Aircraft Speed Calculation Using Correction Loop and Protection Radius
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Solution Overview
Problem
Existing methods for calculating aircraft speed are unreliable when the satellite positioning system fails, as they do not account for the temporal variation of position errors, leading to large speed errors even within the protection volume, and require significant computational resources, making them unsuitable for avionic systems with limited capabilities.
Innovation Solution
A method that calculates a reliable aircraft speed by integrating inertial measurement unit data with satellite positioning data, using a correction loop to adjust speed measurements based on position differences and accounting for inertial measurement unit imperfections, with a focus on reducing computational requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If speed is calculated using satellite positioning system data, then speed information is obtained, but the measurement becomes unreliable when the GPS system fails or experiences temporal variations in position errors
Solution Approach 1:
The patent combines GPS position measurements with inertial measurement unit (IMU) data to calculate speed. The correction loop integrates corrected speed to obtain calculated position, then corrects measured speed based on the difference between calculated and measured positions. This merging of multiple measurement sources resolves the contradiction by maintaining reliability through IMU data while improving accuracy through GPS correction.
Solution Approach 2:
The patent implements a correction loop that continuously compares calculated position (from integrating corrected speed) with measured position (from GPS) and uses the difference to correct the measured speed. This feedback mechanism ensures that speed measurements remain reliable even when GPS experiences temporal variations or failures, as the system can rely on the inertial integration while being corrected by position differences.
2Reliability
If complex calculation methods like Kalman filter are used to obtain protection radii, then reliable speed calculation is achieved, but the computational resources required become excessive for avionic systems
Solution Approach 1:
The patent extracts only the essential protective function from complex Kalman filter methods by calculating a simplified protection radius based on the maximum expected position error within the protection volume and the time constant of the correction loop. This extraction maintains the reliability function while removing the excessive computational complexity of full Kalman filter implementation.
Solution Approach 2:
The patent changes the approach from using complex state-space model parameters in Kalman filters to using direct physical parameters: the position protection radius, the time constant of the correction loop, and the maximum expected position error variation. This parameter transformation simplifies the calculation while preserving the reliability assessment function.
3Reliability
If the protection volume is used to limit position error, then position reliability is maintained, but large speed errors can still occur due to rapid position variations within the volume
Solution Approach 1:
The patent performs preliminary correction of the measured speed before integration by using the correction loop to adjust speed based on position differences. This preliminary action prevents the accumulation of speed errors that would otherwise occur even when position remains within the protection volume, addressing the issue of rapid position variations causing large speed errors.
Solution Approach 2:
The correction loop provides continuous feedback by comparing calculated position (from speed integration) with measured position and using the difference to correct measured speed. This feedback mechanism detects and corrects speed errors that arise from rapid position variations within the protection volume, maintaining speed precision while position reliability is maintained by the GPS system.
Data Source
AI summary
A method of calculating a speed of an aircraft, a method for calculating a protection radius, a positioning system and an associated aircraft are disclosed. In one aspect, the method includes obtaining a measured speed of the aircraft and obtaining a measured position of the aircraft, associated with a reliability protection radius related to position. The method also includes calculating, by a correction loop, a corrected speed, wherein the calculation of the corrected speed includes calculating a calculated position by integration of the corrected speed, and correcting the measured speed as a function of a difference between the calculated position and the measured position. The method further comprising calculating a reliability protection radius related to the corrected speed.