80 Pounds of Force

[bps]

Recently, I've been jumping quite a few objects in the PCA/Static-line range. (everything else has always been 300ft+)

I'm still asking questions and forming opinions about this deployment method...now I want yours.

I know that 80lb breakcord seems to be the standard. (besides tape and plastic grocery bags!) Does 80lbs seem too high to anyone? I realize that too high might be better than too low, but I was wondering if 80lbs is placing unnecessary center-cell stripping on the canopy? Any thoughts on this...

C-ya,

Bryan

[base615]

Hi Brian,

I had this view myself and in fact due to jumping with someone who's done most of their jumps in oz I started using tape. On the jumps that I did, the tape seemed to perform better than the break tie had with less centre cell stripping and faster pressurisation.

While using this method on a particularly low object with a mate in August my PC came off with the shrivel flap still attached, The other guy deployed correctly with the same method. We can't deduce how or why this happened but I ended up freefalling 120 ft on to VERY hard earth, getting bottom skin inflation only and breaking myself. When I get back up for another SL jump (probably not that low again) I'll be using 80 lb break tie just for the consistancy.

I've noticed a few guys over here using 50 lb break tie which seems to work ok. There's a hell of a lot of jumps made at a low cliff in California with 80 lb though. I reckon that's testament to it working pretty well.

Cya

Craig

P.S. Even though it was unintentional does anybody reckon a 120 ft freefall is a record? It'd be nice to have something to show for it!!

[guest]

I reckon you've got the record for "lowest freefall jump survived." Unfortunately, all the records seem to be for "lowest walked away from."

Darn it! If the records were just for survival I could lay claim to lowest pull!

[guest]

Hey Bryan:

This past summer I did a bit of experimentation with this stuff with an eye to an ultra low object near my house. I broke out a spring scale and dropped packed rigs off a 35' bridge.

As you know, I'm a habitual user of electrical tape, so I tested that, as well as 80 lb. break cord. I tied the static line at the end of the bridle, and did some drop tests. I also repeated the tests with a camera and a spring scale, then went back and did a frame advance to look at force at various points. My sample size was only 18 drops--six each with tape, break cord and spring scale (three on each rig).

Note that I was only dropping rigs--I did not have an appropriate weight to test the system with proper body weight. I know that Todd and Anne have a dummy weight, but I doubt they've tested anything other than break cord.

Here's what I found.

1) The highest force exerted on the break cord was at the moment that the rig reached bridle stretch (i.e. first impact with with the shrivel flap) for a Velcro rig (I used my Vision). This was typically around 25 lbs of pressure. By priming the velcro, I was able to reduce the pull force at this point to approximately 10 pounds. Priming to less pull force left me with a shrivel flap that I did not consider adequately closed to exit with. For comparison purposes, the same rig pulled the shrivel flap with approximately 15 pounds of pressure in a floor test (standing, sitting or laying and having someone else just pull the shrivel flap). The force exerted at this point with my pin rig (Prism) was approximately 10 pounds. The pin rig pull force was consistent with the bridle routed under the tuck flap or outside of it--the tuck flap did not increase the pull force.

2) For the pin rig, the highest force exerted on the break cord was approximately 20 pounds, which occured at the moment the canopy bundle began extraction from the pack tray (I don't think you could tell the difference between this moment and pin extraction unless your canopy is equipped with a multi--I only mention this because mine was and I know that yours is not). I would guess that this is approximately the same force that was exerted on canopy extraction for the velcro rig, but it was difficult to tell since the canopy in the velcro rig had no multi (hence less time and distance separation between the shrivel flap and the canopy).

3) Center cell strip occurred on every test drop (since the weight of the rig alone was insufficient to break the cord). I would suspect that either tape or break cord will induce center cell strip. An alert PCA holder (who can release the PC at line stretch) is probably the best solution. However, note that this requires practice (I personally pretty much suck at it), so I'd train the PCA holder off a higher object first.

4) The breaking force of my electrical tape (I do two wraps under the bridle, then five above) was approximately 50 pounds. Note that the breaking force of the tape varied by as much as 20 pounds (45-65 lbs). The break cord broke, as advertised, consistently at 80 pounds. I did not test various rolls of tape, but I suspect that there may be even more significant variance from roll to roll.

And my disclaimers:

a) My statistical sample was quite small. Before trusting your life to the results (say by using 40 lb cord), I'd verify them yourself, with your rigs (especially canopy extraction, since yours are bigger than mine).

b) I am not an expert (witness my current condition). Trust yourself.

Let me know if you want more info on my extensive 18 drop testing program, or if you find out anything else.

--Tom Aiello
tbaiello@ucdavis.edu

[guest]

When I first heard about plastic shopping bags thought it was said as a joke. Tensile consistency would be hard to maintain as (IMHO) it would vary depending on the number of folds (twists) in the plastic. I haven't done any ground testing of this technique (why bother?) but maybe someone knows different. I can't believe that anyone who goes to the trouble of aquiring altitude can't get it together enough to carry a roll of insulation tape with them.

My contribution..... I've found that using 3 x #62 or #63 rubber bands tied in parallel works pretty well for me. I haven't done that many jumps to give this system high acclaim but it is certainly my choice for the stuff between D-bag & F/fall.

Also... on the subject of D-bags, I read in a post a while back that someone recommended a s/line back-up for the D-bag. This is not a reccommendation I CALL IT ABSOLUTELY MANDATORY. Basically, if you are using D-bag deployment without a bridle attached from the bag to the object then I CAN GUARRANTEE A CONCRETE NASAL IMPLANT IS COMING YOUR WAY SOON. This is especially so given the convenient trend recently to use whuffo's to hold the bag. That bridle is your insurance policy. Surely this post was a joke too. C'mon boys & girls, don't be so lazy and complacent. Have foresight and KNOW that you will never have it "all covered". I'm so sick of attending funerals.

And what is the current opinion on the number of turns of tape used? I've heard four is the norm. but would like to hear other opinions.

BTW, Craig.....you DO have something to show for your 120' f/fall - your life. Juicy story though!! Thanks.

Wishing fun for everyone.

Gary Penglis BASE# (read - peer pressure #) not necessary

[base615]

Well I did walk away but my left leg looked like it had 2 knees!!!

How's your back doing?

Craig

[Dwain]

>>I had this view myself and in fact due to jumping with
>>someone who's done most of their jumps in oz I started
>>using tape.

>>While using this method on a particularly low object
>>with a mate in August my PC came off with the shrivel
>>flap still attached


In Oz I have noticed that a number of jumpers have used electrical tape to static line incorrectly.
The tape must be wrapped through the eyelet on the bridle (or some people tie a loop in the bridle and then wrap the tape through the loop).
I have noticed some jumpers incorrectly just wrapping the electrical tape around the bridle (often near the p/c attachment) and not through anything. When the tape starts to load (as it takes extracts the shrivel flap/pin and takes the weight of the canopy prior to line stretch) the tape can stretch out and the p/c can slip under the tape.

There have been close to a thousand known static lines in Oz using electrical tape. Correctly used it has resulted in very few problems. Obviously the quality and consistency of the tape is critical.
Four wraps of tape are most common (i.e. 4 wraps of tape are broken on line stretch) with canopies around the 220 square foot weight (7-9 lbs). 5 wraps are also common, I've used 3 on many occasions and 2 wraps worked a couple of times. With 7 or more wraps severe center cell stripping starts occurring and pressurization consistency is affected.

However I noticed/experienced that 3 wraps of tapes was prone to FREQUENT failure on canopy extraction when deploying a Multi equipped canopy (but not with a single bridle attachment point). I theorized that this was because the reduced center cell strip on canopy extraction from the container created a greater snatch force (and subsequently the initial loading on the tape at canopy extraction was greater).

One must remember what job a static line performs. A canopy (weighing anywhere between 6 to 12 pounds) is dropped 9ft and then hangs from the static line until line stretch is achieved. The static line receives three distinct snatch forces during a deployment (which you can feel when performing a PCA). Firstly on shrivel flap/pin(s) extraction, secondly on canopy extraction and thirdly on line stretch. The job of the static line is to withstand the first two snatch forces and fail on the third snatch force with minimal center cell strip.

Finally, not to subtract from the glory of surviving a static line failure from 120' over hard earth, but a static line failure is NOT a freefall.
During a go'n'throw (low airspeed) freefall there are three very distinct stages of deployment.
The first stage is from pilot chute release to the p/c reaching bridle stretch above you and inflating.
The second stage is canopy extraction (from the container through to line stretch).
The third stage is canopy inflation and pressurization.

When using a very large p/c (48”-52”), the time taken for stage 1 to occur is often the same amount of time for stage 2 to occur (I.E. Stage 1 is a significant part of deployment on low freefalls).

While a static line failure does not perform the stage 2 function, it still assists stage 1 and subsequently speeds up deployment. Therefore a static line failure cannot be equated to a freefall BASE jump (unless the static line fails just as the jumper leaves the object). You generally will open higher with a static line failure than with a go'n'throw freefall.

As well as break cord, electrical tape and plastic shopping bags, condoms have also been successfully used (two condoms tied for a total of 5 wraps - make sure the knots don't slip out).
Remember; Always practice safe BASE!!!

BSBD,
Dwain

[Dwain]

>BTW, Craig.....you DO have something to
>show for your 120' f/fall
>- your life. Juicy story
>though!! Thanks.

Hey Gary,

How about relating YOUR juicy story? That would make for some interesting reading!!!

BSBD,
Dwain

[base615]

Hi Dwain,

Good post. I used 4 wraps of tape through the bridle eyelet as you've detailed above.

Craig

[base570]

Dwain said...
"While a static line failure does not perform the stage 2 function, it still assists stage 1 and subsequently speeds up deployment. Therefore a static line failure cannot be equated to a freefall BASE jump (unless the static line fails just as the jumper leaves the object). You generally will open higher with a static line failure than with a go'n'throw freefall"

Hey Dwain, we have a term for that. We call it a "freefall assist". Someone said it one day and it just stuck. Thanks to everyone for all of the good info. I guess, The more you know the lower you can go... Hey that sounds like a "nugget"!! Tom, since Thanksgiving is coming up in the states I bet you won't have any trouble finding a fat tukey to use in your test drops!!! Stay safe, Jason

[guest]

Dude,
I did a 120 Cliff (d-bag) and it scared the heck out of me, I would never freefall that low and I will never again even d-bag that low.

Ken

[guest]

buy a roll of waxed tack cord from paragear or someone else, it has a breaking strenght of 80 lbs. I've used it quite a lot with good results. Only one pass of it will do, but do tie a good knot that will hold, that's quite important.

Ken
BASE 536

[guest]

Thanks everyone..... what a lot of info on various testing given over the last 24hrs. Priceless.

Dwain, I didn't think you remembered THAT story with MY face.... I did post a while back in the archives when Nick asked "What's your biggest BASE mistake?" but used a psuedo. I'll start another thread and tell all.

Thanks again all of you! - G.

[guest]

Funny, Last time I saw electical tape properly used was when I was wrapping wire nuts on an electrical installation. I did not know 3m was crossing over to the rigging industry.
I have a hard time believing that with stuff like brake cord available, which is designed and tested specifically for static line aplications, one would choose to use a completly unsuitable and unreliable medium like electrical tape.
I guess if you all insist on reinventing the wheel
so be it.

Brian Choppin

[guest]

When people started BASE jumping they were using gear designed for skydiving, I guess all the original pioneers weren't trying to re-invent the wheel then?

Craig