Flight control systems allow pilots to control aircraft attitude, direction, and stability during flight. Understanding how different control systems operate is essential for safe and effective aircraft handling.
This section explains the flight control systems pilots use to control aircraft attitude, direction, and aerodynamic forces. Flight control systems and handling characteristics vary depending on the type of aircraft. The most basic flight control system designs are mechanical and date back to early aircraft. They operate with a collection of mechanical parts, such as rods, cables, pulleys, and sometimes chains to transmit the forces of the flight deck controls to the control surfaces. Mechanical flight control systems are still used today in aircraft where the aerodynamic forces are not excessive. [Figure 1]
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| Figure 1. Mechanical flight control system |
As aviation matured and aircraft designers learned more about aerodynamics, the industry produced larger and faster aircraft. Therefore, the aerodynamic forces acting upon the control surfaces increased significantly. To reduce pilot control forces, aircraft engineers designed more complex systems. Early solutions included hydromechanical systems, consisting of a mechanical circuit and a hydraulic circuit, developed to overcome the limitations of purely mechanical systems. [Figure 2]
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| Figure 2. Hydromechanical flight control system |
As aircraft became more sophisticated, the control surfaces were actuated by electric motors, digital computers, or fiber optic cables. Called “fly-by-wire,” this flight control system replaces the physical connection between pilot controls and the flight control surfaces with an electrical interface. In addition, in some large and fast aircraft, control forces are assisted by hydraulic or electric actuators. In both the fly-by-wire and boosted controls, artificial feedback systems simulate control feel for the pilot.
Current research at the National Aeronautics and Space Administration (NASA) Dryden Flight Research Center involves Intelligent Flight Control Systems (IFCS). The goal of this project is to develop an adaptive neural network-based flight control system. Applied directly to flight control system feedback errors, IFCS provides adjustments to improve aircraft performance in normal flight, as well as with system failures.
Today’s aircraft are equipped with a variety of flight control systems. For example, some aircraft used by sport pilots rely on weight shifting while hot-air balloons use burner systems to control altitude. Helicopters use cyclic control to tilt the rotor disc in the desired direction, along with a collective to manipulate rotor pitch and anti-torque pedals (rudder pedals) to control yaw. [Figure 3]
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| Figure 3. Helicopter flight control system |
The following sections introduce the major aircraft flight control systems, including primary flight controls, advanced control technologies, and autopilot systems used in modern aircraft.