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Quagmirian

My little project

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I've seen a ton of airfoils and most paraglider a use a rounded bottom. The shape of the bottom skin would have to be inversely shaped to the top skin. Where the top skin bulges at the thickest point, it would need to be taken in at that same point. Line trims would be harder to calculate, but what the hell. It's all done on computers now anyways and it practically does everything other than sew it for you. There's got to be another reason. All of the ones with curved bottom ribs are older designs and 0-3cfm. Any zp models use the full shape?

One possible issue I can think of is distortion between attachment points getting worse due to the outward bulge, creating a sort of dimpled bottom skin. Especially on larger canopies. Also opening issues if the a's aren't the shortest. If the nose has extra slack to move free of the slider stops the nose could catch too much air, spread open into a u shape around the slider during deployment causing slammers.

Sure it's crude, but why should it be. A tapered bottom skin in theory should help eliminimate the wash under of air at the opening that creates turbulence in the airflow over the bottom skin. Sure, if it's not broke, don't fix it.... But I'm not satisfied. Hmmmmmmm
I was that kid jumping out if his tree house with a bed sheet. My dad wouldn't let me use the ladder to try the roof...

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Alexg3265

I've seen a ton of airfoils and most paraglider a use a rounded bottom. The shape of the bottom skin would have to be inversely shaped to the top skin. Where the top skin bulges at the thickest point, it would need to be taken in at that same point. Line trims would be harder to calculate, but what the hell. It's all done on computers now anyways and it practically does everything other than sew it for you. There's got to be another reason. All of the ones with curved bottom ribs are older designs and 0-3cfm. Any zp models use the full shape?

One possible issue I can think of is distortion between attachment points getting worse due to the outward bulge, creating a sort of dimpled bottom skin. Especially on larger canopies. Also opening issues if the a's aren't the shortest. If the nose has extra slack to move free of the slider stops the nose could catch too much air, spread open into a u shape around the slider during deployment causing slammers.

Sure it's crude, but why should it be. A tapered bottom skin in theory should help eliminimate the wash under of air at the opening that creates turbulence in the airflow over the bottom skin. Sure, if it's not broke, don't fix it.... But I'm not satisfied. Hmmmmmmm




I'm not sure I understand this correct, so forgive me if I got it wrong.
You are saying paragliders have smaler cells on the edges and larger in the center?
A BT pro also has that shape, and with a tricell (not crossbraced, straight ribs) on the first and last cells.

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I think he's talking about the rib section rather than the cell width across the span. Like on this foil, where the bottom skin curves upwards towards the nose.

[inline sim_2016_small.png]

There's some aerodynamic stuff going here which I don't really understand, but apparently it's a better design, which makes me wonder why all the manufacturers don't do it. I'm guessing construction simplicity or maybe a strength thing. Loads of old Paraflite canopies used the 7808 foil.

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Flat bottom airfoils are substantially more stable in turbulence.

Staying with a standard relatively low AR square canopy, and using a curved bottom airfoil, would offer little to no performance increase, with a large sacrifice to stability.

Fluid wings is playing with a comp version of their swoop canopy (think petra-esque) that heavily borrows from paraglider design, like internal seams and curved bottom foils, intended for select hands only.
"As soon as you're born you start dying. So you might as well, have a good time."
-CAKE

I'm crazy not stupid. There is a difference.

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Quagmirian

I think he's talking about the rib section rather than the cell width across the span. Like on this foil, where the bottom skin curves upwards towards the nose.



There's some aerodynamic stuff going here which I don't really understand, but apparently it's a better design, which makes me wonder why all the manufacturers don't do it. I'm guessing construction simplicity or maybe a strength thing. Loads of old Paraflite canopies used the 7808 foil.




Yes, like that. Exactly. I have to disagree with the stability thing. This shape of a convex bottom airfoil can tolerate more pitch before folding under an edge in turbulence. Or should in theory. When it has a flat bottom, it'll have more of a tendency, to over fly. (Think ground launching) of course cg and trim effects this. Just something I've noticed. Or thought I did? The ones with the tapered bottom, when kiting, tend to hold their pitch better, and don't over fly. I'm working on a dedicated quadcopter, canopy test vehicle. Basically fly the quad up, cut the blades, dump the canopy which is attached to the quad, then steer it back down with servos. I've been dropping just shot bags under the canopies till now.
I was that kid jumping out if his tree house with a bed sheet. My dad wouldn't let me use the ladder to try the roof...

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Bad picture, quick sketch. This is what I'm talking about.
When rounded the air can separate and flow more smoothly and distribute the pressure more evenly, and it'll help the leading lower edge smoothly deal with the overflow air from the stagnation point around the opening. That's how it works in my head anyways.
I was that kid jumping out if his tree house with a bed sheet. My dad wouldn't let me use the ladder to try the roof...

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Good news everyone!

After searching for somewhere to cut out my pieces for six months, I've been allowed to use the basement under my flat. I've put down some hardboard and I've just about finished assembling the cardboard patterns. I've already cut out a new slider and sewn it together. I will try to get pictures at some point.

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I could draw around a pattern and then cut it out. You have to with heavier fabrics were you're going to use a higher powered hot knife. But for light fabrics where I'm going to use my small knife I generally just weight the pattern and cut along the edge. It's a little hard on pattern paper but it will last long enough for a couple of proto types. And it's faster. You've cut it in the time that you would have spent drawing.

It's a little trickier pealing the fabric lose. You have to kind of get the knack for it and do it in the right direction along the bias of the cut so you don't fuck up the edge.

Lee
Lee
lee@velocitysportswear.com
www.velocitysportswear.com

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But curves are a pain in the ass. I never could get that to work. High temp Formica does well even with heavy knives and it doesn't drain the heat of the hot knife like aluminum. Although Al is easy to cut with a powered nebular.

Lee
Lee
lee@velocitysportswear.com
www.velocitysportswear.com

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This is my setup. I draw all the panel shapes in Photoshop, and then transfer them onto paper to make my pattern pieces:

[inline parts_small.png]

[inline pattern_start.jpg]

Then I punch holes in the paper patterns so I can plot match up marks with a pen before cutting. Then I cut out the fabric with a soldering iron. I put some metal tape on the crossports of the rib pattern because the edge was really suffering there, pulled threads and whatnot.

[inline photo.JPG]

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Hi Quag,

Quote

cut out the fabric with a soldering iron



You are going to spend a lot of time & effort on this project.

I would strongly recommend getting something better to cut things out with. A good hot knife will leave you with nicely cut edges and make the work go a lot faster.

When I first starting cutting fabric/webbing ( back in the Stone Age ) I also used a soldering iron, that I had sharpened. BTDT B|

I implore you to spend a few dollars/pounds & buy something good.

Try this, it may come in 220V: http://products.mmnewman.com/item/heavy-duty-hot-knife-and-tips/heavy-duty-hot-knife/hk-60?

JerryBaumchen

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I have most of the parts cut out now. Most of the crappy edges with pulled threads will be on the inside anyway. :D I've done a little bit of sewing and I made a new slider too. I bought some cheap, British made grommets and a die too. Hopefully they're up to the job.

[inline grommet.jpg]

[inline slider.jpg]

[inline slider_close.jpg]

[inline stabiliser.jpg]

[inline stabiliser_close.jpg]

Bridle attachment reinforcment
[inline bridle_patch.jpg]

Hilarious comedy warning label version 2
[inline label.jpg]

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Outstanding. Motor onwards. Sew, sew, sew. We want to see the vid from the first jump.

Build it and go jump the shit. But one thing I do notice is your reinforcement for your slider stops. I think I would make the fold unders longer. All the way across so that you had three layers. That way you slip the chip between two layers of tape rather then just f-111. There's going to be a lot of load between the bar tack and the chip. In the long term you might need something heavier to contain the chip on opening. I'm thinking wear issue, long term. But go jump it. If you need to change it later do so. You can always sew another layer on top of it later.

Lee
Lee
lee@velocitysportswear.com
www.velocitysportswear.com

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