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  1. Sep 24, 2019 #21

    Topaz

    Topaz

    Topaz

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    Some thoughts, roughly in the order of your questions:
    • If you've got easy access to a laser cutter or CNC machine, sure. But remember that 90% of the full-depth foam composite airplanes out there were done with paper templates glued to masonite and cut out with a hand-saw, and then finish sanded to final shape. All those VariEZ's, LongEZE's, Quickies, Q2's, Cozy's and so on seem to be flying just fine. I wouldn't do a top-end competition sailplane that way, but then you're probably going to invest in molds for that sort of highly-laminar airplane anyway.
    • "Are we too worried about plans accuracy?" Probably. To put more of a point on my statement in my last post, if you can't make it to 0.005" accuracy in your shop, you don't need a print to 0.005" accuracy, either. Just because you can design it to six decimal places in a CAD system doesn't mean it needs to be accurate to six decimal places in the real airplane. I'm not advocating for "sloppy", but you can spend more time and effort on needless precision, too, with little to show for it in the end.
    • I was taught to only use the dimensions on a drawing, too. And dad also said that, if there was some dimension you couldn't read off the drawing, the drawing was badly dimensioned in the first place. He wasn't talking about things like airfoil hot-wire templates, but you get idea. Paper stretches, expands or shrinks with changes in humidity, and generally changes shape with age.
    • One of the best lessons I ever got about working in almost any material, for complex shapes like airfoils, was to scribe or just draw oversize, then sand or grind down to finished size. Don't try to cut finished size initially. Plus, again, you can blue, scribe, and even rough-cut, grind, and then file to precisely the finished shape called out - and then have your press equipment not be capable of forming that into a rib without distorting and stretching the whole thing a little bit.
    In the end, it's about balancing how critical accuracy is to the purpose of the part, against how much effort it will take to attain that accuracy. We tend to look at highly-accurate CAD drawings and link that to a need for that level of accuracy in the final part that, in fact, may not exist.

    Once again, my favorite engineering cartoon, explicitly about manufacturing tolerances which, ultimately, are what we're talking about here:

    the_guy_with_the_wrench (2019_03_01 17_12_00 UTC).jpg
     
    Last edited: Sep 24, 2019
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  2. Sep 24, 2019 #22

    Hephaestus

    Hephaestus

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    1/16" on a template isn't going to make that much of a difference.

    No homebuilt gets built with that degree of accuracy. All of the RAF drawings got printed likely on whoever's machine was cheapest, not most accurate. *Edit. And guaranteed the majority were nowhere near as accurate as we get now.

    Quick Google search says nobody has died yet because of a printing error resulting in a construction failure on a homebuilt aircraft.
     
    Last edited: Sep 25, 2019
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  3. Sep 25, 2019 #23

    Aerowerx

    Aerowerx

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    A question...

    Do you really need to print a 36 inch chord? Will the actual rib be in 2 pieces, divided at the main spar?
     
  4. Sep 25, 2019 #24

    Topaz

    Topaz

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    If you want to do a profile-checking template, over more than half the chord, yeah, you kinda do. To make ribs? No, probably not, unless you've got a big airplane.
     
  5. Sep 25, 2019 #25

    cavelamb

    cavelamb

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    A lot has changed in printer technology in the last decade or so.
    Color printing and photographic prints are the rage.
    And that's okay.

    But we've lost some capability as well.

    The old Epson dot matrix printers and Window printer drivers (up to Win 98) could print to within .01 inches. That's a hundredth of an inch - and plenty good for printing patterns.

    My last effort was for a friend's project - which is about finished now.
    Mike Hoye's "Speedster" which was started by Paul Poberezney.
    Single seat low wing, strut braced.
    It was basically the fuselage frame - welded up and on the gear, tail feathers, spruce for spars.
    Paul supplied a root rib, but the idea was for an elliptical plan form.
    That was where I came in....

    The rib turned out to be a 23012 airfoil.
    So working from that, and Mike's requirements for span and area, I drew up his airplane for him.
    I use DesignCAD - 3D max for drafting.

    But when it came to prints, the local print shops just could not get the scale right.
    It would be off in one or both axis - no matter what they tried.

    So I pulled put my Win98 laptop and a barely working Epson FX100 and make rib templates for him.
    To 1/100th inch - which surprised everybody.
    That poor old printer held it together long enough to get the rib patters printed, then gave up the ghost completely.


    Those drivers were dropped when Windows XP came out - in favor of photographic printing.

    I can still print to that accuracy using the HP Laserjet (P1006) but that's limited to 8.5 x 11 paper.

    Some print shops have large format printers that will take a PDF file and produce accurate prints.
    But it's best to give them a dimensioned check print before getting to excited about their size.




    Zwing01R.png
     

    Attached Files:

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  6. Sep 25, 2019 #26

    mcrae0104

    mcrae0104

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    This got me curious about my plotter, which I'd never checked before. Over 48", it was consistent in the X and Y direction, but 0.3% undersize (roughly 1/32" for every 10").

    Not that I need more precision than this, but how precise can today's plotters be?
     
  7. Sep 25, 2019 #27

    Hephaestus

    Hephaestus

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    I do 30mm² grids (24x48" test page)o mine to verify before I run something. I've never seen beyond 1-1.5mm off. That's less than a 1/16th of an inch so...

    But it's definitely an older one.
     
  8. Sep 25, 2019 #28

    Pops

    Pops

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    When Dallas Shell and I were building the fuselage jig for the first of 4 Bearhawks, Dallas was spending a lot of time with the measurements of the jig to hold the tubing to very, very close tolerances. On day Bob Barrows stopped by, ( Bearhawk designer ), and I brought the subject up, Bob said for the fuselage tubing, 1/8" was close enough. Thought Dallas was going to faint. :)
     
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  9. Sep 25, 2019 #29

    Jay Kempf

    Jay Kempf

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    Plotters and printers are normally dead on. It's the paper that's the problem. It creeps, shrinks, stretches, not evenly, not in one direction. That's why you print a lot on one sheet on a roll and you have scale legends in all directions all over the place. It's just like CNC machines. They can position a tool with lots of accuracy but soft materials, clamps, lost steps, tool wear, inclusions, voids, yadda...
     
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  10. Sep 26, 2019 #30

    Dennis DeFrange

    Dennis DeFrange

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    Holy Hell . What have I started ? At least you guys that are program savy are finding ways to tune up your processes . I haven't a clue what any of this means and I really don't think that if you don't know or understand any of the above , you cannot build a rib or even further , an airplane . I've decided to take an easier approach . I'm now looking for ribs from abandoned or unfinished projects , with the airfoils that I am looking for . I feel more comfortable with a real hard copy ( real rib ) in hand , that I can actually hold up in place on the project and reference the actual fit . Don't get me wrong , I definately appreciate all input , my fault that I don't completely understand 90% of it . Thanx very much .
     
  11. Sep 26, 2019 #31

    TFF

    TFF

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    You have a print of your airfoil. Draw a line through the cord. Mark about 20 equal spaced marks on the line. Measure straight up or down from the line to the airfoil. Figure out how many times the real airfoil needs to be of the drawing. Draw the cord line on paper or wood top. Use the same ratio to add the same 20 marks to the line. Use the same ratio measured up and down. Use curve templates to connect the dots. You then have your large airfoil.
     
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  12. Sep 26, 2019 #32

    Hephaestus

    Hephaestus

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    It's really quite simple. You're overthinking it.

    Go to http://airfoiltools.com/plotter/index

    Select your airfoil. Set your chord as needed and thickness.
    X and Y grid are good reference to use 6" or 300mm or whatever suits your fancy.
    Click plot, then Download pdf file. Take to Staples hand them money.

    You're not building a transonic supercruising aircraft... It'll be close enough.
     
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  13. Sep 27, 2019 #33

    pictsidhe

    pictsidhe

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    I've found that airfoil tools has many airfoils with an inadequate number of points. If your chosen one, looks faceted, it would benefit from better data, or smoothing. I second the idea of taking a file to staples. Adding some calibration lines to check it is fairly accurate is not a bad idea, though.
     
  14. Sep 27, 2019 #34

    BJC

    BJC

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    Some years ago I questioned the effect of a 12” long, smoothly faired, low, 1/8” distortion of the upper surface of the Glasair III airfoil, the LS(1)-0413 aka GA(W)-2. Simulation runs on Boeing’s computers predicted a 3 knot reduction in top speed. Any reasonably smooth hand drawn airfoil in the scale of typical E-AB aircraft will have a deviation from ideal in the order of 1/64”.


    BJC
     
  15. Sep 27, 2019 #35

    PacerPlus

    PacerPlus

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    Dennis

    I rarely have time to get on here but saw your problem with the prints so thot I'd put this up ............... I've used just about every kind of printer out there. But if you can find someone in your area that has a track fed pen plotter you will have the most accurate drawing possible. The only thing I have found to offset the dimension (X) is the thickness of the paper going over the drum/track. This is minuscule. The plotter will be more accurate than the thickness of the pen line , usually .001 - .002. If you cant find what you need in your area send me the files in a .dwg, .dxf, .plt, .cdr or .ai format and I can plot them for you when I have time. But for the speeds the sections you mentioned will fly in, the deviation of a dimension in printers from a .jpg/.bmp type image would be more than adequate. What are you considering building? These sections are quite different.
     
  16. Sep 27, 2019 #36

    Dennis DeFrange

    Dennis DeFrange

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    Hello pacer , I have two Smith Miniplane projects . I have two sets of wings and the first mini will be put togrther with the standard wing that is the clark airfoil . My intention is , somewhere down the road I will be wanting to get a little feisty with performance so I was looking at different airfoils . I like the M6 profile and the NACA23012 also . Again , just thinking and somewhat planning the future , thats the way my head works . I am aware of the Smith Miniplane 2000 that is upgraded to the NACA23012 airfoil . I talked to Jerry there at SkyClissics this morning and will have a set of plans headed this way next week . So that print search is taken care of . I already have two sets of original Smith plans so that is taken care of also . I am also interested in looking at the M6 as a possibility . Spar spacing is 18'' on center . The first Acro I Sport was was built with the M6 airfoil and upgraded to the NACA23012 to introduce the Super Acro Sport and also has a 18'' spar spacing . I think what I'm really looking for is a copy of print for a rib for the Acro Sport I with the M6 wing . I know that this post is lengthy and I've been a pain in the Butt on here but I do want all of you that have interjected your knowledge and expertise to know that you are very much appreciated , a bit over my head but appreciated . I also think that if I had a wing rib of each profile in hand to actually reference in place , things would be more realistic to me . Many thanx to all . Ya can always teach a Monkey new tricks .
     
  17. Sep 27, 2019 #37

    BJC

    BJC

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    The Samson Mite uses the NACA 23012 airfoil, as did Samson.


    BJC
     
  18. Sep 28, 2019 #38

    Dennis DeFrange

    Dennis DeFrange

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    And the Samson Mite is remarkable in every respect . Good to know on the airfoil . THANX
     
  19. Sep 28, 2019 #39

    ToddK

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    I have an HP Z6100 that I use to print plans and wing ribs. Its has automatic paper advance calibration, but even with that when running really long prints it can "grow a bit" in length up to a 1/4 inch. My solution has been to do a few test prints, then adjust the file, save a temporary dated copy of it for printing, then print a good size batch of reasonably accurate ribs. The ribs were very well drawn with what looks like a marker, so the thick lines allow a bit of room. In the end, it is up the builder to make sure the distance between the spars and other fittings are correct.
     
  20. Sep 28, 2019 #40

    crusty old aviator

    crusty old aviator

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    May be a tad off topic, but what are you planning to use these airfoils with? The Clark Y isn’t very efficient, but is docile enough, the M-6 is very stable, as the CP moves forward in a dive and aft in a climb, but it’s too limited for aerobatics. For agility, the 23012 is best, and probably the best overall of the three for GA type aircraft.
     

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