Chapter 1 - Air Data Computers

Question 1

What does the pressure transducer operate on?

Answer 1

Force balance system

Question 2

In the pressure transducer of the ADC, what happens when a change of air pressure occurs?

Answer 2

The capsule assemblies act on a pivoted beam causing it to deflect the ‘I’ bar between the ‘E’ bar outer limbs

Question 3

How does the ‘E’ bar work?

Answer 3

The ‘E’ bar is excited with 18v AC 400 Hz

Deflection induces a voltage into one of the secondary windings due to unbalanced flux

Question 4

What is total air temperature (TAT)?

Answer 4

Static air temperature (SAT) increased by an amount accounted for by the forward motion of the aircraft

Question 5

Why does a TAT probe require airflow through it?

Answer 5

To avoid heating of the measured air

Question 6

In a CADC altitude module, what does the phase of the tachometer generator signify?

Answer 6

Whether the aircraft is climbing or descending

Question 7

In a CADC altitude module, what does the amplitude of the tachometer generator signify?

Answer 7

How fast the aircraft is climbing or descending

Question 8

What is the state within the CADC altitude module when the aircraft is parked or holding altitude?

Answer 8

Force exerted by the spring balances the force exerted by the evacuated bellows

I-pickoff armature has been moved to a stable position

Question 9

What are the outputs of the altitude module?

Answer 9

• VSI
• FDR
• Altitude
• ATC transponder
• AFCS Alt hold
• Cabin pressure
• S part of the Mach equation to the computed airspeed module
• Failure flag on the indicator/CWP

Question 10

What are the outputs of the computed airspeed module?

Answer 10

• FDR
• Autothrottle
• AFCS gain control
• Failure flag on the indicator/CWP

Question 11

What are the outputs of the Mach module?

Answer 11

• Static source error correction
• Temperature correction for TAS and SAT indicator
• Autothrottle
• AFCS gain control
• AFCS Mach hold
• Failure flag on the indicator/CWP

Question 12

What are rate generators used for in the mach module, computed airspeed module and the altitude module?

Answer 12

Feed a velocity signal as a feedback signal to the amplifier

Question 13

How does the TAT sensing module work?

Answer 13

Externally mounted probe forms part of a bridge network consisting of two fixed resistors and a motor driven potentiometer

Changes in temperature result in an imbalance and servomotor rebalances the bridge through the potentiometer

Question 14

What does the calibration for the bridge mean for the angle of rotation for the servomotor?

Answer 14

It is proportional to the log of the root of the measured temperature

Question 15

What features are common in each of the modules of the air data computer?

Answer 15

• Warn logic
• Feedback signal from rate generator

Question 16

What is the vital element in each pressure data converter in a digital air data computer?

Answer 16

Vibrating diaphragm pressure transducer

Question 17

What is the range of pressures and the range of frequencies that the vibrating diaphragm pressure transducer will sense?

Answer 17

4 kHz to 1 kHz for frequencies from 1523 hPa to 34 hPa

Question 18

What is the TAT signal necessary for in a DADC?

Answer 18

Computation of SAT and TAS

Question 19

In the DADC, the signals from the microprocessor are fed directly to what?

Answer 19

• FMS
• Autopilot
• Performance Data Computer
• Flight Data Recorder
• Altitude reporting system