Minimum plywood skin thickness

Discussion in 'Wood Construction' started by highspeed, May 23, 2011.

Help Support HomeBuiltAirplanes Forum by donating:

  1. May 23, 2011 #1

    highspeed

    highspeed

    highspeed

    Well-Known Member

    Joined:
    Apr 10, 2011
    Messages:
    275
    Likes Received:
    13
    Location:
    Spring, TX
    I am designing an airplane very much akin to a single seat Falco and I'm wondering if anyone has any thoughts on minimum skin thickness to minimize hangar rash and airshow moron damage? I know that panel buckling criteria are a main driver of skin thickness (though I haven't gotten to the point of figuring out how to analyze that) but there must be a minimum thickness to prevent careless ground handling from doing damage to the skin.
     
  2. May 23, 2011 #2

    fly2kads

    fly2kads

    fly2kads

    Well-Known Member HBA Supporter

    Joined:
    Jan 2, 2010
    Messages:
    1,450
    Likes Received:
    526
    Location:
    Justin, TX
    Plywood is actually reasonably tough. From what I have seen, 1/16" and 3/32" are common skin thicknesses for aircraft of normal homebuilt size. I understand some European light aircraft go down to 0.1mm in metric ply.
     
  3. May 23, 2011 #3

    NorthwestJack

    NorthwestJack

    NorthwestJack

    Well-Known Member

    Joined:
    Feb 9, 2008
    Messages:
    73
    Likes Received:
    4
    Location:
    Monroe ,Wa ( close to Seattle)
    I used 1.6 MM Finnish( from Finland) Birch for the top of my wing. it is very strong. the only problem I had /have is that with a spacing of 14 inches between ribs there is waviness in the plywood betwwen the ribs ( which is affected by moisture). If I had to do it over I would space the ribs closer or make some kind of intermediate stiffener. I was trying to get the top of the wing to be absolutely perfect. I was able to get it pretty good with a liberal application of lightweight body filler.
    Here's a picture of part of the wing, looking towards the wing tip.
    Jacq
     

    Attached Files:

    Last edited: May 23, 2011
  4. May 23, 2011 #4

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,732
    Likes Received:
    2,540
    Location:
    Rotterdam, Netherlands
    Make that 0.1 centimeter or 1 millimeter ;-)

    Most commonly is indeed the 1.6 mm (roughly 1/16") for the low and slow type of craft. The thinnest I've seen was 1.2mm (3/64").
     
  5. May 23, 2011 #5

    fly2kads

    fly2kads

    fly2kads

    Well-Known Member HBA Supporter

    Joined:
    Jan 2, 2010
    Messages:
    1,450
    Likes Received:
    526
    Location:
    Justin, TX
    Indeed! Thanks for that, it was rather late....
     
  6. May 23, 2011 #6

    snaildrake

    snaildrake

    snaildrake

    Well-Known Member

    Joined:
    Mar 20, 2010
    Messages:
    247
    Likes Received:
    5
    Location:
    Albuquerque, NM USA
    Paging forum member Ron Heuschele [sic?] to the white courtesy phone...

    Ask Ron what the Asso V Champion plans call for in plywood thickness and rib spacing (his own ship is redesigned and uses stouter dimensions). Sr. Vidor has designed many microlight planes for Euro builders, and knows what works as well as anyone in the world. I believe most of the Asso V skin is 1.5mm and 2mm, but don't quote me. That plane is amazingly lightweight, carries 2 passengers (small ones) with a Rotax 912 and retractable gear, comes in about 630 lbs. empty. It's been around since 1991, and there are well over 50 flying. Originally it called for okoume ply and spruce, though more recently the plans were revised for birch GL-2 and Doug fir, since both are tougher and easier to source.

    As regards material strength, here are some shear and compressive strength values I saved from one of PTAirco's posts:

    GL1/GL2 ply (Finnish birch):
    From 1mm to 2 mm thickness :
    Shear at 0 degrees to face grain :
    1mm = 600 psi
    2mm = 800 psi
    At 90 degrees to face grain :
    1mm = 2050psi
    2mm = 2100 psi

    Compression strength ranges from 710 to 820 psi for 0/90 degrees to face grain and 860 to 1080 psi when used at 45 degrees.

    -Dan
     
  7. May 23, 2011 #7

    highspeed

    highspeed

    highspeed

    Well-Known Member

    Joined:
    Apr 10, 2011
    Messages:
    275
    Likes Received:
    13
    Location:
    Spring, TX
    Thanks for the responses, I'll file the info away for when I do the structural workup. Now I just need to teach myself how to do the structural workup.
     
  8. May 23, 2011 #8

    rheuschele

    rheuschele

    rheuschele

    Well-Known Member

    Joined:
    Jan 13, 2010
    Messages:
    533
    Likes Received:
    41
    Location:
    Chicago Il. USA.
  9. May 24, 2011 #9

    rtfm

    rtfm

    rtfm

    Well-Known Member

    Joined:
    Jan 3, 2008
    Messages:
    3,187
    Likes Received:
    571
    Location:
    Brisbane, Australia
    :) Tell me about it... I know exactly how you feel...

    Regards,
    Duncan
     
  10. May 24, 2011 #10

    Lucrum

    Lucrum

    Lucrum

    Well-Known Member

    Joined:
    Jun 10, 2008
    Messages:
    956
    Likes Received:
    189
    Location:
    Canton, GA
    EAA - More information from EAA Sport Aviation Magazine

    Scroll down to June 2005 Wood design worksheet.
    I think skin thickness is on the second page of the spreadsheet.
     
  11. May 24, 2011 #11

    highspeed

    highspeed

    highspeed

    Well-Known Member

    Joined:
    Apr 10, 2011
    Messages:
    275
    Likes Received:
    13
    Location:
    Spring, TX
  12. May 24, 2011 #12

    rheuschele

    rheuschele

    rheuschele

    Well-Known Member

    Joined:
    Jan 13, 2010
    Messages:
    533
    Likes Received:
    41
    Location:
    Chicago Il. USA.
    Let's see if I can tell you what I did and why. My plans called for 3mm okume skin on all the fuselage. After many forum conversations with other builders (my plane and other designs), I decided to change it to 2mm birch. My reasons where as follows. When the designer designs the plane he usually specs out for local materials, not something so far away that it cost the price of a car. It is my understanding that it is easier to get the Okume in Italy than the Birch. My plane called for 3mm Okume and I could only find 4mm in the states. Even if I could get 3mm Okume, it was approx 25% heavier than 3mm birch but with a lower tensile strength. So then I looked into 2mm Birch, quite a bit lighter, great tensile and available stateside.
    As for a minimum, I'm not sure there is such a thing other than what the plans call for. After that it will be up to you
    to do the homework on who designed and why, and when. If the plane was designed in 1945, you must consider what was available compared to modern inventions and products. If someone is designing a plane, it is just my opinion that everyone going this route should build one first before attempting to design.
    Ron
     
  13. Jun 23, 2011 #13

    Rik

    Rik

    Rik

    New Member

    Joined:
    Mar 16, 2010
    Messages:
    2
    Likes Received:
    0
    Location:
    South U.K Based
    Hi Highspeed, I've recently built (2010) a Taylor Titch JT2 with a covering of 1/16" birch ply and open four bays on the outboard wing tips. She is fantasticly strong and puts up with my fastish 170 knot dashes around the local area. all the ply sections are scalf jointed at 45 degrees, steemed to profile and bonded with aerodux resin. over the ply I have pre doped (Rando-proof) ceconite 102 and stitch over the open bays. Theres only about six Titch's flying in the UK, but a lot more in the states and Africa apparently.
     
  14. Aug 15, 2011 #14

    taildragger

    taildragger

    taildragger

    Member

    Joined:
    Feb 11, 2007
    Messages:
    18
    Likes Received:
    0
    Location:
    UK
    Minimum thickness of the plywood skin is defined by required strength and at the last queue is about careless or careful handling:)
     
  15. Aug 15, 2011 #15

    highspeed

    highspeed

    highspeed

    Well-Known Member

    Joined:
    Apr 10, 2011
    Messages:
    275
    Likes Received:
    13
    Location:
    Spring, TX
    Yes minimum thickness for the design is based on the required strength, but many cases the thickness needed to acheive the required strength falls under that for impact resistance and durability in ground handling. In that case the handling durability becomes the constraint.
     
  16. Oct 15, 2011 #16

    conestogaman

    conestogaman

    conestogaman

    Active Member

    Joined:
    Mar 5, 2009
    Messages:
    34
    Likes Received:
    1
    Location:
    Sack-O-Tomato, CA
    The American designed Mitchellwing U2 uses 1mm ply for leading-edge 'D' tubes, gussets, and stabilator leading edges.
     
  17. Nov 21, 2011 #17

    topspeed100

    topspeed100

    topspeed100

    Banned

    Joined:
    May 4, 2009
    Messages:
    4,063
    Likes Received:
    63
    Location:
    Oulu/Finland
    0,8 mm is available...I have it here at my house too.
     

Share This Page

arrow_white