OpenTX - Application Note 35
Air Speed Sensor
This application sets up the Air Speed sensor with air speed displayed on a telemetry screen, air speed announcements and a stall warning.
Mounting the Sensor and Pitot Tube
The pitot tube is mounted under a wing about 40 cm out from the fuselage, well out of the turbulence caused by the propeller.
Taranis Transmitter Configuration
Search New Sensors
Turn power on the receiver. On the Taranis telemetry set up screen, select “Discover new sensors” and press Enter. The variable “ASpd” appears with an ID of 10. 10 is the default address that this sensor has on the smart bus. Press Exit to stop discovery.
Modify Variable Parameters
Edit the “ASpd” parameters to set the unit to kph (instead of knots) and to enable logging, tick the “Logs” box.
To log data on the SD card, use the following special function to enable data logging when switch SC is in the middle position.
Telemetry Screen Display
Display air speed ‘ASpd’ and maximum air speed ‘ASpd+’ on a telemetry screen.
Announcements and Warnings
Switch SD is used to enable a stall warning and air speed announcements as follows.
The stall warning is announced if the airspeed is less than a set value. This value is dependent on your aircraft. The air speed value, when enabled, is announced every 4 seconds.
The first thing to do is to determine the aircraft stall speed. Enable data logging so that the airspeed is logged. Fly to a ‘three mistakes high’ altitude (very high but in good visual range), turn off the throttle and raise the nose above level to slow the aircraft. Allow the aircraft to stall and recover several times. After the flight on Companion, display the graph of ASpd and determine what the stall speed is.
The following graph shows a graph of airspeed (blue) and throttle (red). The throttle was dropped to zero four times (with elevator pulled slightly back) during which the airspeed dropped until the plane stalled. The aircraft then fell nose first and picked up air speed again.
The following graph shows a section of the graph above. The airspeed drops to about 24 kph during the stall before rising again when the aircraft falls. I chose to set the stall warning at 30 kph.
Use this logic switch and special function to announce a warning when the airspeed drops below 30 kph..
The audio file ‘stallwng.wav’ says ‘stall warning’ and is not a standard Taranis file. It must be created and put in the [SOUNDS]/[en] folder of the SD card. To create audio files, refer to Application Note 4.
After taking off, switch SD to the middle or down position to enable this warning.
Announce Air Speed
During a landing approach is a good time to know what your airspeed is. Use these logic switches and special function to announce the air speed every 4 seconds when switch SD is in the middle position and the air speed is less than 50 kph. If switch SD is in the down position, the air speed is announced regardless of air speed..