User`s manual
Table Of Contents
- Introduction
- User Interface
- Display Elements
- Cross Country Tasks
- Glide Computer
- Atmosphere and Instruments
- Airspace, Traffic and Team Flying
- Avionics and Airframe
- Quickstart
- InfoBox Reference
- Configuration
- Data Files
- About XCSoar
- GNU General Public License
5 GLIDE COMPUTER
Similarly, when below final glide altitude, the MacCready ring setting my be decreased, resulting
in a lower speed to be commanded. Because the ring setting has decreased, the pilot may be
prepared to stop and circle in weaker thermals.
Auto MacCready performs this adjustment automatically and continuously. Typically it is meaning-
less to enable this mode before reaching final glide altitude, or nearly so, because early in the flight
the glider will be very much below the final glide altitude and the Auto MacCready function would
then drive the MacCready ring setting to zero.
Average climb
This method sets the MacCready to the average climb rate achieved across all thermals in the
current flight. As such, it takes into account the time spent centering the thermal. The value is
updated after leaving a thermal.
Since MacCready theory is optimal if the MacCready setting is the average climb rate of the next
expected climb, this method may give suboptimal performance (commanding speed too slow) if the
conditions are improving; and similarly may be non-conservative if the conditions are deteriorating
(commanding speed too high). Similarly, if the pilot continues to climb in weak thermals, this will
reduce the average and may therefore encourage the pilot to continue to select weak thermals.
As a result of these limitations, the pilot should be aware of how the system operates and adjust
his decision-making accordingly.
5.3 Glide polar
The glide polar can be defined in the configuration settings (see 11.7). The glide polar specifi-
cations of a small selection of glider types, representing major classes of gliders, are built into
XCSoar, and these may be used as an approximation for other gliders if no better glide polar can
be found. However, for most accurate results, it is advisable to use the correct glide polar for your
particular aircraft type.
The glide polar is adjusted in flight by XCSoar to account for degraded performance due to bugs
and ballast.
47 XCSoar Manual (Altair version) • XCSoar-A-EN