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ryan_turner

Rear Riser Pressure

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How does canopy size affect rear riser pressure? I searched the forums and found a lot information about how canopy size and WL can affect front riser pressure, but I didn't find much about rear risers.

I have jumped a Silhouette 150 at a 1.4 WL and had what I would consider normal rear riser pressure. But when I flew a Navigator 280 at a 1.4 WL, the rear riser pressure was so great that it required me to use both hands to pull it down less than an inch. The Silhouette and Navigator are similar and I was jumping them at the same WL, so the only difference was canopy size. Everything else being the same, do smaller canopies have less rear riser pressure?


Edit: The Nav 280 WL was on a Mr. Bill, it's not a typo.

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... so the only difference was canopy size. Everything else being the same, do smaller canopies have less rear riser pressure?



You answered your own question. ;) Yes the larger the canopy the higher the riser pressure, all other things being equal.
"We've been looking for the enemy for some time now. We've finally found him. We're surrounded. That simplifies things." CP

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How does canopy size affect rear riser pressure? I searched the forums and found a lot information about how canopy size and WL can affect front riser pressure, but I didn't find much about rear risers.

I have jumped a Silhouette 150 at a 1.4 WL and had what I would consider normal rear riser pressure. But when I flew a Navigator 280 at a 1.4 WL, the rear riser pressure was so great that it required me to use both hands to pull it down less than an inch. The Silhouette and Navigator are similar and I was jumping them at the same WL, so the only difference was canopy size. Everything else being the same, do smaller canopies have less rear riser pressure?


Edit: The Nav 280 WL was on a Mr. Bill, it's not a typo.



For a canopy in a steady glide, the sum of the pressure on the four risers equals the suspended load. Increase te load and that pressure goes up. Size doesn't matter.
"There are only three things of value: younger women, faster airplanes, and bigger crocodiles" - Arthur Jones.

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For a canopy in a steady glide, the sum of the pressure on the four risers equals the suspended load. Increase te load and that pressure goes up. Size doesn't matter.



A question along those lines, though. Would you agree that larger canopies have more pressure resisting a change in the deflection of the canopy via the risers. So you are either doing a 1-armed pull up or fighting against the canopy?
--"When I die, may I be surrounded by scattered chrome and burning gasoline."

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[
A question along those lines, though. Would you agree that larger canopies have more pressure resisting a change in the deflection of the canopy via the risers. So you are either doing a 1-armed pull up or fighting against the canopy?



I've made a solo jump on a tandem canopy and didn't notice any difference in pressure from my solo canopies. Of course it did require hauling the riser down a lot further to get similar results.
"There are only three things of value: younger women, faster airplanes, and bigger crocodiles" - Arthur Jones.

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I've made a solo jump on a tandem canopy and didn't notice any difference in pressure from my solo canopies.



Sure, but the EZ-384 has a bit higher riser pressure then the Sigma 370 and still more then the Icarus 360 and/or the A2. It still isn't has high as the rear riser pressure on the Vector tandem reserves.

What does that tell me? Different canopies have different riser pressures and comparing a tandem to a sport main isn't quite the best example.

Having jumped a Navigator 200, 240, 280 and 300 for a good handful of jumps on each. The 300, to me, had high riser pressure then the 200. Same all the way up the board, scaling with each canopy.

I do not doubt what you said in any way, just that I think that a larger canopy typically has higher riser pressure then a smaller canopy of the same design.
--"When I die, may I be surrounded by scattered chrome and burning gasoline."

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I don't doubt that the rear riser pressure on one canopy could be higher/lower than the rear riser pressure on another canopy, but the pressure on the front risers must also change by a proportional amount in the opposite direction so the vector sum of the riser pressures equals the weight of the load.
"There are only three things of value: younger women, faster airplanes, and bigger crocodiles" - Arthur Jones.

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I understand what you're saying. That there is only 1 weight of the jumper and it won't change, there is only that weight distributed over 4 risers. What I'm saying is that although that is true, to get deflection of the canopy you have to take into account the pressure inside the canopy as well as the pressure on the outside of the canopy and the size of the area of the canopy involved in the movement. All of those work together to add resistance. Otherwise the pressure on each riser would simply be 1/4th of the jumper's weight.

I could be completely wrong, but I would like to be shown how I'm wrong so I can learn from it. Know what I mean?
--"When I die, may I be surrounded by scattered chrome and burning gasoline."

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As far as pressure in the canopy, sure there is more air and more fabric on which that pressure is distributed, but I suspect that would be offset by the higher pressure of a smaller, faster flying canopy.

The distribution of the fore/aft riser pressure is influenced by the line attachment points. As an extreme example, I'll offer the original 7-cell 189 ParaFoils. These had non-cascaded "A" lines attached to the front risers. The "D" lines were cascaded into the "C" lines, then the "C" lines cascaded into the "B" lines. So 3/4 of your suspension line attachment points ran to the rear risers, and 1/4 ran to the front risers. This had some interesting properties:

- You could change the trim of the canopy just by changing the length of the A lines. The cascade points in the B/C/D lines would shift fore/aft to keep the canopy flat w/o buckling.

- The front riser pressure was trivial. You could haul the links down to your belly and dive like a Stuka.

- The rear riser pressure was huge. Flaring with rears was not fun.

After the initial production run, they switched to convential A/B & C/D cascades. [:/]
"There are only three things of value: younger women, faster airplanes, and bigger crocodiles" - Arthur Jones.

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