Originally Posted by A33Zab
Temp controlled by the probe itself, the PHC contains the switching logic and monitoring circuits.
Thank you for the schematic. Looks like the probe temperature of the probe is controlled by the actual heater coil itself which is probably made like a an old style wire wound ballast resistor. The temperature coefficient of resistance would then regulate the current & heat. The PHC is just switching the units between On and Off, ground and air mode, and also monitoring the current to be sure each heater is actually working and has not burned open.
I have an old Rosemount pitot probe on my desk, and although these things look fairly uniform between models, there is all sorts of room for variation as to how thick the metal is in various areas (controlling the thermal mass and time constant to conduct heat to the other side), input wattage, heating coil location, what metal is used, and where the drain holes are relative to the elbow and heat sources.
I would think they would avoid putting the heating coils where moisture can actually impinge since you would then be generating steam and pressurizing the probe.
The 3 channel design of the Airbus does provide sensible redundancy for everything downstream of the probes, but no real redundancy for a common mode sensing problem. A better design would involve alternative sensors such as a laser airspeed sensor (but I note that several websites touting such equipment a couple of years ago are now out of service).
Another concept would be to place the probe behind a vane that would bend the airflow into the pitot inlet, but which would centrifugally separate ice particles so that they would miss the inlet for reasonable yaw angles under cruise conditions.
Originally Posted by Owain Glyndwr
In normal law any further THS nose up movement is inhibited when alpha protect switches in. I can't for the life of me see why this logic was not carried over to Alternate and stall warning respectively.
Amen to that.
It is if someone in conceptual design had decided that the AOA systems were not to be trusted.
Originally Posted by Owain Glyndwr
Apply this simple change and I suspect that most of the other controversial points discussed in earlier threads decline into insignificance.
Fully in agreement.
