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. Apr 11, 2016 #561

    Topaz

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    Yes, and that's what's happening to me here. I need to just make a decision and move on. Thanks for the nudge.

    I'm heading out to lunch now. I'll have a decision by the time I get back. Thanks to everyone for the suggestions and ideas. You've given me much material with which to work.
     
  2. Apr 11, 2016 #562

    mcrae0104

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    Has corrugated cardboard been considered as a possible energy-absorbing material? Sort of a DIY honeycomb structure.

    I'm imagining you could build a shallow box filled with a grid of ribs (similar to a torsion box). The ribs would have the corrugations running vertically. Some experimentation could reveal the effect of rib spacing and overall height of the box on energy dissipation rate. You could even tailor it to make it progressive by stacking several boxes (say, three or four at 1" tall each) of varying density.

    It could be placed below the seat surface, or you could use it like a seat cushion--just plop it on the seat surface, add some foam and upholstery, and you're good to go. Nice thing about doing it this way is that it's easily replaceable.
     
  3. Apr 11, 2016 #563

    Jan Carlsson

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    I was thinking a central keel would come up into the cockpit, not so if they are under the fuse sides. but a thick sandwich of corecell might be as good and a strong wheel house for the central wheel

    the Vanguard also can be had with EFI, in both 33 and 35 BHP versions
    http://www.vanguardengines.com/engines/
    the about only one i know that made the conversion them self is Igor Spacek, but with the smaller one, he put the flywheel in a lathe to get the weight down, rpm seems fine with 3600, just under a liter on two cylinders, smaller foot print too.
     
  4. Apr 11, 2016 #564

    RPM314

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    Why not get the required under-butt depth by increasing the recline angle of the pilot? It might add some length to the fuse, but that's not as bad as height, I'm gathering. If the pilot's rear shifts forward and up, over-the-nose visibility should not change, at the expense of a little more neck bending.
     
  5. Apr 12, 2016 #565

    Topaz

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    I have an 18' maximum length requirement, due to garage storage. That gets a little dicey, as the airplane is already exactly 18' long. Preserving the full over-the-nose angle would require the pilot's head to not only move backwards, but also upwards along the over-the-nose sightline 10° from horizontal. It's a very creative idea, but it gets a bit problematic in this case.

    I'm back from lunch, and I've made up my mind on this subject. Posting to the design thread now.
     
  6. Apr 12, 2016 #566

    RPM314

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    I understand your trepidation, but glad that you're holding momentum.

    To quote myself: "Life's short, chicks dig scars, I'm just gonna build it."
     
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  7. Apr 12, 2016 #567

    Hot Wings

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    but they're really long levers, too, so I'm not sure how well that really works

    It works very well. Just after the prop grinds itself to bits the canard breaks in half at the end if the upper stiffener so there is no rebound. Lots of Quickie landing crashes in the early days, but surprisingly few injuries.
     
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  8. Apr 13, 2016 #568

    autoreply

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    Layers of foam, stacked between thin layers of glass, Kevlar or carbon do the same thing, but take less space and are more predictable.

    Cardboard is so weak that "blowback" of the built-up pressure inside is considerable compared to the original impact. Foam on the other hand is typically 1-2 orders of magnitude stronger than environmental pressure. Leave the sides of the foam open and you will not have any blow-back.
     
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  9. Apr 13, 2016 #569

    cheapracer

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    Just a thought, you could conceivably easily make crush structures from recycled paper.

    Add newspapers/paper into a blender with hot water and pour the mix onto a preformed mesh strainer and leave to dry for a few days. I used to make thick paper and figurines with the kids in times past.

    [video=youtube;IKQKJ8GnH8M]https://www.youtube.com/watch?v=IKQKJ8GnH8M[/video]
    [video=youtube;mE2VWojDb1g]https://www.youtube.com/watch?v=mE2VWojDb1g[/video]
     
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  10. Apr 13, 2016 #570

    cluttonfred

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    Somewhere I posted a series of NASA crash test clips that included large, crushable energy-absorbing pyramids of corrugated cardboard that are apparently used when parachuting pallets of supplies out of a cargo plane. I would think that corrugated or honeycomb light aluminum, perhaps between top and bottom "trays" to protect from the edges, would be easier to maintain quality, plus fireproof and waterproof. I am still working out how to do this with beer cans!
     
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  11. Apr 13, 2016 #571

    Topaz

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    All these discussions of cardboard, paper, and so on are nice on their face, but you can't simply focus on the one point-use-case of the impact itself. Any impact attenuator solution has to remain effective and intact for the lifetime of the aircraft, or at least through a reasonable service interval.

    Humidity, spilled drinks, and getting out of the cockpit in a rain-shower are all ways that a cardboard/paper attenuator can be degraded by getting wet. We also tend to step on aircraft seats during normal ingress/egress of smaller airplanes, and that puts off-center point loads on the attenuator, meaning likely to break it down even further. This latter is also an issue with foams, honeycomb, etc.

    After reading various resources, I'm more and more convinced that mounting the seat on a set of beams (S-beam or even simple straight ones) that yield under the necessary impact loading is the way to go. The results are predictable, consistent, and the system is really enduring in day-to-day use, simple, and made of inexpensive materials.
     
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  12. Apr 13, 2016 #572

    Swampyankee

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    Honeycomb is a great energy absorption mechanism. It doesn't have to be aluminum -- at Sikorsky, I think the most common variety was Nomex.
     
  13. Apr 13, 2016 #573

    cluttonfred

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    That sound great, but who's got the will and the engineering chops to design a generic S-beam seat mount or honeycomb impact attenuator for other aircraft homebuilders to emulate? It might well reduce injuries and even save lives.
     
  14. Apr 13, 2016 #574

    proppastie

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    I had similar thoughts along the line of a simple drop test or static test for the "engineering challenged" among us (me too). It might be easier to develop it that way.
     
  15. Apr 13, 2016 #575

    autoreply

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    Why go through the complexity of engineering one (fairly complex task, even in metal tubing). Foam on the other hand is nicely customizable, ridiculously easy to calculate, you can control the direction and dead cheap. (Divinycell/glass/Divinycell/glass etc sandwich)
     
  16. Apr 13, 2016 #576

    Jan Carlsson

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    My son and I went to Circus this evening, it was a good one, when leaving I stepped on a lot spilled popcorn on the board walk, and this thread popped up in my head, soft crunchy absorbing. if it goes well with spilled soda on the cockpit floor, I don't know, :)

    More serious, saw a test with different foams, and corecell was very good, and was used in boat hulls for the Swedish navy
     
  17. Apr 13, 2016 #577

    StarJar

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    As the wheel's mounting is a part of the protection, I'm going out of flow here a bit, to mention that carrier landing aircraft have unique gear qualities that might apply.
    Once I heard a pilot say, that upon returning from the ship to the ground base, his eyeballs shook and it was hard to see clear while TAXIING, because the tires still had high pressure in them for deck landings. I think this would also indicate very stiff gear suspension.
    Well this is sort of repeating what I was saying earlier, about shifting priorities. But heck, what do gliders do? I've never flown one. How stiff are they? Maybe we are forging new technology.
     
  18. Apr 14, 2016 #578

    proppastie

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    Since this is a "Conceptual Design" only, just put a note on the drawing with an arrow to under your seat, "Energy absorbing material"
     
  19. Apr 14, 2016 #579

    Topaz

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    Who's got a generic airplane into which to bolt it? Point being, every design is a different case. That is one of the major themes of the NASA/AGATE report - you have to tailor the system to the individual aircraft.

    Much as I hate to snip off a good discussion, I'd like to keep discussion in this thread more-or-less confined to my particular project. This is very fruitful and informative stuff that everyone is posting, and it deserves to not be buried in a thread about my particular design. I believe there was a recent "Crash Safety" thread (or similar). Perhaps that one should be revived for this, more general, material?
     
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  20. Apr 14, 2016 #580

    proppastie

    proppastie

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    I am curious to see what is next, seems to me there is a whole lot of detail for "concept only" not a criticism just very different than my idea of "concept". In the corporate world the hand wavers and suits provide the concept and its up to the engineers to go from there.
     
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