Jul 11, 2012, 12:17 PM
Post #1 of 459
My little project
In this thread I'll be posting progress pictures of my (hopefully jumpable) canopy. If I can't get it out of a plane it'll be towed behind a car something. So far I have completed most of the planning and cut out a few parts. I'm going to do a bit of sewing to make sure everything matches up correctly or whether I need to adjust the templates. I'm in two minds about adding a bridle attachment thingy and I welcome technical advice.
Design Information 9 cells Clark Y(ish) airfoil section Span: 7.02m (23 feet) Chord: 2.74m (9 feet) Area: 210 square feet Full cell chordwise I-beam style construction, like a Skymaster Colour: babyshit brown
(This post was edited by Quagmirian on Jul 11, 2012, 12:18 PM)
Not sure exactly what you're aiming at here. I will preffes all my comments by saying that unless you're looking for something very specal, a specal aplication there is absolutely no advantage in trying to build your own canopy from scratch. And from what little I see you don't seem to have a good grasp of the back ground nessasary to do it. Not ragging on you just saying.
Now haveing said all of that. I thinkl it's really cool that your strikeing out on a project like this. Way to go. Regardless of all else you will learn a great deal even if your canopy never gets off of your computer. Small minded people here will give you a lot of shit so just ignor them. I will answer your questions to the best of my abillity and help you with what little I know.
First off could you fill us in on your back ground, skill set, and resorces specificly equipment.
second. It sounds very much like you're starting from scratch. Before you try to reinvent the wheel you might start by examining past designs and looking at some of the infomation out there. Bad news is that most of the knowlage is locked away in peoples skulls or in companies but I seemk to recall a few papers and presentations from pia etc. I don't have them in front of me. Hell why don't you take apart an old canopy and try to copy it.
I'll start tossing out some thoughts. Just bits of info that you may or may not be aware of.
If your starting from scratch and you've never done this before start small. How bout you build a kite. say 50 sq ft. It would give you a chance to work out how to main seam, your construction, play with your trim, etc. Start by kiteing the damn thing. Use that to measure your glide angle, lift, give you an idea of how these things change with your break input. Give you some notion of your... I'll call it pitch stiffness. A tendence to stay at one angle of attack and not for instance over fly and role it's nose under. A jumpable model on your first try is probable a bridge too far.
Some other thoughts. It looks like your panels are rectangular. No panels are not rectangles. In fact a good bit of the secret magic is in the panel shape. At the very least think of it as a shape of rotation. I degress further on this but I'm short of time. where did you get your fabric? Canipy fabric is almost like baseball bat wood. You can't make it out of just any thing. The cloth that you cut it from has to be straight. Take a marker and draw a line across the fabric following one of the ripstop lines. Then lay one long ruler paralel to the warp of the fabric. and use a big frameing square to lay another ruler 90 deg to it. You'll probable find that the shit is crooked. It can bow, it can be at an angle, it can be in an S. Some time you can cutr from the center of the roll. Another trick is to flip the panels so that they form a shevron when you sew them togather. What machines do you have? Any pullers?
Look I could go on and on but I have to go ship some thing.
I'd build a kite first which would allow you to make mistakes without costing you too much canopy material. Once you've got something that looks about right then do the real deal.
I don't know you'd be able to jump your canopy without dispensation (and you'd have to use a cutaway rig in any case).
But yeah.. gotta admire your aspiration to do this. I am sure you will learn a lot on how they are made, how the deployment sequence works, how they fly and a ton of other stuff in the process even if you don't eventually produce the jumpable product.
P.S. realised I'd kinda paraphrased the guy above. ^^^ What he said.
(This post was edited by adamUK on Jul 11, 2012, 1:31 PM)
Not sure exactly what you're aiming at here... ...Lee
Thanks for reminding me of a few things I should have put in my first post. This picture should explain a bit.
I have looked at past designs, that's where I've got most of the information for making this thing. I have also noticed that information is locked away and I have had to second-guess a lot of stuff. That's where I thought this thread might be handy. Copying an old canopy is on my list of things to do, and it's essentially what I'm doing here.
I have built something a bit like this before, and no I didn't jump it, but I did fly it behind a car. I feel like this is a good step forwards.
Yes, the top panels are rectangular. Have I missed something? They certainly look like they should be.
The fabric is where the fun begins. It's some kind of military cargo fabric, definitely not exactachute. I use it because it's very to cheap to practice on. Yes, the cloth is on the cock. The ripstop lines are not at right angles, which is something I've just been ignoring, what a fool I look now. I'll take on board the chevron idea though, thanks.
My machine is a little home thing which struggles to go through lots of material and doesn't have anything useful on it.
Try to get your hands on a Parakit/Lone Star manual. Back int h late 1980s, Lone Star sold pre-cut kits to sew your own ram-air canopy. I sewed two of them and put a total of 500 jumps on those two canopies. Both canopies are still air-worthy, but F-111 canopies have fallen out of fashion. My copy of the Lone Star manual is staring at me from across the room. Hint: if you are willing to pay the cost of photocopies and mailing, I might share my Lone Star manual with you. Since the company is long out of business, I do not worry about copyright.
Honestly at some point you're going to have to learn about real sewing machines. You can get by for now building little kites on your home machine, honestly that's what you should probably be doing right now any way. But eventually yopu're going to need a real machine or a couple. First off where ever you went to buy your home machine don't go there. I don't know what it's like in the uk but here in the us there is like two diffrent worlds. One has the little old ladies that build quilts and clothes to embaris there grand children. And then there is the real world of industreal sewers that use real machines, real fabric and real thread. The two groups do not over lap. At all. If you've been going to a little craft shop, don't go back there, don't talk to them, don't lissen to any thing they say. Pull out the phone book and find a shop that deals with industrial sewing machines. Develop a relation ship with them. You'll know the place when you see it. It will be a wearhouse in an older part of town, there will be no show room. It will just be big shelves with old heads and stacks of tables in the corners and one old guy that knows way way more about what you need then you do. The good news is that what you're looking for is for the most part cheap. Light weight garmit machines are every where and not in great demand. Make sure you get a 110 moter with a good clutch. Start out with just a straight stitch with a reverse, say a consew 230. A needle feed would be nice but you could get by with a drop feed. Next you need a double neadle probable a 1/4 inch gague. It would be nice if it was a reverse. With a binder you dont need that but for this it would be good. Puller. Pullers don't grow on trees. What you need is one like a singer 112-w-116 A bottom puller with a top side roller so you can have a whole pile of shit underneath your arm. You may have to look around to find something like this at a decent price. You need to start thinking about your seam construction and what you will need in terms of folders, tape feet, etc. You're probable going top want to get the folders and plates so that you can swap them out on that one double needle. Odds are they will all be custom. Rarely have I found ane thing off the shelf. You get what you pay for. Expect to send in samples of fabric, seames, tapes, etc. Both sewn and unsewn. figure on several hundred dollars per folder so have this well thought out and don't forget about any tapes that will have to run through the folder. They will need to leave room for them. These are fairly high percision hand made devices with more then a little magic in them. Do not trust any one under 60 years old to build your folder for you. It's a lost art.
Old mill fabric? Look you're going to need 0-3 fabric, eventually you're going to want to use zp. I don't know what you've got but you're not goint to learn much other then how to sew with out tight fabric. You're going to have to learn about supliers. Don't hold your breath on buying any thing, and I mean any thing locally. Do not go bach to the local shop. If it doesn't come on a roll you don't want it.
Air foil. Clark Y? Yah it's been around but it's probably not what your looking for. This aint alumanum. I don't think I'd put a whole lot of brain power into the air foil but I'll toss out some thoughts, keep in mind they are worth exactly as much as your paying for them. First off you're bottom seam is probable going to be flat. It's a compromise on ease of construction. Second you're probable going to want a good bit of camber. third I'd wand the camber and thickness pritty far to the front of the canopy. I think you're looking for a pritty strong moment. I think that would help to keep the front of the canopy from unloading. Beyond that, it's a big fucking sack that only has a passing resimbalance to the rib so don't go over board.
panels. If they're just rectangles then the thing looks like a flat wing. Think about what happens when you bend it. Think about the angle of attack across the wing and how it will bend. The outer ribs will wind up leaned inwards at the ends. Think about the angle of the lines as it opens like a fan. The top skin has to be wider then the bottom skin. No rectangles. Now I'm going to talk a little more out of my ass here. I don't have derrect knowlage of how the diffrent manufactorers make there decisions but I'll toss out some ideas. Lets say you tuuk a line along the glide angle of your canopy. So that is your free stream line. through the end of your riser. Then you have the canopy, center cell loaded rib above that. Then lets say you rotated that airfoil around that line so that you have a positive angle of attack all the way across the canopy reletive to the glide angle/free stream line. So think of it as a surface of rotation. In essence the zero lift line of the canopy would form a cone around the free stream line passing through the riser with a constant angle of attack. The surface is of course more complicated but not by much. Basically intergrate along the surface, just add up the distances along the curve, and at each point look at the distance perpendicular to that line of rotation. That based on the angle for each rib gives you the width of the panel at that point. Very easy for a rectangular canopy. If you get fancier, eliptical, where you basically change the airfoil at each rib you have to get a bit more sneaky. You can form the panel shape by basicly doing an intergration through the law of cosigns to unwrap the panel off of the canopy into a flat plane. In a sence it's basicly a sort of cone. as long as you don't have any sections of... negative gausen curvature it's not a problem. But that's for another day. Set your self up a spread sheet and think about panel shapes. Keep in mind that what I've described here is very... basic. You can actually do a lot between the line trim and panel shape to control the angle of attack across the canopy. This is some of the secret stuff that I can only guess at. And keep in mind that even with this it's still going to be a bit weird when it inflates. Keep in mind that the tail being thiner will "swell" more then the thick part of the canopy. So it will tend to bow the canopy backwards slightly. What I've described is not really adiquite knowlage to build a canopy I'm just giving you an example of how you might start to generate a design or at least where I might start. Take it for what it's worth.
Sounds like my second sewing machine: a Pfaff 230. Just a little single-needle that would also do a simple zig-zag stitch. The zig-zag function is handy for sewing bridle attachments, line attachments and suspension line junctions.
I mainly used the straight stitch function to sew both of those kit parachutes. The key point is that was a 1960s-vintage home machine made of cast iron. Cast iron is the key when sewing through multiple layers of nylon. Cast iron is the only material that will hold the needle in precise alignment with the hook (underneath).
When searching for a parachute-sewing machine, take along samples of the fabric you intend to sew along with a spool of nylon E-thread (military specification and Parachute Industry Association Specification) also known as civilian size 69.
If they try to sell you needles any smaller than 19 gauge, walk away. Most parachute sewing is done with size 21 or 22 needles, ball point or universal point. The key to needles for sewing nylon is ball points that gently push the nylon fibers aside, leaving them structurally intact.
If they try to sell you chisel-point needles (meant for sewing leather) .... they will ruin your nylon fabric.
I built, from scratch, quite a few canopies, starting in the mid 1970's. That seems close to the design time frame you are in. My initial strategy was to copy an existing canopy. It was a 189 square foot foil, a very under appreciated canopy. It flew great. My teammates liked them too. Building a copy gives you a big advantage when you first jump a canopy you built.
Later, after I was confident in my construction methods and skills, I started doing my own designs. There are some minor and major tricks to it, some of which have been mentioned above.
I'll be glad to share with you. PM or email me and we can talk on the phone or Skype.
Did you chop it or land it? How were it's dynamics? It's pitching? What stability checks are you doing? How's the front riser tension? Any points of... mushiness on the front riser stroke?
What kind of rig are you jumping it in? The easiest way to deal with this is to put it in a tersh on a set of mini risers on larg ring harness. With the cutaways on the risers. You can make a container compleatly seperat from the harness so no alteration to the tso'd container. That's how I've always done it. Poor mans tersh rig.
Come on, you got to spill some details. We demand more pictures.
Woah woah woah, I didn't jump it. It's just got nylon cord for lines at the moment. The airfield owner towed me behind his truck (I know, I know). As far as flight characteristics go, it's pretty shit, and lacks flare power. I took off on the rears and landed on the toggles and it just seems pretty docile. There's only so much I can do with limited knowledge of canopy design and military cargo fabric.
Rectangular is fine of bottom skins, but if you use rectangular tip skins, you will end up copying some of Domina Jalbert's earliest prototypes (circa 1970). OTOH if you start tapering top skins, you soon be sewing copies of 1975 vintage canopies.
To quote Dan Poynter's "The Parachute Manual, Volume 2", page 322 - "Crown rigging: Normally all lines at the same chord position (e.g. "A" lines) are of the same length. This anhedral (19-27 degrees, often 21 degrees) "crown rigging" simplifies construction. the slider, risers and harness affect the designed arc. The arc is also temporarily changed by dynamic maneuvers. Crown rigging dictates that lower cell surfaces should be narrower than than upper surfaces. If the surfaces are cut the same width, the canopy wil open slower and fly slower. Flat rigging is inherently less stable than crown rigging, yet flat rigging yields a notable glide improvement in steady state, full flight because the lift forces are more vertical. However, flat-rigged canopies do not pen well and do not recover well from dynamic maneuvers.".
IOW "crown rigging" means that loaded ribs continue up along the same angle as suspension lines (when viewed form the front).
Start by guessing the length of harness and risers at 1 yard (er ... one metre for Europeans), then copy "A" line length from a similalrly-sized production canopy. Then draw a bunch of rectangular bottom skins. Then calculate cell height at every six inch interval back from the leading edge. Then calculate the circumference of that (21 degree) arc. Starting at the tail, draw a top skin the same width (span) as the bottom skin. Then mark it every six inch, moving forward. Calculate widths. Top skins will be trapezoidal (e.g. straight-edged) for more than half the chord, with all the curves in the last third (near the leading edge.
Clark Y is a fine airfoil for parachutes, considering that the Clark Y was invented back (1922) when 98 percent of airplanes had fabric-covered wings.
Thanks for all the information. Please keep it coming. I'm sure you understand that I'm using rectangular top skins and tapered bottom skins to simplify design and construction. Another thing I have to consider is my ribs. For this design, both the non-loaded and loaded ribs use the same template, again, to simplify construction. At my level of competence, I can't see the extra difficulty of designing, fabricating and sewing curved top skins being matched by any appreciable increase in performance. Of course, I understand its significance on higher performance canopies and I might try it on my next build.
Depending on the angle of attack of the bottom skin and what line you chose to rotate the airfoil around the bottom skin may or may not be a rectangle. If the airfoil is flat on the bottom side, and a rectangular canopy, then it will be some form of trapizoid. Could be a rectangle but only if that bottom skin is parallel to the line of rotation. The top skin will just be bowed outwards a bit. It's just a bit of work when you make the patern then it's all the same and it will give you a much nicer spread on the top skin of your canopy. How important is it? That depends on your span width and line length. But right now you're bowing something that doesn't want to be bowed. The top skin, angle of the ribs, every thing gets... funky when you try to do that. The earlier comments relate to whether you try to bow the canopy at all. The earliest canopies they actually tryed to make as flat planes by varing the line set spanwise. The probblem is that this actually wants to make the canopy collaps spanwise from side to side. This led to the really low aspect ratio long line set canopies that you see in pictures. By makeing all the lines the same length you direct the lift outwards all along the arc of the canopy. What you're doing right now is trying to take the first canopy and bend it into the other. Not only does this mess with the wing but it also messes with the angle of attack spanwise across the canopy.
This isn't super high speed race car shit that we're laying on you. It's actually pretty basic and comenserit with the level of tecnology that you're playing with right now. Do you have good patern paper? It feels almost like poster board. Are you hot cutting around it? Even with just a paper patern you can get away with that if you have good paper. You may have to buy a pretty big roll to get it. Ask the indutreal sewing guys. I don't recall the proper term they use a lot of shit as well but you might be able to get or order a smaller quantity. It's not hard just knuckle under and do it on your next design.
I'll try to put togather a little spread sheet for you that will help you with your panel shapes. Bit busy right now but I'll see what I can do.
From my observations, it's all good, but I think I've shortened the B lines by an inch or two too much. Someone on the ground observed that my right hand stabiliser was flapping like mad, although from watching the video I can now see that it was one of my end cells.