Airspeed Conversion Modeling With Altitude-Adjusted CAS-TAS Estimation
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Solution Overview
Problem
Current methods for converting between Calibrated Airspeed (CAS) and True Airspeed (TAS) are computationally intensive and prone to significant errors, especially on non-standard days, with existing rule of thumb methods producing errors exceeding 95 knots at high altitudes and 123 knots on temperature deviations.
Innovation Solution
An avionics system with data processors that generates calibrated airspeed, converts it to true airspeed, determines an initial approximate relationship based on pressure altitude, and adjusts this relationship to estimate future airspeeds using an adjusted approximate relationship, reducing computational intensity and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the full TAS to CAS equation is used, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent segments the airspeed conversion process into distinct functional modules: a CAS generation module that produces calibrated airspeed from sensor data, a TAS computation module that converts CAS to true airspeed using the segmented equation, and a relationship determination module that establishes the CAS-TAS relationship. This modular segmentation reduces computational complexity by organizing the complex equation into manageable, reusable components that can be executed efficiently in sequence.
Solution Approach 2:
The patent applies preliminary action by pre-computing and storing standard atmosphere parameters (temperature, pressure, density) at various altitudes in lookup tables before flight operations. During actual flight, the system retrieves these pre-computed values instead of calculating them in real-time, significantly reducing the computational burden of the TAS conversion while maintaining accuracy. The CAS-TAS relationship is also determined in advance for trajectory planning.
2Device complexity
If the rule of thumb method is used, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The patent dynamically adjusts the conversion parameters based on actual atmospheric conditions measured during flight. Instead of using fixed rule-of-thumb percentages, the system modifies the conversion factors according to real-time temperature, pressure, and density measurements. This allows the simplified computational approach to adapt to varying atmospheric conditions, maintaining better accuracy while keeping the device complexity low.
Solution Approach 2:
The system implements feedback by continuously monitoring the actual atmospheric conditions and comparing them against standard atmosphere models. Based on this feedback, the system adjusts the CAS to TAS conversion factors in real-time, correcting deviations from standard conditions. This feedback mechanism enables the use of simpler computation methods while compensating for their inherent inaccuracies through continuous adjustment based on measured data.
Data Source
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AI summary
Systems, methods, aircraft, non-transitory media, and memories are provided. An avionics system for an aircraft includes a storage device and one or more data processors. The storage device stores instructions for converting between airspeed types and the one or more data processors is configured to execute the instructions to: generate a calibrated airspeed of the aircraft; convert the calibrated airspeed to an actual true airspeed of the aircraft; determine an initial approximate relationship between the calibrated airspeed and a computed true airspeed as a function of a pressure altitude of the aircraft; generate an adjusted approximate relationship based on the actual true airspeed and the initial approximate relationship at a chosen pressure altitude; and estimate a future airspeed of the aircraft based on the adjusted approximate relationship and a future altitude.