closing "valves" on cells - pros/cons?

[billvon 2,435]

>This adds a degree of rigidity to the canopy, similar to what cross-bracing does
>(although NOT the same as cross bracing).
I'm not sure that's true. If a structural engineer wanted to add a stabilizing mechanical member to a ram-air parachute, he'd probably add a cross-brace in the nose - and an airlock is a pretty good cross brace. I've never seen any data at all that show canopy A with a higher internal pressure due to airlocks doing better in turbulence vs canopy B, which is identical to A except it has permeable airlocks, doing worse due to the lower internal pressure.
It _seems_ like it should make a difference, based on common sense. Often, the answer is more complex than our common sense takes into account, though. Aerodynamics is often too complex for "gut feel" to work correctly.
-bill von

[billvon 2,435]

>there are several patents on airlocks for skydiving canopies.
Yep, including one from 1973 by Domina Jalbert, one of the inventors of the ram-air. His patent (called "aerial sled") described a ram-air parachute and included "a normally open flexible valve for the opening closeable by the air pressure to seal the opening when pressurized air is admitted to the wing." Airlocks have been around for a long time.
-bill von

[rapper4mpi 0]

All I can say is that the people I know who have any of the Brian Germain Canopies, including the Jedei's and Jonathans feel they are superior airfoils, way ahead of their time!
-Rap

[billvon 2,435]

>All I can say is that the people I know who have any of the Brian Germain
>Canopies, including the Jedei's and Jonathans feel they are superior airfoils, way
>ahead of their time!
Oh, I agree. I jumped a Jedei 120 around the time they first came out, and I was very impressed, both with normal handling and stability in turbulence. I agree that they are good canopies - I just don't think that the blanket statement that it is the airlocks maintaining high internal pressure that makes them good canopies has been well proven.
Take another example. Let's say the two canopies on the market were the Stiletto and the Nova. Would it be a fair conclusion to say ellipticals pressurize their cells better than squares do, just because a Stiletto is more stable than a Nova? Probably not - there were other issues.
-bill von

[polarbear 1]

As I said earlier, the other design parameters (airfoil, trim, planform, etc.) are probably more important to both stability AND performance than just airlocks. However, my personal experience has been that airlocked canopies really do feel more solid and don't change shape as much as other canopies when in turbulence, and they also perform very well.
Just yesterday, I was playing around with a Samurai in deep brakes. I immediately noticed that the canopy looked different than any other I had seen. In non-airlocked canopies, in deep brakes, the sides of the canopy "pull back" a little while the nose "protrudes forward", sort of a "pre-bowtie" shape. The samurai did not do this. In fact, the best way I can describe it is that it looked like somebody had taken a balloon and was squeezing it. The only explanation I see for this is that the internal pressure was maintained by the airlocks, which provided the "rigidity" I talked about earlier.
I will say it again. Airlocks are NOT the be-all-and-end-all of canopy design, but given that the rest of a design is sound, airlocks do seem to help.

[billvon 2,435]

>In non-airlocked canopies, in deep brakes, the sides of the canopy "pull back"
>a little while the nose "protrudes forward", sort of a "pre-bowtie" shape.
My Triathalon 135 does not do that; yet it has no airlocks. My Safire 129 does do the pre-bowtie. In addition, how much a tandem canopy bowties seems to depend a great deal upon whether or not you use flare toggles with it, which indicates that brake line placement affects it greatly as well. This is not to say that the airlocks don't have an effect, but evidence of dimensional stability (or lack thereof) during deep brakes can have a lot of other reasons.
-bill von

[Canuck 0]

First let me state that I have never jumped an air-locked canopy, so I will not make any assumptions about them. I have no affiliation with any manufacturer. Right now I own a Crossfire and a Cobalt.
I do however have a problem with this thread. Parachutes collapse sometimes. Period. It's happened with PD canopies, it's happened with Icarus canopies, it's happened with Glide Path canopies, it's happened with Precision canopies, and unless I'm mistaken, the canopy that collapsed on John Matthews in Florida last year leaving him in a coma was an airlocked canopy. Correct me if I'm wrong, that's just what I read somewhere. We are invloved in a high risk sport. We enter that knowingly. Of course I think manufacturers should always be trying to improve on the safety of their designs, but they shouldn't lead people into a false sense of security. They also shouldn't slam competing manufacturers trying to boost sales...
Canuck

[polarbear 1]

Yeah, I would agree with that. I would think a higher aspect ratio canopy would be more likely to bowtie. Also, I would think that a canopy which has "more tail pulled down per toggle stroke" would also be more likely to do the pre-bowtie. But the airlocked just looked different in deep brakes. All the non-airlocked canopies have a sort of "soggy" look to them, sort of like a helium ballon that has been laying around and has had some of the helium leak out. The airlock, like I said earlier, looked like someone had taken a ballon and was squeazing it.
Being a test engineer, I fully recognoze the importance of data. It certainly is true that I have seen no data to confirm that airlocks have an effect. However, I also have seen no data that confirms that my Mirage will actually accept a 3000 lb shock load like the TSO says, or that elliptical planforms lend themselves to higher performance, or that cross-bracing actual makes a canopy more rigid, or...
I have found it very hard to come by actual data in this industry. Without data, I am only left with my intuition and experience, both of which tell me that airlocks must help, albeit maybe only a little bit.

[Engovatov 0]

It seems CRW could benefit from such increased rigidity the most? Hard to wrap an inflated matress around yourself.
Whadda you think?

[polarbear 1]

Maybe, maybe. I just don't know. Like I said, I have seen no data that confirms that airlocks make a difference.

[BrianSGermain 1]

Parachute stability, when considering a "stable design" comes down to two variables:
1) Parachute inflation/pressurization:
If you don't have air in the wing, it's simply not a wing. A parachute with no air in it will fall like a brick, period. Airlocks do exactly what is needed for this aspect of stability. Better to have something inflated over your head then nothing at all.
2) Suspension line tension/"G" Forces:
If the lines are not taught, the parachute can distort, despite the internal pressure. It is up to the pilot to monitor the "G's", and apply the toggles to increase the angle of attack when a zero "G" moment is beginning. Many in-flight maneuvers can induce line slack as well, and should be avoided at all costs in turbulence.
We have resolved only half the battle by installing Airlocks in your canopy. The rest is up to you. You have enough jumps, you can skip one or two if it's not safe.
"It's better to be on the ground,
wishing you were in the air,
than in the air,
wishing you were on the ground."
Brian Germain
www.bigairsportz.com
P.S. There's an article on Airlocks on our site, check it out!

[cobaltdan 0]

red from flight concepts told me he built an airlocked 135 crew canopy a few years ago...
-dan

[billvon 2,435]

>1) Parachute inflation/pressurization:
>If you don't have air in the wing, it's simply not a wing. A parachute with no air in
> it will fall like a brick, period.
I think I have to disagree here. BASE canopies regularly open and start flying before canopy inflation; they get bottom skin inflation and take off. A video of bridge day deployments will show this phenomenon of flight before canopy pressurization. In addition, plenty of single surface canopies (i.e. the Paradactyl, Rogallo wings) managed to fly with no internal pressure whatsoever. They were archaic by modern standards, but certainly did not "fall like a brick."
I do agree that internal pressure helps canopy stability, though.
>2) Suspension line tension/"G" Forces:
>If the lines are not taught, the parachute can distort, despite the internal
>pressure.
I agree, and I think that this is the dominant factor in parachute stability in turbulence.
-bill von

[polarbear 1]

I agree about the bottom surface inflation, but...I'm not sure I'd want to land my 150 with only bottom surface inflation.

[Designer 0]

As someone who supports Brian,s canopies I understand your point.This is a cost vs return thing.Sure the numbers would be a great study.Worth the cost?Most would say no.Actual empirical evidence proves Brian,s point.

[Designer 0]

We built a test CRW canopy with airlocks.The guys who flew it loved it.Perhaps if we had seen or there had been a market for such a canopy we might have continued the research.