User manual

XCSoar User Manual

The QNH is only updated if the aircraft is on the ground for more

than 10 seconds, so that if XCSoar is restarted during ﬂight, QNH

will not be adjusted. The update only occurs also if the terrain

database is valid at the current aircraft location.

5.5 Speed command display

When used in conjunction with an intelligent variometer that pro-

duces indicated airspeed measurements, a speed command chevron

is drawn on the right side of the map display. If the glider is ﬂy-

ing slower than the optimal speed, the chevrons are red and point

downwards. If the glider is ﬂying faster than the optimal speed,

the chevrons are green and point upwards. If the speed is approxi-

mately optimal, no chevrons are drawn.

Depending on the conﬁguration, speed command chevrons can be

displayed on the right side of the map area, or on the variometer

gauge.

5.6 Speed to ﬂy

XCSoar continuously calculates two types of speed to ﬂy:

MacCready speed : This is the best speed to ﬂy during cruise in still air, adjusted

for wind if in ﬁnal glide mode.

Dolphin speed : This is the instantaneous, best speed to ﬂy in rising or de-

scending air, adjusted for wind if in ﬁnal glide mode.

The user can specify a maximum manoeuvring speed in the conﬁg-

uration settings, which limits the speed-to-ﬂy in MacCready cal-

culations to realistic values.

Different pilots have personal preferences as to whether they pre-

fer to ﬂy in so-called ‘block MacCready’ style, in which they

ﬂy constant speed between thermals according to the MacCready

speed; or to ﬂy in ‘dolphin’ style, in which they ﬂy at varying

speeds according to the continuously changing Dolphin speed value.