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Author Topic: Ok....I'm browsing for a good UL/SUL  (Read 2562 times)
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damp_weather
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« Reply #30 on: March 15, 2014, 03:41 PM »

Interesting topic. I have a Nirvana SUL that I can't do much with considering the low mass.
That's interesting.  It was seeing videos of Nirvana SULs flying and tricking that first put me on to the possibilties for tricking in hardly any wind.  In particular there is R-Sky's video of the Nirvana SUL tricking (mostly back-spinning) in an Alpine scene, and more impressively: the "a morning in Venice" video showing the NSE WW being tricked by Samuel Roger and Laura Mastromaura in a misty Venice.  I can't tell the wind speed for the Venice video, but assume it must be very low as it is misty.  It was this that got me hankering after an NSE WW, but I never got to try one.  Then the Ocius SUL came along, which is a kite that promises to do the sorts of low wind flying shown in the Venice video.
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Is it me or do the other SULs with similar mass require the same amount of skill to coax tricks? I might definitely go for something that I could trick better but I'm thinking that low mass is low mass and it's a matter of skill, experience, and ability to move and put air into the sail. (I don't fly the Nirvana SUL too much because if the leaves are barely moving on the trees there isn't anything closer to the ground that will keep the kite in the air. Maybe I should look at something like the Prism Zero G...) Thoughts? Suggestions? Is the ATM as wonderful as everyone suggests?
(Have no personal experience of the ATM or Zero G.)
Regarding the mass of dual line SULs, I doubt that is the primary issue for tricks.  I think it is more a matter of sail shape.  Traditionally, zero wind dual line kites have had fairly low aspect ratio and flat sails.  (Aspect ratio roughly means the ratio of width squared to the sail area)  The relatively low aspect ratio means that there is more sail area for the same spar weight, and therefore more sail to catch the air for the kite's mass.  The flat sail helps get more lift from the sail.  Examples include the ProDancer SUL and the Benson Inner Space. 
As an experiment, try throwing a dual line kite around without having flying lines attached.  Compared to a more modern high aspect ratio The Inner Space isn't very pitchy.  But if you pull a modern kite like an Ocius SUL or perhaps your Nirvana through the air by the tow points and then let go, I expect that it will flip nose backwards much more willingly than the PD SUL or Inner Space.  In other words, I think it is the sail shape that determines how the kite will trick, because it determines how the kite moves as it cuts through the air.

...One of the big mistakes I made as a new beginner was to believe that in order to go from a flare to a fade, one pulled the nose towards yourself, so that it went underneath the tail, with the momentum of the nose overcoming wind resistance.  It was playing around with throwing and dropping lightweight kites that made me realize that even with standard weight kites, the trick was to give the kite some velocity in the direction slightly belly side of the tail, and the kite would then fly itself backwards in an arc from the flare to fade position.  - It was the lift from the trailing edge that was doing the turning.
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ae
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« Reply #31 on: March 15, 2014, 05:09 PM »

Weight plays still a significant role on how easy a trick can be executed.
Especialy in rotational tricks, since you need momentum to carry the kite through them, and with less weight, less momentum. To overcome the drag of rotating the kite.
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SkyRags
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« Reply #32 on: March 23, 2014, 01:16 AM »

Weight plays still a significant role on how easy a trick can be executed.
Especialy in rotational tricks, since you need momentum to carry the kite through them, and with less weight, less momentum. To overcome the drag of rotating the kite.

This is certainly true from what I've found in learning

I have no one to teach me hands on in NZ (I believe I'm the only one out of 4+Mil people in my country that trick flies)

When trying to lazy my Talon UL after launching from the tide - the kite now being wet and heavier- it was much easier to execute the rotation than when the kite is dry

The same principle is involved in a side slide - where somewhat a portion of centrifugal force is applied in sliding the kite
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In my bag: Benson SuperFly, Jest of Eve Talon UL, KaoS Charisma
damp_weather
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« Reply #33 on: March 23, 2014, 07:40 AM »

I’d been struggling with if I had anything helpful to say in response to Andre’s (ae’s) posting, and I was going to leave alone.  But SkyRag posting has pushed me into saying something.

Andre, in making and flying very lightweight kites indeed: XULs, has gone further than my experience, and therefore has the opportunity to know and the authority to say the difference that weight makes.

Moreover there is a simple scientific argument: Energy is proportional to mass, and drag depends on materials and shape.  So one would expect that a SUL version, being very similar to but having less mass than a standard kite, would have less kinetic energy at the start of a slack line trick than a standard, but be subject to the same amount of drag.  So the SUL would slow down faster than a standard kite in a slack line trick as a greater percentage of the kinetic energy was consumed by the drag.


But, but, but:  My problem is that the simple argument above for standard kites tricking better than SULs is contradicted by everyday personal experience.  Any trick I can do, I can do whether the kite is a SUL or a standard.  Indeed some tricks are widely known for being easier to learn on a SUL – like the taz, and I also know this from personal experience.
Moreover, experience says that sometimes adding weight calms a kite down – for example I added the tail weight to an Ocius UL the other day and it became noticeably nicer on the ends of the lines.  The natural backflip wasn’t as deep, but I could do more with it, like more turns in a multi-lazy before the kite hit the ground or flipped over into a wrap, and being able to pull straight out of the backflip rather than having to go into a fade from a half-rotation.

My personal trouble is, I haven’t figured out the story of how significant kite weight is.  There are so many other things that affect the kinetic energy verses drag issue.  For example:
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When trying to lazy my Talon UL after launching from the tide - the kite now being wet and heavier- it was much easier to execute the rotation than when the kite is dry

The same principle is involved in a side slide - where somewhat a portion of centrifugal force is applied in sliding the kite
…my first thought was that you are flying with a wet sail and so the way the sail catches the wind may have changed, as may have the amount of drag from air passing over the sail’s surface.  It would be quite a challenge to devise experiments that separate out and identify the contributions of a) wet sail shape/flexibility, sail weight’s contribution to kite’s inertial mass, and wet sail’s change in drag.

Does Cuben fibre have the same drag as Icarex?  (Yes they are both used for spinnaker sails of racing yachts – but those sails are so large, and their job is to pull the yachts along, so maybe a difference in drag would be less noticeable there than with a dual line kite doing a slack-line trick.)  What about the relative drag of mylar?

I do have direct experience that an Icarex sail with some flight hours flies better (and in lower winds) than a sail fresh and new.  We found this out from pairs flying practice.  And from comparing brand new and well used Icarex sails, I know it isn't that the sail has stretched.  The well used sail feels softer and less crisp.  - But does this change the drag due to the wind passing over a sail of the same shape, or is it that the softer sail can more quickly adapt to the optimum sail shape for the conditions, or interacts differently with turbulence??


So in summary, I don’t know.  And to me it is very complicated.

Pete

...And I do like the discussion on kite design evolution in the thread on "straight or curved leading edge design".
« Last Edit: March 23, 2014, 07:47 AM by damp_weather » Logged
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