Coaxial Rotorcraft Lift Offset Control for Cruise Performance
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Solution Overview
Problem
Coaxial, counter-rotating rotorcrafts face a trade-off between aircraft performance, hub loads, and tip clearance during cruise flight, leading to suboptimal performance due to a-priori knowledge-based optimal point settings and increased structural requirements with stiff blade designs, which result in unstable dynamics and difficulties in conventional main rotor control.
Innovation Solution
A lift offset management system that includes oppositely rotating first and second rotors with sensors generating hub moment, tip clearance, and lift offset data, an input unit generating a target lift offset reference, and a feedback system combining this with correction commands to control blade pitching, optimizing lift offset based on measured aircraft states and flight conditions, while also incorporating a control system that mixes main rotor inputs with hub moment and tip clearance feedback to minimize hub moments and maintain adequate tip clearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a-priori knowledge-based optimal point settings are used for lift offset, then the control system is simple, but aircraft performance is suboptimal during cruise flight
Solution Approach 1:
The patent implements dynamic lift offset adjustment by continuously varying the lift offset command based on real-time flight conditions (airspeed, altitude, acceleration) rather than using fixed a-priori settings. The control system dynamically calculates optimal lift offset values during cruise flight to maximize aircraft performance while maintaining stability.
Solution Approach 2:
The patent employs feedback control by using measured aircraft states (acceleration, airspeed, altitude) to continuously adjust the lift offset command. The control system monitors actual flight conditions and modifies lift offset settings in response to measured performance, creating a closed-loop control system that optimizes aircraft performance during cruise flight.
2Strength
If stiff blade designs are used to reduce hub loads, then structural requirements increase, but dynamics become unstable and conventional main rotor control becomes difficult
Solution Approach 1:
The patent changes the control parameter from direct hub moment control to lift offset control. By controlling the differential lift between the two main rotors, the system achieves hub load reduction without the instability problems associated with stiff blade designs. This parameter transformation allows effective control while maintaining rotor dynamics stability.
Solution Approach 2:
The patent introduces lift offset as an intermediary control variable between pilot input and main rotor blade pitch control. Instead of directly controlling hub moments which causes instability with stiff blades, the system uses lift offset command as an intermediate step that indirectly achieves hub load management while maintaining stable rotor dynamics.
Data Source
AI summary
Lift offset management and control systems are provided for a rotorcraft including main rotor and auxiliary propulsor assemblies, the main rotor assembly including first and second rotors disposed to oppositely rotate relative to an airframe about a same rotational axis, and sensors disposed to generate hub moment, tip clearance and lift offset data of the main rotor assembly.