Yaw stability system operates in accordance with lateral acceleration inputs and it provides
required characteristics for aircraft yaw stability due to the aircraft having relaxed statistic yaw
stability. This is due to the peculiar properties of the Su-27’s aerodynamic configuration aft of the
center of gravity, elongated lateral wing area of the fuselage, and forward fin displacement. The
operating principle of the Su-27’s yaw stability system is similar to that of the pitch stability
augmentation system.
Yaw damper provides the required characteristics needed for lateral dynamic stability.
In order to decrease loads on the fins and the aft fuselage as a whole at the speeds of over 600
km/h, and when the landing gear is up, a spring mechanism is connected to the directional control
system providing for the locking stop in the mid-travel of the pedals to each side. It is forbidden to
override the locking stop of the pedals at the airspeeds over 600 km/h. This is why pedal travel at
these speeds is reduced by half in this simulation.
Nozzle Control System
The nozzle control system is intended to change the diameter of the exhaust nozzle in accordance
with the desired law.
Before engine start, during the ignition and when in IDLE mode, the nozzles are completely open to
provide the most favorable conditions for engine start: the greatest torque of the turbine, minimum
overheating, and the minimum thrust during IDLE mode. When the throttle is moved forward to 77-
81% of the engine RPM, the nozzles close partially in order to produce improved thrust
characteristics. When the afterburner is switched on, the nozzles opens in order to maintain the
turbine exhaust temperature. As the thrust augmentation ratio increases, the nozzles open.
When the landing gear is extended, the nozzles partially closed in order to preserve the power
margin and to avoid nozzle contact with the runway during the touchdown. Due to this, the thrust is
increased when on the glide path. In order to decelerate, the speedbrake should be used.
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