Cross-Country Soaring 2004
User Guide 
9.1 Customizing Thermals
Without any customization by you, Cross-Country Soaring (CCS) will randomly create thermal conditions within certain parameter ranges. You may, however, customize the conditions to represent your real-world soaring area or to set up specific conditions for practice or competition. The following thermal-specific parameters are customizable using the CCS Control Panel.
See House Thermals for a discussion of house thermals and how to configure them.
“<minimum> to <maximum>” (feet MSL, whole numbers, no commas)
Use this setting to control the altitude to which thermals reach in conditions without cumulus clouds. If when CCS is started the lowest cloud layer is cumulus and has a base below 20,000’ MSL, then CCS will ignore this setting and automatically set the lift “ceiling” to the base altitude of this cumulus cloud layer. Otherwise, CCS will randomly pick a value within the range specified. If no range is specified (range entered is “0 to 0”), then CCS automatically sets a value between 3,000’ and 10,000’ AGL (not to exceed the base altitude of the lowest cloud layer). If you want to set an exact ceiling altitude, then enter both numbers the same (e.g., “8000 to 8000”). You may want to set an exact ceiling altitude if duplicating a real-world soaring flight or if competing with another pilot (who’s using the same settings). This is a “global” setting. That is, individual thermal ceilings will vary slightly around the number you set or the number CCS picked randomly. This keeps a realistic element of the unknown in each thermal.
Weak Surface Layer Height
(feet AGL, whole number, no commas)
This is the altitude (AGL) below which thermal lift/sink strength gradually diminishes to zero. The minimum and maximum values allowed are 0 and 3000, respectively. If you enter a number outside this range, the program will use its default setting of 1000. Use this setting to make “low saves” realistically more difficult. This setting may, however, cause CCS thermals to be weaker than expected when flying low over mountains. Scenery (BGL) lift and CCS slope lift/sink are not affected by this setting.
“<minimum> to <maximum>” (feet per minute, whole numbers, no commas)
Use this setting to control thermal strengths. Specifically, this value is the vertical air velocity in the strongest part (center) of an average strength thermal. When CCS is started, it will randomly pick a value within this range. If no range is specified (range entered is “0 to 0”), then CCS automatically sets a random value between 400 and 900 fpm. If you want to set an exact value, then enter both numbers the same (e.g., “800 to 800”). You may want to set an exact value if duplicating a real-world soaring flight or if competing with another pilot (who’s using the same settings). Because thermal strength diminishes as you get farther from the core, it may take some practice to correlate this value to the climb rate you can achieve. The maximum value allowed is 3000. This is a “global” setting. Individual thermal strengths will vary up to +/- 40% around the number you set exactly or the number CCS picked randomly. This keeps a realistic element of the unknown in each thermal.
“<minimum> to <maximum>” (feet, whole numbers, no commas)
Use this setting to control thermal diameters. Specifically, this value is the diameter of the lifting area (each thermal is surrounded by sinking air) of a thermal. If no range is specified (range entered is “0 to 0”), then CCS automatically sets the range to 2100-6100 feet. The strongest thermals will be the smallest, and the weakest will be the largest. Thermals will be created of all diameters within this range during a flight. As in reality, however, there will be more small thermals than large ones. If you want to set an exact value, then enter both numbers the same (e.g., “4000 to 4000”). You may want to set a narrower range or an exact value if duplicating a real-world soaring flight or if competing with another pilot (who’s using the same settings). Because thermal strength diminishes as you get farther from the core, it may take some practice to correlate this value to the diameter in which you can actually climb. The minimum and maximum values allowed are 500 and 10000, respectively.
“<minimum> to <maximum>” (minutes, whole numbers)
Use this setting to control thermal durations. This value is the number of minutes for which a thermal exists. If no range is specified (range entered is “0 to 0”), then CCS automatically sets the range to 15-25 minutes. Thermals will be created of all durations within this range during a flight. There will be more thermals with durations near the middle of this range than near either edge of the range. If you want to set an exact value, then enter both numbers the same (e.g., “20 to 20”). You may want to set a narrower range or an exact value if duplicating a real-world soaring flight or if competing with another pilot (who’s using the same settings). Because a thermal's strength builds at the beginning of its life and wanes at the end, the usable duration of a given thermal will be less than its total duration. This setting is the total duration. The minimum and maximum values allowed are 10 and 45, respectively.
Thermal Coverage
(number per 100 square miles)
Enter a specific value for the average number of thermals per 100 square miles. The minimum and maximum values allowed are 5 and 50, respectively. If you enter a number outside this range, the program will use its default setting of 15.
Thermal Lean Factor
A higher number will make thermals lean less. The minimum and maximum values allowed are 0.30 and 3.00, respectively. CCS will ignore any digits beyond the second decimal place (hundredths). If you enter a number outside the allowable range, the program will use its default setting of 0.70.
More Detail: This factor is the result of the division of two numbers, each of which is also the result of the division of two numbers. Let’s break it down. Two things control the lean angle of a thermal in CCS: the thermal’s effective ascent rate and the thermal’s effective horizontal velocity. The angle between the thermal and the horizon can be defined as the inverse tangent of (effective ascent rate / effective horizontal velocity). A stronger thermal will cause a larger angle, which means a thermal that leans less. Conversely, a higher wind speed will cause a higher horizontal velocity, which will cause a smaller angle (more lean). CCS assumes that a thermal’s effective ascent rate can be expressed as a percentage of the thermal’s peak (at the very center) lift strength. Let’s call this percentage the “effective ascent rate factor”. Likewise, CCS assumes that a thermal’s effective horizontal velocity can be expressed as a percentage of the wind speed. Let’s call this percentage the “effective horizontal velocity factor”. Thus the equation for the thermal lean factor is: lean factor = effective ascent rate factor / effective horizontal velocity factor. If you’re scientifically-inclined, you may want to use this knowledge to come up with and test your own theories on real world thermal effective ascent rates and horizontal velocities.
The Lean Factor and Clouds: You may find that a lean factor that seems realistic when flying without clouds seems to make thermals lean too much when flying with BGL clouds designed to be aligned with CCS thermals. The thermals lean the same in either case. However, in CCS each thermal is modeled as having a fixed ground point, where in reality most thermals have ground points that drift with the wind. This means that in reality the thermal feeding a cloud is typically fairly directly beneath the cloud, despite any wind. Because the clouds created for use with CCS are fixed, though, the thermals are fixed, too.
A higher number will make the sink around the edges of thermals stronger. The minimum and maximum values allowed are 0.0 and 3.0, respectively. CCS will ignore any digits beyond the first decimal place (tenths). If you enter a number outside the allowable range, the program will use its default setting of 1.0.
More Detail: The CCS default thermal edge sink strength is multiplied by this value. For example, a value of 1.3 will make all CCS sink around the edges of thermals 30% stronger.