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Author Topic: "overblown" kite and how to deal with it ?  (Read 1820 times)
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LittleSkink
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« on: June 21, 2011, 09:12 AM »

this might be considered a beginners question I guess (apologies if it is in the wrong place)

Got a fair few single line kites that I fly just to relax (but may end up doing some KAP sooner or later) and mostly I know what sorts of winds they like and dont think too much about what is going on for them

But a couple of days ago my 3.3m T-Delta was up nicely, and then the wind really whipped up (some bad weather was coming in). It was gusting from Bft3 to Bft6 and more easily. The kite kept heading to the side of the wind window and looked like it wanted to come down - I know this as "over blown" but dont know the proper term

Now I assume it was loosing lift due to distortion of the kite so adding a tail would not have helped (in those conditions on that day I wouldnt have tried it anyhow). But I am curious to better understand what happens to a kite as it exceeds its wind range and how to deal with it

I am also curious to know if it will really do the kite any harm in terms of stretching fabrics etc too

Generally my answer to flaky flying is a fuzzy tail but this particular kite has a build in 5.5m tail anyhow - but tails only really seem to help in shifting wind direction conditions not heavy gusty conditions

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chilese
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« Reply #1 on: June 21, 2011, 10:57 AM »

It looks like you are asking several questions.

1 What happens when a kite is flown in wind speeds above its recommended range?

Theoretically, a perfectly balanced kite in smooth, ever increasing wind, will rise and bow more until it breaks. However, if the spars or sail are not symmetric, the kite will veer to the weaker and/or heavier side.

2 How do I make a T-Delta behave in very turbulent winds?

In my limited SLK thinking, I would add a floaty/long tail to the very bottom of the spine. This should re-orient the spine along whatever the current wind condition is and tip the entire kite to a higher angle of attack, which should reduce the apparent sail area. You could also shift the tow point to reduce the AOA. I have a 100' x 7" dia tube tail which I use on my Roks when the wind gets feisty.

3 Should I be concerned about fabric stretch?

If the fabric is Nylon, it should stretch and recover more than the modern fabrics, which are much stiffer. In material terms we would say Nylon is ductile and Icarex (e.g.) is brittle. Think of the way in which a grocery bag fails whether it is a plastic (ductile) or paper (brittle) bag.

There are many people here more versed on the subject. I'm sure they will chirp in soon.
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John Chilese: Las Vegas, NV
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« Reply #2 on: June 22, 2011, 01:03 AM »

The T Delta isn't rated to fly in Beaufort 6, so it isn't surprising it has problems at that wind speed.  In standard configuration it's optimal speed may be around half that.  I'm pretty sure the standard tail on the T Delta is around 5 or 6 metres - perfectly adequate, but not particularly long for a delta of that wing span

A 3 metre wide delta will lift a considerable tail, even in light winds.  I normally fly my 3 metre deltas with 20 metre long tube tails ('cos that length looks nice).  If the wind is particularly strong, I'll even add a second tail to the end of the first to make a 40 metre tail.  This configuration will tame the kite and increase the top of its wind range significantly.  On one particularly windy day I had 3 tails line astern - 60 metres (nearly 200 feet).  The kite flew fine, and looked great.

As John mentioned, this extra tail drag tends to lift the rear of the kite, so the surface of the kite is less "front on" to the wind and lessens the amount of pull.

HOWEVER...  strong wind tends to stress the fabric of the kite, especially when the fame flexes and allows fluttering to occur.  Much like the trailing edge of a flag on a flagpole in strong wind, it doesn't take long for a tiny flaw to become a major failure.
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Kevin Sanders

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LittleSkink
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« Reply #3 on: June 22, 2011, 04:29 AM »

thanks folks really informative

what I plan to do next is get a pair of tails for the wing tips of the T-Delta and see what happens - it never occured to me the angle of attack would change for the better

The T-Delta was a recent gift and much as I like to fly it the winds round us can go over 4Bft (it's recommended max) without much warning so, for the sake of the kite, I need to have some means of coping

Generally I avoid changing bridle settings (rather put up a kite more suited to conditions) anyhow, but the T-Delta has a keel attachment that isnt movable so tails are about the only way I can see to modify things

Now I have two tough decisions - tube tails, flat tails or fuzzy tails ? And what colours ?
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KaoS
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« Reply #4 on: June 22, 2011, 07:03 PM »


Now I have two tough decisions - tube tails, flat tails or fuzzy tails ? And what colours ?

Tube tails tend to flap less, as the internal pressure overrides the external buffeting.  If you want a tail that doesn't move around as much, this is the way to go.

Flat tails weigh less than tube tails of similar dimensions (quite a bit less fabric), but are less "rigid" than tube tails.  Beautiful rippling movements in lighter winds, can get a bit buffetted around in strong winds, especially the free end.

Fuzzy tails weigh about the same as flat tails.  Because of the "fuzziness", the tails generate much more drag than flat tails as the wind increases.  In fact, they higher the wind speed the greater the difference in drag when compared to a non fuzzy tail.  They can look a bit thin at times (personal taste).  Dead easy to store - just stuff them into a small bag, no folding.  Easy to use either as a single length tail, or looped from wingtip to wingtip.

Colours?  That's your problem  Grin
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Kevin Sanders

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« Reply #5 on: June 29, 2011, 08:05 AM »

The bridle setting was mentioned briefly before.  I do agree with all of the comments on the tail.  I have played with bridle settings on kites in high wind.  Generally the setting is moved up so that the kite will plain more with the wind and not catch as much of it.   A longer tail is definitley required with this setting as the back end of the kite will want to sway around more.
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Fore Check
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« Reply #6 on: July 23, 2011, 01:59 AM »

I know this thread hasn't been active in a few weeks, but I was reading up and thought I'd give my take.

A way of helping the kite that I don't think was discussed - in terms of raising the wind range - would be to increase the stiffness of the spars.  Particularly the leading edges of the wings and the spreader (spine?  Maybe.  But not as critical.) 

Adding tails may just straighten out a distorted kite.  (May.)  Stiffening the frame will lessen the distortion, which will straighten it out and keep the flight angle high.  You may still need a tail, because (generally speaking) as the wind speed increases, the amplitude of the inevitable variations in that wind are greater and the kite can look skittish.  But in that case your tail is helping with a fluky wind, not simply keeping an overpowered kite in the air.

With all of that said, it sounds like Kevin and John have more experience with Deltas in this area than I do, so I respectfully add my $0.02 as a possible approach.   Wink
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