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determine the range of roll rates for divergence in yaw or pitch. Assume Cnp =
0.045. Except for this change, all the other parameters remain the same.
7.2 The aircraft of solved Example 7.2 has another steady-state spin mode at
cx = 55 deg and takes 2.2 s per turn. Assuming that the aircraft spins with its right
wing 3.5 deg below.the horizo-ntal plane, determine (a) descent velocity, (b) spin
radius in terms of wing senuspan, (c) angular velocity components in body-fixed
axes system, and (d) inertia and aerodynamic coefficients act:ing on the airf)lane.
Assume that the aircraft is operating at an altitude of 6000 m and the resultant
force coefficient at ct = 55 deg is 1.30.
8.1 Introduction
8
Stability and Control Problems
at High Angles of Attack
8.2 A Brief Historical Sketch
Flight at high angles of attack, or even at angles of attack close to the stall
angle, was recognized to be disastrous from the very early days of aviation. The
Wright Brothers had experienced perhaps the first rm7itary accident in 1908 during
ademonstration flight b:ause ofaninadvertent stall andloss ofcontrol. During this
early period and up to the end ofWorld Warll, several accidents occurred because
ofinadvertent stall, loss ofcontrol, and spin. These events led airplane designers to
focus their attention to the study of spinning problems with an objective to develop
successful spin recovery techniques. Such an approach continues erren today in
civil aviation for the design and operation of light general aviation airplanes,
with increased emphasis on improving spin resistance and spin avoidance as we
discussed in Chapter 7. Howe'ver, for military aul,lanes, the design philosophy has
undergone a revolutionary change.
In the years following World War II and up to the 1950s, military airplane
designers, especially in the United States, emphasized theimportance ofhigh speed
and high altitudelflying.] Such capabilities were essentialfor an interceptor aircraft.
The scenario envisioned was one involving an aerial combat beyond the visual
range (BVR) consisting of missile launches between enemy aircraft that would
never come within the visual range (WVR). Because of such belief, the prevailing
requirement for achieving air superiority in close combat in WVR disappeared.
The F-104 (Star Fighter) and the F-105 designs were based on this philosophy. The
belief that fiight at high angles of attack must be avoided at all costs still persisted,
673
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674 PERFORMANCE, STABfLITY, DYNAMICS, AND CONTROL
and airplanes were equipped with artificiallimiters like stick pushers to limit the
angle of attack. '
A turnaround in the thinlang concerning the importance offlight at high angles
of attack occurred in the late 1960s and 1970s. The Southeast Asian conflict and a
large number ofother fatal accidents caused by inadvertent stall,loss ofcontrol, and
spins contributed to the realization that, rather than concentrating on spin recovery,
attention must be d,evoted to the prevention of departure from controlied flight at
high angles of attack Furthermore,it dawned on the military planners and airplane
designers in the 1970s that the development of such technologies like elecXonic
countermeasures and radar jammers severely limited a positive identification and
acquisition of enemy aircraft in BVR. They also realized that close encounters in
WVR would be inevitable in future aerial combats. This kind of changed thinking
led to a resurgence of interest in high angle of attack aerodynamics and control
technology and to the development of such fighter aircraft like the U.S. F-15 and
the F-16, the Israel Lavi, the Swedish Grippen, the French Rafale and the Mirage
fil, the European Fighter Aircraft, and the Soviet MiG 29 and the MiG 31.
The line of thinking in the area of high angles of attack took another turn in the
late 1980s and early 1990s when it was further realized that the maximum sustained
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