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wing surfaces. Recovery from deep stall can be quite difficult or even impossible
because control surfaces may be totally ineffective because of immersion in the
stalled wake,
The F-16 aircraft has a deep-stall trim poinL around a - 50 deg. In view of'
the limited nosedown pitch authority, the'~aximum roll capability 'gf the F-16 is
limited, and an alpha limiter is also used to prevent the aircraft from getting locked
up in a deep-stall trim point dLming velocity vector rolls.46
Therefore, for high angles of attack/poststall maneuverability, sufficient control
authority about all three axes must be available, Usually, sufficient roll control
authority is always available. The limitations usually arise in yaw and pitch control
authority as we have mentioned earlier. These limitations plus any susceptibility
of the aircraft to pitch divergence on account of inertial coupling may force the
use of an alpha limiter. However, in this process the combat effectiveness of the
aircraft is reYduced.
To overcome the above deficiencies in yaw and pitch control at high angles
of attack, combat aircraft designers are currently exploring a variety of control
concepts. Some of these concepts are schematically shown in Fig. 8.68. However,
the two concepts that have received considerable attention are forebody vortex
control and propulsive or thrust vectoring control (TVC).
8.13.4 Forebody Vortex Contro/
The purpose of forebody vortex conLrol is to systematically manipulate the
forebody vortices to generate controlled yawing moments at high angles of attack
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┃ PITCH ┃axtensionsr6n:wr,:~a7.j,.,.e ┃
┃ ~ ┃ ┃
┃ is as ┃ ┃
┃ s ┃ ┃
┃ I ┃ ┃
┃Canard ┃ ┃
┃TraillngBLr,,-y. U Ch~oUtalal ┃ ┃
┃ tails ┃ ┃
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PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL4(99)
