Buttercup tail

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by berridos, Apr 29, 2010.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Apr 29, 2010 #1

    berridos

    berridos

    berridos

    Well-Known Member

    Joined:
    Oct 10, 2009
    Messages:
    804
    Likes Received:
    47
    Location:
    madrid
    Hi guys

    I was defining the parameters of my high wing plane (similar to Buttercup but cleaner).
    Starting with the initial guessing I saw the the leverarm for the horizontal tail is 2,7 the wing chord. Strojnik recommends not less than 3,5.
    Wittman seems to compensate that, using a fairly thick inverted clark Y tail airfoil.
    The tail surface is 26 sqft and maybe 23sqft netting for the fuselage tail (dont have the data in front of me).
    My standard calculated value is 23.6sqft, if I estimate a 0,4 additional lift coefficient with full flaps.
    Do you think he used Clark Y because of stability reasons or because of stol characteristics?
    Would you think it could make sense to put a horizontal stabiliser with an inverted GA37315 or with less pitch a NACA747315
    How a re the stall characteristics of the NACA747315
    I suppose the pitch in the tail thru the lever arm becomes an important criteria.
     
  2. Apr 29, 2010 #2

    lr27

    lr27

    lr27

    Well-Known Member

    Joined:
    Nov 3, 2007
    Messages:
    3,216
    Likes Received:
    465
    Airfoil in stab will NOT affect static stability, although obviously it affects trim. If the flaps cause lots of nose down, perhaps it will help hold the nose up for a slower landing when cg is forward.

    Sure looks like a flat plate airfoil to me:
    (warning, fairly large file, a couple of megs or something, I think)
    http://luceair.com/images/replica/may_1989.pdf
    note that this is the original, not the reproduction
     
  3. Apr 29, 2010 #3

    lr27

    lr27

    lr27

    Well-Known Member

    Joined:
    Nov 3, 2007
    Messages:
    3,216
    Likes Received:
    465
    P.S. It will only help hold the nose up if it's trimmed far enough.
     
  4. Apr 29, 2010 #4

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,732
    Likes Received:
    2,540
    Location:
    Rotterdam, Netherlands
    The leverarm isn't that important for stability as long as the tail volume (leverarm times tail surface area, as calculated from the quarter chord point) is sufficient.

    Why he did use the Clark-Y I don't know, but LR27's idea could very well be the reason.
     
  5. Apr 29, 2010 #5

    addaon

    addaon

    addaon

    Well-Known Member

    Joined:
    Feb 24, 2008
    Messages:
    1,686
    Likes Received:
    100
    Location:
    San Jose, CA
    Yep. The tail usually provides some downforce; minimizing drag at a chosen condition (cruise, for example) would cause selection of a cambered tailplane.

    Lever arm does effect damping, although not static stability.
     
  6. Apr 30, 2010 #6

    lr27

    lr27

    lr27

    Well-Known Member

    Joined:
    Nov 3, 2007
    Messages:
    3,216
    Likes Received:
    465
    From those pictures, I'm pretty sure he didn't use any airfoil except a flat plate.

    In addition to damping, Strojnik probably figured the drag of a bit more tailboom would be less than that of a large tail plane.
     
  7. Apr 30, 2010 #7

    berridos

    berridos

    berridos

    Well-Known Member

    Joined:
    Oct 10, 2009
    Messages:
    804
    Likes Received:
    47
    Location:
    madrid
    Well I bought the plans from Earl Luce. Maybe the replica differs from the original.
    Anyway an inverted Clark Y looks flat when photographed from the top.
    What tail airfoil would you use (simetrical or asimetrical)? Any proposals' The wing is laminar.
     
  8. Apr 30, 2010 #8

    lr27

    lr27

    lr27

    Well-Known Member

    Joined:
    Nov 3, 2007
    Messages:
    3,216
    Likes Received:
    465
    But does an inverted Clark Y look about 2 percent thick when viewed from the front? Check out ALL the photos in the link I gave again.

    I should think the way to decide what foil to use in the tail is to look at what the loading on the tail would be in all flight conditions. You want something that won't stall in any of them, and that is low drag at the range of angles of attack seen at higher speeds. Maybe that's almost always the same range, for all I know, in any normal airplane. Certainly it isn't the same for aircraft that are proportioned differently, like the Avanti I looked up and saw today. (Of course I heard it first.)
     
  9. May 2, 2010 #9

    Mild Bill

    Mild Bill

    Mild Bill

    Member

    Joined:
    May 1, 2010
    Messages:
    10
    Likes Received:
    3
    Location:
    Just south of the (Wisconsin) border
    Not any wing using the NACA 2412 (the original Buttercup's airfoil section
    according to the article at http://luceair.com/images/replica/may_1989.pdf).

    If the Luce plans specify a different airfoil section, what is it?
     
  10. May 2, 2010 #10

    berridos

    berridos

    berridos

    Well-Known Member

    Joined:
    Oct 10, 2009
    Messages:
    804
    Likes Received:
    47
    Location:
    madrid
    Sorry guys. When I wrote the post i hadn't the plans in front of me. I mixed up the tail surface design with another design. In fact when reviewing the plans it is a thin simetrical foil.
    Regarding the laminar wing...thats my mod.
     
  11. May 3, 2010 #11

    Mild Bill

    Mild Bill

    Mild Bill

    Member

    Joined:
    May 1, 2010
    Messages:
    10
    Likes Received:
    3
    Location:
    Just south of the (Wisconsin) border
    What airfoil section are you contemplating for your mod?
     
  12. May 3, 2010 #12

    berridos

    berridos

    berridos

    Well-Known Member

    Joined:
    Oct 10, 2009
    Messages:
    804
    Likes Received:
    47
    Location:
    madrid
    GA37A315
    However to stay in the middle of the laminar bucket with that foil I would have to use a CL-design of o,4.
    Don`t you think it should be between 0,2 and 0,3?
     
  13. Mar 13, 2014 #13

    planecrazzzy

    planecrazzzy

    planecrazzzy

    Well-Known Member

    Joined:
    Aug 16, 2003
    Messages:
    330
    Likes Received:
    13
    I just made mine up.... Buttercup prints and Tailwind prints... and figure the square inches... Hmmm, I call it Buttwind Plus, I added an upside down airfoil.... see pictures . Gotta Fly...
     

    Attached Files:

Share This Page

arrow_white