TECHNOLOGY AREAS: Air Platform, Materials/Processes, Sensors

ACQUISITION PROGRAM: JSF - Joint Strike Fighter Program Office ACAT I

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 3.5.b.(7) of the solicitation.

OBJECTIVE: Develop a method to calibrate strain sensors on in-service fleet aircraft to be used in individual aircraft structural life tracking.

DESCRIPTION: In order to obtain a load history for individual fleet aircraft, strain sensors are placed on the aircraft that are monitored and recorded through the flight. This data is downloaded and used in structural fatigue life tracking methods to determine how much structural life has been used up by the aircraft. The readings on these strain sensors can vary by 10% or more from aircraft to aircraft due to manufacturing and installation issues. The variation must be accounted for before using the output of those sensors in the fatigue life tracking method. The ideal way to calibrate a sensor is to place the entire aircraft in a full scale test rig, have known loads put onto the airframe and take a reading of the sensor output. This is too expensive and time-consuming for most aircraft fleets. An alternate method has been developed that use in flight calibration. This method has the aircraft fly a tightly proscribed maneuver where the loads can be fairly well determined, and compares the strain sensor output to the known load. This method is considerably less accurate and maneuvers that can repeat loads on certain portions of the airframe, such as the vertical tail or canopy sill, are difficult to proscribe. We are looking for an innovative way to obtain the strain gage calibration on each aircraft individually that will give us the accuracy of a full scale test rig.

PHASE I: Develop an innovative method that can be used to calibrate a strain sensor that has been installed on a fleet aircraft, so that the aircraft-to-aircraft variation due to installation and manufacturing variation can be captured.

PHASE II: Mature and verify the method developed in phase I through coupon, component and possibly full scale test applications.

PHASE III: Mature the process so that it can be used by maintenance personnel in the fleet to get a calibration factor for any newly delivered aircraft or any strain gage that was replaced in use. This would include developing and maturing any equipment or models necessary to a fleet readiness state.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Civil aircraft are heading toward structural life tracking where strain gages may be installed and would need similar calibration. Civil aviation, commercial airlines as well as private, could benefit.

REFERENCES:
1. Grover, Horace J. "Fatigue of Aircraft Structures." Batelle Memorial Institute, 1966 (NAVAIR 01-1A-13).

2. Molent, L. "A Review of a Strain and Flight Parameter Data Based Aircraft Fatigue Usage Monitoring System." Proceedings of the USAF Aircraft Structural Integrity Conference (Dec 3-5, 1996).

KEYWORDS: Calibration; Strain; Tracking; Fatigue; Sensor; Structures

TPOC: (301)342-9325
2nd TPOC: (301)342-9321

** TOPIC AUTHOR (TPOC) **

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