? Any wing will stall when AOA is exceeded. I thought the idea of the "air locks" was to help with canopy collapse in turbulence.
Certainly that was the intent. However the internal pressure of a ram air is ambient. The term "Ram Air" is misleading. A canopy inflates by ingesting air into the cells which are trying to expand from the reduced pressure on the outside. Nature hates a vacuum. After the cell fills it does not become ridge until a flow occurs over the top skin reducing the external pressure. That differential causes the wing to become ridge. As long as the wing is flying it has an ambient pressure on the inside and a reduced pressure on the top outside caused by the flow. In turbulence the "Boundary" layer (Reduced pressure area) is blown off disturbing the reduced external pressure and the wing relaxes into a loss of rigidity and it falls out of the air (Stalls). Ram air parachutes just like ridge wings loose lift and stall when the flow is irrupted. Sometime from AOA change and sometimes from turbulence. Air locks do inhibit ingestions of air (inflation) but they don’t do anything to keep the wing ridge in turbulence. As that rigidly is dependant solely on the reduced external pressure. An airlock canopy might stay inflated on the ground after landing forever but it is not producing lift as there is no flow.
billvon (D 16479)
May 7, 2012, 3:09 PM
Post #27 of 41
>Also, I think comparing a crossbraced to an airlocked canopy is like >comparing apples to walnuts. The purposes of those two features are >completely different.
I think they do much the same thing, actually. I think a lot of the benefit of airlocks is that you are adding a square "brace" to the canopy's inlet.
I am sure there are some similarities, but...
a canopy will have multiple cross-braces PER CELL lined up chordwise. They (a set of two per cell) are attached diagonally at the top and bottom skin (see pic)
airlocks are built to span the cell and are attached at the bottomskin and at the ribs to topskin junction, and only cover the distance from the leading edge halfway to the B line attachment point (using a Jedei as an example, as that's what is sitting in front of me)
I think if one was to quote the bracing effects of the airlock, it would be more of a torsion bar as opposed to true crossbracing - the airlock will do very little to prevent vertical distortion of the cell.
I am not an designer nor an aerodynamics engineer, so it woudl be interesting to hear from someone who is (i.e. I'd love to hear Brain Germain's response to this)
Your photo of the Lotus is a nice one -- one can see the diagonal tension in a lot of the airlock panels, and that always corresponds with which ribs have lines or no lines. So one can see how the airlocks are providing diagonal bracing to the canopy, for the ribs without lines. As you say, likestojump, that's only in the nose area. But it is at least a more highly loaded area and more critical to aerodynamics.
on this website about strange paragliding stuff you can see how much effort went into development of size, shape and functionality of almost any part of paragliders, which mostly also are RAM Air canopies.
The site is not very young, but notes are in english and french.. And teher are still loads of innovations
I have done the vast majority of my jumps on Samurai's and have just moved to a Katana.
I think the airlocks had some benefits, for example I found they helped keep the shape in the canopy if you were flying close to the stall point. Through turbulent conditions they keep the canopy feeling solid, but like others have said the wing depressurising is only part of the problem - you still need good airflow to generate lift. Also the best defence to turbulent conditions is a jumpers experience that tells them where to fly and when to sit on the ground.
If there were still airlocked canopies being made would I have bought one instead of the Katana? Airlocks would not have been a deciding factor, I would have been far more interested in the overall flight characteristics of the canopies available. I've loved my Samurai's, they have been great canopies and I am keeping one in my second rig but that's because I like how they fly, not because of the airlocks.
This is why I think they have fallen out of favour. The market just wasn't demanding them. AFAIK the only airlocked canopies were the Lotus, Samurai and Vengeance. The Lotus and Samuari were eventually manufactured by PD for Big Air Sportz (Brian Germain's company). The Vengeance was made by PD by licensing the Airlock Patent from Brian. Now PD is no longer make any of those canopies and Brian is no longer making them himself and he is now working with Aerodyne. I have no idea why PD and Brian discontinued their relationship but if PD had continued to manufacture them then perhaps they would have caught on more. But since they are not that common, many people aren't aware of airlocks and the problems they solve are not causing the market to demand them, so the manufacturers are not going to license the patent if it won't help them sell canopies.