Cross braced canopies

[FlyingBlueJay 0]

I've got a question. I searched for it, but didn't get anything worthwhile.

What is the difference of a cross-braced canopy from a "normal" canopy? What makes it so much faster? Is it just the speed that makes them more challenging to fly or are there control issues as well? Why are they the choice for swooping?

Newbie with a million questions,
-R

There is an art, or rather a knack to flying. The knack lies in learning to throw yourself at the ground and miss. Pick a nice day, and try it. - Douglas Adams

[CanuckInUSA 0]

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What makes it so much faster?

By default they aren’t automatically faster. The speed is a by-product. The x-braced canopy is rigid wing because of the cross braces. If you look at the connection points between each cell on a traditional canopy versus that of the x-braced version, you will see that the traditional canopy has it’s rounded edges between each cell while the x-braced is much flatter. The traditional canopy looses some lift because of the rounded edges on the top skin between cells while the x-braced canopy maintains more lift because the air is allowed to flow smoother over the flatter airfoil. Also because it is a rigid wing, it allows a much high wing loading and this is where the speed comes in. Oh and they also tend to be thinner wings with higher aspect ratios resulting in less drag.

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Is it just the speed that makes them more challenging to fly or are there control issues as well?

The x-braced canopy is incredibly efficient. They can be flown straight in (you do not need to swoop them) and you will automatically notice how much better of a flare they will have. But they are also a beast. When things go wrong, they go wrong real fast. One or two spinning rotations in a matter of seconds during an opening malfunction can result in an altitude loss of a 1000 feet or more. Plus even in full flight, they travel across the sky much faster than the traditional canopy and everything happens just that much faster. So because of this you don’t want inexperienced people flying them. Everything from openings, to potential altitude lose, to flying in the pattern to landings happen faster on the x-braced canopy.

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Why are they the choice for swooping?

They allow for a higher wing loading, meaning more speed and since they are more efficient when it comes to lift, they can be swooped across the ground further.

I’m sure a Brian Germain type character could explain it better than this …

Try not to worry about the things you have no control over

[DrewEckhardt 0]

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I've got a question. I searched for it, but didn't get anything worthwhile.

What is the difference of a cross-braced canopy from a "normal" canopy? What makes it so much faster? Is it just the speed that makes them more challenging to fly or are there control issues as well? Why are they the choice for swooping?

The cross-bracing makes a stiffer wing with more of the individual cells' lift vectors pointing away from the ground which with all else equal gives you acceptable landings (without running or sliding) out of a smaller canopy than you otherwise would. The final landing speed on a 104 cross-braced canopy doesn't seem too different than a 120-135 square foot conventional elliptical or 150 rectangular planform. It allows the cells to be wider which means you can have fewer lines with less total drag for a given span (8 sets instead of 10).

The efficiency appears to allow the use of thinner airfoils which have less lift (remember it's pointed in the right direction) and drag which allows the canopies to go faster especially in a dive, and retain that speed longer after planing out.

Since smaller canopies which go faster and farther are ideal for swooping the other design characteristics are adjusted to better that goal, like steeper trim and a longer line set which causes the canopy to take longer to return to level flight after a speed inducing maneuver and build more speed in a dive. You could have a cross-braced canopy without those characteristics but there probably wouldn't be too many people willing to pay for the construction and pack volume when their conventional canopies already land acceptably.

[AggieDave 6]

Here's a good visual to understand what wingloading does to a canopy.

Think of an air matress and a fat chick (or dude...whatever you want). The air matress distorts, right? Well our canopies do that too, the top skin won't maintain an efficent airfoil shape, so the canopy just won't fly quite as well. There were different thoughts on this, but about 20 years ago a handful of people came up with the same idea: crossbracing. There was a few different ways they tried it at first, but what you see now is what won out of those original designs.

What the xbracing does is keep the canopy from changing shape at what would have been considered extreme wingloadings just 15 years ago. That allows us to have a smaller canopy, which gives us more speed, which we need to be the best swooper for our skill set.

The other two answers said that, but they didn't have a cool (gross?) visual to help the initial concept which the rest was based on.

--"When I die, may I be surrounded by scattered chrome and burning gasoline."

[FlyingBlueJay 0]

Thanks for the detailed answers.
I get it now!
-R

There is an art, or rather a knack to flying. The knack lies in learning to throw yourself at the ground and miss. Pick a nice day, and try it. - Douglas Adams

[d123 4]

Sorry for adding more wood on the fire but .... I'm really interested in that subject.

I have an XBraced kite and all the para-gliders that I've seen were XBraced too. I've been asking myself a lot why that XBraced thing makes the wing so much efficient. I've found myself a small acceptable explanation and I'm wonderig if it's any good. Please correct me if you feel that I'm wrong.

Let's say we have a wing with 3 cells, 5 vertical ribs and 4 sets of ABCD lines (connected to the ribs).

I'm thinking that:
- in flight, the middle cell for instance, because of the internal pressure will bulge and by doing that it will force the wing to lose span and projected area. (up left corner of the attachment)

- To correct this problem we place 3 more ribs (one in middle of each cell). Those ribs can be attached to lines or not.

- Case 1: If they are attached to lines it's just like we double the number of cells. We add more drag because of the extra lines. (down left corner of the attachment)

- Case 2: If the 3 extra ribs are are not attached to lines the cells will still deform but in a zigzag kinda way (up right corner of the attachment).
We can fix this last problem by adding the XBraced fabric that force the free ribs to stay locked (on the vertical axis) relative to the other ribs. This is reducing the lost area due to cell bulging. (down right corner of the attachment)

So in the end, with the XBrace setup, for the same nylon surface we get more projected surface without adding extra drag. Does it make any sense?

Please Discuss.

Lock, Dock and Two Smoking Barrelrolls!

[jakee 1,594]

You've got the x-bracing structure wrong.

In x-braced canopies there are three chambers between each line attatchment point, 2 with diagonal braces and a central one without.

This magnifies the effect of getting a thinner, higher aspect ratio wing with fewer lines.

Do you want to have an ideagasm?

[d123 4]

I've just checked and you are right! On parachutes & paragliders each cell is divided in 3, just like you describe it.

In the attachment I've drawn the cross braced setup that I have on my kite. I agree with you, that adding 3 ribs with 2 diagonal braces for each cell makes the wing more efficient compare with 1 rib + 2 brace per cell. Don't know exactly why they chose that method.

http://www.cobrakite.com/beamer2.html

Lock, Dock and Two Smoking Barrelrolls!

[jakee 1,594]

I'm always right!

But of course different disciplines have different needs. Icarus and PD have both now built canopies with quad braced cells, with 2 braced each side of the line and one central non braced chamber in each cell. Neither are released yet and there is some debate as to whether they ever will (market forces and all that).

What is really interesting is the bracing used in PG Comp wings (far, far more efficient than anything currently used in skydiving). Ozone used to have a page whare you could see the basic structural schematics of each wing they made, but they seem to have overhauled their website and got rid of it. If you can find any schematics or photos of high performance PG wings you'll see an complete mix of quad, tri, half tri and non braced cells across the span of the glider. Cool stuff.

Do you want to have an ideagasm?

[d123 4]

Gee, Every day you learn something new and ...
Once again you are right.

If I'm not wrong all the current products from PD are non x-braced. I didn't know that PD had made in the past a few x-braced canopies. After I've read your post I've googled arround and I've found (not far away from here) about the z-braced.
http://www.dropzone.com/cgi-bin/safety/detail_page.cgi?ID=566

How come Excalibur and other x-braced canopies are no longer available in PD current line of products?

Lock, Dock and Two Smoking Barrelrolls!

[jurgencamps 0]

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If I'm not wrong all the current products from PD are non x-braced. I didn't know that PD had made in the past a few x-braced canopies. After I've read your post I've googled arround and I've found (not far away from here) about the z-braced.
http://www.dropzone.com/cgi-bin/safety/detail_page.cgi?ID=566

How come Excalibur and other x-braced canopies are no longer available in PD current line of products?

Velocity http://www.performancedesigns.com/products.asp?product=ve

[jakee 1,594]

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How come Excalibur and other x-braced canopies are no longer available in PD current line of products?

The current PD x-braced canopy is the Velocity. It's probably the most popular x-braced wing out there right now.

The Excalibur was F-111, I gather that it was discontinued when conventional ZP canopies came out that outperformed it. The gap between that and current x-braced canopies was (I think) partly because there was no need for them, conventional canopies were being developed that were bringing enourmous performance gains - and partly because of problems in getting them to open acceptably. Icarus brought out the first 'modern' x-braced canopy with the FX.

Do you want to have an ideagasm?

[riggerrob 643]

The Excalibur was F-111, I gather that it was discontinued when conventional ZP canopies came out that outperformed it.

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Excalibers did not last very long, because their fabric did not last very long. Sure, F-111 fabric may have porosity of 0 to 3 cubic feet per minute, when it is new - and Gelvenor Textile Mills used to brag that their fabric was consistently 0 .5 cfm (out the door), but after 70 jumps, non-coated fabric (i.e. F-111) starts to loosen up. By 300 jumps, Excalibers landed too hard.

A couple of years after Excaliber was introduced, Parachutes de France started (circa 1988) making canopies from silicone-coated nylon fabric that had xero-porosity when new and held that zero porosity for many hundreds of jumps. ZP fabric has dominated the market ever since.