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National Advisory Committee for Aeronautics, Report - The Tail Plane

The following paper which has been prepared for publication by the National Advisory
Committee for Aeronautics deals with the calculation of the tail plane. I try to simplify
the present theory of longitudinal stability for that particular purpose so as to obtain one definite
coefficient characteristic of the effect of the tail plane. The more general theory hitherto devel—
oped gives no such compact result. It has indeed a wider aim, to calculate not only the tail
plane, but the exact character of flight to be expected. The method is so complicated, however,
and the results so uncertain that at present it seems to be unfit for application in design. For
the present at least it has to be confined to the desks of some special investigators. It is not
impossible on the other hand that the following method may be developed later so far that it "
covers also this more general task. In its present form the aim is not so ambitious.

The coefficient mentioned is obtained by substituting certain aerodynamic characteristics
and some dimensions of the airplane in a comparatively simple mathematical expression.
I take care to confine all aerodynamical information necessary for the caculation of the coeffi—
cient to the well-known curves representing the qualities of the wing section. I am able to
do so by making use of the recent results of modern aerodynamics. All formulas and relations
necessary for the calculation are contained in the paper. They give sometimes only an approxi-
mation to the real values An example of calculation is added in order to illustrate the appli-
cation of the method.

Moreover, it was necessary to discuss more general and simple questions concerning the
subject before starting with the new contribution. Statical' and dynamical stability, slope
of the moment curve, travel of the center of pressure, metacentric height are conceptions which
are old and comparatively simple. They have given rise, however, to controversies and there is
not yet general agreement as to their meaning and usefulness. The discussion of some other
questions related with the tail plane forms the last part of the paper.