42" PC From 300'?

[Zennie 0]

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?

- Z
"Always be yourself... unless you suck." - Joss Whedon

[hookitt 0]

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.

My grammar sometimes resembles that of magnetic refrigerator poetry... Ghetto

[Zennie 0]

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.

- Z
"Always be yourself... unless you suck." - Joss Whedon

[hookitt 0]

Did ya catch my edited version?

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

My grammar sometimes resembles that of magnetic refrigerator poetry... Ghetto

[TomAiello 25]

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.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[brits17 0]

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.

_______________________
aerialkinetics.com

[CrazyThomas 0]

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

[Faber 0]

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

Stay safe
Stefan Faber

[SickMonkey 0]

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.

[Lee846 0]

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'.

Between two evils always pick theone never tried

[jkbasejumper 0]

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.

big country
base998

[3ringheathen 0]

Quote

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.

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

If you have time to panic, you have time to do something more productive. -Me*
*Ron has accused me of plagiarizing this quote. He attributes it to Douglas Adams.

[Ronald 0]

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]

[BASE813 0]

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!

[bps 0]

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

[Skydawg 0]

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

[TomAiello 25]

Quote

... If you toss at under a second you could tow a 42' all the way down.

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

Thanks.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[Skydawg 0]

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.

[DexterBase 0]

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.

Quote

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

Thanks again Dwain!

[TomAiello 25]

Hmmm. Very interesting.

Quote

5.3kg/0.2sec...for a 42" PC
6.9kg/0.22sec for a 48" PC

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...

Quote

at bridle stretch the time taken for the PC to inflate

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

Quote

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".

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.

Quote

A 42" PC at or under one second the Velcro may not peel

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

Quote

and if you're slightly head down you could find yourself at 2.5 seconds with a PC in tow.

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.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[Perche61 0]

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....