Chapter 5: Airspeed Sensor Configuration

First-Flight Setup After Installing the Airspeed Sensor

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

2.ARSPD_OPTIONS = 15 (select DisableVoltageCorrection)

3.ARSPD_AUTOCAL = 1

4.ARSPD_SKIP_CAL = 1

After changing all of the above parameters, save them immediately and power-cycle the flight controller. After the restart, verify that ARSPD_OFFSET equals 0. If it does not, set it to 0, save, and power-cycle the flight controller again. Every Fapple airspeed sensor is precisely calibrated for offset before shipment, so ARSPD_SKIP_CAL can be set to 1. This eliminates the need to cover the sensor when the flight controller powers on and prevents wind during ground startup from affecting calibration. First-flight automatic calibration

After takeoff, fly circles in RTL or Loiter mode for at least 5 minutes so the flight controller can perform automatic calibration. The calibration value is saved to ARSPD_RATIO every 2 minutes. The OSD displays status messages during automatic calibration.

After automatic airspeed-sensor calibration is complete and the aircraft has landed, disable automatic calibration by setting ARSPD_AUTOCAL = 0, and check ARSPD_RATIO. Automatic calibration must remain disabled during normal flight. If the installation angle of the airspeed sensor is changed or the sensor is replaced, reset ARSPD_RATIO=2.0 and repeat automatic calibration.

Normal flight using the airspeed sensor: Enable airspeed control only after automatic calibration is complete by setting ARSPD_USE=1 or 2. 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 installed 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 carefully according to the aircraft and within safe limits. The values below assume direct parameter editing; convert units as required when using the graphical interface.

AIRSPEED_CRUISE: Target airspeed in automatic-throttle modes (unit: meters per second, M/s). Before ArduPilot 4.5, this parameter was named TRIM_ARSPD_CM; note that the legacy parameter uses centimeters per second.

AIRSPEED_MIN: Minimum airspeed under automatic throttle (used for climbing and descending). Set this at least 20% above the stall speed. (Unit: meters per second, M/s.) Before ArduPilot 4.5, this parameter was named ARSPD_FWB_MIN.

AIRSPEED_MAX: Maximum airspeed under automatic throttle (used for climbing and descending). Set this at least 50% higher than ARSPD_FWB_MIN so sufficient throttle is available during automatic climbs. (Unit: meters per second, M/s.) Before ArduPilot 4.5, this parameter was named ARSPD_FWB_MAX.