To support measurements of starting and landing distances, the radar display can be equipped with a groundsensor. I am using an Lidar ground sensor, which is capable of measuring up to 12 m distance. After first strarting with a cheap lidar sensor, then experimenting with an ultrasonic sensor, the best solution is now a more powerful and expensive sensor.

The following sensors are supported:

• Benewake TFMini Plus Lidar Sensor, e.g. available here: Amazon
• Benewake TF02-Pro Lidar Sensor, e.g. available here: Amazon

Using this sensor with stratux enables the instrument to detect, whether the plane is still on the ground or not. This can then be used to calculate take-off or landing distances as well as the required distance for 50 ft obstacles. Of course the measurements are only accurate with a good GPS or barometric source, but this is typically available in stratux.

The sensor needs to be installed with direct visibility towards ground. Best position is near the main gear or at the bottom of the fuselage. The sensor is then connected via 3 small cables to the stratux display using UART serial connection.

When stratux is powered up the ground distance is measured. The display assumes airborne when this distance is more than 30 cm higher. These are the current technical settings (can be changed in grounddistance.py):

• airborne: distance > initial distance + 30 cm
• landed after flight: distance < initial distance + 15 cm
• distance measurements per second: 10 times
• speed before start or after landing, when calculation of landing distance is done: 5 kts

After a stop is detected (less than 5 kts) the statistics are appended to /home/pi/stratux-radar-display/config/stratux-radar.stats. You can evaluate this file manually for all flights later on. But of course you can also see them while the display is still powered on the display under "Stats" (pressing left button when being in distance-mode).

Remark: If you do a touch-and-go and your speed will not be less than 5 kts, this landing will not be calculated and saved. So for a proper landing calculation you have to reach less than 5 kts on the runway. If you do a touch and go, the start will be safed as well as the last landing.

Installation example

In my taildragger installation of the sensor is in the crossing of the gear legs (bungees).

Sensor connections to Raspberry:

Connection point at ground sensor	Pin number on Pi
VCC +5.0V	GPIO #2 5V
GND	GPIO #6 GND
TX	GPIO #10 RX
RX	do not connect