LXNAV S10 Series, User Manual

Page: 87 / 121

Rev #37
Version 8.0 April 2021
Page 87 of 121
7 Hawk
7.1 Introduction
HAWK system was developed by prof. Heinrich Meyr* and Peng Huang† in cooperation with
LXNAV. It features a completely new approach towards measuring three-dimensional wind
vector which is essential for glider pilots to understand movement of the air in the vicinity of
glider.
A conventional vario measures the vertical air mass movement based on an energy
conservation principle. In perfectly smooth air, the change of the vertical kinetic energy
(velocity) is compensated by an equal amount of potential energy (altitude). A total energy
compensated (TEK) vario works well under the condition of constant horizontal velocity.
However, any change of the horizontal velocity (horizontal wind gust) is interpreted by the
TEK vario as a change of the vertical velocity (kinetic energy), thus causing the well-known
false reading of the TEK vario.
HAWK applies an “extended Kalman filter” (EKF) algorithm: it jointly estimates all three
dimensions of the air mass movement.
We emphasize the key property of the EKF: It estimates the instantaneous three-
dimensional wind. This is one of the fundamental differences between the TEK vario and the
EKF algorithm. From the previous explanation, it also follows that the EKF needs no
compensation, since it uses no law of energy conservation. This is an important advantage in
the practical application.
*
RWTH Aachen University and Barkhausen Institut, Dresden, Germany.
†
Vodafone Chair Mobile Communications Systems, Technische Universität Dresden, Germany.
7.2 Wind Model
The EKF requires a mathematical model of the three-dimensional wind vector. Figure below
shows wind field estimated by HAWK. The wind vector
d
(
x, y, z
;
t
) depends on the three
Wind field estimated by HAWK.
spatial coordinates (
x, y, z
) and the time
t
. The wind field is described by very complex
mathematical equations. For our purposes, it is sufficient to use a greatly simplified model.