Midwing musings

Discussion in 'Hangar Flying' started by cluttonfred, Oct 16, 2017.

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  1. Oct 16, 2017 #1

    cluttonfred

    cluttonfred

    cluttonfred

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    What do folks think of the idea of a midwing design along the lines of the Malmö MFI-9/Bölkow Bo 208 Junior (derived from the Björn Andreasson's original BA-7 homebuilt) but with a thicker, cantilever wing lowered to about the level of the top stiffener on the MFI-9 fuselage? The wing would still use a little forward sweep to keep the spar behind the cockpit, so visibility would be great but it could use a more conventional bubble canopy, or maybe a flat-wrapped forward-hinged canopy like a Gardan Minicab, and a straight upper longeron from firewall to tail.

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    Last edited: Oct 16, 2017
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  2. Oct 16, 2017 #2

    Pops

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    I like it .
     
  3. Oct 16, 2017 #3

    Victor Bravo

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    IMHO this creates some issues. Having briefly flown the Cygnet, which is also a forward swept shoulder wing aircraft, I can say that the access to and from the cabin is more difficult than if the wing were above or below the cabin. With a thicker cantilever wing this would probably not get any better.
     
  4. Oct 16, 2017 #4

    cluttonfred

    cluttonfred

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    Thanks, Pops. Good point, VB, though perhaps that could be mitigated in some way. The Cygnet and Junior both already use the trick of cutting back the leading edge at the wing root for access and visibility, maybe actually attaching the root leading edge to the canopy like a Praga Air Baby would help? I have seen the similar Pottier P.130 Coccinelle (RSA Bleu Citron project) with both forward- and rear-hinged canopies. A forward-sliding canopy would also seem to provide the maximum amount of access. Then again, maybe it's just something to get used to.


     
    Last edited: Oct 16, 2017
  5. Oct 16, 2017 #5

    don january

    don january

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    I think it would be a very forgiving aircraft. Like pops I like it. once your in then all ya have to worry about is getting out.:smile:
     
  6. Oct 16, 2017 #6

    Himat

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    Why thicker wing?
    Make the wing a one piece composite wing and an ordinary light plane thickness ratio should be ok. The trick would be to have the one piece spar of a cantilever wing to pass behind the cockpit.
     
  7. Oct 16, 2017 #7

    cluttonfred

    cluttonfred

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    Thanks, Don. Himat, the rationale behind a somewhat thicker wing was to keep the wing light and stiff without a bracing strut. The Junior variants had an unusually thin NACA 23008.5 airfoil and I think a 12-15% airfoil would make more sense for a modest homebuilt to keep the weight of the cantilever spar to a minimum. I have in mind a glider-style, "bending beam," removable, two-piece wing in which the wing root attachments function as hinges allowing the wing to flap up and down but not twist or bend backwards and the left and right spars are bolted to each other to take care of bending. Wing halves could be as long as 18' and still be built and/or stored in a small workshop or 20' ISO shipping container. Even a 4' overlap (48" wide fuselage) would still give a 32' wing span, though of course you could make the fuselage narrower to reduce frontal area or the wing span shorter (for the same area) to reduce spar weight further.
     
    Last edited: Oct 16, 2017
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  8. Oct 17, 2017 #8

    Autodidact

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    I see nothing wrong with a thicker wing, the section characteristics usually show a less precipitous stall break, and the thicker section will be good for all of the structural issues of a cantilever wing, too IMO.
     
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  9. Oct 17, 2017 #9

    BBerson

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  10. Oct 17, 2017 #10

    TFF

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    I would not call 12% particularly thick. Taylorcraft thickness; Most RVs are 13.5%. 15+ would be. Meld Stits Flutt-R-Bug with a Playmate II wing.
     
  11. Oct 17, 2017 #11

    cluttonfred

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    There was a photo of a side-by-side prototype Stits Flut-R-Bug in an old Sport Aviation that tickled my fancy. I was looking for plans at one point but they don't appear to have ever been sold, either because it didn't work out well in practice or because Ray Stits got out of the plans business. That design put the spar in front of seats, but I think the spar behind the seats with just enough forward sweep to keep things balanced is a better solution, perhaps with outboard vortex generators and inboard stall strips to ensure docile low-speed handling. This also seems like a great application for the Ercoupe-style wing with the front spar, diagonal ribs and rear spar forming a triangular truss resisting torsion and drag. Another approach I have considered is an unswept, constant-chord wing with the main spar further aft than usual and tapered flaps (or fixed panels) and ailerons so that the chord line and trailing edge are swept forward but the leading edge remains straight.
     
  12. Oct 17, 2017 #12

    tspear

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    If you want a mid wing, why have the spar go through the cabin?
    Make the fuselage a donuts at that point with the side attachments. Therefore the load path can go over and below the cabin.
    It likely would weigh more, but it would allow you to position the wing exactly where you want and mostly ignore the interior configuration problems.

    Tim
     
  13. Oct 17, 2017 #13

    cluttonfred

    cluttonfred

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    Because I also want very straightforward, "heck, I could do that" construction, likely fabric over aluminum tube and gusset, and what you are describing would be anything but simple.

    A mid wing actually allows the spar to be a couple of inches forward of a shoulder wing because of the slant of the seat back while reducing wing-fuselage intersection drag compared to a low wing.
     
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  14. Oct 17, 2017 #14

    ScaleBirdsScott

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    I don't think a 'donut' is all that complex. You just make the spar get really big in the middle and then poke a hole in the middle big enough for your legs. That's assuming you're putting the pilot behind the spar. And it does mean having to introduce something to make the donut bulge if you're relying on extrusion to build up a C or I beam spar. But it's a solved problem there's a lot of aircraft having a jet engine or other such thing poke through the spar, or having a bulked out mid-section spar area that ties into the fuse. Could be really useful if one wants to go with a blended wing sort of style.

    It is somewhat more work than just a straight spar, I'll concede. But maybe it's not significantly more. And if a little more complexity in one area saves a lot of work down the road then is it a bad thing? Who's done a lot of work trying to simplify one thing, only to realize the workarounds for the other systems are now anything but simple? Yeah.

    I like the idea of a mid-wing that's bout even with the head so when you turn around you just see the leading edge, feel you'd have plenty of visibility above and below and the wing then 'mostly' disappears. You'd just have to be turning and banking to scan for traffic along your same elevation, so that would be not perfect.
     
  15. Oct 17, 2017 #15

    TFF

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    At slower flight speeds, intersection drag reduction is a nicety. If measurable on anything in this class. Mid wings look cool and are probably the most unrealistic configuration to build. Racer is one thing maybe a world record, but useable normal airplane makes it the worst. Give up everything for looks; visibility, ease of building, ease of entry and egress, structural placement of components. Different to be different is a terrible reason to design something. Designing something with requirements and it takes a certain form is the right way.
     
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  16. Oct 17, 2017 #16

    cluttonfred

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    All good points, gents, but I will point out that I did not arrive at this configuration from a "different to be different" point of view but rather from years of daydreams about a "21st century Volksplane" that would both be and look easy and cheap and fast to build with "heck, I could do that!" as the project motto.

    Think of any number of model RC models in which the wing just sits on a flat-topped fuselage. Maybe I need really big rubber bands? ;-)

    The problem with a mid-wing is that the spar wants to go through the people. I don't think a slightly forward-swept wing is that big a complication especially if you do it in a way that keeps things as simple as possible (identical ribs still at right angles to the spar, just a kink and special rib at the wing root, possibly full-span ailerons.)

    I am thinking of a simple box fuselage (likely aluminum square tube and/or angle with gussets, covered with Oratex aft and maybe removable aluminum or plastic panels around the cockpit) with a cutout for the head and shoulders of the passengers; Oratex-covered aluminum wing and stab just sitting on top of the longerons, similar fin and rudder, a roll bar and/or seat harness frame and a simple canopy.

    The quick sketch I did at the beginning of this thread was just to illustrate the configuration, what I would actually build would look much more "Volksplane-ish" than even the original BA-7.
     

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  17. Oct 17, 2017 #17

    tspear

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    There was another thread on here about the NACA 6 series airfoils.
    The major point of these airfoils was the ability to push the spar backwards. Depending on configuration, this may be enough to have the spar basically go just under the back seats.
    The end result is it almost a mid wing, easy to build....

    Tim
     
  18. Oct 17, 2017 #18

    ScaleBirdsScott

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    Is the only reason to give the wings in this scenario a forward sweep to account for CG of having a tractor engine? Seems a glider gets away with these kind of wings all day without problem so it's the only reason I can think of.

    Could always straddle a lightweight engine a little to try and scoot the CG back (and then its also a candidate for a MOTA!) The other option is go electric and use a lightweight e-motor up front and throw them batts behind the wing. Either way it just means a cockpit bolted to the front of the spar, which is just as simple as can be straight and square.

    Of course the other option is move the engine from being in front altogether, which, lots of options.


    (A lot of my thoughts on a mid-wing design layout come from trying to figure out how I'd build a mini Wildcat, btw. I think it'd be rather nifty. Not exactly the same as this bird tho.)
     
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  19. Oct 17, 2017 #19

    cluttonfred

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    Yup, the forward sweep in this case is just to keep the spar away from where the people ought to go while still retaining the simple wing-plopped-on-fuselage concept like a big RC model. It also fixes many of the access and visibility issues that come from a midwing with the pilot behind the main spar. As you said earlier, a shoulder-wing can have fantastic visibility except directly left and right, moving the wing down a little cuts in to the downward view but the forward sweep means you'd still have a clear view straight down and forward on either side.

    I really hope you do continue with your mini-Wildcat plans. I'd love to see a nice Fleet Air Arm FM-2 replica of this one to confound the armchair aviation buffs. I tend to like underdogs and my favorite WWII aircraft tend to be those considered obsolete but still providing yeoman service through the end of the war (Hurricane, P-39, P-40, Wildcat, Dauntless, Hs-123, Ki-36, Val, Polikarpovs, etc.).

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  20. Oct 17, 2017 #20

    Arthur Brown

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    You have to find some place for the spar! Over or under the pilot seems better than through him. The WWII Lancaster failed to make a civil airliner because the spar of the mid wing went through the possible passenger space, ideal to hang bombs from not so good for the moneyed elite of the late 40s who wanted luxury in a big space.

    It seems odd to have the spar over the pilot's knees as in the Cassut, but it seems to work for a flat wing racer.
     

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