Ugly Fiberglass Airplane

Discussion in 'Composites' started by durabol, Apr 9, 2011.

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  1. Apr 9, 2011 #1

    durabol

    durabol

    durabol

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    I was wondering if their are any box fuselage, constant wing cord composite airplanes? Similar to how the Volksplane is for wood construction. This should make for the fasted built time and keep the stress analysis fairly simple.

    Brock
     
  2. Apr 10, 2011 #2

    JMillar

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    Why bother? Make it out of aluminum, or steel tubes and fabric. Composites are for curves. Admittedly you can get smoother surfaces, but really, why sacrifice the best aspect, the ability to form curves? I don't think it would simplify it enough to be worth the tradeoff. Find some of Orion's posts on "metal thinking in composites."
     
  3. Apr 10, 2011 #3

    wsimpso1

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    +1 on JMillar
     
  4. Apr 10, 2011 #4

    142yx

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    Well, you could probably make an ugly, boxy fiberglass airframe much faster than an ugly, boxy aluminum airframe
     
  5. Apr 10, 2011 #5

    Dana

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    Maybe, maybe not. But why bother? You can make a nice, curved fiberglass airplane just as easily as an ugly, boxy one.

    -Dana

    "If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy." James Madison, while a United States Congressman
     
  6. Apr 10, 2011 #6

    rheuschele

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    I'm not sure that I follow the premise, but isn't the Vision, a squared off composite fuselage all the way from front to back?
    Ron
     
  7. Apr 11, 2011 #7

    Topaz

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    Yeah, you'd think...

    Point 1: Much as I like composites, if your goal is to simply "fly" and you don't care what the airplane looks like or are not trying to wring maximum performance out of it, aluminum sheet and aero-quality pop-rivets is going to be faster and easier than anything else. Probably lighter, too. (Lighter means cheaper, and lighter means a smaller engine, which means cheaper, too.)

    Point 2: Structural analysis of composites is anything but easy, if you're going to do it right. And it doesn't matter what the shape is - what drives the complexity is the fact that the structural material is a composite of two or more other materials, some of which have more strength in one direction than another.

    I've seen a very basic, single-seat, airplane done all in aluminum sheet. It had a sharp-cornered box fuselage, straight constant-chord wings and tails, and a simple blown blister for a canopy. The VW-conversion engine was only minimally cowled. Wasn't even painted. It was ugly as sin.

    But it flew, and looked like something that could've been pieced together from scratch by one guy in about three or four months. In that sense, it was beautiful.
     
  8. Apr 11, 2011 #8

    durabol

    durabol

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    I don't agree, it takes quite a bit of time sanding and contouring the foam to get a rounded structure. The rounded structures I have read about use much thicker foam as well which adds to weight. Also a boxy fuselage perhaps in the shape of an airfoil would give more lift than a rounded one, if a fuselage is allowed to contribute to lift.

    I have read that the stress analysis of a box structure is quite a bit simpler than a rounded one. I only know simple ways to say size a composite spar but perhaps with the aid of a computer program I could "do it right" as was suggested, if I choose to design my own airplane.

    Brock
     
  9. Apr 12, 2011 #9

    wsimpso1

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    There is no way around foam in a little airplane that you are going to keep light. For airfoils and control surfaces, hotwiring is really pretty darned quick and nearly foolproof too. Fuselage? Big sanding sticks, wooden longerons, and a few cardboard templates make quick work of it. Go visit somebody who is building a Cozy... The thing that does take some time is finishing scratch built fiberglas.

    Billski
     
  10. Apr 12, 2011 #10

    Dana

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    Rounding big foam blocks takes some time, but not much compared to the total build time. A boxy fuselage has no aerodynamic advantages; indeed the square corners cause a significant increase in drag.

    Perhaps simpler for simple loads, but the smoothly curved shape will likely be stronger for the same weight. As for computer stress analysis, it's a useful tool, but only a tool... it saves time but you still need to understand the underlying principles.

    -Dana

    Of all the forces in the world, only the Federal Government has enough power left to destroy America.
     
  11. Apr 12, 2011 #11

    RJW

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    A box beam will be more efficient in bending than a round tube by a substantial amount. I’m pretty sure a box is more efficient in shear too. Torsion the tube wins over the box. Since torsion is the least of the worries in a fuselage a box fuselage should be more efficient than a pretty round one. But as has been said it would be draggy.

    Rob
     
  12. Apr 12, 2011 #12

    roverjohn

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    Isn't there a fiberglass/foam faux Cub called the chipmunk or squirrel, or something like that? Sorry that I can't remember the name but I've been to the website and the words "simple", "quick", and "easy" appear often. I don't remember the designer calling it ugly.

    Here it is:
    http://www.flysquirrel.net/
    I don't know if plans are available because the original site I looked at does not seem to be functioning anymore.

    Here's the original site. Maybe it will work when you try it.
    http://www.m19flyingsquirrel.com/

    I don't think it's that ugly but I kind of like simple, boxy planes with Hershey bar wings and nearly rectangular appendages. Well, as long as it's a taildragger which makes it cooler than any tri gear.
     
    Last edited: Apr 12, 2011
  13. Apr 12, 2011 #13

    autoreply

    autoreply

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    I guess that even for larger aircraft, the skin doesn't see anywhere near the max stress and the thickness is driven much more driven by airshow morons (term by Billski ;-) ) and buckling strength.

    A circular tube is easier to calculate too. A rounded square has stress concentrations, a bending/torqueing tube is pretty straightforward.
     
  14. Apr 12, 2011 #14

    RJW

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    “Airshow morons.” Agree. A lot of these curvy planes are kind of silly if you ask me. They are designed for looks more than anything. Efficiency is secondary. The designers take a big hit in the weight department to look cool and save a few square inches of wetted area. Their planes would be faster and lighter if they would lay off the extreme compound curves a bit.

    Rob
     
  15. Apr 12, 2011 #15

    autoreply

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    That might certainly be valid for several (most) designs. When looking around for good fuselage shapes (beyond the normal "rules" like maximum taper), I got the impression most people just design something and aerodynamics is almost an afterthought. Goldschmied and Boermans seem to be one of the very few who actually did serious research in this. If done properly, the aerodynamic result is impressive, as witnessed by for example the Stemme which performs the same as a C172 on a quarter of the effective HP.

    A good composite fuselage can be very light especially for faster designs (where the skin is much more loaded, but the "moron gauge thickness" remains the same). My design for example would very likely be quite a bit heavier if done in metal and the Sparrowhawk:
    Windward Performance - Specifications/Performance

    Is a good testimony to how light you can design in composites. The fuselage structure (minus h-stab, landing gear, instruments and wings) weights abouts two crates of beer. I'm pretty sure that you can increase the wing area and fit an engine and still be Far 103 legal..
     
  16. Apr 12, 2011 #16

    Topaz

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    And yet that's what sells airplanes. We can be engineering purists and say "Efficiency is everything!" but that neglects marketing reality. And a business is in business to sell product. You can chastise "the masses" all you want about the illogic of their decisions, but it's not going to do a bit of good. Aesthetics counts as much - and sometimes even more - than absolute numbers and efficiency, when the goal is a profitable product line. That's just the way it is.
     
  17. Apr 12, 2011 #17

    RJW

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    All too true. I remember one “high performance” version of the Ford Mustang was substantially slower than the base model because it had to haul around something like 300 pounds of useless ground effects. Of course the performance model was the one that everybody wanted. This doesn’t bug me so much in the marketing of a car. Given the market, this kind of strange desire (willful ignorance?) is expected. Though I like to think otherwise, the airplane market seems driven by much the same kind of desire. Who would buy a Questair Venture when instead a sexy Lancair could be had?

    Sorry about the grumbling. I guess I’m feeling chatty and a bit negative lately. A positive, structure-based question is forthcoming.

    Rob
     
  18. Apr 12, 2011 #18

    autoreply

    autoreply

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    Yes, unfortunately, very optimized shapes aren't seen as sexy, too "feminine" or too "soft". This is clearly seen from the eco-friendly cars for example that easily do 300 mpg, but look like a girls toy. Might be a problem for more efficient aircraft in the future too. Stuff like body wake propulsion or laminar flow fuselages don't "look" good and might slow or prevent advance in GA.
    That's one of the issues with my design too. It looks so odd, compared to what we know that many people probably already discount it on the looks :speechles
    There's great therapy for that. 10 minutes a day will do ;)
     
  19. Apr 12, 2011 #19

    Will Aldridge

    Will Aldridge

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    I have been so broke for over a year that I haven't been able to log 1 hour (okay I could have, but not easily).

    I call that video torture. My heart aches watching that.
     
  20. Apr 12, 2011 #20

    RJW

    RJW

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    Thanks for the therapy suggestion, auto. You are quite right. About the best I could do would be some stalls, lazy eights, and maybe a “high speed” pass or two in a rented C150. Still it would probably be enough.

    Do you have any sketches or models of your design that you could share? I looked back at your earlier posts and read some of the details of your design but did not find any sketches. I have always liked the Do335. What little understanding I have of this arrangement makes me think it would make a killer racing plane.

    Rob
     

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