The air speed indicator is an instrument that is used for displaying the air speed, especially in the knots to the pilot. The air speed indicator is also known as the air speed gauge. It is an instrument that is used to measure the speed of an aircraft speed that is relative to the surrounding air. The Speed Indicator is one of the instruments that are used along with the Altimeter for measuring the aircraft’s velocity. The air speed indicator is used at an Altitude by the Flight Director for using the differential between the pressure of still or static air and the pressure of moving air that is compressed with the forward movement of the craft. This is also known as the ram pressure in the air speed indicator.

Without complex electronic control, synchronous motors are inherently constant-speed motors. They operate in absolute synchronism with line frequency. As with squirrel-cage induction motors, speed is determined by the number of pairs of poles and the line frequency.

Synchronous motors are available in subfractional self-excited sizes to high-horsepower direct-currentexcited industrial sizes. In the fractional horsepower range, most synchronous motors are used where precise constant speed is required. In high-horsepower industrial sizes, the synchronous motor provides two important functions. First, it is a highly efficient means of converting ac energy to work. Second, it can operate at leading or unity power factor and thereby provide power-factor correction.

There are two major types of synchronous motors: nonexcited and direct- current excited.

Nonexcited motors — Manufactured in reluctance and hysteresis designs, these motors employ a selfstarting circuit and require no external excitation supply.

• Reluctance designs have ratings that range from subfractional to about 30 hp. Subfractional horsepower motors have low torque, and are generally used for instrumentation applications. Moderate torque, integral horsepower motors use squirrel- cage construction with toothed rotors. When used with an adjustable frequency power supply, all motors in the drive system can be controlled at exactly the same speed. The power supply frequency determines motor operating speed.
• Hysteresis motors are manufactured in subfractional horsepower ratings, primarily as servomotors and timing motors. More expensive than the reluctance type, hysteresis motors are used where precise constant speed is required.

DC-excited motors — Made in sizes larger than 1 hp, these motors require direct current supplied through slip rings for excitation. The direct current can be supplied from a separate source or from a dc generator directly connected to the motor shaft.

Synchronous motors, either single or polyphase, cannot start without being driven, or having their rotor connected in the form of a self-starting circuit. Since the field is rotating at synchronous speed, the motor must be accelerated before it can pull into synchronism. Accelerating from zero rpm requires slip until synchronism is reached. Therefore, separate starting means must be employed.

In self-starting designs, fractional horsepower motors use methods common to induction motors (split phase, capacitor-start, and shaded pole). The electrical characteristics of these motors cause them to automatically switch to synchronous operation.

Although dc-excited motors have a squirrel-cage for starting, the inherent low starting torque and the need for a dc power source requires a starting system that provides full motor protection while starting, applies dc field excitation at the proper time, removes field excitation at rotor pullout, and protects the squirrel-cage windings against thermal damage under out-of-step conditions.

Despite their superior qualities, brushless motors still run second to brush types in motion-control applications. Brushless systems are usually preferred, however, where their benefits outweigh their higher price. And they cost less than brush types in some applications when energy, maintenance, and downtime costs are included in the comparison between the two approaches.

Amplifier costs for both systems have dropped in recent years, moreover, and are forecast to drop further. Thus, the cost differential between the two approaches is an increasingly smaller percentage of total system cost. The situation has brought a large number of competitors into the market, helping to reduce prices for brushless systems. A result is that brushless motor sales have risen rapidly in the last few years. And sales of brushless motors continue to increase.

Conventional brushless motors come in a variety of configurations. The most widely used look much like brush-type motors. But brushless motors have a wound stator that surrounds a permanent-magnet rotor, an inverse arrangement from that for brush motors. And stator windings are commutated electronically rather than through a conventional commutator and brushes.

Brushless motors generally contain a three-phase winding, although some operate four phase. Brushless motors powering small fans and other constant-speed equipment are often two phase.

Power for brushless motors generally is a trapezoidal ac wave form, but some of the motors operate with sine waves. Trapezoidal-powered motors develop about 10% more torque than those on sine-wave power. Sinusoidal-powered motors, however, exhibit less torque ripple and operate smoother at low speed. Thus, sinusoidal-powered motors are often used for machining, grinding, coating, and other operations calling for fine surface finishes.

Because they have no commutator, brushless motors are more efficient, need less maintenance, and can operate at higher speeds than conventional dc motors. High efficiency and small size are especially important for military, aircraft, and automotive applications, and for portable instruments and communications equipment.

The cost of both brush-type and brushless motors likely will rise because of increasing costs for iron, steel, copper, aluminum, and magnets. The increases will be partly offset by use of neodymium-iron-boron magnets. The magnets are often more powerful than samarium-cobalt magnets and promise to be much less expensive.

Amplifiers for brushless motors are more complex than brush types and generally call for two additional solid-state power switches. These switches account for most of the cost differential between the two types. But switch cost continues to drop, in part because of increased use of MOSFET and insulated-gate type switches. Costs also are dropping for ICs used in commutation, feedback interpretation, and PWM circuits. The lower costs reduce but do not eliminate the price differential between amplifiers for the two types of systems.

Industrial applications use dc motors because the speed-torque relationship can be varied to almost any useful form -- for both dc motor and regeneration applications in either direction of rotation. Continuous operation of dc motors is commonly available over a speed range of 8:1. Infinite range (smooth control down to zero speed) for short durations or reduced load is also common.

Dc motors are often applied where they momentarily deliver three or more times their rated torque. In emergency situations, dc motors can supply over five times rated torque without stalling (power supply permitting).

Dynamic braking (dc motor-generated energy is fed to a resistor grid) or regenerative braking (dc motor-generated energy is fed back into the dc motor supply) can be obtained with dc motors on applications requiring quick stops, thus eliminating the need for, or reducing the size of, a mechanical brake.

Dc motors feature a speed, which can be controlled smoothly down to zero, immediately followed by acceleration in the opposite direction -- without power circuit switching. And dc motors respond quickly to changes in control signals due to the dc motor's high ratio of torque to inertia.

DC Motor types: Wound-field dc motors are usually classified by shunt-wound, series-wound, and compound-wound. In addition to these, permanent-magnet and brushless dc motors are also available, normally as fractional-horsepower dc motors. Dc motors may be further classified for intermittent or continuous duty. Continuous-duty dc motors can run without an off period.

DC Motors - Speed control: There are two ways to adjust the speed of a wound-field dc motor. Combinations of the two are sometimes used to adjust the speed of a dc motor.

A synchronous and synchronous electric motors are the two main categories of ac motors. The induction ac motor is a common form of asynchronous motor and is basically an ac transformer with a rotating secondary. The primary winding (stator) is connected to the power source and the shorted secondary (rotor) carries the induced secondary current. Torque is produced by the action of the rotor (secondary) currents on the air-gap flux. The synchronous motor differs greatly in design and operational characteristics, and is considered a separate class of ac motor.

Induction AC Motors: Induction ac motors are the simplest and most rugged electric motor and consists of two basic electrical assemblies: the wound stator and the rotor assembly. The induction ac motor derives its name from currents flowing in the secondary member (rotor) that are induced by alternating currents flowing in the primary member (stator). The combined electromagnetic effects of the stator and rotor currents produce the force to create rotation.

AC motors typically feature rotors, which consist of a laminated, cylindrical iron core with slots for receiving the conductors. The most common type of rotor has cast-aluminum conductors and short-circuiting end rings. This ac motor "squirrel cage" rotates when the moving magnetic field induces a current in the shorted conductors. The speed at which the ac motor magnetic field rotates is the synchronous speed of the ac motor and is determined by the number of poles in the stator and the frequency of the power supply: n_s = 120f/p, where n_s = synchronous speed, f = frequency, and p = the number of poles.

Synchronous speed is the absolute upper limit of ac motor speed. If the ac motor's rotor turns exactly as fast as the rotating magnetic field, then no lines of force are cut by the rotor conductors, and torque is zero. When ac motors are running, the rotor always rotates slower than the magnetic field. The ac motor's rotor speed is just slow enough to cause the proper amount of rotor current to flow, so that the resulting torque is sufficient to overcome windage and friction losses, and drive the load. The speed difference between the ac motor's rotor and magnetic field, called slip, is normally referred to as a percentage of synchronous speed: s = 100 (n_s - n_a)/n_s, where s = slip, n_s = synchronous speed, and n_a = actual speed.

Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information. First developed in the 1970s, fiber-optic communication systems have revolutionized the telecommunications industry and have played a major role in the advent of the Information Age. Because of its advantages over electrical transmission, optical fibers have largely replaced copper wire communications in core networks in the developed world.

The process of communicating using fiber-optics involves the following basic steps: Creating the optical signal involving the use of a transmitter, relaying the signal along the fiber, ensuring that the signal does not become too distorted or weak, receiving the optical signal, and converting it into an electrical signal.

Radar(radio aid for detection and ranging) is an object detection system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations, and terrain. The term RADAR was coined in 1941 as an acronym for radio detection and ranging. The term has since entered the English language as a standard word, radar, losing the capitalization. Radar was originally called RDF (Radio Direction Finder, now used as a totally different device) in the United Kingdom. It is the only word in the English language that is both an acronym and a palindrome^.

A radar system has a transmitter that emits microwaves or radio waves. These waves are in phase when emitted, and when they come into contact with an object are scattered in all directions. The signal is thus partly reflected back and it has a slight change of wavelength (and thus frequency) if the target is moving. The receiver is usually, but not always, in the same location as the transmitter. Although the signal returned is usually very weak, the signal can be amplified through use of electronic techniques in the receiver and in the antenna configuration. This enables radar to detect objects at ranges where other emissions, such as sound or visible light, would be too weak to detect. Radar uses include meteorological detection of precipitation, measuring ocean surface waves, air traffic control, police detection of speeding traffic, determining the speed of basesballs and by the military.