User manual

XCSoar User Manual

• Both (ZigZag and Circling)

Circling wind algorithm

XCSoar estimates the wind magnitude and direction when cir-

cling. It does this using a sophisticated algorithm that incremen-

tally improves the wind estimate from completed turns. Poor qual-

ity turns, where the bank angle changes signiﬁcantly, are rejected

or have minimal impact on the overall wind estimate. The best

turns are those with constant bank angle.

Estimates are only obtained if the average GPS ﬁx rate is better

than one every two seconds. This results in improved ﬁdelity of

estimates in the presence of GPS dropouts.

Zig-Zag algorithm

For aircraft ﬁtted with intelligent variometers connected to XC-

Soar, a so-called ‘zig-zag’ wind estimation algorithm is being de-

veloped. This enables the wind estimate to be updated continu-

ously during long glides without circling.

This allows the wind estimate to be updated during cruise while

the aircraft performs a zigzag manoeuver. No speciﬁc manoeu-

ver is required, in many cases the estimate will be updated as the

aircraft’s heading changes naturally as the pilot hunts for lift. In

general, however, the technique requires the aircraft heading to

change over 40 degrees.

If the wind changes signiﬁcantly while in straight ﬂight, the zig-

zag algorithm is used to update the wind estimate even if the air-

craft’s heading does not change much. This provides greater accu-

racy in long ﬁnal glides.

Compass algorithm

For aircraft ﬁtted with intelligent variometers and digital com-

passes connected to XCSoar, a wind estimation algorithm making

use of magnetic heading and airspeed is being developed. This

provides another method of updating the wind estimate during

cruise and does not require zig-zag manoeuvres.

6.5 Wind settings dialog

The wind dialog allows the initial estimate of the wind speed and

direction to be entered, usually prior to ﬂight.

This is accessed via the menu under: