HAWK Real-time Wind Indication
Real-time Wind Indication
For the glider pilot, it is essential to know how the air mass is moving in its surroundings. Today's TEK Varios work very well for measuring vertical airmass movement if the airplane's speed is approximately constant, e.g., when circling.
As important as the vertical movement of the airmass is the horizontal component, which we commonly refer to as wind. Especially in mountain flying, slope flying, and wave flying, pilots appreciate the wind information that is precise to the second. But the wind information is also especially important for lowland pilots to find and center the thermals, convergent lines, etc.
How do we get wind information in the glider when we haven't had an accurate real-time display of the wind for a long time? The reason is that the algorithms known today for wind estimation require a very long averaging time using a magnetic sensor. You can only estimate the average of a constant wind which is of very limited use.
We completely abandon the conventional approach. The airmass movement is three-dimensional. We, therefore, designed the algorithm HAWK which jointly estimates all three components of the air mass dynamics: It delivers horizontal wind and the vertical wind (“vario”) in real-time. No more separation of the wind calculation and the vario.
The HAWK unit consists of an ARM processor and a sensor unit. The sensor box contains the following sensors: GPS, pressure sensors for static and dynamic pressure, and an IMU (inertial measurement unit) with a three-axis accelerometer and a three-axis gyro sensor (angle changes). Depending on the sensor, signals are processed at a clock rate between 10 and 100 Hz. Most important: we do not use a magnetic sensor which is subject to random electromagnetic field disturbances difficult to compensate for (if at all) and large static error in the model of the earth magnetic field. What sounds a trivial detail but is a key property of the algorithm. The HAWK algorithm is based on an extended Kalman filter.
Therefore, HAWK does not require a hardware update for LXNAV units. HAWK is an SW library.
A good question is why has this not done before? Why now? The answer is: thanks to advances in semiconductor technology, the computing power of microprocessors is now enormous. This allows us today to implement highly complex algorithms, which 10 years ago were only used in military technology for cost reasons, in numerous other applications today. Semiconductor sensors, with amazing accuracy, have also become very small and very cheap.
Experimental Results
HAWK has been tested in over a hundred flights by different pilots flying different gliders. During the flight, all sensor signals have been recorded and analyzed later in the lab. The reports of the pilots are very positive. Here is a quote by the world record pilot Klaus Ohlmann
The second log shows very nicely the approach from the Durance to Serres with the strong wind increase and west turn in the Venturi between the bathtub and the Crete de Selles, which is typical for north winds. Really fantastic to follow this phenomenon live in the instrument. In addition to the currently valuable information for approaching the correct slope, this provides an excellent opportunity to analyze and understand the complex flow conditions in the mountains. ‘ (translated)
What about the “vertical wind”? Does HAWK yield improved information versus a conventional TEK vario? First of all, conventional TEK vario work very well in stable thermals. However, even a perfectly compensated TEK shows us horizontal wind changes (gusts) as climbing (if the wind shear is positive) or sinking, although there is no vertical air motion (see banner photo). These false indications are due to the measurement method (one-dimensional energy conservation) and cannot be compensated The EKF (Extended Kalman Filter) estimates all three dimensions of air mass movement simultaneously. It is designed to correctly process time-varying air masses. When flying, this is the decisive advantage of the "EKF Varios". If the EKF indicates a climb during fast forward flight, the indicated climb value is equal to the climb of the vertical airmass, independent of the speed of the aircraft and horizontal speed or flight path changes.
From the above follows that the HAWK needs no calibration since it not based on an energy conservation law.
More detail can be found in a detailed report HAWK wind calculation • LXNAV Gliding
HAWK is a product from the LXNAV company and has been developed by Professor Heinrich Meyr and his Ph.D student Peng Huang
Heinrich Meyr is a professor of electrical engineering at RWTH Aachen in Germany and a cofounder of Successful Startups. Dr. Meyer received his M.Sc. and Ph.D. from ETH Zurich, Switzerland. He has been flying gliders for many years. Today, flys an ASH25. His top flying destinations are Switzerland, Germany, France, New Zealand, South Africa (Gariep).
