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Quagmirian

My little project

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Just my opinion but I don't think cutting on concrete is a great way to cut cloth anything. It can really dull the knife blade very quickly. Do you have a sewing shop nearby, there not very large, about 3 feet by 3 feet but they have some cutting boards with a slightly resilient surface that makes a nice surface. Any spare Masonite or plywood boards?


Also canopies get retired quite often, you might consider sending out some posts to various riggers, or here and offer to pay the post for some de-commissioned canopies to take them apart if that is something your interested in?? But be advised many people like to disable their old canopies so that they don't end up being used ever again,...like cut in half,...but I think you still could get some knowledge from them anyways??

Anyways good luck, and stay safe!!! :)
C
But what do I know, "I only have one tandem jump."

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Wrapping confluence tapes around those joints will dramatically increase bulk, but add little to strength. The added strength will only help during hard openings. Openings so brutally hard that wish you were not awake. The biggest problem with confluence tapes is that they might increase the thickness of the seam that your sewing machine might break needles. Then you dodge fast-moving pieces of sharp steel!

Keep your prototypes simple.

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Yes RiggerLee, at this stage of the game I am thinking about simplicity.

I tried to make my shitty slider collapsible but it didn't go very well. Oh well, at least they're nice and cheap to replace.

[inline HPIM4350_small.jpg]

[inline HPIM4351_small.jpg]

[inline HPIM4352_small.jpg]

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Quagmirian

Yes RiggerLee, at this stage of the game I am thinking about simplicity.

I tried to make my shitty slider collapsible but it didn't go very well. Oh well, at least they're nice and cheap to replace.

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???
Not quite sure why you are apologising????
The sewing looks great.
The only limitation looks like tiny grommets, which will probably still work with the thinnest of HMA suspension lines.
The major point is that you learned most of the sewing techniques used in building sliders.




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I don't have anything exciting to report on at the moment. I bought a 'military elliptical parachute', probably a Bluetrac, from a surplus store and that should help with my studies. I've been in contact with my local mill and they're quoting £6.55/meter ($10/yard) for first quality Zero P fabric, is that about right? On the subject of fabric quality, what are the problems and dangers associated with using seconds quality goods for canopies like I am? Assuming the strength is good and it's not too bowed, porosity seems good etc, what can go wrong?

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Last time I bought f-111 it was about $4.00 per yard. It's been a while since I ordered any ZP so I'm not sure what it's going for.

As to seconds. I think you just listed all of the main issues that might affect you. There can also be a lot of variation in the coating. There are all kinds of imperfections that can occur in the weave of fabric. Seconds are basically goods that had too many to pass muster. Most of these things, other then esthetics, would not affect you at all. Or you could cut around them. Bowing is probable the real problem. That's the sort of thing that could make whole sections of a roll unusable. For something like this I would go with first quality goods, but even more the that I'd sit down with your rep and talk about how much bow or skew you can really tolerate. Be ready to inspect all goods that come in to the factory and make it clear to him that you will be returning all rolls that do not pass your QC program.

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

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Not much to report on at the moment. The Bluetrac is built like a tank with heavy spanwise reinforcement, rolled seams and type 4 line attachments. The fabric also seems quite heavy as well.

I also found this interesting explanation in big air sportz's manual.

[inline germain.png]

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Still nothing exciting to report on, but I have a few things I'd like to share. I still haven't found anywhere suitable to cut out my pieces, so as something to do I've been taking apart the BT-80. I have discovered some interesting things.

  • Needle gauge is 3/16" rather than 1/4"
  • No chordwise reinforcement in the bottom seams or anywhere else
  • All inner ribs are f111 type material. What are the pros/cons of this?
  • Line attachments are type 4 tape and are partially sandwiched into the bottom seam
  • V tapes on the loaded ribs are made from 1" type 3 tape. A lot of other tandem canopies are like this too Why is this?
  • No ribs have any crossports, but we've already covered this one.
  • There was also some blue 700lb Dacron in the bag too. Who makes this?


I finally got on the blower to the industrial sewing machine guy and he immediately tried to turn me off old Singers. Instead, he's trying to flog some new Diamond double needles with electronic control (no clutch) for $2000 new or $1350 used. Is that about right? They do come complete and ready to sew.

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...
  • All inner ribs are f111 type material. What are the pros/cons of this?
...

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F-111 has the same strength as ZP fabric. Porosity is un-important in inner ribs. Remember that most other manufacturers increase geometric porosity by cutting cross-ports through inner ribs.
Higher porosity ribs (and bottom skin) make it easier to squeeze air out of canopies when you pack.

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RiggerLee

On a separate note it looks like the tape is a little short. Like it doesn't go all the way to edge where it over laps at the corner. Personally I leave it long and fold it under a good ways at the end so that the grommet is going through at least 4 layers of that tape.
...
Lee

Which by the looks of it, is exactly what PD does.

[inline pd_slider_detail_2.png]

I know thus isn't exactly compelling stuff, but I am learning all the time.

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It's good to know I'm not wasting DZ.com server space then.:D

I can't really make anything at the moment, but I should be getting in some more old gear to have a look at soon, and maybe even going to a dropzone to get current again.

What I'd like to know more about is different canopy fabrics. The samples I got from William Reed Fabrics are supposed to be the equivalent of F111 and ZP, but they just don't look or feel quite right. For example, the low po fabric loses its shine and gets all creased from handling very quickly, and the ZP isn't slick and slippery at all. Also, it is very easy to make the fibres slip in both fabrics by pulling apart with the fingers. This isn't something I can do even on older canopies I've looked at. Both fabrics also feel 'lighter' and more 'frail' than what I am used to.

Am I looking at a completely different spec here or is all this normal?

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I bought a load of old equipment for reference, including a
Super Raven and 3 Furies. I've been having a look at them and the and I've noted a few things.

  • Very little if any tail reinforcement. I'm guessing this is a more modern thing? The Fury has a single piece on each inboard steering line, and none at all on the Raven.

  • The non-loaded seams are sort of semi rolled, I've no idea how it could have been done on a double needle.

  • The rib sections generally look more like the one below, with less curve at the nose than what I am designing. What's the reason for this?
    [inline ribs_compare_3.png]

Additionally, I just want to check a few things for my planned seams.
My plan for the bottom loaded seam is to fold up the edges manually, mainly to look nice but also for a bit of strength. Which one of these will work better?
[inline bottom_seams.png]
On the top loaded seam, does the seam need to be attached to the rib itself or is it alright to be left 'loose' like this?
[inline top_seam.png]

Thanks to everyone who's been following this, with a bit of luck I should be moved out soon and I'll be able to get a proper machine and get making something at last.:D

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Quagmirian


  • The rib sections generally look more like the one below, with less curve at the nose than what I am designing. What's the reason for this?



I'm guessing designers were just conservative. Canopies were what we might call "open nosed". A big open nose worked. Canopies were big, slow, more porous, and so a large open area made sure the canopy stayed pressurized at all normal angles of attack.

Only later did "closed nose" canopies start appearing. An early example of the tendency would be the PD Sabre. The top skin was brought down a couple inches along the "diagonal" that forms the normal nose inlet, without actually changing the nose profile.

Only later did we get inlets that got smaller and more integrated into a fully rounded canopy nose -- more like those on crossbraced Icarus canopies. You still don't see noses like that on intermediate level canopies, and there's talk of how canopies with such small nose openings are poor in turbulence at low wing loadings and thus low airspeeds. (The Icarus 'diamond' nose opening may be small but in the center of the diamond has enough vertical distance that it handles whatever shift there may be of the stagnation point as angle of attack changes.)

The consensus would be that fairly large nose openings are still important for good flight characteristics.

Have a look at paragliding canopies though - they have done more with keeping nose inlets small, for a whole range of canopies and not just for the very high end market. They don't have the opening problem, but do have to deal with low wing loadings and turbulence.


(Slightly earlier than the PD Sabre with its zero-p material was the short lived PD Excalibur in F-111. There was also the Paraflite Evolution, although with a lip extending up from the bottom of the inlet, not down from the top. Paraflite even mentions a patent they licensed for it, US 4406433, but what they had on the Evolution was not the fancy curved nose system seen in the patent.)

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"... Very little if any tail reinforcement. I'm guessing this is a more modern thing? The Fury has a single piece on each inboard steering line, and none at all on the Raven. ..."

..................................................................................

The amount of tail reinforcing is a compromise between low pack volume and strength. No reinforcing tapes weight the least, but as wing-loadings and deployment speeds increase, you risk tearing the control lines off, so need to add more reinforcing tapes.
The first step is to fold 6 inches of tape into the tail seam near the control line attachment, but most manufacturers find it less labour-intensive to just run one piece of tape all the way across the tail.
The second step involves adding wider (3 or 4 inch wide) tapes near each control line (tandems).
The next step involves sewing diagonal tapes (Smart reserve).
The next step is to add short tapes running forward along the ribs.

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I went down to the dropzone this weekend and got to see all the riggers there (I even managed to jump :o). One thing that was mentioned was that it would be very helpful if I had some drawings to go from. Does anybody have anything like this, paper copy or digital? I'm going to contact the manufacturers, but I don't think they'll give up even their older designs easily.

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"...The non-loaded seams are sort of semi rolled, I've no idea how it could have been done on a double needle. ..."

.....................................................................................

They were probably sewn with two separate passes on a single-needle machine.
The first row of stitches aligns all the raw edges of the rib, bottom skins, etc.
Then you fold them over twice (to hide the raw edge) and sew it a second time.
Most parachute seams are sewn with 2 rows of stitching for redundancy. In case one thread gets damaged, the canopy will still hold together long enough for a soft landing.

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Maybe someone can answer this.... Why the flat bottom on all of the ribs?
I've been experimenting with scale canopies (5-15sq ft.) and I get far better glide, stability and less tendency to collapse under in a crosswind/turbulence with a non flattened bottom. Someone had mentioned something about a paraglider handling low speeds, and turbulence far better.
So back to the question, is it an opening issue? I know the b lines would end up being slightly shorter than the a lines on a flat trimmed canopy. I have to be missing something. Are they already doing this on hp canopies and I'm oblivious? Is it extra drag?
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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Ease of construction. Look through a book of airfoils and you'll see a vast array of designs. In the end it's not about whether it's flat, or curved, or hollow. It's about the pressure distribution across the skin. Our shit is just crude.

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

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reinforcing the tail really isnt about keeping lines from tearing off.its about keeping the canopy from ripping at the shortest steering line, usually the inboard most one. Strato Stars were initially made without a reinforced tail, but as more jumps were accumulated on a canopy we saw them ripping at the inboard most steering line.and so Para Flite started reinforcing the tails all across the canopy

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