Coaxial Rotor Gust Alleviation via Active Elevator Mixing
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Solution Overview
Problem
High-speed operation of coaxial rotor helicopters in gusty environments reduces tip clearance and increases rotor hub loads, making it difficult to maintain sufficient clearance and control, and increasing aircraft weight by requiring larger rotor hubs.
Innovation Solution
A flight control system that includes a gust detector and alleviation control logic, which reduces lift on the main rotor system and mixes collective and cyclic commands to minimize pitch response and lift-offset changes, using an active elevator to counteract gust-induced loads and maintain tip clearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If forward flight speed increases, then productivity is improved, but tip clearance decreases due to lift offset
Solution Approach 1:
The patent applies dynamic control by continuously adjusting the collective pitch angle of rotor blades in response to detected gust conditions and flight parameters. The control system dynamically modifies blade pitch to counteract lift offset effects, maintaining tip clearance while enabling high-speed forward flight. This dynamic adjustment resolves the contradiction by making the system adaptable rather than static.
Solution Approach 2:
The patent implements a feedback control mechanism where gust detectors monitor wind conditions and tip clearance sensors provide real-time clearance measurements. This feedback loop enables the control system to detect deviations from desired tip clearance and automatically adjust collective pitch to restore proper clearance, thus maintaining safety margins while operating at high forward speeds.
2Reliability
If rotor hub size increases to handle loads, then reliability is improved, but weight increases
Solution Approach 1:
The patent replaces purely mechanical load handling (larger rotor hub structure) with an active control system that uses aerodynamic forces generated by variable blade pitch to counteract gust loads. The control system substitutes mechanical strength requirements with aerodynamic load management, allowing lighter rotor hub construction while maintaining reliability under gust conditions.
Solution Approach 2:
The patent changes the operational parameters of the rotor blades by dynamically adjusting pitch angles in response to detected gust conditions. This parameter change enables the same rotor hub structure to handle varying load conditions without requiring increased physical size, thus maintaining reliability while avoiding weight penalties.
3Length of moving object
If collective control is used to maintain tip clearance, then tip clearance is improved, but pitch response and lift offset change
Solution Approach 1:
The patent segments the control function into separate components: gust detection, tip clearance monitoring, collective pitch adjustment for clearance maintenance, and separate pitch attitude control. This segmentation allows the system to adjust collective pitch for tip clearance while independently managing pitch response stability through dedicated pitch control channels, preventing adverse interactions between clearance maintenance and pitch stability.
Solution Approach 2:
The patent introduces an intermediary control system that coordinates between collective pitch adjustments for tip clearance and pitch attitude control. This intermediary layer ensures that collective pitch changes intended to maintain tip clearance do not create excessive pitch responses, by coordinating with pitch control actuators to counteract unwanted pitch movements.
Data Source
AI summary
One aspect is a flight control system for a coaxial rotary wing aircraft including a main rotor system and an active elevator. The flight control system includes a flight control computer with processing circuitry that executes control logic. The control logic includes a gust detector that produces a gust error indicative of a wind gust encountered by the coaxial rotary wing aircraft. The control logic also includes a gust alleviation control that reduces lift on the main rotor system with collective, based on the gust error, and mixes a collective command to a main rotor cyclic and a differential cyclic to reduce an aircraft pitch response and a lift-offset change. The gust alleviation control also reduces a main rotor pitching moment with the main rotor cyclic, based on the gust error, and mixes a main rotor cyclic command to the active elevator to reduce the aircraft pitch response.