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Vented classic accuracy canopies ??

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Note; This discussion is about ram-air style canopies not rounds.

I've recently been informed by several people with many, many more years in parachuting sports that there are vented Classic accuracy canopies in existence. Yet, I've never seen one, I can't find information on them anywhere, nor pictures (I do have an inquiry into Eiff Aerodynamics right now though.) .

The real reason I'm interested though is why would you need them on a classic accuracy canopy ? I know why they are on certain Base canopies.

I couldn't find any pictures of an Eiff Classic alone. So below is a link to their site. The canopy on the front page doesn't appear to be vented.

http://eiff.com/

Attached are a series of pictures. The 1st picture is of a Troll Base canopy. The white strip towards the nose is the inlets for the vent/valve system. The 2nd and 3rd pictures I'm told, are of Strato Clouds. Again no vents. Unless some were modified via scissors. Although if you check around the Base community I'm sure you will find out much about flare performance on early vented canopies lacking valves (covers) .
"No cookies for you"- GFD
"I don't think I like the sound of that" ~ MB65
Don't be a "Racer Hater"

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The next time you see him, could you find out why it is vented ? I'll probably have an answer from Eiff by then if not.

Edit to add: After enough searching I was able to find a diagram with 2 small ports (As Eiff calls them) on the bottom skin. I still don't know what they're for though.

http://eiff.com/manuals/ANATOMY.html
"No cookies for you"- GFD
"I don't think I like the sound of that" ~ MB65
Don't be a "Racer Hater"

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I have never jumped one. But as I recollect, the idea is to give air a way to get INTO the cells during near vertical descents. I guess that the very slow forward speed didn't "ram" enough air into the front of the cells.
The choices we make have consequences, for us & for others!

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it also helps the canopy fall straight. the "holes" help with inflation as stated but there are also slits between the bottom skin and the stabilizers.

With no vents or slit between bottom skin of the canopy and the stabilizers then you have, in effect, an upside down bowl, and when pressure builds up underneath it as you drop down rather than forward, you rock uncontrollably and do not have a predictable flight.

back in the late 70's early 80's it was not unusually to do RW, then CReW and shot accuracy! (many competitions combined 4way RW added to team accuracy to get the winner) When canopies started to have joined stabilizers and bottom skins we used to cut slots into them to allow air to spill out equally on both sides and therefore be stable rather than rock from side to side.

The I did this to my strato star, then my Unit for sure in the early 80's and I think to my Pegasus (can't remember on this one).

I attached a picture of 2way CReW to show the design of the StratoStar with the vents underneath the canopy and an alternate design of stabilizers on a para foil. The second picture is a cloud/cloud lite in deep brakes. It shows the vents in the bottom skin and the gap between the bottom skin and the stabilizers. You will notice that the stabilizers are tucked/blown inwards under the canopy as air is pushed out the sides keeping the canopy from rocking and therefore giving it a predictable flight.

not sure if this is actually how it all worked from an aeronautical perspective but it was I thought/felt like happened when I was flying the canopies and the reactions to the design or changes I made to my canopies to be able to shoot accuracy consistently in competition.

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The next time you see him, could you find out why it is vented ? I'll probably have an answer from Eiff by then if not.

Edit to add: After enough searching I was able to find a diagram with 2 small ports (As Eiff calls them) on the bottom skin. I still don't know what they're for though.

http://eiff.com/manuals/ANATOMY.html



.....................................................................

The Eiff diagram calls them "soft cell ports" because they are designed to RELEASE internal pressure, softening cells, reducing control pressures.

Bottom skin vents - on BASE canopies - have the opposite role. BASE vents allow air INTO the canopy - early in the inflation process - to speed openings.

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those vents were first used on para flite strato clouds. when DIck Morgan was working on the prototypes, (dick was a former golden knight and was responsible for MUCH of the ram air development that steve snyder is credited with). they are there to lessen the toggle pressure by making the cell soft.note the vents are in the cell next to where the short inboard steering line is.after the single vent was tested morgan liked it so much he vented a canopy all across the bottom. made it too soft and it wanted to roll up like a window shade

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Essentially correct.

Jimmy Hayhurst explained to me - after exhaustive test-jumping of Eiff prototypes - that sometimes, air flows SIDEWAYS under the bottom skin of accuracy canopies.
In deep brakes, the tail traps too much air, which then tries to burble out at random, ruining stability and your approach to the target.
Vented stabilizers allow that excess air to escape out the sides, for a more stable descent.
That is why accuracy canopies have vented stabilizers.

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Thanks for all of the informative replies. :)
Below is the response I received from John Eiff ;

Hello ,

The Classic accuracy canopy that we built comes standard with bottom surface
vents. We call them "Soft Cells", which act as shock absorbers. They
enable the canopy to absorb side loads from turbulence that otherwise would
displace the jumper a small distance when maneuvering over the score pad.

Check out our web site for more information. The manuals tab will have a
picture and description of the soft cell.

www.eiff.com

John Eiff
Eiff Aerodynamics, Inc.
"No cookies for you"- GFD
"I don't think I like the sound of that" ~ MB65
Don't be a "Racer Hater"

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...

The Classic accuracy canopy that we built comes standard with bottom surface vents. We call them "Soft Cells", which act as shock absorbers. They enable the canopy to absorb side loads from turbulence that otherwise would displace the jumper a small distance when maneuvering over the score pad.

...

John Eiff
Eiff Aerodynamics, Inc.



That is exactly the description I got from Elek Puskas of ParaFlite in about 1978.

Also, I think the Pioneer Viking had round holes, to distinguish it from the rectangular holed Cloud.

I was doing canopy design and construction at the time, so I studied up on this stuff. I looked closely at canopies with such vents, and put them in a couple of my canopies too. I had problems with this explanation though, because under no circumstances could I discern that the pressure in those cells was lower than adjacent cells. Lower pressure would affect the cell geometry, and I couldn't detect any geometric difference.

Jeff

-- Jeff
My Skydiving History

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