Hover Rotor Mast Damping for Axial and Flexural Vibrations
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Solution Overview
Problem
Current damping devices for helicopters are ineffective in fully mitigating both axial and flexural vibrations transmitted to the mast, particularly at frequencies corresponding to the rotation speed and number of blades, and lack the ability to adjust tuning frequencies to actual operational values.
Innovation Solution
A rotor design incorporating a passive vibration-damping device with a mass and elastically deformable rod to counter flexural vibrations and a separate system of springs to manage axial vibrations, allowing for tuning adjustments to match the specific pulse rate of the rotor's operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a damping device is tuned to a predetermined frequency value, then vibrations at that specific frequency are contained, but the device cannot adapt to actual operational pulse rates that differ from the nominal value
Solution Approach 1:
The damping device incorporates adjustable parameters that allow its natural frequency to be dynamically tuned to match actual operational conditions. The rod's flexural stiffness and the springs' axial stiffness can be adjusted to change the damping frequency, enabling the device to adapt from a fixed predetermined frequency to a dynamically adjustable frequency that matches the actual rotor pulse rate during operation.
Solution Approach 2:
The patent employs parameter changes in the physical properties of the damping components. By modifying the stiffness parameters of the rod and springs, or the mass parameters, the natural frequency of the damping device can be changed to match different operational conditions. This allows the device to be tuned to the actual pulse rate generated during helicopter operation, rather than being fixed at a nominal design value.
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 solution effectively reduces both flexural and axial vibrations transmitted to the mast, providing improved comfort and reducing the need for extensive redesign, while allowing for fine-tuning of damping frequencies to match operational conditions.
Implementation Method 1
a rod, which is coaxially supported by the mast at its first axial end and is connected to the mass at its second axial end opposite to the first end. More specifically, the axial stiffness of the rod is sufficiently high to constrain the mass in a substantially fixed position along the axis of the rotor. Contrarily, the flexural stiffness of the rod is such as to allow vibration of the mass in a plane orthogonal to the axis of the rotor
Implementation Method 2
a plurality of springs arranged radially around the rod and stretching in parallel to the axis of the rotor and elastically connected to the mass and the rod
Implementation Method 3
the flexural stiffness of the rod is such as to allow vibration of the mass in a plane orthogonal to the axis of the rotor and with a frequency corresponding to N*Ω pulses and, therefore, such as to oppose the transmission of flexural vibrations generated by rotation of the hub and the blades to the mast
Data Source
AI summary
A rotor for a hover-capable aircraft is described, comprising: a hub rotatable about an axis and, in turn, comprising a plurality of blades; a mast connectable to a drive member of the aircraft and operatively connected to the hub to drive the hub in rotation about the axis; and damping means for damping vibrations transmitted to the mast, which comprise a mass designed to oscillate in a plane transversal to the axis so as to contain flexural vibrations of the mast generated by rotation of the blades; the damping means also comprise elastic means having a desired stiffness along the axis and operatively connected to the mass to contain vibration of the mast along the axis.