Terminal PCs

[FIREFLYR 0]

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

"One flew East,and one flew West..............one flew over the cuckoo's nest"
"There's absolutely no excuse for the way I'm about to act"

[JohnnyUtah 0]

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Any reason why most people go floating for their 36 or 38 but go external for their 32 incher?

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)

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.

Have Fun, Don't Die!
Johnny Utah
My Website
email:[email protected]

[JohnnyUtah 0]

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Tom could always refer to post#18

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.

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.

Have Fun, Don't Die!
Johnny Utah
My Website
email:[email protected]

[TomAiello 25]

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...I think...

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Are you sure...?

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

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[JohnnyUtah 0]

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...I think...

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Are you sure...?

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.)

Have Fun, Don't Die!
Johnny Utah
My Website
email:[email protected]

[tfelber 0]

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.

[JaapSuter 0]

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.

[460 0]

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.

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

[Zennie 0]

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

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

[Zennie 0]

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/

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

[base428 1]

All,

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

(c)2010 Vertical Visions. No unauthorized duplication permitted. <==For the media only

[DexterBase 0]

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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...)

[Sean621 0]

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.

http://www.extreme-on-demand.com

[base736 0]

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It's an easy and decisive experiment.

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.

[Faber 0]

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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.

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

Stay safe
Stefan Faber

[toni 0]

- 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.