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National Advisory Committee for Aeronautics, Technical Notes - A Study of the Application of Power Spectral Method of Generalized Harmonic Analysis to Gust Loads on Airplanes

The study of gust loads on airplanes is a twofold problem requiring
the adequate representation of the characteristics of atmospheric turbu-
lence and the determination of the airplane response (loads or motions)
in rough air. These problems have been recognized since the inception
of gust-load research but because of the difficulties involved only
limited approaches to the problems appeared practical. The methods that
have been used are described and discussed in detail in reference 1.

In general, the approach has been to use simplified airplane~response theory
for the determination of the characteristics of discrete gusts from air-
plane measurements of load. The "gusts" derived on this basis are then
used to calculate loads on other airplanes. Although these procedures
appear reasonable for transferring loads to similar airplanes, as indiu
cated in the reference, they are of questionable value for airplanes of
widely different characteristica (such as, configurations and stability
characteristics). These limitations have, however, not proved serious
in the past since the transport airplanes which were primarily affected
by gust standards appeared, in general, to follow conventional design.
Available data indicate that new transport airplanes experienced gust
loads which were, in general, compatible with those predicted from past
work.

Trends in aeronautics-toward higher speed and the development of
missiles have served to introduce a widening range of unusual configura-
tions and aircraft stability characteristica. Furthermore, the gust-
1oad design requirements, which formerly were of concern for transport
and bomber airplanes only, appear to have become important for other
aircraft as well. As a consequence of these developments, the need for
more generally applicable techniques, both for the measurements of the
characteristics of atmospheric gusts and for the calculation of the gust
loads on new airplanes, has become more urgent.