Canopy Stress

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by mladen.k, Aug 3, 2010.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Aug 3, 2010 #1
    Hi, does anybody know how to calculate acrylic or polycarbonate molded canopy thickness based on it's area for pressurized tandem 2 seat airplane? Pressure difference is 5psi. I'm not sure if canopy can be made from 1 piece or separate for pilot in front seat and 2nd. pilot in back seat. I understand that you can seal connection point of canopy and aircraft body with inflatable rubber seal so you can pump air inside canopy without leak, but haven't found any information in books or internet about calculating canopy area and thickness. Thanks in advance.
     
  2. Aug 3, 2010 #2

    orion

    orion

    orion

    Well-Known Member

    Joined:
    Mar 3, 2003
    Messages:
    5,800
    Likes Received:
    135
    Location:
    Western Washington
    Assuming a blown shape that can be approximated with a spherical loft, the stresses within the material can predicted using the following:

    sigma = [q x r]/[2 x t]

    where "q" is the pressure over the face; "r" is the approximate radius of the shape: and "t" is the thickness of the shell.

    For a more precise calculation though it would be beneficial to actually build a finite element model so you can account for the actual shape and any edge fasteners or other details of shape or mounting that could introduce stress risers or concentrations.
     
  3. Aug 3, 2010 #3

    wsimpso1

    wsimpso1

    wsimpso1

    Super Moderator Staff Member

    Joined:
    Oct 19, 2003
    Messages:
    6,158
    Likes Received:
    3,463
    Location:
    Saline Michigan
    I assume that if you are pressurizing the bird, it is also pretty fast. You have a couple things further raising the delta P you have to deal with. First is the fact that the air inside is stationary and the air outside is moving at some fraction above free stream velocity. This will add considerably. Worst case is probably max G at Va and max G at Vd. The pressure field from the wing wraps around the fuselage (and presumably the canopy).

    On my unpressurized bird, those loads drove design of the canopy frames, hinges, and latches. By the time I was done, it was stiffness (deflection) that drove the design, not strength.

    Billski
     

Share This Page

Group Builder
arrow_white