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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Autopilot. History of invention and production
Directory / The history of technology, technology, objects around us The autopilot is a combination of several devices, the joint operation of which makes it possible to automatically, without human intervention, control the movement of an aircraft or rocket. The creation of the autopilot constituted an important era in the history of aviation, as it made air travel much safer. As for rocket technology, where all flights are carried out in an unmanned mode, without reliable automatic control systems, this technology could not develop at all.
The main idea of automatic piloting is that the autopilot strictly maintains the correct orientation of the vehicle moving in space. Thanks to this, the device, firstly, is kept in the air and does not fall, and secondly, it does not stray from the set course, since the trajectory of its flight depends primarily on the correct orientation. In turn, the orientation of the apparatus in space is determined by three angles. Firstly, this is the pitch angle, that is, the angle between the longitudinal axis of the apparatus and the ground plane (or, as they say, the horizon plane). Tracking this angle allows the aircraft to maintain longitudinal stability - not to "nod", and a missile flying along a ballistic trajectory - to hit the target more accurately. Secondly, this is the yaw angle, that is, the angle between the longitudinal axis of the device and the flight plane (as we will call the plane perpendicular to the horizon plane and passing through the starting point and the target point). The yaw angle indicates the deviation of the device from the set course. And, thirdly, this is the roll angle, that is, the angle that occurs when the apparatus body rotates around its longitudinal axis. Timely correction of the roll allows the aircraft to maintain lateral stability and dampens the erratic rotation of the rocket. Automatic control of the apparatus would be impossible if there were no reliable and simple way to determine these angles. Fortunately, there is such a way, and it is based on the property of a rapidly rotating gyroscope to keep the position of its axis unchanged in space. The simplest gyroscope is a children's spinning top, rapidly rotating around its axis. Try to knock it down with a click, and you will see that this is impossible - the top will only bounce to the side and continue to rotate.
However, the axis OA of the top does not have a constant orientation, since its end A is not fixed. Gyroscopes used in technology have a much more complex device: the rotor (actually, the top) is fixed here within (rings) 1 and 2 of the so-called gimbals, which makes it possible for the AB axis to take any position in space. Such a gyroscope can make three independent rotations about the axes AB, DE and GK, intersecting at the center of the suspension O, which remains fixed relative to the base. The main property of a rapidly rotating gyroscope, as already mentioned, is that its axis tends to stably maintain in world space the original direction given to it. For example, if this axis was originally directed to some star, then with any movements of the device itself and random shocks, it will continue to point to this star even when its orientation relative to the earth's axes changes. For the first time this property was used in 1852 by the French physicist Foucault to experimentally prove the rotation of the Earth around its axis. Hence the very name "gyroscope", which in Greek means "observe rotation".
The second important property of a gyroscope is revealed when some external force begins to act on its axis (or frame), tending to rotate it relative to the center of the suspension. For example, if the force P acts on the end of the axis AB, then the gyroscope, instead of deviating towards the action of the force (as it would be if the rotor did not rotate), will tilt in the direction strictly perpendicular to the action of the force, then is (in our case) will begin to rotate around the axis DE, and at a constant speed. This rotation is called the precession of the gyroscope, and it will be the slower the faster the gyroscope itself rotates around the axis AB. If at some moment the action of the external force stops, then the precession stops at the same time, and the AB axis stops instantly.
Precession can also be observed in such a simple gyroscope as a children's spinning top, in which the fulcrum plays the role of the center of suspension. If the top is unwound in such a way that its axis is not perpendicular to the floor, but is inclined to it at some angle, then you can see that the axis of such a top deviates not in the direction of gravity (that is, down), but in a perpendicular direction, that is, the axis begins to rotate around the perpendicular to the floor, lowered to the fulcrum. These two properties of the gyroscope are the basis of several instruments used in the autopilot. In the 70s of the XNUMXth century, gyroscopes began to be used in military affairs in automatons for the course of sea torpedoes. At the moment of launching the torpedo, the rotor of the gyroscope mounted on it spun up to a speed of several thousand revolutions per minute. After that, its axis was always directed to the target.
An eccentric was attached to the axis of the gyroscope - a disk, the center of which was shifted from the axis of the vertical ring of the machine. The eccentric rested against the spool rod: when the torpedo went exactly to the target, the spool pistons closed the openings of pipelines 1 and 2, and the steering piston remained motionless. If, for some reason, the torpedo deviated from the course, then the eccentric connected to the gyroscope remained stationary, and the spool rod, under the action of a spring, slipped to the left or right and opened a hole through which compressed air through pipeline 1 or 2 entered the steering machine. Under the action of compressed air, the piston of the steering machine came into motion and shifted the steering wheel, so that the torpedo returned to the correct course.
Then gyroscopes found wide application in aviation. In the chapter on the airplane, it was already mentioned what an important problem for the first aviators was to maintain the correct orientation of the aircraft in flight. Many designers then thought about the creation of automatic stabilizers. In 1911, the American pilot Sperry developed the first automatic stabilizer with a massive gyroscope. The first aircraft with such a stabilizer took to the air in 1914. And in the early 20s, the Sperry company created a real autopilot. The first autopilots controlled only the rudders and monitored the preservation of the specified flight mode. Their further development led to the emergence of systems that automate the control of both rudders and aircraft engines. Such autopilots already allowed unmanned flights and remote control of the aircraft. They found use in the first rockets. Earlier than others, German designers, the creators of the first V-2 ballistic missile, faced the problem of automatic missile control. The V-2 stabilization machine consisted of the Horizon and Verticant gyroscopic instruments.
"Horizon" made it possible to determine the horizon plane and the angle of inclination (pitch angle) of the rocket relative to this plane. The rotor 1 of the gyroscope was at the same time the armature of an asynchronous electric motor, the winding 2 of which was fed with alternating current. Before the launch of the rocket "Horizon" was placed in such a way that the axis of rotation of the rotor was parallel to the horizon. For this purpose, the control system included a pendulum (plumb) 5, which fixed the deviation of the gyroscope axis. If this axis deviated up or down from the horizontal direction, the pendulum also deviated to the side and made contact on one side or the other. In this case, the electromagnet 6 received a signal of one or another polarity. The electromagnet began to act on the axis of the gyroscope along the axis Y up or down from the center of rotation. As a result, a precession appeared, turning the gyroscope perpendicular to the deflecting force. The precession continued until the rotor axis returned to the horizontal position. As soon as this happened, the contact of the pendulum 5 opened and the precession instantly stopped. Before the start, the corrective device was turned off. The deviation of the rocket from a given pitch angle was recorded using a potentiometer - a simple sensor with a variable resistance. It was a ring-shaped frame on which the wire was wound. A contact brush slid along this frame. If the brush was at the beginning of the frame, a smaller number of turns of wire was included in the circuit, respectively, the resistance of the potentiometer was smaller and the output voltage also turned out to be insignificant (as you know, the voltage drop U is determined by Ohm's law U = I • R, where I is the current strength , R - resistance). If the brush moved to the end of the frame, the resistance of the potentiometer increased, and, consequently, the output voltage increased. The brush was connected to a sensitive device that registered the slightest changes in voltage. If during the flight the angle between the longitudinal axis of the apparatus and the plane of the horizon for some reason began to deviate from the specified one, then the potentiometer 8 associated with the body of the apparatus rotated with it relative to the gyroscope fixed in space and the contact brush connected to it. In this case, an electrical signal appeared at the output of the potentiometer, proportional in magnitude to the deflection angle. This signal was amplified and fed to the horizontal rudders of the steering machine, which leveled the rocket. Such a simple device, however, could work effectively only with a relatively short flight time. During a long flight, the rotation of the Earth had to be taken into account, so in this case a correction had to be made in the direction of the gyroscope axis. "Horizon" allowed not only to save, but also to change the pitch angle in accordance with a given program. It can be seen from the described scheme that if at the set moment the potentiometer 8 is turned to some given angle, then the rudders will work as if the device itself had deviated by the same angle. Therefore, turning the potentiometer can cause the rocket to turn. "Horizon" included a very simple program mechanism, consisting of a metal tape 10, an eccentric 11, a stepper motor 12 and a ratchet wheel 13. The eccentric had a surface profile corresponding to a given program. The stepper motor set it in motion through a worm gear (the stepper motor was an electromagnet with an armature, when an impulse was applied to the electromagnet, the armature was attracted to the magnet and shifted the ratchet wheel by one tooth with its edge). Thus, the speed of rotation of the ratchet wheel depended on the frequency of the pulses applied to the electromagnet. Stopper 14 was a latch that prevented the ratchet wheel from turning in the opposite direction.
Identical with the "Horizon" worked "Verticant". Before the launch of the rocket, the axis of the gyroscope rotor was located perpendicular to the intended flight plane, so the gyroscope turned out to be insensitive to the evolution of the rocket in pitch, but responded to turns in roll and course. The gyroscope correction was the same as that of the Horizont, and was carried out before launch using pendulum 3 and electromagnet 4. After takeoff, potentiometer 5 responded to the yaw of the rocket and transmitted signals to the rudders. Since the axis directed at the target coincided with the longitudinal axis of the missile, then, when a roll occurred, potentiometer 7 moved in flight relative to the fixed engine (brush) connected to the gyroscope. The signal was transmitted to the rudders, which corrected the roll. Author: Ryzhov K.V.
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