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  • 1
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    The Modern Design of Experiments: A Technical and Marketing Framework (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A new wind tunnel testing process under development at NASA Langley Research Center, called Modern Design of Experiments (MDOE), differs from conventional wind tunnel testing techniques on a number of levels. Chief among these is that MDOE focuses on the generation of adequate prediction models rather than high-volume data collection. Some cultural issues attached to this and other distinctions between MDOE and conventional wind tunnel testing are addressed in this paper.
    Keywords: Aerodynamics
    Type: AIAA Paper 2000-2691 , Advanced Measurement Technology and Ground Testing; Jun 19, 2000 - Jun 22, 2000; Denver, CO; United States
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  • 2
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    A Factorial Data Rate and Dwell Time Experiment in the National Transonic Facility (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This report is an introductory tutorial on the application of formal experiment design methods to wind tunnel testing, for the benefit of aeronautical engineers with little formal experiment design training. It also describes the results of a Study to determine whether increases in the sample rate and dwell time of the National Transonic Facility data system Would result in significant changes in force and moment data. Increases in sample rate from 10 samples per second to 50 samples per second were examined, as were changes in dwell time from one second per data point to two seconds. These changes were examined for a representative aircraft model in a range of tunnel operating conditions defined by angles of attack from 0 deg to 3.8 degrees, total pressure from 15.0 psi to 24.1 psi, and Mach numbers from 0.52 to 0.82. No statistically significant effect was associated with the change in sample rate. The change in dwell time from one second to two seconds affected axial force measurements, and to a lesser degree normal force measurements. This dwell effect comprises a "rectification error" caused by incomplete cancellation of the positive and negative elements of certain low frequency dynamic components that are not rejected by the one-Hz low-pass filters of the data system. These low frequency effects may be due to tunnel circuit phenomena and other sources. The magnitude of the dwell effect depends on dynamic pressure, with angle of attack and Mach number influencing the strength of this dependence. An analysis is presented which suggests that the magnitude of the rectification error depends on the ratio of measurement dwell time to the period of the low-frequency dynamics, as well as the amplitude of the dynamics The essential conclusion of this analysis is that extending the dwell time (or, equivalently, replicating short-dwell data points) reduces the rectification error.
    Keywords: Aerodynamics
    Type: AIAA Paper 2000-0828 , 38th Aerospace Sciences Meeting and Exhibit; Jan 10, 2000 - Jan 13, 2000; Reno, NV; United States
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  • 3
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    Check-Standard Testing Across Multiple Transonic Wind Tunnels with the Modern Design of Experiments (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper reports the result of an analysis of wind tunnel data acquired in support of the Facility Analysis Verification & Operational Reliability (FAVOR) project. The analysis uses methods referred to collectively at Langley Research Center as the Modern Design of Experiments (MDOE). These methods quantify the total variance in a sample of wind tunnel data and partition it into explained and unexplained components. The unexplained component is further partitioned in random and systematic components. This analysis was performed on data acquired in similar wind tunnel tests executed in four different U.S. transonic facilities. The measurement environment of each facility was quantified and compared.
    Keywords: Aerodynamics
    Type: NF1676L-14983 , 28th AIAA Aerodynamic Measurement Technology, Ground Testing, and Flight Testing Conference; Jun 25, 2012 - Jun 28, 2012; New Orleans, LA; United States
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  • 4
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    A Practical Methodology for Quantifying Random and Systematic Components of Unexplained Variance in a Wind Tunnel (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper documents a check standard wind tunnel test conducted in the Langley 0.3-Meter Transonic Cryogenic Tunnel (0.3M TCT) that was designed and analyzed using the Modern Design of Experiments (MDOE). The test designed to partition the unexplained variance of typical wind tunnel data samples into two constituent components, one attributable to ordinary random error, and one attributable to systematic error induced by covariate effects. Covariate effects in wind tunnel testing are discussed, with examples. The impact of systematic (non-random) unexplained variance on the statistical independence of sequential measurements is reviewed. The corresponding correlation among experimental errors is discussed, as is the impact of such correlation on experimental results generally. The specific experiment documented herein was organized as a formal test for the presence of unexplained variance in representative samples of wind tunnel data, in order to quantify the frequency with which such systematic error was detected, and its magnitude relative to ordinary random error. Levels of systematic and random error reported here are representative of those quantified in other facilities, as cited in the references.
    Keywords: Aerodynamics
    Type: AIAA Paper 2012-0764 , NF1676L-14030 , 50th AIAA Aerospace Sciences Meeting and Exhibit; Jan 09, 2012 - Jan 12, 2012; Nashville, TN; United States
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  • 5
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    Uncertainty of Videogrammetric Techniques used for Aerodynamic Testing (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The uncertainty of videogrammetric techniques used for the measurement of static aeroelastic wind tunnel model deformation and wind tunnel model pitch angle is discussed. Sensitivity analyses and geometrical considerations of uncertainty are augmented by analyses of experimental data in which videogrammetric angle measurements were taken simultaneously with precision servo accelerometers corrected for dynamics. An analysis of variance (ANOVA) to examine error dependence on angle of attack, sensor used (inertial or optical). and on tunnel state variables such as Mach number is presented. Experimental comparisons with a high-accuracy indexing table are presented. Small roll angles are found to introduce a zero-shift in the measured angles. It is shown experimentally that. provided the proper constraints necessary for a solution are met, a single- camera solution can he comparable to a 2-camera intersection result. The relative immunity of optical techniques to dynamics is illustrated.
    Keywords: Aerodynamics
    Type: AIAA Paper 2002-2794 , 22nd AIAA Aerodynamic Measurement Technology and Ground Testing Conference; Jun 24, 2002 - Jun 26, 2002; Saint Louis, MO; United States
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  • 6
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    Fractional Factorial Experiment Designs to Minimize Configuration Changes in Wind Tunnel Testing (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper serves as a tutorial to introduce the wind tunnel research community to configuration experiment designs that can satisfy resource constraints in a configuration study involving several variables, without arbitrarily eliminating any of them from the experiment initially. The special case of a configuration study featuring variables at two levels is examined in detail. This is the type of study in which each configuration variable has two natural states - 'on or off', 'deployed or not deployed', 'low or high', and so forth. The basic principles are illustrated by results obtained in configuration studies conducted in the Langley National Transonic Facility and in the ViGYAN Low Speed Tunnel in Hampton, Virginia. The crucial role of interactions among configuration variables is highlighted with an illustration of difficulties that can be encountered when they are not properly taken into account.
    Keywords: Aerodynamics
    Type: AIAA Paper 2002-0746 , 40th AIAA Aerospace Sciences Meeting and Exhibit; Jan 14, 2002 - Jan 17, 2002; Reno, NV; United States
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  • 7
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    Wind Tunnel Database Development using Modern Experiment Design and Multivariate Orthogonal Functions (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A wind tunnel experiment for characterizing the aerodynamic and propulsion forces and moments acting on a research model airplane is described. The model airplane called the Free-flying Airplane for Sub-scale Experimental Research (FASER), is a modified off-the-shelf radio-controlled model airplane, with 7 ft wingspan, a tractor propeller driven by an electric motor, and aerobatic capability. FASER was tested in the NASA Langley 12-foot Low-Speed Wind Tunnel, using a combination of traditional sweeps and modern experiment design. Power level was included as an independent variable in the wind tunnel test, to allow characterization of power effects on aerodynamic forces and moments. A modeling technique that employs multivariate orthogonal functions was used to develop accurate analytic models for the aerodynamic and propulsion force and moment coefficient dependencies from the wind tunnel data. Efficient methods for generating orthogonal modeling functions, expanding the orthogonal modeling functions in terms of ordinary polynomial functions, and analytical orthogonal blocking were developed and discussed. The resulting models comprise a set of smooth, differentiable functions for the non-dimensional aerodynamic force and moment coefficients in terms of ordinary polynomials in the independent variables, suitable for nonlinear aircraft simulation.
    Keywords: Aerodynamics
    Type: AIAA Paper 2003-0653 , 41st AIAA Aerospace Sciences Meeting and Exhibit; Jan 06, 2003 - Jan 09, 2003; Reno, NV; United States
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  • 8
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    Estimation of Supersonic Stage Separation Aerodynamics of Winged-Body Launch Vehicles Using Response Surface Methods (2008)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A collection of statistical and mathematical techniques referred to as response surface methodology was used to estimate the longitudinal stage separation aerodynamic characteristics of a generic, bimese, winged multi-stage launch vehicle configuration using data obtained on small-scale models at supersonic speeds in the NASA Langley Research Center Unitary Plan Wind Tunnel. The simulated Mach 3 staging was dominated by multiple shock wave interactions between the orbiter and booster vehicles throughout the relative spatial locations of interest. This motivated a partitioning of the overall inference space into several contiguous regions within which the separation aerodynamics were presumed to be well-behaved and estimable using cuboidal and spherical central composite designs capable of fitting full second-order response functions. The primary goal was to approximate the underlying overall aerodynamic response surfaces of the booster vehicle in belly-to-belly proximity to the orbiter vehicle using relatively simple, lower-order polynomial functions that were piecewise-continuous across the full independent variable ranges of interest. The quality of fit and prediction capabilities of the empirical models were assessed in detail, and the issue of subspace boundary discontinuities was addressed. The potential benefits of augmenting the central composite designs to full third order using computer-generated D-optimality criteria were also evaluated. The usefulness of central composite designs, the subspace sizing, and the practicality of fitting low-order response functions over a partitioned inference space dominated by highly nonlinear and possibly discontinuous shock-induced aerodynamics are discussed.
    Keywords: Aerodynamics
    Type: 26th Congress of International Council of the Aeronautical Sciences (ICAS 2008); Sep 14, 2008 - Sep 19, 2008; Anchorage, AK; United States
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  • 9
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    Comparison of Force and Moment Coefficients for the Same Test Article in Multiple Wind Tunnels (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper compares the results of force and moment measurements made on the same test article and with the same balance in three transonic wind tunnels. Comparisons are made for the same combination of Reynolds number, Mach number, sideslip angle, control surface configuration, and angle of attack range. Between-tunnel force and moment differences are quantified. An analysis of variance was performed at four unique sites in the design space to assess the statistical significance of between-tunnel variation and any interaction with angle of attack. Tunnel to tunnel differences too large to attribute to random error were detected were observed for all forces and moments. In some cases these differences were independent of angle of attack and in other cases they changed with angle of attack.
    Keywords: Aerodynamics
    Type: NF1676L-16794 , AIAA Ground Testing Conference; Jun 24, 2013 - Jun 27, 2013; San Diego, CA; United States
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  • 10
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    Experimental Optimization of a Free-to-Rotate Wing for Small UAS (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper discusses an experimental investigation conducted to optimize a free-to-rotate wing for use on a small unmanned aircraft system (UAS). Although free-to-rotate wings have been used for decades on various small UAS and small manned aircraft, little is known about how to optimize these unusual wings for a specific application. The paper discusses some of the design rationale of the basic wing. In addition, three main parameters were selected for "optimization", wing camber, wing pivot location, and wing center of gravity (c.g.) location. A small apparatus was constructed to enable some simple experimental analysis of these parameters. A design-of-experiment series of tests were first conducted to discern which of the main optimization parameters were most likely to have the greatest impact on the outputs of interest, namely, some measure of "stability", some measure of the lift being generated at the neutral position, and how quickly the wing "recovers" from an upset. A second set of tests were conducted to develop a response-surface numerical representation of these outputs as functions of the three primary inputs. The response surface numerical representations are then used to develop an "optimum" within the trade space investigated. The results of the optimization are then tested experimentally to validate the predictions.
    Keywords: Aerodynamics
    Type: AIAA Paper 2014-2273 , NF1676L-17724 , AIAA Applied Aerodynamics Conference; Jun 16, 2014 - Jun 20, 2014; Atlanta, GA; United States
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