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Speed 3 DLX 12 leading edge dimples

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direnc
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Speed 3 DLX 12 leading edge dimples

Postby direnc » Mon Sep 21, 2015 12:13 pm

Hi,

I have a second hand Speed 3 12m DLX. It has deep dimples on its leading edge during flight. I learned this is caused by low internal pressure. The depower velcro on the central valve is open, and the kite does not have any rips. I also tried coating the kite with silicone dissolved in turpentine, but still have the dimples. The fabric is airtight, but I suspect the needle holes of the seams may be causing the leak. My breath passes through seams easily. Should I try sealing the seams as well? Or is it normal to have a dimpled leading edge?

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Re: Speed 3 DLX 12 leading edge dimples

Postby Johhnn » Mon Sep 21, 2015 5:34 pm

I have both the S3 12 DLX, the S3 19 DLX and the S4 12 Lotus. In flight they all have a concave area at the front of each cell. They were this way from the beginning, even with the nose valve fully open. I never have flown them with the valve closed. I also have the S4 8 and 10 DLX. These are a little better in this regard, but they have the stiff plastic lines in the leading edge of each cell to help define the shape.

The kites would probably fly better without the dimples, but it doesn't seem like it is possible to overcome the force of the air with just the ram air pressure. As long as the kite flies ok, just learn to live with it. They're still nice kites.

Any Chrono or Elf riders out there? Are their leading edges nice convex shapes?

direnc
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Re: Speed 3 DLX 12 leading edge dimples

Postby direnc » Thu Sep 24, 2015 9:25 am

Thanks Johhnn,

It's a releif to to learn that they are like that even when new, but I am surprised to learn that. I have had Peter Lynn ARC kites before, and even with fewer intake valves, they had no dimples on the leading edges. I can't help thinking that those dimples on the leading edge hinder the performance of the kite. With those dimples its far from a nice airfoil anymore...

I do not know if it's doable, or worth it, but I am wondering if it is possible to tape (easier than sewing) some ribs on the leading edge.

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Re: Speed 3 DLX 12 leading edge dimples

Postby joriws » Thu Sep 24, 2015 9:49 am

I think "dimples" are part of making airfoil more stabile and less prone to front stall aka hindenburg.

So the kite is tuned for dimples in place which also affects flying speed which is more matched to twintip riding speeds.

But if you install some ribs, please report how you did it and what was the effect. Because I am thinking the same for Psycho4 6m but I would be doing it just for fun.

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Re: Speed 3 DLX 12 leading edge dimples

Postby Bille » Fri Sep 25, 2015 4:04 am

joriws wrote:I think "dimples" are part of making airfoil more stabile and less prone to front stall aka hindenburg.

...
NOPE ; but i'm glad Ya have a way to rationalize it !!

And now for the reality of the situation :
dimples in/on the LE of an airfoil , (Any airfoil) ; they represent a Very Poor example
of engineering for the aerodynamics who made that crap example of something that
can fly.

Dimples = Drag.
If you need dimples to make your machine fly ; then you Suck ! :lol:

Bille

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Re: Speed 3 DLX 12 leading edge dimples

Postby joriws » Fri Sep 25, 2015 7:27 am

Exactly dimples are drag but they are present with non-LE-enforced-foil so you need to take them into account for your design over the designed speed ranges. Similar to "loose" fabric at seams etc.

Struttless LEI's are another example of designed drag into kite. I am meaning with this that foil-dimples are not designed by purpose but they are there. But struttless LEI you design the drag profile from the beginning.

Strutt-LEI's needs to loosen canopy fabric as well which increases drag but on turns you need to dissipate lift from turn's outside wing. Otherwise the kite would have tendency to oppose the turn because outside of turn is flying faster and generating more lift & drag due to speed than inside of the wing. That's why you hear the loud flapping sound on high speed kite turns.

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Re: Speed 3 DLX 12 leading edge dimples

Postby Skywalker7 » Fri Sep 25, 2015 10:30 am

Yes, those dimples is absolutly intentional to make the kite more stable and the result of a very complex engineering. This effect is created when you push up the bar, so when you want less power. When you pull the bar or the angle of attack is high the profile is perfect. I am paragliding for 21 year so I knew when rigifoil technology came out it will be good for the foil kites as well, so I got a 19 sqm proto built in 2011 with rigifoil technology from a Kitetech Fly3. (Kitetech is a Hungarian closed cell foil kite making company) Needless to say the kite became insanely unstable and got a huge instict rushing through the windwindow and collapsing. So the kite had to be totally retrimmed by the designer, and while it got slightly more performance than the original version it was 3 times more unstable. This year I changed this kite to a Speed 3 15M and my Speed 3 has way more performance and stability that my previous kite tuned with rigifoil. To correctly set the internal pressure in a foil kite in the different AoA-s to find the perfect balance of performance and stability is a huge engineering work. To use rigifoil and make it a stable a kite it is also huge challange, and you need to use reflex technology etc. to make the kite stable. If you want to fly a kite without dimples, than have a ride on an Ozone Chrono or Flysurfer Sonic Fr and you will feel the difference in stability.

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Re: Speed 3 DLX 12 leading edge dimples

Postby plummet » Fri Sep 25, 2015 4:56 pm

Out of whack mixer and line lengths can make the dimples worse. Also after some years flying the material its self becomes porous. At that stage you need to replace the kite. its stuffed and will never fly like it used to again.

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Re: Speed 3 DLX 12 leading edge dimples

Postby Johhnn » Fri Sep 25, 2015 6:31 pm

I think they should try having a big, inflatable bladder in the leading edge to eliminate the dimples, while still, somehow, keeping the intakes for ram air and the double surface. My understanding from paraglider design people is that the smoothness of the leading edge is very important.

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Re: Speed 3 DLX 12 leading edge dimples

Postby Kamikuza » Sat Sep 26, 2015 5:30 am

Yeah, normal... kind of. Old kites are worse, but it doesn't matter too much.

Incidentally, if you wanted to add LE stiffeners, it wouldn't be difficult or require much in the way of sewing -- there's already a double-row seam that creates a pocket around the LE.... You could pull the kite put through an intake, slit the pocket, insert the stiffener, close it up again. You'd have to be careful about the material you use, and make sure the ends don't poke through but it's doable. Good project for an old kite, I reckon...


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