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Kites! Kites! Kites! => Sport Kites => Topic started by: xuzme720 on March 12, 2010, 09:09 PM



Title: a question on vented...
Post by: xuzme720 on March 12, 2010, 09:09 PM
I was wondering about something...

Are vented kites solely for higher winds or will they also help smooth out gusty winds on less than ideal days? Today was one of those days where it was everywhere from 2 to about 12MPH and just turbulent/bumpy air. Would a vented help in gusty stuff like this? I know they wouldn't be good on the low side but I just wondered about the bumpy...


Title: Re: a question on vented...
Post by: mikenchico on March 12, 2010, 09:38 PM
That is part of the reason for Lam's 'Light Vented' kites in the Sea Devil & Fearless lines. He uses minimal venting and framing between the UL & Standard. The kites retain a pretty high upper wind limit since they will bleed some pressure off while keeping a pretty good low wind range too. Lam has also been known to show up at indoor comps with a vented kite.

Venting is a science to do right I guess, done wrong it changes the whole character of the kite. There has been some experimentation with using it to get more efficient airflow over the sail too, not just to make the kite flyable in a hurricane. I think there is still a lot to learn in that area.

Could properly placed & sized vents reduce the turbulence behind a stalled kite and increase its stability and controllability while stalled? Or is that turbulence what gives a stalled kite stability, I recall the Kamm back design in racing cars was found to keep them going in a straight line better then a completely aerodynamic shape did.



Title: Re: a question on vented...
Post by: xuzme720 on March 12, 2010, 09:49 PM
Hmm...food for thought! Thanks!

I have seen all the Fearless talk lately. I've been wondering about that, too...


Title: Re: a question on vented...
Post by: tpatter on March 12, 2010, 10:34 PM
Vents help alot, but they can only do so much. 

The best thing is to find an area to fly where the wind is coming across a large open space - my favorite is near any large body of water.  If the wind is coming through many buildings, trees, etc in order to get to your kite, then it is going to be pretty bumpy.  Someone once described it to me as working just like a stream - where you can see the disturbance of the water as it flows around rocks to divide, join, and ripple. 

Most vents are just not very good - they are too heavy, or too mushy feeling, or they pull too much, or don't trick well, or feel completely different from their standard.  I'd try to find someone in your local area who recommends one that works well there.


Title: Re: a question on vented...
Post by: stapp59 on March 12, 2010, 10:47 PM
Vents help alot, but they can only do so much. 

The best thing is to find an area to fly where the wind is coming across a large open space - my favorite is near any large body of water.  If the wind is coming through many buildings, trees, etc in order to get to your kite, then it is going to be pretty bumpy.  Someone once described it to me as working just like a stream - where you can see the disturbance of the water as it flows around rocks to divide, join, and ripple. 

Most vents are just not very good - they are too heavy, or too mushy feeling, or they pull too much, or don't trick well, or feel completely different from their standard.  I'd try to find someone in your local area who recommends one that works well there.


Agreed with most of the above.  Nothing takes the place of nice smooth wind.  Many of us don't get that though.  Sigh.

A good variable vent will minimize the problems you correctly point out with many vented kites.  Open just enough vents to take the edge off the gusts and still allow the kite to fly during the lulls.

Screens along the face of the kite will help smooth the gusts as well.

To repeat, nothing takes the place of a nice smooth breeze  :)


Title: Re: a question on vented...
Post by: obijuankenobe on March 13, 2010, 01:58 AM
Smaller venting might contribute to changing the turbulence across the sail as well. 

I seem to remember reading about the bumps on the flukes of whales helping decrease resistance somehow in this way.  I also remember reading something about how this might also help on airplane wings.  I can imagine how smaller vents would also have similar effects.  The question is whether it's a positive or negative.

Vents get annoying when they affect 'normal flight'.  A great example off the top of my head is the XTs vented.  With all the vents open, that thing will hardly hold a fade because the surface needed for that position is almost all vent.

I do think Lam does everyone a favor by showing us that little vents can contribute alot to improving the high end without affecting the low end too much.  Never flown a Cosmic vented, but this kite also has pretty small vents. 

obi


Title: Re: a question on vented...
Post by: Carlton on March 13, 2010, 03:18 AM
Along these lines, does anyone have any experience with the Ying Yang?  It's suppose to take gusty winds, but in a different way, with a split right down the middle.....


Title: Re: a question on vented...
Post by: Bob D on March 13, 2010, 08:24 AM
I read something about the Ying-Yang on the old GWTW forum. It seems that the venting strategy didn't help any of its ability to do tricks. In light of what's available  now, they might be more of a novelty than a serious competitor to the technology used to do venting now.

I have the Nirvana HW and the Transfer xt.r VV and both have vents that you can adjust for  how hard the wind's blowing. If it's blowing too hard even the vents don't do a whole lot to make them trick easily. You really have to move to do anything.

At the bottom end where you'll need some venting, both help being able to pull out tricks you'd have trouble doing with a standard.



Title: Re: a question on vented...
Post by: RonG on March 13, 2010, 09:23 AM
A nice loud trailing edge does a better job of smoothing out gusts than venting IMO.  Think of it as dynamic drag - you pass through a gust, and the TE buzzes more, but the kite doesn't speed up or skate around so much.  Compare that to what a nice, quiet, "smooth" kite does in a similar situation.

I use a vented when I need to take the edge off the pull (i.e. the wind is nuking), but I've never found it to be a good solution for the issue of variable or bumpy winds.  The lulls always leave you wishing you had something on the lines without holes in it.

But I'm a little biased of course...as always YMMV.


Title: Re: a question on vented...
Post by: xuzme720 on March 13, 2010, 10:13 AM
A nice loud trailing edge does a better job of smoothing out gusts than venting IMO.  Think of it as dynamic drag - you pass through a gust, and the TE buzzes more, but the kite doesn't speed up or skate around so much.  Compare that to what a nice, quiet, "smooth" kite does in a similar situation.

I use a vented when I need to take the edge off the pull (i.e. the wind is nuking), but I've never found it to be a good solution for the issue of variable or bumpy winds.  The lulls always leave you wishing you had something on the lines without holes in it.

But I'm a little biased of course...as always YMMV.
I did notice that, when flying the Z, after the E3 just hated the conditions. The Zeph's TE would go into buzzsaw mode during the gusts but never had the forward drive go ballistic. Obviously, smoother air would be better, but super wide open areas are hard to come by here. I was in a larger field by my house that is usually smoother, but the overall wind was just gusty and the direction made it bumpier than I've ever seen it there..


Title: Re: a question on vented...
Post by: inewham on March 13, 2010, 10:32 AM
As another alternative to vents for gusty conditions I like a bendy LE - in a gust the lower LE will deform in, letting the sail bucket causing drag and slacking the TE letting it buzz and introducing more drag.

An extreme example is the way a Beetle copes with higher winds with only a 3mm LE.

A friend and I used to favour a pair of Acaras with prosport 6mm pultrude LE's and soft stretchy nylon sails for high winds. We've flown them in gusts up to a measured 20mph - The tips would bend like crazy but the speed and pull would stay steady and manageable:
(http://www.iannewham.com/images/acara006a.jpg)

Sometimes modern kites with super stiff frames and no give Icarex sails can make gusty winds hard work.


Title: Re: a question on vented...
Post by: stapp59 on March 13, 2010, 11:07 AM
Some very interesting ideas here.  Certainly Lam, Ron, and Ian have a lot of real world experience.  Mine is still developing.  Most of my bag contains stiff LEs, Icarex sails and tight TEs.  Works well for most conditions I fly in but options are always good. Hmmm.


Title: Re: a question on vented...
Post by: RonG on March 13, 2010, 11:23 AM
As another alternative to vents for gusty conditions I like a bendy LE - in a gust the lower LE will deform in, letting the sail bucket causing drag and slacking the TE letting it buzz and introducing more drag.

An extreme example is the way a Beetle copes with higher winds with only a 3mm LE.

A friend and I used to favour a pair of Acaras with prosport 6mm pultrude LE's and soft stretchy nylon sails for high winds. We've flown them in gusts up to a measured 20mph - The tips would bend like crazy but the speed and pull would stay steady and manageable:
([url]http://www.iannewham.com/images/acara006a.jpg[/url])

Sometimes modern kites with super stiff frames and no give Icarex sails can make gusty winds hard work.


All very true.  Same concept - allowing the sail to deform to minimize acceleration/loss of tracking in gusts.  I know this has at times been attempted with dynamic venting, but I've never found a system that truly did as good a job as basic TE drag.  I used a dynamically-vented Aerodrone Speed Limit for my high wind equipment in my first couple of competition seasons, but it seemed to introduce almost as many problems as it solved.


Title: Re: a question on vented...
Post by: ezme6 on March 13, 2010, 12:25 PM
The Ying Yang was never ment to be a tricky kite. I have an original and still enjoy flying it on days when I can't trick anyway because of the wind speed. Even in high winds it has a light pull. Older desighn but still a good fly.


Title: Re: a question on vented...
Post by: DaveH on March 13, 2010, 06:30 PM
Vents help alot, but they can only do so much. 

The best thing is to find an area to fly where the wind is coming across a large open space - my favorite is near any large body of water.  If the wind is coming through many buildings, trees, etc in order to get to your kite, then it is going to be pretty bumpy.  Someone once described it to me as working just like a stream - where you can see the disturbance of the water as it flows around rocks to divide, join, and ripple. 
Most vents are just not very good - they are too heavy, or too mushy feeling, or they pull too much, or don't trick well, or feel completely different from their standard.  I'd try to find someone in your local area who recommends one that works well there.


Yeah, but not everybody's home field sits on the banks of lake Washington  :D


Title: Re: a question on vented...
Post by: stapp59 on March 15, 2010, 06:05 PM
So a summary of ways to handle gusty variable wind conditions would include:

- Dynamic parasite drag to control speedup during gusts using a buzzing TE
- Bendy frame (LE) that lets the sail dump excess wind
- Small or variable vents to take the edge off the gusts
- Screens to slow the gusts and/or the kite
- Longer heavier lines
- Bridle and standoff tweaks
- Waiting for better conditions   :o
- Finding a better field  ::)
- Having a beer instead  :D

The best approach would depend on your purpose.  Competition ballet or pairs would put a premium on speed control. 

For me I want to be able to fly my favorite kites is as broad range of conditions as possible.  Vents, screens, standoff tweaks, and perhaps a bridle tweak gets me through most higher wind and gusty days.  As mentioned my kites have fairly stiff frames, Icarex sails, and taut TEs. I find bendy frames tend to chatter in higher winds.  I like quiet kites though certainly see the value in dynamic drag. YMMV certainly applies.

Other ideas out there?



Title: Re: a question on vented...
Post by: inewham on March 16, 2010, 02:33 AM
Another one is a variable width keel.

As an example BMKs come with 3 positions for the inner standoff. Move it out widening the keel and narrowing the channel, that slows the kite in stronger winds . Move it in narrowing the keel and widening the channel improves low wind performance.

On other kites that idea can be made dynamic by removing the inner two standoffs and replacing them with a length of bungee so that when there is a lot of pressure in the outer part of the sail it stretches the bungee widening the keel; When there is little pressure the bungee pulls it back narrowing the keel.

The AirCrafts Sidekick used to have an arrangement like this and it was moderately effective. It did feel a little spongey, although some of that was due to a K42 sail and a 6mm frame.

ISTR the Aerodrone stripes had a variable keel too, although I can't remember if that was a similar mechanism.


Title: Re: a question on vented...
Post by: stapp59 on March 18, 2010, 06:35 PM
Thanks for the info Ian.  Had not thought about the dynamic keel width idea. I assume the bungee goes between the inner standoff holes and behind the kite.

Certainly the multiple inner standoff holes are effective as are adjustable standoffs like Aerostar uses on the Sano to modify the TE profile.

Cheers,
Steve


Title: Re: a question on vented...
Post by: inewham on March 19, 2010, 01:49 AM
I assume the bungee goes between the inner standoff holes and behind the kite.

Yes


Title: Re: a question on vented...
Post by: RonG on March 19, 2010, 06:20 AM
ISTR the Aerodrone stripes had a variable keel too, although I can't remember if that was a similar mechanism.

Yes, dynamic keel on the Stripes.  I'd have to say though that it was marginally effective at best.  I always said that the Stripes was a fantastic competition kite in the 5-9 mph wind range.  Below that it was basically a boat anchor, above that it you might as well buggy with it.  But in that sweet spot...a wind window that went on forever, and about as smooth as you could want a kite to be.