Is a XAOS less stable than an FX

[ramon 0]

This is a theoretical discussion only I am not pointing fingers and it is sort of a rehash of riser pressure/stability. Plus we probably should not be trying what we were.
Facts: Looks like an FX (or a velocity for that matter) but modifications in nose shape, stressed stabilizers, non cascaded lines, line trim (angle of attack and center of gravity change), and of course line material (minor).
The canopy does have lighter riser pressure than it's cousin the FX. General discussion with pilots seems to point to possible shallower angle of attack in fullflight. I am no expert but I heard this can be achieved by moving the center of gravity further back on the wing somehow (ala Cobalt or Alpha). I am unsure how you can make the canopy have a shallow angle of attack without shifting this weight and therby lessening the riser pressure. But the stilletto which supposedly has a shallow angle of attack has high riser pressure.
Anyway.
Item 1. There was a fellow who had his small xaos (68 I beleive) collapse on one side then go into line twists, in VA. No I have no knowledge of this incident at all. He seemed to have low jump numbers (for that canopy..maybe 500?) and maybe he did somehting to induce the canopy to colapse (possible deep brake turne bordering on stall turn). I just don't know, but somehting resembling that happened report said he was amking a slight correctionat 50' and that is kinda low. alegedly winds were 10 mph with gusts to 16. I know that could be dangerous if the right gust at the right time happens, but most cross brace pilots brag about how stable their canopies are in gusty weather...beats me.
item 2. My friend Wane and I are fans of doing small Crew with whatever we are jumping Samurai, vengeance, FX etc. We have done a 2 stack with me FX109 (2.0) him Extreme 99 (1.8). Canopies appeared stable though it was twitchy ans if I applied a little brake his wanted to outlfy me ever so slightly. Wane bought a Xaos 80 (loaded 2.2) he tried a 2 stack with an FX 84 (my friend hoop) loaded about (2.2). Twice when the Xaos tried to dock on the FX it would colapse and spiral up. I videoed this so it seemed like air to the nose would be bleed out and sides would do their own thing, or that the nose wouldn't have anywhere to go and then the sides would out fly it. It was really violent and after the second time wane kicked out of twists almost cutting away they gave up.
item3 We had a couple of locals with the corssfires requireing modifications. My friend JD was boasting about his extremely light riser pressure. bulletin came out, he got it back and the riser pressure was now in the high range.
Final discussion topic. If a canopy is trimed steeper should it be more stable and how can you trim a cnopy shallow and have heavy riser pressure (stilleto) can you do the reverse?
ramon

[ramon 0]

Item 4 This is total hearsay from someone who will be left un named. Red Bull Blade Raid. There were high winds. Two canopies collapsed during competition before they stopped the competition. hearsay has it that they were both jumping XAOS, one of them was Andy Farriginton and one of them (not sure which) was bruised pretty good from the incident.
sorry I totally forgot that in the original post but I wanted the canopy intelligensia to read it.
ramon

[Hooknswoop 19]

I'm sure Quade can do a much better job w/ this one, but this is my understanding.
The shape of the airfoil determines where the low pressure above the wing is centered. If the low pressure is located near the nose of the canopy, front riser pressure will be higher and the canopy more resistant to collapse. If the center of lift (low pressure) is located farther back, the front riser pressure is lighter, but then there is also less force pulling on the lines and more prone to folding under.
A canopy is restrained from folding up by your weight and the lines. It can fold downwards. What keeps a canopy from folding down is the pressure differential between the top and bottom of the canopy and it's rigity from the ram-air coming in the nose. The steeper a canopy is trimmed, the faster it will fly, creating a higher internal pressure, all other things being equal. Turbulence pushing down on the canopy can cause any canopy to fold under if it strong enough.
So it seems to me that a canopy w/ high front riser pressure is more resistant to having the nose fold under. Of course, hook turners like a low front riser pressure for those long dives. What is the right answer? That's for the guys w/ the cool CAD progams to figure out.
Hook

[freeflyguy 0]

Yah, I guess what I can say, is you appear to have a brain in your head.
That is important.
From my experience, flying a XAOS 21, I have no issues with it. I have close to 100 jumps on them. I like it, and think it is a safe canopy. One time, in gusty weather, I pulled a riser to start my turn, and it instantly went to my chest. I have had that happen on other canopies too. But it is never fun, and makes you think. We fly balls of fabric that depend on the wind doing what the desighners think it should. That is usually good. But sometimes, bad.
As far as the Blade raid. Yah. I watched Andy's video of his mishap. Not a happy event. But keep in mind that was the XAOS 27, it hasn't been released to the public. They are still tweaking it. I don't think Andy has even taken it to terminal. Although it did kick ass in Venezuala.
Another thing about that blaid raid. It is spooky. They exited at about 13K, swooped at near 10k. That day the winds were at 60mph at 16k, or something. So there were some wicked gusts, tree factor included. It wasn't just the Precision canopies that had issues. Watch the video. There were a number of canopies, I watched a Velocity go wacko, then come back. Scary stuff, but all of the canopies did it, in that wind. That is why they called the competition. Scary stuff.
One thing all the Manu's must have got from all that is mass amount of R & D.
Anyway. That said. yah, it was a scary video

[ramon 0]

It was impossible to find any info out there on blade raid.
I wonder if the other team member was on a 27 also?
ramon

[eames 0]

First off, I have two Xaos 98's loaded at ~2.4 and I have ~150 jumps on them. They have been equally (or more) stable than any canopy that I've ever jumped.
Item #1. That jumper was flying his Xaos 68 over a spot that was known for bad rotors and he was flying in a relativetly low-speed flight mode. I went over to their dz after it happened, and from what I gathered, it could have happened to any canopy. Another jumper also told me about her Triathalon 135 collapsing in the same spot, in similar conditions. Was it the Xaos? I really don't think it was.
Item #2: Crew with FXs, Velocitys, Xaos'? And you're complaining about stability in a stack? Imagine that Xaos in tight wrap with those HMA lines around your ankle. High performance canopies are not designed with crew in mind. Do you think the manufacturer was thinking, "hmm... when someone docks on our extremely high performance 80 sqft canopy, it loses pressure... what can we do about that"? No. Complaining that ANY of those canopies is unstable in crew is like complaining that a Corvette is not good for off-roading.
I think you may be on to something with the front riser pressure vs. forward canopy stability. Maybe it does allow front end collapses more easily.
Moral of the story: Don't jump any canopy in very turbulent conditions. They ARE fabric, and at some point, they will ALL fail. Also, you don't expect a crew canopy to swoop... so don't expect a swoop canopy to be good for crew.
Jason

[billvon 2,998]

>The shape of the airfoil determines where the low pressure above the wing is
>centered. If the low pressure is located near the nose of the canopy, front riser
>pressure will be higher and the canopy more resistant to collapse.
Riser pressure is also greatly influenced by line placement. If the line attach points are situated such that one front riser pulls down 20% of the canopy, it will tend to have lighter front riser pressure than a canopy rigged such that a front riser will pull down 30% of the canopy.
-bill von

[cobaltdan 0]

airfoil and line trim primarily determine riser pressure.
to a smaller degree planform.
sincerely,
dan
atair
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[polarbear 1]

Would you mind giving a brief description of how the above factors affect riser pressure? Seems like it would be good, just for general knowledge.

[ramon 0]

don't get me wrong, I'm just making observations.
ramon

[ramon 0]

You have adroitly put several times that the stilleto and the FX have the same airfoil, line trim and plan form must be slightly different, but they both have hard riser pressure.
I can't imagine the Xaos having a different planform and airfoil than the fX so it must all be line trim there...
Am I correct?
ramon

[alan 1]

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You have adroitly put several times that the stilleto and the FX have the same airfoil, line trim and plan form must be slightly different,

I asked Simon Mundell at Icarus if the FX and Stiletto had the same airfoil. He said they did not.

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I can't imagine the Xaos having a different planform and airfoil than the fX

I asked Chris Martin at Precision if the Xaos and FX had the same airfoil. He said they did not.
Quade has in earlier threads referenced some published materials that may give you some insights. They had to do with principals of lift and aerodynamics( from a thread about stalling?). A search of his posts or a request to him should provide the links. You are looking for the relationship between the airfoil design, center of lift, center of mass, center of gravity, angle of incidence, wing loading, planform and how they all interact to effect canopy pressurization. I don't understand it well enough to attempt a summary here in just a few paragraphs. Quade, care to try?
alan

[ramon 0]

I'll go back and read more of the stalling thread

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I asked Chris Martin at Precision if the Xaos and FX had the same airfoil. He said they did not.

This sort of puts to rest any wacko theories I had about line trim changes.
I appreciate it.
ramon

[cobaltdan 0]

paul martin (jyro) designer of icarus canopies told me on record that all icarus canopies use a stilletto airfoil.
its no big deal. in fact so many canopy companies use this airfoil it is simply refered to by designers as the pd airfoil.
sincerely,
dan

[alan 1]

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paul martin (jyro) designer of icarus canopies told me on record that all icarus canopies use a stilletto airfoil.

......hmmmmmm, seems as if Paul and Simon should get together and talk, so they give consistent information, or better yet, join Dan Preston, Bill Booth, Chris Martin, George Galloway, Bill Hallett and the others who have been posting here directly (sorry if I missed anyone). The contributions they have made have been valuable to the many skydivers that read Dropzone.com and follow their favorite forums. The real value comes in differring opinions, points of view and information that are supported with experience, sound reasoning and research or testing data. It gives each of us the opportunity to evaluate it for ourselves and form our own opinions. It does not need to mean that one has to be pitted against the other, but many rumors and myths about skydiving and the gear we use could be dispelled and a healthy debate in a moderated forum can result in the exchange of important information. With the amount of money manufacturers spend on advertising to get out information about their products, it amazes me that they don't all post here, especially given that it is free and the number of readers that Dropzone.com has. That is not an open invitation to come here and openly/blatantly advertise or promote their products, but to simply respond to requests for information, whether it is about performance, maintainence, safety concerns, etc.. I think that Dropzone.com has a more personable flavor to it than the skydiving related printed media.

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its no big deal. in fact so many canopy companies use this airfoil it is simply refered to by designers as the pd airfoil.

As an interesting side note to this, John L. has stated that the Stiletto uses the same airfoil as the Sabre, and more recently, they used that same airfoil on the Spectre. It just demonstrates that a good airfoil design can be the basic building block of performance, but planform, line trim and other factors all interact to determine the performance and flight characteristics of a canopy.
alan