valved and vented vs. non-vented - which is the better choice?

[whatever]

I realise that there have been plenty of posts on this topic and I have tried to read them all.

Feel free to post links, though.

The reason for me posting this is that valved&vented canopies have been in the field much longer now and there are more experienced jumpers who have loads of jumps on non-vented canopies who now also have loads on jumps on vented canopies.

PLEASE post your views and the experiences that help to form them. Also, for the benefit of those who do not know everyone, please include your experience level and specifically experience with the different canopies.

here's an e-mail I just sent to a friend who is planning to take up BASE in the future and is starting to look into what kind of canopy to get, he is fairly set on a specific non-vented canopy, theory being that he will rarely do anything but terminal walls in Europe and that valved&vented would open so much harder in those scenarios that it's not worth having:

"I think there are more factors to consider than just the quicker time
to get flying and the possibly harder slider up openings.

I believe a vented/valved canopy will generally stay inflated way
better than a non-vented when you do strike an object with one, also,
I believe they will slow you down more while you are dragging down a
dam wall or cliff or side of a building and they give you a much
better chance of backing it up off such an object strike / drag
scenario and get flying again enough to make your landing a whole lot
more survivable and less injurious.

I do not believe they inflate much quicker, rather they pressurise
much cleaner and faster and therefore they start flying that much
sooner, which means you have can start controlling the canopy that
much quicker.

I do not think they open that much harder at terminal (inflation =
almost same as non-vented, pressurisation is faster) and you can
always go with a small mesh slider instead of a large mesh.

I am convinced vented/valved canopies will also re-inflate quicker and
more often in scenarios where you have collapsed your canopy (lost
pressurisation) and they chew up much less altitude doing it.

I also believe they are more stable around the stall point, recover
faster and better from being stalled straight down (or backing up to a
stall) and they are more reactive to input during this kind of
'flight'.

SO, planning to do mainly terminal jumps are fine, just read up on
Nick's list and see how many big walls have claimed even experienced
base jumpers through object strikes. Some even had thousands of
skydives, yet they too screwed their exit etc.

If it can happen to them...
(and it did)

- it can happen to you
(and here's the kicker)

AND it will someday if you base jump, it's just a matter of time.

Yes, there are experienced jumpers out there with hundreds (or more)
base jumps who have not had this happen yet, but I truly believe it is
just a matter of time and so do most of them.

SO, why not stack the deck in your favour? Why not take every little
increase in the probability of you landing better you can get?

in BASE jumping, I believe, you should not base your gear choice,
set-up and procedures on assumed succesful jumps - you should always
base what you jump and how you jump it (or if you decide to walk down)
on what your options are likely to be when it goes wrong.

SO, again, I do not think that (maybe they are only marginally harder
anyway) harder slider up openings are a reason to give up
vents/valves, when they have quite likely saved people when things have gone awry.
Also, buy gear based on that one low jump you MIGHT do back home - you
know what they say, better to have it and not need it than to need it
and not have it!

CAVEAT - I only have 93 BASE jumps now. They are all on my
Blackjack260. They are at least 85% slider off and the slider up jumps
are no longer than 4 second delays. I do have 6 skydives on it too, 2
of which were at terminal in my S3, deployed in full flight, no bag,
large mesh slider. I didn't think that opening was particularly hard,
I would say it felt like maybe 2-2.5 seconds slider off on my
Blackjack. I have done 3 seconds slider off and that was noticeably
harder than the slider up winsguit openings. Besides, if you think
terminal slider up openings on Blackjacks are hard, what about
something like XXX's landing on the railway tracks at theXXX? -
that was HARD and a vented/valved canopy would have made that scenario
MUCH better for him. I have never jumped an unvented BASE canopy and
I am pretty damn sure I will never buy one to BASE jump with."

PS - I just ordered my second Blackjack260, putting my money where my mouth is.

cheers
sam

edited for spelling

[Tom Aiello]

The following are my personal opinions. I'm not presenting them as fact, or gospel, or whatever. I'd love to hear what other people think, especially if you can point out holes in my reasoning.

My personal bottom line: I'm jumping canopies with secondary inlets exclusively on solid objects (or anything else with strike potential). I'm also using them exclusively on sub 200' exits. The only situation in which I'll consciously choose an unvented canopy is one where pack volume is a major concern (usually this is aerodynamic, and related to wingsuit or tracking flight, but it can also be a stealth consideration for difficult access objects).

I believe a vented/valved canopy will generally stay inflated way better than a non-vented when you do strike an object with one...

I think this is true in some object strikes. However, it is also possible to strike an object in such a way that the secondary inlets really don't matter to pressurization.

I also think it's perhaps a little over simplified to say that the vented canopy stays inflated better. In my opinion, it gets deflated by the strike the same. The difference is in re-inflation, after the strike. Since the nose can often be pinched off by continued contact with the object (i.e. you're sliding down it with the front of the canopy), secondary inlets can be invaluable in re-inflation post-strike. Also, since you will often have very limited forward speed in this post-strike "slide" phase, secondary inlets can allow reinflation from (relative) upward airflow, where traditional nose inlets require (relative) forward airflow into them.

Note that if your post strike slide does not involve a pinched off nose, the difference between a vented and unvented canopy is much less noticeable (although, still, in my opinion, present--the vented canopy will allow you to regain control faster).

I believe they will slow you down more while you are dragging down a dam wall or cliff or side of a building and they give you a much better chance of backing it up off such an object strike / drag scenario and get flying again enough to make your landing a whole lot more survivable and less injurious.

I concur. By allowing more rapid reinflation in the event of a nose-to-object slide, the secondary inlets will increase your survival chances by giving you a slower descent rate and a quicker recovery of control.

I do not believe they inflate much quicker, rather they pressurise much cleaner and faster and therefore they start flying that much sooner, which means you have can start controlling the canopy that much quicker.

I don't entirely agree with this. I do agree that a canopy with secondary inlets will become responsive to control inputs sooner in the inflation sequence.

However, I do think that bottom skin inlets can lead to slightly faster overall inflation.

"Inflation" is a much used and poorly defined term. I think I need to digress a bit here.

To really oversimplify a vastly complex and chaotic procedure:

A slider down canopy opens in steps (skipping ahead to line stretch):

1) Canopy reaches line stretch
2) Air catches canopy at full line stretch and begins bottom skin expansion
3) Tailgate controls back of canopy while front bottom skin expands
4) Tailgate blows open, and rear of bottom skin expands
5) Air begins to inflate cells
6) Canopy becomes responsive to control inputs
7) Cell inflation is completed
8) Canopy is "flying" and responding normally to control inputs.

Note that the canopy wad is still "responsive" to control inputs from step (1) on. You can twist that wad of nylon up at any time after the lines go tight. It just won't have any net effect on your motion (forward or downward) until the cells begin to inflate.

For purposes of this discussion, let's say that the entire process (1-8) is "inflation" or "inflation sequence." Let's call steps 2-4 "bottom skin expansion," and steps 5-7 "cell inflation."

Remember that this is just a simplification for discussion purposes. Canopy inflation is a massively chaotic and poorly understood process.

Ok, done with the digression...

Bottom skin inlets primarily effect steps 5 and 7. In my opinion, they can reduce step 5 to almost nothing (making top skin expansion follow botton skin expansion so closely that there is almost no perceptible "lag" time, when the jumper can yard on a riser but have no control response). They also speed up step 7, reducing overall cell inflation time by a wide margin.

However, bottom skin inlets can actually slow bottom skin expansion (steps 2-4), because when the airflow hits the bottom skin (and would normally begin pushing it apart), some of the air is diverted through the inlets, performing a sort of pre-pressurization of the cells, but being lost to it's "normal" flow of bottom skin expansion.

Overall, I believe that the reduction in time during cell inflation (steps 5-7) more than compensates for the (very slight) increase in bottom skin expansion (primarily in step 2, but also possible in 3 and 4). In my opinion, the net effect is a reduced overall time for the inflation sequence.

I do not think they open that much harder at terminal (inflation = almost same as non-vented, pressurisation is faster) and you can always go with a small mesh slider instead of a large mesh.

I completely agree. While my experience has been that, all else equal, vented canopies do open slightly harder at terminal, it's easy to counteract this by simple changes in packing (or in more extreme cases reefing) style. The level of control we have over opening speed by changing out sliders (large mesh, small mesh, F-111 with holes, F-111, ZP) is very large (if somewhat gross--i.e. not subject to fine adjustment). If your vented canopy seems to be slamming you, I guarantee you can tame it (perhaps too much, so be careful) by changing to a ZP (in the most extreme example) slider. Fear of hard slider up openings is a silly reason to avoid bottom skin inlets.

I also believe they are more stable around the stall point, recover faster and better from being stalled straight down (or backing up to a stall) and they are more reactive to input during this kind of 'flight'.

I definitely agree. A canopy with secondary inlets will hold stable in deep brakes (near stall) much better than an unvented canopy.

There are two caveats to this:

(1) A canopy with uncovered (2 way) vents (like the original Vtec) will be more susceptible to turbulence in brakes. Turbulence can more easily deflate these canopies because there is a secondary outflow point (the vents) on the bottom skin.

(2) The effect of the secondary inlets on deep brakes varies dramatically depending on other canopy characteristics. If you add vents to a FOX, for example, you can notice a huge difference. The Ace, on the other hand, is very well engineered as an unvented canopy, and the effect on deep brake stability of adding secondary inlets (i.e. the difference between Ace and Blackjack) is not nearly so great. I believe it's noticeable, but it's nowhere near the order of magnitude improvement you see in some canopies.


One point that I think bears repeating: The effect of the secondary inlets is going to vary dramatically depending on the other design characteristics of the canopy.

Sorry to write a book. I can just see dozens of people popping their head in, saying "what the heck is Tom blathering on about now?" and heading back to finish packing.

[spinerugo]

1) Canopy reaches line stretch
2) Air catches canopy at full line stretch and begins bottom skin expansion
3) Tailgate controls back of canopy while front bottom skin expands
4) Tailgate blows open, and rear of bottom skin expands
5) Air begins to inflate cells
6) Canopy becomes responsive to control inputs
7) Cell inflation is completed
8) Canopy is "flying" and responding normally to control inputs.
h

I think that step 5. start at the same time when step 2. starts. If you wach openings from above, you can easily see that there is much air in cells when tailgate relise the lines. The proces is simultaneous. I think that when TG relises the lines, that is final presurisation.

[Tom Aiello]

I think that step 5. start at the same time when step 2. starts. If you wach openings from above, you can easily see that there is much air in cells when tailgate relise the lines. The proces is simultaneous. I think that when TG relises the lines, that is final presurisation.

Are you saying for vented, or unvented canopies? Or both?

I think that the vents tend to synchronize bottom skin expansion and cell inflation, so I can see your point, for vented canopies.

Still, I don't think they are exactly simultaneous. You can see (even on vented canopies) pressure waves crossing the top skin after bottom skin expansion. I believe these pressure waves are the result (or perhaps indicator?) of cell inflation.

[spinerugo]

I'm speaking about both.
It happening becouse of nose shape, and angle of icidence. I don't have any hard data (of course) but plain logic say to me that inflation proces start the same time that canopy (during opening proces) loses his monodsimensional (pack) shape, or to say better, when botom skin expansion start. I think that bottom skin expansion helps cell inflation, an then cell inflation helps bottom skin expansion...proces is simultaneous and one thing promotes another, cirkullar (sp?)
If you think more, you can ask youself where will air use less force to travel? Trough vents, or nose? And can air have that much force to spread uper skin and bottom skin, restricted with mesh? It is like trying to spread closed plastic bag, when you create vacum force. (If inflation starts after bottom skin expansion, then you practically have 2 dimensional canopy, wich air must spread, so even that less force should be trough nose) So if inflation starts after BSE (not CJD, or mad cow desease) :-p are then any benefits from vents? (at that part of opening proces, ofcourse)
I think that vents are starting to "work" real at the point when there is some amount of air in canopy.
We must not forget that we are trying to explain one chaotic proces, and stated above are thouts of some guy that don't know s***, but like to think BASE.

Have fun,

I.

PS: I hope that you understand what I mean't, english (obviousli) is not my first language. :-)
Say and I'll try to rephrase it diff.

[Tom Aiello]

I understand what you are saying, and I think you've definitely got good points.

I do think that the bottom skin reaches full expansion before the top skin, just from personal observation. I've seen (many) canopies with fully tight bottom skins that still have "ripples" where the top skin isn't tight, so I assume that even thought the bottom skin is fully expanded, the cells are not yet fully pressurized. During this phase, I'd expect to see the jumper still travelling mainly downward (not yet travelling mainly forward), because the canopy is acting more as a traditional parachute (aerodynamic decelerator) than as a wing (ram air canopy).

Hey, look, we're actually having a good technical discussion on the BASE board.

[spinerugo]

>Hey, look, we're actually having a good technical discussion on the BASE board.

I think that in last few days Blinc has more post then base zone. :-)

PS: Maybe will manufacturers some day use big skydiving airtunels for researching opening proces, PC inflation, ofheadings... They just nead to calculate (measure) relative wind speed during real jumps, and adjust airspeed in airtunels to slow down like relative wind in real jumps. It would be real cool to see these tests.

BTW: The more that I think about opening proces and inflation, (and everything else) the less i know. :-)
Atleast I know what I will be dreaming tonight. (If I manage to sleep)

[whatever]

Hey, look, we're actually having a good technical discussion on the BASE board.

yes, we are!

thanks for posting, it pointed out how much more detail there is to take in

we're going to have to discuss this in person when I make it out your way later this year

I also plan on getting a LOT of video of deployments, from several angles, I'll be putting that bulletcam to use again.

Saw a cheap RF cordless web/helmet cam setup that might be cool if we can find a safe way to stick it on the end of the bridle, giving the PC's 'view' of deployment. I think you'd want a PC rather on the bigger side for that!
(I would try it static-line first, though.)

later
sam

[Tom Aiello]

Saw a cheap RF cordless web/helmet cam setup that might be cool if we can find a safe way to stick it on the end of the bridle...

Do you have a link, or did you see it IRL?

I'd love to stick one inside the cells, particularly to examine valve action.

[whatever]

Do you have a link, or did you see it IRL?

I'd love to stick one inside the cells, particularly to examine valve action.

Tom
I saw it online or in a flyer, I forget which, couldn't find it, but found these which look promising:

http://www.factorydirect.ca/catalog/product_spec.php?pcode=LO3788



http://www.factorydirect.ca/catalog/product_spec.php?pcode=CA0812


75ft - that's enough so that you can put the receiver and recording device plus batteries on the jumper....

the first one looks pretty slimline too!

that's the store where I think I saw the cheaper version, Logitech's website seems to lag their product releases, but here's a link to the technologies section:

http://www.logitech.com/index.cfm/products/technology/documents/US/EN,crid=810

now all we need is a couple of really small camcorders with A/V ins and a few of these wireless cameras and it's testing time!

I'm also going to get my hands on a (cheap, but hopefully not too nasty) three axis accellerometer sometime and connect that up to some data capturing device if I can find a way to make an acceptably accurate system cheap enough for my budget.

my background in engineering and testing and development is going to come in handy one day...

cheers
sam

PS - thanks for helping out with the titles