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National Advisory Committee for Aeronautics, Technical Notes - Experiments with Fabrics for Covering Airplane Wings, to Determine Effect of Method of Installation

The following notes relate primarily to the effect of .
changes in the loading and in_the disposition of the support-
ing”framework (regarded as rigid) on the covering fabric:

The magnitude of the air forces to be taken into account
and the corresponding factors of safety to be expected will be
discussed later.

In the same way, the important inter-relations between
the loading of the fabric and the deformation of the framework
will be reserved for further researdh. The strength of a fabric
is of prime importance in deciding upon a wing.covering. This .
does not depend on the properties of the fabric alone, but also
on the supporting framework. Another factor, almost as impor-
tant, is the deformation of the fabric during flight, whiCh, un-
der certain circumstances (by alteration of the shape of the wingf,
section), may have a determining effect on the aerodynamic proper:
ties of the wing.

Lastly, secondary stresses are produced by the mutual reac-
tions between fabric and frame, which must be allowed for in cal—
culations and turned to account in the designing of the ribs.

Since the tensions in a loaded wing covering can not be ob—
served directly, an effort must be made to determine them by
means of distortion, through comparison with the tensions given
by the N;C. (normal coefficients) for similar distortions
For a uniform Wing loading, the tensions and distortions
were determined in a subsequent investigation. The calculation
take a someWhat different form for the fabric on a wing with ini—
tial double curvature. The ribs determine the curvature in the
direction 2, but, in the other direction 1, at right angles,
the radius of curvature is originally infinite.