Can somebody explain this a bit for me?

I.e. as I understand:

If the Pitot tube freezes/ becomes blocked, the ASI would no longer have a change in the pressure (dynamic + static) from the pitot tube, but would have only change in static pressure from the static port.

So, in that case:

If on ground (before takeoff), the ASI would not become active.

A. On climb, the total pressure from the pitot remains the same, whereas the static pressure decreases, so relatively the pitot pressure would be higher compared to the previous moments, there would be some change, but the ASI would under read. Is that correct?

B. If climbing in cruise, same as A. above, correct?

C. On descent, the static pressure would increase, but the total pressure (dynamic-and-static-pressure) from the pitot tube would be very low, so the ASI would under-read, is that correct?

What about with the static port? I.e. if the static port is freezed over?

D. In a climb, there is no change in the static pressure, and the total pressure systems from the pitot is working, the ASI would still under-read due to the density decrease in altitude. Is that correct?

E. In a descent, the static port is frozen, no change in static pressure, but the lowering altitude would mean higher density, therefore the ASI would over-read, is that correct?

Any help would be greatly appreciated.


1 Answer 1

Airspeed = Pitot Pressure (Dynamic + static) - Static Pressure (static)

For a pitot tube that freezes (along with the drain) but the static port is clear.

As aircraft altitude increases, the static pressure decreases. Since the pitot pressure remains the same, the difference between pitot and static pressure increases and the airspeed indicator will read higher than it should.

As aircraft altitude decreases, the static pressure increases. The difference between the pitot and static pressure decreases and therefore the airspeed indicator reads lower than it should.

A. If on ground (before takeoff), the ASI would not become active.

The airspeed indicator will increase with altitude as stated above. If the PITOT STATIC differential is 1.0" Hg, the airspeed indicator would read 145 KTS. If you were to takeoff with a clogged pitot port (and drain), and climb 1000' MSL, the airspeed indicator would also read 145 KTS.

Luiz Monteiro Pitot-Static Simulator

If the static port is clogged while the pitot port is clear, you can use the same formula above to determine the result.

If the aircraft climbs with a clogged static port, the pressure differential will decrease (PITOT pressure decreasing while static pressure remains the same) and the airspeed will read lower than it should.

If the aircraft descends, the pitot pressure increases while the static pressure remains the same and the differential increases, causing the airspeed to read higher than it should.


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