Andy Ross wrote: > > David Megginson wrote: > > The idea is that users should be able to set any reasonable sea-level > > pressure and see reasonable behaviour -- that's why I set the tables > > up with deltas rather than absolute values. I can see, now, how that > > would be a problem at higher altitudes, but what should we see? If > > the altimeter setting at ground level is 28inHG or 31inHG, what would > > you expect at, say, 20,000 ft? Would a factor rather than an offset > > most appropriate? > > Obviously, getting this truly correct is a meteorology problem that > requires bunches of scientists and a supercomputer or two to solve. > > But I'd argue that using a factor would be saner from a flight > simulation perspective -- if the sea level pressure at a location is > 95% of nominal, then the pilot would naively expect that the air > density at all altitudes would be 95% of nominal. Certainly the use > of an offset mechanism is going to be surprising, and for the extremes > of sea level pressure will lead to super-hurricanes up at altitude. > > Actually, I'm fairly certain that high altitude phenomena tend to > "smooth out" pressure differences down below, so in fact the relative > difference between pressures at the flight levels should actually be > less than that at sea level. Maybe you could try a factor that > asymptotically approaches 1.0 as altitude increases? I don't have > much background in meteorology, though.
As I wrote before, there's a function in the WeatherCM code that calculates the air pressure based on the air pressure at a given altitude and at a given teperature profile. It is based on the well known (but incorrect) baryometric (SP?) formula but doesn't suffer from its limitations. When you feed it, the standard conditions it will return the standard atmosphere. When you adopt that code, you'll automagicly get the correct results. CU, Christian PS: Based on the formula the phenomena won't smooth out. -- The idea is to die young as late as possible. -- Ashley Montague _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
