Airspeed Sensors

Airspeed sensors are highly recommended for fixed-wing and VTOL frames. They are so important because the autopilot does not have other means to detect stall. For fixed-wing flight it is the airspeed that guarantees lift not ground speed!

Digital airspeed sensor

Hardware Options

Recommended digital airspeed sensors include:

• Based on Pitot tube

  • MEAS Spec series (e.g. MS4525DO, MS5525)

    • mRo I2C Airspeed Sensor JST-GH MS4525DO (mRo store)

    • Digital Differential Airspeed Sensor Kit (Drotek).

  • EagleTree Airspeed MicroSensor V3 (eagletreesystems)

  • Sensirion SDP3x Airspeed Sensor Kit

  • Holybro Digital Air Speed Sensor

• Based on Venturi effect

  • TFSLOT Venturi effect airspeed sensor.

All the above sensors are connected via the I2C bus/port.

:::note Additionally, the Avionics Anonymous Air Data Computer can be connected to the CAN bus to determine not only high-accuracy airspeed, but also true static pressure and air temperature via onboard barometer and an OAT probe. :::

Configuration

Enable Airspeed Sensors

Airspeed sensor drivers are not started automatically. Enable each type using its corresponding parameter:

• Sensirion SDP3X: SENS_EN_SDP3X

• TE MS4525: SENS_EN_MS4525DO

• TE MS5525: SENS_EN_MS5525DS

• Eagle Tree airspeed sensor: SENS_EN_ETSASPD

You should also check ASPD_PRIMARY is 1 (see next section - this is the default).

Multiple Airspeed Sensors

If you have multiple airspeed sensors then you can select which sensor is preferred as the primary source using ASPD_PRIMARY, where 1, 2 and 3 reflect the order in which the airspeed sensors were started:

• -1: Disabled (no airspeed information used).

• 0: Synthetic airspeed estimation (groundspeed minus windspeed)

• 1: First airspeed sensor started (default)

• 2: Second airspeed sensor started

• 3: Third airspeed sensor started

The airspeed selector validates the indicated sensor first and only falls back to other sensors if the indicated sensor fails airspeed checks (ASPD_DO_CHECKS is used to configure the checks).

The selected sensor is then used to supply data to the estimator (EKF2). The EKF fuses the airspeed data if it's above EKF2_ARSP_THR and has a low innovation compared to groundspeed minus windspeed.

Sensor-specific Configuration

Other than enabling the sensor, sensor-specific configuration is often not required. If it is needed, it should be covered in the appropriate sensor page (for example TFSLOT > Configuration).

The specific configuration for sensors that do not have a separate page is listed below:

• Sensirion SDP3X: CAL_AIR_CMODEL (provides overview of required settings), CAL_AIR_TUBED_MM, CAL_AIR_TUBELEN.

Calibration

Airspeed sensors should be calibrated by following the instructions: Basic Configuration > Airspeed.

Developer Information

• Airspeed drivers (source code)