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 Post subject: current LEI designs
PostPosted: Fri Jul 11, 2014 3:46 pm 
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Sorry if I ask something stupid (I know nothing about aerodynamics) but are there any advantages for having the canopy on top of LE/struts vs the other way around (ie canopy on the bottom)?
To me it seems that the bottom side of the kite does all the work, so removing those air pockets on the bottom may result in better aerodynamic design.


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 Post subject: Re: current LEI designs
PostPosted: Fri Jul 11, 2014 4:03 pm 
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That would be like turning upside down an airplane wing. Think about. You will see what I mean.


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 Post subject: Re: current LEI designs
PostPosted: Fri Jul 11, 2014 4:38 pm 
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Its the upper surface that is the important one. A lower pressure area is created by the flow of the air on the top of the surface. Its not really based on the wind pushing on the lower inside surface as such except if the wing is backstalled.

They put tell-tails on the upper surface of sails to help keep the flow laminar. They do also have tell-tails on the lower surface, but the upper one is the most important one for getting drive from the sail.


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 Post subject: Re: current LEI designs
PostPosted: Fri Jul 11, 2014 4:47 pm 
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the faster air goes the more drag it creates this is proportional to the velocity squared. If you look at a wing, the air has to move in an arc around the outside of the top of the wing, but underneath the wing it can go straight across, thus the velocity across the top of these surfaces is in an arc you can calculate it with some radius times pi times the arc and the width, while the velocity under the kite is simply the width of the kite.

The struts cause a lot of drag so you must put them underneath the wing to reduce drag.

Good idea though! It is this sort of thinking outside the box that can lead to new and better wing designs.

When the kite is in the power zone you do need the kite to catch all the air and these struts get in the way. However most of the time the kite is not power looping instead it is at about 45 with most of the flow going on top of the wing.

Notice aaron hadlow often would get his kites designed to remove the middle strut for just this reason so when he popped off the water or kitelooped the kite would generate more power.

There has been plenty of experimentation removing all or most of the struts with the cloud or liquid force solo.

In my opinion you don't practically gain any upwind capabilities by removing the struts, what you do gain is quicker kite to pump up and better packdown.


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 Post subject: Re: current LEI designs
PostPosted: Thu Jul 17, 2014 8:01 am 
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Slingshot split-strut... best solution?


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 Post subject: Re: current LEI designs
PostPosted: Thu Jul 17, 2014 1:15 pm 
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The intrados (bottom side) matters more than some think!
To say it's the top surface only would be a gross oversimplification.
It's true the low pressure top side is sensitive to disturbance of air flow (which is already separating anyway over most of the canopy).
But the bottom is important, and especially in the "shoulders" of the kite.
Having this area clear of struts gives a power advantage. This is seen with 3 strut (and strutless) more than with 4 strut designs.
Pressure is developed over the bottom of the kite. You can tell that when a kite is crashed LE down and still pulling you out to sea! The top of the kite is more about controlling drag, from my POV. There is more than one way to look at it though, for sure!
Look up unconventional airplanes and airfoils, it's interesting...


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 Post subject: Re: current LEI designs
PostPosted: Thu Jul 17, 2014 11:06 pm 
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Lots of bollocks here....

Just think of 1 thing: A plane can fly upside down :thumb:

You can fill the rest in.


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 Post subject: Re: current LEI designs
PostPosted: Thu Jul 17, 2014 11:25 pm 
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what´s wrong with struts on the bottom? i think they look good


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 Post subject: Re: current LEI designs
PostPosted: Thu Jul 17, 2014 11:49 pm 
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No struts = No drag and No weight...

Image


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 Post subject: Re: current LEI designs
PostPosted: Fri Jul 18, 2014 3:21 am 
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Quote:

Quote:
No struts = No drag and No weight...

Amen to that!


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