Hey dirtbag, in aint theory. it is fact..feel free to contradict me in this public forum or private,.witnessed more base deployments than probaly any one else in the world. Aint no voodoo to it..example; After the strike at petronas due to an orbital pc/ linetwist , they checked all competitors, their pc attatchment point symmetry,if you donīt believe me thatīs okay, but state your source of knowledge to be credible. I welcome any challenge that advances the sport..
Check out video 2. exactly as I predicted? lucky guess? or experience? simple symmetry is a science as is all skills for base. "Hey everybody wave your PC in the air,hook it it up like you just donīt care, and eat the object an say itīs unfair, cause you just didnīt take the time to care..."
take care,
space
>Keep in mind that many theories are more voodoo
>and if it aint broke, don't fix it in nature
>than the products of good science.
>
>Common sense and choosing your Yoda's carefully
>is the best insurance.
>
>Anything that contributes to body stability and
>symmetry can't be too bad.
:o :o
Hi Tom,
It works like this; phase #1....pc attachment; use the reinforcement tapes to confirm symmetry in these steps. 1. check north with south, 2. east with west, 3. east with south (as an example).from my experience, more than one cm difference can be very decisive on stability.phase #2....Since a PC has a pulled down apex, it inflates from one side, so the symmetrical attachment must be solid.. or it will slip and start orbiting..
normally one can relate the twist in the bridle to the direction of the off heading assuming no sleeve is used.
make sense?
kick back anyone..
take care,
space..
>Hi Space:
>
>Could you describe what is meant by "assymetric
>attachment" of the PC?
>
>Are we talking about getting mesh pinched in the
>larkshead? Or larksheading in part of the
>centerline? Or letting the larkshead slip down
>to the side of the attachment loop?
>
>I guess I'm having trouble visualizing how
>assymetric attachments happen, and why they are
>so common.
>
>--Tom Aiello
>tbaiello@ucdavis.edu
Thanks Space!
It makes a lot more sense now.
I tried hooking my PC up assymetrically on purpose and towing it down the street. It oscillated like mad (although my best symmetric attachment still wobbled a bit, too). Can't wait to get my A-V PC's from Adam and try it with them.
Thanks again.
--Tom Aiello
tbaiello@ucdavis.edu
>After the strike at
>petronas due to an orbital pc/ linetwist , they
>checked all competitors, their pc attatchment
>point symmetry
In my experiences/opinion oscillating or orbiting p/cs contribute to a large percentage of offheading openings. The bridle not being perfectly centered on the p/c load tapes is a major cause (aside from bad p/c design or construction). Ive reviewed thousands of jumps both in person and on video and done some tests with statistical analysis and come to some pretty convincing conclusions (in my mind anyway).
One example (of many): During the Petronas event the offheading on the first object strike was clearly due to an aggressively orbiting p/c that resulted in line twists and a 170-degree offheading. Inspection of the gear showed that the bridle was attached to the p/c load tapes well off center. Anne and I then inspected everybody p/cs (about 130 rigs were at the event). Out of that 130 we found maybe 25 p/cs which were significantly attached to the bridle off-center. I asked every single jumper if they had used that rig since they attached the p/c, and if so what was the heading on opening. Nearly all of those jumpers who had used the rig replied that they had an offheading of 45 degrees or more.
Also every single jump from the Petronas (about 570, nearly all in the 4-6 sec range) was reviewed on video (shot from a top view). Time and time again we watched oscillating or orbiting p/cs clearly turn the canopy as it lifted it to line stretch. If the p/c pulled or rotated to the right then the canopy nearly always opened offheading to the right and vise versa. I dont think anybody had any doubts as to the potential effects of oscillating / orbiting p/cs at the end of that event.
This is not to say that every time a p/c oscillates or orbits that the canopy will definitely open offheading. Or if a p/c is stable then the canopy will always open on-heading. There are many, many other factors that come into play which may enhance or be counter productive to the p/cs effect on heading.
It is a well-established fact that pilot chutes which are attached to the bridle off center will oscillate or orbit badly. However pilot chutes which are perfectly centered on the bridle are also known to oscillate or orbit on occasion (zp more so than F111 p/cs). This is because the basic principal of pilot chute design is flawed. Pilot chutes are just two circles (a mesh circle and a f111/zp circle) stitched together (known as 2 dimensional design) a really cheap and fast (and nasty) way to manufacture them.
Tandem drogues are constructed in a 3 dimensional shape (i.e. they are constructed in the inflated shape) with vents at the apex and are incredibly stable given the airspeed at which they operate. Round canopies are constructed in a 3 dimensional shape with an apex vent. The earliest versions (pre-aircraft days) didnt have vents at the apex and were known to oscillate badly.
Pilot chutes with a vented apex have been used with great success for a number of years in Europe (I first heard about the idea back in 95 or 96) and finally the larger BASE manufacturers are showing significant interest in this design (and CR has recently started selling them). There were a number of apex vented p/c pilot chutes at Petronas (mostly of French design) and these p/c's were clearly more stable than the non vented p/c's.
The argument against 3 dimensional pilot chutes by some manufacturers is mostly that the construction cost would be too high and the market wouldnt be interested. I personally would be happy to pay $150-$200 (the estimated cost) for a p/c that reduced my chances of an object strike. I'd use the expensive 3D vented apex p/c's on criticial jumps and the cheap 2D p/c's on stuff where heading wasn't as much of an issue (as I currently do with vented apex p/c's).
BTW: One of the reasons for the higher on-heading rate of PCA or static line jumps is believed to be because the extraction point is fixed not moving around as in the case during a freefall deployment.
I am packing toward the tail and I am not doing any 45 degree, just 2 folds.
It works!, I jumped 2 times without any off-heading.
1/ I checked my PC attachment, and the reinforement tapes were not symmetrical, at least 1-2 centimeters off-center. (My PC is rigger made, I ordered a factory one).
2/ For both jumps I thrown the PC not on my right but in a front of me.
3/ Both jumps were done with no wind at all, which was not the case for the previous jumps (left 2-3 knots). I did not mention it because I thought 2-3 knots was not significant.
4/ Concerning legstrap, jumping a Velocity 103, I was already aware and always carefully checked it.
Today, I learned something: I need to attend a training session, any interested coach?
Thanks
Jerome
Switzerland;-)
>Ive reviewed thousands of jumps both in person
>and on video and done some tests with statistical
>analysis and come to some pretty convincing
>conclusions (in my mind anyway).
In your statistical analysis, what parameter did you use to quantify the degree of pilot chute orbiting?
Michael
Hello Jerome!
Here are as follows my 2 cents on the PC subject.
First of all, check that the PC is SYMMETRIC since its manufacturing: this is not so obvious, and I would not make any difference between rigger made and factory made (I could show you PC's made by an Italian rigger (who does not manufacture PC's any more... ...sigh...) that are perfectly and simmetrically manufactured and PC's made by a main factory (no name, sorry) that got reinforcement tapes in the wrong direction). Simply, check PC simmetry and manufacturing, at any time and anyway.
Once granted that the PC is symmetrically made, and with reinforcement tapes along bias direction ("bias reinforced")(ask Tracy for more information about the issue), we do the following (I have been taught by my BASE instructor and mentor and jumping mate etc. etc.).
Do a larks head knot with your bridle comprising all the right tapes (reinforcement tapes and central tapes of PC), start tightening your l.h.k. (larks head knot) but not completely, leaving 2 cm of slack in your l.h.k..
Now, with your left hand grab the r.t. (reinforcement tape) n° 1 (could be any to start with!) and pinch it with your thumb and finger exactly in correspondence of "mesh-cloth" line along the r.t. itself. Now grab the r.t. n° 2 (the adjacent one to r.t. n° 1, in any direction, just keep going in the same direction further on in the exercise!) and superimpose the "mesh-cloth" line of r.t. n° 2 on top of the "mesh-cloth" line of r.t. n° 1. Keep on superimposing the "mesh-cloth" line of all r.t.'s you have got, keeping the tapes same side. r.t.'s could be 4, could be 6, could be 8. Once you have superimposed precisely all the r.t.'s, grab them strongly with your left hand, being very, very careful not to move the "mesh-cloth" line (!!!!!), and with your right hand pull the bridle as much as you can, tightening the larks head knot. After having tightened, make another verification about precise superimposition of all the "mesh-cloth" lines of all r.t.'s on top of each other.
What you have got now is a symmetric PC assembled symmetrically onto your bridle!!!
Stay safe out there
Blue Skies
Andrea #689 :D
This is truly cool!
BASE has reached another level in understanding.
I cannot think of a simpler way to so greatly improve opening heading without inhibiting opening speed. I wouldn't have thought the openings would be so influenced on short delays by the PC attachment symmetry. BTW, Legg says hello.
CU - Chris
Posting Permissions
Reply With Quote
Bookmarks