Airfoil selection for the TS-2 (ultralight glider)

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Rienk, May 15, 2014.

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  1. May 15, 2014 #1

    Rienk

    Rienk

    Rienk

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    I would appreciate some help in selecting an airfoil for our TS-2 concept, an ultralight glider, using the Tab & Slot method of wood and fabric construction.

    A few years ago, I was asked to do a presentation at the ESA conference. I presented the TS-1 POC, as well as the Solo LSA that evolved from it. There was interest in developing a low-cost, quick build glider, so with the encouragement and offered help of several engineers there (which never really materialized). I began to draw up the initial concept.

    Dan Armstrong did offer some advice, including starting with the e604 airfoil.
    However, another aero engineer (for NASA) thought that it was a poor choice for the type of glider we were envisioning. Unfortunately, he quickly faded from the scene, and so I let the project collect cobwebs.

    Since my son and I don't yet have an ultralight to build for him, and since I'm working on teaching him CAD, I thought it would be a fun and appropriate project to redesign the TS-2 (see attached). Even though it may not leave the drawing board, there is a chance that we might build it, and if so, I'd rather start off with designing something that might actually be usable. Even if the fuselage has to go through several iterations, hopefully the wing can continue to be used.

    The concept is for a very light glider; hopefully 103 ultralight legal, but that is not critical. It is meant to roll launchable with very low wing loading (similar to an "airchair" but a little higher).

    Anyway, I'd appreciate some input from engineers and designers with glider experience/expertise.
    Keep the airfoil we're using?
    Change to something more appropriate?


    And of course, if anyone would like to help in anyway, please let me know - PM me and I can email the actual CAD files.
     

    Attached Files:

    Last edited: May 16, 2014
  2. May 16, 2014 #2

    StarJar

    StarJar

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    One unique situation you have is a cantilever wing, with lower speed situations- compared to higher performance/more expensive gliders. If that's the case, it mat pay to use a thicker airfoil, like 16 or 17 percent to keep your spar weights down. The thicker airfoils can actually have better l/d ratios than the thinner airfoils, at the lower airspeeds.

    May I also suggest the geodetic bracing method for the wing. To also keep the weight down.

    Thalman T-3 with geodetic wing (and fuselage) bracing:

    thalman3.jpg


    Edit: I see the e604 is 18.8% thick. OK, THAT is thick, and I like that part. But it appears to be designed for laminar flow. What covering will you have on your wing??

    The e604 also has a cm of -.12 in your operating range. That is a high trim-drag price to pay, if you are not getting the laminar flow, IMO.
     
    Last edited: May 16, 2014
  3. May 16, 2014 #3

    Rienk

    Rienk

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    The wing will have a plywood D-tube for about 40-50% of chord, then fabric covered.
    I do not believe it will truly be laminar.
    Can you suggest a more appropriate airfoil for this type of wing, in the flight regime it is intended for?
     
  4. May 16, 2014 #4

    StarJar

    StarJar

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    If your D-tube goes to 40- 50%, it seems to me that the e604 might be a good airfoil. According to JavaFoil, even in the not smooth condition (painted fabric), it still performs pretty well.

    If you can really smooth the top and bottom plywood, then add thin fiberglass and then a sanded filler, the e604 may work really well.

    You could get rid of a bit of the high Cm, by modifying the the rear bottom cusp, so it is a little more of a straight slope.

    That's my opinion after compairing to other thick airfoils, on JavaFoil, set at AR=10.
     
  5. May 17, 2014 #5

    autoreply

    autoreply

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    Copy as much ofthe Ka6E as you can. Doesn't get much better than that.
     
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  6. May 17, 2014 #6

    Matt G.

    Matt G.

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    Why the rounded wingtips? Several sources I've read state that they decrease the effective aspect ratio of the wing, thus hurting the performance.
     
  7. May 17, 2014 #7

    StarJar

    StarJar

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    I've been very high on the concept of angling the tip back at 50 degrees. Somewhat like the Wittman Tailwind. I got this idea from Orion.

    Not only are you blocking the tip vortex, but the 50 degree angle should delay the stall of the tip, with vortex-lift effect.

    The leading edge radius of this 'cut' area, is still a mystery to me, but maybe a small radius is OK. Don't the fighter jets use a sharp LE for vortex effect?

    Sorry, got off the OP subject a bit.
     
  8. May 17, 2014 #8

    Jay Kempf

    Jay Kempf

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    Actually a good idea. But I think Rienk is trying to keep all the ribs the same. One could build extra long wing tips with only a few ribs that taper as you say and get a nice overall span loading without a lot of washout.
     
  9. May 17, 2014 #9

    autoreply

    autoreply

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    There's a lot of opinions about tip shapes. As long as you stay planar, a simply faired tip is about as good as it gets (Simply revolve upper and lower half of the airfoil around the chord-line)

    Sweeping the tips back agressively helps a lot... but only if you go non-planar... thus winglets..
     
  10. May 17, 2014 #10

    StarJar

    StarJar

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    I don't think that is accurate. If it wasn't for shorter spans, for clearance and reduced root bending, the aerodynamic advatage goes to planar, as I understand it.
    I mean think about, if the vortex cannot swirl, then you have a great wingtip, regardless.
     
  11. May 17, 2014 #11

    JamesG

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    The spanwise vortex doesn't care. It follows the pressure gradient. You could do curly-cues if you wanted to.
     
  12. May 18, 2014 #12

    autoreply

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    No, not at all. A good non-planar (wingletted) wing, no matter whether we're talking AR=5 or AR=57 can reduce induced drag by about 30% over an optimal planar (elliptical) wing.
    When you have air moving two ways (downwash and freestream), that's your wasted energy (induced drag). The tip vortex is only a side-effect of that.

    Having the aileron end inboard (or extending/wingletting the tip) will help a lot with aileron control, but apart from that, there is so much misinformation about tips that it's almost laughable.
     
  13. May 18, 2014 #13

    StarJar

    StarJar

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    After reading this, I became a bit confused.
    Tips dealing with wingdownwash, more than the tip vortex?
    Please clarify. I always thought the tip vortex was the main thing tips dealt with, (to improve efficiency).
    What else can they do, they are at the tip! (At least that's how I always looked at it.)

    Also, on a 57-1 aspect ratio wing, it seems that there is very little a special tip can do, because the tip is so small. That's how I picture it. You say up to 30% increase is possible with winglets? Is that possible?

    Regarding eliptical wing planforms, I don't think they have efficient wing tips, although everything else about them may be great!:) Have a nice day.
     
  14. May 18, 2014 #14

    autoreply

    autoreply

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    It's a different perspective.

    A winglet counters part of the spanwise flow at the tip by lifting against it. That allows a bigger downwash (and more lift) at the tips. Interestingly, the local tip vortex becomes stronger with a winglet since there's a bigger difference in flow direction over a short distance. The total downwash (and vortex field) though becomes weaker. With the higher lift at the tip you have to lift a bit less in the center of the wing, reducing the total energy in the downwash of the wing and thus also lower induced drag.

    With really big ones. That's structurally (flutter, bending moment) not feasible, but even on open class ships you see a 5-10% reduction in induced drag due to winglets, rather impressive given how small they are.
     
  15. May 18, 2014 #15

    Rienk

    Rienk

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    What airfoil does it use?

    Any chance of pointing me to somewhere I can see plans of how it's built? My search didn't yield anything.
    I'd like to know more about the all-flying tail.

    I'm also going to need to some help on tow-hook and wheel placement, should anyone like to help out.
     
  16. May 18, 2014 #16

    StarJar

    StarJar

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    5-10% over what? A crescent tip would do the same thing as a winglet, but without the interference drag, IMO.
     
  17. May 18, 2014 #17

    autoreply

    autoreply

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    Look for schleicher ka 6 or so, lots of info on the inet. Airfoil is an early Wortmann, fx40?
     
  18. May 18, 2014 #18

    autoreply

    autoreply

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    Over the very best possible planar wing.
     
  19. May 18, 2014 #19

    StarJar

    StarJar

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    R-i-g-h-t. Just like a giant winglet will help a 57 AR wing, by 30%. I give up, I've got other things to do.;)
     
  20. May 18, 2014 #20

    autoreply

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    StarJar likes this.

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