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National Advisory Committee for Aeronautics, Technical Notes - Curves Showing Column Strength of Steel and Duralumin Tubing

The following set of column strength curves are intended
to simplify the method of determining the size of struts in an
airplane structure when the load in the member is known, and to
simplify the checking of the strength of a strut, knowing the
size and length.
In the past it has been customary to compute the size of a
strut by trial and error, with the use of the basic formulas,
or by the use of nomographic charts, which were conducive of
error because of the necessity for referring to tables to be
sure that the strut came within Johnson‘s or Euler's range.
With the following curves no computations are necessary,
as in the case of the old—fashioned method of strut design; no
straitedge is needed to connect points, as in the case of the
nomographic charts; no reference need be made to tables to as—
certain the limiting-length of a strut, as the curve for each
size strut is complete in itself through the range of long and
short columns. The process is so simple that draftsmen or oth~
ere who are not entirely familiar with mechanics can check the
strength of a strut without much danger of error. If it is de—
sirable to use the lightest tube available for the same strength
it can be seen at a glance which are the lighter, because the
tubes ascend the ordinate of zero length with increasing cross—
sectional area and hence greater weight. Therefore, if two or
more tubes give the same strength for a given length, the light—
est can'be determined because its curve will intersect the ordi—
nate of zero length in the lowest position. If a member (as in
the case of some fuselage members) is designed by tension, the
size can be determined from these charts if the yield point is
used as the allowable tensile strength. The tensile strength
is to be found on the ordinate of zero length.