Plank Progress

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Mike W, Nov 17, 2016.

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  1. Nov 17, 2016 #1

    Mike W

    Mike W

    Mike W

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    Following on from my various submissions in the thread. “Characteristics of a straight-wing, tailless model in the Langley free flight tunnel”, which detailed my efforts to design and construction a single seat plank aircraft. Now that the aircraft is nearing completion, I thought a more dedicated thread would be more appropriate.

    The aircraft is now structurally complete and only requires covering and so the moment of truth is fast approaching.

    The MW10 was designed to the original CAA specification for a single seat de-regulated aircraft (SSDR) which called for an empty weight of 115Kg (253LB) and a wing loading of less than 10Kg/SQ M. The uncovered aircraft weighs in at 257 LB using bathroom scales. The bad news is that some 20Lb of lead will be required in the nose to maintain the correct CG location, however if the aircraft looks promising some of this will be replaced by a starter battery. Initially jump leads will be used to start the engine. Luckily the old definition has been scrapped and replaced by an AUW of 660 Lb and a max stall speed of 35 Kts.

    Hopefully flight attempts will commence early in the New Year.

    p4 (1).jpg p7 (1).jpg
     
  2. Nov 17, 2016 #2

    StarJar

    StarJar

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    Keep us posted. That's fantastic.
     
  3. Nov 17, 2016 #3

    TerryM76

    TerryM76

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    Any possibility of moving main gear forward and losing the nosewheel? That would shave off a few pounds as well as bring useful weight forward and hopefully pull your CG into range without adding ballast.

    Your project looks great. I love the simplicity of planks.
     
  4. Nov 17, 2016 #4

    choppergirl

    choppergirl

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    Reminds me of a BD-5
     
  5. Nov 17, 2016 #5

    Victor Bravo

    Victor Bravo

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    I'm sorry to be Captain Obvious if that is the case, but it seems that moving the engine rearward might be less painful than living with 20 pounds of ballast.

    63133762.jpg
     
  6. Nov 17, 2016 #6

    bmcj

    bmcj

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    But he needs the weight in the nose, not the tail.
     
  7. Nov 17, 2016 #7

    TerryM76

    TerryM76

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    And it doesn't look possible to move that engine any farther forward.
     
  8. Nov 17, 2016 #8

    TerryM76

    TerryM76

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    Yep....just like one with a raised cockpit, no tail, rectangular platform wings with vertical surfaces.....other than that, just like one.
     
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  9. Nov 17, 2016 #9

    plncraze

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    A nosewheel might be useful for another reason; some short aircraft can have an issue with controlling pitch angle. I wish I could remember specific references for this. If I run into them I will post them.
     
  10. Nov 17, 2016 #10

    Victor Bravo

    Victor Bravo

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    Oh... no problem, my wife will start cooking for him. 30 days - problem solved.
     
  11. Nov 18, 2016 #11

    Sockmonkey

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    He said he was going to use the battery for ballast eventually so problem solved.
     
  12. Nov 18, 2016 #12

    ultralajt

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    I believe that this plank has plywood planking of the torsion nose of the wing? ;)
     
  13. Nov 18, 2016 #13

    ultralajt

    ultralajt

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    I believe that this plank has plywood planking of the torsion nose of the wing? ;)
     
  14. Nov 20, 2016 #14

    Mike W

    Mike W

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    Thanks for all your comments.

    In answer to some of the points raised.

    Unfortunately, it is a bit late at this stage for major relocation of components.

    Thanks Victor Bravo for the offer of your wife’s cooking which I’m sure would be delicious. The only problem is that I am 14 St at present and would like to be lighter. To compensate for the lead in the nose I would need to be 17 St, unfortunately weight wise this is all going the wrong way.

    Pincrase has a good point about rotation of short coupled aircraft. I have left the nose wheel pivot tube long to allow for adjustment of the wing ground angle, if required to assist any un sticking problems. The present wing is set at 7.5 deg ground angle which allowing for ground cushion effect should allow the aircraft to fly off at 45 MPH with controls neutral.

    The nose ply does not form a D box and is only there to maintain the profile of the reflex section, also you will notice a false spar across the cusp area, this is to hold the fabric against quilting in a region critical to the stability of the section.

    Like most of my designs the torsional and bending stiffness comes from a large diameter tube positioned at the wing CP location during max g. So that in theory the torsional stress is zero at high g levels. Same as the Kolb aircraft.
     
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  15. Nov 21, 2016 #15

    ragflyer

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    Mike,
    Thanks for sharing your progress. Could you tell us how the wooden ribs are fastened to the Al spar tube? Thanks!
     
  16. Nov 23, 2016 #16

    Mike W

    Mike W

    Mike W

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    Clutton Fred asked me to do a write up on my wing construction which I was going to do when the Plank was finished, however I have attached a drawing showing a typical rib spar joint and also a picture showing one of the joint tests. The joint took 8740 Lb in without failure despite the ply beam also twisting. the test was limited by the size of the spring balance. Calcs suggest the max torque on a MW5 rib to be some 2065 LB in.

    Polyester resin A was used as it shrinks more than epoxy and gets a better grip.

    The drawing shows safety rivets in the joint because the resin has a greater expansion rate than aluminium and taking a black painted aircraft in the Sahara desert the joint may separate although this has never occurred in practice. The MW7 and Plank have a diagonal drag brace running from root to tip, although the Plank does not need a drag brace, the spar being built in at the root in all directions. This again to provide some fail safe design in that if a rib joint comes loose the drag tube will carry the rib load to each adjacent rib and prevent collapse of the wing.

    Two pics of the MW7 which was designed to be aerobatic.

    Hope this helps. I will do a more comprehensive write up later.

    wing spar joint test.jpg wing joint.jpg mw7spar.jpg mw7 bad wilcox.jpg
     
  17. Nov 28, 2016 #17

    ragflyer

    ragflyer

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    Thanks Mike! Many thanks in advance and eagerly awaiting comprehensive write up.
     
  18. Apr 30, 2017 #18

    Mike W

    Mike W

    Mike W

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    Painting at present, not going well as usual. I have now switched to water based paint which works better. Hoping for flight attempt at Rufforth Airfield near York next month May.



    DSCN0214.jpg DSCN0215.jpg
     
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  19. May 1, 2017 #19

    lr27

    lr27

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    Looks good!

    I suppose you've read Al Backstrom's account of a similar airplane he designed and built? As I recall, his was heavier. He had problems with the engine, as I recall, although I think it was supposed to be well behaved otherwise. His powered plank was also set up with a significant positive deck angle as it sat on its gear. I think the articles were in Sport Aviation some years ago. Here's the first one:
    http://www.retroplane.net/forum/files/plank7602_014_191.pdf
    If memory serves, there was a later article which included things like increasing the deck angle.

    Somewhere I have a note from Mr. Backstrom where he agreed that extending the aileron chord, as discussed in Nickle and Wolfhardt, might be a good idea. If done right, the idea is that the lift distribution will remain about the same at different speeds. At least at the designed c.g.
     
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  20. May 1, 2017 #20

    Mike W

    Mike W

    Mike W

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    Thanks Ir27 for your suggestions. I do still have the original Sport Aviation magazines containing Al Backstroms articles. I must have had a feeling that I would need them later. My aircraft is designed within the guidelines he specifies in the articles.

    You will notice the front wheel pivot tube is left long so that I can adjust the take off angle if necessary and will be cut off after test flights. See my entry earlier in this thread.

    Mike
     
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