# keith82687

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1. ## Help with airfoil/rib shape making a canopy

Another logbook entry on the project. After going through all the different fits for different canopies I've settled on an airfoil/rib shape: http://i.imgur.com/C2qw5ql.jpg Now I'm going to use that to get top and bottom skin panel dimensions. Then I add in cross-ports, vents, and sewing margins to everything. I updated the amazon drive folder to have the most current files.
2. ## Help with airfoil/rib shape making a canopy

Pretty good summary :p regarding "knots": let's say you plot just the top surface of the ram-air airfoil...the theoretical plot goes from x = 0 to 1 and the y values give you the top surface. If I use 5 knots it means that the interval x = 0 to 1 gets broken up into 4 sections. For each section (between each knot), matlab finds the best 3-degree polynomial fit for your upper surface with supplied constraints. One constraint I used is that the top surface can only be concave down (forcing the second derivative to always be negative). The "smoothing spline" consists of the 3 degree polynomials for each section between knots. So if I add more knots it subdivides the top (or bottom) of the airfoil into more and more, smaller, and smaller, pieces. For each piece it does the best it can to give me a 3-degree polynomial fit. If you use too few knots, you get a bad fit (you can't model an airfoil upper surface well with just a 3 degree polynomial)...BUT, also, if you use too many knots, you get into issues with the resolution of your data and you start to get a fit that may seem pretty good when you zoom out, but as you zoom in you notice there are shit ton of squiggles as matlab tries to fit a 3rd degree polynomial between just a handful of data points. So the idea is to use constraints and an appropriate number of knots to best model the airfoil shape as smoothly as possible. I'm working on figuring out that part now. I did a little more work on it tonight: In the amazon drive folder there are now a lot of ".png" image files. If you open, for an ideal example, "20 Mojo 240top.png" you'll see a scatter plot. The x-values are the same as they were for the top surface of the airfoil. The y-values are = [the 20 knot smoothing spline with constraints function] MINUS the original scanned image values. It's an easy way to see visually where, and by how much, my model differs from my originally analyzed image. I'm still working on the code so the pngs aren't complete (I need to make sure my fitting options and constraints are good before I can say those pngs are useful) From these, for each canopy AND for each of the upper and lower curves of the airfoil, I'll choose whichever # of knots gives the best fit. Theeeeeen I'll have my representation of each of the 7 canopies. Please know, I realize the accuracy of this is limited and it's likely overkill, but it's how my brain works and the best method I came up with at the time. But I could modify the code and use it on a more accurate image of an existing airfoil and immediately turn that into a 2D model, which I'm happy about. The flow "simulation" will be an absolute joke since it's a shitty 2D representation of an infinitely more complex system, but I'll still do it. As long as I keep within my original stipulation (don't change an existing airfoil more than the variance between airfoils), it'll be fine. Oh ya, and to Quagmirian..."adequate resources" are relative Regarding sewing, I have the most basic supplies (materials and a heavy duty / cheap single needle machine i made a 37.5sq ft model BASE canopy on), BUT I'm going to get the patterns CNC cut (an actual ZP/F-111 cutting CNC machine from a canopy manufacturer) when I get to that point
3. ## Help with airfoil/rib shape making a canopy

In case anyone is interested, I'm still making progress (albeit slowly with work, play, and all the other things I'm doing atm). I started using smoothing splines with variable knot positioning which led to a much better fit for the top and bottom surfaces than the polyfit function. I'm keeping the same amazon drive folder updated (link at the bottom of this post). The main folder has untiitled.m which is my matlab script file I've been using to run the code. The folders labeled "5 knots", "10 knots", etc have the m-files for each of the 7 canopies (with each folder corresponding to how many knots are used in the smoothing splines...more knots doesn't mean a better fit so I'm going to go back through them for each canopy's top and bottom surface to figure out how many knots give the best fit). If you want to check them out, you'll need the shape modeling language files from the matlab file exchange here (or just download the entire amazon drive folder, which has the shape modeling language files): https://www.mathworks.com/matlabcentral/fileexchange/24443-slm-shape-language-modeling/content/SLMtools/slmengine.m I really wanted to use the 'regularization','cross' options to get a really superb data fit, but trying to do that with 15 knots kept either taking too long (over 2 days and my computer would be restarted when I came back) or, most likely, crashing. The link for my amazon drive folder for the project is available to anyone here: https://www.amazon.com/clouddrive/share/12tPElq7QHwIdnZWQuQbDLflYpFlwuFWZQgIc9Hksjq?ref_=cd_ph_share_link_copy I won't post another update until I have something more. It's been nice to get back used to using matlab for this project!
4. ## Help with airfoil/rib shape making a canopy

See this: http://www.edmundoptics.com/resources/application-notes/imaging/advantages-of-telecentricity/ A photograph without any special lenses or post-processing will not give you an accurate 2D representation of the rib shape. Why not do this with a protractor and a ruler? By "the scaling is off", I meant that there is something wrong with my matlab code (I'll figure that out another day...i just needed to stop working on it so I could get my actual work done ). I knew before I even took the pictures that images do not portray 2D shapes accurately. I'd say that me using a protractor and a ruler on a pinned-out canopy would not necessarily be better than the image method (especially considering the size and the difficulty of managing the fabric/tension/etc). Someone also suggested that I count the rip-stop squares and use them as reference to some points...but they aren't exactly "square". I think it seems easier to get the rib shape than it actually is. In a perfect world, I'd be able to stitch rip it out and use a vacuum table + (a most gentle) iron + a giant scanner...or just have the manufacturer send the rib pattern I think the image way will work well enough though.
5. ## Help with airfoil/rib shape making a canopy

Thanks Dave! I'm so early in the project that right now my only goal is to look at the differences between the 7 canopies I have images for. If I do make changes to the rib shape, I will only make a change that is less significant than the variance between the canopies.

7. ## Help with airfoil/rib shape making a canopy

Thanks for the reply! This is a very long term project I don't want to rush. A success is something that flies, but I want to reach as far as I can to learn as much as I can in doing it. Once I have an airfoil choice, everything from there on will be much more fun. I know how to generate the top and bottom skin panel dimensions based on the line set and airfoil top and bottom surfaces. I have vent/cross-port designs. Once I get the canopy sewn, I know that a huge part of the flight characteristics is line trim. For that I plan to use a 4-risers per side, all continuous line system that can be trimmed in-flight (I think that's what Nick Burden does) to come to a decision about trim and then design the actual line set from that. Another thing he did that I really liked and may do is to have 3 risers per side for the final canopy. The rearmost riser, on which the toggles are stowed, would be a different/bright color and only go to the D lines and control lines. That way riser input is much more efficient. If/when I have the motivation, I think the direction I'll go next is to take the BASE airfoils I have now, somehow smooth them out (not optimize), get 2D models for those, create another set that are optimized, and then compare existing BASE canopy airfoils as well as their potentially optimized counterparts. I'd still love any information, suggestions, or points of contact anyone may have.
8. ## Help with airfoil/rib shape making a canopy

Does anyone know anyone toying around with such fluid dynamic simulations? I'd love to know who is out there doing it, with what software, and their major hurdles.
9. ## Help with airfoil/rib shape making a canopy

Thanks for the reply Lee! Was the guy building his own canopy the thread where he called one of his models "the brown thing"? I followed that one and it was AMAZING! So awesome to see him do it over the years. Thanks for taking a look at the drawings. They were for the little scale model. A lot of rushing/shotty work done it on just since it was for dropping weights, kiting, and learning. For the full scale I'll be using double the margins like you're talking about! I think we're at a point with fluid dynamics simulations that we can use existing software (COMSOL / matlab / etc) to simulate the airfoil with more realistic parameters to differentiate the simulation from those applied to airplanes, wind turbines, etc. The amount of time it takes me to make a canopy with the equipment I have is very very long so I'm taking my time and doing as thorough of planning as possible. Once I actually have the CAD drawings and get the patterns cut, I'll be in no rush and happy with every seam sewn. Cheers, -Keith
10. ## Help with airfoil/rib shape making a canopy

Heya! So a little over a year ago I started learning to sew on a single-needle singer 4423. I learned a lot and made a 37.5sq ft canopy using the GOE481A airfoil. Some random notes and a picture of me kiting that canopy can be found here. http://imgur.com/a/xUEyH The vents in this picture sucked and the center 3 cells were replaced with a much improved vent design (and in bright pink). It was a proof of concept (and great patience training ) that I learned a LOT from. My goal now is to make a ~240-265 sq. ft, 7-cell, vented BASE canopy. I had a couple incredibly insightful and useful meetings with Brian Germain (he lived nearby) and I will have access to a CNC canopy cutting machine to cut all the patterns. I've already done quite a bit of planning, but I'm stuck at choosing the rib/airfoil shape I want. I know most skydiving canopy rib shapes are a copy of one a few different airfoils. To get a feel for variation in rib shape for BASE canopies, I borrowed several BASE rigs from my friends, pinned the outer-most rib of each canopy out as best I could, and took these pictures: http://imgur.com/a/nwMk9 http://imgur.com/a/cwu0A From the pictures I attempted to get a data set so that I could use something like http://airfoiltools.com/userairfoil/index to calculate some airfoil characteristics. It seemed to not be very useful. The crap resolution, not accurate enough coords are attached as an excel spreadsheet. Here's where I'm stuck. I've debated getting a better trace of the outlaw outer-rib and just going with that, BUT, I really don't want to clone a rib shape. If I wanted to clone a canopy, I'd just buy one. What I'm considering now is to use data representing existing BASE airfoils and simulate/optimize them. I'm going to mess around with http://www.airfoilevaluator.com/home.php that I just found, but I seriously doubt it'll do anything useful. Something I'm more interested in using an analysis along these lines: http://www.sciencedirect.com/science/article/pii/S1018363913000159 https://www.nada.kth.se/utbildning/forsk.utb/avhandlingar/lic/000215.pdf https://www.mathworks.com/matlabcentral/fileexchange/50142-airfoil-optimization-using-xfoil-and-parsec-geometric-parameterization But at this point I'm way out of my element and not even sure if there's a point or benefit in using any of these or similar methods. Anyone know someone I could discuss my project with or point me in any direction? ***disclaimer*** I already own a BASE rig, have ~350 BASE jumps, and do not plan to BASE jump this canopy (at least not without a LOT of skydives/testing on it first)
11. ## Slow motion canopy opening

Thanks for that video! It's kinda scary to see how that thing snivels...it looks like it's just doing the same thing over and over and all of a sudden it opens =P I know it's not the case though. It'd be damn hard to get a good video of full extraction from PC deployment till under canopy.
12. ## Issues with my arch

Beautiful. Thanks! There is a wind tunnel about 5 hours away from where I live and I've considered going there when I have the time/money/people to carpool and split costs. I originally had no plans to go to a wind tunnel...but so far I've had 1 good day of skydiving, 1 day where I got in one jump and sat around the rest of the day, 6 entire days (dawn till dusk) of being at the skydive center and not diving (usually being the only one not diving as AFF student weather conditions are strict), and 6 more days of night-before or day-of cancellation of my plan to go due to weather. Also note the skydive center is a 2.5 hour drive. At this rate it'd be MUCH more economical to just go to the damn wind tunnel w/ a couple friends (one of which used to work there and gets instructor rates..hell ya) and split an hour of wind tunnel time over 2 days.
13. ## Issues with my arch

Hey guys. I'm not sure how to word or ask this but here it goes: I'm on my AFF 5 and my AFF 4 didn't go too well. Mostly it was because my goggles were too loose and were almost completely off after about 15 seconds into the jump (which made me very distracted and it took me several seconds to read the altimeter). If my glasses had come off it would have REALLY sucked as I'm legally blind without them (around -10 prescription). Anyways. It seems like I'm potato chipping a lot. I was told (pretty recently) that I should arch from my hips instead of my back (I'd been arching with my lower back). Can you suggest some ways to train a proper hip arching? Also, a bigger problem I have is that my legs tend to wave in the wind some. When I tense up and have a very rigid arch, I fly much more stable...but my instructor gives me the relax signal and as soon as I try to relax, my legs start to wobble and I start potato chipping. Advice?
14. ## Back brace for hard openings? Need advice

What were the dimensions of the slider you installed?