0
greeny

Static Line 'V' Dbag

Recommended Posts

I have heard for a long time people’s opinion that a 'well executed D-bag' will open faster than a 'well executed SL' for the exact same jumper, object and conditions.

Why??

Why would my static line on a 'Zero Length Bridle' open lower than your D-bag

Definition of a 'Zero Length Bridle':

The static line attachment point above and only very slightly behind the jumper.

The bridle length adjusted to give only 1-2 inches of slack with the jumpers’ toes over the edge.

(no PC, no spare bridle, no carry with you, nothing extra or not specifically needed in the system)


I am not saying a SL will open faster than a D-Bag, but I am saying done right a SL will equal a D-Bag.

Greeny

(Yes I have done the search, Yes I did read it)

Share this post


Link to post
Share on other sites
I think that the 'Dbag' that most base jumpers are talking abot is not one where the canopy is packed in your container, it is one where a person holds the dbag and you jump, giveing it a heading 'guarentee' and in my opinion, a faster functional canopy.

Packed Dbags are scary.
and always tie the bag off, WELL. like its not being heald.

Share this post


Link to post
Share on other sites
This I understand,

I am talking about a hand held D-bag 'V' SL.

I accept the D-bag may give better heading performance, but a well executed SL gives good (in my opinion acceptable) heading performance.

But,

What makes people think the D-Bagged canopy will be flying quicker??

If I can SL my canopy so that my bridle attachment point
(the point where my bridle meets my canopy fabric)
is held at the same level as the mouth of your D-bag why would the D-Bag canopy be flying faster.

Greeny

Share this post


Link to post
Share on other sites
It would seem to me that Tying a static line off to the top of the canopies bridle point attatchement would increase the amount of fabric and lines that may be able to come in contact with the edge of the object you are jumping from. All of my very limited static line experience has been with the other end of the bridle (pilot chute end) being attatched to the object. Is basically tying the top of your canopy to the object with break cord a very commonly done thing?

Ganja

Share this post


Link to post
Share on other sites
The static line always pulls with 80 lbs of force (or 160 lbs, or something in between -- cue debate). It's like a poorly-executed PCA in that, even after the canopy has been successfully extracted from the container, the static line insists on pulling on it some more. It deforms the pack job. The argument, backed up by experience, is that if the canopy would open faster in the deformed configuration, you would have chosen to pack it that way. Which you didn't.

A d-bag is like the ultimate PCA. There long enough to put a canopy in the air, but with zero resistance after that.

Share this post


Link to post
Share on other sites
That's a good point, the force of the S/L itself.

Also on a D-bag jump when the jumper leaves the lines start to un-stow right way and at full line stretch the canopy leaves the bag and starts inflating right away without being deformed.

On a S/L the container has to open first, the canopy extracted, line stretched. At this point the canopy is not in the greatest position for opening having its center cell pulled up. On top of that, as already mentioned, enough force has to be generated to break the cord. When the tarp is finally free, it "springs" back and inflate.
There are just many more steps on a S/L even a short one than a D-bag.

The cool thing about the S/L is that you do not need anyone to help you out and with the CWY version you do not leave anything on the object.

You can d-bag yourself of course but then you must go back and get your bag unless you wish to leave it on the object.
Memento Audere Semper

903

Share this post


Link to post
Share on other sites
The D- Bag Jumper is at the exact same distance below the object when hist pack job leaves the D-bag (Line stretch + canopy) as the SL jumper is when the break cord snaps.

D-bag:
Jumper exits, lines unstow, B-bag opens, canopy extracts, seperation complete

SL:
Jumper exits, Canopy extracts, lines unstow, SL snaps, seperation complete.

So is the only question deformation of the pack job??

My break cord is 'Apex 80lb cord'

Share this post


Link to post
Share on other sites
Center cell deformation/ stripping is not really a bad thing,3 point bridal attatchments can help that, but those are kinda scary. i have seen a few PC tows for SCARY long times on those things. but i guess it doesnt matter which one you would do.
I have free fallen 180', and static lined 400, if i had somebody to hold a dbag for me on a low jump, i would MUCH prefer that to a statice line.

I dont think anybody is actualy SAYING that a Dbag works faster than a SL, but maybe it does work faster. Splitting hairs,at line stretch, a dbag is usualy 5' higher than a SL.

and without center cell stripping, i think the Dbag canopy is inflated faster.

Share this post


Link to post
Share on other sites
Also, with a d-bag, the canopy is often folded like a caterpillar into the bag, rather than just with a couple of big folds. This allows the canopy to be extracted more or less in the same orientation in which it will open.

Take a look at slow-mo video of a static line jumper sometime. As the canopy is lifted off the jumper's back, it takes on angular momentum. This continues until line stretch, at which point the pack job is often horizontal, with the lines making kind of a 90-degree bend at the bottom of the tail pocket. When tension comes onto the lines, the pack job is jerked into a vertical position.

If I was going to jump something shorter than 100 feet, I'd do a few test jumps on higher stuff first to determine if the d-bag might do the job better. But at that point your canopy isn't really flying when you land, so I think there are probably other considerations which are more important than d-bag vs. static line. On higher jumps, I think there are certainly more important considerations (for example, convenience).

Michael

Share this post


Link to post
Share on other sites
I think the main difference is the momentum force at the very first moment of canopy inflation. At this point the energetic connection of the jumper to the canopy with a D-Dag is much stronger than at an SL.
As you never will be able to just push a nail into wood with a hammer but if you hit it with momentum it goes with the abrupt dynamic.
So in my opinion the D-Bag works faster because of the better dynamic when the sequence comes to inflation. The reason is that the D-Bag goes from bottom to top, SL from top to bottom.
Additionally the SL (no matter how short) always creates more vertical acceleration distance compared to a D-Bag. This results into more energy which must be decelerated by the visible longer move of the opening.
Also the single stow (if used) creates a micro delay which supports the vertical acceleration in a SL jump.
Well that's anyway much to much theory. It just feels better with a D-Bag in 75' ...

:P

Share this post


Link to post
Share on other sites
0