An analog computer study of several stability augmentation schemes designed to alleviate roll-induced instability Page: 3 of 51
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2 NACA RM A56H30
Some current fighter aircraft have experienced violent pitching and
yawing motions during aileron-induced roll maneuvers refss. 1 and 2).
The possibility of this occurrence was predicted by Phillips in refer-
ence 3, wherein he shows that, depending upon the amount of damping
present in the longitudinal or directional oscillatory mode, a divergent
yawing and pitching motion can occur during a steady roll when the roll-
ing frequency exceeds a critical value, pc, equal to the lower of the
pitching and yawing natural frequencies of the nonrolling airplane. Thus
two ways to reduce the objectionable yawing and pitching motions accom-
panying rolling maneuvers are: (1) limiting the rolling velocity below
pc of the basic airplane and (2) increasing the value of the critical
rolling velocity by altering the stability characteristics of the air-
plane. The purpose of the present study is to investigate these sug-
gested methods for reducing the undesirable pitching and yawing motions
of an airplane during roll maneuvers. These methods were investigated
using an electronic analog computer wherein changes in the airplane sta-
bility characteristics and roll-rate limiting were obtained by appropri-
ate servo actuation of the control surfaces. The airplane characteristics
used in this study were those of the F-OOQA airplane having the original
small vertical tail as shown in figure 1.
B.P. break point, radians per second in the case of the roll-rate
limiter and degrees in the case of the sideslip limiter
(See fig. 3.)
b wing span, ft
Swing mean aerodynamic chord, ft
Cz rolling-moment coefficientroling moment
C --, per radian
Cep ,(pb/2V) per radian
C01r (rb/2V)' per radian
C , per radian
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Creer, Brent Y. An analog computer study of several stability augmentation schemes designed to alleviate roll-induced instability, report, February 19, 1957; (digital.library.unt.edu/ark:/67531/metadc62909/m1/3/: accessed January 15, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.