Discussion: Conceptual Design of an "Inexpensive" Single-Seat Motorglider

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Topaz, Sep 10, 2014.

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  1. Sep 1, 2016 #601

    Jay Kempf

    Jay Kempf

    Jay Kempf

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    The Song is more of a lower branch off of same family tree. So yes, similar design but less attention to some higher order details found in modern competition sailplanes. Last post on Topaz' thread.
     
  2. Sep 1, 2016 #602

    BJC

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    Yes, that is why I said "evolution".


    BJC
     
  3. Sep 1, 2016 #603

    Topaz

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    I'm interested! One thing I love seeing here on HBA is people working actual designs, and actual builds. It's inspiring and thought-provoking to see other design solutions and methods, and to see real airplanes coming together.

    Anything you're willing to share would be interesting to me.
     
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  4. Sep 1, 2016 #604

    Jay Kempf

    Jay Kempf

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    Just tried to move this over to my older motorglider thread and got this from clicking on a search selection:

    "Not Found

    The requested URL /forums/aircraft-design-aerodynamics-new-technology/11208-motorglider-concept-11.html was not found on this server.

    Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request."
     
  5. Sep 1, 2016 #605

    Topaz

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    Yeah, any link made prior to the software update needs to be updated itself. I just noticed that both of mine in my sig-line are broken (returning 404 errors, just like your experience), and so I'll need to re-do them when I get back to the office.

    Google apparently hasn't re-mapped HBA yet, so we're still getting 404 errors on most external searches. That should resolve over time.
     
  6. Sep 1, 2016 #606

    Jay Kempf

    Jay Kempf

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    But if I copy and paste them into a browser they are still broken. Did I break the internet rules by hijacking your thread? :)
     
  7. Sep 1, 2016 #607

    Topaz

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    Yes! Yes, it's all your fault!!! Somebody get the torches and pitchforks!!!!

    No, the problem is that address in the link itself is no longer correct. The post ID is different after the forum software upgrade, even for old posts. Google is still caching links to HBA from before the upgrade, so theirs are coming up broken too, until they get around to re-mapping the entire forum. Copying and pasting them just copies the old (incorrect) address into the browser. Still comes up broken. :depressed

    EDIT: There, the links in my sig-line are fixed now.
     
  8. Sep 1, 2016 #608

    plncraze

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    This is a little late but I just wanted to encourage the thought that Topaz is putting into crashworthiness. In the August 88 Kitplanes there was an article on designing for crashworthiness and it had pictures of a wrecked Thorp T-18. Remember that Thorp was a very experienced designer and builder. The pictures showed a T-18 which had flipped over. The Thorp had a roll bar but the bar was stronger than the aluminum skin it was attached to and tore out. The center post which was cantilevered off the engine mount /landing gear support, which was probably one of thestronger and stiffer parts of the airframe, bent down with the roll bar and went into the aluminum fuel tank. The fuel tank tank did not puncture. What saved the pilot was the fact that the fuselage came to rest on the top of the engine and the top of the rudder. The top of the rudder bent a bit too.

    My point is that nothing seemed to work as planned in the crash. Topaz has the idea of running the something solid from the top of the fuselage to the bottom and I think that is better than mixing materials. You want to be certain the crash cell won't shrink beyond a certain size and keeping it simple is a good idea for the amateur.
     
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  9. Sep 1, 2016 #609

    BJC

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    And therein lies the challenge of keeping it light but still effective for a huge variety of scenarios.


    BJC
     
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  10. Sep 1, 2016 #610

    fly2kads

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    Not to further hijack Topaz's awesome thread (seriously, this is good), but you may still be able to pull up your old thread with the forum's own "Advanced Search" instead of the Google search.
     
  11. Sep 2, 2016 #611

    Topaz

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    Or just navigate to it directly, and re-bookmark the new address.
     
  12. Sep 5, 2016 #612

    autoreply

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    V-tails don't work for sailplanes. You need a huge fin, but a small H-stab. Either your h-stab is oversized, or the V-angle is so ridiculous that it doesn't make sense. In my design the h-stab is oversized, which I needed for the CG range anyway (two pilots up front).

    The propwash hitting the tail (U or V) is actually handy if you put it so that it hits the tail when aoa is high. Early and very clear notice if you get close to stall.



    Only a monocoque will truly work in most crashes. This one is a great example... 200 mph head-on into a tire wall. Monocoque still intact:
    [video=youtube;p5ER227Y9Ew]https://www.youtube.com/watch?v=p5ER227Y9Ew[/video]
     
    Last edited by a moderator: Mar 20, 2019
  13. Sep 5, 2016 #613

    StarJar

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    That's funny, that's exactly how I felt about Synergy, but maybe I got off on the wrong step back then.
     
  14. Sep 6, 2016 #614

    cheapracer

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    That in no way means that Thorp was an expert in load distributions in a crash. Roll bars punching through the floor is a problem in amateur car racing occasionally where the builders just bolt them to the floor without thought to what happens as example here with this Mustang, note the 2 black roll cage tubes poking through, useless ....

    punch thru.jpg

    Besides blatantly not true verified by hundreds of motorsports crashes every year with simple mild steel roll cages, no one, including you, is building aircraft with Formula 1 spec baked carbon fibre monocoques that have had millions spent on development inclusive of crash testing. Their builds include strict regulations as to where thicknesses and weights are applied - the weight and style of build is simply out of the question for an aircraft period.

    F1 is 700kgs with a 150kg power/drive unit, so that's 550kgs/1200lbs for a small single seat airframe, empty, no engine, etc - not going to happen.

    Wasn't a "head on" either, was a rear in on an angle and had been built to aircraft spec thicknesses and weights, there would be nothing left of it.

    In difference, this is what relatively lightweight, cheap mild steel roll cages that homebuilders can afford and build are capable of, and there's thousands of these examples on Youtube.

    [video=youtube;0MYxBuVvN0M]https://www.youtube.com/watch?v=0MYxBuVvN0M[/video]



    .. but the loads must be fed properly during a crash or they are useless as per the Thorp example.
     
    Last edited by a moderator: Mar 20, 2019
  15. Sep 6, 2016 #615

    Aesquire

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    The Driver's reaction reminds me of Harley Quin in "Suicide Squad" after a rolling crash in a CH-47. "What a Ride!"

    Crashes can exceed any design's limits. I've seen lots of leg injuries in modern street cars.

    Formula 1 is a bizarre combination of bleeding edge tech and Roman Chariot racing. There's a REASON modern cars don't have open wheels. A typical Toyota accident doesn't send the car that clips the one in front into low orbit. Tradition.
     
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  16. Sep 6, 2016 #616

    autoreply

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    We're talking about airplanes here however. Those structures you mention work just fine. If strong enough however they'll be prohibitively heavy, which is why we don't see them in airplanes. Maintenance on a crop duster is a good teacher there.
    You're entitled to your opinion of course.

    Unfortunately for you, most LSA's and microlights use exactly the same materials they use in F1. T700/T1000 are common in both. Same for resins. Same for prepregs and manufacturing methods. Same for test labs even.

    An F1 monocoque is roughly the same mass as a sailplanes ahead-of-wing fuselage mass or me. Both work fine. Pretty sure that safety cockpit design and test expenses are pretty similar.

    Fortunately for us, much of those test reports are more or less public (many via the Idaflieg) and thus we don't have to do anywhere near as much testing ourselves.

    Sure, there's the myth of incredible complexity in making such "high-tech" parts. Having witnessed several such parts being designed and built, I could build every single one of those within tolerance in my shed, except for the lack of an autoclave. Even that is changing with a major shift to OOA, notably infusion.


    Back to the real topic; I'd simply copy the structural layout of the Lange Antares or the ASW27. As good as it gets and calculating the required lamina thicknesses is pretty straightforward since the loads are too.

    For crushing, alternating layers of foam with thin layers of glass is pretty light and very simple to tailor to your specific loads. It's also very easy to implement in the rest of the design, which is the biggest difference with almost every other approach (alu foam, collapsable seat supports and so on)
     
  17. Sep 6, 2016 #617

    Topaz

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    Gentlemen: Might you please break this discussion off into its own thread? Thanks.
     
  18. Jan 11, 2017 #618

    lr27

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    Well, I have to admit I haven't read this whole thread. I HAVE read the design thread.

    Topaz:
    I know you've already decided on an airfoil, but I think there MAY be better choices, especially if you don't like building flaps. polars for Topazs cheap motorglider.jpg
    The polars on some of the airfoils above are reduced to correspond with the reduced chords you could use due to their higher maximum lift. To be fair, you'll have to look at the numbers for correspondingly high lift coefficients, and reduce the drag coefficient corresponding to the reduced chords. For instance, if we wanted to compare the Eppler 749 to the Wortman airfoil at a Cl of 1 with flaps, we'd look at the Eppler's figures for a Cl of 1.32. That's about 0.011. However, due to the reduced chord, we'd multiply by 0.76, giving an equivalent Cd of 0,0084, compared to the Wortman's 0.008. The Wortman is using flaps, though, where the 749 is not, so in the real world it might be a wash. Similarly, the Wortman, at 0 flap, has a Cd of about 0.005. The E749, at a Cl of 0.26, has a corrected Cd of .005 too, or close to it. I threw in the Ara D 20 percent because of the obvious structural advantages of a 20 percent airfoil. Plus the magnitude of the pitching moment is much less than the E749, which is worse than the Wortman. You'll find that the Ara D looks good thinned to 15 percent as well, and in both cases seems to work well with flaps, if you are so inclined. But there may be better options with flaps. Another advantage is that upper surface transition is much sooner, meaning less area to make smooth enough to be laminar. Maybe the rear 60 or more percent could be fabric covered to save weight. The Ara's shape is simpler than the others too. Be sure to cut down the trailing edge width. The Ara was, I think, designed for a wind turbine or propeller, so, unfortunately, the thinner versions are meant for higher Reynolds numbers.

    You might also be interested in my hobbyhorse airfoil (I didn't design it, I just like it), the FZX ng-7, which I think is found on the Xfoil Yahoo group. Another one, with the silly name of Yahoo! AF Group Hi Lift GAV 4, is found on, surprise surprise, the Airfoil Yahoo group.
     
  19. Jan 13, 2017 #619

    Topaz

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    Oops. Somehow this post slipped "below the fold" on the New Posts search without me seeing it. Sorry for the delayed replay.

    Thanks for the suggestions, lr27. I'm a little confused by the mention of "reduced chord" and changing the wing geometry for these new airfoils. My wing loadings, chord, span, and area are set by the performance requirements of the airplane, and an airfoil chosen to suit, rather than the other way 'round. That process is detailed in the design thread.

    In the end, I'm very happy with my choice of the FX79. It meets my design requirements, and is a known and understood quantity. I just don't feel the need to go through the airfoil analysis process again, when I already have something that meets my requirements very well. If you'll recall, exceeding the design performance requirements is not a plus for this project. I want something that performs exactly to the specifications and requirements I've layed out - not worse, and not better.
     
  20. Jan 14, 2017 #620

    lr27

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    Topaz,

    You can change the wing loading depending on maximum lift. The higher the maximum Cl, the less area you need to get the stall down to a reasonable speed. Let's say you had a 100 square foot wing on your airplane, and you wanted to keep the stall the same while switching from a 4412 to, for some reason, an 009. The max Cl for the 4412, according to Profili, is about 1.7 at a Reynolds number of 1.5 million, but the 009's is only about 1.1. Seems to me that you'd have to increase the wing area by 1.7/1.1 or 55 square feet! Of course, that would increase the Reynolds number, so you might not have to add as much if you did it by enlarging the chord, but it would still be a substantial amount.

    One of the other advantages I think you might be able to get with these other airfoils (not the 4412, but the ones I mentioned in an earlier post) is a broad enough lift range that you didn't need flaps. You wanted simple and cheap, right? The other is less area that has to be critically smooth, since the flow goes turbulent anyway at something like 35 or 40 percent chord on the top.

    It seems to me that one can't really divorce airfoil from wing area.

    What am I missing?
     
    Last edited: Jan 14, 2017

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