High-Capacity Internal Balance?

Current internal strain gage balance measurement technology has reached the limit of design strength and sensitivity within the required form factors at AEDC's large scale facilities. Better materials are not readily available, as high-strength materials are already used in existing balance designs. The metal-foil strain gauges used require the balance to incorporate weakened sections to obtain the desired response under load – however, these weakened sections limit the load capacity of the balance. LaminarEdge and Ahmic propose to develop a new internal balance design that leverages advances in semi-conductor and fiber optic strain sensing to deliver higher capacities and greater fatigue life than existing “high capacity” devices. The target end-user is the technical staff of the AEDC 16T and 16S wind tunnels, and the target capability delivery is a high-capacity six-component internal balance in Phase II. Phase I focuses on adapting an existing smaller scale balance to the required 2.5-inch diameter form factor, and enabling customer specified load ranges with a measurement uncertainty less than 0.1%, and a factor of safety of 3.0 on yield and 4.0 on ultimate stress. The balance will be designed to operate at expected 16T and 16S temperatures and pressures. The planned balance design will rely on proven semiconductor technology, as well as the potential integration of fiber-optic grating (FBG) sensors. Optimization of the balance topology will be used to select both sensor locations and flexure mechanisms. Semiconductor sensors provide the benefit of small form factor and high sensitivity, while FBGs have the capability to provide a nearly continuous spatial strain measurement. While existing semiconductor balance designs are being scaled up, 1D proof-of-concept FBG balances will be developed, prototyped, tested, and compared with existing metal-foil and semiconductor 1D balance data. Lessons learned from FBG testing will be applied to integration with a small-scale semiconductor balance design. Small-scale integrated sensor calibration and data analysis will inform the proposed Phase II design. FEA tools will be used throughout the design and analysis phase to enable the integration of the balance with existing health monitoring tools, for full lifecycle tracking purposes. Uncertainty quantification methods will be used to identify ways to ensure the calibrated balances delivered to facilities meet the required specifications. The combined sensor approach is expected to lead to a robust design with respect to temperature as well as dynamic loading. The increased capacity for large scale wind tunnels is expected to enable testing of aircraft at conditions and attitudes previously unachievable, driving down program risk for the Nation’s highest priority aircraft systems.