bearfoil, 1901
I agree. However, if the drain plugged first, the first invalid
excursion of a/s would be an increase. If the aperture plugged up with
the drain, stagnation, and "frozen" sense of "a/s" read while both holes
remain plugged. If the drain unplugged before the Aperture, the ias
would approach zero.
Not sure I agree or understand all this. My take on the pitot
probe fault modes and their results would be:
1) Drain hole blocked: Would only cause an small increase in
airspeed at cruise. The drain hole must be small to avoid loss of
resolution and non linearity at low air speeds, as the probe has an
approximate square law response. Whatever size hole is used, there
will be some non linearity, but this would normally be corrected for
in the sensor electronics via lookup table, in much the same way that
pressure error correction is applied for airframe probe position errors.
2) Both stagnation and drain hole blocked: This would fix the airspeed
at the last measured value before blockage. The value determined to a
degree by the sequence in time in which the stagnation and drain ends
became blocked. If the drain hole subsequently became unblocked first,
the air speed would decay towards zero. If the stagnation end became
unblocked first, the airspeed would indicate the true value + drain hole
pressure loss. Output either no change or step function.
If both ends are blocked by ice, the drain hole end will be shielded
from the cold airflow and could be expected to unfreeze first. Thus,
the airspeed would tend to decay towards zero initially until the stagnation
end became unfrozen, when the airspeed would ramp up to true value.
Take this to bits if you like
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