Variable-Stiffness Rotor Spring for Resonant Blade Pitch Control
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Solution Overview
Problem
Conventional rotor control systems for rotary wing aircraft, especially small Micro Air Vehicles (MAVs), face limitations in speed and wind resistance due to the need for large torque changes and the avoidance of resonance, which restricts their operational efficiency and flexibility.
Innovation Solution
A cyclic pitch control system with a spring system that adjusts stiffness in response to applied torque, allowing for resonant gain and broader rotational resonance frequency ranges, enabling more efficient and flexible rotor control without the need for swash plates and servos.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional rotor control systems avoid resonance, then structural stability is maintained, but operational speed and wind resistance are limited
Solution Approach 1:
The spring member's stiffness is made variable rather than fixed, allowing the system to dynamically adjust its natural frequency. This enables the rotor assembly to operate at higher speeds by shifting resonance frequencies away from operational ranges, while maintaining structural stability when needed.
Solution Approach 2:
The stiffness parameter of the spring member is changed in response to applied torque, thereby changing the natural frequency of the rotor assembly. This parameter change allows the system to avoid resonance at operational speeds while maintaining the ability to return to stable equilibrium.
2Ease of operation
If large torque changes are applied to control blade pitch angle, then pitch control effectiveness is improved, but system complexity and motor size increase
Solution Approach 1:
The system utilizes resonant vibrations and oscillations in the rotor assembly to amplify the effect of small torque changes. By operating near the natural frequency of the spring-mass system, small periodic torque variations produce large pitch angle changes, eliminating the need for large torque inputs and complex control mechanisms.
Solution Approach 2:
The control system applies periodic torque variations at frequencies matching the natural frequency of the rotor assembly. This periodic action resonates with the spring member's oscillation frequency, producing amplified pitch control effects from minimal input torque, thereby simplifying the overall control system.
3Productivity
If resonance is utilized for gain, then control efficiency improves, but the gain factor varies substantially with rotational speed
Solution Approach 1:
The spring member's variable stiffness allows the natural frequency of the rotor assembly to shift with operational conditions. As rotational speed changes, the spring's effective stiffness changes, thereby shifting the resonant frequency to track with operational speed, maintaining consistent control efficiency across a broad rotational speed range.
Solution Approach 2:
The spring member is pre-configured with non-linear stiffness characteristics that anticipate changes in operational speed. The stiffness profile is designed in advance to compensate for speed variations, ensuring that the natural frequency remains aligned with optimal control frequencies throughout the operational range.
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
The system enhances the rotor's ability to control blade pitch angle and horizontal movements, allowing for smaller motors, increased payloads, and operation in windy conditions, while maintaining stability and reducing complexity and cost.
Implementation Method 1
a spring member (14) connected to both the rotor torque assembly (10) and the rotor blade assembly (11) and configured to transfer torque
Implementation Method 2
A spring system varying stiffness with applied force... where the stiffness may change in response to the level of force or torque applied from or by the motor
Implementation Method 3
designed to operate in resonance, where changes in torque control the blade pitch angle... provide a rotational resonance frequency range of the rotor torque assembly within a range of rotational frequencies of operation
Data Source
AI summary
Embodiments disclosed herein present a spring system for use in a torque dependent rotor assembly designed to operate in resonance, where changes in applied torque controls the blade pitch angle and ultimately the movements of a rotary wing aircraft. More specifically, the present invention relates to a spring system used in such a rotor assembly where the stiffness of an associated spring member is allowed to vary in response to the torque applied from a motor to the assembly.