• Version
• 175 Downloads
• 999.76 KB File Size
• 1 File Count
• August 18, 2016 Create Date
• August 18, 2016 Last Updated

National Advisory Committee for Aeronautics, Report - Bending Moments, Envelope, and Cable Stresses in Non Rigid Airships

No simple but comprehensive method of calculating the principal stresses in the envelope
of a non-rigid airship has hitherto been described and published in the English language. The
present report describes the theory of the calculations and the methods which are in use in the
Bureau of Aeronautics, United States Navy. The principal stresses are due to the gas pressure
and the unequal distribution of weight and buoyancy, and the concentrated loads from the car
suspension cables.

The second part of the report deals with the variations of tensions in the car suspension
cables of any type of airship, with special reference to the rigid type, due to the propeller thrust
or the inclination of the airship longitudinally.

The Third Annual Report (1917) of the National Advisory Committee for Aeronautics
contained a translation by Prof. Karl K. Darrow of the report of the investigations by two
German engineers, Dr. Rudolf Haas and Alexander Dietzius, into ”The Stretching of the
Fabric and the Defamation of the Envelope in Non-Rigid Balloons.” That report, prepared
with characteristic German care and exhaustiveness, included a description of the theory and
procedure for finding the stresses in the envelope when the bending moment is known, but
failed to describe how the stresses in the car-suspension cables and hence the bending moment
due to the weight of the car and its load may be determined when the system of suspension
cables is at all complex. The writer was therefore asked by the National Advisory Committee
for Aeronautics to prepare a more comprehensive report on the subject.

The airship designer has an infinite choice of possible arrangements of the car-suspension
system, and even when the layout of the cables is determined there is an infinite number of
ways in which the load may be arbitrarily distributed among them, each distribution producing
its own peculiar variation of the bending moment along the envelope, so that without a theory
of the methods to be followed in the design of the suspension system but little can be done
in the calculation of the stresses in the envelope. The present report is intended to furnish
an account of a theory and method of procedure applicable to modern airships in which it is
customary to suspend a short car close up to the envelope. When the bending moment is
determined in accordance with this procedure, the stresses in the fabric of the envelope due
to the bending may be determined to a good order of accuracy by application of the ordinary
formula for the fiber stresses in a loaded beam, without recourse to the elaborate refinements
and corrections described by Haas and Dietzius.