RE: direct bag

[guest]

I'm looking for info on min. exit with a direct bag. I'm looking at some lower objects in the 140 to 170 range. Any packing suggestions wold alsso be nice. Thanks

[guest]

I believe the lowest jump ever done with a DBag was 63'. So, I'd say that's the established minimum. I would guess that your 140' ought to be no problem with a Dbag (in fact, I can think of a couple madmen who'd probably freefall your object faster than you could say "no worries, mate" ) .

However, every canopy, jumper and Dbag behave differently. My suggestion would be to visit a nice safe (preferably legal) object that has much greater altitude, and Dbag it 10 or 12 times to find out how fast your setup will open. I'd recommend bringing along a laser rangefinder (so you can laser the canopy just after opening and see how fast it really opened).

Remember that just doing it once is not enough. If it opens in 150' once, but then averages 180', you're going to be really bummed on that 160' object.

A few things I learned when packing Dbags:

1) Wrap your tailgate with two loops, and no more. I've seen tailgates hang up at near zero air speed when wrapped too tight.

2) Accordion fold the canopy into the bag. It'll open faster than if you roll or S-fold it.

3) Be absolutely certain that the Dbag is secured to the object. It would suck to hear your bag holder say "ooops," look up, and see the bag coming after you.

--Tom Aiello
tbaiello@ucdavis.edu

[guest]

My buddy and I have several jumps from a 135'
water tower with no problems. Still at least a
5 sec. canopy ride. Todd at B.R. told me that
since the lines were stowed in rubber bands
until line stretch, there was no need to use the tailgate with a direct bag, but you might want to double check with him first.Hope this helps
516

[guest]

>Todd at B.R. told
>me that
>since the lines were stowed in rubber
>bands
>until line stretch, there was no need
>to use the tailgate with a direct bag,

The primary purpose of using a tail gate is to achieve nose-first bottom skin expansion (versus tail-first bottom skin expansion). There are many benefits of nose first bottom skin expansion  just ONE of which is the minimal chance of a line over or tail inversion.

The relationship formula is not:
LINE OVER is avoided by TAIL GATE

It is:
LINE OVER is avoided by NOSE FIRST BOTTOM SKIN EXPANSION which can be achieved by using a TAIL GATE

A deploying slider down/removed canopy will have a tendency to achieve bottom skin expansion tail first. This is because the air hitting the angled bottom skin will pool where the tail is pulled back down by the deep brake settings (similar to how a round canopy inflates from the apex downwards). This in turn will force the tail to expand first resulting in large amounts of stress on the brake lines.
When the tail expands prior to the nose it will make the canopy surge forward prior to cell pressurization. This surge forward usually only shuts of the nose (due to the fact that the canopy hasnt yet acquired sufficient internal pressure to stay inflated against the external pressures) which in turn results in slower and uneven cell pressurization (and subsequently more altitude loss). Also when the tails gets a head start on the nose, the danger exists that the brake lines will flip in front of the nose and a line over will result.

However, if the bottom skin expands nose first it will stress the brake lines less , surge less and subsequently reach cell pressurization faster. There is also significantly less chance that a line over or tail inversion will occur.

BASE jumpers have known the benefits of nose first bottom skin expansion for many years prior to the introduction of the tail gate. In order to encourage a nose first inflation two main areas were focussed on: increasing the speed the nose will inflate (by opening it up when packing) and secondly, trying to slow down or inhibit tail inflation so the nose can get a head start on it.
Many techniques have been used to achieve tail inhibition such as micro reefing (placing more folds in the tail than the nose), the differential stow (only placing the C, D and brake lines in the tail pocket primary stow), and masking tapping the brake lines together.
In late 1996(?) Basic Research introduced to the general BASE community what has become the most widely used and successful method of achieving nose first bottom skin expansion; the Tail Gate.

I have heard some jumpers express concern over using the Tail Gate for jumping low objects. They were worried that by inhibiting the tail, the canopy would take longer to open. Although the Tail Gate does inhibit the tail, it results in a faster pressurization of the cells. In short, you will most likely open slightly higher with the Tail Gate than without (and with less potential problems as well).

In summary, use the tail gate (or some other method of achieving nose first bottom skin expansion) with Direct Bag slider down deployments (especially if you are exiting low without a Vtec canopy).

BSBD,
Dwain

P.S. In my limited experience, direct bag deployed canopies with a resulting line over can detract from the main purpose of the jump.
P.P.S. Having the canopy surge forward and dive at the ground (after achieving tail first bottom skin expansion) on a 60ft bridge jump over knee deep water tends to result in a solid landing (but not so solid as to prevent you from doing it a second time).
P.P.P.S. Tom, the Australian phrase used when attempting to freefall 140 over hard earth would not be "No worries, mate!", but the slightly less confident "Shell be right, mate" (or the very unconfident "I'll let you go first on this one Slim!!!"). ;)