scope:

This document provides a recommended method for calibration of internal strain-gage balances used in wind tunnel testing. The practices include terminology, axis system definition, balance calibration methods, matrix, and documentation. Use of this document will facilitate the exchange of information among users, suppliers, and other interested parties.

Purpose

Internal strain-gage balances are used extensively to measure the aerodynamic loads on a test article during a wind tunnel test. There has been little collaboration on internal balances; consequently, several types of balances, calibration methods, calibration matrices, tare adjustments, and uncertainty evaluations have evolved. The purpose of the group was to pool their information and experiences to enhance each other's capabilities and to develop recommended practices for the use, calibration, tare adjustment, and uncertainty evaluation of internal balances.

The acceptance and universality of a recommended practice is dependent on how well the organizations involved represent the industry. In this instance, the Internal Balance Technology Working Group had membership and participation from many of the major wind tunnel facilities and aircraft developers in the world. The fact that these organizations were able to agree on the recommended practices contained in this document will provide the weight necessary to instill their adoption by organizations around the world.

This document presents the reader with a clear means of designating balance types and gage nomenclature, a concise methodology (including tare corrections) for balance calibration, the reporting of the balance calibration matrix, and for the reporting of statistical and calibration specific information. An example of the balance calibration data reduction process is available for downloading on the GTTC website. The GTTC website can be accessed via the Technical Committees link on the AIAA website. This document also presents guidelines for the user in preparing a calibration load schedule and for selecting coefficients to include in the math model as well as presenting the benefits of using global regression for the computation of balance calibration coefficients. Finally, a data reduction method is presented for calculating the component loads from the bridge readings measured during a wind tunnel test.