An Improved High-Capacity Balance Calibration Methodology

The objective of this research was to improve calibration efficiency for NASA Langley Research Center wind tunnel force measurement instruments (balances) that are rated at 31.14 kN and more. The current high-capacity balance calibration process consists of stacking weights in baskets, assembling hangers, knife edges, and bell cranks, and repeated leveling of the balance and the applied cable loads. New concepts for hardware and calibration execution procedures were designed featuring a hydraulic force application system and a precision applied load measurement system based on a platform balance design. Rather than concentrating on applying precise dead weight loads, the new approach relies on precise measurements using an external reference platform balance force measurement system. A complete design and analysis are presented here, including a solid computer-aided design (CAD) model for the platform balance. The structure was analyzed using finite element methods and a virtual calibration was conducted using a statistically based experimental design.