Why are you still using an airspeed senser

ArduPlane Plane 3.9
1

I flew for the first time with flight controller of matek f405 wing in AR wing,i didn’t use airspeed sensor ,so i have to pay much attention to the ground speed,But something magical happened.

I found the plane have airspeed and wind value in the OSD after the plane in the air .I have know the FC will estimate an airspeed if without airspeed sensor.By comparing with another aircraft equipped with airspeed sensor, I found that the airspeed estimated by f405 wing is quite accurate.

One thing I’m curious about is how flight controller estimates the airspeed?
What do we need to pay attention to when there is no airspeed sensor ?
I don’t know if I believe the airspeed estimated.?

2

I have get the answer from FAQ :

How is airspeed used with no airspeed sensor?

When you have an aircraft with no airspeed sensor Plane uses a range of techniques to fly as reliably as possible despite the lack of airspeed sensor data. The techniques are:

  • a synthetic airspeed estimate is calculated by the AHRS system by combining a wind estimate, the GPS ground speed and the response of the aircraft when turning. This airspeed estimate is usually quite good, although it is not as accurate as a real airspeed sensor.
  • for speed and height control, a different algorithm in TECS is used that does not rely on an airspeed measurement. The algorithm primarily relies on using throttle to maintain the desired height, relying on the fact that an aircraft will start to sink if its airspeed is too low. See the TECS code for full details.
  • For surface speed scaling (the change in control surface movement needed with different airspeed) the synthetic airspeed estimate is used.
  • For stall prevention (if enabled) the synthetic airspeed is used

When no airspeed sensor is available some parameters are not used for some purposes:

  • the TRIM_ARSPD_CM parameter is not used as an airspeed target in auto flight. Instead the TRIM_THROTTLE parameter is used as base throttle, with extra throttle added/removed to retain the target altitude
  • the ARSPD_FBW_MIN and ARSPD_FBW_MAX parameters are not used for airspeed limiting in TECS, but they are still used for the stall prevention code, using the synthetic airspeed value
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