mirror of
https://github.com/PX4/PX4-Autopilot.git
synced 2026-05-28 10:46:33 +08:00
New Crowdin translations - uk (#26016)
Co-authored-by: Crowdin Bot <support+bot@crowdin.com>
This commit is contained in:
@@ -0,0 +1,106 @@
|
||||
# Airspeed Scale Handling
|
||||
|
||||
:::info
|
||||
This section complements the existing [Airspeed Validation](../advanced_config/airspeed_validation.md) documentation.
|
||||
:::
|
||||
|
||||
The airspeed scale is used by PX4 to convert the measured airspeed (indicated airspeed) to the calibrated airspeed.
|
||||
This scale can be set by [ASPD_SCALE_n](../advanced_config/parameter_reference.md#ASPD_SCALE_1) (where `n` is the sensor number), and logged in [AirspeedWind.msg](../msg_docs/AirspeedWind.md).
|
||||
|
||||
Note that the airspeed scale is different from the airspeed sensor offset calibration done on the ground at 0 m/s. The airspeed scale accounts for errors in the airspeed measurement during flight, such as those caused by sensor placement or installation effects.
|
||||
|
||||
This topic describes how to set an initial airspeed scale for a new fixed-wing vehicle during its first flight. Correct scale calibration ensures reliable airspeed data, accurate TAS calculation, robust PX4 airspeed validation, and consistent controller performance.
|
||||
|
||||
## Airspeed in PX4
|
||||
|
||||
PX4 handles multiple types of airspeed:
|
||||
|
||||
- **IAS (Indicated Airspeed):** The raw measurement from the airspeed sensor, directly influenced by sensor characteristics and installation effects (e.g., pitot-static errors).
|
||||
- **CAS (Calibrated Airspeed):** IAS corrected for sensor-specific and installation-related errors.
|
||||
- **EAS (Equivalent Airspeed):** _Not explicitly handled by PX4_ - Calibrated airspeed corrected for compressibility effects.
|
||||
While PX4 does not currently model EAS separately, this correction is negligible at low speeds and altitudes, so EAS is treated as equivalent to CAS for simplicity.
|
||||
- **TAS (True Airspeed):** CAS adjusted for atmospheric effects such as air pressure and temperature (i.e., altitude and atmospheric conditions).
|
||||
|
||||
The standard conversion chain used in PX4 is: `IAS → CAS (= EAS) → TAS`.
|
||||
|
||||
## CAS Scale Estimation
|
||||
|
||||
PX4 estimates the IAS to CAS scale (referred to as the CAS scale) during flight using GNSS ground speed and wind estimation.
|
||||
To compute the final TAS, standard environment conversions are applied (CAS → TAS).
|
||||
|
||||
:::warning
|
||||
Important
|
||||
A GNSS is required for scale estimation.
|
||||
:::
|
||||
|
||||
PX4 uses a two-stage approach to robustly estimate the scale:
|
||||
|
||||
1. **Continuous EKF Estimation**: A wind estimator constantly compares your measured airspeed against what it expects based on ground velocity (from GNSS) and estimated wind.
|
||||
If there's a consistent bias, it adjusts the scale estimate.
|
||||
The estimated scale is logged in the `AirspeedWind.msg` as the `tas_scale_raw`.
|
||||
2. **Validation**: To ensure robustness, PX4 collects airspeed and ground speed data across 12 different heading segments (every 30°).
|
||||
This averages out wind estimation errors.
|
||||
The validated scale is only updated when the new estimate demonstrably reduces the error between predicted and actual ground speeds across all headings.
|
||||
The validated scale is logged in the `AirspeedWind.msg` as the `tas_scale_validated`.
|
||||
|
||||
### Understanding the Scale: Physical Intuition
|
||||
|
||||
The CAS scale is essentially a correction factor that accounts for systematic errors in your airspeed sensor installation.
|
||||
|
||||
- A scale of 1.0 means your sensor reads perfectly (no correction needed)
|
||||
- A scale > 1.0 (e.g., 1.1) means your sensor _under-reads_ by 10%, so measured airspeed (IAS) must be multiplied by 1.1
|
||||
- A scale < 1.0 (e.g., 0.9) means your sensor _over-reads_ by ~11%, so measured airspeed (IAS) must be multiplied by 0.9
|
||||
|
||||
### What Affects the Airspeed Scale
|
||||
|
||||
The primary factor influencing the airspeed scale is **sensor placement**.
|
||||
|
||||
Biased readings can be reflected in the scale estimate for pitot tubes installed:
|
||||
|
||||
- In regions experiencing disturbed flow (commonly near blunt aircraft noses)
|
||||
- Near propellers
|
||||
- Under aerodynamic surfaces
|
||||
- At an angle with respect to the airflow
|
||||
|
||||
### Symptoms of Incorrect Scale
|
||||
|
||||
Symptoms of an incorrectly scaled airspeed measurement include:
|
||||
|
||||
- Stalling or overspeeding
|
||||
- Persistent under- or overestimation of the TAS relative to wind-corrected groundspeed
|
||||
- False positives or missed detections in [airspeed innovation checks](../advanced_config/airspeed_validation.md#innovation-check)
|
||||
- Degraded tracking of the rate controllers
|
||||
|
||||
## Recommended First Flight Process
|
||||
|
||||
During the first flight of a new fixed-wing vehicle, allocate time for the CAS scale to converge to a reasonable initial estimate.
|
||||
Follow these steps:
|
||||
|
||||
1. **Set an Initial Scale**
|
||||
|
||||
Use a conservative starting point: set the CAS scale (`ASPD_SCALE_n`) slightly under 1.0 (for example 0.95).
|
||||
This biases the system toward over-speed rather than under-speed, reducing stall risk.
|
||||
|
||||
2. **Perform a Flight**
|
||||
|
||||
After takeoff, place the vehicle in loiter for about 15 minutes to allow the scale estimation to converge.
|
||||
|
||||
3. **Check Scale Convergence**
|
||||
|
||||
After the flight, review the estimated scale in logs.
|
||||
Verify that:
|
||||
|
||||
- `tas_scale_validated` in `AirspeedWind.msg` converged during flight.
|
||||
- `true_airspeed_m_s` (TAS) in [AirspeedValidated.msg](../msg_docs/AirspeedValidated.md) is consistent with groundspeed corrected for wind.
|
||||
|
||||
4. **Update the Airframe Configuration**
|
||||
|
||||
If using an [airframe configuration file](../dev_airframes/adding_a_new_frame.md): update `ASPD_SCALE_n`with the estimated CAS scale for future flights.
|
||||
For similar vehicles with similarly mounted sensors, this value is typically a reliable starting point.
|
||||
|
||||
:::info
|
||||
If you are not able to perform the steps outlined above ...
|
||||
|
||||
For a quick manual CAS scale estimate, compare groundspeed minus windspeed (from the [VehicleLocalPosition](../msg_docs/VehicleLocalPosition.md) and [Wind](../msg_docs/Wind.md) messages, respectively) to indicated airspeed values (in the [Airspeed](../msg_docs/Airspeed.md) message).
|
||||
The ratio of indicated airspeed to groundspeed minus windspeed can provide a reasonable starting estimate for `ASPD_SCALE_n`.
|
||||
:::
|
||||
@@ -3,7 +3,7 @@
|
||||
Fixed-wing configuration and calibration follows the same high level steps as other frames: selection of firmware, configuration of the frame including actuator/motor geometry and output mappings, sensor configuration and calibration, configuration of safety and other features, and finally tuning.
|
||||
|
||||
:::info
|
||||
This topic is the recommended entry point when performing first-time configuration and calibration of a new multicopter frame.
|
||||
This topic is the recommended entry point when performing first-time configuration and calibration of a new fixed-wing frame.
|
||||
:::
|
||||
|
||||
Основними кроками є:
|
||||
@@ -20,3 +20,5 @@ This topic is the recommended entry point when performing first-time configurati
|
||||
- [Fixed-wing Altitude/Position Controller Tuning Guide](../config_fw/position_tuning_guide_fixedwing.md)
|
||||
|
||||
- [Fixed-wing Trimming Guide](../config_fw/trimming_guide_fixedwing.md)
|
||||
|
||||
- [Fixed-Wing Airspeed Scale Handling](../config_fw/airspeed_scale_handling.md)
|
||||
|
||||
@@ -17,6 +17,8 @@
|
||||
- Надмірні виграші (і швидкий рух серводвигуна) можуть порушити максимальні сили вашої конструкції повітряного корпусу - збільшуйте виграші обережно.
|
||||
- Налаштування крену та тангажу слідують тій самій послідовності.
|
||||
The only difference is that pitch is more sensitive to trim offsets, so [trimming](../config_fw/trimming_guide_fixedwing.md) has to be done carefully and integrator gains need more attention to compensate this.
|
||||
- Disable automatic [gain compression](../features_fw/gain_compression.md) ([FW_GC_EN](../advanced_config/parameter_reference.md#FW_GC_EN)) to avoid over-tuning.
|
||||
Remember to re-enable it when tuning is done.
|
||||
|
||||
## Встановлення базового каркасу повітряного корпусу
|
||||
|
||||
|
||||
Reference in New Issue
Block a user