User`s manual

Table Of Contents

5 GLIDE COMPUTER

When calculating the arrival heights of landable ﬁelds (for map display purposes and in abort

mode), a safety MacCready value can be speciﬁed in the conﬁguration settings. This safety value

is set to zero by default. Larger values make the arrival height calculation more conservative.

All these safety heights can be deﬁned in the conﬁguration settings on the page ‘Safety factors’.

5.7 Final glide calculator

The ﬁnal glide calculator uses many sources of information when determining the altitude required

to reach your goal or the next waypoint. These are:

• The glider’s polar data;

• The wind speed and direction;

• The distance and bearing of the goal or waypoint;

• The MacCready setting;

• The altitude of the waypoint or goal;

• A user speciﬁed safety margin (arrival height).

• The glider’s total energy if XCSoar is connected to an instrument with an air speed indicator.

From the parameters shown above, two altitudes are derived.

• Altitude required This calculation is the total altitude required for the glider to reach the goal

plus any user safety margin.

• Altitude difference This calculation is the altitude required to glide to the goal plus any safety

arrival altitude plus the altitude of the goal, minus the altitude above mean sea level of the

glider. The result represents either your height above glide slope, or your arrival height at

goal. If no goal altitude is provided in the turn-point ﬁle, XCSoar will use the terrain ﬁle

altitude at the goal.

The ﬁnal glide calculation is extended to calculate the altitudes required and difference to complete

the entire task. This capability is sometimes referred to as ﬁnal glide around multiple turn points.

The altitude difference to complete the task is displayed continuously as an arrow and in numeric

form on the left hand side of the map area of the screen.

The height required is adjusted for energy height, compensating for the fact that the kinetic energy

of the glider can be converted to height (potential energy). The kinetic energy that is convertable

to height is calculated from the difference in the true airspeed to the true airspeed for best glide.

This compensation is most accurate when airspeed data is available to XCSoar, otherwise the true

airspeed is estimated from the wind speed and ground speed.

XCSoar Manual (Altair version) • XCSoar-A-EN 52