What do these airfoil ordinates mean?

Discussion in 'General Experimental Aviation Questions' started by Hot Wings, Jul 2, 2019.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Jul 2, 2019 #1

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    6,437
    Likes Received:
    2,343
    Location:
    Rocky Mountains
    I'm trying to wade through this old set of plans and just can't figure out what a few of the numbers represent. I've tried the old circle on a slope at a point for the nose curve and some other odd ideas but I just can't seem to figure this one out. Any ideas about the set of numbers in the column with the blue box?
    ordinates.jpg
     
  2. Jul 2, 2019 #2

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    6,953
    Likes Received:
    1,915
    Location:
    North Carolina
    Upper and lower nose radii?
     
  3. Jul 2, 2019 #3

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    6,437
    Likes Received:
    2,343
    Location:
    Rocky Mountains
    Tried that, but I'm either just not getting it right or it's something else. The lower number is outside the normal lower curve. The rest of the numbers make a nice looking curve through the negative number for the leading edge. Being a nose radius on a FW I don't want to make any assumptions.

    My plan "B" is to put this into Xflr or Javafoil.
     
  4. Jul 3, 2019 #4

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    6,953
    Likes Received:
    1,915
    Location:
    North Carolina
    How does it look if you make the nose radius 77.035 and end it into the rest of the curve at x=4.65mm top, 13.95 mm bottom?
    Many old airfoils had a circular arc at the nose as it made construction so much easier than some arbitrary shape.
    I'd draw out the ordinates onto an old fashioned piece of paper and playing with assorted coins to try cracking this.
     
  5. Jul 3, 2019 #5

    Topaz

    Topaz

    Topaz

    Super Moderator Staff Member

    Joined:
    Jul 30, 2005
    Messages:
    13,827
    Likes Received:
    5,461
    Location:
    Orange County, California
    Radii of some kind, I agree. Usually expressed in terms of percentage of chord. Question is, where on the airfoil is "r1" and where is "r2", which are the field titles at the top. Any idea from the plans?
     
  6. Jul 3, 2019 #6

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    6,437
    Likes Received:
    2,343
    Location:
    Rocky Mountains
    The scan above is from what is left of the plans. In fact this is the "master" that was being used. I've been through the build manual and there isn't any explanation there either.
    foilSW.JPG

    My first thought was an old school circle for the nose but ?!??? This is what I get when I plot this out in CAD:

    The 2 points in the little circles are the mystery points. The flat bottom was used during build as a reference plane to make the spar normal.
    SWfoil2.JPG
     
    Last edited: Jul 3, 2019
  7. Jul 3, 2019 #7

    12notes

    12notes

    12notes

    Well-Known Member Lifetime Supporter

    Joined:
    Aug 27, 2014
    Messages:
    849
    Likes Received:
    523
    Location:
    Louisville, KY
    This is a shot in the dark, but could those be the numbers that define two elipses that create the shape of the leading edge of the airfoil, using 1/4 of each elipse?
    x^2/4.65+y^2/89.12=1 for the lower surface and x^2/13.95+y^2/42.47=1 for the upper.
    I don't have an easy way to graph them together and align them to check. The individual graphs are roughly the right shapes.
     
  8. Jul 3, 2019 #8

    Arfang

    Arfang

    Arfang

    Well-Known Member

    Joined:
    Aug 10, 2014
    Messages:
    89
    Likes Received:
    75
    Location:
    Switzerland
    You're right, except r1 and r2 center points have different coordinates. Take a look at drawing number 2:

    R1R2.jpg
     
  9. Jul 3, 2019 #9

    Arfang

    Arfang

    Arfang

    Well-Known Member

    Joined:
    Aug 10, 2014
    Messages:
    89
    Likes Received:
    75
    Location:
    Switzerland
    There's another view on drawing 2 labeled ''Tracé des nervures'' providing an example on how to read the coordinate values with rib n°20:

    On the coordinate sheet we read:

    n20.jpg

    Here's what that means:

    r1 is a radius of 57.5mm and its center point located at X 57.5mm behind the datum line, the value 3 means the radius ends 3mm behind the datum

    r2 value is 27.4mm, center point X 27.4 behind datum and radius ends 9mm behind datum line.

    Both radii centers coordinates values on the Y axis are the same as the leading edge foremost point: 49.7mm

    The datum is always located at X0, as showed on the original drawing.

    N20drawing.jpg
     
    proppastie and wsimpso1 like this.
  10. Jul 3, 2019 #10

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    6,437
    Likes Received:
    2,343
    Location:
    Rocky Mountains
    Many thanks!!:):cool: It all fits now!

    Looks like some of this was lost in the English translation of the plans. Have you built one of these planes?

    Expect a PM with some more questions. ;)
     
  11. Jul 3, 2019 #11

    Arfang

    Arfang

    Arfang

    Well-Known Member

    Joined:
    Aug 10, 2014
    Messages:
    89
    Likes Received:
    75
    Location:
    Switzerland
    You're welcome. I didn't build one, yet, but I have the complete set of drawings for the AV-36/361 and -22 so feel free to ask any question. In case you didn't know, plans for the -36, -22 and now -45 can be purchased from the Angers aviation museum in France, that's where I got mine:

    https://www.musee-aviation-angers.fr/documentation
     
  12. Jul 4, 2019 #12

    lvaero

    lvaero

    lvaero

    Member

    Joined:
    Sep 24, 2018
    Messages:
    22
    Likes Received:
    3
    Location:
    Spring, TX
    Thanks for bringing this topic up. We have never seen this format for airfoil coordinates, so we will study it for enrichment. Who would have thought there was a way other than just x-y coordinate sets? Very neat, and as for the museum, we are kicking ourselves in the rear for not knowing about it. Was only 45 minutes from where we were at a couple weeks ago...Le Mans!

    Either way, thank you!
     
  13. Jul 4, 2019 #13

    Hot Wings

    Hot Wings

    Hot Wings

    Well-Known Member HBA Supporter

    Joined:
    Nov 14, 2009
    Messages:
    6,437
    Likes Received:
    2,343
    Location:
    Rocky Mountains
    Again, thanks for the education and for the link! I have the AV-45 documentation ordered. My ultimate goal is a modern version of the AV-48.

    You must be under 40 and grew up in the CAD era? Take a look in TOWS at any of the NACA airfoils.
    I actually feel kind of obtuse after having it pointed out that a dual LE radius was the answer. The fact that I didn't see it I'll blame on the cold I've had for a week.....Yea, that's it. The little bugs in me did it. o_O
     
  14. Jul 4, 2019 #14

    Arfang

    Arfang

    Arfang

    Well-Known Member

    Joined:
    Aug 10, 2014
    Messages:
    89
    Likes Received:
    75
    Location:
    Switzerland
    I wish you success then, there's not enough of these Fauvel wings around!
     

Share This Page



arrow_white