Pre-Test Assessment of the Upper Bound of the Drag Coefficient Repeatability of a Wind Tunnel Model

Ulbrich, Norbert; L'Esperance, Alan

doi:10.2514/6.2017-0484

Cited by 1 publication

(13 citation statements)

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“…The derivation of a pre-test estimate of the precision error of the drag coefficient of a wind tunnel model is discussed in detail in Ref. [1]. Therefore, only the most important assumptions related to definition and calculation of the precision error estimate are reviewed in this section.…”

Section: Precision Error Assessmentmentioning

confidence: 99%

“…The authors developed a new method in 2016 that computes a pre-test estimate of the upper bound of the precision error of the drag coefficient of a wind tunnel model so that the "repeatability" of the drag coefficient during a wind tunnel test can be assessed (for more detail see Ref. [1]). The upper bound is defined as a "conservative" estimate of the contribution of (i) the precision error of the angle of attack measurement and of (ii) physical characteristics of the strain-gage balance.…”

Section: Introductionmentioning

confidence: 99%

“…⇒ Conclusion 1: The contribution of the uncertainty of the dynamic pressure measurement is less that one drag "count" for most of the dynamic pressure range of a typical subsonic/transonic production wind tunnel (see Ref. [1], p. 6). ⇒ Conclusion 2: The authors' method examines drag coefficient differences between "repeat" points; consequently, the precision error contribution associated with the use of a multivariate regression model of the balance calibration data for the load prediction can be neglected (the contribution will practically be identical for pairs of repeat points assuming that identical sets of electrical outputs are used for the prediction of the balance loads).…”

Section: Introductionmentioning

confidence: 99%

“…⇒ Conclusion 3: Drag coefficient differences between sets of repeat points must primarily be associated with the precision error of the angle of attack measurement; this error can indirectly be "observed" as small differences between long-term averages of corresponding balance gage outputs of sets of repeat points; the authors relate this contribution to an empirical gage output variation of one microV/V (for more detail see Ref. [1], pp. 7-10).…”

Section: Introductionmentioning

confidence: 99%

“…Similarly, it is sometimes useful to plot analysis results versus Reynolds number and total pressure (see Ref. [1]). Recently, it was also decided to plot analysis results versus angle of attack and Mach number while keeping the total pressure constant.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Strain-Gage Balance Characteristics on the Precision Error of the Drag Coefficient

Ulbrich

L'Esperance

2019

AIAA Scitech 2019 Forum

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Improvements and results of a new method are presented that computes a pre-test estimate of the precision error of the drag coefficient of a wind tunnel model. The error estimate is defined as the part of the drag coefficient's precision error that is primarily associated with the precision error of the angle of attack measurement and physical characteristics of the chosen strain-gage balance. The method indirectly describes the precision error of the angle of attack measurement by using an assumed balance gage output variation of one microV/V. The physical characteristics of the balance, on the other hand, are described by partial derivatives of the axial and normal forces with respect to the strain-gage outputs. These derivatives can directly be obtained from the data reduction matrix of the balance. The precision error estimate itself is calculated by applying a simple explicit equation that uses the model reference area, the dynamic pressure, the angle of attack, the coefficients of the linear terms of the data reduction matrix, and the electrical output variation of one microV/V as input. Precision errors at constant angle of attack may be visualized as contour plots by plotting them, for example, versus the Mach number and the total pressure. Characteristics of NASA's MC60E balance are used in combination with the reference area of a generic wind tunnel model in order to demonstrate that error estimates are independent of both the balance load format and the units chosen for the description of balance loads, model reference area, and the dynamic pressure. Finally, experimental data from a wind tunnel test of the Ames Check Standard Model in the NASA Ames 11-ft Transonic Wind Tunnel illustrates the application of the method to real-world test data.

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Section: Precision Error Assessmentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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