Su-27 for DCS World

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The Su-27, NATO codename Flanker, is one of the pillars of modern-day Russian combat aviation. Built to counter the American F-15 Eagle, the Flanker is a twin-engine, supersonic, highly manoeuvrable air superiority fighter. The Flanker is equally capable of engaging targets well beyond visual range as it is in a dogfight given its amazing slow speed and high angle attack manoeuvrability. Using its radar and stealthy infrared search and track system, the Flanker can employ a wide array of radar and infrared guided missiles. The Flanker also includes a helmet-mounted sight that allows you to simply look at a target to lock it up! In addition to its powerful air-to-air capabilities, the Flanker can also be armed with bombs and unguided rockets to fulfil a secondary ground attack role.

Su-27 for DCS World focuses on ease of use without complicated cockpit interaction, significantly reducing the learning curve. As such, Su-27 for DCS World features keyboard and joystick cockpit commands with a focus on the most mission critical of cockpit systems.

Release: 08/31/2017

Directional Channel

Directional yaw control is performed by symmetrical deflection of the rudders. Transmission of inputs from pedals to the rudders is conducted by means of a mechanical linkage. Additionally, yaw sub-channel servo units of the fly-by-wire system are mechanically connected to the rudders with half-travel authority.

Directional channel rudder control schematic block diagram

Directional channel rudder control schematic block diagram

The yaw sub-channel of the fly-by-wire system includes the following automatic devices:

Roll-Yaw crossfeed system operates in accordance with side stick inputs. It deflects the rudders to the same side as the control stick. This eliminates adverse sideslip caused by the difference in drag by half-wings. It also improves a lateral controllability, especially at high angles of attack.

Rudder – AoA diagram

Rudder – AoA diagram

Due to this, lateral control is preserved up to an angle of attack of 28 degrees and there is no roll reversal due to control stick movement.

Roll rate – AoA diagram

Roll rate – AoA diagram

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.

Engines

The powerplant of the Su-27 includes two АЛ-31Ф (AL-31F) engines, each of which has its own turbine starter ГТДЭ-117 (GTDE-117). Because both engine have a separate starter, both individual and simultaneous starting of both engines is possible.

Engine Ground Start

In order to start the engines on the ground, one should:

  • Turn on electric power
  • Set the engine throttle to the IDLE stop
  • Press keys to start the left and right engines

After this, the engine starter doors will open, the door limit switch actuates and puts the starter circuit into operation. Based on the starter circuit command, fuel is provided to the turbine starter and the annunciator "ЗАПУСК" (START) is lit in the cockpit.

The starter circuit turns on the electrical starter motor, ignites the turbine starter, and supplies oxygen to the turbine starter. After ten seconds, the turbine starter will turn off these accessories and simultaneously turns on ignition of the main chamber. The turbine starter spins up the engine rotor and the fuel control unit controls fuel flow to the main chamber. After ignition in the main chamber, the turbine comes into operation and accelerates the engine rotor together with the turbine starter. At 35% of the engine RPM, the ignition exciter in the main chamber switches off. At 53% of the engine RPM, or after 50 seconds, the turbine starter and starter circuit are switched off, which is indicated by the annunciator "ЗАПУСК" (START) turning off. The engine then reaches IDLE mode automatically.

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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