M.Sc Thesis

M.Sc StudentCohen Shira
SubjectModel of Uncertainty Determination in Calibration for
Strain-gage Balance Measurements Complying with
DepartmentDepartment of Quality Assurance and Reliability
Supervisor PROFESSOR EMERITUS Amos Notea


The present study was carried out at the wind-tunnel laboratory of the Technion Faculty of Aerospace Engineering. Wind-tunnel experiments are an integral part of the development stage of aircraft, with a view to determining the aerodynamic forces and moments they would undergo in flight under full-scale conditions. The measurements involved are most commonly realized with the aid of aerodynamical balances of the strain-gage type, attached to a model inside the tunnel. Operation of a strain gage is preceded by a calibration process, on which the present study focuses. The uncertainty involved in the measurements is an important factor which must be recognized and minimized. To-date, no published approach is available on evaluation of the calibration uncertainty for the strain gage to be in compliance with ISO GUM (1995) requirements. The aim of the present work is development of a methodology for evaluating the uncertainty in calibration of strain gages, to serve as an example of a pilot for handling balances of this type in wind-tunnel experiments. A model for evaluating the uncertainty in the measurement results at the calibration stage will help wind-tunnel laboratory engineers in choosing the gage that would achieve the closest results to the customer’s requirements. The approach developed shows how to group all the operative sources in “families”, so that the uncertainty of the “patriarch” of a family can be determined from those of its members. Obviously, whoever applies this methodology will have to use the data available at their laboratories and supplement them through experimentation.