LXNAV S10 Series, User Manual, Page: 92 / 121

Rev #37
Version 8.0 April 2021
Page 92 of 121
In segment C the sideslip angle is decreased to -6.2 degrees. The string is slightly pointing
outside, as usual.
We first analyse segment B where the sideslip angle is -12 degrees. The glider climbs with
1.8 m/s (2nd row in Table 1). The vertical wind (Netto EKF) equals 4.4 m/s. The Vertical TAS
(sink rate) is estimated as -2.9m/s. Base on the vertical wind triangle, the summation of
these two values equals 1.5 m/s. Due to the short-term averaging the difference is not
exactly the climb rate 1.8 m/s. We next compare the Netto EKF to the readings of the TEK
vario. The most striking result is that the Netto values of TEK and EKF differ by 1.8 m/s
because the glider suffers from a large sink rate due to the large sideslip. The Netto TEK is
derived by adding a fixed constant to Vario TEK. This constant does not consider the impact
of circling and sideslip.
We next analyse segment C. The glider climbs with 2.1 m/s faster than in the segment B.
This is expected due to a smaller sink rate in a smaller sideslip. The sink rate EKF is
decreased to -2.4 m/s. The Netto TEK increases from 2.6 m/s (B) to 3.2 m/s (C). This
increment is due to less drag in the segment C. There is still a large difference of 1.3 m/s (C)
between the Netto values of TEK and the EKF, but the difference is less than in the segment
B. The sink rate of the EKF decreases from 2.9 m/s to 2.4 m/s. The difference between the
sink rate EKF and the circle polar sink rate is 1.1 m/s. It equals the loss of the climbing rate
due to a sideslip caused drag.
7.4 Summary and Recommendation
Despite being mathematically correct, from a user point of view the large Netto EKF values
of segment B and C are misleading.
If a user has the impression that the Netto EKF shows consistently a far too optimistic value,
then the “two needle approach” is suggested. If the red needle (Netto TEK) shows a
consistently smaller value than the blue needle (Netto EKF), the difference between the two
values is the potential for improvement in centring the string.
7.5 HAWK system activation
In order to run HAWK system, a HAWK option must be purchased. Please contact your local
dealer or LXNAV directly to get your HAWK option. Once you receive option file from us refer
to Chapter 9.5.5 for installation procedure.
HAWK system can also be tested free of charge for a period of 31days. Please visit
www.lxnav.com to obtain you demo option for HAWK system.
7.6 Setup parameters
7.6.1 Netto Vario
For a conventional TEK vario the term “Netto Vario” is understood as the vertical air mass
movement. However, the TEK vario only approximates the vertical air mass movement by
adding the minimum sink rate to the measured value of the vario. But for practical purposes,
the difference is negligible. For this reason, we also use the term “Netto Vario” for the EKF.
This allows comparing the two algorithms in flight by activating the second needle in the
SETUP menu.