Originally Posted by
snowfalcon2
Another potentially usable technology would be the
hot wire mass flow sensor, where the air flowing past cools down an electrically heated wire and the airspeed can be calculated from the wire's electrical resistance which changes according to temperature. But this is not seen on airliners either. Anyone knowing if this is due to inherent drawbacks compared to pitot tubes, or just an aversion to try new technology?
Hot wire anemometers are used a lot in wind tunnels, I am only familiar with the type that run at constant temperature/resistance - then the input power is direct measure of the heat loss via conduction to the air mass passing, you also don't have to worry too much about the wire changing in length/tension due to expansion. You would still need good measurement of static pressure and temperature for air density and calibration. The hot wires in the lab are pretty delicate, but I suspect they wouldn't work well at all in rain or ice because the heat loss due to latent heat of melting or evaporation would be confused with high flow...
I suggest it is impossible to stop pitot tubes from ever blocking when snowballs thrown at them, but it must be possible by design to ensure the drain hole stays clear of ice. The ability to generate a false reading, which is 'live' with altitude changes when blocked, has been the killer in the past.
Perhaps could use microwave heating of the pitot cavities so not rely on conduction from metal surface to sharp ice crystals? Currently most heat will be lost by the 'wind-chill factor' on the outside of the tube. But even just upping the applied heating voltage by say 20% (power by 40%) without any mechanical/electrical pitot design change would take years to introduce even if feasible...