paul@ubvax.UUCP (Paul Fries) (08/30/85)
I just want to put extra emphasis on Ken Scofield's remarks about the time to wait before going to reserve. Ken's comment said six seconds was the limit. This sounds just right to me, and a little math will prove it. Consider the distance travelled during the snivel. First, to convert mph to fps, use a factor of 1.46, i.e. 100 mph == 146 fps. If your freefall rate is 100 MPH (low side) you travel 146 fps. If your freefall rate is 120 MPH (high side) you travel 176 fps. The six second snivel (for discussion, the actual malfunction is a bag lock, so the drag does not significantly reduce your speed) uses between 876 and 1056 feet of your available altitude. If your pull was at 2500 ft AGL, you are well into the "pucker" zone (at least I pucker if I don't have SOMETHING working by 1700 feet) by this time. (Note: USPA recommends 1800 feet as the decision altitude, 1500 as the execute altitude for a cutaway). The only think I would like to add to this is that we do not have to simply wait during the six seconds. We can be watching what is going on over our heads! Without taking a lot of time, a shake on the riser may be just what is needed to get it open. At least you can be sure that you are not chopping a good main. BLUE SKIES! Paul Fries C-17147
kas@hp-pcd.UUCP (kas) (09/12/85)
I think Paul's mathematical approach to the snivel problem was excellent, and I won't refute anything he said. However, it drummed up a couple more thoughts that I think are worth sharing, so I'll beat this horse a little more. > The six second snivel (for discussion, the actual malfunction is > a bag lock, so the drag does not significantly reduce your speed)... I have heard the term "snivel" applied to everything from a pilot chute bobbing around uselessly on your back to a streamering canopy. It's important to note that the descent rates and appropriate reactions for each variety of "snivel" can be significantly different. The more "junk" you have above you, the slower you will fall -- a streamering canopy, for instance, may slow you down to about 80 MPH. Although this gives you a little more time, a six second wait is STILL the maximum. Actually, I would not wait more than three or four seconds, if my canopy was streamering. By the way, to prevent pilot chute hesitations, and to make opening shock more bearable, I always "sit up" immedi- ately after dumping. Just pull your knees up as though sitting in a chair -- but don't do a backloop! This also puts you in an excellent position to watch your canopy open. > The only thing I would like to add to this is that we do not have to > simply wait during the six seconds. We can be watching what is going > on over our heads! Without taking a lot of time, a shake on the riser > may be just what is needed to get it open. At least you can be sure > that you are not chopping a good main. I guess I made a rash assumption that everybody watches their canopy open. I'm probably wrong. It's particularly important for you new jumpers out there to get in the habit of watching EVERY opening. I, for one, want to be the first to know if something is going wrong. The "sit up" position during open- ing is so comfortable that you won't get a whiplash or strained neck muscles by watching your canopy open. Here are some remedies that may help in some situations: Pilot Chute Hesitations: Either sit up as I described above, or dip a shoulder and roll slightly sideways (I prefer the former). If that doesn't work immediately, the pilot chute is probably snagged on something, so it's reserve time. Remember: once you change your position from "flat and stable", your speed increases and available time decreases -- so don't waste a lot of time trying to un-snag it!! Container Lock: Either your pin is bent or your bridle is misrouted. You can't do a damn thing about either situation, so dump the reserve. (A pre-jump gear-check would prevent either of these situations, unless you bent the pin during exit). Bag Lock: IF YOU HAVE THE PRESENCE OF MIND to do it without losing track of time and altitude, grab a riser and give it a hard jerk, not just a steady pull. If it doesn't break loose immediately, GIVE UP and do a break-away. You are falling FAST in this situation! If you do anything at all before breaking away, do it BEFORE six seconds have elapsed, as Paul suggested. Streamer: Same remedy as for Bag Lock. BUT -- there are many accident reports I've read, and one which I personally witnessed, where a jumper "went in" because he/she lost track of time while trying to shake a canopy open. I probably would not bother to try. I have had my canopy streamer for as much as three seconds, and then open with no assistance from me. If it went longer than that, I'd chop it anyway, but I've never yet had to. Stuck Slider: Grab the toggles and pump them up and down several times. If the slider doesn't work its' way down with each pump, it's break-away time. As long as the slider is 1/2 to 2/3 the way down, the canopy should be safely flyable. But then, if it is that far down, it should be easy to get it the rest of the way down. Collapsed Cell: Cross-porting generally prevents this, but if it happens, grab the toggles and pull 50%-75% brakes. The cell should immediately inflate unless something else is wrong, such as a blow out. A friend of mine once had an end-cell blow out during opening shock, but he was still able to control the canopy and make a safe, albeit harder, landing. My own philosophy is that if there is something over my head that is controllable and landable, I will stick with it, even if it's not 100% good. I consider a break-away as a last-ditch effort to be used only if those two criteria are not met. Every jumper, on every jump, must analyze the situation and make that decision -- fast. * / \ |---/---\---| Ken Scofield C-9355 | Gone | Hewlett-Packard PCD | Jumpin' | Corvallis, OR |-----------| {ucbvax!hplabs, harpo, ogcvax}!hp-pcd!kas
kas@hp-pcd.UUCP (kas) (09/18/85)
Well folks, here's another exchange of mail between Dane Meyer and myself,
which contains some clarifications on the "six seconds" subject.
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Ken,
Thanks for the net news. That philosophy about holding out for 6 seconds
after encountering some sort of canopy openning problem is interesting, but
I'm not one to wait around that long. There are TOO many reports, like you
were saying, of people that lose track of time while trying to fool around
to shake open a canopy -- guys that have a couple of thousand jumps go
in because of this, not just the novice. So, my idea is not to
put any additional effort in getting a canopy (or bag lock, or
whatever) open. I watch it -- if it doesn't work within a short time
(maybe 3 secs), then it's gone and I get to see my reserve. I trust
it with my life! I've used my reserve 3 times (350 jumps), all during
slow speed malfunctions, but it works nicely.
Dane
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Howdy, Dane,
Thanks for your mail. I think I need to clarify a point about the "six
seconds" theory, both for you and for the net. I don't want anyone to mis-
interpret my meaning.
In the message that I first mentioned the words "six seconds", I was
describing what I felt might be a typical scenario with a snivelling canopy.
A main canopy typically takes three seconds to open under normal conditions.
If a snivel is occuring, it will take the jumper two or three seconds to
realize it. By the time the brain has decided that something might be wrong,
and the order is issued to yank the break-away handle, and the handle is
located and grasped, at least a couple more seconds have elapsed. So far, my
canopy has always decided to open at this point, just before I actually yanked
the handle (it's only happened a couple of times). Thus, I was sitting under
an open canopy somewhere around five or six seconds after deploying, instead
of the usual three or four. So you see, the DECISION to cut away might come
three or four seconds after deployment, but the ACTION probably won't happen
until five or six seconds have passed. I DO NOT advocate watching a snivelling
canopy (or bag lock, etc.), for six seconds before DECIDING to take emergency
action. But the ACTION need not, and probably won't, happen much sooner
because of the reaction times involved. If you re-read your last message, I
think you'll agree that we're saying about the same thing -- i.e., the decision
comes after about three seconds.
*
/ \
|---/---\---| Ken Scofield C-9355
| Gone | Hewlett-Packard PCD
| Jumpin' | Corvallis, OR
|-----------|
{ucbvax!hplabs, harpo, ogcvax}!hp-pcd!kas