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My little project

 

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Alexg3265  (C 42218)

Aug 16, 2014, 9:44 AM
Post #251 of 290 (2114 views)
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Re: [RiggerLee] My little project [In reply to] Can't Post

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


Hellis

Aug 17, 2014, 11:11 PM
Post #252 of 290 (1995 views)
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Re: [Alexg3265] My little project [In reply to] Can't Post

Alexg3265 wrote:
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.


Quagmirian  (A 110392)

Aug 18, 2014, 5:41 AM
Post #253 of 290 (1926 views)
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Re: [Hellis] My little project [In reply to] Can't Post

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.
Attachments: sim_2016_small.png (8.22 KB)


ineed2fly  (A 57696)

Aug 18, 2014, 10:17 AM
Post #254 of 290 (1871 views)
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Re: [Quagmirian] My little project [In reply to] Can't Post

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.


Alexg3265  (C 42218)

Aug 18, 2014, 10:51 AM
Post #255 of 290 (1851 views)
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Re: [Quagmirian] My little project [In reply to] Can't Post

Quagmirian wrote:
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.


(This post was edited by Alexg3265 on Aug 18, 2014, 10:52 AM)


Alexg3265  (C 42218)

Aug 18, 2014, 11:05 AM
Post #256 of 290 (1838 views)
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Re: [Alexg3265] My little project [In reply to] Can't Post

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.
Attachments: image.jpg (147 KB)


Quagmirian  (A 110392)

Sep 8, 2014, 1:22 PM
Post #257 of 290 (1524 views)
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Re: [Quagmirian] My little project [In reply to] Can't Post

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.


riggerrob  (D 14840)

Sep 9, 2014, 8:56 AM
Post #258 of 290 (1419 views)
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Re: [Quagmirian] My little project [In reply to] Can't Post

Good on the table.
Do you have a hot-knife?


Quagmirian  (A 110392)

Sep 9, 2014, 9:09 AM
Post #259 of 290 (1411 views)
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Re: [riggerrob] My little project [In reply to] Can't Post

I use a 30 watt soldering iron. With a good technique (I find the fabric has be under a little tension), I can get a really nice edge.


riggerrob  (D 14840)

Sep 9, 2014, 9:13 AM
Post #260 of 290 (1402 views)
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Re: [Quagmirian] My little project [In reply to] Can't Post

May I suggest that you also use a metal (steel or aluminium) ruler?
The best rulers have cork or rubber glued to the underside.


Quagmirian  (A 110392)

Sep 9, 2014, 9:20 AM
Post #261 of 290 (1402 views)
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Re: [riggerrob] My little project [In reply to] Can't Post

I don't understand. What would I use a metal ruler for?


riggerrob  (D 14840)

Sep 9, 2014, 9:24 AM
Post #262 of 290 (1389 views)
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Re: [Quagmirian] My little project [In reply to] Can't Post

Use the metal ruler to clamp fabric to the table while you slide your hot-knife along the edge.


(This post was edited by riggerrob on Sep 9, 2014, 9:26 AM)


RiggerLee

Sep 9, 2014, 9:36 AM
Post #263 of 290 (1372 views)
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Re: [riggerrob] My little project [In reply to] Can't Post

I thought that was what the pattern peace's were for?

Lee


riggerrob  (D 14840)

Sep 9, 2014, 9:39 AM
Post #264 of 290 (1363 views)
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Re: [RiggerLee] My little project [In reply to] Can't Post

Metal patterns are often used in production.
Prototypes are more often cut with metal rulers, carpenter's triangles, coffee cans, French curves, etc.


RiggerLee

Sep 9, 2014, 10:00 AM
Post #265 of 290 (1345 views)
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Re: [riggerrob] My little project [In reply to] Can't Post

 
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


riggerrob  (D 14840)

Sep 9, 2014, 10:18 AM
Post #266 of 290 (1335 views)
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Re: [RiggerLee] My little project [In reply to] Can't Post

Another option is to protect the edges of your paper/cardboard patterns with adhesive metal tape.


RiggerLee

Sep 9, 2014, 10:54 AM
Post #267 of 290 (1305 views)
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Re: [riggerrob] My little project [In reply to] Can't Post

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


Quagmirian  (A 110392)

Sep 12, 2014, 3:20 PM
Post #268 of 290 (1134 views)
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Re: [riggerrob] My little project [In reply to] Can't Post

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





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.


Attachments: photo.JPG (406 KB)
  pattern_start.jpg (141 KB)
  parts_small.png (23.8 KB)


JerryBaumchen  (D 1543)

Sep 12, 2014, 3:58 PM
Post #269 of 290 (1114 views)
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Re: [Quagmirian] My little project [In reply to] Can't Post

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 Pirate

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

Try this, it may come in 220V: http://products.mmnewman.com/...uty-hot-knife/hk-60?

JerryBaumchen


Quagmirian  (A 110392)

Sep 17, 2014, 2:26 PM
Post #270 of 290 (905 views)
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Re: [JerryBaumchen] My little project [In reply to] Can't Post

I have most of the parts cut out now. Most of the crappy edges with pulled threads will be on the inside anyway. Laugh 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.











Bridle attachment reinforcment


Hilarious comedy warning label version 2

Attachments: grommet.jpg (517 KB)
  bridle_patch.jpg (668 KB)
  label.jpg (676 KB)
  slider.jpg (622 KB)
  slider_close.jpg (630 KB)
  stabiliser.jpg (620 KB)
  stabiliser_close.jpg (694 KB)


RiggerLee

Sep 17, 2014, 3:12 PM
Post #271 of 290 (886 views)
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Re: [Quagmirian] My little project [In reply to] Can't Post

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


Quagmirian  (A 110392)

Sep 17, 2014, 3:28 PM
Post #272 of 290 (880 views)
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Re: [RiggerLee] My little project [In reply to] Can't Post

I've been waiting to jump something for about 3 years now. As much as I enjoy this and sharing it with you, it is about damn time. And on the slider stops, I will be putting the washer in its own little type 12 pocket a la PD style:


Attachments: pd210_slider_stop.jpg (278 KB)


Quagmirian  (A 110392)

Oct 4, 2014, 6:49 AM
Post #273 of 290 (540 views)
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Re: [Quagmirian] My little project [In reply to] Can't Post

I've done a bit of practice sewing. I've got the last of my materials on their way, tape, line & slinks etc; and someone's double needle to use. I can't wait... Cool




Attachments: stab_1.jpg (661 KB)
  stab_2.jpg (639 KB)


mcordell

Oct 4, 2014, 7:08 AM
Post #274 of 290 (527 views)
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Re: [Quagmirian] My little project [In reply to] Can't Post

I assume you are going to get video of your opening and flying of your new canopy and share that with everyone who has been following this since the start?


Quagmirian  (A 110392)

Oct 4, 2014, 7:59 AM
Post #275 of 290 (513 views)
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Re: [mcordell] My little project [In reply to] Can't Post

Definitely some video from the ground, maybe some from the plane and perhaps some from the test jumper, depending on whether he's happy with taking a gopro. I'm trying to wrap my head around what would be a good cutaway setup. I already have a rig with the container removed.


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