6. Staying Aloft - Thermaling
As the sun heats the earth, the earth in turn heats the air near its surface. Since warmed air drops in density and is thus lighter than the surrounding air, this warmed air at the surface eventually breaks away from the surface and begins to rise. As the air rises, it cools, and it continues to rise until it either reaches air that is equal or higher in temperature or until it reaches air at the dewpoint temperature, in which case a cloud is typically formed. In general, thermals originate at places on the surface that are warmer than their surroundings and often break off at disturbances, or "triggers", on the surface. Thus dry, dark fields and parking lots are good thermal generators; and trees, buildings, and hills are good triggers.
The typical soaring day starts with weak lift that builds to its peak in the early afternoon and wanes away until sunset. The peak heating time of the day is naturally the time when the sun's rays most directly hit the earth, or what soaring pilots refer to as "noon, local sun time". Because it takes time for the surface to heat, though, the time of day for peak thermal strength is typically an hour or two after "noon, local sun time". This daily thermal strength cycle makes it more difficult to stay aloft in the early morning or late afternoon. The "X-C Soaring, San Francisco" flight places you in the Schweizer 2-32 sailplane at 2500' MSL just north of the Golden Gate Bridge at 12:15 p.m. on a summer day. You may choose your aircraft (before starting the adventure, but not during it), your starting altitude, the season, and the time of day, but Cross-Country Soaring 98 will set the wind's speed and direction, the cloudbase altitude, the amount of cloud coverage, and all thermal positions and characteristics.
To find thermals in this adventure, simply press "CTRL-c". You'll be given the bearings and distances to two nearby thermals. Depending on your altitude, you'll either be given the position of the trigger or the cloud. At lower altitudes, you'll be pointed to thermal triggers; and at higher altitudes, to clouds. Since thermals typically lean downwind, expect to find the lift downwind of the trigger and upwind of the cloud. Because the compass on the instrument panel displays magnetic heading and the wind is reported in true degrees, it's important to know the local magnetic variation in order to more precisely navigate into a thermal. Press "CTRL-v" to display the local magnetic variation. A magnetic variation of 16 degrees (as in the San Francisco, California area) means that the true heading is equal to the compass (magnetic) heading plus 16 degrees.
Once you've found a thermal, you must maneuver to stay in it. The thermal can be envisioned as a circular column with the strongest lift at the center and diminishing lift towards the edges. Since the thermals only last for about 10 to 20 minutes and you don't know when you find one how long it's already existed, you must quickly establish yourself in it and in the area of best lift to gain the most altitude. Once you find a thermal, slow to around minimum sink speed, so you can fly a smaller circle and thus stay nearer the thermal's core. Don't start turning immediately upon entering a thermal, though. Wait until your climb rate levels out or drops off slightly, so you can know that you haven't turned even before reaching the core. A common technique for maintaining a good circle around the core is to increase bank as climb rate decreases and decrease bank as climb rate increases. A continuous compromise must be made between bank and climb rate. A steeper turn increases the glider's sink rate but allows it to get nearer the core (flying in smaller circles), while a flatter turn minimizes the glider's sink rate but keeps it farther from the core (flying in larger circles). Using the map view can help you stay in the thermal, but be aware of the wind speed and direction in order to anticipate the amount and direction of thermal drift. Flight Simulator's course tracking feature can also help you "see" the thermal and its leaning. Here's how to use course tracking to help in your thermaling:
Flight Simulator offers the option of recording a plane's flown course
by saving the plane's position every few seconds. The pilot can then
display the tracked course as a series of red line segments in the sky.
If you're having trouble climbing in lift, you may want to turn on course
tracking. You can then look at the track and see where the plane
was climbing and where it was descending. Maneuver into the part
of the track where the plane was climbing, and you'll be in the lift again
(unless the thermal has expired in the meantime). You may also set
course tracking to record, but not display, your course. You can
then toggle the display of the course as you wish, allowing you the option
of seeing the last few minutes of the flight at any time. To use
course tracking:
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