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Kite design take 5003- Nerds only need apply

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shunter
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Postby shunter » Fri Nov 22, 2002 2:35 pm

Kite design question 5000 and 3. How does luff curve effect the way a kite flys/behaves. Here are my theories on luff curve ( the sweep the leading edge makes)

A healthy luff curve (Slingshots GTO) will make a kite easier to relaunch due to the fact that the kite when sitting down on the water will have the canopy sloping into the wind. When the canopy is perpendicular to the water the tips should be off the water and hence the fat little babys will roll over. Flater curved kites like the Supertype/X2 can be hard to flip on there backs as with the flater curve when the canopy is perpendicular the tips will still be on the water.

A healthy luff curve will make a kite wont to nose over (luff out) easier than a straighter curved kite. The supertypes are very stable in the sky and when the old 4.1 would have noised over the supper will sit there. The X2 are another stable kite. Is this because the COE (centre of effort) will be closer to the High luff curve attachment points and hence it takes less movement of the leading edge to tip the balance.

So far a Plus and a minus for healthy luff curve. What other effects will curve play?

Please help a frustrated engineer with too much time on his hands

Ahei Pai Hau Koru (Maori for “may good winds blowâ€

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sq225917
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Postby sq225917 » Mon Nov 25, 2002 9:57 am

just because the canopy is sloping into the wind doesn't make the kite any easier to flip, the wind hitting it is suimply forced down to water level, sbmerging the leading edge or pushing the kite away from you.

you need the air to be forcing the canopy back due to the low pressure created behind the canopy, the conditions you describe just induce great rotor behind the trailing edge as it sits on the water. the easy flippability of the gto is much more to do with the fact that its centre of balance is closer to the centre of the leading edge due to its low ratio of length to chord section depth. ie the longer the arms of the kite the greater the weight that has to be leavered by an increasign small area, due to the smaller centre chord.

ie high aspect kites have less presented sail and more weight effectively in the wingtips that kites with depper centre chord.


notice i'm trying hard not to get into the discussion of what is aspect ratio, as kite manufacturers still haven't all decided to use the same formula, unlike all the aero and para' companies.

try making some models out of letter l shape bits of wood and try flipping them over. mmmm that few degress make 'f-all' difference.

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shunter
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Postby shunter » Mon Nov 25, 2002 2:23 pm

On 2002-11-25 09:57, sq225917 wrote:
the wind hitting it is suimply forced down to water level, sbmerging the leading edge or pushing the kite away from you.

you need the air to be forcing the canopy back due to the low pressure created behind the canopy


Yes and no grass popper I dont think low pressure behind the kite canopy is whats flipping it over? Its a bluff body type wind force.

The fatter the profile the Higher away the C.O.E will be from the leading edge so will the centre of force acting to tip the kite. So you are right about that.

More interested in the effects on kite preformance in the air and how luff curve will effect flight.


I will SEE you your wood models and Raise you a paper model (take a bit of paper and cut a luff curve in it and put it LE down and then roll it off the desk) Seee it flipped easier didnt it?

All my wood models float ok but i be buggered if i can get then to fly unless i tow them at 100 km/h behind the car.

Big airs soft landings

Shane


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