Checking it twice
by Phillip Luan
July 23, 1999
We recently finished a balance check for the High Speed Civil Transport test in the 12-foot wind tunnel.
This is the last in a series of tests for a high speed passenger concept plane. The balance used for this test is a newer single piece design from NASA Langley. Traditional Ames balances consist of multiple components that are assembled together, measuring three forces and three moments. Amazing improvements in machining technology allows this balance to be machined out of a single piece of metal.
This balance was calibrated previously at NASA Langley. Therefore, instead of calibrating the balance here again, we decided to check Langley's calibration with a series of check loads in the Cal Lab. The results from the check loads came out in agreement with the Langley calibration. The next step was to send the balance over to the 12-Foot and have them wire the balance up to their data system. Later, we got a call from the 12-Foot saying they were getting different outputs from the balance than what we were getting. It turned out to be a wiring problem. The 12-Foot wired the balance up in a different configuration than what we did in the Cal Lab. Usually there's no problem with our Ames balances because it uses a four-wire setup. But because this Langley balance uses a six-wire setup the difference in wiring mattered. It was a miscommunication between the Cal Lab and the 12-Foot. Sometimes you get use to doing something the same way and when something different comes along and you forget to think it out. We decided in the future to provide a wiring diagram to the wind tunnels about how the balance should be configured.