Aircraft Flight Envelope Prediction for Flutter and Buffet Onset
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Solution Overview
Problem
Existing methods for predicting flutter and buffet in aircraft are inadequate, lacking a satisfactory theory to determine eigenmodes and eigenvalues, requiring iterative procedures and approximations, and failing to account for aeroelastic feedback mechanisms.
Innovation Solution
A method that simultaneously determines all relevant aeroelastic eigenvalues and eigenvectors for flutter and buffet onset by coupling structural and aerodynamic models, using a state-space realization and Loewner matrices to track eigenmodes, eliminating the need for initial estimations and approximations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If iterative procedures with initial eigenvalue estimation are used to calculate aeroelastic eigenvalues, then the calculation can be performed step-by-step, but the calculation time and complexity increase significantly
Solution Approach 1:
The patent applies preliminary action by performing a global stability analysis that calculates all relevant aeroelastic eigenvalues and eigenvectors simultaneously in a single computational step, rather than using iterative procedures that require multiple steps with initial estimations. This approach determines the complete set of eigenvalues upfront, eliminating the need for repeated calculations and significantly reducing computational time while maintaining accuracy.
2Productivity
If reduced-order aerodynamic models are used to approximate generalized aerodynamic forces, then the computational load is reduced, but the prediction accuracy of flutter and buffet onset deteriorates
Solution Approach 1:
The patent applies parameter changes by performing a global stability analysis that directly computes the complete set of aeroelastic eigenvalues and eigenvectors without relying on reduced-order aerodynamic models or iterative approximations. This approach changes the computational parameters to solve the full-order system simultaneously, achieving both high calculation efficiency and accurate prediction of buffet and flutter onset conditions.
3Reliability
If the flight envelope is determined with large safety margins from predicted flutter and buffet onset, then aircraft safety is improved, but the operational range and maneuverability are excessively restricted
Solution Approach 1:
The patent applies mechanics substitution by replacing traditional safety margin-based flight envelope determination with a physics-based global stability analysis. This analysis accurately predicts the actual flutter and buffet onset conditions by computing all aeroelastic eigenvalues, allowing the flight envelope to be defined based on real physical thresholds rather than conservative estimates. This substitution enables maximum operational range while maintaining safety through accurate scientific prediction.
Data Source
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AI summary
To define a flight envelope (24), structural properties of an aircraft are described in a structural model (13). A structural eigenmode is determined from the structural model (13) under the assumption that no aerodynamic forces (Fa) act. In an aerodynamic model (14), aerodynamic properties of the aircraft in the flow (3) are described under the initial assumption that the aircraft performs movements (15) according to the structural eigenmode and that the flow (3) has no influence on these movements (15). This determines a dominant flow eigenmode of the flow (3) and aerodynamic forces acting on the aircraft. The aerodynamic model is converted into an aeroelastic model (12) by coupling the structural model (13). The dynamic pressure (qdyn) is then successively increased, with the structural eigenmode and the dominant flow eigenmode being monitored with regard to their eigenvalues (16, 18, 20).A flutteron set is detected when a real part of an eigenvalue of the structural eigenmode becomes positive, and a buffeton set is detected when a real part of an eigenvalue of the dominant flow eigenmode becomes positive. A boundary (27) of the aircraft's flight envelope (24) toward higher Mach numbers is defined such that the flight envelope (24) maintains a distance from the flutteron set and the buffeton set.