In the context of aviation and aerospace, an "Active Control System" refers to a type of control system that uses sensors, actuators, and control algorithms to actively control the behavior of an aircraft or spacecraft in real-time. The primary goal of an active control system is to improve the stability, maneuverability, and overall performance of the vehicle by actively adjusting its control surfaces, such as ailerons, elevators, and rudder, or by modifying its thrust vector.

Active control systems are commonly used in modern aircraft and spacecraft to:

1. Enhance stability: By actively controlling the vehicle's attitude, altitude, and airspeed, active control systems can improve its stability and reduce the risk of loss of control.
2. Improve maneuverability: Active control systems can enable tighter turns, faster roll rates, and more agile flight maneuvers.
3. Reduce pilot workload: By automating certain control functions, active control systems can reduce the pilot's workload and improve their ability to focus on other tasks.
4. Increase safety: Active control systems can help prevent accidents by automatically correcting for pilot errors or unexpected changes in the flight environment.

Active control systems typically consist of:

1. Sensors: These measure the vehicle's state, such as its attitude, airspeed, and acceleration.
2. Actuators: These are the devices that apply forces to the control surfaces or modify the thrust vector.
3. Control algorithms: These are the software programs that process the sensor data and generate commands for the actuators.
4. Feedback loops: These allow the system to continuously monitor its performance and make adjustments as needed.

Examples of active control systems in aviation and aerospace include:

1. Fly-By-Wire (FBW) systems: These use electronic signals to control the aircraft's flight control surfaces.
2. Flight Control Computers (FCCs): These are the brains of the active control system, processing sensor data and generating control commands.
3. Autothrottle systems: These automatically adjust the engine thrust to maintain a set airspeed or altitude.
4. Autopilot systems: These use a combination of sensors and control algorithms to automatically control the aircraft's attitude, altitude, and airspeed.

Overall, active control systems play a critical role in modern aviation and aerospace, enabling the development of more sophisticated and capable aircraft and spacecraft.