Apr 29, 2012, 6:52 PM
Post #1 of 9
Hi. Was wondering why no reserve canopies seem to be vented like BASE canopies? Of course vents have other BASE specific purposes like keeping inflation during object strike, but it also seems like a less complicated way to increase opening speed than a MARD (but i'd guess a MARD would still open it a fair bit faster?). You wouldn't want every cell vented, but was thinking that a few cells could help. Maybe at head down speeds the opening shock to the canopy would still be too much? Yes, i've got very low jump numbers, and still learning basics about the gear, so this is probably a dumb question, but haven't seen it discussed anywhere. I'm sure there is good reasons why reserves aren't vented, just interested to know what they are. Thanks.
Full disclosure - I'm not particularly familiar with BASE canopies and the way they're vented, but I just wanted to help you out with an understanding of MARDs. A MARD, at least all the ones I'm familiar with, speeds up the process of getting a reserve to line stretch and taking the freebag off of the canopy. From that point on, reserve "opening" or "inflation" or "pressurization," whatever terminology you want to use, is pretty much a function of reserve design and rigger skillz. So that being said, I don't think it's a "MARD" vs "venting" situation - the venting might be useful in conjunction with a MARD. My $0.02.
Vents aren't of much use on slider up deployments, unless of course you have an object strike. Unless something really strange happens, a skydiving reserve will never find itself in either of those conditions.
Eric, wasn't really thinking of the vents for terminal openings after a high speed mal (same kind of speeds as a SU deployment), more for chops from a low speed mal, or a very low altitude bail from a plane in an emergency. Vents could help here couldn't they, or am i completely misunderstanding?
Ken, other than a bit of reading, im not at all familiar with BASE canopies yet (as you'd hope for just over 50 skydives). Rereading it, think i made the question a little confused by the way i mentioned MARDs. Agree that they help a different stage of the deployment, so could potentially work together. Mentioned MARDs, as vents seemed to be addressing the same basic problem of "get a flying canopy in less altitude". In fact, they should both help in similar mals where there the main is at least outside of the dbag if not partially or fully inflated. After some reading, im no longer convinced i want a MARD, as they sound more likely to help in mals that a simple to deal with, and can potentially complicate ones that are already a bit trickier. Of course that is purely personal choice after weighing up the pros and cons, MARDs are probably the right choice for other people.
(This post was edited by drop-bear on Apr 30, 2012, 10:37 AM)
Keep in mind that the low speed opening caricteristics are not the only thing driving the design process. You also have to pass the high speed, heavy weight tests. Once a point of time every one compeated and bragged about the speed of the openings of their reserves. Low pulls were one of the big killers. People pulled, and by this I mean they though there pilot chute, at 2000 ft. Not saddeled there. If you dumped higher then that people would at best call you a student and more often a pussy and want to know why you weren't there for that last point. Keep in mind back then canopies opened faster, mals were less violant, and you knew right away if it was good.
I'm not saying that people don't still die from low reserve deployment but the number of accedents where that was a factor is way down. All the altitudes have gone up.
Now look at the oposit end of the picture. Speeds have gone up, that's actually a big deal. and wing loadings have gone up. People are demanding that there reserves carry almost as high of a wing loading as their mains. and the main thing is a little out of hand IMO. I remember I had this conversation with some one at quincy a number of years ago. I was telling her that we were going to start breaking things and that it would start with canopies. Help me out with my memory here. We've broken lines on Ravens, torn line attachment points off the M series, broken lines on tempos. That's just off the top of my head. Any one else care to add to the list? I'm not so much bashing manufactorers as just pointing out that we're running up against the limitations of our gear on what were always thought of as excelent canopies.
Although there have been a few incedents we really haven't seen as many harness failures as I'd expected by now. Still waiting on that. But what I have personally seen is people killed or injured or paralized by hard openings. I've personaly seen three deaths and one parapligic. I'm not even going to count the kneck and back injuries that are makeing some of my friends lives a living hell. Now as it just so happend those fatalities were all on mains but I have seen people put down for weeks by reserves.
So riddle me this how much faster do you really want some thing to open?
Thinking a bit more about it, they wont both help in exactly the same circumstances. There is probably enough drag from a streamer for a MARD to help, but too much speed for vents to help (though they wouldn't make it any worse, other than a hard opening).
But still, if there is no other complications with the streamer, it should be very easy to deal with. My time to find out is on its way
Hi Lee. Only just saw your post after posting my last one. Your right that extremely hard openings need to be avoided. Maybe can get away with three vents before it gets too much, and maybe that's not enough to noticeably speed up low speed pressurisation. That's probably the reason why venting is not an option on current reserves. Could heavier Dacron lines absorb a little more of this opening shock? It does have a little more give than Spectra, HMA, etc doesn't it? Isn't the increased deceleration from a MARD going to cause the same issues? Cheers.