Airspeed Sensors
Last updated
Last updated
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!
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)
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. :::
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).
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.
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.
Airspeed sensors should be calibrated by following the instructions: Basic Configuration > Airspeed.
Airspeed drivers (source code)
