TECHNOLOGY AREAS: Air Platform, Information Systems, Materials/Processes

ACQUISITION PROGRAM: PMA-261 - H-53 Heavy Lift Helicopters Program

OBJECTIVE: Develop an innovative analysis tool which uses combined analytical modeling and experimental measurement to dramatically improve the accuracy of predictions for rotor loads and stresses in dynamic components on in-service rotorcraft.

DESCRIPTION: The accurate prediction of rotor and dynamic component stresses remains an elusive goal. Despite major advancements in computational fluid dynamics techniques, prediction of the unsteady aerodynamic loads acting on the blades continues to be a formidable computational task, and the accuracy of these predictions remains problematic. Since the loading history is not known with sufficient accuracy, fatigue and reliability analyses are difficult to perform, and in all likelihood, the resulting designs are overly conservative. Even if analytical predictions were accurate, the actual flight conditions and resulting loading spectrum are not known with sufficient accuracy to predict stresses in rotor dynamic components.

Innovative, combined analytical modeling and experimental measurement methods are sought to dramatically improve the accuracy of predictions for loads and stresses in dynamic components. These predictions will need to be made in the absence of actual flight conditions and loading spectrums. These methodologies should be applied to develop an analysis tool that receives actual load, strain and/or acceleration data from a limited number of key dynamic components that are instrumented on fleet aircraft. This analysis tool could use this data to constantly improve the fidelity of a predictive model as more data is made available over time so that estimates of loads throughout the rotor system can be made.

PHASE I: Provide proof-of-concept of a combined analytical/experimental rotor loads model based on government-furnished data (rotor system as well as associated measured airloads database). Demonstrate the differences between measured airloads and analytically computed airloads. Propose a method for predicting dynamic component (hub, swashplate, actuators, etc�) loads based on analytical rotor loads. Consider the effect on accuracy when a limited number of on-aircraft sensors provide data to the analytical model. The proof-of-concept should consider minimal data available, such as in the early stages of a rotorcraft program.

PHASE II: Quantify the potential improvement of the Phase I methodology when more accurate, measured airloads are used. Exercise system identification algorithms to create models relating the strains to the input aerodynamic loads for various sensor types and locations within given flight regimes. Evaluate the accuracy of the approach and verify this approach experimentally. Develop a prototype predictive analysis tool and apply it experimentally to actual test aircraft.

PHASE III: Develop a flight test program where an instrumented rotor system will be used to identify airloads. Assess the accuracy of the overall procedure and its ability to improve fatigue predictions and health monitoring of dynamics components. Develop the final analytical software package and the minimum instrumentation system required for use on in-service Navy rotorcraft

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Combined analytical-experimental rotor load predictions will have broad application in both the commercial and military aerospace industry where fatigue prediction of dynamic components is an issue.

REFERENCES:
1. Maley, S., Plets, J., Phan, N.D., "US Navy Roadmap to Structural Health and Usage Monitoring � The Present and Future" Presented at the American Helicopter Society 63rd Annual Forum, Virginia Beach, VA, May 1-3, 2007 (www.vtol.org)

2. Arms, S., Augustin, M., Phan N.D., "Tracking Pitch Link Dynamic Loads with Energy Harvesting Wireless Sensors" Presented at the American Helicopter Society 63rd Annual Forum, Virginia Beach, VA, May 1-3, 2007. (www.vtol.org)

3. Polanco, F., "Estimation of Structural Component Loads in Helicopters: A Review of Current Methodologies" DSTO Aeronautical and Maritime Research Laboratory, Melbourne Australia, 1999

KEYWORDS: Helicopter; Loads; Stress; Aerodynamics; Aeroelasticity; Prediction

TPOC: (301)342-8511
2nd TPOC: (301)757-5531

** TOPIC AUTHOR (TPOC) **

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