Aspect Ratio/Chord/Span vs Section Depth

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by stankap, Feb 6, 2012.

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  1. Feb 6, 2012 #1

    stankap

    stankap

    stankap

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    Guys,
    I'm building a one off design, standard low wing all aluminum aircraft. Right now I am playing around with AR vs. section depth. Here are some preliminary figures:

    Empty 450~500lb
    Gross 730~775lb
    Wng section USA 35B
    Wing Size:
    (option 1) 3.50' chord x 21.28' span = 74.5ft^2 AR = 6.08 Section depth 5.02"
    (option 2) 4.25' chord x 17.50' span = 74.4ft^2 AR = 4.11 Section depth 6.09"

    Looking at Hummelbird plans and Davis DA-2A/DA-5 plans I see two different spar construction techniques, but I'm wondering if it is better to go with:

    (option 1) shallow section/ large AR (more complicated spar buildup)
    (option 2) deep section/small AR (simpler spar buildup)

    This all has to do with complexity of spar construction vs aicraft performance (AR), vs wing weight.

    Some informative discussion from the more advanced aircraft designer members is requested (please).

    Thanks,
    Stan
     
  2. Feb 6, 2012 #2

    gordonaut

    gordonaut

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    Last edited: Sep 26, 2012
  3. Feb 6, 2012 #3

    stankap

    stankap

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    Gordon,
    I appreciate the comments and would love to go with 15% thickness but neither of these (2415 or 4415) have a flat bottom. I was only considering Clark Y or USA 35B to keep the wing design simple so it can be made on a flat bench without worrying about building in any inadvertent twist during manufacture.

    Thanks,
    Stan
     
  4. Feb 6, 2012 #4

    gordonaut

    gordonaut

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    Last edited: Sep 26, 2012
  5. Feb 6, 2012 #5

    stankap

    stankap

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    Gordon,
    Good question on the tail, and yes I did plan on using a symmetric profile. I still think it would be a little tricky building a non flat wing without inducing some unwanted warp or twist.

    How about some of you guys who have built aluminum wings of non flat bottom airfoils, did you have any difficulties getting a true unwarped wing?

    Stan
     
  6. Feb 6, 2012 #6

    orion

    orion

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    For a small, light airplane, I'd strongly urge you to go with the higher aspect ratio as the lower one might hurt you in take-off and climb. The slight weight benefit I don't think is justifiable. For most GA work, an aspect ratio of 6.0 is often considered a very minimum.

    I also agree that a 15% section would be of benefit for no real cost.
     
  7. Feb 6, 2012 #7

    stankap

    stankap

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    Thanks Orion
     
  8. Feb 6, 2012 #8

    AV8N247

    AV8N247

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    The RVs are built vertically with a plumb between the spars. Seems to work well for them.
     
  9. Feb 11, 2012 #9

    bifft

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    Just commenting on the flat bottom wing thing. Having built most of an RV, it was easy to get the wing straight with plumbobs and tight string.

    Building flat on a table would also not be hard, just put some spacers under your front and rear spar, so that the wing is flat over the table. Put in enough spacers so that the spar doesn't sag (shouldn't be a problem if the spar is stiff enough for the wing, unless you have a very long wing), then set the ribs based on the spar positions. With the spacers, you would also be less likely to glue your wing to the table.
     

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