no D lines

[RiggerLee 61]

I have absolutely no fucking clue why you would say that I'm the best person to ask. Have you not grasped the fact that most of what I say comes straight out of my ass?

I do enjoy setting around and theorizing on this shit. Scratch my head, scratch my butt, muse about a design. What else is there in my life? But please don't miss represent me as a knowledgeable source of information.

But it is an interesting question. You've had me thinking a lot about the aero elastic issues lately. I'm not sure what would be the best way to model some thing like that.

Let's say that the fabric is stable. In other words it does not distort on the bias. But it is fabric so it supports tension but it can not support compression. So what actually supports the wing? Each section of the cord is supported by a line attachment on each end. I suppose you could look at it as the lift distributed across that section of the cord and examine it as a beam with a bending moment. Based on the height of the rib would it be fair to look at the internal pressure. Thinking of it as a hinge point at the top surface and looking at the compression that you could support between the lines. You would also see a compression in the top surface above the line attachments.

So the tendency towards waviness would depend on the rib thickness, the lift distribution, and the inflation. Rib thickness is a question of design. Lift distribution, a product of the Cp curves, line spacing, and wing loading. And inflation should depend on dynamic pressure and nose design. The internal pressure should mostly depend on the nose cut and the pressure across it at that angle of attack. So it should be some percentage of Q.

I would expect it to be more of a problem at lower speeds like on flare. But at that point you're pulling down on the tail and adding support to areas where you might expect to see the most distortion. I guess it's a question of what you think you can get away with. For example larger canopies can have seven line attachments rather then four or three. And they may have fifteen or more cells rather then nine although they may not be that much higher in AR. I'm honestly not sure how much of that is rib distortion and how much is just distributing the load both during and after opening.

I wonder if it would be better to look at the fabric as being some what softer. I suppose you could look at it in terms of forces along the fabric and tapes. Looking at it as the incremental lift along the cord transferd down along the fibers of the fabric to the diagonal tapes. Then based on the angle of the tape down to the attachment point. So it's three ways. Fibers down to the tape. Fiber between the diagonal tapes at that height, and the tape down to the line. You could integrate that along the cord and look at the compressive force between the two line attachment points. I'm not sure it would give you any better of an answer. It's probable just another way to think about it. It still comes down to the same thing.

I got to thinking about this because you're friend sent me a pic of the single skin canopy he was playing with and I was thinking about how big the flares would need to be with out the inflation of the bottom skin.

Lee

Lee
[email protected]
www.velocitysportswear.com

[erdnarob 1]

I have to add two types of canopies where one or two D-lines are missing.
1) the Katana has only 4 D-lines on each side due to the tapered end
2) the Stiletto has only 3 D-lines on each side due to the tapered end
3) the Nitro and the Nitron have also 3 D-lines on each side for the same reason
OTOH these four canopies have 5 C, B and A lines on each side since they are 9 cell canopies

Learn from others mistakes, you will never live long enough to make them all.

[mcordell 2]

Mine has 5 a, b, and c lines and no d lines cause it's a 9 cell ;-)

www.facebook.com/FlintHillsRigging

[piisfish 135]

Can you tell us more about the canopy ? I am interested in "older" designs and also jump a Batwing and a BT40. Always hungry for knowledge

scissors beat paper, paper beat rock, rock beat wingsuit - KarlM

[mcordell 2]

piisfish

Can you tell us more about the canopy ? I am interested in "older" designs and also jump a Batwing and a BT40. Always hungry for knowledge

I posted a pic a somewhere in the thread and it is the one in my avatar. Here is the data panel. The story as I understand it is that bill gargano built the model for his wife and my mom ran into them at a boogie in california and liked the joule so he built her one. Not sure how many he made but this is the second one. It is a 9 cell and even with no d lines it flies very well but the glide angle is pretty steep. This canopy has less than 200 jumps...may be less than 100 but can't say that for sure. It flares like a dream. I have an exit weight of 195-200 and my primary rig is a sabre 2 210 but this gives me landings every bit as soft...I just can't make it back from a bad spot. I don't jump it too often but it is packed in her vector with a raven 1 reserve. I had it reharnessed by tom dolphin so I could take her gear for a spin every so often. It's as close as I can get to jumping with her.

www.facebook.com/FlintHillsRigging

[RiggerLee 61]

I was going back and looking at some of the pictures earlier in the thread. It's a great picture of the unit. Look how bowed the bottom seams are at the end of the flare right before the stall when the inflation pressure is so low. You can see all the lift that it's trying to support between the a and b lines.


Lee

Lee
[email protected]
www.velocitysportswear.com

[likestojump 3]

Some more GQ Unit pics.

I love the lines too :)

[piisfish 135]

Thanks for that part of history and for the pic of the data panelPlus the canopy does have some personal and sentimental interest

scissors beat paper, paper beat rock, rock beat wingsuit - KarlM

[riggerrob 558]

Quagmirian

***I guess this no-D-line design reduces packing bulk somewhat, as well as air drag for the speedsters. But it seems like it would also put additional load on the remaining A-B-C lines. Does it cause them to break more often or sooner?

As far as I know, reducing the number of chordwise lines is actually a bad thing in terms of load distribution to the canopy. The fewer lines you have, the bigger the gap between them and the bigger the bulge upwards in the wing as there is less to support it. So at a certain point you will offset any reduction in line drag with a decrease in canopy efficiency.


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Clear concept, but eventually the extra drag (from too many D lines) out-weighs the extra drag from airfoil distortion.
That could all be rubbish by the way, best to ask RiggerLee.

[zoobrothertom 5]

I loved my Unit because of the 'awesome' openings! The last version of the Unit I was made with F-111 and opened even slower!

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I'm back in the USA!!