For now you can learn a great deal about it's stability and dynamic caricteristics by playing with it up high and then chopping it. If you hook a small weight to one of the toggles, little sand bag, just before you cut away it will streamer straight down very nicely. That's really where you should beguin with this in any case. You really don't want to feel comited to landing some thing that you know little about only to find that it has stabillity problems or does not pitch well dynamicly.
You might look around for a master rigger that would be interested in your project and enjoy working with you on it. Even just an endorsment or sign off on aplications would go a long way towards makeing you look legitament. There has to be a process here. Where do new manufactorers come from any way? And I think you'll find that a lot of the older... board members, or what ever, that you're dealing with may remember the days when the "manufactorers" were working out of their garage. As long as they think you are serious and responcable they may be willing to help you. Try to have a plan when you talk to them. Start documenting and building files. Develop paper work to record your testing and gather real data. Graphs in a computer always impres people. I think you'll find that if they have faith in you they will bend over to help you.
What times of the day are you around? I've been trying to keep an eye on skype but you always seem to be off line.
(This post was edited by RiggerLee on Dec 4, 2012, 11:10 AM)
I had a very productive conversation with J Wragg; he answered a lot of my questions and make me think about a few things that hadn't crossed my mind. I may have hit a snag as far as testing goes, see the BPA ops manual:
"Parachutes may only be used if they are manufactured for Sport Parachutists or Military Parachutists, by recognised parachute equipment manufacturers or riggers with the necessary qualifications."
However: "BPA ‘A’ Licence parachutists and above may perform cutaways (at a club PLA/DZ) with a cutaway `rig’ designed for the purpose, provided they have CCI permission and have been thoroughly drilled in the cutaway procedures."
So technically I could do a cutaway jump on my A licence, but I'd have to leave the test jumping for someone else for now.
Is the offer of 100 quid to anyone at the DZ that jumped your canopy still standing?
I might jump it, damned if I'll try and land it though......
Does anybody know what 400 lb dacron looks like? I nicked the stuff I have off an old swift reserve, R3 1660, Nov 1982, but it looks to be completely different stuff to what I'm seeing elsewhere. Help?
There are two kinds of dacron that you are likely to see, flat braided and round braided. Flat dacron looks, well, flat, like a shoe lace. Flat dacron isn't commonly used on newer sport parachutes, but it was used on Swifts and many other canopies in the 80s and early 90s. 600 lb and stronger round dacron is pretty common on sport canopies but I've only seen 400 lb used on low-volume BASE canopies like the Flik Lite and the Feather.
Poynter's manual does say that 400 lb is the minimum for any sport canopy, and centre lines should be stronger than that. The only reason I'm using it for the suspension lines is because it's what I've got, it makes sense to use what I have. This model probably will never see the sky anyway, and if it does, it won't be going to terminal. I will strengthen the centre lines anyway though, as good practice.
Anyway, I have been experimenting with the bottom loaded rib seams. I am going to be putting a piece of 3/8" type III along the whole length of the seam, and that, coupled with the leading edge tapes and line attachments will make my traditional rolled seam unacceptably thick. I am considering a spanwise lower skin to simplify and thin out this seam. Here are some pictures. Apologies for the crappy quality, these were taken with my button camera.
Please do take some pictures. I thought I had my head round what kind of lines there are, and now I have no idea. Here is a picture of what I have. The 400 lb Dacron I bought is on the left, with the narrower, thicker stuff on the right. Any ideas?
No ideas on what the line is then? I've sent it back to the shop, they'll probably know anyway.
The good news is I've had some luck with my bottom seams. I've switched to some lighter reinforcement tape (no idea what it is either), and I managed to make the difficult bit at the leading edge, line attachment included. I think I'm going to go for spanwise construction on the bottom skin to minimise bulk in this area.
Attached is some pictures of this and my proposed seams. I'm running a piece of reinforcement tape completely along the loaded bottom seams.
I'm guessing you've picked up some kind of roll attachment. Just for the record you can probable go simpler. Loaded rib top seam, you can probable get by just sewing the stack togather as long as you have a bit of excess on the out side. Loaded rib bottom seam, I think you could use one less roll, so just an up fold. You might try baisting the tape on the rib to make it easy. Un loaded ribs, again I think you could just sew it down as long as there is a bit of excess beyond the seam. Stabalizer, Again I think one fold is enough. this all assumes you are hot cutting every thing. In the past we did put in extra folds, try to hide edges, and all that. Now that we're hot cutting every thing we're getting lazy and for the most part finding that it's strong enough. There have been a few time we've gone to far. As an example, Germain tryed something fucked up for a while. Eventually the ribs just came loose. It was just an over lap of the top skins and the ribs. He might have gotten away with it if he's had more seam allowance but it just pulled out at the two edges. Knew a guy with an old Jonithen like that. But honestly you're makeing it a bit hader then necasary.
Ok, after lots of swearing at my sewing machine, I may have decided on my bottom seams (picture attached). Even though I am hot cutting all my pieces, I really don't like the idea of raw edges, as the poorly cut material my saw into the rest of the fabric. I've come to a compromise of sorts. The bottom skin will be spanwise constructed, the top skin chordwise. This should maximise what little strength I have as well as keep the loaded bottom seam thin. It's not folded, but because it's a spanwise panel there are no raw edges either. I am going to put a piece of 3/8" type 3 for the full length of all the loaded bottom seams, and I may lightly reinforce spanwise too.
I've just finished making a modification to my crappy white thing, I was replacing the stabiliser to test the design. Turns out I need to take line attachment and seam height into account. I don't have any pictures yet, but when I do I'm sure you'll all be impressed and you can send my master rigger's rating in the post.
Sorry if someone already asked this, but I've read this thread and I'm very curious, what is your background/education? How do you know things not only about aerodynamics, but about this sewing stuff, you know :) Wish you success in your passion :)
Ok, here we go again. I've decided that I really liked my last model, nd I'm going to bring back the airfoil, with a few improvements. It's still got a thickness of 16% and the basic shape is still there, but I've smoothed it out a bit in an attempt to improve performance. I've also steepened the leading edge inlet by about five degrees.
As for the seams, they're about as simple as you can get, and according to RiggerLee, I should be able to get away with them, for a few jumps a least. They'll also be super easy to mark and sew.
I've drawn up a stabiliser, based on the predicted line lengths, this time taking into account the length of the bottom seam, tape and lark's head knot. The line trim will probably change, but now I know that I can replace the stabilisers on the finished model if I need to.
I haven't drawn any patterns yet, and I'm interested to hear what people think about this.
Keep in mind that they leave a bit of edge beyond the last row of stitching on the unloaded and top skin. On the bottom I might sew the tape a bit higher with the top seam and then tuck the three edges on the bottom under and sew the last line. That's one of the heavier load points. You could use a wider tape there if you needed to. You might want to have you're B line slider stop at least as low as the A line Or make sure to put a stop on the outer A. A's like to shrink and pull through the grommets. You can get functions that way depending on how you build the attachments.
When going up the line, it is imperative that you do the "noddy dog routine". As you get higher there is a distinct possibility that the wind direction will change slightly or that you will be pulled through a thermal. As this happens the wing will turn away from the winch. If you don't watch what the wing is doing, this turning will eventually result in a lockout as a direct result of being pulled through the air. The wing will be so far off the 90 degree angle to the winch you won't be able to get it back on course. Think of a kite when it turns over in the air and heads for the ground in a strong wind. The only way the pilot can get out of a lockout is to get off the tow line. But since he/she would be struggling with the brakes and worrying about how hard they are going to hit the deck, there won't be much time to find the release. A good winch driver will save the day by cutting the line and allowing the pilot to recover the wing and then release the tow line. An even better winch driver will see the pilot flying off course and will reduce the power. When the wing comes back on course he will apply the power again.
(This post was edited by sundevil777 on Mar 2, 2013, 5:55 PM)