Autopilot Technology
- 2. INTRODUCTION AUTOPILOTS ARE SOPHISTICATED SYSTEMS THAT PERFORM THE SAME DUTIES AS A HIGHLY TRAINED PILOT • Automatic pilots, or autopilots, are devices for controlling spacecraft, aircraft, watercraft, missiles and vehicles without constant human intervention. • In aviation industry, autopilot is generally referred to as Automatic flight control system (AFCS) • Original purpose of autopilot was to support pilot by sharing the cabin workload and help in tedious stages of light, such as high altitude cruise control, advanced autopilots can do much more highly precise manoeuvres, such as aircraft landing in low or zero visibility. Image : A350, the advantage of a side stick
- 3. INTRODUCTION • Primarily, there are three control surfaces, elevators (pitch control), rudder (yaw control), and ailerons (roll control). • A single-axis autopilot controls an aircraft in the roll axis only. • A two-axis autopilot controls an aircraft in the pitch axis as well as roll axis with pitch- oscillation-correcting ability. • A three-axis autopilot adds control in the yaw axis • The basis for autopilot system operation is error correction. When an aircraft fails to meet the conditions selected, an error is said to have occurred. The autopilot system automatically corrects that error and restores the aircraft to the flight attitude desired by the pilot.
- 4. • To gather the intelligence required to control the plane, the processors communicate with sensors located on the major control surfaces • There are also control modes that maintain airspeed, heading and flight path. The flight is kept in its path and desired orientation with the help of servo motors. • The basic schematic of an autopilot looks like a loop, with sensors sending data to the autopilot computer, which processes the information and transmits signals to the servo, which moves the control surface, which changes the attitude of the plane, which creates a new data set in the sensors, which starts the whole process again. OPERATING PRINCIPLE
- 5. • An 3 axis AFCS block comprises of an input block, a controller block and an actuator block. • The input measures the angular velocity and acceleration of the setup. • A 3-axis accelerometer axis used which gives precise acceleration measurements along the 3 axes. These acceleration values are later used to obtain the angular tilt along the 3 directions. • A combination of the values from the accelerometer and gyroscopes are used and different control systems are given these 2 sets of values. OPERATING PRINCIPLE Image : Typical analogue autopilot system components.
- 6. • The input data is taken to the controller Analog to Digital Converter (ADC) modules. • It is then passed to the Kalman filter for estimation. • The estimated values are further taken to the fuzzy controller unit where the magnitude change from the desired orientation is used for the decision making. • The controller also includes the Command module with LCD interfacing unit, the storage unit and the computer interfacing unit. • The interfacing units are for transferring the log data into the computer for calibration of the input devices. OPERATING PRINCIPLE
- 7. The servo motor interfacing unit decides the amount of rotation of the servos to help the flight maintain the desired orientation. • The servos take the computer's instructions and use motors or hydraulics to move the craft's control surfaces, making sure the plane maintains its proper course and attitude OPERATING PRINCIPLE
- 8. INERTIAL MEASUREMENT UNIT Accelerometer • An accelerometer measures the acceleration relative to freefall. Single- and multi-axis models are available to detect magnitude and direction of the acceleration as a vector quantity, and can be used to sense orientation, vibration and shock. • Conceptually, an accelerometer behaves as a damped mass on a spring. When the accelerometer experiences an external force such as gravity, the mass is displaced until the external force is balanced by the spring force. The displacement is translated into acceleration. • Generally, micro electro-mechanical systems (MEMS) accelerometer is used for this purpose. KEY COMPONENTS
- 9. INERTIAL MEASUREMENT UNIT Gyroscope • A gyroscope is a device for measuring or maintaining orientation and angular velocity, based on the principles of angular momentum. • The traditional form of a gyroscope is a spinning wheel or disk whose axle is free to take any orientation. This orientation changes much less in response to a given external torque. Since external torque is minimized by mounting the device in gimbals, its orientation remains nearly fixed, regardless of any motion of the platform on which it is mounted. • Generally, micro electro-mechanical systems (MEMS) gyroscopes are used for this purpose. KEY COMPONENTS
- 12. CONTROLLER KEY COMPONENTS 1. Amplification Increases the signal level from the sensor to a high enough level to be effective as an output. In the simplest form this equates to gearing in a mechanical system. Also known as gain. 2. Integration Integrators can be used to derive pseudo-information. (i.e. rate information can be integrated to produce attitude data). There are problems integrating small (i.e. near zero) signals. 3. Differentiation Differentiation is used in a similar but opposite fashion to integrators (i.e. attitude data can be differentiated to produce rate information). They cannot detect small changes in rate. 4. Limiting Used to restrict the effect of parameter changes to certain limits. For example, may not permit values greater than x0 /s of rate to be used. 5. Shaping Signal shapers are used to adapt the computer output, to produce the desired handling characteristics or flight path of an aircraft. May be considered non-linear amplifiers. 6. Programming Programs are used to produce outputs that will allow an aircraft to fly predetermined manoeuvres.
- 13. CONTROLLER Kalman Filter • Kalman filter is a way to get a best estimate about the process variables (position i.e. location and orientation of aircraftf) from the noisy measurements. Fuzzy Controller • Autopilot requires the control system to behave similar to a human response fuzzy logic is used. It has the advantage that the solution to the problem can be cast in terms that human operators can understand, so that their experience can be used in the design of the controller. KEY COMPONENTS
- 14. CONTROLLER • In the majority of cases, it is the practice to integrate an AFCS with a flight director system (FDS) to provide more precise automatic flight guidance. • As the operating mode requirements for attitude, radio navigation and certain manometric data, e.g. airspeed and altitude, are common to both systems, the relevant control panels are commonly grouped together. • There are many variations in the 'make-up' of panels depending on the operational requirements to be met by specific aircraft/ AFCS/FDS combinations. KEY COMPONENTS
- 15. ACTUATORS • The output signals from the computer must be converted to produce physical movement of the control surfaces; this is normally effected through some form of actuator, utilising either electro-mechanical, electro-hydraulic, or pneumatic principles. • Illustration of a servo-actuator designed for use in one particular type of three-axis autopilot system consists of • An electro-magnetic valve assembly, comprising dual poppet valves which are connected via pressure ports and orifices to two cylinders containing pistons sealed against pressure loss by rolling diaphragms (also called 'rollframs'). KEY COMPONENTS • The valves are controlled by electrical command signals from the autopilot signal processing element, and the pressure for actuation of the pistons is supplied either from an engine-driven pump or from a tapping at a turbine engine compressor stage.
- 16. APPLICATIONS AIRCRAFT Autoflight : Flight level control Autoland : Instrument landing system
- 17. APPLICATIONS AIRCRAFT Autothrottle : Constant flight speed
- 19. APPLICATIONS ROTOR CRAFT Helicopter autopilot : 3-axis - HFC-150
- 22. APPLICATIONS UNMANNED AERIAL VEHICLE (UAV) UNMANNED COMBAT AERIAL VEHICLES (UCAV)