1. 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
Explanation: 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.
2. The instrument which combines both the static and total pressure is _______
a) Dynamic probe
b) Static probe
c) Pitot static probe
d) Stagnation probe
Explanation: 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.
3. The dynamic pressure can be used in all flows from incompressible to hypersonic.
a) True
b) False
Explanation: 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.
q=0.5*ρ*V2.
4. 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
Explanation: 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).
5. The pressure difference (p0-p1) holds good only for incompressible flow.
a) True
b) False
Explanation: 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).
6. 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
c) 0
d) infinity
Explanation: 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.
7. 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
Explanation: 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.
8. Pitot tube with flat faces are more sensitive.
a) True
b) False
Explanation: 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.
9. In a pitot tube, the kinetic energy is converted into _________
a) potential energy
b) total energy
c) pressure energy
d) internal energy
Explanation: 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.
10. 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
Explanation: 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.