why not 100 inch PC's ?????

[cesslon 0]

forgive my lack of knowledge on this subject.

I know there has been debates about the diff between 48 and 50inch PC's etc

but what is the reason people dont use some massive size PC off very low objects ?
is it due to once the main is out the large PC would be pulling the main out of shape or some other reason ?

[SullyFlyer 0]

I like discussions like this. As an engineer, I love coming up with an idea that seems crazy. Then, as a group we can bring it back to reality.

I think this big PC of yours would take too long to open. Then it would take a lot of pressure to hold it's form. And, you're rite, it would ancor the canopy real good

The biggest reason is that the 48 does the job, and why f with a good thing.

Tom, what do you say - wanna try it over water?

PCs may be the most important part of gear and discussions like this may prove very helpful.

~
Fear is the thief of dreams...

[TomAiello 25]

I've made jumps on PC's as large as 60". At one time, larger PC's were pretty standard.

I think the main problems are what sullyflyer explained. Bigger PC's take longer to open, because there is more fabric there. They are also more prone to hesitation. There is some point of diminishing returns where the extra extraction force can't make that up, and you end up with a slower overall opening. There is much healthy debate on where this point occurs, but I've heard knowledgable jumpers putting it anywhere between 38 and 60 inches.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[460 0]

And a super enormous pilot chute will damage the bridle attachment point, in addition to pulling your canopy terribly during flight. Imagine having a huge anchor behind your canopy. No forward flight in your ram air, hence no ability to properly flare.

Looks like a death sandwich without the bread - Steve Deadman Morrell, BASE 174

[NickDG 23]

When we used Hank's 52" (the bomb drogues used in Vietnam that Para-Innovators built) we'd throw pilot chutes like they were hand grenades. Then (after cheap video was invented) we found deployments would follow in the same direction depending on how hard you threw all that heft.

No matter though, in the future we're all going mortar deployed. I want to be the first to cock, jump, and fire . . .

NickD BASE 194

[NickDG 23]

>>I think this big PC of yours would take too long to open. <<

Sometimes this can work to your advantage. Not to the 100-inch stage of course, but at some sites, if you're trying to maximize freefall time and it's low, you can get the deployment under way sooner, but still look like Joe Delay.

NickD BASE 194

[jalisco 0]

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>>I think this big PC of yours would take too long to open. <<

Sometimes this can work to your advantage. Not to the 100-inch stage of course, but at some sites, if you're trying to maximize freefall time and it's low, you can get the deployment under way sooner, but still look like Joe Delay.

NickD BASE 194

Just so's nobody gets the wong idea, you do mean that the person is not actually taking a longer delay -- it just looks like they took a longer delay because the pc takes longer to inflate, right?

[DexterBase 0]

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Just so's nobody gets the wong idea, you do mean that the person is not actually taking a longer delay -- it just looks like they took a longer delay because the pc takes longer to inflate, right?

Wrong.

Define delay. I think of "delay" as the time between your feet leaving the object and the moment you release the pilot chute, not the time until pins pop, your container opens, you hit linestretch, or you're under canopy.

If you jump and toss the pilot chute after half a second, you took a half second delay. If the PC hesitates for five seconds you still only took a half second delay.

[Skydawg 0]

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At one time, larger PC's were pretty standard.
Bigger PC's take longer to open, because there is more fabric there. They are also more prone to hesitation.

Has anyone played around with the idea of composite PC's, i.e. A number of equally sized vented PC's grouped together with some sort of non-load-bearing mesh holding them together?

[jonstark 8]

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When we used Hank's 52"...
--------------------------

I useda 52 on my first building jump and the canopy was a small 5 cell Kestral. It sure handled weird but I was so pumped I just landed it and jumped into the getaway van...

jon

[460 0]

This was done on some reserves, where 2 pilot chutes have been used.

Looks like a death sandwich without the bread - Steve Deadman Morrell, BASE 174

[TomAiello 25]

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Has anyone played around with the idea of composite PC's, i.e. A number of equally sized vented PC's grouped together with some sort of non-load-bearing mesh holding them together?

Not in BASE, as far as I know. There are lots of interesting ideas in Knack's Parachute Systems Design Manual, but I haven't had a chance to play with any of them yet. I'm particularly intrigued by the idea of an annular (donut shaped) PC, and the idea of a PC built to spin, and mounted on a swivel.

One day, perhaps, I'll have some time to play with it...

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[Faber 0]

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In Reply To
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Has anyone played around with the idea of composite PC's, i.e. A number of equally sized vented PC's grouped together with some sort of non-load-bearing mesh holding them together?

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Not in BASE, as far as I know

we did so whith Teddy(bear) as we PCAed him off 7th floor.I seems to rember the 2 pcs made 1,5twist compared to Teddy from that alti.However Teddy could have been unlucky as it were the only jump he made(whath did he think of jumping off 7th floor at his first jump).
Personaly im of the same oppinion as Tom.
only time i use a(to me)big pc is as i freefall sub 200ft,at that point i use a 48 above that i use vented 46 and vented 42(slider off envioment)

Stay safe
Stefan Faber

[sabre210 0]

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where 2 pilot chutes have been used.

Anybody who has seen CB's BASE tape 2 will have probably marvelled at some of the weird and wonderful pilot chute setups and experiments Carl, Jean, Phil (x2) and others played around with, including multiple pilot chute deployments, one from each hand.

During their jumps from a particular Canyon, there seemed to be some interesting pilot/drogue configurations, including a jump which consisted of what appear to be an umbrella sized round and a slightly larger (but not by much) freebagged round.

Jean also does a jump with a conventional pilot chute - round main, but holding in her left hand a further drogue which she doesn't bother to deploy.

Can anyone enlighten me as to what the thinking was behind this third chute and what conclusions were drawn. The setup seemed to cause wild oscillations and unpredictable pendulumming beneath the canopy or was that just the small canopy struggling with a high loading???

I would love to hear.

[NickDG 23]

One thing to be said of Carl Boenish (and there is a lot) is his first interest is in filming and he loved goofy ideas involving parachutes. In fact the whole idea for the El Cap jumps in 1978 stemmed from the fact it was a goofy idea involving parachutes and Carl wanted to film it.

The Grand Canyon jumps you mentioned are done at a time when having a 180 with a square parachute was still a big fear so they would jump rounds whenever possible. Especially, whenever there was a water landing.

These are the first (WAD?) type jumps. They figured all they needed to do is slow down enough to survive a water landing, so they hand held 16-foot round cargo parachutes, sometimes two, and it made good film footage. Carl had a thing for multiple canopy shots since he filmed the Gypsy Moths back in 1969.

If you have the same version of the Grand Canyon jumps I do, and you look closely, you'll see Carl Boenish almost killed when an overzealous boat driver runs him over while trying to pick him up after a jump. Also Jean, in this film, is still nursing a broken leg she sustained jumping from a plane and landing on a tall cliff in South America (Atuna, I think).

There is also a great video from around this same time of Phil Smith, BASE 1, jumping from a moving train while it's crossing a river. He has small round parachutes in each hand . . .

NickD BASE 194

[sabre210 0]

Nick

Now i'm not sure as i don't know US geography as well as I perhaps should, but the canyon i'm referring to is somewhere in your legal Cliff playground site. Anyway, this later footage shows them freefalling the cliffs into water , doing what seem to be very solid delays and using these various dubious mini parachute/pilot chute configurations. Yes Carl gets run over by the boat and there's some mud wrestling bonding going on with the boys. BUT.... Jean also jumps wearing what can only be described as a lurid blouse and bright red skirt.

I guess goofy is the right word.

edited to a/ get my facts right about the footage, b/remove a site name even though it's legal c/ explain why i edited my first post and d/ correct my spelling mistakes

[jimmyp 0]

One dramatic disadvantage to a larger pilot chute is the amount of drag on the center cell once the canopy is flying. For instance, with a 222 sq. foot canopy and a 52 " PC, the canopy end cells will begin to outfly the center cell and create a stalling situation. This is especially pronounced when you go to flare and slow down the forward speed of the canopy, reducing the pressurization of the canopy. This is especially dangerous because it usually causes the canopy to collapse at about 10-20 feet off the ground. So if you are going forward with any of these experiments, do it over water as suggested!
There is definitely too much of a good thing and too much pilot chute is bad. Over the years, the BASE community has pretty much figured out what size pilot chute works best with what size canopy and delay. These numbers are not arbitrary but a result of many years and many people testing different configurations.
Jimmy P.

[Skydawg 0]

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I've made jumps on PC's as large as 60". At one time, larger PC's were pretty standard.

I think the main problems are what sullyflyer explained. Bigger PC's take longer to open, because there is more fabric there. They are also more prone to hesitation. There is some point of diminishing returns where the extra extraction force can't make that up, and you end up with a slower overall opening. There is much healthy debate on where this point occurs, but I've heard knowledgable jumpers putting it anywhere between 38 and 60 inches.

I found something DW once wrote on the subject of 52" pc's;

DW-------

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Regarding 52" p/c's:

There are six main phases in deployments (note: some of these phases overlap in sequence):
Phase 1: Pilot Chute (p/c) is released (via BOC or hand held)
Phase 2: p/c reaches bridle stretch
Phase 3: p/c inflates
Phase 4: p/c extracts canopy to line stretch (there are multiple sub-stages here such as container opening, extraction of canopy from container and lifting of the canopy to line stretch)
Phase 5: canopy achieves bottom skin inflation (there are multiple sub-stages here)
Phase 6: canopy achieves cell pressurization (there are multiple sub-stages here).

The 52" p/c in very low airspeeds will speed up Phase 4 slightly compared to a 48" p/c. However due to the extra weight of the p/c it can slow down Phase 2 slightly. Also due to the extra size of the p/c it can also slow down Phase 3 slightly. So basically a 52" p/c (compared to a 48") will generally make Phase 2 and 3 worse, but improve Phase 4.

The net result of a 52" p/c is still positive, but only small. From video analysis my conclusions were that a 52" p/c results on in a higher opening of maybe
about 10-15 feet on average. Still, if you are freefalling very low objects then this can make a big difference.

I don't really care if I have a 48" p/c or a 52" p/c until my exit height gets below 170 feet. However this is with canopies around the 220 - 245 square foot / weight range. For the bigger canopies (293) I would probably recommend using a 52" p/c for anything under 190' to be safe (I'm just guessing here).

The construction of the 52" p/c is very important. Weight is a critical factor that will slow Phase 2, and to some extent, Phase 3. My 52" p/c does not have any load tapes on the ZP material (as they aren't needed for re-enforcement as the p/c is only used in low airspeeds). Load tapes on the mesh are very important as they limit the mesh from stretching and therefore air from spilling out around the skirt. I have 8 load tapes on the mesh of my 52" p/c (same as the BR 48") and I think it is a good balance of weight versus the amount that the mesh can stretch.

The technique you use for freefalling very low objects is the most critical. It takes almost the same amount of time from Phase 1 to Phase 3 to occur as it does for Phase 4 to occur (about 1.3 seconds on average for Phase1-3 and about 1.5 seconds on average for Phase 4, but this varies hugely from jump to jump). Using a 52" p/c will speed up Phase 4 slightly, but the biggest difference you can make is on Phase 2. If you just throw the p/c to the side it will go into freefall with you. You will then need to fall faster than the p/c to overtake it before it will reach bridle stretch. The p/c won't fully inflate until after it reaches bridle stretch and is being dragged through the air by your body. However if you throw the p/c up when you exit it will reach bridle stretch quicker and the p/c will begin to inflate sooner. The sooner after the exit the p/c becomes inflated and starts doing its job, the better. Your acceleration is exponential, so something done up front which will shave a fraction of a second off the end, will make a big difference. If you throw a 46" p/c up to bridle stretch on exit you will open much higher than if you throw a 52" p/c to the side. The best technique is similar to throwing a basketball through the hoop. You jump up in the air and you throw the basketball(p/c) upwards and forward when you are at the top of your jump. In a perfect ultra-low freefall the p/c should inflate above the exit point and already be starting to pull on the shrivel flap (or pop a pin) when it becomes level with the exit point. In a way it is cheating as you are getting part of the deployment to occur above the exit point. There are other techniques as well that help, such as the forward push on your launch, your body position in freefall (to minimize swing through on line stetch), and the way you release your brakes, but I won't go into them here.

In summary, the 52" p/c will help a little but technique will make a bigger difference. I suspect a 52" p/c may make a more noticeable difference on heavier canopies (eg. Flik293). For you to notice the difference of a 52" p/c over a 48" p/c you will have to be really pushing the envelope of low freefalls. 99.9% of BASE jumpers won't freefall something low enough to need a 52" p/c which is why BR doesn't make them as standard.

Also the glide of the canopy will suffer with a 52" p/c (more of a difference on smaller canopies) so they can cause more problems then good depending on the jump.

If you are planning to freefall some very low stuff then I'd recommend getting a 52" "Big Bertha" from BR.

Also keep in mind that the opening height variability of low freefalls is huge – even when everything else is the same (packjob, p/c, canopy, technique, etc etc). Sometimes you open super high and sometimes you open in the dirt. I've done 13 freefalls from 156' over hard earth and this height does have a small margin for error. On the best freefall from this object I had enough height to pop my brakes and make a 90 degree turn before doing a nice soft flare. On my worst freefall I opened and then hit the ground straight away. Gear and technique remained constant but the opening height varies wildly (I also have about 80 freefalls from under 185 feet with the same results of wild variation in opening height). My point is to not draw any conclusions after just a few jumps. Hesitations eventually will occur during some phase of the deployment sequence so make sure you have some margin for error built in.

Hope this helps,
Dwain

[TomAiello 25]

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So basically a 52" p/c (compared to a 48") will generally make Phase 2 and 3 worse, but improve Phase 4.

The problem I've seen is that the slow down in phase 3 is far less predictable than the improvement in phase 4. Sometimes it's almost no slowdown, and sometimes it's a whole lot. Variation worries me at low altitudes.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com