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Autopilot


Autopilot
Autopilot is a combination of several devices that work together to give the ability to automatically, without human intervention, control the movement of aircraft or missiles. Creating the autopilot was an important epoch in the history of aviation, as did Air flights much safer. As to missile technology, where all flights are operated in the unmanned mode, without reliable automatic control systems in general, this technique could not be developed. The main idea of ​​the automatic piloting is that the autopilot is strictly maintains the correct orientation of the device moving in space. With this apparatus, firstly, it is held in the air and does not fall, and secondly, not break predetermined rate because the correct orientation and depends primarily its flight trajectory. In turn, the orientation of the vehicle in space is determined by three angles. Firstly, the angle of pitch, i.e. the angle between the longitudinal axis of the vehicle and the ground plane (or, say, the plane of the horizon). Tracking this angle allows the aircraft to maintain longitudinal stability - no "nod", and rocket to fly on a ballistic trajectory, - more precisely hit the target. Secondly, it is the yaw angle, i.e. the angle between the longitudinal axis and the flight plane of the apparatus (so we call plane perpendicular to the horizontal plane and passing through the starting point and target point). Yaw angle indicates the deviation of the vehicle from the set course. And thirdly, this roll angle, i.e. the angle that occurs when the machine housing is rotated about its longitudinal axis. Timely correction of the roll allows the aircraft to maintain lateral stability and dampens indiscriminate rocket rotation. Automatic machine control would not be possible if there were no reliable and simple way to define these angles. Fortunately, there is such a method, and it is based on the property of rapidly rotating gyroscope to maintain the same position in space of the axis.

The simplest gyroscope is a spinning top children, rapidly rotating around its axis. Try to knock down it with a click, and you will see that this is not possible - only the top bounces away and will continue to rotate.

However, the top axis OA has a constant orientation, since its end A is not fixed. Gyroscopes are used in the art, have a much more complex device: a rotor (actually a top) is attached here within (rings) 1 and 2, the so-called gimbal that allows the axis AB occupy any position in space.

This gyroscope can perform three independent rotation about the axis AB, DE and the GK, which intersect in the center O of the suspension, which remains stationary relative to the base.

The main feature of a rapidly rotating gyroscope, as has been said, is that its axis tends to remain stable in space gives it the original direction. For example, if the axis is originally directed to some star, then for any movements of the device itself and casual thrusts it will continue to point to the star even if its orientation with respect to Earth's axes will change. For the first time this property is used in 1852 by French physicist Foucault for the experimental proof of the Earth's rotation around its axis. Hence the name "gyro", which translated from Greek means "to observe the rotation."

The second important feature of the gyroscope is detected when its axis (or frame) starts to operate some external force tending to rotate it relative to the center of the suspension. For example, if the force P acts on the end of the AB axis, the gyro instead deflected towards the force (as would be the case if the rotor is rotated), is tilted in a direction strictly orthogonal to a force that yes (in this case) begin to rotate around axis DE, with a constant speed. This rotation is called precession of a gyroscope, and it will be all the more slowly the faster revolves around the AB axis gyroscope itself. If at any point the action of an external force stops it at the same time it stops and precession, and the AB axis movement stops momentarily.

Precession can be observed in such a simple gyro, as is the children's top, which plays the role of the center of the suspension pivot point. If a top unwind so that its axis is not perpendicular to the floor, and is inclined to it at some angle, it can be seen that the axis of the gyroscope is deflected not in the direction of gravity (i.e. downwards) and in the perpendicular direction, ie the axis begins to rotate around the perpendicular to the floor, dropped in the fulcrum.

These two properties of a gyroscope based several devices used in auto-pilot. In the 70-ies of the XIX century began to use gyroscopes in military machines in the course of naval torpedoes. When the torpedo launch rotor mounted thereon gyro spun up to speed of several thousand revolutions per minute. After that, it was all the time axis is directed at the target.

It was attached gyroscope axis eccentric - drive, whose center was shifted from the axis of the vertical ring machine. Eccentric rested on the valve stem when the torpedo was right on target, porshenki valve closes the opening of pipelines 1 and 2, and the piston steering gear remained motionless. If the torpedo for whatever reason, deviate from the course, the eccentric associated with the gyroscope remained stationary and the valve stem by the spring slipping off to the left or right, and open hole through which the compressed air through line 1 or 2 fed into the steering machine. Under the influence of the compressed air piston steering gear in motion and shifting the steering wheel, so that the torpedo back on the right course.

Then gyroscopes are widely used in aviation. In the chapter on the airplane, already talked about what an important issue for the first aviators was the preservation of the aircraft in flight correct orientation. Many designers think while on the creation of automatic stabilizers. In 1911, an American pilot Sperry developed the first automatic stabilizer with a massive gyroscope. The first aircraft with the stabilizer took to the air in 1914. And in the early 20-ies created a firm Sperry autopilot already present. First autopilots managed only rudders and monitored keeping a predetermined flight condition. Their further development led to the emergence of systems that automate the management of both rudders and engines of the aircraft. These autopilots have allowed flights without crew and control of the aircraft at a distance. They have been used in the first rockets.

Previously, others with the problem of automatic missile control faced by German designers - creators of the first-ever ballistic missile "V-2". (More on this rocket will be discussed in the next chapter.) The automatic stabilization "V-2" consisted of gyroscopic instruments "Horizon" and "verticant".

"Horizon" allowed to determine the horizontal plane and the inclination angle (pitch angle) missiles on this plane. 1 gyro rotor was at the same time anchor asynchronous motor winding 2 which is powered by alternating current. Before the start of the "Horizon" missiles placed in such a way that the rotor axis of rotation is parallel to the horizon. For this purpose, the management system was part of a pendulum (plumb) 5, a fixed deflection axis gyroscope. If this axis is deflected upward or downward from the horizontal direction, the pendulum is also deviated to the side and closed the contact with one or the other. In this case the electromagnet 6 acted signal varying polarity. Electromagnet started to act along the y-axis gyro axis up or down from the center of rotation. Consequently occurred precession unfolding gyro is perpendicular to the deflecting force. Precession lasted as long as the rotor axis is not returned to the horizontal position. Once this happens, the pendulum pin 5 is opened and the precession stopped instantly. Before the start of the correction device is turned off.

The deviation from the target missile pitch angle recorded using a potentiometer - easy on the device sensor with variable resistance. It was a ring-shaped frame on which the wound wire. In this frame sliding brush contact. If the brush was in the beginning of the frame, in the circuit includes a smaller number of turns of wire, respectively potentiometer resistance when it was smaller and the output voltage also has a negligible (as is known, the voltage U is determined by Ohm's law U = I • R, where I - current , R - resistance). If the brush is moved to the end of the frame, the potentiometer resistance increased, and therefore increasing the output voltage. Brush has been linked to a sensitive device that marked the smallest voltage changes.

If during the flight the angle between the longitudinal axis of the vehicle and the horizontal plane for some reason started to deviate from the target, the potentiometer 8 associated with the machine body, turned with it in respect to the fixed gyroscope and connected thereto, the contact brushes. At the same time appeared on the potentiometer output electrical signal proportional in magnitude to the deflection angle. This signal is amplified and fed to the horizontal rudder steering apparatus, which leveled rocket. This simple device, however, could only work effectively with relatively little flight time. During the long flight should take into account the rotation of the Earth, so in this case in the direction of the gyroscope's axis had to make a correction.

"Horizon" allowed not only to preserve but also to change the pitch angle in accordance with a given program. It is clear from the scheme described above, if within the specified time potentiometer 8 to turn at some predetermined angle, the wheels will work as if the same angle deviated unit itself. Therefore, by turning the potentiometer, you can call a turn missiles. "Horizon" included a very simple software mechanism, consisting of a metal strip 10, the eccentric 11, the stepper motor 12 and the ratchet wheel 13. The eccentric has a surface profile corresponding to a given program. The stepper motor drive it into motion through a worm gear (stepper motor is an electromagnet to the armature when the electromagnet pulse was applied, the armature attracted to a magnet, and its edge shifted the ratchet wheel one tooth). Thus, the ratchet wheel rotational speed dependent on the frequency of the pulses supplied to the electromagnet. Detent clip 14 is not allowed ratchet wheel in the opposite direction.

Identical to the "Horizon" worked "verticant". Before the start of the rocket gyroscope rotor axis is perpendicular to the intended flight of the plane, so the gyroscope turned out to be insensitive to the evolution of the missile in pitch, but react to turns and roll rate. Gyro Correction was the same as that of "Horizon", and carried out before the start of using the pendulum and electromagnet 3 4. After takeoff potentiometer 5 responded to the missile yaw and transmit signals to the handlebars. Since the axis directed at the target, coincides with the longitudinal axis of the missile in the event that the potentiometer 7 roll in flight moved relative to a stationary engine (es) associated with the gyroscope. The signal is transmitted to the wheels that roll corrected.

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