User manual

XCSoar User Manual
The bugs setting (’clean’) determines the amount the polar is de-
graded due to contamination during a long flight. A ’clean’ setting
of 100% will cause the software to use the clean polar. A ’clean’
setting of 50% will degrade the polar by 50%, effectively doubling
the sink rate.
The ballast setting is used to modify the polar to account for any
water ballast carried during the flight. A ballast setting of 100%
modifies the polar to account for a full load of water ballast.
Use this dialog both before and during the flight to record the mean
sea level atmospheric pressure, also known as QNH pressure. The
software uses the values entered to convert airspace flight levels
into altitudes. If connected to a supported intelligent variometer
with an altimeter, the altitude is updated on this dialog as the QNH
pressure is adjusted. This makes it easy to set the QNH pressure if
the airfield elevation is known.
The maximum forecast ground temperature is used by the convec-
tion forecast algorithm (see Section 6.8) in its determination of
estimated convection height and cloud base.
It is possible to configure XCSoar to display the basic settings
dialog when it starts up.
On system startup, after the GPS has acquired lock, and if a baro-
metric altitude source is connected (e.g. Vega, AltairPro, FLARM),
the QNH is automatically adjusted. This adjustment sets the QNH
such that the barometric altitude equals the terrain altitude.
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