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Do wing attach fittings of semi-cantilevered plane (i.e. ultralights) ever get subjected to shear force? For example during roll, does the centrifugal force of the wings load the wing attach fittings with shear?

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    $\begingroup$ shear in which direction? $\endgroup$
    – Federico
    Commented Dec 14, 2018 at 9:28
  • $\begingroup$ Span wise direction $\endgroup$ Commented Dec 14, 2018 at 11:32

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In general, the answer is yes. The answer depends on the details of the fittings. Note that most realistic loadings are a combination of tension rsp. compression and shear. If - for example - the wing of your ultralight is held together by shear pins (note the name!) which are inserted in vertical (up-down) or horizontal (forward-backward) direction, they will transmit those centrifugal loads as shear from one wing bushing to the other.

The same goes for the transfer of lift forces inside the spar and - again, depending on the details - into the fuselage. The web of the spar is meant to carry the shear loads and those are transferred by ribs to the attachment points. Other designs use a front and rear spar which attach directly to the fuselage.

B-17 front spar attachment

The picture shows the front spar attachment of the B-17 (source). Granted, this is not exactly an ultralight, but the same principles apply. At positions C, D and E it uses shear pins to transfer the lift loads into the fuselage bulkhead.

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