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A few of us are having a friendly little debate.

We have a very sweet 300' B in our area. I wanted Brit to jump it (congrats on the B ) so I lent her my 46" PC. I had my rig ready to go but with a 42" PC.

I've done several cliffs out west with a 42" and never had any problems, but I was with someone else so I never was able to laser to the talus (will this year heh). Still, I just didn't feel right going from 300' with the 42... even though I have a pin rig.

One friend said a 42 would not have been a problem. And I've heard of people doing a certain 240' span with a 42. Others have said they wouldn't have done it either.

So I'm submitting it for open discussion. Whatcha think? Problem or no problem?

I wonder what friend said to use a 42? Crazy f***er he is.

Nah, just kidding.

I use a 42 at 300. I've used it off a 260 B as well and am quite comfortable with it. I've watched... but don't agree with... a 42 from 210.

If there's any doubt, just use the 46. Try a few go and throws with a 42 from the legal span in Idaho to see how it works for you. You can video tape me in the process.

edit: If the landing area is far away or there's obstacles that effectively reduce the altitude, such as 40 foot palm trees in the meridian, I'd go with the 46.

If you're doing a "throw up" and/or near 0 delay, My preference would be the large PC.

From 300, if it's a clean drop to the street, I'd take a 1ish then pitch. In that case I'd personally use a 42.

Heh didn't want to subject you to potential flameage bud.

These sort of questions are sort of tricky. Obviously if you walk away, you made the right decision. But at the same time, you can't progress without pushing your limits... so long as it's within the sane capabilities of the gear. That's what I'm trying to get a handle on.

I don't have enough experience with low jumps (damn 1700' elevator towers ) to make what I felt was an informed decision. The BR chart indicated that wasn't such a hot idea so I decided to err on the side of safety and then ask around.

Hence the post.

Did ya catch my edited version?

edit.. DOH.. MY.. not me...

Not my first choice, but I'd do it without too much worry if that was the only PC I had.

I think there is room for some serious research into PC's. At those kind of moderate altitudes, the 42 will likely inflate faster, but pull slower, and it might actually turn out to be a complete wash.

I think that the BR chart and manufacturer's recommendations place PC sizes with delay times so that it should be undisputable for all.

I'm sure with a proper 1-1 1/2 sec delay a 42 will be just fine. However, like I was saying yesterday, I've always been one to not press anyone past their comfort zone in a sport such as this, including myself. For my first 300, surely I was not going to use a 42. Although I was determined to take a lil delay, I had never experienced an object of this height and wasn't 100% sure of what my reaction time would be. Better safe than sorry.

I remember reading on BLINC some stuff that was posted about this type of subject.

Something about Throwing Up! .
And no SickFlicka, it is not a bunch of vomit picks.

Something to the tune that one must also factor in the size of the canopy in use. A light female jumping a 205-225 might get away with using a 42" PILOT CHUTE FOR HER BASE RIG, where a heavier built guy jumping a 310 may run into some interesting ground rush because the PC doesn't have enough force to lift the canopy off of the back.
I think Mr. Aiello's son has posted some stuff on BLINC before about this also. I do believe there is a chart or two floating around out there about PC size, and how much force it generates given the delay taken.
Someday I may get motivated enough to find that also.


Thomas

i posted no problemo,i use my 42´zp av pc all the way down to 250ft if its a clean drop.

Last time i were in UK,a freind of mine used my 42´zp av pc from 230ft whith a velcro rig and an unvented canopy he took aprox 1 sec delay each time(4 jumps total if i rember correct) no problems at all.

however i use my vented zp 46 below 250ft and an unvented(to prefere)45 below 200ft freefalls or SL(i have done "serval" 180ft freefalls whith the 46´zp av pc whith out any problem.

I jump a Wertex containing a fox 265 vtec,multi and 5th line mod(no vents/valves).

Congrats whith the B,Brit

My crew and I did a 290' 'B' the other night , two with 42" pilot chutes, one with a 48". All three of us had plenty of time under canopy and no real pc hesitation. Then again it was only one jump, so what do I know.

I voted "no problem"...
I usually jump from low object (270', 300', 360') with my 42" AV PC. It works good. We've made several 2-way jumps from such objects (300' and 360'). I was the upper and made 0,5 or 1 second delays with 42" PC and the lower jumper made 2 or 2,5 with 48".
I have 2-pin rig, vented canopy and vented ZP 42" PC. The second jumper's gear is 2-pin rig and non-vented canopy.
I like this PC and I use it for all sub-terminals delays.
And I haven't any problems with it jumping 2 seconds delay from 300'.

i have used a 42 on 270 "A"s before and had no trouble.but of course if i had owned a larger pilot chute at the time i would have used it just for ease of mind.

 

That's the general consensus amongst our collectively low to moderately experienced local crew.

I've gone hand held from 250 and still had roughly eleven seconds of canopy flight with a Mojo.

There may very well be a difference in average opening time, but so far I haven't been able to *perceive* it.

Maybe some experimentation is in order over memorial day weekend?

Can I borrow a rig?
In the name of science, of course.
-Josh

I have done several jumps from 300 feet with a ZP 36 inch, hand-held and BOC. No problems, always under a flying canopy after 4 seconds, giving at least 10 seconds canopy ride.

I only used a 48, 42 and 36 inch PC sofar in my base career. Not according to the manufacturers book, but then, they have an interest selling lots of PC's.

Ronald Overdijk

[www.liveskyproductions.nl]

it would also depend on canopy size and container closure method - a guy jumping a pin rig with 220 canopy may bee cool with jumping a 42 at sub300 but a guy with a 310 velcro closure perhaps would not be as cool.

I have taken a 42 from around the 220 mark - and too be honest I beleive a 42 can yeild more consistant initial inflation. But generally I jump a 46 below 250 - well I used to until my forced vacation!

Hello --

This is a very good subject and one that I've been pondering on for the last couple of years.

In the Utah desert, I've noticed a growing trend of jumpers using a 42" PC at progressively lower and lower heights. (down to 210ft)

Can a 42" ZP work at low altitudes? Yes. But what scares me is that many jumpers out there will take that statement at face value and will blindly huck themselves off an object with a "42" Pilot Chute" without analyzing all the variables.

How much pin tension do I have?

How tight or loose is my velcro?

How am I deploying my pilot chute and how is it folded in my hand (or stowed i nmy BOC)?

What is my field elevation (believe me, this can make a big difference when you are at higher altitudes)?

Am I jumping with a strong tailwind (as often is the case on an antenna)?

Is it a 220 or a 310 lifting off your back?

Well heck, if a 42" works fine, why wouldn't my 40" PC do the job equally as well?

Who manufactured this 42" PC? (pilot chutes from different manufacturers often measure differently when compared to one another -AND- the amount that the apex is pulled down from the centerline can greatly effect inflation times)

And the list goes on and on.

In my limited experience, I feel as if I get a cleaner canopy extraction and inflation with a 42" PC (when compared to a 46" PC), but I cannot prove this on video yet and this is just how it "feels" to me. However, I pretty much always use a 46" PC on all jumps under 300ft as I am not yet convinced that a 42" is the way to go. (with all the variables involved)

I'm very interested in hearing other's opinions and as jumpers continue to push it further and further, we'll undoubtedly learn more.

Bryan

48/46" depending if its a go and throw or not... If you toss at under a second you could tow a 42' all the way down.

A 42" PC at 1 second only develops around 5.3 kg's drag.
A 46" 6.3 kg's
A 48" 6.9 kg's

This seems quite counter-intuitive. Can you elaborate on what leads you to this conclusion?

Thanks.

I guess it would be to do with how fast the PC loads the rig, or "snatch force".

At 1 second an average jumper is travelling at around 9.5 m/s and the t(L) time over which the load is initially generated is around 5.3kg/0.2sec (at bridle stretch the time taken for the PC to inflate) for a 42" PC compared to 6.9kg/0.22sec for a 48" PC. Therefor generating an extra 1.6 kg's drag over roughly the same time.

The drag builds comparatively slowly from this point until at 4.5 seconds (295ft) the drag is 97Kg's for the 48" and 74Kg's for the 42". Most interesting though is at around 2.5 seconds (97ft) the drag is 39Kg's for the 48" and 29Kg's for the 42".

Experiment :
Velcro rig suspended flap down (new Velcro), 5.3kg weight tied at 1ft on the bridle with some break cord and a large tandem sized rubber stow (to simulate the time load 0.2ish seconds). Drop the weight.
I found that 22 times out of 100 the Velcro did not peel or peeled partially.
I then did the same with 6.9kg's; The Velcro peeled 94 times out of 100.

I then loaded the closed rig with 30kg (slowly) and it peeled every time, but when I angled the rig at a 45' it didn't peel.

Conclusions: A 42" PC at or under one second the Velcro may not peel and if you're slightly head down you could find yourself at 2.5 seconds with a PC in tow.

Here's part of an email I got from Dwain. It's referring to larger PC's but if you read the whole thing it really sheds some light on pilot chute sizes for low altitudes/ airspeeds. Check it out.



Thanks again Dwain!

Hmmm. Very interesting.


What kind of apparatus did you use to measure these numbers? Maybe i'd better go break out a spring scale and start dropping stuff off the roof...


This may be a bad assumption if the jumper is using an upward PC toss. In that case, the numbers could be significantly lower.


Do you know where the drag ought to hit 10 kg? I've never seen any rig measure more than 22 pounds of force to open.


I'd definitely agree with that, based both on personal observation, and on what you've said here.


I'm not sure about the 2.5 seconds, though, as the 39kg you measured (calculated?--not sure how you generated the numbers) is going to be far more than is needed to open a velcro container.

I think that the really important thing to take away from this discussion is that velcro ought not to be used for ultra low freefalls. Since a pin can be adjusted (for example by using spectra loops) for very low tension, you can minimize the (very early) container opening hesitation, which will save you a significant amount of altitude lower down.

42 will be fine, take a second delay or if you have the gonads, take two, and all will be fine if you pack properly, as most of my jumps are from this sort of altititudeless.....if you know what I mean...

Base # 536

Refer to Vertigo's alti-dist chart and it will be no prob...I have the chart if you need it....

dragging up an old post.

I was in a discussion the other day, and was looking to see what others think.
two jumpers. one jumper is 160lbs and jumps a 260 BlackJack, the others 200 lbs and jumps a 305 Troll.
300' A clear LZ
going stowed, what PC size would you use?
42" vented for both? 46" vented? or other?
and why?
would size chute and body weight as outlined at that height change your decision?



Yes, I am the 200 pounder that jumps that big as chute and I like my 46.
But our conversation lead to another opinion that if I used a 42" it might be the better choice. so looking for other thoughts.

Why do you feel body weight has anything to do with it? If you weigh more than the canopy then extraction to line stretch will happen at the same rate, whether you weigh 100lbs or 300lbs.

I jump a 308 and have stowed a 46/48 before, but why would you have to stow from 300?

I personally always like to error on the side of caution and choose a bigger PC when unsure, but there will always be critics of stowing bigger PCs.

I used to regularly go 42" stowed from 300' but had a couple of 90's that were a bit close so I've switched back to 46 stowed. With a clear LZ I would go 46" un-vented because heading performance is less of a worry. P.s. I always stow just before I jump and not the night before... seems to make a noticeable difference for me.

Body weight was a question we had since on e at terminal weight should not matter but starting with no speed a denser/heavier mass will accelerate At a faster rate (at least to my physics knowledge). So at low height a two second delay in therory should have two unequal masses/densities at different heights. Or I am truly off base and would love to hear from guys with much more real experience then me.
To answer the other question of why stowed? 99%of my jumps r hand held but I find I have better control over pitch timing when stowed and I recently found a jump I didn't want to go HH on due to NEEDING the delayed pit h

Mildly edited .... Did not mean thermodynamics. That was auto corre film on iPhone. Rest of question? ? ? If still "say what" then I am probably mentally masterbating the question too much

Larger jumpers have larger canopies. If all else is equal, larger canopies weigh more and may require more extraction force (to move their larger mass).

John, in your case, I'd stick with the larger PC. I've seen 300+ canopies experiencing noticeably slower extraction at low airspeed. The difference between the 2 jumpers in your case may primarily be caused by the difference in canopy weight.

This is one of the cases where I'd be interested to swap in an ultralight canopy and see if you can notice any difference.

thanks Tom

Exactly, Tom. So my point is that body weight has nothing to do with it, canopy size does, which is why I asked without just assuming.

OP:
You are not connected to your canopy until it gets to line stretch so weight is not a factor until you are suspended from it. Human density wont change your fall rate enough to notice on a 2 second delay.

And for the record, I'm 210 lbs. I used to jump a 260. Now I jump a 280 and a 308. I open at the same place I always have on all three canopies from 250 feet because the weight of the canopy doesn't change enough to make a noticeable difference compared to the drag of a 48" PC.

Are any of them light or ultralight canopies?

The biggest differential I've seen is on low airspeed (0-1 seconds) deployments using standard weight canopies and 42" PC's. The standard weight 300+ canopies seem to be extracting slower than the smaller standard weight canopies, and the difference is enough that I can notice it.

I notice it when I have a delay of less then two seconds and use a 42. But not with the 48. and not with delays of more then 2 seconds. The Flik 308 is first generation light. It still weighs 2 lbs more then the 260 did.

After 1 second you fall at roughly 20 mph. At 20mph my 48" creates over 20 lbs of drag (cheap spring scale). My heaviest canopy weighs just over 12 lbs with the lines stowed. So a difference of 2 lbs isn't going to make a noticeable difference as I continue to accelerate away from my canopy that is being suspended by a 20+ pound opposing force.

Right? I think we're on the same page here.