BY RIHESH RAVEENDRAN 4 th sem MCA

Automatic pilots, or autopilots, are devices for controlling spacecraft, aircraft, watercraft, missiles and vehicles without constant human intervention  An autopilot can refer specifically to aircraft, self-steering gear for boats, or auto guidance of space craft and missiles.  How do these heavy machines take to the air? To answer that question, we have to enter the world of fluid mechanics.

In the early days of aviation, aircraft required the continuous attention of a pilot in order to fly safely. The first aircraft autopilot was developed by Sperry Corporation in The autopilot connected a gyroscopic Heading indicator and attitude indicator to hydraulically operated elevators and rudder.

 It permitted the aircraft to fly straight and level on a compass course without a pilot's attention, greatly reducing the pilot's workload. Lawrence Sperry (the son of famous inventor Elmer Sperry ) demonstrated it two years later in 1914 at an aviation safety contest held in Paris. At the contest, Sperry demonstrated the credibility of the invention by flying the aircraft with his hands away from the controls

This autopilot system was also capable of performing take-off and landing, and the French military command showed immediate interest in the autopilot system. In 1930 test a more compact and reliable auto- pilot which kept a US Army Air Corps aircraft on a true heading and altitude for three hours, that was probably of the type used by Wiley Post to fly alone around the world in less than eight days in 1933.

 Also, inclusion of additional instrumentation such as the radio-navigation aids made it possible to fly during night and in bad weather.

 Thrust, whether caused by a propeller or a jet engine, is the aerodynamic force that pushes or pulls the airplane forward through space.  The opposing aerodynamic force is drag, or the friction that resists the motion of an object moving through a fluid.  For flight to take place, thrust must be equal to or greater than the drag.

Every object on Earth has weight, a product of both gravity and mass.  Weight's opposing force is lift, which holds an airplane in the air.  This feat is accomplished through the use of a wing, also known as an airfoil.

 The faster-moving air moving over the wing exerts less pressure on it than the slower air moving underneath the wing. The result is an upward push of lift. In the field of fluid dynamics, this is known as Bernoulli's principle.

 How does an airplane turn in the air? How does it rise to a higher altitude or dive back toward the ground?  Consider the angle of attack, the angle that a wing (or airfoil) presents to oncoming air. The greater the angle of attack, the greater the lift. The smaller the angle, the less lift.  A typical wing has to present a negative angle of attack (slanted forward) in order to achieve zero lift. This wing positioning also generates more drag, which requires greater thrust.

 The tail of the airplane has two types of small wings, called the horizontal and vertical stabilizers. A pilot uses these surfaces to control the direction of the plane.  On the horizontal tail wing, these flaps are called elevators as they enable the plane to go up and down through the air.

 Meanwhile, the vertical tail wing features a flap known as a rudder.This key part enables the plane to turn left or right and works along the same principle.  Finally, we come to the ailerons, horizontal flaps located near the end of an airplane's wings. These flaps allow one wing to generate more lift than the other, resulting in a rolling motion that allows the plane to bank left or right.

Some l arger aircraft, such as airliners, also achieve this maneuver via deployable plates called spoilers that raise up from the top center of the wing.

 Avionics entails all of an aircraft's electronic flight control systems: communications gear, navigation system, collision avoidance and meteorological systems.  Air traffic control system ensures the safety of commercial and private aircraft as they take off, land and traverse vast distances without incident.  Through the use of radar, computerized flight plans and steady communication, air traffic controllers ensure planes operate at safe distances from each other and redirect them around bad weather.

 In the world of aircraft, the autopilot is more accurately described as the automatic flight control system (AFCS).  Three basic control surfaces that affect an airplane's attitude.  The first are the elevators, which are devices on the tail of a plane that control pitch.  The rudder is also located on the tail of a plane. When the rudder is tilted to starboard (right), the aircraft yaws -- twists on a vertical axis -- in that direction. When the rudder is tilted to port (left), the craft yaws in the opposite direction.

 Ailerons on the rear edge of each wing roll the plane from side to side.  Autopilots can control any or all of these surfaces. A single-axis autopilot manages just one set of controls, usually the ailerons. A two-axis autopilot manages elevators and ailerons. Finally, a three-axis autopilot manages all three basic control systems: ailerons, elevators and rudder.

The heart of a modern automatic flight control system is a computer with several high-speed processors.To gather the intelligence required to control the plane, the processors communicate with sensors located on the major control surfaces. The processors in the AFCS then take the input data and, using complex calculations, compare it to a set of control modes. These calculations determine if the plane is obeying the commands set up in the control modes. The processors then send signals to various servomechanism units. A servomechanism, or servo for short, is a device that provides mechanical control at a distance.

 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. This type of feedback loop is central to the operation of autopilot systems.

Let's consider the example of a pilot who has activated a single-axis autopilot. 1. The pilot sets a control mode to maintain the wings in a level position. 2. However, even in the smoothest air, a wing will eventually dip. 3. Position sensors on the wing detect this deflection and send a signal to the autopilot computer. 4. The autopilot computer processes the input data and determines that the wings are no longer level.

1. The autopilot computer sends a signal to the servos that control the aircraft's ailerons. The signal is a very specific command telling the servo to make a precise adjustment. 2. Each servo has a small electric motor fitted with a slip clutch that, through a bridle cable, grips the aileron cable. When the cable moves, the control surfaces move accordingly. 3. As the ailerons are adjusted based on the input data, the wings move back toward level. 4. The autopilot computer removes the command when the position sensor on the wing detects that the wings are once again level. 5. The servos cease to apply pressure on the aileron cables.

 A common problem is some kind of servo failure.  A bad motor or a bad connection.  A position sensor can also fail, resulting in a loss of input data to the autopilot computer.  Fortunately, autopilots for manned aircraft are designed as a failsafe -- that is, no failure in the automatic pilot can prevent effective employment of manual override. . To override the autopilot, a crew member simply has to disengage the system, either by flipping a power switch or, if that doesn't work, by pulling the autopilot circuit breaker.

 Many modern autopilots can receive data from a Global Positioning System (GPS) receiver installed on the aircraft.  A GPS receiver can determine a plane's position in space by calculating its distance from three or more satellites in the GPS network.

 An autopilot is a mechanical, electrical, or hydraulic system used to guide a vehicle without assistance from a human being.  Given the flight plan and the aircraft's position, the FMS calculates the course to follow. The pilot can follow this course manually (much like following a VOR radial), or the autopilot can be set to follow the course.

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