Discussion in 'Recovery' started by cwbullet, Jun 19, 2016.
Does anyone have this template? I lost it.
Hopefully it works, courtesy of the Internet Wayback Machine....
This is the spreadsheet that produces the patterns based on rocket weight etc.
View attachment chutecalc1.xls
Chuck- pm Stealth6-pretty sure he still has one or several iterations.
try this https://web.archive.org/web/20150516222737/http://www.vatsaas.org/rtv/tools/computationtools.aspx the description says
"A descent rate calculator for for elliptical-cupped (Rocketman™) Parachutes. This calculator also provides the dimensions for making your own elliptical-cupped parachutes at precisely the size you need for your rocket. It was written as part of the how-to instructions available"
The Vatsaas Brothers website was an amazing place to explore...it's a shame it went away...thank goodness for the internet archive! https://web.archive.org/web/20150910054712/http://www.vatsaas.org/rtv/
Thanks for the link. I tried for hours and came up empty handed...
LOL I couldn't find it directly on the Wayback Machine, so I googled "vatsaas brothers" and a hit from TRF came up, a post by chuck with the link to the home page
I need to find a sewing template for these.
My main interest is in the reduced # of shroud lines. Can't say I'm crazy about the look. I love the look of multiple gored chutes (especially ringslots/ringsails) but as they get past a certain point in size the number/bulk/mass and tangling qualities of the lines becomes difficult to deal with. While it would obviously be WAY easier to just buy chutes, it simply dosen't come with the satisfaction of having made them yourself.
I found a good PDF.
Any opinions on material choice? I really like working with 1.1oz ripstop but I've never used such large pieces for a single panel. Assuming it would be best to cut them on the bias, would 1.1oz have the necessary strength for a 40lb recovery weight? Seems like most of the manufacturers use 1.9oz for this style of chute. Is that mainly done for strength due to large panels or is it more due to economics? Packing area should not be a concern, mainly mass and the fact that the lighter weight cloth seems to open/fill/pack more easily...
I don't know for sure, but I would suspect it is all about economics. Most of the manufacturers will charge you more for chutes made with lighter nylon.
That's pretty much falling in line with what I'm finding as far as pricing different weight material. And being a bit more difficult to work with...
I keep loosing this thread, so making a post to keep it in my history.
I'm a seasoned pro at losing virtually everything. No need to explain. Have you tried making one yet? I figured I'd give it a shot by making a small (20"?) drogue. Made some scaled graph paper out of dollar store poster board, "sketched" the patterns and cut the pieces out of some scrap ripstop. Very first move I made was to sew 2 of the straight sides together, then I took the time to actually look at the diagram. After scrapping those, I cut 2 more and made a feeble attempt at sewing the (correct, this time) radiused sides together. Turns out it's really F'n hard to sew a doubled up seam with that tight of a curve. Flipped it over and looked at the crazy/crooked/puckered/bunched up lumpy mess and put everything in a bin in the garage. I suspect it'd be much easier with some lighter weight material. One of these days I'll pick up some more 1.1oz. and re-visit it. If anyone has success with one please post pics and pointers....
Does anyone know where the best place is to buy the soft ripstop nylon? I went to JoAnn fabrics the other day and all they had was the heavy stiff kind...not good.
No, I haven't tried it yet. I'm thinking about posting the link to that design on the "Mr. Excel" website and ask the experts there if they could figure out a way to have Excel actually plot the patterns with the correct grid size so I could take it to someplace like Staples and print it out full size.
Ripstopbytheroll.com would be my choice.
I'll post pics of my first attempt tonight when I get home. It's a royal pain in the butt to wrap your head around the pattern, and after a year of staring at it, I'm still not sure that I did it right.
Ripstopbytheroll is the ONLY place to get nice ripstop that's NOT at crazy sport parachute prices. Just be aware that when you look at their website, you're likely to be overwhelmed by choices initially!
Flymarket kites iirc is fairly priced as well, and they carry the very lightweight thin mill nylons like .75oz which makes for a very small packing chute.
I've bought some fabric from them, and it's fairly priced.......but there's some different stuff out there in the kite world that uses the same words, but it's not what you expect. The last few pieces that I got from them was not the supple, gentle fabric that we're all familiar with, it was stiff and krinkly. Not sure what the brand or designation was right now, I'd have to look that up at home.
On another note, they're my favorite place for getting the braided dacron cord that I use for shroud lines when I can't get it from my local kite shop.
Stiff & crinkly sounds like maybe Cuben to me?
what do you need?
I drew one up for a 3lb rocket at 250' ASL (forgetting I'm moving to the York, VA area where I'll be, what, 12' above sea level?).
I had to dicker with Excel to get my grids the correct size (2.25"), and when I print from Excel, the grids are correct, but if I convert it to a PDF, the grids are short (by 1/8") in the vertical axis.
Anyway, I'm gonna cut some ripstop to shape and send it all to my cousin, who is a former costume designer/seamstress and have her give it a go.
I also posted it (as a .xlxs file) on the Model Rocketry Fanatics Facebook page https://www.facebook.com/groups/modrf/permalink/2292223137487880/
It wont take the .xlxs but it will iirc take .xls the older format.
Thanks! I Googled and it said to save it as a Microsoft Excel 97-2003 Worksheet. I did, and re-opened it and it all looks the same, so let's see if anyone has any trouble with it.
That type of ripstop is used a lot in kite building. We never like it for chutes.
I'm guessing that the template does not need to be dead nuts on, right? I mean if I'm supposed to hand draw out a grid then hand draw in the curves for the template, .001" accuracy is not really required.
I used the template I drew out last week, then made a better (IMHO) one piece template that is just a little bigger in some spots on the curves and is a symmetrical as I can do it using what I have (Microsoft Publisher).
I've attached a couple examples.
The first "Overlay" is my original pattern (red lines) overlain on my updated pattern (black line/orange fill) and you can see it's a little bigger in the "Y" axis, and pretty danged close in the "X" axis.
Overlay by JonathanOtt posted May 14, 2019 at 7:02 PM
The second "Layout" is how it'll look when the patterns are cut, laid out and ready to sew (no seam allowance).
Layout by JonathanOtt posted May 14, 2019 at 7:04 PM
The third "Modified shape with hem allowance" in my vision of it, if I were to transfer it to the fabric, in one large piece. Fold it on the centerline (Y), stitch the interior seams together; open it up, fold on the other center line (X), stitch the interior seams. I'm thinking a French-fell seam would be best (lays flat and super strong, if not a real bear to stitch on a curved and rounded piece).
Modified Shape With Hem Allowance by JonathanOtt posted May 14, 2019 at 7:02 PM
I printed out a paper "model", trimmed it to the colored lines, folded and stapled it together (very high tech). It looks like it'll work out. It kinda looks like a 2/3 sphere with notches cut into it.
If I invest in actually producing one of these, I'm going to test it (rigorously) by throwing it off a building with a two-liter bottle full of water (~4.4 lb/2kg) which calculates (by the Vatsaas spreadsheet) to 18 ft/sec -- 12.3 mph. I can always adjust the water level to lighten it up to actual "flying" weight.
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