What is the difference between static pressure and pitot pressure?

• A. Static pressure is ambient pressure; pitot pressure is total pressure measured by the pitot tube.
• B. Static equals total pressure; pitot is dynamic pressure alone.
• C. Pitot pressure equals ambient pressure; static is total pressure.
• D. Both are identical in normal flight.

Answer: (A)

In a Pitot-Static system, static pressure is the ambient air pressure at the aircraft’s location, measured through static ports. Pitot pressure is the total pressure the pitot tube measures as air is brought to rest inside the tube; it equals the ambient pressure plus the dynamic pressure created by the aircraft’s motion. The dynamic pressure is q = 1/2 ρ V^2, reflecting the air’s kinetic energy.

The key relationship is Pt = Ps + q. The airspeed indicator uses the difference between total pressure and static pressure (Pt − Ps), which is the dynamic pressure, to display speed. The static system provides the reference pressure for instruments like the altimeter and VSI, which rely on ambient pressure alone.

So, static pressure is ambient pressure, and pitot pressure is the total pressure measured by the pitot tube. They are not the same in normal flight because dynamic pressure is present when the aircraft is moving.