Interesting cross port design...

[hackish 8]

Interesting cross port design. I can understand that the designer is trying to stop the rib from deforming at the port. I'm curious if this is solving a problem that doesn't exist? I wonder if the stress riser of a sharp corner creates as much of a problem as it solves - stronger rib but with a concentrated point to start tearing...

I'm interested in what others have to say about this, especially from an engineering point of view.

-Michael

[Chrysopelea 0]

Those are vertical on the rib, right? And the stress forces are vertical too. So there really isn't any tear forces on those pointy ends. All the stress just goes straight down past them. They would be a concern if stress was perpendicular to those pointy ends, but canopies don't really have nose-to-tail stress on opening. Nothing is pulling on them in that direction.

[Hellis 0]

Skylark?

[hackish 8]

Chrysopelea

Those are vertical on the rib, right? And the stress forces are vertical too. So there really isn't any tear forces on those pointy ends. All the stress just goes straight down past them. They would be a concern if stress was perpendicular to those pointy ends, but canopies don't really have nose-to-tail stress on opening. Nothing is pulling on them in that direction.

Nearly every torn cross port I've seen so far this year is in the up/down direction. Since ports are always going to be between line attachment points I wonder if the force is being applied more in a diagonal direction. This canopy is a firebolt by the way. I guess the part I'm curious about is that it's the only one I've seen made like this.

-Michael

[JohnSherman 1]

Quote

This canopy is a firebolt by the way. I guess the part I'm curious about is that it's the only one I've seen made like this.

All FireBolts have always been made this way. Some 20 + Years. It is how Parachute Labs does all of their canopies, AngleFire Reserves, Blackhawk Mains and Reserves and Nighthawk mains and reserves. Racer Tandem Reserves and Mentor Student Canopies. It is done to reduce rib distortion.

[hackish 8]

JohnSherman

Quote

This canopy is a firebolt by the way. I guess the part I'm curious about is that it's the only one I've seen made like this.

All FireBolts have always been made this way. Some 20 + Years. It is how Parachute Labs does all of their canopies, AngleFire Reserves, Blackhawk Mains and Reserves and Nighthawk mains and reserves. Racer Tandem Reserves and Mentor Student Canopies. It is done to reduce rib distortion.

My entire dropzone has 2 racers and I don't feel comfortable packing or maintaining them so I guess that explains why I have never seen this style before.

John, have you seen main cross ports fail on old heavily used canopies? No real way to say if it is the same, better or worse with reliability. I can assume a higher cost to have to cut all of these things out but I was wondering how much of a difference all that extra effort made?

Do other manufacturers do it on their ultra-high performance canopies or do they shape the ribs to deform into the desired shape? Or maybe they just don't care?

I find "different" things like this interesting.

-Michael

[accumack 14]

Para-Flite did these back in the 1980s elliptical crossport with a strip in the center. We were seeing distortion and this eliminated it. We were using elliptical crossports for years prior without the strip.

[darkwing 5]

For a long, long time now I've thought it might be useful to just use a high porosity fabric, rather than port it. I certainly understand that a soft, uncoated, high porosity fabric might be harder to handle during manufacture, but it still seems worth trying.

-- Jeff
My Skydiving History

[JohnSherman 1]

Quote

For a long, long time now I've thought it might be useful to just use a high porosity fabric, rather than port it. I certainly understand that a soft, uncoated, high porosity fabric might be harder to handle during manufacture, but it still seems worth trying.

Can't find one with the proper characteristics. 1.1 isn't permeable enough.

[riggerrob 643]

Trying to remember all the different sizes and shapes of cross-ports I have seen over the years. ....

First generation cross-ports were the same size and shape as tomato juice cans.
Then some-one introduced race-track shaped cross-ports.
Then some one cut three race-track cross-ports side-by-each.
Then some-one cut oval cross-ports.
The some-one cut triangular cross-ports, with rounded corners ...

I have only had to repair cross-ports with square tears in the upper or lower corners. They tend towards a square shape.
The first hundred frayed cross-ports ... I just re-cut (hot knife) slightly larger.
Really badly torn cross-ports get a sewn patch the entire height of the rib. By the time I re-sew the rib to the top and bottom skins, the repair gets rather expensive. $$$$$

[ZeroPorosity 0]

riggerrob

First generation cross-ports were the same size and shape as tomato juice cans.

Probably sounds odd to most people. But for those who aren't old-timers, this is because cross ports were made by heating up a tomato juice (or coffee) can on a stove, then pressing it against the rib to melt a hole through the nylon.

[Beatnik 2]

A history tidbit, I believe the first canopy to have cross ports from the factory was the Jalbert Para-Sled. The cross ports had cotton binding. Like most things of that era, they were over built.