Junkers external airfoils on elevator?

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by rtfm, Oct 6, 2019.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Oct 6, 2019 #1

    rtfm

    rtfm

    rtfm

    Well-Known Member

    Joined:
    Jan 3, 2008
    Messages:
    3,192
    Likes Received:
    572
    Location:
    Brisbane, Australia
    Hi,
    Another thought experiment:
    I know that external airfoil flaps/ailerons (ie Junkers style) are very effective, but I have never seen this employed on the elevator. So - what would be the pros/cons of using external airfoils on the elevator?

    Regards,
    Duncan
     
  2. Oct 6, 2019 #2

    bmcj

    bmcj

    bmcj

    Well-Known Member HBA Supporter

    Joined:
    Apr 10, 2007
    Messages:
    12,974
    Likes Received:
    4,919
    Location:
    Fresno, California
    The ailerons enjoy a form of redundancy because if you blank out one side, the other side is in clean air. Also, I think the ailerons are set up to give some pro-verse drag.

    For an elevator, you ideally want the same response in both directions (not blanked out) and you don’t want it adding drag the way a differential aileron does.
     
    Last edited: Oct 6, 2019
  3. Oct 6, 2019 #3

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    6,448
    Likes Received:
    2,360
    Location:
    Rocky Mountains
    The two biggest negatives to Junkers are that they tend to be sticking out and therefore more prone to ground handling damage.
    The other is flutter/weight. For every ounce that is needed to balance the Junkers flap about it's quarter chord point there needs to be around 4 ounces of weight in the wing forward of the quarter chord point to balance the whole. Some of this weight is just naturally there due to structure but if not the rest needs to be added as just plain dead weight or more structure for stiffness. This can work out well for a large structure like a wing but on a small elevator it causes problems. Sticking the weight out on a long arm helps but then the probability of ground damage goes up.

    I went through this circus a few years ago trying to use Junkers on a Spratt wing. It's in my "lessons learned" file.
     
    pictsidhe and bmcj like this.

Share This Page



arrow_white