Propeller Thrust Protection Against Vortex Ring State in Descent
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Solution Overview
Problem
Aircraft with electric propulsion systems, particularly multi-rotor aircraft, face instability due to propellers entering a vortex ring state during descent, which is difficult to detect and avoid, affecting thrust generation and aircraft safety.
Innovation Solution
A flight control system that detects the proximity of propellers to a vortex ring state and automatically adjusts the aircraft's descent rate or maneuvers to prevent entry into the vortex ring state, providing warnings and setting limits to avoid instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the aircraft descends at a high rate to improve productivity, then the descent speed increases, but the propellers may enter a vortex ring state causing instability and thrust loss
Solution Approach 1:
The flight control system proactively monitors descent rate and propeller performance parameters before vortex ring state fully develops. When approaching critical conditions, the system preemptively adjusts pitch attitude or descent rate to prevent VRS entry, rather than reacting after instability occurs.
Solution Approach 2:
The system continuously monitors propeller performance parameters (RPM, thrust, vibration) and descent rate, using this feedback to dynamically adjust flight control outputs. When VRS conditions are detected or predicted, the control system automatically modifies pitch or descent rate commands to restore stable airflow through the propellers.
2Productivity
If the aircraft maneuvers aggressively to improve productivity, then the maneuver speed increases, but some propellers may enter vortex ring state while others remain unaffected, causing instability
Solution Approach 1:
The system independently evaluates vortex ring state risk for each propeller based on its local airflow conditions, which vary with aircraft attitude and maneuvering. This allows differential monitoring and control adjustments for individual propellers, addressing local instability conditions rather than applying uniform constraints to all propellers.
Solution Approach 2:
The control system dynamically adjusts flight parameters based on real-time propeller performance data. When asymmetric VRS conditions are detected during maneuvers, the system adaptively modifies pitch, roll, or yaw commands to restore symmetric airflow conditions across all propellers, enabling continuous stable operation during aggressive maneuvers.
3Measurement precision
If the system monitors each propeller individually to improve measurement precision, then detection accuracy increases, but the device complexity increases
Solution Approach 1:
The flight control system uses a unified control architecture that handles multiple functions: normal flight control, VRS detection for all propellers, and automated recovery. This multi-functional approach avoids the need for separate dedicated VRS detection systems for each propeller, reducing overall system complexity while maintaining precise individual propeller monitoring.
Solution Approach 2:
The system combines VRS detection logic with the existing flight control system, merging monitoring, detection, and recovery functions into a single integrated control platform. This consolidation leverages existing sensors and processing capabilities, avoiding duplicate systems and reducing complexity compared to separate dedicated VRS protection systems.
Data Source
AI summary
The present disclosure relates generally to flight control of electric aircraft and other powered aerial vehicles. In one embodiment, a method is disclosed, comprising: receiving a descent rate command from a pilot input device, determining a proximity of each propeller of at least two propellers to a vortex ring state; and controlling the aircraft's descent rate to be less than the commanded descent rate when at least one of the at least two propellers is within a first threshold proximity to the vortex ring state.