Spherical Joint Actuator for Flight Control Flutter Damping
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Solution Overview
Problem
Aircraft face the challenge of preventing flutter in flight control members due to unstable aerodynamically-induced oscillations, which can exceed the strength capability of the mounting system, particularly exacerbated by the elasticity in hydraulic actuators driven by compressible hydraulic fluid.
Innovation Solution
The implementation of a joint assembly with an extension member and linear members that provide spherical motion and two orthogonal rotational degrees of freedom, incorporating a dampened actuator with an inerter integrated within a hydraulic actuator, and a flywheel system for active control of the flight control member's orientation, including a motor and brake for dynamic damping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If hydraulic actuators are used to drive flight control members, then the actuation force and speed are improved, but the elasticity of hydraulic fluid causes compressibility that contributes to control member flutter
Solution Approach 1:
A spherical joint with two orthogonal rotational degrees of freedom is introduced as an intermediary component between the hydraulic actuator and the flight control member. This joint provides a mechanical connection point that allows the actuator to apply force while the joint's geometry and constraints prevent the elastic compression of hydraulic fluid from causing flutter oscillations. The joint acts as a mediator that decouples the actuation function from the flutter-prone direct connection.
2Speed
If the flight control system operates at high bandwidth, then the control response speed is improved, but the operating bandwidth may overlap with the resonant frequency of the flight control surface causing flutter
Solution Approach 1:
The spherical joint introduces dynamic characteristics with two orthogonal rotational degrees of freedom that allow the system to respond quickly to control inputs while naturally filtering out oscillations at resonant frequencies. The joint's mechanical properties create a dynamic response that separates the high-bandwidth control signal from the resonant frequency range, enabling fast response without triggering flutter.
3Strength
If a rigid connection is used between the actuator and flight control member, then the structural strength is improved, but the elasticity in the system cannot be accommodated leading to potential failure
Solution Approach 1:
The rigid connection is segmented into two functional parts: the spherical joint and the actuator mounting. The spherical joint provides a standardized, pre-engineered connection interface that handles the flexibility requirements through its orthogonal rotational degrees of freedom, while the actuator mounting can focus on providing strong, rigid attachment. This segmentation allows each component to be optimized for its specific function without compromising the other.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces actuator load oscillatory amplitude at resonance, preventing undesirable oscillations and enhancing the dynamic response of flight control members, thereby stabilizing the aircraft's flight control systems.
Implementation Method 1
The joint provides a spherical motion of the flight control member relative to the base achieving two orthogonal, rotational degrees of freedom
Implementation Method 2
The linear members are configured to change an angular orientation of the flight control member relative to the base by moving the second end of the extension member relative to the base
Implementation Method 3
reduces actuator load oscillatory amplitude at resonance
Implementation Method 4
hydraulic actuators can exhibit a linear spring response under load due to compressibility of the hydraulic fluid. The compressibility of the hydraulic fluid can be characterized by the cross-sectional area of the actuator piston, the volume of the hydraulic fluid, and the effective bulk modulus of elasticity of the hydraulic fluid
Data Source
AI summary
Methods and devices for adjusting a position of a flight control member relative to a base of an aircraft. The devices and methods include a joint that movably connects the flight control surface to the base. An extension member is connected to the flight control surface and extends through the joint. Adjustable linear members of the base are connected to the extension member and configured to adjust the position of the extension member. This adjustment results in re-orienting the flight control member relative to the base to adjust the flight of the aircraft.