Aerodynamics Multiple Choice Questions & Answers (MCQs) on “Pitot Tube”.
1. The most common device used for measuring air speed is __________
c) pressure gauge
d) pitot tube
Clarification: Pitot tube is a tube bent in L shaped. The one end of the pitot tube is exposed to air so that it can directly come in contact with the flow velocity. The pressure inside this tube is used to measure the velocity.
2. The randomness of the molecules gives us ________ pressure.
Clarification: Static pressure is the measure of purely random motion of the molecules of the gas. It is the pressure which we can feel when we ride along with the gas at the local flow velocity. For reference, we always consider pressure as static pressure.
3. How does the pitot tube help in measuring the airspeed?
a) Using temperature
b) Using velocity
c) Using mach number
d) Using the pressure difference
Clarification: The pitot tube is closed at one end and is opened from other ends. When the air is filled inside the tube, the pressure at the open end equals to total pressure and it differs from the pressure outside the tube. Using this pressure difference and applying Bernoulli’s equation, the speed of air can be calculated.
4. The instrument which combines both the static and total pressure is _______
a) Dynamic probe
b) Static probe
c) Pitot static probe
d) Stagnation probe
Clarification: A pitot static probe is to combine the measurement of static and total pressure. It measures p0 at the nose of the probe and p1 at a suitably placed static pressure tap on the probe surface downstream of the nose.
5. The dynamic pressure can be used in all flows from incompressible to hypersonic.
Clarification: The dynamic pressure can be used in all kinds of flow. It is denoted by ‘q’ and is the grouping of density and velocity in which the density is halfed and the velocity is squared.
6. The dynamic pressure can be given by ____________
a) difference of total and static pressure
b) sum of total and static pressure
c) product of total and static pressure
d) double of total and static pressure
Clarification: In incompressible flow, the dynamic pressure has a special meaning, it is a difference between the total pressure and the static pressure. Let p0 be the total pressure and p1 be the static pressure.
Therefore, the dynamic pressure (q)= total pressure (p0)- static pressure (p1).
7. The pressure difference (p0-p1) holds good only for incompressible flow.
Clarification: The difference between total pressure (p0) and static pressure (p1) gives dynamic pressure holds true only for incompressible flow. The Bernoulli’s equation cannot be solved for compressible flow and also the pressure difference is not equal to dynamic pressure (q).
8. When the local flow velocity is zero itself then _________
a) total pressure is not equal to static pressure
b) total pressure is equal to static pressure
Clarification: When the local flow velocity, the static pressure and the total pressure is the same. Consider the air flow in the room, assuming the air is motionless and the standard sea level pressure is 101314.1 pa or 1 atm.
9. An aircraft is flying at cruise level with a velocity of 110m/s at an altitude of 10 km and the dynamic pressure is 5.43kN/m2. Now assume the aircraft is flying is at sea level with a speed of 65m/s and the same dynamic pressure. In the above data, the velocity 65m/s refers to __________
a) true air speed
b) equivalent airspeed
c) free stream velocity
d) cruising speed
Clarification: Equivalent airspeed refers to the speed of an aircraft at which it should fly so as to maintain the same dynamic pressure. In the above example, 65m/s is the equivalent airspeed at an altitude of 10km flying with a true airspeed of 110 m/s.
10. Pitot tube with flat faces are more sensitive.
Clarification: Pitot tubes with flat faces are least sensitive. For these tubes, the total pressure measurement varies only 1 percent for misalignment as large as 20 degrees.
11. In a pitot tube, the kinetic energy is converted into _________
a) potential energy
b) total energy
c) pressure energy
d) internal energy
Clarification: When the velocity of the flow becomes zero, the pressure is increased due to the conversion of kinetic energy into pressure energy which leads to the generation of the pressure difference.
12. The lower end of the pitot tube is bet at an angle of ____________
a) 120 degrees
b) 360 degrees
c) 90 degrees
d) 45 degrees
Clarification: The lower end of the tube is bent at an angle of 90 degrees. The liquid rises up in the tube due to the conversion of kinetic energy into the pressure energy. The velocity is determined by measuring the rise of the liquid in the tube.
13. The errors generated in the pitot tube due to the location are called __________
a) position errors
b) normal errors
c) negligible errors
d) positive errors
Clarification: The errors that occur due to the location of pitot tube on an aircraft and also due to the effect of localized airflow over the pitot tube are called as position errors. These errors are needed to be considered while calculations.
14. When an aircraft is grounded, the pitot static tube is generally covered.
Clarification: In the grounded condition, the pitot static tubes are generally covered so as to prevent them from atmosphere effect. If the atmospheric air enters into it, it may show certain variations in the reading.
15. The pressure measured relative to vacuum is ______
a) total pressure
b) static pressure
c) dynamic pressure
d) absolute pressure
Clarification: Absolute pressure is measured with respect to vacuum. A vacuum has an absolute pressure of 0 psi. It is also defined as the sum of gauge pressure and atmospheric pressure.