Balances may be calibrated either via a manual calibration process or by using the Automatic Balance Calibration System (ABCS); this is the only machine of its type located in the United States. The ABCS uses load cells, hydraulic actuators, and a computer control and data acquisition / reduction program to automatically generate an extensive balance calibration. It is capable of simultaneously loading all six balance components to obtain a third-order, 6 X 96 balance calibration matrix that is more representative of actual in-test load conditions than a calibration produced by manual loading. The unique ability of the ABCS to apply any combination of loads allows it to apply any calibration load schedule, which includes six component wind tunnel test load combinations to validate the performance of the balance in actual test type conditions. The ABCS data system has 25 balance channels available. This allows back up bridges to be calibrated at the same time as the primary bridges so that a repeat loading is not required.
Standard ABCS Calibration
The standard method of calibrating most of our internal balances is to use the ABCS with several individual calibrations being performed during the calibration process. The standard ABCS load schedule (935 to 1970 points) is performed, loading every component with incremental cycles of a single component and in combination with every other component at incremental steps. The full load schedule completes all four quadrants of each component plotted vs. the other 5 components. A repeat of the load schedule is completed to document repeatability and to have a separate set of data to cross calculate and check the matrix. A generic six component load schedule developed to simulate a typical wind tunnel pitch sweep is applied to the balance during the ABCS cal process. This verifies balance performance in actual multi-axis test type load conditions. The balance is also loaded with manual dead weight loads to verify the performance of the calibration versus dead weight loadings. The standard calibration procedures have been developed since we began ABCS calibrations in 1997 and continue to mature and change as new requirements are requested.
Features and Benefits
- Full Six Component combined loadings
- Affordable, high accuracy calibrations in less time
- Conforms to AIAA Recommended National Balance Calibration Standards Formats
- Fully Automated
- 2~3 days vs. 4-6 weeks for manual calibration
- Highest accuracy balance calibration system
- Able to apply 6 component real world test loads
- Can redefine the reference moment center to almost any location, allowing larger balances to be calibrated
Our calibration lab has several independent calibration rigs; loads can be applied through dead weight and hydraulics, up to 100,000 lb. We have integrated data acquisition systems and computerized calibration matrix reduction. The rigs can apply single component or combinations of 3 forces and 3 moments to the balance. Calibration hardware can be provided for end users to maintain the accuracy of delivered balance systems. Calibration equipment is fabricated to exacting tolerances.
Large Load Rig (LLR)
Originally designed to calibrate large Semi-Span balances, the Large Load Rig applies load to the balance via hydraulic actuators linked to precision load cells with flexures on each end of the load chain. The loads are applied in sequence per the load schedule that is selected in the operator’s program. The load condition is maintained within a close set tolerance level. The balance and each axis are manually realigned to an orthogonal position for each load prior to taking the data point.
The load cells and flexures are changed to match the load range of the balance, by matching the load range for each balance the machine is able to provide increased resolution and accuracy for a wide range of balances and instrumented stings.
The versatility of the system was demonstrated when a torque tube was calibrated to very demanding loads: 800,000 in-lb of torque along with 200 lbs of thrust.