Airspeed sensors are crucial for fixed-wing and VTOL aircraft because they provide the only means for the autopilot to detect a stall. This is essential since, in fixed-wing flight, it's the airspeed that ensures lift, not the ground speed.
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Digital Airspeed Sensor
Hardware Options
For digital airspeed measurements, the following sensors are recommended:
- Pitot Tube-based Sensors:
- MEAS Spec series (e.g., MS4525DO, MS5525)
- mRo I2C Airspeed Sensor JST-GH MS4525DO (available at mRo store)
- Digital Differential Airspeed Sensor Kit (available at Drotek)
- EagleTree Airspeed MicroSensor V3 (available at eagletreesystems)
- Sensirion SDP3x Airspeed Sensor Kit
- Holybro Digital Air Speed Sensor
- Venturi Effect-based Sensor:
- TFSLOT Venturi effect airspeed sensor
All these sensors connect through the I2C bus/port.
Additionally, the Avionics Anonymous Air Data Computer can connect to the CAN bus, providing high-accuracy airspeed, true static pressure, and air temperature measurements with its onboard barometer and an OAT probe.
Configuration
Enabling Airspeed Sensors
Airspeed sensors require manual activation through specific parameters:
- For Sensirion SDP3X:
SENS_EN_SDP3X - For TE MS4525:
SENS_EN_MS4525DO - For TE MS5525:
SENS_EN_MS5525DS - For Eagle Tree airspeed sensor:
SENS_EN_ETSASPD
Ensure ASPD_PRIMARY is set to 1, which is the default setting.
Multiple Airspeed Sensors
Using multiple airspeed sensors is considered experimental. To specify a primary sensor, use ASPD_PRIMARY with values 1, 2, or 3, corresponding to the order sensors were activated:
- 0: Synthetic airspeed (groundspeed minus windspeed)
- 1: First airspeed sensor (default)
- 2: Second airspeed sensor
- 3: Third airspeed sensor
The system prioritizes the selected sensor, resorting to backups only if the primary sensor fails checks configured by ASPD_DO_CHECKS. The chosen sensor feeds data to the estimator (EKF2) and controllers.
Sensor-specific Configuration
Typically, sensors do not require additional configuration beyond activation. When necessary, specific settings are found on the respective sensor's configuration page or listed directly for those without a dedicated page, such as:
- Sensirion SDP3X:
CAL_AIR_CMODEL,CAL_AIR_TUBED_MM, andCAL_AIR_TUBELEN.
Calibration
Follow the Basic Configuration > Airspeed section for calibrating airspeed sensors.
Further Reading
For more information, see:
- Using the ECL EKF > Airspeed
- Airspeed drivers (source code)
- Operating VTOL aircraft without an airspeed sensor