Autopilot Control System


An autopilot is a mechanical, electrical, or hydraulic system used to guide an aerial vehicle without assistance from a human being. It also maintains the orientation of the plane by monitoring the relevant flight data from inertial measurement instruments and then using that data to cause corrective actions.

In this project an attempt has been made to design, implement and develop an autopilot for a glider plane. 3-axis accelerometer and gyroscopes are used to input the acceleration and tilt data into the controller. This data is then used for further estimation and fuzzy logic is implemented for decision making. The required corrective measures are affected by a set of servo motors which helps the flight path and orientation to be maintained at the desired levels.



In the early days of aviation, aircraft required the continuous attention of a pilot in order to fly safely. As aircraft range increased allowing flights of many hours, the constant attention led to serious fatigue. An autopilot is designed to perform some of the tasks of the pilot. Along the flight path the vehicle is under the influence of various accelerating forces in all directions and these factors cause it to deviate from its desired path. So the plane loses its heading as well as orientation. This is where autopilot comes into picture.

There are three levels of control in autopilots for smaller aircrafts. 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 and is not required in many small aircraft. The 3 different axes mentioned are shown in Fig 1.1. The flight may also receive inputs from on-board radio navigation systems to provide true automatic flight guidance once the aircraft has taken off until shortly before landing.

Angles of Rotation
Fig 1.1 - Angles of Rotation


The first aircraft autopilot was developed by Sperry Corporation in 1912. Lawrence Sperry demonstrated it two years later in 1914, and proved the credibility of the invention by flying the aircraft with his hands away from the controls and visible to onlookers. The autopilot connected a gyroscopic heading indicator and attitude indicator to hydraulically operated elevators and rudders. It permitted the aircraft to fly straight and level on a compass course without a pilot's attention, greatly reducing the pilot's workload.

The autopilot control systems have evolved drastically since the turn of the century. Modern autopilots use computer software to control the aircraft. The software reads the aircraft's current position, and controls a flight control system to guide the aircraft. In such a system, besides classic flight controls, many autopilots incorporate thrust control capabilities that can control throttles to optimize the air-speed, and move fuel to different tanks to balance the aircraft in an optimal attitude in the air. Although autopilots handle new or dangerous situations inflexibly, they generally fly an aircraft with a lower fuel-consumption than a human pilot.

Problem Defination

The basic objective of our project is to design and develop an auto pilot control system which can maintain the desired orientation of the glider. The acceleration data in all 3 axes are obtained by the combination of accelerometer and gyroscopes and the angles of roll, pitch and yaw are calculated. These values are taken for estimation using a Kalman filter and the resulting values helps us in the decision making. The flight is kept in its path and desired orientation with the help of servo motors.