| Wind tunnel balances are used with aircraft models, propellers, and components to measure applied forces and moments. The design and manufacture of a balance is often for a specific test, test article and conditions. This paper discusses the theory, design, calibration, and testing of a new small propeller balance for use in a low-speed wind tunnel. The new balance is named the ODU15X15.;Theory discussed herein covers how the two measurement components, thrust and torque, affect the balance design. These loads generate strains which are in turn read by strain gages arranged in Wheatstone bridges. The design follows well known practices established at NASA Langley for single-piece balances.;Design considerations include constraints on geometry shape/size, thermal compensation, vibration inputs, balance sensitivity requirements, and safety. Analysis of the balance is performed using solid computer aided design models and iterative finite element analysis. Goals for this design were to create a cost effective balance, made using only conventional machining, made out of a single billet or section of tubing, and to create a balance capable of measuring loads more accurately then those commercially available for the relatively low loads predicted. The ODU15X15 is designed to read 15 lbs thrust and 15 in-lbs torque.;Calibration, including theory, set-up, design, and procedures, follows the principles of Design of Experiments. A LabView code is used to record voltage outputs from Wheatstone bridges with known loads applied to the balance. Fixtures are used to apply the static thrust and torque loads. Calibration of the balance resulted in less than +/-0.1% full-scale error at a ninety five percent confidence level. Confirmation points provided additional assurance of model adequacy.;Wind tunnel trials were performed with a Scorpion SII-4020-420kv motor, and a 3 blade 16 X 8 Master Airscrew propeller at conditions representative of previous testing with NASA GL-10 propeller candidates. While further testing is needed, results indicate that the balance performance was superior to the commercial load cell. |
