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
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
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