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National Advisory Committee for Aeronautics, Report - Charts for the Minimum Weight Design of 24S-T Aluminum Alloy Flat Compression Panels with Longitudinal Z-Section Stiffeners

Design charts are developed for 248—1? aluminum—alloy fiat
compression panels with longitudinal Z-sect-ion stifeners.
These charts make possible the design of the lightest panels of
this type for a wide range of design requirements. Eramples
of the use of the charts are given and it is pointed out on the
basis of these examples that, over a wide range of design condi-
tions, the maintenance of lrucklejree surfaces does not conflict
with the achievement of high structural eficiency. The achiere—
ment of the maximum. possible structural efitciency with its-T
aluminum-alloy panels, homer-er, requires closer stifi'ener
spacings than those now in common use.

In a longitudinally stiffened compression panel, in which
all the material is active in carrying load, the requirement of
minimum weight is tantamount to that of carrying the load
at the highest possible average stress. The average stress
developed by such a panel under the loading conditions
imposed is thus a direct measure of the structural efliciency
of the panel. If longitudinally stiffened compression panels
are to be designed for high structural efficiency without a
large number of cut-and-try computations, it is desirable
that design charts be prepared to indicate the average stress
attainable under various loading conditions. The prepara-
tion of such charts requires that a suitable design parameter
in which the important loading conditions are incorporated
be found.

It has been found that a suitable parameter for longi-
tudinally stiffened compression panels in the design of
where P, is the compressive load per inch of panel width,
L is the panel length, or distance between supporting ribs,
and c is the coefficient of end fixity at- the ribs. The quantity
P;, which is essentially independent of the distribution of
material in the compression panel, can be estimated for a.
wing panel from the bending moment on the wing and the
thickness and chord of the wing. The length L may be
fixed by the presence of such installations as fuel tanks or
armament or may be arbitrarily assigned for the purpose of
arriving at a trial design.