User manual

XCSoar User Manual
In addition, an automatic MacCready mode is available as de-
scribed in Section 5.12.
5.3 Glide polar
The glide polar specifications 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 de-
graded performance due to bugs and ballast.
The build-up of bugs on the wing’s leading edge, as well as rain
droplets on the wing, affect the aerodynamic performance. It is
the pilot’s responsibility to judge and update the bugs value during
flight. The bugs value is expressed as a percentage of the clean
glider’s performance. For example, at 100% bugs value, the glider
performs as a clean glider, and at 50% bugs value, the glider’s sink
rate is doubled when compared to a clean glider.
The ballast value is expressed as a percentage of the glider’s total
ballast capacity. Depending on the specific construction of the
glide polar file, this may optionally include a weight margin to
provide for different pilot weights. When flying with no ballast,
a heavy pilot may set a ballast value of perhaps 10% so that the
polar is appropriately adjusted for the increased cockpit weight.
The current glide polar can be reviewed in the analysis dialog as
described later in this chapter.
5.4 Basic settings dialog
Use the Basic settings dialog to modify the polar of the glider both
before and during flight, as well as to set the QNH pressure.
This is accessed via the menu under
CONFIG . Setup Basic
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