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Hey,

does anybody using a 32 inch PC with a floating handle? Any reason why most people go floating for their 36 or 38 but go external for their 32 incher?

Does anybody have an opinion on 36 versus 38? Or get both? In case the weight of the canopy matters; I'm jumping a vented 266 canopy.

For an 8 second delay off a cliff, what's your first choice; 32, 36 or 38? Would you comfortably use a 32, even when it's not your first choice?

Thanks,

Jaap

And while we're at it, does anybody have any thoughts on large-hole mesh versus small-hole mesh for pilotchutes, in relationship to the different available sizes, inflation speed, as well as snag potential for bridle and centerline.

Thanks,

Jaap

38 vented for an 8 second delay would be my choice. I use that for pretty much anything sub-terminal slider-up.

However you would probably find that more often than not, a smaller pilot chute would work as well in some capacity. I know of someone who took a 30" skydiving pilot chute on a 4 second delay from 700ft and got away with it. Another example is a 500ft cliff we have here. Most use a 42, but it often gets jumped with a 38.

For terminal a lot of people use an F111 36 instead of ZP 32. It fits in the BOC better.

In regards to mesh size, BR (Apex or whatever they are now) construct their terminal pilot chutes (F111 36) with small hole mesh. I'm no scientist but I'm pretty sure it has to do with the higher deployment speed. Perhaps they can give you the specific answers you want.

Jaap,
I can't comment on the 32" PC, other than to say it is too small for my comfort. I currently have a vented 265 canopy and I'm comfortable with my 36" ZP on it for delays of 5+ seconds.

Since I'm stepping up to a 322 canopy (looking forward to seeing it soon ), I ordered a vented 38" ZP PC with it - primarily due to weight considerations. Unfortunately, it will probably be a while before I have any terminal or near-terminal experience with that canopy/PC...

Mark

I think that's mostly history. Adam F. put the 38 handle inside, and the 32 outside. Then, the internal got converted to floating, and the 32 got left. Personally, I kind of like the floating handle for everything (but I've got both external and floating handles in both 32 and 38).

I'd ask the manufacturer. I don't know that anyone makes both a 36 and a 38, and the "named" size is less important than the role (i.e. drag and inflation) that the manufacturer is making it for. You may find that a 36 from one manufacturer is intended for the same role as a 32 from another.

38 ZP with a vent.


Yes.

I don't have any experience with a floating handle PC, although I've considered it for my 38's...I only use 38" both vented and not for sub T slider ups...and I WOULD feel comfortable using a 32" for the 8 second delay. Now I always use 32" Vented for terminal, but I've considered going bigger when using a tracking suit. I jump 310 sq foot canopies both vented and non, and have good results with the above setups.
I'm 'guessing' the reason folks tend not to use floating handles on 32's is that is 'usually' a terminal PC, whereas my understanding is that most PC/bridle entanglements have been documented in the sub-terminal environment. Except in skydiving...but of course you know, this aint skydiving
Read....'guessing' and 'usually' etc, cause I don't really know, just sharing what works well for me with the larger-ish canopies.
YMMV
Later
Blair

I that with your particular equipment configuration, or across the board?

Would a person with a 310 and a person with a 185 experience similar results with this airspeed and pilot chute?

The mass you're trying to decelerate can certainly come into play. I think at the extreme ends of the canopy size spectrum, the PC selection may matter a little more. In the middle sizes though, it probably matters slightly less.

At airspeed approaching terminal, a 32 has SOOOOO much drag. I've always thought it would be fun to sew a soft handle onto the end of a bridle and pitch a 32" PC in freefall then attempt to hold on to the handle. I'm just afraid what it would do to my shoulder. I'm positive there's no way I'd be able to hold onto the damn thing though.

I can think of a BASE fatality with a PC/bridle entanglement at terminal, on a wingsuit. I suspect the wingsuit increases the likelihood of this malfunction, as there have also been a couple cases of this reported on skydives, which you can find if you dig through the wingsuit forum.

My configuration. I'd do it with any of my canopies down to 260 though. With a 240? Hmmm. A toss-up, I guess. I'd probably be happy with whatever PC I had on there.

I've seen a 32 used at 5 seconds on a 300+ canopy repeatedly with no adverse effects.

Righto Tom, I should've clarified, I don't 'really' consider wingsuit as a 'terminal' jump, even though I know your vertical decent rate is decreased significantly, your horizontal speed increases greatly
...hence one of the reasons I use a 38" on WS BASE jumps. I think I'm familiar with the fatality you are referring, and wasn't this on a 'hacky' style handle?
I do understand what you are saying, just wanted to clarify my statement.
Later
Blair

Thanks for the replies everyone.

Somebody brought up an interesting point. I'm planning on jumping with my Phoenix pants and jacket. I'm also fairly tall, but very light. All that results in a terminal falling speed that is far below average.

Now imagine that worst case scenario, I'm using a 32 inch PC, and I chicken out or I count too fast, and I pitch at 6 seconds....

Am I going to die?

Mmm, perhaps I should just borrow a 36/38 from somebody. Should be no problem.

My own 38 is on order already. Thanks everyone!

Yep. It was also the incident which spurred the development of the floating handle.

Are you certain?

I haven't done the math, so I don't really know, but remember that you need to add your downward and forward vectors to determine your actual relative wind speed during deployment. Wingsuits and tracking garb decrease the vertical vector, but they increase the horizontal vector--I'm not sure what the net effect is.

Yeah, because I just stall out my tracking suit and fall straight down.

Kidding. You're right, that's something I hadn't thought of. Duh...

It's one of those things. It'll probably work, but for my first slider up base jump, I'll feel better at the exit point with a bigger PC. I've taken 42 from 300ft, but I feel better with my 46. Same in this case.

Thanks!

Good thinking. Decisions like that will keep you alive... or at least give you optimum opportunity.

I thought it was interesting when you asked about marquisette netting vs. large hole mesh on a BASE pc. I originally thought large mesh would inflate faster, seemed logical to me. But I did a search and found there were some very good information regarding PC inflation. Quoted from Treejumps:
A pilot chute generates lift exactly as a ram air canopy does, by having the air flow over the wing (around the round canopy).
in this thread.

So in conclusion, I'm not sure it would matter what type of mesh you'd use for a terminal jump. I'd like to hear more theories on this.

I'm pretty sure it matters, although not by how much.

Assume for a moment that Treejumps is right about this, which I'm not entirely convinced of, the pilotchute would still have to get to its wing-like shape before the effect fully kicks in. For this to happen, air needs to enter the volume in between the mesh and the ZP.

Now reason ad absurdum; instead of the mesh part, use a solid fabric with only a tiny hole at the bottom. Is this PC going to inflate fast? I doubt it.

A small-mesh hole will let less air through than a large-hole mesh, given the same amount of pressure and time. Hence, a large-hole mesh inflates faster.

This reasoning won't hold up scientific scrutiny, but 460, 736, 974 and all other intelligent people on this board can just look away for second. I'll trust my instincts and what manufacturers tell me.

Thats the post where Tree (Treejumps) exclaims that:
Im sorry, and Im not trying to take a dig at Tree, but those two statements have got to be two of the dumbest things I have ever heard.

Regardless of what the air pressure is on the outside of the material, a PC captures air to inflate. That is what holds its shape.

A post of mine from that same thread.



Some basics:

Square canopy
A square canopy is an airfoil, a wing, a glider. The pressurized wing generates lift because it is an airfoil shape. In this thread, round canopies seem to be the topic, so…

Round canopy
A round canopy is a drag device. The canopy captures air as it is pulled in a direction. This capturing of air pressurizes the canopy with static pressure holding the round canopy in its inflated shape. The shape of the round canopy creates drag, which is the opposing force to whatever is pulling the payload in the said direction (i.e. gravity). It is this drag that allows a person to land with a safe rate of decent under a round parachute.

Inflation of a round
For a round parachute to be considered inflated, it needs to be pressurized with air. For air to get into the round parachute, it goes in through the opening at the skirt, not the apex. Air exits through any hole at the apex.
During a round deployment with some airspeed, the canopy starts out in a stretched out streamer type of shape. The skirt of the canopy is gathered together in the center and therefore the opening at the bottom is very small if any. Because there is some airspeed, the airflow across the canopys outer surface creates a low pressure. Since there is a lower pressure on the outer surface of the canopy than on the inside of the canopy, the streamer shape begins to expand. The opening at the skirt begins to expand as well.
As this happens, air does go in there.
The air keeps collecting inside there, and it is at the apex of the canopy where it collects for the most part. Once the opening at the skirt becomes large enough to let in enough air to completely expand open and pressurize the canopy, then that is what happens.

The low air pressure on the outside of the canopy during initial inflation, helps the canopy change from a streamer shape to an expanded, more open shape.

IMHO- If a round parachute were deployed with its skirt completely opened up (full diameter), then it would inflate (pressurize) immediately and the need for an external low-pressure to help expand the streamer and open the skirt up (as during initiating inflation), would not be needed. I agree that the static pressure created by the canopy capturing air is greater than the external pressure and therefore the canopy stays open.

Pilot Chutes
I have no doubt in my mind that when doing a high airspeed deployment, there is a low pressure created on the outside of the PC which helps it to initially expand. It seems to work very well and that is why I use a regular mushroom for those types of jumps.

In this thread we were talking about a very low airspeed PC hesitation. My point of view is that if you can get the mesh/rip-stop seam of the PC opened quicker (and reliably) on its own, then air will go right in there and pressurize the PC that much quicker. That is why I was mentioning the Super Mushroom. Thats its purpose.

If you pack the PC so that it is dependent on airspeed to begin to open, then you need sufficient airspeed at deployment time or enough altitude to get away with a hesitation (like we see in the video).

With the regular mushroom, sometimes you can do a throw and go and the PC opens immediately with nil to very little airspeed. I believe this works because enough air successfully flows through the opening of the seam and successfully inflates it. However, sometimes the airflow is not so successful to get in and inflate the PC at low airspeeds with the regular mushroom. The result is an occasional hesitation. In the video, it probably hesitated until an external low pressure did happen and helped get the PC to open. Not ideal in my opinion.

Hello Jaap

I use following (with FOX 245 and FLIK 242)

4-6s:
38', ZP, large mesh

6-12s:
36', F111, fine mesh
36' ZP, vented, fine mesh

I began useing the 36', after I felt that the snatch-force of the 38' PC became very hard, the moment when the PCs work is most important. The opening speed after line strech was feeling the same than with a 38'.

>12s: 32', vented, fine mesh
I used quite some time the 36' on delays up to 15'. At some spots, where it is better to pull in full track, I felt a big difference between 36 and 32, I began useing the 32' from 12seconds.

This is just to give a different input about the PC sizes, since I see that people tend to use bigger sizes than I use. I think, that useing too big PCs can be very bad too, not only because of the harder opening more I think about of line-overs/twists/off-headings (I think that a too big PC and not useing a good direct slider control is the main factor of slider-up line-overs).

For your questions:

- Floating handles I don't use.

- 36' vs. 38': Get both

- 32' for a 8s delay: Sure, it works fine, but to feel confident: It depends...


Hope it helps
/t.

Good post toni.

My preferences are mostly the same as yours.
I prefer my 38-inch PCs to be vented.
I currently have large-hole mesh on my 32-inch PCs.
Have you had a chance to compare a 32-inch with large mesh against a 32 with fine mesh? If you have, just curious what you thought. Thanks.


I agree. Jaap, there will be times when you will want one over the other.


Along the lines of what toni is saying about too much snatch force and malfunctions/line-twist/off-headings.
You want to always consider the degree of center cell strip your set up will cause on that jump.

Here are a few excerpts from a post I wrote a while back in this thread about center cell strip:

Center cell strip distorts and undoes your pack-job. At or close to terminal velocity, there is always some degree of center cell strip (unless you are using a sleeve). The goal is to minimize it without causing too lengthy of a deployment.
The more center cell strip you have, the greater the chance of having a malfunction/line-twist/off-heading.

edit to add:
If you are ever unsure about the best PC size for a particular jump, my philosophy is:
It is safer to error to the side of one size too big instead of one size too small.

1. Where you live there is no terminal object
Are you going to Europe any time soon?

2. This is my set up (ACE 240).

0-1.5 46" Z-po vented no handle large mesh

2-4 42" Z-po non-vented disk large mesh (soon to be replaced)

5-8 and WS Z-po 38" vented internal handle large mesh

Terminal Z-po 32" vented external handle small mesh

I am making a 42" now that will look like a tandem drouge but vented. The specs are: Z-po, internal handle, vented. Bottom skin: the skirt will be fine mesh (about 1") , then z-po fabric (50% of the length), then fine mesh again (the other 50%).

 

I don't know how fast it will inflate in the BASE environment, but this is what's used for Relative Workshop's reserve pilot chutes. It like one big nylon bag over the spring. The reasoning here is that if the pilot chute comes out sideways, a conventional pilot chute loses some drag since the air can flow straight through one side of the mesh and out the other. With an all-nylon pilot chute, the drag is about the same regardless of orientation.

I don't know if it's fast enough for the BASE environment, but RWS seems to think it's fast enough for a reserve deployment system.

Michael

Personally, I use the following PCs for the following delays.

0-1: 46" ZP apex vented.
2-5: 42" ZP apex vented.
5-12: 38" ZP apex vented. Internal non-floating handle.
12+: 32" ZP apex vented. External handle.

I have a 36" non-vented with an external handle but I never use it. I opt for the 38 or 32 depending on the delay.

For an 8 second delay I'd go with the 38. I'd use the 32 given no other choice.

Of course there are exceptions to every rule. Just the other night my jump buddies (*cough*brit*cough*chris) banned me from trying a gainer at 300 so we climbed up to about 450 or so. I set up for a very short delay so I had my 46 with me. I wound up taking about a 3 or so with no problems. Like Johnny pointed out, I was erring on the larger side so it really wasn't a big deal.

Just out of curiosity, has anybody noticed a difference in inflation times when going stowed with a 46+ vs a 42? I've noticed on a couple of occasions now that the stowed 46 seems to inflate a tad slower than the stowed 42. Almost like there's a point of diminishing returns as the PC gets bigger and there is more fabric to unfold & inflate.

I'm no fluid dynamics expert, but I did stay at a Holiday Inn Express last night.

I’m wondering if we actually have two discussions going on here. The discussion in the referenced post seems to relate mainly to the mechanism by which a PC or other round canopy inflates. That is, there is a pressure differential between the inside and the outside of the parachute which causes air to be drawn in. This is also the same principle which causes a square parachute’s cells to pressurize (which I think is what Brit was driving at).

You physicists & aerospace engineers correct me if I’m wrong here, but that said, once inflated/pressurized, I don’t think you can say that round and square canopies operate on the same principle.

As best as I can tell, both are drag devices. Both have an underskin which provides air drag/resistance to counter the downward force of gravity. The round parachute, by virtue of its shape, is a pure drag device. It cannot, as best as I can tell, produce lift. A square canopy has more of an airfoil profile which DOES produce lift. That lift is produced by giving the foil an angle of attack which generates forward momentum and thus forces air to flow over the top and bottom of the canopy.

For instance, I don’t think you can get off the ground by attaching a motor device to a round parachute. It will just slow down your forward progress. You CAN, however, attach a motor to a square parachute and get airborne.

I'm no physics expert either, didn't even graduate high school. But here's one to wrap your head around....

Drag IS lift.

From a physics point of view the two may (or may not... 460???) be the same.

Personally, when I'm referring to lift vs drag, I see drag as primarily a "pushing" counterforce as opposed to lift, which I'm seeing as a "pulling" counterforce.

And just to clarify a bit further what I'm talking about.

When I'm referring to drag I'm referring to the force created when a semi-permeable (or non-permeable) solid (i.e. canopy fabric) has velocity through a fluid (i.e. air). The fluid forced into (or through) the object produces a frictional "pushing" force that I'm referring to.

When I refer to lift, I'm referring to the upward force created when you have differential airflows over a solid, creating a vacuum (i.e. "pulling") effect.

Umm, false.

Lift, by definition, is a force perpendicular to the undisturbed airflow (http://scienceworld.wolfram.com/physics/Lift.html). Drag, by definition, is a force into the undisturbed airflow(http://scienceworld.wolfram.com/physics/Drag.html). Therefore:

(1) Drag never coincides with lift; and
(2) Lift can not be responsible for pulling a pilotchute away from the jumper (though it can be responsible for pilotchute oscillations).

Thanks for playing.

There are a lot of different explanations for lift.

I've had an actual aero professor tell me almost exactly the same thing Lou said ("drag _is_ lift"), as well as telling me that the above explanation for lift (which is the same one I have generally accepted for most of my life) was basically incorrect (according to him, the majority of "lift" in a wing is actually coming from deflection of air from the bottom skin--i.e. drag).

I think there is plenty of complexity in the subject, which includes big disagreements even between folks with a lot of high level education and a bunch of toys (like wind tunnels) to test their ideas.

Personally, I'm happy that it just works somehow. I've not got the time, energy, or brainpower to worry too much more about it, after realizing that people have spent entire academic careers trying to pin it down.

If I read that correctly, though, it also implies that:

(a) Drag cannot be responsible for a PC inflating (a force perpendicular to the airflow, not back into it),

and;

(b) our most likely cause for PC inflation would be lift (which pulls the sides of the PC in a direction perpendicular to the airflow--drag would actually pull the PC back toward the jumper?).

Interesting stuff. I'm sure there's an application buried somewhere in the theory, probably having to do with Nick's drogue-built PC.

More useful information. Thanks everybody!


Very interesting! In my infinite lack of skydiving experience I was unaware of such pilotchutes. I assume the the nylon is at least slightly permeable?


Actually, there is one about two hours from here, in your country. Before the end of the summer though, there will be a new local terminal wall, or my name is not Jaap Suter. And I'm not talking about the local pet-rock. That thing will unfortunately never be terminal despite its height. Stay tuned, come visit Canada!


Unfortunately not. I'll be visiting North America's legal big wall, about twelve hours driving from here.


Word.

Thanks everybody for the information.

Actually it returned via Barelylegal, but I digress.
Now Winkleport is one I have never heard before.
Thanks for making me smile.
But cant you at least spell it Winkelport?
Seriously though Tree, you can do better than that; with that name there are endless possibilities.

I didnt say it was the dumbest thing I have ever heard. I said it was two of the dumbest things I have ever heard.
You were a real contender when you said this one though Tree:

How does the air get into the PC if there are no holes?

Im pretty sure youre talking about a Vector reserve PC (right?)
Well Tree, theres a hole there man, right at the bottom of the spring, and I would imagine air goes in that way. Maybe Bill knows.

Have you ever seen a Vector reserve PC? Ive packed loads of them.....I own one. Theyre cool man...totally groovy! I dont think I would ever BASE jump with it though.....but then again Im not that hardcore.

Tree points finger --> Johnny points finger --> Brit points finger --> Jaap... hey he asked the question, I just went searchin for an answer!

Just for further debate's sake... I was thinking about a tandem drouge. Something like a 56"(?) big ass balloon piece of f-111, with a small hole at the bottom, much smaller than RWS's reserve pc. To boot, I would think that little hole is hanging out above the instructor's burble. So... why do manufacturers not prefer a large mesh bottom half if this is the most reliable inflation method?

Johnny you probably have more tandem jumps than anyone on this forum so thats why I thought of this question. Edited to add: Keep in mind the original question is regarding terminal pc inflation. With all this nitpicky, down to a more than exact science debate, just making sure all the elements are in place for the equation problem solving ;)

Yea Jaap....what the hell? (and yes Im laughing my ass off)


1. A tandem exit is 6,000 to 13,000 feet
2. The drogue is so big that even with its current design there is drogue shock when its deployed at tandem terminal. I can only imagine what would happen if the lower half of the drogue was all mesh
3. The drogue actually collapses when the drogue release is pulled. You actually feel your fall rate speed up a bit before the chute comes out (trap door effect). The collapsed drogue has ample drag to pull out the two-man chute.

edit to add:
4. They design them to maintain a certain average fall rate.

Tree, Johnny,

Please read this discussion of personal attacks.

I've reproduced the most relevant portions below:



Consider yourselves warned. This thread has a lot of interesting technical information, and good input from both of you. Throwing in the "no, you're dumberest time infinity..." bit makes it sound like 2nd grade.

Oh sure, bring actual documented definitions into it.

Lou

Yeah, I see everything you're saying. I think the point I was trying to bring up is that... it seems the evidence provided by the drogue remaining inflated throughout the freefall portion of the skydive would imply that "A pilot chute generates lift exactly as a ram air canopy does, by having the air flow over the wing (around the round canopy)" instead of air entering the pc from the bottom and hence, inflation.

I think the big problem here is that we're approaching this from a Newtonian rather than a Quantum perspective...

I know nothing about BASE, but I have a fair bit of knowledge about aerodynamics given I have a graduate degree in it. It has been mentioned before on this thread, but lift is produced only perpendicular to the flow of air. So when falling straight down, lift can only be produced to the sides, where as drag is only produced parallel to the flow of air, i.e. up. The force exerted by a pilot chute (or round canopy for that matter) is soley drag by way of air deflection. When it comes down to it, a modern day parachute is actually working mostly by the same principle of air deflection, so in a way both people are correct as the pilot chute creates lift by way of air deflection, which at the same time can be referred to as drag.

Can you comment on the inflation of the PC? Does the PC inflate through drag or through lift? Or some other mechanism?

Why do I have the sick feeling that this thread is going to result in 460 checking his references again?

Cause people just dont get it.

Tom could always refer to post#18


edit to add clicky

My academic experience is with airplanes, i.e. things that don't inflate, but the background can carry over. Without getting overly technical, lift occurs due to a pressure difference, which the case of a wing is due to difference in airspeed over the two sides of the wing. In the case of a pilot chute, prior to complete inflation the airspeed within the pilot chute will become turbulent and most likely reduce in speed, while the external speed does not decrease in speed, so there would be higher static pressure on the inside, essentially pressurizing the pilot chute during inflation, so in a way there is some lift contributing to the inflation, but by and large, the inflation (I would imagine) would be primarily due to air deflection, i.e. drag. The lift will be more useful after inflation in that it will increase the rigid pressurization of the pilot chute, as the higher static pressure air will want to leave the pilot chutes through the side, there by keeping the pilot chute inflated and rigid. Of importance to this situation is that were the pilot chute to be fully within a burble, then dynamic pressurization like this cannot occur as the air surrounding the pilot chute would not be traveling quicker, another good reason for a strong reserve pilot chute spring or big ass pilot chute for you BASErs.

I think this runs the risk of rapidly degenerating into a debate along the lines of whether a dam is technically "earth" or "building". The solution, IMHO, being that it's neither. When you inflate a balloon, is the force that opens it up lift or drag? The answer, again, is "neither". Direct inflation pressure is neither lift nor drag, in any meaningful sense.

Anyway, in the spirit of being more productive...

How can we tell whether inflation pressure or lift dominates in "inflating" the PC? May I suggest the following experiment. Take an all-fabric PC a la RW and hook it up the usual way, open end down. So that inflation pressure is allowed. Make a few jumps (or, if you prefer, measure the pull force from a moving vehicle or something). Now, hook it up the opposite way, open end up. Make a few more jumps.

Lift will operate equally in both cases with respect to opening the pilot chute, since it's about the bulk of the fabric (and not about the hole, except as a way for air to get in passively). Inflation forces, however, will act to force air into the PC in the first case, and out of it in the second case.

SO... If lift dominates, the PC will work equally well both ways. If inflation pressure dominates, you'll be glad you didn't jump the second configuration (or very, very upset that you did). If lift is at all important, the second configuration will still be "okay", even if it's not quite as good as the first.

It's an easy and decisive experiment.

The force that a PC pulls back with is certainly drag almost to the exclusion of any other type of force. But that wasn't the topic of the original "lift" post.

It's simply enough: add a tension datalogger on the bridle for the same pilot chute with large mesh, marquisette mesh, and with and without tashengerts (sp?), in a controlled environment such as a launching system on a vehicle at deterministic speeds. ya know?

I don't see how that would isolate lift forces from inflation forces... Perhaps you could elaborate?

So, something that you wrote on this forum is as authoritative as a textbook used by a Ph.D. physicist? I'm not doubting that you've got some good insight into these things, but I'm still going to ask as many people as I can.

I'm unlikely to accept that the answer is x, y or z simply because someone (whoever that someone is, be they you, me, or Dwain Weston and Carl Boenish speaking through mediums) proclaims that they know the answer.

I am currently in LAUTTERBRUNNEN, I was in Norway last week and used a 34 inch vented pc with an outside handle (large mesh slider,Mojo canopy) all good! I got my pc from Marty at Asylum.
I went to Lauterbrunnen and started using my 38 inch vented pc. 10 seconds....180 with a half line twist. next jump, I got a full line twist with a nasty but self clearing lineover caused by a wildly occilating pilot chute. I went back to the 34 and all has been solid.
I like having an outside handle on the 34 and a floating handle on the 38 ,it helps for easy identification of the two as they are the same color.
J

Are you sure its not because the 32-inch PC has so much less material to it that having the actual PC material stick out of the BOC at all, would make it more likely to come out of the BOC prematurely, especially at terminal?

Its common knowledge in the skydiving world that you dont want any of your PC fabric sticking out of the BOC, whether your belly flying, free flying, or wingsuit flying. This is because there has been lots of incidents from the PC coming out prematurely.

Well actually a Ph.D. physicist (460) did review it and made a post (in the original thread) saying he had no problem with it. Im sure you saw that since you posted right after.

I offer you a place to reference, and you come back with that.
Whats with the attitude?
Actually, I think I know what it is.

No. That's why I began my statement with "I think..." rather than "I'm sure..."

Gee, again with the attitude.

I didnt mean are you sure that literally. I was just using it as a common phrase in the English language. I thought that reply I made was quite nice. It was polite, stated as a question, informative, and to the point. You probably already knew about what I was saying though. (OR maybe you didnt know about it...yea, thats it.)

I'm in agreement with larsrulz. Lift from a round can be seen when a parasail is pulled by a boat and the person is lifted into the air. The instant the boat stops pulling the lift goes to zero and the drag of the parachute keeps the person from going into freefall.

Regarding inflation... When a no permiable object is thrown into a moving stream of air the laminar flow of air around the object creates a partial vaccum on the downwind side of the object. This partial vaccum would ten to aid inflation of a PC. However, the PC still functions as a scoop until full inflation or equillibrium is reached. At that point in time it operates as stated in larsrulz and my paragraph above state.

Why is everybody forgetting that the Reynolds Number only applies after nondimensionalizing the Navier-Stokes equations? Given an average Ro of < 30, we find an experimental Poiseuille (laminar) flow that isn't turbulent enough to exhibit viscosity.

I honestly have no clear cut idea on what the physics are, since I don't have a good foundation in fluid dynamics beyond the basics. One note though: it is widely regarded in the aerodynamics community that the parachute opening is the most difficult and poorly understood problem in aerodynamics. This is the reason there are groups using supercomputers, etc to simulate such processes. See for example

http://www.mems.rice.edu/tafsm/

And for a description of how a round opens:

http://www.mems.rice.edu/TAFSM/PROJ/FSI/axi_para.html

The primary issue in my mind is obtaining reliable data. I worked with a physicist from U.C. Berkeley and Lawrence Berkeley National Laboratory who once described an ultrasound positioning system that would be ideal for charactering an opening sequence and the subsequent flight sequence without affecting either opening or flight. That added with other sensors such as pressure (and other things) would be first steps to understanding these issues ... and resolving many of the current debates.

Made clicky...

This is the reason there are groups using supercomputers, etc to simulate such processes. See for example

http://www.mems.rice.edu/tafsm/

And for a description of how a round opens:

http://www.mems.rice.edu/TAFSM/PROJ/FSI/axi_para.html

Also on the site that 460 referenced, there are a number of pages devoted to ram-air parachute studies.

You can view those here...

http://www.mems.rice.edu/TAFSM/PROJ/AS/

All,

Put your calculators and physics books down and go make a jump.....

No doubt... But just for fun, I tested my 42" AV pilot chute off a nice 500' smokestack this morning.

A 42" AV PC works great on a 2 second delay from 500, just like always.



edit: typo (I think I'm just going to make this part of my signature...)

here in the uk the 42" ZP vented is the weapon of choice from 215 up to 500...some people use 46" at the lower alts but having been the victim of a 46" doing the hesi on me on more than one occasion i dont even own one any more.I do however jump a normally aspirated troll and a mojo240...both of which dont really need a 46" to drag em out...based on my limited experience and what ive seen.

on the terminal pc issue i use a 32" f111 fine mesh with external toggle for 8 seconds and up and a 36" ZP internal toggle for the 4 to 8 second range.all of these use a wide mesh slider..both in Baffin and Norway i experienced very comfortable openings
with these configurations.

anyone using a slidergate who could give me some feedback on opening impedence would be a good thread to start.

Woke up early this morning with the intention of heading out to the mountains. Weather sucked. Anyway, I was inspired to run the experiment I suggested -- talk is cheap, right? So I built a 20" pilot chute of the type I described above and did some drop tests -- five each, "normal" and inverted.

I've uploaded a video of the whole thing to http://www.skydivingmovies.com; it should show up soon as "pctests.mov" in the miscellaneous section. You can check it out and make your own conclusions. Mine go something like this:

First, I rock at building pilot chutes.

Second, and not at all surprising to me, the pilot chute was most efficient (ie, gave the longest descent time) when it was dropped open side down. It was also the most stable in this configuration, and inflated most quickly.

Third, and perhaps most interesting, although it was unstable, the pilot chute did repeatedly fully inflate when it was dropped inverted (frame-by-frame will confirm this; sorry about the interlacing).

The Big Conclusion: Lateral lift forces are, in fact, important in inflating a pilot chute! It is entirely possible that they are dominant in that respect. Direct inflation pressure is also important, but perhaps only in providing a "reserve" of pressure to keep the pilot chute stably inflated.

Alternatively: The pilot chute was most stable when the red side was up. It's therefore also possible that pilot chutes with red topskins are the most stable, while those with purple topskins are black death.



Edit to add: Couple of frame grabs here (no interlacing), one inverted and one normal.

perhaps we just shouldnt ask you to sew our self 20" invented pcs in purple as we know you cant make them work

Good job making theese test,really cool tanks

- What is the configuration you jump?
- How did you control the slider?
- Were the jumps in the afternoon?

- Do you think too big PC was the problem?

Take care, conditions are not great currently. Gusts like yesterday afternoon and valley-wind can be very tricky to handle, especially on the yellow wall.