Basejumper.com - archive

Dwain in a thread on March 3rd 3003:
“Bottom skin venting was introduced into the BASE world to improve slider down pressurization and canopy response to rear riser input with deep brakes set”.

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Tom Aiello in a thread on December 10th 2003:
“I’d say that vents are hands down better for solid objects. The basic upshot is that the canopy is responsive to rear riser input sooner in the inflation sequence”.

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Asylum's “Seven” canopy, from what I can gather seems to have introduced a revolutionary airfoil design that possibly does not require vents for slider down jumps from solid objects. If this is true then I imagine that other manufacturers will eventually scrap their vented designs and will begin to produce similar airfoils.

Question
Are “Seven” type airfoils equal to or better than older airfoils utilising vents in terms of consistent and rapid pressurization?

Good question, I too wonder about this also!

Hopefully one day I will be able to personally
test BASE jump some of these new wings and
see for myself... because it is only a matter
of time till another hungry tree or antenna
takes a bite out my Trolls

[sans green for John's delicate sensitivities]

seen very impressive things out of the Seven...amazing glide, great flare...amazing at almost everything.

recently watched a friend do a go and throw off a low B with one...looked sketchy, did not pressurize fast at all and sunk out a lot...2 fliks with VTEC out flew it.

my personal opinion (take it or leave it :) the canopy is the best non-ultralight fabric slider up canopy on the market, and great/decent for slider down if your taking a delay greater than 1 second.

I have jumped vented canopies on everything from sub 200 ft static lines to Troll Wall...they've perform well for me, no reason yet for me to switch to something like the seven...but I do see its benefits

The other advantage of bottom-skin venting is that the canopy is more likely to stay pressurised after a cliff strike, as the canopy keeps trying to drive at the rock face as you slide down the wall. I've watched it. Not sure an unvented canopy would keep the aerofoil shape under those conditions.

Airfoil shape does not matter under those conditions because the wing is not moving forward and thus not producing lift.

But I get the spirit of what you're saying, even if I don't completely agree with it.

Probably didn't phrase it too well; however it did stay inflated and keep me from accelerating towards the ground!

I did notice the canopy driving at the wall, which it would then "bounce off" from, only to drive at it again. It was trying to fly... hence I actually hit the wall 3 times - part of this would have been caused by the pendulum action of me bouncing off... if that makes sense.

From my observations, vents don't make much difference during an object strike. The design of the canopy is more important to staying inflated, a slow sink rate in general. One reason for this is valves, unless the lines are un-tensioned the valves are closed, maybe letting a small amount of air in, but enough to make any significant difference? If the lines are slack, the canopy is de-pressurizing vented or non.
It seems you get lucky and not hit anything sharp and pointy on the way down, or you don't...

I don't understand. What has led you to this conclusion?

Can you explain?

Valves are designed to closed when the canopy is fully inflated from my understanding. So the valves are only really open during inflation, under line tension the material is pulled taught over the vents.

That's not my understanding at all.

The valves that I have played with are designed to close when the pressure on the inside of the bottom skin exceeds the pressure on the outside of the bottom skin, and open in the reverse situation. The lines (and any tension on them) don't really play into that.

If you put a valved canopy into a deep sink, you can get often get the valves to pop open and admit airflow, because the air pressure on the bottom skin exceeds the internal pressure of the canopy.

This same situation could apply in the situation we were discussing (post object strike, with a slide down the face of the object), where the pressure against the bottom skin (from the canopy falling/sliding downward) can exceed the internal pressure of the canopy. Assuming that the nose is somehow pinched off by the strike and slide along the object, the canopy could still experience air inflow through the bottom valves (or vents) regardless of the state of the lines.


As an experiment, you could take your valved canopy, drag it out to line stretch, hold it there with bungee cords, and then use a fan to blow air into the bottom skin valves.

Would you expect the valves to stay closed in this situation, on account of the lines being tensioned?

If you removed the tension from the lines, would you expect the valves to open regardless of the pressure on the bottom skin? What if you laid the canopy out and set the fan at the nose, to inflate the canopy without any tension on the lines? Would you expect the valves to stay open in that situation, on account of the lack of line tension?

Or in laymans terms the vents will close, "When the airflow into the nose of the canopy becomes greater than the airflow onto the bottom skin", or alternatively "When your canopy stops falling and starts flying". Hence the vents opening again when you put your canopy into a stall.

Tom A,

I know that you don't have first hand experience on each and every bit of kit that emerges but from speaking to jumpers and possibly even designers what is your general view to:

... in view of airfoil developments do you think we are moving away from or have already moved away from the need for vents/valves for solid, low jumps or do you think vents/valves still have a role to play?

Thanks in advance

John

I think secondary inlets (vents, valves, perhaps some other things we haven't thought of yet) still have a role to play.


There is definitely a real discussion to be had here, but I don't think that changes in airfoils available on the market are the central point.

Various people whose opinions I greatly respect have long thought that secondary inlets weren't necessarily the way to go, and I don't think that the change in canopies available on the market has been a factor in their thinking, because they've maintained that position since the introduction of vented canopies 10 years ago.

My experience exactly. Whilst sliding down the face, I could see that the valves were completely open - the material flaps were fluttering in the breeze!

Having no experience with a wall strike on a non-vented canopy (and no future plans to have such an experience), all I can say is that my BlackJack stayed inflated with its nose to the wall for hundreds of feet while I tumbled down a mountain and that is enough for me to keep jumping vents (although the fifth control line of the BJ and its possible involvement in my probable tension knots makes me want to switch vented canopies to one with four control lines above the cascade).

Sounds like I need more experience w/ vented canopies... But as far as the experiment go's, I would say it's not valid. W/ out the canopy fully inflated and equal line tension from the weight of a jumper the performance of the valves would not be correct.

Who here has had an object strike w/ a non-vented canopy and watched it stay open down the wall? A good friend bounced down a couple hundred ft. of unfriendly rock with one, stayed inflated the entire time and set him down softly...

I would have thaught the air that comes in the vents will just as easily go back out the nose and if if it couldnt the vents would be closed.

Isn't the primary purpose of vents/valves to promote rapid/even inflation of the canopy? In my understanding, a canopy will have the same surface area/drag while sliding down an object. Vented or not, it's not enough drag for a landing I would want. A flying wing is your friend. Also, vents will probably maintain even inflation longer than no vents, (while sliding down the wall) but the nose cells are obstructed either way. The only difference with a vented canopy in this scenario is more air exchange within the canopy. There just isn't really enough data to fully support either theory. That said, I'm in the vented canopy camp, but for different reasons than what happens while sliding down a wall. (Backward flight, for example) I suggest turning that thing around, rather than checking out your bottom-skin situation for a few hundred feet. :)