naca-tn-2195
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National Advisory Committee for Aeronautics, Technical Notes - A Flight Investigation and Analysis of the Lateral Oscillation Characteristics of an Airplane
Flight tests were conducted and an analysis mde to determine the
causes of undesirable dynamic lateral—stability characteristics of an
airplane. Various rudder modifications were flight tested with the rudder
free and fixed over an indicated airspeed range from approximately 200 to
l+50 miles per hour. Rudder—hinge—momsnt and other pertinent data were
obtained by flight and wind—tunnel tests.
The oscillation period and time required to damp to one—half ampli—
tude measured in flight are compared with calculated curves in which these
characteristics are given as functions of the important rudder hinge—
moment parameters.
An analysis of the data showed that there were no significant changes
in the basic rudder—fixed stability derivatives with indicated airspeed,
and the rudder—fixed damping characteristics were predictable with suffi—
cient accuracy if the product—of—inertia terms were considered.
Freeing the rudder brought about a reduction in the damping of the
oscillation at low speed; this is attributed to the low negative rate of
change of rudder hinge—moment coefficient with rudder deflection and a
negative rate of change of rudder hinge—moment coefficient with angle of
sideslip. [Ehe further deterioration with indicated airspeed is attribu—
table to the effects of Mach number and rudder—tab deflection on these
hinge—moment parameters
A number of military airplanes recently have exhibited poor lateral—
oscillation characteristics in high—speed flight. The objectionable
motions of the airplane in yaw usually are characterized by constant—
amplitude oscillations or by poor damping in conjlmction with a short
period. In an effort to determine the causes of these phenomena, the
Ames Aeronautical laboratory has conducted a detailed investigation of
the dynamic—lateral—stability characteristics of an airplane for which
undesirable oscillatory behavior at high airspeeds had been reported.
At the outset of an investigation of this type there always exists
the question of whether the undesirable damping characteristics are due
to the basic static—stability derivatives (control fixed), the hinge—
moment parameters of the control surfaces (control free), or random
separation phenomena. It was therefore convenient to isolate the effect
of rudder freedom by determining first the dynamic—stability character—
istics with the rudder fixed.
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