Basejumper.com - archive

Ok, I usually bug the piss out of Tom about this but I thought I'd put it out there to get some peoples thoughts.
I jump a 285 and a 293. The guy I jump with most of the time jumps a 205 and a 220. Other than the fact he opens higher and his canopy pressurizes faster than mine he for sure has better on heading preformance than I do. Mine is not bad but there is always room for improvement.

Sorry, I forgot to say for 1 second delays and less. More so on go and throws. Anything after say 1.5 second delay and my on heading preformance goes up.

Are the canopies the same model?

Are the containers the same model?

Is the same person packing both?

Is the PC the same?

Body position...

There are just so many variables.

I've always thought there was a correlation between opening speed and on-heading accuracy. The correlation being, the faster the opening the more on heading the canopy opens, limited of course by the shoulder levelness of the jumper. There is some limited data by Tim Harris of a frame by frame analysis of bridge day jumps that clearly demonstrate this phenomenon, and interestingly, highly independent of all other variables.

Smaller canopies - less fill volume - quicker opening.
Larger canopies - large fill volume - slower opening.

Therefore, if the logic holds, smaller canopies should open more on heading than larger canopies.

But this only my 2 cents.

I'm kind of talking in general. Saying all factors are the same. Nothing specific.

I know a bigger canopy needs more air to inflate. What I don't know is if that correlates with heading.

From skydiving we know that heading and size of the canopy does not correlate: you got a model that opens right on in one size and not so good in another either bigger or smaller.

In BASE I just don't know.

Alright, Who says my packing sucks?! You will be taken off my Christmas card list.

I agree.

i did i wasnt on any way

What about wingload? (just noticed that nobody has mentioned it so far...)

Having worked for one of the major canopy manufacturers and looking at what kind of openings people experience on the same model of canopy (but different wingload), I've noticed that this can strongly vary due to difference in wingloading.

Next to that I think that body position, correct pilot chute size for the type of delay and a reasonable packjob have more influence on the heading performance than size of the canopy.

my 2 cents...

J.

I totally agree with that.... Dave
....................

Do the smaller BASE canopies have more consistent on heading openings than the larger ones?

Answer - No

Wingloading also matters, in my opinion.

so back to a question I had in the past...

What are the specialized situtations where a smaller canopy will open faster since you would be W/L it more?

I guess I will also like to throw in a certain 134' cliff jump into water near me

I can't imagine a scenario where it'd be a factor worth considering.
You are assuming that a smaller canopy does inflate faster, which I'm not convinced is true. I asked DW about it once, he said it was a common misconception.
Further, if the jump was low enough for that to be a consideration, you probably should re-think jumping it.
Food for thought: a 260 that's say 85% inflated has more surface area to produce drag than does a 220 fully inflated. If the jump is so low that you wont have time to fly and flare, drag is all that's gonna matter, right?
-Josh

Good Point made

Opinion or fact? You may be right but wingloading as a parameter hides a multitude of sins. It is calculated simply in terms of area, mass and acceleration but it's effect on canopy performance is non-linear so as an engineering coefficient it has about as much use as a chocolate condom. It gives you a flava but it provides no protection (I believe that's original. Royalties required for use.)

Also, the speed of inflation is dependant upon size (unsure if this is area or volume related for the purposes of this discussion - I guess it depends on whther you are considering bottom skin inflation or full pressurization) and rate of inflation. The rate of inflation of the bottom $kin will be proportional to airspeed raised to a power that I can't be bothered to consider right now. The pressurization rate is proportional to relative forward speed (again raised to a power - probably squared but don't quote me today. I can't be arsed to think about it), size of vents and tons of other stuff that I can't be bothered to think about.

Bottom line without thinking too hard...off heading openings due to differential inflation rates are initiated by events / conditions rather than properties so to say that a larger canopy is inherently more prone to off headings is only valid in the context of empirical data from a high level rather than from theoretical analysis (if indeed you have this data and you trust it's validity). I'd contend that fat jumpers with big canopies are just more fucking clumsy.

I'm on vacation for a coupla weeks now so I may do some analysis and try to figure this out. On the other hand I may just smoke some PCP and gnaw my own fucking leg off. Both sound pretty good.

Trust this bores the living shit out of you.

Festive cheer to one and all...

See above.

Seriously, I think the major wingloading differences only start to show themselves at very low wingloadings (say, .5 and under), and are much less important than a multitude of other factors.

I think you're right, Tom (can't vouch for the 0.5 figure) but the relevant factor is related to the ability of the falling body to overcome wind resistance and thereby induce an effective relative airspeed. What the split is, I don't pretend to know. I have a gut feel (like most folks) and since this is based on empirical observation I tend to think it's fairly accurate. I wouldn't use it to predict performance where what happens in the next 30 feet matters since, as you so rightly say, other factors may have the greater contribution. Bottom line...your mileage by analysis may vary resulting in severe death and horrible dismemberment or glory and stardom. Think about that on your next sub200 footer.

My fucking leg is killing me. What's up with that?

 

What? You have PCP and you ain't sharing?? You deserve to have your leg gnawed off, by rabid homosexual baboons

Too late...still have the left one...baboons had to split...address under separate cover...feeling weak...

dude, you crack my $hit up!!!

while that's probably completely true... i'd be willing to bet invisible and/or unforseen wind currents are going to give you many more off heading openings than simple adjustments to WL's... and even the most perfect pack job won't prevent that. just ask the guy who went thru the window.

~E

I'll bet you're right, young fella m'lad...begs the question "how many 180s are voluntary"?

What exactly does a visible wind current involve?

of course i meant "invisible" as the wind you can't see with chalk or toilet paper your letting go at the exit point.

ha, and i'm an idiot, so don't take anything i say too seriously...

~E

someone beat me to a smart ass comment? speechless...

OK, let me see if I have this straight:

the hypothesis is (supported by some observations apparently) that smaller canopies inflate quicker.

this makes total sense from a purely applied mathematics point of view, since:

-surface area is a 2nd order function of linear size

-volume is 3rd order function of linear size

SO,

the bigger the canopy, the smaller the surface area to volume ratio, and since all the canopies' volume has to be filled through the surface areas of it's openings, it's easy to see why a smaller canopy, assuming an exactly scaled down version of the larger design, will inflate quicker

cheers
sam

The inflation rates will not necessarily be the same. Both canopies are subject to some constants which are independant of the canopy size (pilot weight, accn due to gravity, air properties). You said you were assuming an "exactly scaled down version". Does this not imply that due to it's larger openings that the larger canopy could accept air at an increased rate and therefore pressurize in the same time as a small one?

I doubt that the models give you identical geometry either. Why would a 220 stay the same shape in flight as a 280 with the same pilot? He gained no weight for the big canopy. Why should he dangle the same? This lends itself to Tom's wingloading discussion.
The hypthesis as stated is not supported by the observed data. It has failed to be rejected as a result of the obervations. That's a very important distinction.
This is way too heavy for this early in the morning with this big of a hangover.
Maybe I'll dabble in the numbers now that I can no longer walk.

When you look at airfoil inflation smaller canopies may be faster. I think larger canopies may consume less altitude during opening. I was explained that the size of the lower surface of the canopy is important. Initially it is the lower surface that is slowing you down on deployment (once the canopy is flying the lift takes over). So a larger canopy equals a larger lower surface and more fabric to slow you down.

When you look at airfoil inflation smaller canopies may be faster. I think larger canopies may consume less altitude during opening. I was explained that the size of the lower surface of the canopy is important. Initially it is the lower surface that is slowing you down on deployment (once the canopy is flying the lift takes over). So a larger canopy equals a larger lower surface and more fabric to slow you down.
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If the wing loading was the same would the larger canopy still inflate higher? I ask only because we recently jumped an S(sub-200) and both were pca'd. My 277 opened a tad higher than my buddies 244.We just shrugged it off to packing.

Larger canopies are generally inflating over heavier loads (i.e. bigger jumpers). It takes more time/energy to slow a heavier load moving at the same speed as a (theoretical) smaller load. In my experience, this factor (weight of jumper) is the critical one in determining effective parachute height (i.e. not just when it's open, but when it has slowed you down enough to survive impact) at the margin (i.e. in ultra low deployment situations).

I totally agree with you there Tom.

This must be a humorous pole ?
So the Pole say's :
More people think that Smaller square footage of canopy.

Will open.. "On Heading More Often" With more consistency.
than the same canopy of Larger square footage ???

Am I reading this right ?
People actually think this ?

47 % - of people think it's actually a packing problem ?
.

Here's something Dwain once said, that's relevant.
http://www.dropzone.com/...pen%20higher;#360708

Dwain's points are right on the money. Playing devil's advocate, Dwain is not always 100% accurate though, so if there are open questions, they should be openly discussed.

The data that is so relevant in his analysis quoted is really somewhat inaccurate. What we need is 3-dimensional accelerometer data from exit all the way through opening to really quantify the distance and speed versus delay, because I do not believe the results quoted for the time-versus-speed-versus delay, especially as a function of pilot chute, canopy size, wingloading, and other relevant variables in this problem.

Atair Aerodynamics has such a device. They even once offered to loan it out for canopy tests, if such tests could be done from an aircraft, at sufficient altitude and with reserve systems to protect their (expensive) gear. Unfortunately, I was unable to line up the necessary things, and couldn't pursue it further.

yes...smaller base canopies are better on heading.
If jou can controle your body and your mind..
with that nice crosswind shoulders even in the expected airstream.

because the are smaller. the open faster,fly faster, react faster by your input.
to handle this, you have to be verry fast!
thaths wy I have a litlle bit bigger canopy with bottom vents now .
so I expect a faster opening with quiker control on input more flare and glide.
so more on heading for me.

Now I 'm happy, I can make my dreams come thrue.
In a couple of years when I think I 'm faster so that I 'm faster, I maybee buy an smaller one so I a have more consistent on heading openings.......yes I 'm beating time.
less time!
beating time

Yes...mel-t.....are you any relation to ...Faber ?
You are Fast- Fast- Fast....and when your dreams come true your Opening Headings will be consistent
and you will, beating time, less time !, beating time
That thing about " beating time" ?
If Time is Infinite ? Does that mean the Beatings never Quit ???
also :
You need one of those " Particle Accelerator Meters " (that thing Tom is talking about)
I saw one of those on Star Trek the other night.
I don't know how, Atair Aerodynamics got hold of it. I bet Capt.Picard is pissed off.
.
also:
I still see 9 wrong votes in the pole for " YES "
.
.

were all brothers and sisters

I´ll give ya a hug as we meet(hopefuly next summer),then your allowed to belive im even more wrong

Hey Ray,
For me personally, off headings seem to be more of an issue of what container I'm jumping. Might sound dumb but my log book doesn't lie. (Well, maybe on the delay I took) As of now my "Vision" gives me dead on openings most of the time. My other velcro rig and my pin rigs are not as consistant. Again, I'm talking on go and throws or delays of less than a second. I'm still kind of new to jumping pin rigs slider off so my packing and closing of pin rigs may not be up to par yet.
I would guess that the large pack tray and ease of use are the reasons that I get such great on heading preformance when I jump my "Vision".

Or...Dennis is a f#*king genius and designed the perfect rig.

Those old Visions had a Tray that would open up big and clean.
The Tray-bottom was real shallow on the corners to.

I have some thoughts but no proof / and I may not even know what I am talking about.
Very little pin tension -verses- a little more pull force needed to open Velcro.
on low & slow delays. (if you think about it)....Velcro takes that extra fraction of
a second to let the Pilot Chute do its job of pulling the "Folded Pack Job out of Tray."
That fraction of a Second gives - extra snatch force or when it " lets-loose"(releases) - ripping it faster
through the closing flaps of the container.
The -Packed Canopy- is what opens the 4-flaps of your Container.
Not your Pilot-Chute. the "Pin or Shrivel-Flap"- is opened by your Pilot-Chute.
That 10 to 12 pounds of Fabric ripping, up and though the 4 flaps / opens the container.
I don't know, these are just some rambling crazy thoughts from a delusional moron...but you never know.

I just designed and built a 1 pin container system over the last couple months.
A couple months of work/three cuttings... but several years of thought before I even
started to pattern it out, cut and sew.

I seriously have some concerns about using very little pin tension on Very-Low air speed deployments.
I believe there should be a definite "SNAP" of energy when the Pin is pulled from the closing loop on opening.

If the container is OPEN and your Air-Speed is LOW...(think about it)....Closing sequence of CLOSING FLAPS ??

Think about Low - Slow air speed deployments.... Low Speed = low energy

Velcro OPENS /releases, both of the SIDE FLAPS at the SAME TIME..when pulled off.
OK.....now think about the "Closing Sequence of FLAPS" - on a - 1 or 2 Pin Rig.
WHAT - FLAP starts to release the energy of the Packed Parachute FIRST ???
Not an Even release of energy...Not Smooth... At LOW Air Speeds.

>>> WARNING <<< >>> WARNING <<<
(read the above thoughts at your own risk)
.............................................
I have never Owned a Pin BASE Rig but I jumped one about 4 years ago... one time.
so I may not know anything ..and maybe talking out my Ass.
.
.

Thought of a name for your pin rig yet?
~J

i use low pintention(and spectra loops) on many of my jumps,i really rare have offheaddings(more than 10 degrees),i jump a Gargoyle(only about 30 jumps on that one so far but none offheaddings) and a Vertex 1 containing 2dif vented BR canopyes.

i jump in the 0-4sec range slider off

Thats a no brainer.

Velcro rig- "Soft Cock"
Pin rig --- "Hard Cock"

Mel, you're describing parameters associated with heading sensitivity rather than heading accuracy.
Smaller, faster, more reactive will lead to faster offheading openings. Accuracy, or rather minimizing the median angular displacement from the desired opening heading is what you want. A big heavily damped system which opens the same way ragardless of other factors would be the ideal. Starting to sound like a big canopy? Maybe. Of course, heading correction ability is at least as important. If you do open off heading you need a reactive system to give you sufficient correction speed.

What a cunning web of intrigue we weave...

Holiday fun, one and all.

>>As far as I'm concerned, Dennis is a f#*cking genius the Vision is elegant in it's simplicity, and I love how easy it to close without distorting your pack job and the consistent pull force required to open it. Pin rigs scare me but what the hell do I know anyway

Pin rigs scare me too!...
My Soft Cock ROCKS!
~J

So wrong, in so many ways...

>>Seriously, I was impressed with it when I watched you close it up...
I wonder how I can trick Ray into making me one?

Tom will put in a good word eh?
Chicks dig my soft cock(in so many ways)
~J

Ray is focusing his rigging efforts on his new 1 pin rig. After he's got it just the way he likes it, you may be able to talk him into building one. I have one and it's every bit as nice as the Vision it's sitting next to (IMHO).

I think he should call it the Sabot

So wrong, in so many ways...

Dexter:
Ray is focusing his rigging efforts on his new 1 pin rig.
..............................

"Rigging Efforts"
Dude what are you talking about I have never been trained as a Rigger.

The ol Lady is doing a shift in the Lab at the hospital tonight so I am doing a
fourth cutting of the 1 pin rig tonight and putting most of the pattern from paper
to plastic. with CCR cranked to max on the pc.
The fucking thing actually looks like nice Rig. Nice flat and trim wedge.
the Riser Covers turned out "Exceptionally well".- trim & smooth / tracking worthy.

I did a lot of work to work out the pin tension on the 1 pin.
I originally started to cut a 2 pin but said "fuck it" and threw it in the trash can...( 1- pin / less is more.)
A - 2 pin - would have been much easier on my brain to build.
The 1 pin was a bitch to figure out how to contain 285 sq. ft. canopy and (make it look good.) +
with a consistent (acceptable) pin tension when you got it strapped to your back and moving around.

I never owned a pin BASE rig before so I had Spence come over the other night and see it all packed
up. He put it on and checked it out. he said ..."It fucking rocks. make me one."
I got the third cutting packed right now (ready to jump) with a 285 sq. ft. v-tec and I got the
pin tension down to 4 to 5 pound pull / in the flat and stable position.
If you are.... Stalled-out, on your Back, Head-Down and Kicking & Screaming, with the Bridal going
over your Shoulder after you pitch the pilot-chute.... (good luck)... you Will need it.
.

But what if you exit, de-arch, and pull your knees up toward your chest?

WHAT.....THE.....Fuck....?

I come back from changing a couple Bobbins and Tapping a Top-Flap and the...

Thread has been SPLIT and there are 13 Posts ???????

Then the whole fucking new Thread that was split just DISAPPEARS while I am trying to post this there ???

seems like I just walked away and everyone else just goes STUPID on me...

(like I stated at the "END" of my last POST... )

"I still see there are still 11- Wrong "YES" votes in the poll."
.
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Ooooh. and SKIN does like and listen to ...
American, Country Western Music...(in the closet)