Forums: Skydiving: Gear and Rigging:
"D" bag fabric composition

 


kirils  (D License)

Jan 23, 2002, 12:27 PM
Post #1 of 22 (1498 views)
Shortcut
"D" bag fabric composition Can't Post

I have seen deployment bags made of cotton, ZP and F-1 11
nylon. Some are quite heavy material and some thin as paper.
Are there safety or performance advantages of one over the other?

Thanks!

Skydiving is not a static excercise with discrete predictability...


Premier PhreeZone  (D License)
Moderator
Jan 23, 2002, 12:55 PM
Post #2 of 22 (1490 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

Other then the lowered pack volume and the fact you can slide a canopy into a ZP bag easier, none that I've heard of.

I want to touch the sky, I want to fly so high ~ Sonique


alan  (D 17868)

Jan 23, 2002, 1:47 PM
Post #3 of 22 (1475 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

I've heard of several zero-p d-bags failing, one of which resulted in a main malfunction. I can recall of no fatalities associated to this as of yet. My advice is to use the d-bag that comes with the rig as it is a designed component of that unit. Size, shape and even fabric to fabric friction all have
an effect on the D-bag that was designed to be compatible with the main pack tray of you rig. The manufacturer is the correct source of information.

alan


riggerrob  (D 14840)

Jan 23, 2002, 10:17 PM
Post #4 of 22 (1435 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

Main d-bags made of F-111 and ZP fabric work as well as parapack d-bags. The lightweight d-bags just don't last as long.

Cotton or more correctly, polyester-cotton blend d-bags are a hang over from the days when sleeves were made of cotton. Because of the long distance the canopy had to slide out of the sleeve, there was serious risk of burning and melting the canopy fabric. When you consider how short most d-bags are, friction becomes irrelevant.

But skybytch had a good point about sticking with a d-bag from the same company that built the container. Harness/container manufacturers devote a lot of time and effort to tailoring d-bags so they will fit gracefully into a specific size of container and will open consistently.



kirils  (D License)

Jan 24, 2002, 3:38 AM
Post #5 of 22 (1414 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

Point taken... thank you.

Skydiving is not a static excercise with discrete predictability...


Premier SkymonkeyONE  (D 12501)

Jan 24, 2002, 5:12 AM
Post #6 of 22 (1406 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

Pete Culbreth at Skydive Opelika makes nylon mesh d-bags which are really cool. Not flimsy at all like one might imagine, and very easy to compress the air out of (obviously). He sells them in any custom size for around $30.

Chuck

My webpage HERE


DBTECH  (B 21186)

Jan 27, 2002, 7:01 AM
Post #7 of 22 (1350 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

I've had D-bags made from 1.9 Nylon ripstop, but never F-111 or ZP.
I do see a durability issue with F-111 or 1.2 ZP.
The Nylon mesh idea sounds sounds good--maybe I should build one of my ram-air sleeves with Nylon mesh for faster compression of the canopy. (loaded sleeve compressed when installing in container)

Dave Brownell



kirils  (D License)

Jan 27, 2002, 6:07 PM
Post #8 of 22 (1327 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

what do you mear by "ram air sleeve"?

Skydiving is not a static excercise with discrete predictability...


DBTECH  (B 21186)

Jan 27, 2002, 8:13 PM
Post #9 of 22 (1315 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

Subject: Ram-air Sleeve R&D Rev 7-6-01

DB Technologies: Prototype sleeve for ram air canopies. Rev 7-6-01

My latest project (1997) is a sleeve for a ram air canopy--one that I know will make packing a zero porosity canopy much easier.

The sleeve is 39" long and 15" wide laid flat before loading. (was used with a Spectre-170) (now used with a Cobalt-135 & a Stiletto-135 after some shortening from the top.(6") After it is loaded with the podded canopy with the mouth turned up and the lines stowed it is 29" long (23" with Cobalt-135 or Stiletto-135) and 12" nominal in width. There are three locking stows. The first stow is made at the center, then the left stow followed by the right stow. The last four stows will be explained later in the text.

The sleeve is then brought over the rig so that the mouth end is against the reserve wall and the lines are on the bottom of the pack tray. At that point I half the sleeve two times. First I bring the top over to meet the mouth end at the reserve wall, then I bring the remaining folded sleeve over also. Then I close the container. Unlike a D bag, the sleeved canopy "fills" the container, I believe better.

The sleeve is made of 1.9 oz ripstop with appropriate reinforcements. The sleeve retaining line is 12" long. (TY 4--5/8") (one piece TY 4--5/8" bridle all the way to the canopy on my sleeve only. (21" ZP pilot chute used)

My new line stow technology for the last four stows will now be described in the following text.

For the last four stows there are two "pairs" of # 3 grommets with internal stiffeners. One above the other just below the left and right # 4 locking stow grommets.
A continuous loop of 3/4" elastic strap, THREE inches long laid flat; then sewn at the center point is used for the four "Post" locking stows. This elastic strap has an elongation spec of 110%. This is more than most elastic shock cords. The center of this strap is then tacked on the inside of the sleeve at the center point between each of the two # 3 grommets. The spacing between the OD of the two grommets is 5/8" (1 1/2" cntr. to cntr.) The internal stiffener (.060" MDS) makes sure this dimension never changes. The tack points are pre drilled in the MDS stiffeners, as are the punched oversize holes for the grommets.

At this point I bring the ends of the loops through the grommets. There is only about 3/4" of laid flat loop outside the grommets. The total laid flat length of each stow is of course 1 1/2", or half of the total loop length.

The "Grip" on the line bite is more than adequate considering that I have two of what I call, "center mass lifting loops," one above the other mid span between the left and right stow points. They are made of 5/8" type 4 square weave with a laid flat length of 2" below the stitch point. Their purpose is to provide a line anchor at mid point between the 10 inch stow span. These midspan "Lifting points" will remove 33% of the load on the left and right stows during pilot chute extraction. But there is a lot more to it than that. With a 2 1/2" stow bite there is an equal mass of line on each side of the stows! ( 2 1/2" ea. side of the stows). These center "Lifting points" provide "Lift" for the remaining center 5" of line. (2 1/2" each side of the center.

The easiest way to see the physics here is to imagine cutting all the lines halfway between the left stow point and the center lifting loop--and also the same cut on the right side. You would then have three lifting points with 2 1/2" of line on each side. The mass on each side of the three lifting points would be the same!
Goodbye line dump forever! Enough tech talk, let's stow the lines!

When stowing lines (post locking), simply bring the "bite" of lines through the proper center loop "on it's way" to being stowed. The bite of lines passes very easily through these loops because of there larger size. However, they do not hold the line with a tight grip. There is no need for that as the mass/load is equal on both sides.
The need for very tight stows is no longer needed for the last four stows-because of equal mass on each side of the stow.

I have had great on heading openings, with the exception of minor line twist on a few openings.
As of 7-6-01 I have 300+ deployments on one of my prototype sleeves. Some of the early deployments were done with a psycho roll from the top, and one was S folded in the container. I believe that the psycho roll can increase the likelihood of line twist and a line over malfunction. It also does not fill the container very good.
The best method is the one described earlier in the text.

Interesting information: At line stretch the sleeve inverts from the top down. The mouth is the last to invert.

Note: The four post locking stows/elastics are original after 300+ jumps--they still look new!

I have built five new sleeves for field evaluation as of late 98.

David B. Brownell
DB Technologies
Mesa, AZ.




skymedic  (C 33561)

Jan 27, 2002, 8:20 PM
Post #10 of 22 (1313 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

OK Dave, how about in english this time for us less than knowledgable on the poynter parachute books.......

marc
"...a mind stretched with new idea's will never regain its shape"


DBTECH  (B 21186)

Jan 27, 2002, 8:29 PM
Post #11 of 22 (1312 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

The only other text I have on my sleeve is the packing instructions--would you like to see that?

Dave Brownell



AndyMan  (D 25698)

Jan 27, 2002, 9:33 PM
Post #12 of 22 (1307 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

How about an "executive summary"?

_Am



DBTECH  (B 21186)

Jan 27, 2002, 9:45 PM
Post #13 of 22 (1303 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

New ZP packing is a breeze-never any line dump, and no big inventory of rubber bands, are ever needed.

Dave Brownell





Premier skybytch  (D License)

Jan 27, 2002, 9:48 PM
Post #14 of 22 (1301 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

In reply to:
I've had D-bags made from 1.9 Nylon ripstop, but never F-111 or ZP.
Aerodyne Research sells what they call a ZP d-bag. Is it really not ZP fabric?

pull and flare,
lisa
--
Life is tough, but I'm tougher


AndyMan  (D 25698)

Jan 27, 2002, 10:08 PM
Post #15 of 22 (1298 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

I don't know if it's real, but Aerodyne shipped me a demo Diablo in one. I found it very dificult to use. The sliperiness made it more dificult to control the canopy while putting it into the bag.

In addition, the bag was tearing at the seams. I had to have my rigger put some bar tacks into the seam of the bag.

I don't recomend the Aerodyne ZP bag.

_Am



riggerrob  (D 14840)

Jan 28, 2002, 7:53 AM
Post #16 of 22 (1282 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

Definition of a "sleeve" a fabric tube roughly the same width as the container and the same height as the flaked canopy. Sleeves have been around since the 1950s. With round parachutes, sleeves serve the same function as diapers or deployment bags: they hold the mouth of the canopy closed until it has reached line stretch, thereby vastly reducing opening shock and malfunction rates.
When Parachutes de France introduced the first zero-porousity parachute in the late 1980s, they offered sleeves to ease the packing process.

A sleeve allows you to divide the folding process into two separate steps: long folding and lateral folding. Basically, you lay the canopy on the floor and dress it to the same width as the sleeve/container and slide the sleeve around the canopy. Close the mouth of the sleeve and stow most of the lines in rubber bands. Now that the canopy is all nice and neatly contained by the sleeve, it is easy to S-fold into the container. Close the container in accordance with the container manufacturer's instructions.



AndyMan  (D 25698)

Jan 28, 2002, 7:57 AM
Post #17 of 22 (1279 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

Cool.

Is it simply a packing tool, one which you leave on the ground when done, or does it get rolled into the pack job? If so, how does it attach so you don't lose it on deployment?

Sounds interesting... Just another of those useful tools that got thrown away long ago. I think my new PD canopy might benefit from one!



riggerrob  (D 14840)

Jan 29, 2002, 8:21 AM
Post #18 of 22 (1244 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

Try thinking of a sleeve as really long deployment bag. A sleeve is slid around the canopy and gets folded into the container. The sleeve remains folded in the container until you toss your pilotchute. The sleeve continues to hide the canopy until you reach line stretch, then it slides off the canopy and becomes useless.
A sleeve is attached to the canopy by a sleeve-retainer line roughly as long as the canopy is "high." The sleeve retainer line saves you the hassle of searching through the weeds after every jump.

Let's be careful about terminology.
When Performance Designs first started building canopies in the late 1980s, they build a series of F-111 seven and nine cell canopies called "PD-280, PD-150, etc." Since they were made of F-111 fabric they were not half as slippery as modern canopies and didn't need fancy packing aids.
I suspect that you are referring to a canopy that Performance Designs made out of slippery, zero-porousity fabric. A sleeve will make it easier to control a z-p canopy.



DBTECH  (B 21186)

Jan 29, 2002, 10:16 AM
Post #19 of 22 (1234 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

Some facts about deployment sleeves.

The sleeve retaining line can be very short, as the sleeve will always invert from the top down, because of the huge pressure differential when the mouth is open. (ram-air pressure at open mouth, and a partial vacuum at the top of the sleeve) The above is true for a round parachute also!--yes, I have seen this.

As far as the claim, for a sleeve causing canopy burning; this is in fact a fallacy, as the 'force per unit area' is way to small.

Dave Brownell



freeflir29  (D 10000000)

Jan 29, 2002, 10:23 AM
Post #20 of 22 (1231 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

So, what kind of drag is produced by this sleeve on a string behind your canopy after deployment?

"I got some beers....Let's Drink em!!!"
Clay


DBTECH  (B 21186)

Jan 29, 2002, 10:50 AM
Post #21 of 22 (1225 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

The sleeve is inverted after deployment, and, like a D bag, does not extend behind the tail of the canopy.
I would say that my sleeve has slightly less drag than a D bag, because of it's much softer material.
(not that either have much drag, compared to even a small inflated pilot chute!

Dave Brownell



freeflir29  (D 10000000)

Jan 29, 2002, 10:53 AM
Post #22 of 22 (1221 views)
Shortcut
Re: "D" bag fabric composition [In reply to] Can't Post

Yeah...I guess on a square the bag would actually be pretty small. I was picturing the old ones on Paracommanders and T-10's that looked to be 10 ft long or better. (Just saw it on TV once)

"I got some beers....Let's Drink em!!!"
Clay



Forums : Skydiving : Gear and Rigging

 


Search for (options)