Digital Airspeed Sensor For Airplane Drone UAV VTOL

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, and CAL_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