Calspan Force Measurement Systems (FMS) recently developed three new balance/model positioning systems for use in two test sections of a new wind tunnel.
A model positioning system provides a mechanism to easily and accurately change the attitude of a model in a wind tunnel. Coupled with Calspan’s highly responsive force and moment balances, very precise data can be collected during a test.
To outfit the two test sections of the new wind tunnel, Calspan Force Measurement Systems developed a Crescent Model Positioning System with a sting mounted internal strain gauge balance, a Side-Wall Balance Model positioning system, and a Pyramidal External Balance with a Single Strut mount to be used with a wind tunnel model.
The Pyramidal External balance was designed to operate in the smaller high-speed section of the wind tunnel. It has a single strut configuration in which the models are mounted along the tunnel centerline. The pitch mechanism is contained within the single strut assembly allowing for a compact design that allows for high angle settings and resolution.
The Crescent style model positioning system (MPS) was designed to be located in the larger low-speed test section of the wind tunnel. The internal strain gauge balance is fixed to the sting and mounted to the crescent arm which allows the model to be pitched and yawed in the test section by remote control. Roll angles can be manually set in 15-degree increments at the aft end of the sting. The crescent can be retracted beneath the tunnel floor and stored internal to the MPS system, leaving a clean test section for tunnel calibration.
The Sidewall system was designed to operate in either the high speed or low-speed test section. To meet this requirement it has a rolling cart which mounts to the base and allows for easy movement of the system between both test sections. The five component balance for this application was configured as a left-hand wing to support semi-span type model testing.
FMS utilized their assembly lab for the build and calibration of each of these systems. In doing so, an extensive multi-component manual calibration was performed on the Pyramidal External balance. It was calibrated so the balance moment reference center would coincide with the center of the single strut bayonet at the tunnel center. The Sidewall semi-span balance and internal sting balance were calibrated using the Automatic Balance Calibration System (ABCS). This machine allows for all six aerodynamic load components to be loaded individually or applied simultaneously with hydraulics.
This project will culminate with a factory acceptance test at the FMS facility in San Diego prior to hardware delivery to the customer’s facility.