Apex vent in round canopies

[pbla4024 0]

Does anybody here know when was it used first time? I'm talking about this hole in middle of canopy which should prevent oscillations.

Fido

[mnealtx 0]

According to Parachute history .com......

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In 1797, Andrew Garnerin made the first jump with a parachute without a rigid frame. One of Garnerin's balloon jumps from 8000 feet, a very high altitude for the time, was observed by a French astronomer, Lalandes. As the parachute descended, severe oscillations were induced in the canopy. Lalandes suggested cutting a small hole near the apex of the canopy to inhibit the oscillations. This modification is now known as the vent and does indeed dramatically reduce canopy oscillations.

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[mjosparky 4]

The apex vent does not prevent oscillations. It vents high pressure air during deployment reducing opening shock. The come is a variety of sizes and designs.

Vents such a “double L”, 5TU and tri-vent are designed to prevent oscillations by allowing air to vent out one side of the canopy. A by product of this is limited forward speed.

Sparky

My idea of a fair fight is clubbing baby seals

[mnealtx 0]

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The apex vent does not prevent oscillations. It vents high pressure air during deployment reducing opening shock. The come is a variety of sizes and designs.

Vents such a “double L”, 5TU and tri-vent are designed to prevent oscillations by allowing air to vent out one side of the canopy. A by product of this is limited forward speed.

Sparky

I thought that oscillations were caused by air escaping under the skirt of the canopy? Would the apex vent not alleviate that?

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[wmw999 2,555]

It alleviates it, but definitely doesn't prevent. Just consider how big the hole at the skirt is, and how small the apex hole is. Then add to that the fact that there's often elastic-bound fabric at the apex to close the hole...

It can help to keep the oscillations down, but a flat unmodified round oscillates. A lot.

Wendy W.

There is nothing more dangerous than breaking a basic safety rule and getting away with it. It removes fear of the consequences and builds false confidence. (tbrown)

[mnealtx 0]

Thanks, Wendy -

I knew I'd read that somewhere...but couldn't remember where!

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[skydivingdutch 0]

Cool, someone dedicated an entire website to parachute history. The internet is awesome.

http://dropman.com

[ripcord4 0]

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The apex vent does not prevent oscillations. It vents high pressure air during deployment reducing opening shock. The come is a variety of sizes and designs.

Vents such a “double L”, 5TU and tri-vent are designed to prevent oscillations by allowing air to vent out one side of the canopy. A by product of this is limited forward speed.

The apex vent WAS designed to reduce oscillations and does so to some extent. The various modifications were used to give forward speed and turning ability and along with the deployment sleeve made sport parachuting possible. Any oscillation dampening is a serendipitous by-product.

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[mjosparky 4]

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The apex vent WAS designed to reduce oscillations and does so to some extent.

The apex vent is there to prevent over-pressure of the canopy during deployment. Without it the opening would be explosive and would almost always damage the canopy.
The smaller the canopy, the larger the apex vent needs to be relative to size. A 24’ flat with an 18” vent will oscillate to the point of making you sick. More air comes in the 24’ foot bottom than can vent out of the 18” top. Vent near the skirt allow the air to vent while still maintaining a good positive pressure near the top.

Every unmodified round canopy oscillates.

Sparky

My idea of a fair fight is clubbing baby seals

[CReWLL 0]

Any well-designed round canopy will NOT oscillate. The vent was put in to prevent oscillation. The vents could be made smaller when drive slots were added. (If you take a Phantom 24 and cover the vent it will indeed open hard. It is a lightweight canopy designed with a vent and drive slots). The proper calculations of fabric permeability combined with the geometric porosity of the canopy (which includes all openings; drive slots & vent) should give you a canopy that does not oscillate. By having too much venting, you will ensure a stable canopy, but you will increase the rate of descent. It is better to err on the side of a mild oscillation.