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Aerodynamically better leading edge

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FrederikS
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Re: Aerodynamically better leading edge

Postby FrederikS » Tue Jan 17, 2017 2:32 pm

ASV had it on their newest racing inflatables. It did not work and I think even took in water. Look at Hansen's illustration the flow probably separates early on and besides it is to the front, and on the high pressure side of the foil which is probably the least of your worries when designing a kite.

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xray
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Re: Aerodynamically better leading edge

Postby xray » Tue Jan 17, 2017 2:34 pm

Puetz wrote:
Peter_Frank wrote:Yes, North did in in 2002 or 3 as far as I I remember, an oval two chambered front tube :D
But left it again.

I can not see many advantages, as if you decrease the diameter ever so slight, the double tube added stiffness with two tubes will quickly be "lost".

Meaning, stiffness is proportional to diameter cubed, so if you have the double stifness from two tubes, you can only decrease the diameter about 20% instead of 50%, so the gain is small compared to all the other disadvantages :roll:
But hats off that they tried it :hut:

8) Peter
... nah it was Gaastra that made the double chamber LE, not North,,,, Gaastra Phoenix.
Still have a 25 in my garage

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tegirinenashi
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Re: Aerodynamically better leading edge

Postby tegirinenashi » Tue Jan 17, 2017 9:58 pm

ShaveTheWhales wrote:Gaastra phoenix double
Wait a minute... They put smaller diameter tube in front of the bigger one? That doesn't make any sense.

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Peter_Frank
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Re: Aerodynamically better leading edge

Postby Peter_Frank » Tue Jan 17, 2017 10:20 pm

tegirinenashi wrote:
ShaveTheWhales wrote:Gaastra phoenix double
Wait a minute... They put smaller diameter tube in front of the bigger one? That doesn't make any sense.
Why not ?

It is the LE diameter that is too "bulbous" and causes drag.

The "trailing edge" of the front tube is not really important - as there is stagnant air behind it, so close to a double surface low drag foil :thumb:

If if was ONLY the front tube and no wing, yes, it would be lower drag having the small diameter tube behind, so teardrop shaped yes - but this is not the case for a lifting kite.

Almost same thing as a jedelsky wing, quite efficient and simple and works great :rollgrin:

8) Peter

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tegirinenashi
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Re: Aerodynamically better leading edge

Postby tegirinenashi » Wed Jan 18, 2017 12:59 am

Peter_Frank wrote:It is the LE diameter that is too "bulbous" and causes drag.

The "trailing edge" of the front tube is not really important - as there is stagnant air behind it, so close to a double surface low drag foil :thumb:

If if was ONLY the front tube and no wing, yes, it would be lower drag having the small diameter tube behind, so teardrop shaped yes - but this is not the case for a lifting kite.
It maybe true that LE alone (that is stripped off the canopy) may cause increased drag compared to classic inflatable kite design -- I simply don't know. Still, teardrop shape is well known to have the optimal aerodynamic profile. This translates to idealistic kite with 2 canopy surfaces (lower and upper) behind LE. Current setup with a gap is just an invite for turbulence.

What I fail to believe is that having smaller LE bladder in front of the bigger one (as in that infamous Gaastra photo) would bring any benefits at all. On the contrary, having smaller diameter bladder behind main LE would approximate the shape to the ideal teardrop.

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Re: Aerodynamically better leading edge

Postby Puetz » Wed Jan 18, 2017 4:45 am

xray wrote:
Puetz wrote:
Peter_Frank wrote:Yes, North did in in 2002 or 3 as far as I I remember, an oval two chambered front tube :D
But left it again.

I can not see many advantages, as if you decrease the diameter ever so slight, the double tube added stiffness with two tubes will quickly be "lost".

Meaning, stiffness is proportional to diameter cubed, so if you have the double stifness from two tubes, you can only decrease the diameter about 20% instead of 50%, so the gain is small compared to all the other disadvantages :roll:
But hats off that they tried it :hut:

8) Peter
... nah it was Gaastra that made the double chamber LE, not North,,,, Gaastra Phoenix.
Still have a 25 in my garage
... me too. :thumb:

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Re: Aerodynamically better leading edge

Postby ronnie » Wed Jan 18, 2017 10:31 am

It might seem this would be better.


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LetsFlyaKite
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Re: Aerodynamically better leading edge

Postby LetsFlyaKite » Wed Jan 18, 2017 1:05 pm

ronnie wrote:It might seem this would be better.

Sorry bud, but it's not. If you watch the end of your own video it says it has no real effect on the kite. But good try though

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Re: Aerodynamically better leading edge

Postby ronnie » Wed Jan 18, 2017 2:20 pm

LetsFlyaKite wrote:
ronnie wrote:It might seem this would be better.
Sorry bud, but it's not. If you watch the end of your own video it says it has no real effect on the kite. But good try though
I know - that's why I posted it.

It does show that it has been tried and wasn't better.

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Peter_Frank
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Re: Aerodynamically better leading edge

Postby Peter_Frank » Wed Jan 18, 2017 4:57 pm

tegirinenashi wrote:
Peter_Frank wrote:It is the LE diameter that is too "bulbous" and causes drag.

The "trailing edge" of the front tube is not really important - as there is stagnant air behind it, so close to a double surface low drag foil :thumb:

If if was ONLY the front tube and no wing, yes, it would be lower drag having the small diameter tube behind, so teardrop shaped yes - but this is not the case for a lifting kite.
It maybe true that LE alone (that is stripped off the canopy) may cause increased drag compared to classic inflatable kite design -- I simply don't know. Still, teardrop shape is well known to have the optimal aerodynamic profile. This translates to idealistic kite with 2 canopy surfaces (lower and upper) behind LE. Current setup with a gap is just an invite for turbulence.

What I fail to believe is that having smaller LE bladder in front of the bigger one (as in that infamous Gaastra photo) would bring any benefits at all. On the contrary, having smaller diameter bladder behind main LE would approximate the shape to the ideal teardrop.
I think you forget to take the stagnant air behind the LE into account ?
It is the reason why our kites fly so well, just like a jedelsky wing as said - the lower side of a wing is not nearly as important compared to the upper side.

Also, look back to page 3, Hansens post and illustration.
This is with a "trip" seam to give even more stable stagnant air yes, but the principle is the same.

Thus maybe you will actually get higher drag with a teardrop shape, than a "cut" shape, just like the trailing edge that is blunt (rounded) are higher drag than a "square" one.
The reason a square trailing edge can have lower drag than a round one, is also because of another trip effect, that gives less turbulence and less drag usually.
(Of course a sharp trailing edge is the lowest drag - but often not possible nor safe and irrelevant in this topic.)

They are called "Flatback" airfoils when trailing edge is squared off with sharp corners, instead of rounded.
Just like we do on our surf fins and hydrofoil wings.

It is not this easy though, as at some point a double surface will have lower drag than even a round "trip" LE, at least at higher angle of attack.
And a lot of discussion whether the flatback TE really is better than a round TE, or reverse :roll:

But no, current setup with a gap behind the LE (only on the lower side) is not an invitation to that much turbulence because of the stagnant air :D

8) Peter


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