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National Advisory Committee for Aeronautics, Report - A Study of the Problem of Designing Airplanes with Satisfactory Inherent Damping of the Dutch Roll Oscillation

Considerable interest has recently been shown in means of
obtaining satisfactory stability of the Dutch roll oscillation for
modern high-performance airplanes unthout resort to compli-
cated artificial stabilizing devices.
[cm is to lay out the airplane in the earliest stages of design so
that it will have the greatest practicable inherent stability of the
lateral oscillation. The present report presents some prelimi-
nary results of a theoretical analysis to determine the design
features that appear most promising in providing adequate
inherent stability. These preliminary results cover the case of
fighter airplanes at subsonic speeds.

The investigation indicated that it is possible to design fighter
airplanes ‘ to have substantially better inherent stability than
most current designs. Since the use of low-aspect—ratio swept-
back wings is largely responsible for poor Dutch roll stability,
it is important to design the airplane with the maximum aspect
ratio and minimum sweep that will permit attainment of the
desired performance. The radius of gyration in roll should be
kept as low as possible and the nose-up inclination of the
principal longitudinal axis of inertia should be made as great
as practicable.

The problem of obtaining satisfactory stability of the
Dutch roll oscillation is especially difficult for jet-propelled
swept-wing airplanes designed for operation at high speeds
and altitudes. The present trend is toward the use of
artificial stabilizing devices to provide satisfactory stability
since it is usually not possible to modify an em'sting airplane
to provide satisfactory inherent stability. One of the
fundamental reasons for the poor inherent stability seems to
be that very little consideration is given to dynamic stability
in the early stages of design; that is, the basic design of the
airplane is determined from other considerations and at-
tempts are made later to improve the dynamic stability by
the minor changes m configuration which are then permis-
sible in the design.