# Avionics MCQs – Pressure Measurements

1 - Question

The different probes that disturb the airflow is called ______
a) Air data probe
b) Data probe
c) Intrusive probe
d) Static probes
Explanation: All of the sensing probes, except for the flush mounted static probe, are intrusive because they disturb the local flow over the body of the aircraft. Thus they are also called intrusive probes.

2 - Question

The absolute pressure of the still air surrounding the aircraft is called as______
a) Static pressure
b) Stagnation pressure
c) Constant pressure
d) Absolute pressure
Explanation: static pressure is the pressure of the still air surrounding the aircraft body even when the aircraft is moving. It is measured using static ports placed along the aircraft skin.

3 - Question

Where are self-aligning pitot tubes used?
a) Bomber planes
b) Commercial airliners
c) High angle of attack fighter aircraft
d) General aviation
Explanation: When the angle of attack and the sideslip angle are under 10°, they do not affect the pressure measurements much. In applications such as high angle of attack fighters, special self-aligning pitot tubes are used to measure the stagnation pressure

4 - Question

What is the difference between the actual free stream pressure and the measured static pressure called?
a) Static error
b) Static defect
c) Free stream error
d) Dynamic pressure
Explanation: The pressure that is sensed via the pitot-static port will be different from the actual free stream pressure due to the interference from the skin, angle of attack and the sideslip angle. This difference is referred to as the static defect.

5 - Question

Which of the following is done to reduce the static defect?
a) Streamlined configuration of the whole aircraft
c) Wind tunnel tests to find spots of body-flow interference
d) Deploy Flaps and slats
Explanation: Various wind tunnel tests are done to predict the optimum location for the static port so that the interference of the flow with the body is minimum. Since static defect is predictable, it can be corrected in the air-data computer.

6 - Question

What are the tubes in the aircraft that carry the air pressure to the instruments is called as?
a) Pneumatic plumbing
b) Pressure lines
c) Pressure tubes
d) Blue lines
Explanation: Pipes that carry the air pressure sensed from the pitot tube or the pitot-static tube to the air data computer and the various other flight instruments such as the airspeed indicator, altitude indicator and the vertical speed indicator is collectively referred to as pneumatic plumbing.

7 - Question

What is the difference between the static pressure and the stagnation pressure when the aircraft is stationary?
a) Infinite
b) Any random value
c) No difference
d) Static pressure
Explanation: when the aircraft is stationary, the pressure sensed by the static port is the free stream air pressure and the stagnation pressure ports are zero. Since the aircraft is not moving stagnation pressure is zero and hence the difference between the two values is the static pressure.

8 - Question

The impact pressure and the dynamic pressure are the same.
a) True
b) False
Explanation: Both impact and dynamic pressures are the difference between the stagnation and the static pressure but impact pressure is the dynamic pressure with compressibility effects taken into account.

9 - Question

At supersonic speeds, a normal pitot tube cannot be used for speed measurements.
a) True
b) False
Explanation: At supersonic speeds, the pressure sensed inside the pitot tube is ideally the pressure after the formation of shock waves inside the tube. Hence the value of stagnation pressure is different from that actually experienced by the aircraft.

10 - Question

Which of the following instruments use the pitot-static probe for its input?
a) Airspeed indicator
b) Altitude indicator
c) Vertical speed indicator
d) Attitude indicator