• Version
• 102 Downloads
• 1.26 MB File Size
• 1 File Count
• January 17, 2017 Create Date
• January 17, 2017 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - An Approach to the Prediction of the Frequency Distribution of Gust Loads on Airplanes in Normal Operations

As a basis for the prediction of the gust—load history of airplanes
in service operations, the statistical concepts of random variables and
probability distributions are applied to the "sharp edge gust“ formula.
Expressions are derived for the frequency distribution of gust loads in
terms of distributions of the related variables such as effective gust
velocity and airspeed. Solutions are obtained under assumptions that
appear reasonable on the basis of present practices in gust research.
The results are applied in an example and the predicted load experience
is compared with the available flight loads data for this case.

The prediction of the gust and gust—load experience of an airplane
in operational flight is a problem requiring continuing study for the
development of safe and efficient aircraft. After a basic design is
selected, one of the problems faced by the designer in setting the ulti-
mate and fatigue strength of the primary structure is the prediction of
the airplane gust—load history. Because the load applied to an airplane
when encountering a gust is a function of both the gust velocity and a num—
ber of associated operating conditions, such as airspeed and altitude,
information is needed not only on the characteristics of atmospheric tur-
bulence but also on how and where the airplane will be flown.

In operating practice, the gust intensities encountered vary in an
irregular manner over a wide range of intensities; in addition, the air-
speeds and altitudes at which gusts are encountered also vary over an.
appreciable range for a given airplane. The load history of an airplane
thus depends upon combinations of conditions in guSt encounters, Since
the particular combinations of conditions that occur in gust encounters
are, within certain physical limitations, largely irregular and beyond
control, the load experience exhibits some of the characteristics of
chance phenomena and may be described by probability methods.

The statistical nature of the gust—load history has been widely
recognized and considerable effort has been expended in the collection
and analysis of gust—loads flight data. Until recently, these data were
largely collected by use of NACA V—G recorders from which information
could be obtained only on the larger loads and gusts. With the develop-
ment of time-history recorders, such as the VGH recorder of reference 1,
suitable for operational use, the entire range of gust and load inten-
sity may be studied. In this connection there exists the problem of
developing methods appropriate to the use of these data for purposes of
load prediction. This problem is considered in the present paper in
which an approach to the prediction problem based on probability methods
is presented.