Air Data Computer-Anologue

The air data computer (ADC) is an additional and improved means of supplying the pilot and co-pilot with airspeed, altitude, vertical speed and mach number.  Previously, air pressure was supplied to the primary pitot/static flight instruments by long lengths of P/S pipelines.  To minimize these, a central unit was developed where the pitot and static pressures could be fed. This unit is known as ‘The Centralized Air Data Computer’.  The outputs from the CADC are in the form of synchro signals therefore, the CADC may be referred to as being an analogue device.  These are still widely used, although later generation aircraft have switched to digital units.

The simple pitot static system is still fitted in almost all aircraft and will be used as a safety/comparison factor against the CADC and vice versa.  Two independent CADC systems would be installed, the input to each would be from independent sources for safety reasons.

A modular arrangement is shown along with a typical transmission system. 

Aircraft Antennas

Air carrier operations ideally require uninterrupted communications between both air traffic control agencies, and company operations, and/or out-station handling agents.  Much of these communications are achieved by voice, using either short range VHF, or HF for long distance communications.  This situation is changing in that information is being digitized and routed over data links including satellites with print-outs available as required.  The antenna map shows the typical equipment installed in a modern jet transport for communication purpose.

 

Obviously there are many equipment manufacturers producing communications and navigation equipment.  In these lessons no attempt is made to portray any specific type, and the diagrams should be regarded as typical of the many and various models available.

Velocity Control Servomechanisms

In some applications it is the rotational speed of a shaft and not its position that must be controlled.  A Rate Servo is shown in the diagram .  The input demand signal is used to control the angular velocity of the output shaft and not its position.  To make the speed of the driving motor exactly proportional to the input demand a servomechanism is essential.  If a servomechanism were not used the speed of the output motor would vary with changes in the supply voltage or any changes of the friction in the motor or its load.

Note that there is no position feedback.

Movement of the speed control potentiometer produces a voltage proportional to the demanded speed.  The tacho-generator provides a voltage proportional to the angular velocity of the output shaft.  If there is a difference between these two signals an error voltage will be fed to the amplifier.  The output of the amplifier will accelerate or decelerate the motor until the output of the tacho-generator produces a voltage exactly equal to the input demand voltage and the motor will run at the demanded speed.