Rotor Blade Test Fixture Minimizing Tip Deflection
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Solution Overview
Problem
Existing fixtures and methods for load testing of rotor blades in rotorcraft are inadequate in controlling tip deflection during axial or centrifugal load testing, leading to imprecise measurements and inability to accommodate long blades or those with weight pockets, which affect test results.
Innovation Solution
A fixture system with a structural frame assembly and pivotal linkage assemblies, including pitch and flap actuators, that minimizes tip deflection of rotor blades during testing, allowing for precise axial load measurements and accommodating weight pockets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If axial or centrifugal loads are applied to the rotor blade during testing, then the load-carrying capability is tested, but the tip of the rotor blade twists and deflects, adversely affecting the axial or centrifugal loading characteristics
Solution Approach 1:
The fixture applies preliminary counteracting forces through its structural design to offset the twisting and deflection caused by axial or centrifugal loads. The rigid frame and positioning mechanisms pre-establish constraints that prevent tip displacement during load application, ensuring accurate measurement conditions are maintained throughout the test.
Solution Approach 2:
The fixture acts as an intermediary between the load application system and the rotor blade. It transfers and distributes the applied loads while maintaining precise control over blade positioning and orientation, isolating the measurement system from the adverse effects of blade deflection and twisting.
2Measurement precision
If known fixtures are used to control tip deflection, then measurement precision is improved, but only very short rotor blades or partial rotor blades can be tested
Solution Approach 1:
The fixture incorporates adjustable and configurable components that can be dynamically adapted to accommodate different rotor blade lengths. The structural design allows modification of support positions, clamping locations, and measurement point configurations, enabling the same fixture to precisely test blades of varying lengths from short to full-size.
Solution Approach 2:
The fixture is designed with universal capabilities to handle multiple rotor blade configurations. It can accommodate full-size rotor blades with adjustable support spans, configurable clamping mechanisms, and adaptable measurement systems, making it suitable for testing various blade types and lengths without requiring specialized fixtures for each case.
3Stability of the object's composition
If weight pockets are added to balance the rotor blade, then flight performance is improved, but test results of axial or centrifugal load testing are affected
Solution Approach 1:
The fixture design isolates the weight pockets from interfering with the load measurement process. By carefully positioning support points and measurement devices, the system extracts or separates the balancing function (performed by weight pockets) from the load testing function, ensuring that the presence of weight pockets does not contaminate the axial or centrifugal load test results.
Solution Approach 2:
The fixture applies localized measurement and support at specific critical points on the rotor blade, away from the weight pocket locations. This ensures that the balancing masses do not interfere with the local stress and strain measurements, maintaining test accuracy while allowing the weight pockets to perform their balancing function.
Data Source
Figure 1
Figure 2~3
Figure 4A
AI summary
A fixture (10), system (300), and method (400) are provided for testing (63) one or more axial loads (64a) in a flexible aerodynamic member (12). The fixture (10) has a structural frame assembly (70) with a first end portion (72), a second end portion (74), and an intermediate portion (76). The fixture (10) has a first pivotal linkage assembly (90) pivotable about a pitch axis (92), a pair of pitch actuators (114) to apply a pitch moment (116a) to the first pivotal linkage assembly (90), a second pivotal linkage assembly (120) pivotable about a flap axis (122), and a pair of flap actuators (140) to apply a flap bending moment (116b) to the second pivotal linkage assembly (120). The fixture (10) has a third pivotal linkage assembly (150) pivotable about the pitch axis (92), and has a pair of chord actuators (166) to apply axial load (64a) to the flexible aerodynamic member (12). The fixture (10) minimizes deflections (66) of a tip (28) of the flexible aerodynamic member (12) during testing to provide an improved accuracy (67) of axial load measurement data (68a).