer faster foilkites which needs to be bigger or flown actively now and then.
Others prefer a more powerful small foilkite which can be parked.

Just the basics.

8) Peter
Yes, this is pretty much correct. However if you make ultra-stable low camber kite it will lose some power and also upwind capability.
If you have high camber kite it accelerates fast and pulls hard. But stability suffers so you can't let it fly very far in the WW to get good upwind performance because it will collapse. Some old buggy/power kites were like that, Flexifoil Blade is typical example. These kites have fixed AoA and they pull hard all the time.

Current method to achieve very high performance (and depower) is to increase AR quite high, make wing itself as smooth as possible, decrease bridle drag, avoid losing too much lifting area because of too high canopy curvature and to use airfoil which is stable enough, not having too much camber.

So there is many variables and there is not one truth. Speed3 was perhaps the first modern high AR foil kite and since then nothing revolutionary has happened. And before that FS had Psycho3 which is quite high performance kite by today's standards - but of course it isn't a race kite.

But if you take 2006 13m Psycho3 and say new 14m North Reach and have a upwind race on hard surface Psycho will crush Reach easily. It will go to much higher angle or lower angle faster.

I once were on 20km kite trip having 14m five strut LEI and my friend had 13m Frenzy. Even though I was lighter in weight and much more experienced kiter I struggled to keep up with him. And Frenzy isn't nearly as efficient kite as Speed or Psycho is.

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Re: What makes one foil kite have more lift then another besides the size and aspect ratio

Postby sflinux » Fri Jan 12, 2024 4:16 am

Foil profile is first to come to mind. Play with the program XFLR5 to give you an idea.
Angle of attack comes to mind next. Some foil kites the aoa is dynamic with respect to sheeting.
I would think a good crusing buggy kite would have a low angle of attack for less vertical lift to prevent you from jumping, but have good horizontal pull to keep you moving.
I havent noticed a trend in lift with respect to foil profile depth. But it seems like thicker foil cross sections have a slower descent in jumps.

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Re: What makes one foil kite have more lift then another besides the size and aspect ratio

Postby edt » Fri Jan 12, 2024 4:50 am

wings are pretty complicated. I don't have an answer but I do have a pretty picture.

Image
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Re: What makes one foil kite have more lift then another besides the size and aspect ratio

Postby Herman » Fri Jan 12, 2024 10:51 am

The above is e great answer or a shoal of red herring, wish I new which. Perhaps the cat could do the math and find out what "lifty" s supposed to mean because I still don't know either!

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Re: What makes one foil kite have more lift then another besides the size and aspect ratio

Postby Peter_Frank » Fri Jan 12, 2024 9:23 pm

edt wrote:
Fri Jan 12, 2024 4:50 am
wings are pretty complicated. I don't have an answer but I do have a pretty picture.

Image

I do (have answers to wing profiles) as I know each and everyone (and loads more) and their "behaviors", so will add some comments and corrections to above picture - which might give an idea.

Put numbers on edt's picture, which is a a fine basic guideline with only few profiles, to keep it simple and easy :D
Profiles.jpg
Lets say #1 is the reference, a quite thin quite flat low cambered profile.

#2 is a classic almost Clark Y like profile.
As written, high lift but also less speed as quite draggy.
Really easy to ride if a (water) foil as low stall speed.
For a foilkite it is more draggy so bad upwind and doesnt accelerate as fast, but more grunt/power.

#3 has even lower drag and even higher lift than #2.
So used for gliders for the best "hangtime" meaning lowest lift^3/drag^2 (lowest possible sinkrate) meaning the most "power" possible in a foilkite for a particular size, but not the max upwind angles.
It will always be better than #2, at high lift - but it has a bit worse performance at low lift/high speed, which is usually most important for waterfoils where you ride at full speed often.

#4 with the reflex, is more stable than #2 and 3 and can be used for stabless foils also.
Makes no sense in foilkites IMO, unless you have overflying and hindenburg problems.
And performance is not up to par with any other profiles, lift^3/drag^2 noticeably worse, and L/D also worse.
Used for stabless foils, sometimes a non-reflex profile but then a swept wing with washout is used - which in total gives the exact same characteristics (not relevant for foilkites though, but for waterfoils)

#5 is maybe a bit like #4 as written, but not fully.
#4 is still better than #5, period.
The reason the symmetrical profile is used, is for aerobatics so flying upside down is the same as "normal" flying.
It is not stable, nor instable - so #4 can actually be more stable and still perform better, if not flying upside down.

#6 has more lift than #5, but drag is not decreased, this is wrong (on the picture text),
It has more lift though, so "performance" (say L/D) is better than #5.
And really easy with good stall characteristics.


Hope above corrections to this picture can explain a bit about the rough principles and be helpful for those wanting to know more?
Foilkite or waterfoil, same same.
Except, a fast (low drag #1) kitefoil accelerates a lot faster, in particular if high aspect, so power on demand when flown in the window, is way better.
Grunt and parked power is rubbish though, unless you ride on ice.

8) Peter
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