Basejumper.com - archive

Hello everyone.

Recently i had to replace my good old Adrenalin pilot chutes and i've decided to try out some pc build by a local rigger.

The sewing seems better than the adrenalin pc's but i've noticed some differences on the top vents: the vents are bigger and uses the same mesh as the bottom skin(while adrenalin uses small mesh for the vents).

Another difference i've seen is in the number of "load tapes":

Adrenalin 38' : 2 load tapes (the pc have 4 "slices")
Custom 38': 3 load tapes (the pc have 6 "slices")

Adrenalin 46': 4 load tapes (the pc have 8 "slices")
Custom 46': 3 load tapes (the pc have 6 "slices")

Ok, these are the questions:

1) The only down side of a bigger vent is less drag ?
2) Is there a reference about the relation between pc dimension and vent dimension ?
3) AFAIK the load tapes are there only to prevent distortion, how can i evaluate if the "3 load tape" configuration is correct ?
4) what else should i look at to understand if the pc is good or trash ?
(I've read a post from base283 where he speaks about "bias" and "block" but i didn't fully understand )


Anyway: these are only speculations because jumping them i didn't feel any difference.

1. Correct

2. The bigger the PC the less venting.
The smaller the PC the more venting.

Former are used with short delays
hence very minimal air speeds.

Latter are used with longer delays
hence more air speed and air flow.

3. Yes, loads tape help prevent distortion.

4. Symmetry - all seams equal length.
Stitching - none missing or bunched up.

RE: Block and Bias

You know how you can pet a dog two ways??
One way feels good to your hand and the dog
and leaves the fur smooth. The other way is
wrong, it feels weird to your hand and to
the dog, makes the fur look like "bed head".

Ripstop nylon has little lines in it that make
me think of graph paper. Here are 2 links:
http://www.challengesailcloth.com/warp-fill-bias/
https://en.wikipedia.org/wiki/Warp_and_woof

If you pull ripstop one way it stretches a lot.
If you rotate it 90 degrees and pull again it
will retain its shape much better.

I take it you know your local rigger, so why wouldn't you get him to answer these questions not only before you buy it but before you jump it? It is such an important part of your setup

Ciao Spector,

Here are my opinions. Be sure to think things through and form your own opinions, though.


It depends on the location of the vent. A large vent placed at the apex of the PC can vent air during the inflation process and increase the hesitation rate.

In theory, the drag issue can be fixed by simply enlarging the PC to compensate for the surface area lost to the vent. In actual practice, I don't think it matters much, because the vent area is so small as a percentage of the total drag production area.



Every manufacturer does it differently. Compare the vent size on an Asylum 46 (largest vent in common manufacture) and an Adrenalin 46 (smallest vent) and you can see that the manufacturers have very different answers to that question.

Personally I prefer a smaller vent, or no vent at all, or best of all a ring vent, on large PCs for short delays, because I think it helps the hesitation rate.




Check to make sure the tapes are running down the bias of the material.

The "3 tape" configuration is often used because it gives an anchor point to match to the bottom skin tapes (the large hole mesh most manufacturers use for the bottom skin has three directions of bias because it is hexagonal, rather than square).




Length of center line: Center line should generally be slightly longer than the bottom skin tapes on most common PC designs in use today.

Correct placement of the tapes relative to the bias of the material.

Symmetry of the tapes: (Video here)

Vent style and PC materials (Videos here)




I'll add a video on that topic to our list and try to create one. It's a LOT easier to understand with a diagram and video than just words. Pictures really do make that much clearer.

Hey spector look at an inflated 2 tape PC and look at an inflated 3 tape PC. Big diff. 2 tape PCs are old shit. I was there. The 2 tape one you have put it in the dustbin. Ans do yourself a favor buy a real PC get a toxic.

Tom, what is a “hesitation rate”? I Should you giving us information on inflation speeds and drag production of PC? Hesitation rate means nothing in base or flying or even really physics in this context so im confused by that and it doesn’t seem like info anyone can use. Also your theory on air escaping through the apex vent and delaying inflation is based on what?

Again how does a ring vent help a hesitation rate and what is a hesitation rate? This is getting more confused.

I've tried to get trough this "bias" thing.

On an Adrenalin 46' i have 4 tapes (that divides the PC in 8 "slices").

Of these 4 two of them are parallel to the wave of the mesh while the other two build a 45° angle with it (obviously).

If I understood it correctly this should work fine because the load tapes must be placed at the bias but not only.

I've also tested the deformation of the mesh, i will ad some pictures as soon as i get home.



Of course i will

I hope that if we clarify it here it could be useful also for others!


I think that with "hesitation rate" Tom means the probability of a hesitation, i don't think is real physic number.


To me it makes sense...

I don't know if a "cap" on the vent would help somehow but for sure using a different (smaller) mesh would help.

Thanks!

up north in below freezing jumps, ZP can get a bit stiff, and if the vent is too big inflation can be slowed a lot!

something to think about, most common in packing warm area then leaving the rig in the car a long time... quick fix shake the PC a few times before jumping, or non-vented or toxic for very cold days.