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Does anyone have a photo of a Troll DW inflating slider down at the same stage as the Rock Dragon in the attachment (originally posted by Calvin19 in the wingsuit forum)?

I'd be very interested to compare the pressurization wave pattern with and without the center cell valve.

Thanks!

What is the canopy in the attachment picture?

Rock Dragon 303 after PCA deployment.

That canopy is also seriously underloaded in that picture..

Note the absence of bridle and PC. Possibly a rollover or tard?

You are correct. My mistake--thanks for spotting that.

I wonder if the absence of the PC is making the inflation significantly different, or just easier to see?

In the original thread in the WS forum, he says it was a "tardover" and also gives his body weight as 140, pointing out the underload.

I thought you would never ask :)

I got 'em (frame grabs) on tards, mcconkeys, and mcconkeys handcam.... as well as regular slider ups and downs.

jumper 173lbs + gear
Troll DW 265 MDV

Hello!!!!
yeah, grossly underloaded, but a good pic.
tard over, Rock Dragon 303. im 140lbs

Do you mean a Troll MDV or do you really want a unvented DW?

Maybe this one is good?
I don't know.
I wieght 155 punds.
This is TROLL DW 245 MDV.

Roll-over
Troll265DW
Wieght - 176 punds

http://www.parashop.ru/BASE/MC/7.jpg
http://www.parashop.ru/BASE/MC/8.jpg
http://www.parashop.ru/BASE/MC/9.jpg
http://www.parashop.ru/BASE/MC/10.jpg
http://www.parashop.ru/BASE/MC/11.jpg

Tom,

Isn't what you're observing here unsurprising? Canopies have "wash-in" (angle of attack at the tips is higher than in the centre - stops you canopy turning into a bag o' washing during turbulance). Wouldn't this make pressurisation at the tips occur first, hence the depressurised centre towards the tail?

Ordinarily, surely this wouldn't happen quite like this, since the pilot chute would pull the centre up, helping in its inflation. Here, the canopy is effectively reinflating from a stall, not a depoyment as such.

Thoughts?

Richard

To my seriously non experienced eye it looks more complicated than that.

It seems like the outer most cells are half inflated, the second from outer cells are the most inflated but that area in the centre looks like its actually being sucked in. I'm probably wrong but it still looks freaky

Yes. I think it's a fairly typical pressurization pattern.

But, the reason I started this discussion is that in the thread in the wingsuit forum, the idea was floated that the reason for the "hole" in the middle of the pressurization wave was the lack of a center cell vent:



What I'm looking for is some kind of evidence to support (or not) this theory. If the center cell is unpressurized because of the lack of venting, then the Troll DW ought to exhibit a markedly different inflation pattern.


I'm not certain that the fact this canopy is being deployed unpacked really makes all that much of a difference in the inflation pattern. In my observation, the circular-looking pressurization waves also occur on packed jumps.

Between Basic Research and Vertigo, Apex has done configurations of almost every possible venting layout. Just the center cell, all of the cells, 5 of the cells, different sizes, etc... Here is a simplified, generalized summary of our findings:
Venting all cells pressurizes the canopy too quickly on anything beyond 2 seconds. We're talking possible structural damage to the canopy, rig components, and jumper. The other main problem with this configuration is that there is so much air entering the canopy on anything beyond a 1 second delay, that the canopy pushes the air out the nose and actually backs up on opening. We just built a canopy with all cells vented for a jumper who is just going to use this canopy for very low jumps, period. Where he lives, this is what he has and he loves it.
Just venting the center cell is ok, but it really doesn't pressurize enough of the canopy to make it worthwhile.
Canopies built with 2 cells vented(one on either side of the center cell) is a pretty good configuration if you don't want quite as much pressurization on opening as a "standard" vented canopy. If you heavily load your canopy or do longer delays, typically.
The "standard" configuration that we use is venting on 4 cells, not the center or the end cells. This has tested the best in all areas of canopy performance.
I know that this is a very general description, but the Turkey Boogie is coming up fast and I gots ta go!
We are currently working on these types of articles for our website complete with pictures and should be ready sometime in the next 100 years.
Thanks!
Jimmy P
Apex BASE

That "depression" which is so obvious on Rock Dragon actually happens on every single opening (regardless of the type of canopy, with or without vents). It is happening because of one single reason - at the very early stage of the opening the centre part of the canopy is in stall position, and the full pressurization will begin when canopy starts to move forward.
Before that it is very common to see the "depression" of the top surface on the central part of the canopy.

The main purpose of the canopy vents (of any kind) is to improve (speed up) slow canopy pressurization at early stage of the opening.

What are the benefits of 5 vs. 4 vents?!

The MDV system was meticulously designed, thoroughly jump tested and proved in the field through the years. 5 vent system allows for the fastest inflation and pressurization of the canopy available nowadays on the market.
Central vent also ensures symmetrical pressurization and helps the pressurization of the central, most critical part of the canopy.

Total area of 5 vents on Troll DW MDV is approximately the same as the area of 4 vents on the other canopies, but proper sizing and placing of the vents is of outmost importance on 5 vent system.

Compared to other 4 vent equipped canopies on the market, the 5 vent equipped Troll canopies have faster, but not harder openings!

I think the "depression" seen in the photo is this, the internal pressure in the center rear-most area of the canopy is less than the out side pressure of that area .Sliderless deployment alows unregulated bottom skin spread, with the payload and canopy traveling in downward direction. A vacuum is formed until airflow over the upper surface is achieved, pushing the upper surface down.Close to what robibird said above, just my way of saying it.

When i posted that i assumed that the reason for the depression was from the lack of a center vent, I didnt think it could be anything else. I lack an extreme amount of knoledge in the exact physics of parachute openings.

I guess i should have asked first?...
I also do not own a vented Canopy,
only daggers. so my firsthand experiance to these is limited also. i do have a Blackjack coming soon, however

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

A variation on your explanation:

Canopies tend to drag a "slug" of air behind them as they start to inflate.
I suspect that the depression in the first photograph is the "slug" pushing down on the top skin of a partially-inflated center cell.
This sort of "rebound" or "post-inflation collapse" can be a big hassle when you try to deploy round canopies at more than 150 knots. It is one of the reasons ejection seats are so frightfully complex and expensive to certify.
For a more detailed explanation of this phenomenon, read Poynter's manual or visit Butler Parachute Systems' website and watch video of HX-series/BAT Sombrero slider drop tests.

 


Just getting home from the Turkey Boogie and having for the first time being able to jump my Troll DW MDV 285 and FOX 285 V-tec back to back I must agree. I would need video to tell if the Troll opens (pressurizes) faster but it definitely doesn't open as hard.

I have to ask this again...

Where are nose airlocks on vented/valved BASE canopies?

Directly above the vent, inside of the canopy. If I understand your question. There are three different style valves that I know of.

No nose airlocks. The "valved" refers to similar valves over the bottomskin vents.

Here are two more pics of canopy inflation. Purpule canopy is a troll MDV 245 with a jumper 165 lbs. The gray canopy is a blackjack 260 with a jumper 160 lbs.

Yes, I am familiar with the vent/valve idea on the bottom skin.

What I'm more interested in is combining those with valves on the nose...

Who will build the first?

what says it already hasnt been done? not talked about? found out it complicated the system to much?

The fact that the circular depression is centered at approximately D line attachment point suggests that it's simply tailgate at work.