How does APM calculate airspeed without an airspeed sensor?

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1

Arduplane gives me airspeed on my OSD as well as wind direction, but I couldn’t find what it uses to compute that data if I don’t have an airspeed sensor

I have APM Plane 3.0.3 on a pixhawk

For instance, at the 4:50 offset of this video, it’s way wrong:

youtube.com/watch?v=Oz1TPiY33rE&t=4m50s

(my airspeed was not 18kph, way below my stall speed, and the wind speed was not 22kph, the rest of the flight never showed that value)

I assume that if I add an airspeed sensor, I’ll get better data, but diydrones.com/forum/topics/airspeed-vs-gps-speed warns that it can be tricky to setup in APM. Still, I think I’ll give it a shot.

2

data from one big cirle at stable altitude, and same throttle, will produce diference in groundspeed when flying with head/tail wind - this data can be used to calculate windspeed and direction.
The accuracy depends on how you fly (data availiable)

  • such data is not used by autopilot, and you cannot trust it to be reliable to maintain low airspeed even if wind is steady.