Thoughts about Z-brace

[morris 0]

To start with I`d like you to have a look at the attached picture. It shows a Velocity96, loaded at 2.4, after a 450degree turn from 1100ft, just before the entrygate. Viewing the canopy from behind and below (almost invisible from the front), you can see that the bottomskin of the centercells in between linegroups are "out of shape", meaning "too high" (of course mostly in the middle of the canopy). The X-braces hold the topskin in place, but can`t do that to the bottomskin. So on a "traditionalbraced" canopy 3/3 of the topskin and 2/3 of the bottomskin are "where they belong". Does anybody agree so far?

Now lets have a look at a Z-brace: The next, additional X-brace(s) - the "Z-brace(s)" - are fastened at a place that is already "too high" this will result in the centercell topskin being "too high" as well (don´t even wanna think about the bottomskin of the centercell!). This problem can´t be solved by just making the brace shorter cause the cell has a given width as well. So on a Z-brace just 2/5 of the topskin is in place, same goes for bottomskin, centercell(s) being even "second floor". This will create kind of a curve of the profil in between line groups, not the way the perfect profil should look like... (and if you look at the picture of the PD prototype on their Z-brace informationsheet from the PIA two years ago, it really looks a bit like that, even though it doesn´t look like being in full flight/full speed)

Now please tell me that I´m totally wrong (and how things are for real), cause otherwise a Z-brace would just be more expensive, more packing volume, but most likely not more performance.
Thanks, Morris

[morris 0]

Here comes the picture once more in higher resolution...

[Samurai136 0]

Quote

To start with I`d like you to have a look at the attached picture. It shows a Velocity96, loaded at 2.4, after a 450degree turn from 1100ft, just before the entrygate. Viewing the canopy from behind and below (almost invisible from the front), you can see that the bottomskin of the centercells in between linegroups are "out of shape", meaning "too high" (of course mostly in the middle of the canopy). The X-braces hold the topskin in place, but can`t do that to the bottomskin. So on a "traditionalbraced" canopy 3/3 of the topskin and 2/3 of the bottomskin are "where they belong". Does anybody agree so far?

Nope. You've got it backwards. Read pages 99- 105 of Brian Germain's The Parachute and It's Pilot

2/3 of the top/ bottom skin are slightly more "deformed" because they are tied to a physically loaded rib. The point of the bracing is to smooth out the normal "ballooning" between loaded ribs on conventional canopies. By introducing more ribs, flattening out the top and bottom skins is achieved; parasitic drag is reduced.

See the attached Photo. The top and bottom skins are deformed in the same 'pattern'.

"Buttons aren't toys." - Trillian
Ken

[morris 0]

So far so good, but how about Z-brace? The centercells in between linegroups on our chutes now are "supported" by X-braces from BOTH sides. This is not the case with the additional cells of a Z-brace (the ones right next to the center), right? On those you got "bracesupport" just from one side...

[RTB 0]

You're not totally wrong but i think you are focusing to much on one aspect of what makes the wing perform.
The span wise shape of the wing is not the most important aspect of lift or performance. It's a tradeoff between all parts that affect flight, the amount of drag from lines being one. So the end result cannot easily be deducted from your analysis, if could quite well be that the sum of the positive and negative aspects of z-brace is positive. And I think the manufacturers will make sure that they get a increase in performance or else the design will never reach production.

[Samurai136 0]

Quote

So far so good, but how about Z-brace? The centercells in between linegroups on our chutes now are "supported" by X-braces from BOTH sides. This is not the case with the additional cells of a Z-brace (the ones right next to the center), right? On those you got "bracesupport" just from one side...

Z-bracing appears to smooth out the top and bottom skin (reducing drag). See attached photo of a JSX Z-braced canopy. It appears to me to be a more efficient wing than the original JVX photo (x-braced).

"Buttons aren't toys." - Trillian
Ken

[proswooper 2]

one of the other things that creates uneven distortion on the velo 96 you have pictured is that it has one cell in everythree that is closed off completely at the nose and has a different pressurization as the rest.

but you are right about the cell structure of normal cross brassing techniques, ie those used on most production canopies. it still leaves alot of room for improvement.