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ok guys, just to clarify I dont have a base number yet (or a Base jump to my name yet) but am working towards this aim.
I was unsure whether to post this in the rigging section but it is more appropriate in the Base specific forum I think..
My question is something that I am slightly confused and very curious about and I'm hoping some experienced folks can answer it for me :)

How do you make the best PC selection for an object?

and also, why is is not safer/better to jump with a big PC all the time?? say 46inch (or larger if they were made?!)

Surely this can only help in extracting the canopy from the container? and give less chance of a PC hesitation?

Or is there extra turbulence or other problems associated with jumping a large PC?

To emphasise!!! this is a question!! and not a statement as Im sure the base community knows a lot better about this than I do. Im just very curious really. cheers

http://www.dropzone.com/...rum.cgi?post=1532537

Is a good start. If you search the forums you will find some of what you are looking for.

It will probably extract the canopy more quickly. What would lead you to believe (and I say this not to question your intelligence, but to suggest a way of thinking about these things) that extracting the canopy as quickly as possible is always a good thing? And that it comes at no cost?

Large pilot chutes don't necessarily provide more immediate drag -- they take a moment longer to unfold. Even if they did, or when they ultimately kick in, extracting the canopy too quickly leads to all sorts of ugliness, much of which can be traced back to distortion in the packjob as it's extracted. It's called a deployment sequence for a reason -- doing it all at once does real damage to performance.

This thread also contains some valuable technical information:
http://www.dropzone.com/...?post=132408;#132408

 
I am confident that any manufacturer's FJC will explain all those questions to you thoroughly, and instruct you in properly selecting components for a jump. Tom A also has a very good course that explains PCs.

I jumped with nothing but an unvented 42" PC for the first 70 BASE jumps i had, that includes big walls, 2000' As, a 180' hand held free fall, 70 is not including a ton of bandit loads.

I did have a dagger 222, so it was a leightweight small parachute in a Warlock, so i would use a 42" pc again off 180'. it was no problem for 3 jumps.

There are several charts floating around (example). My favorite is the one Nick DG made when he was working at Basic Research (the one with the little skull and bones for "bad idea"). Anyone have a copy they want to post to this thread?

Remember that any chart is just a guideline. Proper training and experience are necessary to truly foul things up.



Short answer: You can create problems by using too large a PC, just as you can by using too small.

There ya go !

Wow, I haven't see that for a while . . .

NickD
BASE 194

i used to have a chart that referenced the delay in seconds when selecting a pilot chute, can't find it but i did run across an article on the Australian BASE forum by Dwain Weston that has some of this information. if you go to http://www.basejump.org/ you will find it under articles.

i really like the happy face chart...hadn't seen that before.

It's interesting that Tom's chart recommends a 42" AV at 300ft and Nick's chart shows the skull and bones for this choice and recommends a 48".

Yes, all the charts vary.

Notice Tom does NOT recommend stowing a 46, yet this is common practice in some circles...

Nice info...Thanks. Your right...I had not really thought about the negative factors involved in making the deploymennt sequence too fast..Im starting to see the light on this now

To all other posters...many thanks for your input and guidance. and to the poster of the smiley chart..nice one

To whoever mentioned that I would learn this on my FJC. Yes, Im sure I will learn a helluva a lot about staying alive in this sport on the course, but I've always been very keen on reading a lot around any subject that interests me. Especially when it's as serious and risky as base jumping!!

Please keep the info coming guys. Very impressed with the depth of knowledge and guidance in this forum..

Of course I would expect their opinions to vary, but I was kind of surprised to see them go from one extreme to the other like that.

One thing none of the charts mention is canopy size.

A couple of very experienced jumpers came over here to help me open a new 300ft. A a couple weeks ago. They both had 42s and decided to take PCAs. because of it. One guy said he wasn't comfortable freefalling it with a 42 because of the weight of his 315 sqft canopy.

How much does canopy size/weight play into your decision on which pilot chute to use?

I thought it would be obvious, but I guess its not.

These charts (the skulls one I did in about 1992) are snapshots of what we thought at the time.

All knowledge is fluid . . .

NickD
BASE 194

Some thoughts to echo Nick:

1) Times change, and so do our best guesses. Anything written down was written down at a particular time, so what you're getting is a slice of one (or a group of) jumper's thinking at one specific time.

2) Any chart, handbook, guidelines, or internet advice is just someone trying to help. It's not a comprehensive guide to what you ought to be doing out in the real BASE world. You get to decide that for yourself, and if you're in the habit of strictly following charts to make gear selection (or any other jumping) decisions, I'd recommend you stop that at once, and start thinking for yourself.


Tony, on that 42/46/48 question:

1) Remember that manufacturers rate the sizes of their PC's differently (so, for example one "42" might be unsewn, and one might be sewn, one might be the measurement of the fabric, one might be the dimensions of the shaped PC), so a "42" isn't always a 42. The people who best know the actual performance of any specific PC are the manufacturers of that specific PC, so whenever possible refer to their chart, which was constructed with the performance envelope of their PC in mind.

2) In general, in the last 10 years, I think we've discovered that smaller PC's actually work significantly better than we thought, especially in that they hesitate noticeably less than larger PC's. The general trend appears to be away from gigantic PC's (anyone else still have an old Dennis McGlynn 52"?), and also toward PC's that are better engineered to inflate and pull well (rather than just throwing a bunch of fabric out there).

3) My experience has been that the difference between a 220 canopy and a 280 canopy only amounts to about a maximum of perhaps 20-30 feet on an ultra low style go and throw deployment. In general I think this isn't a good trade off for making the (usually immediate, and often without a good set-up for flare) landing on the smaller canopy.

4) In the ultra low realm, my opinion is that the technique you use to fold and deploy the pilot chute is significantly more important than the size of the PC (for example, from 200', I'd rather have a well thrown, handheld 42 than a stowed 48, all else, equal, and regardless of canopy size).

Hwy Tom. I think you were just making a point that well thrown hand held is better than stowed, but wouldn't you rather have a well thrown hand held 46 or 48 for 200ft?

I was also trying to make the point that I thought the preparation and deployment of the PC was more important than the size difference between 42 and 48.

At 200', the thing that will get you isn't the slower opening--it's inconsistencies in the opening. My strategy at those altitudes isn't to try for the fastest possible opening, but rather to try for the most consistent opening. If I could somehow eliminate hesitations, I'd trade that for some extra altitude that was sometimes there and sometimes not.