El Rudo wrote:lobodomar wrote:Exactly. Even in the closed position, the vented canopy (net+outer ripstop) adds extra drag and weight.
BTW I own a 2011 OR razor, so had my share of first hand experience with the venturi system. It's a nice kite, but in my opinion the venturi is a marketing thing, something to stand out from the crowded kite market. Think about airplane slots: they are close to the LE, not to the TE like on OR kites. It's close to the LE that you need to energyze the boundary layer so that it keeps attached to the wing along the chord. Plus most of the lift is produced in the first half of the kite (center of pressure is usually at about 1/4 of the chord).
But of course OR didn't put the vent in the front, I doubt that a naturally vented (instead of mechanically open-close) slot would not screw up the kite's aerodynamics in a such a critical zone. They put it in the back, where it can do neither harm nor good.
The initial idea of the OR designers was to put the vents more towards the LE. Tell tale testing showed that they would be more effective towards the TE, to suck the flow back on to the canopy at higher AoA's, like Bille describes above. Airplane wings are designed to perform with AoA's differing only a few degrees. Kites fly with way bigger AoA variations depending on what you do with them.
The extra drag and weight you mention are there in deed, but we're talking a few grams and only very little drag.
Even if it's true that the vents manage to reestabilish a less turbulent flow between their location and the trailing edge, it really doesn't matter much if there is any separation between the vent and the front of the kite.
To be fair, because of interference of the leading edge tube, the center of pressure of kites is probably more than 25% of the chord like on regular airfoils. But still, most of the lift is generated before where the vents are located. I still think that OR placed them where neither much harm nor good can be done.