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Some basic knowledge of dampers

Update time : 2021-06-23

Source : Dream Automation

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Some basic knowledge of dampers

When the aircraft climbs to a high altitude, due to the decrease in air density (changes in aerodynamic characteristics), the damping of the aircraft will be reduced, causing the aircraft to easily oscillate. Imagine a situation where oscillations occur due to the low pitch damping of the aircraft. In order to suppress the vibration, the pilot needs to push the lever when the aircraft is raising its head to prevent the aircraft from raising its head, and pull the lever when the aircraft is lowering its head to prevent the aircraft from lowering its head. For pilots, it is very difficult to complete the mission while also stabilizing the aircraft. In order to improve this situation and reduce the workload of the pilot, a device was invented to replace the pilot to complete this complicated operation, namely the damper. The above is just taking pitch as an example, in fact, roll and yaw are similar. The dampers are divided into pitch damper, roll damper and yaw damper. When we know the working content of the damper, it is easy to understand the working principle of the damper. When the aircraft oscillates, an angular velocity is generated. To suppress the oscillation is actually to resist the angular velocity by deflection of the rudder surface in the opposite direction. The sensor that measures the angular velocity of the aircraft is installed on the aircraft. The aircraft has three axes, so three angular velocity sensors are required. When the aircraft oscillates, the sensor senses the angular velocity, and the angular velocity is processed to generate instructions to drive the corresponding rudder surface, and the rudder surface deflection prevents the oscillation. The damper works like this.

For the convenience of explanation, take the aircraft oscillation as an example. In fact, when the pilot normally controls the aircraft, the damper also plays a similar role, so that the aircraft quickly stabilizes to the target attitude. The pitch damper drives the elevator to work according to the pitch rate, the roll damper drives the aileron to work according to the roll rate, and the yaw damper drives the rudder to work according to the yaw rate. Because the lateral and directional signals are coupled with each other, the lateral and directional signals are cross-linked, which means that the aileron and rudder will work together at the same time. After the horizontal heading plug is exchanged, the roll command signal and the yaw command signal are exchanged, and the command enters the wrong channel. That is to say, the original yaw aileron command is used to drive the rudder, and the rudder drive command is used to drive the aileron.

Why did the aircraft become unstable after the exchange? Now we need to introduce another concept, the stability of the flight control system. Dampers are also part of the flight control system. The soul of the flight control system is the control law, which is directly related to whether the aircraft is easy to pilot, and even affects the safety of the aircraft. Designers need to carefully allocate a large number of parameters of the control law to make it work in coordination and have a certain degree of stability.