Question 1

How does a pitot-static tube measure airspeed?

Accepted Answer

A pitot-static tube uses two sets of openings to sense pressures based on Bernoulli's principle. One opening faces the airflow and senses stagnation pressure, while perpendicular openings sense static pressure. The pressure differential between these two measurements is then used to calculate fluid velocity, allowing accurate airspeed determination in aircraft and wind tunnel applications.

Question 2

What is the relationship between stagnation pressure, static pressure, and dynamic pressure?

Accepted Answer

According to Bernoulli's principle, stagnation pressure equals the sum of static pressure and dynamic pressure. Static pressure is the pressure exerted by a fluid at rest, while dynamic pressure results from the fluid's velocity and density. When airflow speed increases, dynamic pressure increases and static pressure decreases, maintaining constant total stagnation pressure.

Question 3

How does a fluid manometer measure pressure differential in a pitot-static tube?

Accepted Answer

A fluid manometer is a U-shaped tube containing liquid that responds to pressure differences. When a pressure differential exists, the manometer fluid height changes. The pressure differential is calculated by multiplying the liquid density, gravitational acceleration, and the height difference. This measurement directly enables airspeed calculation using the pitot-static tube equation.

Question 4

Why is angle of attack important when using a pitot-static tube?

Accepted Answer

Angle of attack measures the pitot-static tube's alignment with airflow direction. Testing at various angles—from zero to 28 degrees—demonstrates the tube's sensitivity to misalignment. Results show that percent differences remain below 4% across measured angles, proving the pitot-static tube is generally insensitive to moderate flow direction misalignment.

Question 5

What equipment is needed to conduct a pitot-static tube airspeed measurement experiment?

Accepted Answer

A wind tunnel with a 1 ft by 1 ft test section and maximum airspeed of 140 mph is required. Additional equipment includes a pitot-static tube, a fluid manometer filled with colored oil marked in water-inch graduations, soft tubing to connect components, and a handheld inclinometer to measure angle of attack during testing.

Question 6

How accurate are pitot-static tube measurements in a wind tunnel?

Accepted Answer

Pitot-static tube measurements demonstrate high accuracy, with percent errors remaining quite small across wind speeds from 50 to 130 mph. Errors arise from wind tunnel air settings, manometer reading precision, and instrument calibration. The consistent low error rates validate the pitot-static tube as a reliable method for measuring airspeed in controlled aerodynamic environments.

Question 7

What is the difference between static pressure and stagnation pressure?

Accepted Answer

Static pressure is the pressure exerted by a moving fluid on its surroundings. Stagnation pressure, also called total pressure, occurs when fluid speed is zero and represents the maximum pressure condition. As fluid velocity increases, static pressure decreases while stagnation pressure remains constant, with the difference between them defining the dynamic pressure component.

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