Measurement of the moments of inertia of full scale airplanes Page: 3 of 18
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N.A.C.A. Technical Note HTo. 265
at Langley Field to do moro than make a start on this collection
of important information and it is hoped that this paper will
stimulate the making of sipil3r rmeasurcments by others.
The. three reference axes of the airolane arc the usual datum
axes about which the moments of inortia cre desired. In the fol-
lowing the axis through the c.g. of the airplane parallel to the
thrust axis is taken as the main reference axis, XX. The other
two reference axes, YY and ZZ, are mutually perpendicular to
the XX axis as shown in Figure 1.
The method employed.consists essentially of swinging the
airplane as a compound pendulum about an axis parallel to the
axis for which the moment of inertia is desired. From the period
and length of the pendulum, the radius of gyration is computed.
From this, knowing the mass of the airplane, the moment of iner-
tia can be determined. Because of the difficulty of suspending
an airplane from an axis parallel to the ZZ axis, the moment
of inertia about this axis is found by swinging the airplane as
a torsional pendulum.
Determination of Center of Gravity Location:
The first requirement is to locate the center of gravity of
the airplane. In all eases the airplane is assumed to be sym-
metrical about the XZ lane and the lateral position of the c.g.
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Green, M W. Measurement of the moments of inertia of full scale airplanes, report, January 1, 1927; (digital.library.unt.edu/ark:/67531/metadc59676/m1/3/: accessed July 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.