Pump up your leading edge H A R D!

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lmontejo
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Pump up your leading edge H A R D!

Post by lmontejo » Sun Apr 16, 2006 8:20 am

Yesterday before the wind picked up (and Charlie quieted down) we discussed the importance of rigid leading edges in kiting.

In aeronautics (and I speak from a sailplane pilot's viewpoint) the only time that one wants a wing to be mushy (the way I feel many leading edges when I help launch somebody) is when a wing hits turbulence. Mushiness (flexibility) allows the wing to absorb turbulence and not break.

But since breaking a leading edge due to turbulence is not an issue in kiting, a stiff leading edge is very important in our sport.

1) It makes the wing behave as the designer wanted it - not a new shape every two seconds as you are out there kiting.
2) It makes your wing faster since changing shapes as it moves I am sure generates micro-turbulence on the leading edge that hampers performance.
3) In the case of bow-kites it prevents them from inverting.

I am personally pumping up the leading edge of my Crossbow 12m to 8psi, and have never had an inversion with it. I also believe that its low wind capabilities are enhanced when the leading edge is as rigid as described.

Check out some sailplane pictures at this site, Minden Soaring Club Gallery
and notice how high performance wings that can make you go 50 miles if you are only 1 mile high.

In short. Pump'em up HARD.
Leo

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Post by Proparoo » Sun Apr 16, 2006 9:16 am

Being new to this I ask,

Is it really important to buy a pressure gage for my pump? Or can I do it by feel?

Is there a chance of over pumping and causing damage to the bladder?

Rich
Rich "ATOM" Baum

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Post by andyandmarlys » Sun Apr 16, 2006 9:50 am

I agree, Hard is good for all kites... The only concern is on hot days, you can pump it up in the cool air of morning (@ RIO) and let it bake in the sun... I am sure we could use this calculator to determine how much heat would affect the pressure.... BTW 8psi = .55 Bar

http://www.chemicool.com/idealgas.html

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Post by andyandmarlys » Sun Apr 16, 2006 9:58 am

Ok.. I just ran a scenario.... go to Rio.. pump up in the AM at 50 degrees to 8psi.... Temp increases to 100 later in the day... pressure increases to 8.77psi... not that bad actually....... However, I suspect that dark kites could get closer to 150+ degrees... That sand at RIO gets really hot.. If the kite gets to 150 degrees, the pressure is now 9.5 psi.....

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Post by Proparoo » Sun Apr 16, 2006 10:16 am

Leo & Andy,

One thing I have found on this site, (this is just feedback, not a cut)
When I join a disscussion and ask a question that I am confident everyone (or most everyone) knows the answer to or at lease has an opinion on, and like this thread I joined in and asked a valid question regarding weather or not I should get a pressure gage, you seem to just bypass my question. It's kind of like being new to a group of friends and trying to join in the conversation but you keep being ignored.

Just feedback,

Rich

This has happened on more than one ocasion and wonder if it is because
Rich "ATOM" Baum

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Post by Bob » Sun Apr 16, 2006 10:17 am

The other factor is for those still crashing their kites. The impact of a leading edge on the water can generate a compression wave that can burst the bladder.

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Post by consumer » Sun Apr 16, 2006 10:20 am

air does not behave ideally until very very high temps.

use this modified version of the ideal gas law and tell me what you get. n is the number of moles of gas. a and B are constants for the type of gas being used.

(P + n^2a / V^2) (V - n*b) = n R T

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Post by Jeff Ruoss » Sun Apr 16, 2006 10:20 am

The increasing pressure is not as big a factor as the decrease in the strength of the materials the kite is made out of. At 150 degrees F you can expect about a 50% drop in the strength of the fabric.

Most top brand kites can take 17 psi at 65 degrees F.

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Post by grumpy » Sun Apr 16, 2006 10:27 am

All the sudden I fell like playing dungeons and dragons

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Post by jjm » Sun Apr 16, 2006 10:34 am

Proparoo wrote:...I joined in and asked a valid question regarding weather or not I should get a pressure gage, you seem to just bypass my question. ...
Hey Rich,

I think they generally are considered to be inaccurate. I have one on mine, but don't use it as the main metric for deciding if the kite is pumped enough.

It kind of gives a rough estimate of pressure. If I was pumping up a kite that recommended say 8psi, and the guage was reading 6 and it felt done to me, I wouldn't go for the additional 2 psi...

So, they are a nice thing to have, but I wouldn't go spend a ton of money on one.

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