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Re: How to test rib strength?

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  • Koen Van de Kerckhove
    Hallo, I found, thanks to the Fly5k yahoo group, this article. Keep that brain spawning wings, Koen °°°°°°°°°°°°°°°°°°°°°°°°°°°°
    Message 1 of 2 , Oct 2, 2004

      I found, thanks to the Fly5k yahoo group, this article.

      Keep that brain spawning wings,


      Rib Testing

      The rib is supported upside down by a jig simulating the wing spars.
      The load, consisting of a single mass suitably divided by balance
      beams, is applied to the upper edge of the rib (as positioned in the
      jig), distributed by pallets of wood as needed to prevent stress

      The test load is divided according to the manner in which lift is
      distributed across the chord of the wing. For the purpose of testing
      airfoils having a thickness ratio of 18% or less intended for
      airspeeds of 150mph or less, the following load distribution has been

      As measured from the nose of the airfoil:

      Zone 1 = 0 to 19.1% of the chord
      Zone 2 = 19.1% to 46.2% of the chord
      Zone 3 = 46.2% to 90% of the chord

      Note that no load is placed on the extreme trailing edge of the rib.

      The test weight is distributed according to the following schedule:

      Zone 1 = Half the weight
      Zone 2 = One-quarter of the weight
      Zone 3 = One-quarter of the weight

      Testing Procedure

      The mass representing the test weight is to be positioned on a tray
      pallet below the test jig, suspended from the mid-point of a balance
      bar, one end of which applies its load to Zone 1, the other end being
      divided by a second balance bar so as to apply its load equally to
      Zones 2 & 3.

      When the testing jig has been assembled and balanced, weights are
      applied to the tray or pallet according to a schedule provided by the
      designer. The objective is to increase the weight in a graduated
      manner beginning with large amounts then tapering off with small
      amounts until the rib fails, at which time the last amount added to
      the pallet is subtracted from the total.

      Practical Aspects.

      Ensure you have enough weights on hand. A properly designed rib
      weighing only a few ounces is usually capable of supporting several
      hundred pounds.

      Lead in the form of pigs, bars or bags of shot has proven to be the
      most practical form of weights.

      Each weight must be individually weighed and marked. The weight of
      the balance bars, pallet and the stays connecting them must be
      included in the total weight.

      Proof of Concept & Quality Control.

      For a new design at least ten samples should be tested in order to
      define the minimum acceptable standard for strength.

      For a proven design, three ribs, randomly selected from each
      production batch should be tested. Should any of the samples fail to
      meet the minimum acceptable strength, the entire batch must be

      - - - - - - - - - - - - -

      The information above has been extracted from static and dynamic
      testing procedures found in the Civil Air Regulations, Part 04 (circa
      1936) and the structural test section of the `Handbook of Instruction
      for Airplane Designers,' Air Corps, U.S.Army (circa 1937)

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