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High Pressure kite by Bruno Legaignoux

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Re: High Pressure kite by Bruno Legaignoux

Postby GregK » Wed Nov 28, 2018 6:59 am

Thank you mixmatters for the links to the papers on Air Inflated Fabric Structures.

They do an excellent job of explaining how a pressurized fabric tube works, very enlightening.

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Re: High Pressure kite by Bruno Legaignoux

Postby faklord » Wed Nov 28, 2018 2:04 pm

tomtom wrote:
Wed Nov 28, 2018 12:19 am
It cannot be so simple

Rigidity is thickness cubed ,skin modul linear and then long long nothing and them core properties. Pressure is infact core
Just had a look at one of the links nixmatters posted:
Air-Inflated Fabric Structures, Naval Undersea Warfare Center Division, Newport, Rhode Island, 2006
https://mega.nz/#!OPhl2IpS!uBL05T8UyKKq ... 5OKLmbkCRE

It seems page 7 concurs with my suggestion that rigidity is a simple function of Pressure * Radius cubed.

BUT this got me thinking.... and much more interesting is it seems that smaller diameter, higher pressure air-beams are actually heavier for the same rigidity.

Calculations taking into account:
1) Smaller diameter = smaller volume (square law) but increased pressure gives increased air mass (cube law): overall air mass is greater.
2) Smaller diameter = smaller surface area so less Dacron (linear relationship) but increased pressure results in more stress in Dacron, even though the diameter is reduced, so Dacron (or whatever) needs to be thicker: overall material mass is increased.

Rather surprisingly the overall outcome of this is, for same rigidity and material stress, the overall mass ratio is the simple ratio of the diameters.
ie an 8cm tube will be 1.5 times heavier than a 12cm tube.

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Re: High Pressure kite by Bruno Legaignoux

Postby tilmann » Wed Nov 28, 2018 5:04 pm

faklord wrote:
Wed Nov 28, 2018 2:04 pm

2) Smaller diameter = smaller surface area so less Dacron (linear relationship)
you forget the factor pi = 3,141
12 cm have a circumference of 12 X 3,141 = 37,692 cm
8 cm have a circumference of 8 X 3,141 = 25,128 cm

No linear relationship

By the way the problem up till now was NOT the material but the seams.
Look how thin the material of Bruno´s hoses is:



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Re: High Pressure kite by Bruno Legaignoux

Postby faklord » Wed Nov 28, 2018 6:11 pm

tilmann wrote:
Wed Nov 28, 2018 5:04 pm
faklord wrote:
Wed Nov 28, 2018 2:04 pm

2) Smaller diameter = smaller surface area so less Dacron (linear relationship)
you forget the factor pi = 3,141
12 cm have a circumference of 12 X 3,141 = 37,692 cm
8 cm have a circumference of 8 X 3,141 = 25,128 cm

No linear relationship

By the way the problem up till now was NOT the material but the seams.
Look how thin the material of Bruno´s hoses is: https://www.youtube.com/watch?v=iGRDfgn ... e=youtu.be
Pi was not forgotten and makes no difference. It affects both sizes by the same amount (as does the length)
Increase the diameter by a factor of x and you increase the area by the same factor (x). = linear relationship.

I agree if the weak point is the just the seam then compensating for the addition stress in Dacron by making it thicker is unnecessary.

I guess I was just simply pointing out that the weight savings from just reducing tube diameters might not be as much as initially assumed. Particularly if they are to be as robust...that is unless new materials &/or manufacturing methods are used.

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Re: High Pressure kite by Bruno Legaignoux

Postby BWD » Wed Nov 28, 2018 8:27 pm

The potential big deal is not weight, but better L/D than normal LEI but with similar or lesser cost.
This would mean more efficiency and range.

I have loved riding with conventional and strutless kites but am aware of their limits, and of the limits of normal foil kites with all their quirks and tangled strings.
I’d love to try one of these kites some day, whether or not they become the next big thing.

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Re: High Pressure kite by Bruno Legaignoux

Postby nixmatters » Wed Nov 28, 2018 9:02 pm

Just discussed with a major supplier of high performance technical yarns to run a trial at one of their customers - a tubular braided hose with additional UD reinforcement in the outer section for increasing the rigidity. Not sure yet if this would make a great difference.
If anyone is interested to jump in this development, feel free to drop me a message.

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Re: High Pressure kite by Bruno Legaignoux

Postby Bigdog » Wed Nov 28, 2018 11:18 pm

Is there any chance of an advantage to bladderless solution with current tech.? I remember a company Seismic?? and one other who had a product WAY back with bladders and bridles similar to Nexus idea.

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Re: High Pressure kite by Bruno Legaignoux

Postby Faxie » Thu Nov 29, 2018 12:37 am

faklord wrote:
Wed Nov 28, 2018 2:04 pm
tomtom wrote:
Wed Nov 28, 2018 12:19 am
It cannot be so simple

Rigidity is thickness cubed ,skin modul linear and then long long nothing and them core properties. Pressure is infact core
Just had a look at one of the links nixmatters posted:
Air-Inflated Fabric Structures, Naval Undersea Warfare Center Division, Newport, Rhode Island, 2006
https://mega.nz/#!OPhl2IpS!uBL05T8UyKKq ... 5OKLmbkCRE

It seems page 7 concurs with my suggestion that rigidity is a simple function of Pressure * Radius cubed.

BUT this got me thinking.... and much more interesting is it seems that smaller diameter, higher pressure air-beams are actually heavier for the same rigidity.

Calculations taking into account:
1) Smaller diameter = smaller volume (square law) but increased pressure gives increased air mass (cube law): overall air mass is greater.
2) Smaller diameter = smaller surface area so less Dacron (linear relationship) but increased pressure results in more stress in Dacron, even though the diameter is reduced, so Dacron (or whatever) needs to be thicker: overall material mass is increased.

Rather surprisingly the overall outcome of this is, for same rigidity and material stress, the overall mass ratio is the simple ratio of the diameters.
ie an 8cm tube will be 1.5 times heavier than a 12cm tube.
Cubed? Wasn't it by the 4th power? (edit: that was with the same pressure)

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Re: High Pressure kite by Bruno Legaignoux

Postby brunolgx » Thu Nov 29, 2018 2:48 am

Bigdog wrote:
Wed Nov 28, 2018 11:18 pm
Is there any chance of an advantage to bladderless solution with current tech.? I remember a company Seismic?? and one other who had a product WAY back with bladders and bridles similar to Nexus idea.
With my brother we started in the 80's making kites with the same kind of fabric than Seasmic (1999) : polyester fabric with coated PU.
We found that it is way heavier and more expensive than two separate materials. A large part of the PU is used to glue
and fill the fabric holes.
Additionally with 2 separate materials each one has exactly the qualities you are looking for. Dacron unshapes little even in the bias. PU sheet is perfectly airproof. Impossible to get the same thing at the same price with a "composite".
Last details :
- weldings are not super strong / reliable
- if the PU is damaged or porous, in one case you change the bladders, in the other one you change the kite...
Just my two cents. Like everyone I would prefer if it was possible to use a composite instead of two separate materials.

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Re: High Pressure kite by Bruno Legaignoux

Postby stefarius » Thu Nov 29, 2018 10:29 am

Hi Bruno, first thanks for developing the tube kites. Waterrelaunchable kites made kitesurfing what it is today. Amazing job the way you connected technology with user experience. :respekt:

Can I ask you another HP kites & user experience question? Nowadays we need wide wings to float, can the High Pressure kite development help to change the airtime/kite size ratio? Smaller kites with more floating characteristics? Playing with airflow, controled bulging canopy or angle of attack change?


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