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Simulating the Weather

Weather consists of many factors. Some items, such as air temperature and pressure, are invisible but have a strong effect on aircraft performance. Other items, such as smog layering, have no effect on the aircraft or piloting duties but contribute to realism (in Los Angeles, for example). In between these limits are many other items, such as wind and cloud, that must be simulated in order to reproduce the challenges facing the aircraft and pilot. Some complex items, such as turbulence, affect the simulation in many ways and are capable of making the aircraft realistically unflyable.

While FlightGear supports all these items, each of which can vary by location, altitude and time, leading to the difficulty of enabling the user to explain the desired configuration without too much effort. Three modes are currently available.

First, a single set of conditions can be specified on the command line which will be applied to the entire planet and do not change over time. This is very convenient for short duration and task specific uses, such as flying a single instrument approach from the IAF to the airport, where the same task will recur for each successive student session.

Second, all the weather configuration is accessible through the property database and so can be tweaked by the instructor (for example). This is useful for training on weather decision making, such as choosing between VFR, SVFR, IFR during deteriorating conditions.

Third, a background thread can monitor current weather conditions from for the closest station. This is useful when conditions may be too dangerous to fly into intentionally, yet the pilot seeks experience with them. Such training, often an opportunity when a training flight is canceled, addresses the situation where the pilot had taken off before the weather deteriorated. Unfortunately, the transitions in weather conditions are necessarily harsh because the official weather reports may be issued as infrequently as once per hour. In any case, when flying between airports, the thread must at some point switch from old airport's report to the one ahead.

None of those is the `correct' approach. All of them are especially suitable for specific situations. Other weather management approaches can be quickly created, if needed, since all the weather configuration parameters are properties and thus can be managed and modified across the network from a small specially-created utility.

The FlightGear environmental lighting model seeks to offer the best image that can be achieved with the limited dynamic range of computer monitors. For dusk and night flights, as shown in the left side of figure 1, it is best to use a darkened room in order that the subtle differences between the dark grays and blacks can be seen.