Chapter 7: Airspeed Sensor Setup

First-Flight Setup After Installing the Airspeed Sensor

1. ARSPD_TYPE = 1 (the other parameters become visible only after saving this change and reconnecting)

2. ARSPD_OPTIONS = 15 (enable DisableVoltageCorrection)

3.ARSPD_AUTOCAL = 1

4.ARSPD_SKIP_CAL = 1

After changing all parameters above, save immediately and power-cycle the flight controller. After power-up, verify that ARSPD_OFFSET is 0. If it is not, set it to 0, save, and power-cycle the flight controller again. Each Fapple airspeed sensor is precision-calibrated for offset before shipment, so ARSPD_SKIP_CAL can be set to 1. This eliminates the need to cover the sensor during flight-controller power-up and prevents wind at the launch site from affecting startup calibration. Automatic Calibration on the First Flight

After takeoff, use RTL or Loiter mode to circle for at least 5 minutes while the flight controller performs automatic calibration. The calibration value is saved to ARSPD_RATIO every 2 minutes. The OSD displays a message during automatic calibration.

After Completing Automatic Calibration and Landing After landing, disable airspeed sensor automatic calibration by setting ARSPD_AUTOCAL = 0; automatic calibration must remain disabled during normal flight. Check ARSPD_RATIO. If the airspeed sensor installation angle is changed or the sensor is replaced, reset ARSPD_RATIO=2.0 and repeat automatic calibration.

Normal Flight with the Airspeed Sensor Enable airspeed control with ARSPD_USE=1 or 2 only after automatic calibration is complete. When ARSPD_USE is set to 2, the flight controller reads airspeed only when throttle is 0. This mode is intended for certain gliders where the airspeed sensor is located behind a nose-mounted propeller. After ARSPD_USE is enabled, the airspeed sensor participates in throttle control in automatic-throttle modes (AUTO, CRUISE, FBWB, RTL).

Configure the following parameters cautiously for the specific aircraft and verify safe operating margins: The values below are described as direct parameter entries. If using the graphical interface, convert the units as required.

AIRSPEED_CRUISE: Target airspeed in automatic-throttle modes (unit: meters/second, M/s). Before Ardupilot4.5, this parameter was named TRIM_ARSPD_CM; note that the old parameter uses centimeters/s.

AIRSPEED_MIN: Minimum airspeed under automatic throttle during climb and descent. Set this at least 20% above stall speed. Unit: meters/second, M/s. Before Ardupilot4.5, this parameter was named ARSPD_FWB_MIN.

AIRSPEED_MAX: Maximum airspeed under automatic throttle during climb and descent. Set this at least 50% higher than ARSPD_FWB_MIN to provide sufficient throttle during automatic climb. Unit: meters/second, M/s. Before Ardupilot4.5, this parameter was named ARSPD_FWB_MAX.