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National Advisory Committee for Aeronautics, Technical Notes - Formulas for the Stress Analysis of Circular Rings in a Monocoque Fuselage

The formulas given in this report provide a Simpli-
fied method for the stress analysis of fuselage bulkheads
that are approximately circular rings of uniform cross
section.‘ Complicated load systems acting on a ring can ,
usually be resolved into simplified load systems; and for-
mulas for moment, axial force, and shear for such simpli-
fied load systems are given in this report. Illustrative
examples showing the use of this method in practical stréts—
analysis work are also included.
many airplanes have fuselages .of approximately circu—
lar cross section which are built around circular metal
bulkhead rings connected by longitudinal metal stringers
and covered with a thin sheet—metal skin. A typical air-
plane of this sort is the Fleetster shown in figure 1.
The locations of the main bulkhead rings in the'Tleetster"
are shown in figure 1. A Sketch of bulkhead ring N6. 2
is shown in figure 2; the centroidal aiis of the ring is
seen to be approximately circular, and the cross section
of the ring is uniform for most of its circumference.
Under the various conditions of flight and landing, this
bulkhead ring is acted on by forces applied at six differ—
ent points on the circumference 6f the ring, and sometimes
also by distributed tangential forces applied through the
skin of the fuselage. Figure 2 shows a typical loading
of bulkhead ring No. 2. The most practical saluti6n for
the stresses in the ring due to a complicated loading sys—
tem of this sort is probably obtained by resolving the com—
plicated loading system into a series of simpler loading
systems for which the general formulas can be.derived. A_
typipal case of such a resolution of forces is shown in
figure 8 where the loading system of figure 2 is resolved
into three simplified loading conditions.