Instrumentation questions.

[Mohit_C]

Hello,

I've got the following doubts whilst doing the Volare Instrumentation question bank.

Q79) If an aircraft is equipped with one altimeter which is
compensated for position error and another altimeter
which is not ; and all other factors being equal...
A) At high speed the non-compensated altimeter will indicate a
lower altitude
B) There will be no difference between them if the air data
computer (ADC) is functioning normally
C) ATC will get an erroneous altitude report SSR
D) At high speed, the non-compensated altimeter will indicate a
higher altitude (mark scheme answer)
-> My thoughts on this are that at high speed, compressibility effects will cause a pressure increase which means the static pressure intake will detect a higher pressure causing the non-compensated altimeter to indicate a lower altitude.

Q282) In a steep turn, the northerly turning error on a magnetic
compass on the northern hemisphere is:
A) none on a 090° heading in a right turn.
B) equal to 180° on a 270° heading in a right turn.
C) equal to 180° on a 090° heading in a right turn. (mark scheme answer)
D) none on a 270° heading in a left turn.
-> I really don't understand the answers.

Q304) With a constant weight, irrespective of the airfield
altitude, an aircraft always takes off at the same :
A) equivalent airspeed.
B) calibrated airspeed. (mark scheme answer))
C) ground speed.
D) true airspeed.
-> In an another question bank it states that A is the right answer. Which one is correct?

Q186) The main advantage of a ratiometer-type temperature
indicator is that it:
A) carries out an independent measurement of the supply
voltage. (mark scheme answer)
B) is simple.
C) can operate without an electrical power supply.
D) is very accurate.
-> Could someone explain this kind of temperature indicator? Doesn't appear in my textbook.

Thanks.

[Tick Tock Man]

Technically an aircraft always takes off at the same EAS as you should consider the effects of compressibility at all airspeeds no matter how small.

However the difference is insignificant at typical takeoff speeds so CAS is effectively the same thing. I suppose the argument is that CAS is what you see in the cockpit, not EAS.

[Olabade]

At high air speeds a slight suction is caused near the static air inlets -> hence higher indication if not compensated.

Olabade

[Reluctant737]

Hi,

For Q79, I should like to confirm what Olabade said regarding his reasoning. Remember an altimeter senses static pressure from the static port, located on the side of the fuselage (normally).

Now remember that an increase in airflow velocity (dynamic pressure) produces a reduction in static pressure, so if the aircraft is flown at a higher IAS, the pressure just outside the static port will be lower, hence indicating a higher altitude.

Unfortunately, I cannot help you with the rest of them, as I have no idea! And they let me fly jets :p

Hope that helps though and good luck, Ad