Compliant Tail Structure for Rotorcraft Detuning
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Solution Overview
Problem
Tiltrotor aircraft face a significant weight penalty due to stiffening airframe structures and mass redistribution attempts to detune fuselage modes from critical excitation frequencies, which are ineffective in separating natural frequencies from driving forces generated by rotating components.
Innovation Solution
A compliant tail structure with resilient tail mounts that establish a nodding axis, allowing for adjustable stiffness to detune dynamic fuselage responses from excitation frequencies, thereby decoupling the tail assembly's dynamic response from fuselage bending frequencies without increasing weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If airframe structures are stiffened to detune fuselage modes, then dynamic response is improved, but weight increases significantly
Solution Approach 1:
The patent changes the stiffness parameter of the tail joint connection by introducing resilient mounts with controlled stiffness characteristics. This allows the tail joint to be flexible rather than rigid, enabling dynamic tuning of fuselage modes without requiring overall airframe stiffening, thus avoiding weight penalties while maintaining reliable dynamic response
Solution Approach 2:
The resilient tail mounts act as intermediaries between the tail structure and fuselage, providing a compliant connection that allows dynamic decoupling. This intermediary element enables the tail to contribute to detuning fuselage modes without requiring the entire airframe to be stiffened, thereby improving dynamic response without significant weight increase
2Reliability
If mass redistribution is used to achieve dynamic tuning, then fuselage modes are adjusted, but dedicated tuning masses increase weight
Solution Approach 1:
Instead of adding mass, the patent changes the stiffness parameter of the tail joint connection by introducing resilient mounts. This parameter change allows dynamic tuning of fuselage modes through compliance rather than mass addition, achieving the same dynamic tuning effect without the weight penalty of dedicated tuning masses
3Strength
If rigid tail connection is used, then structural strength is maintained, but dynamic tuning capability is reduced
Solution Approach 1:
The patent changes the stiffness parameter of the tail joint from rigid to resilient, creating a compliant connection that maintains sufficient strength while enabling dynamic tuning capability. The resilient mounts provide the necessary flexibility for dynamic decoupling without compromising structural integrity
Solution Approach 2:
The patent introduces dynamic characteristics to the tail joint connection through resilient mounts, allowing the connection to adapt its stiffness characteristics dynamically. This enables the tail joint to provide both strength when needed and compliance for dynamic tuning, resolving the contradiction between rigid strength and dynamic flexibility
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 compliant tail structure effectively detunes the fuselage modes from critical excitation frequencies, enhancing the dynamic response and reducing weight penalties by using resilient mounts in the tail joint, allowing for tailored modal frequency adjustments.
Implementation Method 1
The tail joint includes at least four tail mounts configured to establish a nodding axis for the tail assembly. At least two of the tail mounts are resilient tail mounts that are configured to establish a nodding degree of freedom for the tail assembly relative to the fuselage about the nodding axis
Data Source
AI summary
A compliant tail structure for a rotorcraft having rotating components and a fuselage. The tail structure includes a tail assembly having first and second oppositely disposed tail members. A tail joint connects the tail assembly to an aft portion of the fuselage. The tail joint includes at least four tail mounts configured to establish a nodding axis for the tail assembly. At least two of the tail mounts are resilient tail mounts that are configured to establish a nodding degree of freedom for the tail assembly relative to the fuselage about the nodding axis, thereby detuning dynamic fuselage responses from excitation frequencies generated by the rotating components.