Curtis L. Olson wrote:
1) The state/existance of the hazard. Do icing conditions exist? At what altitudes, severity, etc. etc. This should probably live in the environment subsystem.
As far as I recall, icing is most likely between about 0 degC and -10 degC, and is very rare below -20 degC or above 2 degC. Rime icing tends to occur when the dewpoint spread is close to zero (i.e. inside a cloud of supercooled small water droplets); clear icing tends to occur when there is visible precipitation in liquid form (i.e. supercooled large droplets, or freezing rain/drizzle). There is no need for the environment system to set an ice/no-ice flag, as long as it makes enough information available.
2) The result of the hazard on the aircraft. How much ice has accumulated and on which surfaces? This should probably live in some not-yet-existing FlightGear ice accumulation model that is per-aircraft configurable.
Yes, and it will have to know about the aircraft systems as well, including deicing boots, prop heat, carb heat, pitot heat, window defrost, etc., as well as the aircraft's true airspeed. There's no need to worry about that yet, though.
3) The resulting dynamics of the accumulation of the hazard. The FDM would take the state of ice accumulation from FlightGear and calculate the affect on the flight dynamics.
Yes, that's in the future for most FDMs.
But I don't have time for all of that right now. For the moment I want to simply turn 2) on or off (or maybe allow a normalized value) and then pass this to a particular dynamics model that has a simple model wing icing on/off.
Take my earlier suggestions and choose a threshold: if the two properties are past that threshold (say, moderate mixed icing or worse), turn on the flag.
All the best,
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