American Institute of Aeronautics and Astronautics1

Wing Deformation Measurements of the DLR-F6 TransportConfiguration in the National Transonic Facility

Alpheus W. Burner1

William K. Goad2

Edward A. Massey3

Linda R. Goad4

Scott L. Goodliff5

Owen W. Bissett6

Rome Group NASA Langley Research Center, Hampton, Virginia 23681

Wing deformation measurements are presented for the DLR-F6 TransportConfiguration tested in the National Transonic Facility. Induced wing twist and deflectiondue to aerodynamic loading were measured at five spanwise stations. All data were acquiredat 40° F using nitrogen as the test gas at chord Reynolds numbers of 3 and 5 million and atMach numbers of 0.6 to 0.77, with the majority of the data at Mach = 0.75. Most of the datawere reduced using the single-view photogrammetry technique on the right (starboard)wing. An unexpected behavior of flow-induced outboard wing twist measurements at lowvalues of lift coefficient prompted facility personnel to conduct both a static loadingexperiment and a limited repeat wind-on test at 3 million Reynolds Number and Mach =0.75 approximately two months after the conclusion of the original test. For both the staticand repeat wind-on tests, measurements were made on both wings. The static loadingexperiment, which used both single-view and two-view photogrammetry (or stereo-photogrammetry), validated the experimental techniques with comparisons to precisioninclinometers and digital indictors for independent measurements of static induced twist anddeflection. Test-to-test precision (separated by two months) was found to be comparable torun-to-run precision within a single test. Although some deformation differences were foundbetween the right and left wing, both wings tended to have more induced (negative) wingtwist at the low values of lift coefficient than expected. In both the static experiment andrepeat wind-on test the results from the single-view and two-view photogrammetrictechniques were found to be comparable.

NomenclatureAMS = Angle Measurement Systemb = spanCL = lift coefficientFOV = camera field of viewLWn = cameras viewing upper surface of left wing (n = 1 or 2)M = Mach numberNdata = number of data pointsq = dynamic pressureRe = Reynolds number, based on chordRSS = root-sum-squareRWn = cameras viewing upper surface of right wing (n = 1 or 2)

1 Senior Engineer, ROME Jacobs Technology, M/S 267, Associate Fellow AIAA.2 Senior Technician, ROME Jacobs Technology, M/S 267.3 Engineer, ROME Jacobs Technology, M/S 267.4 Senior Technician, ROME Tessada, M/S 267.5 Test Engineer, ROME Jacobs Technology, M/S 267, Senior Member AIAA.6 NTF Facility Manager, ROME Jacobs Technology, M/S 267, Member AIAA.

26th AIAA Applied Aerodynamics Conference18 - 21 August 2008, Honolulu, Hawaii

AIAA 2008-6921

Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc.The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes.All other rights are reserved by the copyright owner.

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TE = trailing edge of wingWB = wing/body configurationWBF = wing/body/faring configurationWBPN = wing/body/pylon/nacelle configurationX = spatial coordinate parallel to the flow directionY = spatial coordinate parallel to the model spanZ = spatial coordinate parallel to the vertical directionη = normalized semispan = Y / b / 2∆θ = flow-induced wing twist∆Z = flow-induced vertical wing deflection at trailing edge

I. IntroductionThe true shape of the model configuration under wind-on test conditions is needed for effective

computational validation. Since the shape of the model can change under aerodynamic loading, it is advantageous tomeasure and correct for this change in shape during wind tunnel testing. This is especially so in pressurized facilitieslike the National Transonic Facility (NTF). A model deformation measurement capability has thus existed at theNTF for over 10 years1. The predominant technique used for these measurements has been the single-viewphotogrammetric technique1,2. The technique has advantages over two-view photogrammetry when view options arelimited or when retroreflective targets are not allowed (requiring the use of diffuse targets) due to surface roughnessand step height restrictions of models. Proper illumination of diffuse targets, which can be very troublesome due totarget-like glints from the highly-reflective mirror-like surface of some models, is less challenging for a single viewthan for multiple camera views of the model. The single-view technique has been used at a number of wind tunneland aerospace facilities3,4 in addition to in-flight measurements of aircraft5. Early in the history of modeldeformation measurements at the NTF, differences between measured and computed deformation led to a staticloading experiment6 conducted in the test section. During this experiment both wings of the model were staticallyloaded in order to compare both optical measurements and computed values of induced twist to referencemeasurements based on precision inclinometers. In that experiment the optically measured values were found toagree better to the reference measurements than the computed predictions. In the most recent test7 (NTF designation179) of the DLR-F6 model transport configuration undertaken in support of the Third AIAA Drag PredictionWorkshop8, similar discrepancies between experimental measurements and computational predictions promptedfacility personnel to conduct both a static loading test to estimate bias errors, and a limited repeat wind-on test todetermine test-to-test precision (at Re = 3 × 106 only). These tests were conducted approximately two months afterthe conclusion of the original main data test. Further discussions of the static simulation and comparison toexperimental data can be found in reference 9. Because of this discrepancy between experiment and computation, anexpanded discussion is presented of the uncertainty of the experimental techniques. The results of the static loadingtest are summarized here along with the model deformation data at M = 0.75 from the original Test 179 and a repeatwind-on test (NTF designation 186).

II. National Transonic FacilityThe National Transonic Facility, or NTF, is the world's largest pressurized, cryogenic wind tunnel (Fig. 1). Its

unique capabilities enable testing of scaled models at flight Reynolds numbers in support of advanced aerodynamicconcept development and assessment, advanced computational fluid dynamics tool validation, and risk reduction forvehicle development. The test section has 12 slots and 14 reentry flaps in the ceiling and floor to prevent any near-sonic flow “choking” effect. The drive system consists of a fan with variable inlet guide vanes for responsive Mach-number control.

The NTF has two primary modes of cooling. In the first mode liquid nitrogen is sprayed into the circuit. The heatof vaporization and latent heat cools the tunnel structure and dissipates fan heat. In this mode, the NTF provides full-scale-flight Reynolds numbers without having to increase the model size. In the second mode ambient-temperatureair is utilized as the test gas. Fan heat is removed by chilled water that flows through a cooling coil. The NTF canextend the air mode envelope by operating in a mixed mode and injecting liquid nitrogen for additional cooling.

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Test Chamber Dimensions• Height: 8.2 feet• Width: 8.2 feet• Length: 25 feet

Performance and Capability• Speed: Mach 0.2 to 1.2• Reynolds Number: 4 x 106 to 145 x 106 per foot• Pressure: 15 to 130 lbs. per square inch• Temperature: -250 to 120°F• Test Gas: Nitrogen and ambient atmosphere• Area: 66.8 square feet• Circuit Length: 497 feet• Contraction Area Ratio: 14.95:1• Drive Power: 135,000 horsepower

III. ModelThe DLR-F6 test article (Fig. 2) is a full-span model of a generic transport aircraft designed and built by DLR10.

Twelve video model deformation targets (Fig. 3) were applied to the upper surface of the right wing and fuselage(and a matching set applied two months later to the left wing for the repeat tests). The wing target pairs were locatedat mean normalized semispan stations η = 0.2775, 0.4497,0.5596, 0.7297, and 0.9497. (The η-stations are designatedas 0.28, 0.45, 0.56, 0.73, 0.95 in the rest of this paper.) Twotargets on the body were used as a reference for the otherten wing targets in order to partially account for stingbending and deflection under aerodynamic load. All targetswere applied with DuPont latex primer and polished to aheight less than 1 mil (0.001 inch). To increase the contrastof each target, half-inch diameter black rings were paintedaround the 0.25-inch diameter white targets (Fig. 4). Aspecial masking procedure ensured there was a gradual riseinstead of an abrupt step height at the target edges. Thesurface roughness of the polished paint targets wasestimated to be less than 20 µinch. The semispan locationsfor the set of targets applied two months later to the left

Figure 1. Aerial View of the U.S. NationalTransonic Facility.

Figure 2. DLR-F6 model in the NTF test section.

Body

η = 0.278

η = 0.450

η = 0.560

η = 0.730

η = 0.950

Body

η = 0.278

η = 0.450

η = 0.560

η = 0.730

η = 0.950

Figure 3. Target layout on right wing. Image isfrom right wing primary data camera RW1.

Figure 4. Close-up of leading edge target onupper surface of right wing.

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wing for the repeat wind-on test matched the right-wing set to within ∆η = 0.0012 (1 standard deviation) asdetermined by photogrammetric surveys of both sets of wing targets. Based on the slopes of induced-twist anddeflection versus η for Re = 5 × 106, the variation in η between the right and left wing data sets would correspond todifferences less than 0.002° and 0.001 inch in terms of twist and deflection respectively at maximum slope.

IV. Photogrammetric Test TechniqueThe single-camera, single-view photogrammetric technique was used as the primary optical technique to reduce

the model deformation data. The technique is sometimes referred to as the videogrammetric model deformation(VMD) technique because of the common use of video-rate cameras, combined with automated image processingand single-camera, single-view photogrammetry data reduction2. (Note, however, that 10-bit digital cameras with1600 × 1200 pixels were used to acquire images for this application.) With the technique, image plane coordinatesare converted to 2D object plane coordinates (which are typically parallel to the flow and the vertical direction)given various camera parameters such as location, pointing angles, lens camera constant, and distortion coefficients.A requirement when using the technique is that one of the three spatial coordinates must be known to allow for asingle-camera, single-view photogrammetric solution. For pitch-sweep tunnel tests without roll, the knowncoordinate is most often the spanwise locations of the targets, which, while remaining constant as the model ispitched without flow, can vary slightly because of flow-induced wing deflection. The effects of this error in theknown spanwise coordinates on the measurement of flow-induced aeroelastic wing twist using the single-viewtechnique are discussed in reference 11. There it is noted that the error is generally small and negligible for targets ata given spanwise location since those targets experience similar deflection and hence have similar biases, whichlargely cancel in the differencing that is used in the induced twist angle computation. However, reference 11 pointsout that the error in angle measurements for control surfaces deflected at large angles can be significant if notcorrected with the methods presented there.

The more standard two-view photogrammetric technique (sometimes referred to as stereo photogrammetry)utilizes two separated cameras that view the object of interest. The two-view technique does not require one of thespatial coordinates to be known, thus eliminating that potential contribution to the error. However, at facilities suchas the NTF where surface finish and step-height restrictions preclude the use of retro-reflective targets andillumination options are limited, the single-view technique has considerable operational advantages over the two-view technique and is more amenable to automation. Both the original and repeat wind-on tests, as well as the staticloading test, employed additional cameras to provide for both single-view and two-view photogrammetric results fora limited set of data. Using both techniques allowed for comparisons of the two techniques as well as increased theconfidence in the results. Both techniques utilize image processing to obtain image coordinates, which are thentransformed to either 2D (for single-view) or 3D coordinates (for two-view)2.

For this application 10-bit Dalsa Pantera 2M30 charge-couple device digital cameras with 1600 × 1200pixels were used to acquire images at a maximum rate of 15 images per second. For most of the data 15 images wereacquired over 1 second and written to disc. Note that each data point requires 58 Mbytes of storage capacity percamera. Since this was only the secondproduction test using newly installedhigh-resolution digital cameras andaccompanying custom software, allimages were saved, unlike previoustests with video-rate lower resolutioncameras where the standard procedurewas to reduce data for each pointwithout storing image sequences. Thestorage of all images for this test wasalso necessary to allow for additionalimage processing necessary for theextra view of the two-view datareductions. The original test (Test 179)employed two of these camerasmounted on the left (port) nearside testsection wall (closest to control room)to view the upper surface of the right(starboard) wing. For the static loading

LW1, LW2

Farwall

Nearwall

RW1, RW2

Z

YFlow (X)

toward viewer

LW1, LW2

Farwall

Nearwall

RW1, RW2

Z

YFlow (X)

toward viewer

Figure 5. Sketch of camera locations and coordinate system lookingupstream. Right and left wing FOVs in blue and red respectively.Cameras LW1 and LW2 only used during Test 186.

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and repeat wind-on test (Test 186) additional digital cameras mounted on the right (starboard) farside test sectionwall (farthest from control room) were used to view the left wing. A sketch of the camera locations is shown in Fig.5 with the right-wing view cameras designated as RW1 and RW2 and the left-wing view cameras designated asLW1 and LW2. The field of view (FOV) of the cameras for the right and left wings are shown in blue and redrespectively. Note that the camera pairs viewing a given wing are at the same height (34 inches) above centerlineand separated by 36 inches.

The coordinate system used for the photogrammetric measurements (also shown in Fig. 5) was approximatelycentered at the balance center with positive X in the flow direction (toward the viewer in Fig. 5), positive Y towardthe right (starboard) wingtip, and positive Z up. For both the single-view and two-view photogrammetry, the inducedwing twist, ∆θ, is the change in angle between wind-off and wind-on at each semispan station as measured in aplane parallel to the X-Z plane. The wind-on values at each semispan station are determined from polynomial leastsquares curve fits from a pair of wind-off calibration polars at the beginning and end of a given run set that bracketthe range of angle-of-attack. The optically determined wind-on body angle is subtracted at each semispan todetermine the induced twist. The vertical coordinate Z at the trailing edge is computed from the slope and interceptof the X-Z data for target pairs at each η-station, based on the distance of the trailing edge from the most-aft target.Flow-induced deflection along the trailing edge, ∆Z, is determined from wind-off to wind-on by differencing the Z-values based on curve fits at each η-station versus optically measured body angle.

A. Uncertainty of Experimental TechniquesDiscrepancies arose early in the first test (Test 179) of the DLR-F6 transport model between experimental and

computational predictions of flow-induced twist at the outboard η-stations for low values of CL. Generally the flow-induced twist for transport models is observed to vary nearly linearly with CL (or equivalently with pitch angle).However, experimental measurements of induced twist for the DLR-F6 model did not show the expected trends.Figure 6 shows the typical expected trend(for the most outboard η-station) versusmodel pitch angle for a run of a transportmodel at the NTF (Test 178) compared tothe unexpected trend for a run of theimmediately following Test 179 of theDLR-F6 model. Note that identicalequipment and experimental procedureswere used for both tests.

This unexpected behavior of theinduced twist was noted throughout Test179. This troubling discrepancy promptedfacility personnel to conduct both a staticloading experiment to estimate bias errorsand validate measurement techniques and alimited repeat wind-on test to determinetest-to-test precision (at Re = 3 × 106 only)approximately two months after theconclusion of the original data test (Test179)7. Because of this discrepancy betweenexperiment and computation, an expandeddiscussion of the uncertainty of theexperimental techniques is presented here.The uncertainty of both the single-view andtwo-view photogrammetric techniques can be taken to be the root-sum-square (RSS) of the bias and precision foreach technique. While the precision can be found from the repeatability of data acquired during testing, bias errorscan be much more difficult to quantify. Reference 12 contains further discussion of the uncertainty of the opticaltechniques used here for model deformation.

1. Bias ErrorFor the static loading experiment used to establish bias error and validate the experimental techniques, the DLR-

F6 model was reinstalled in the NTF test section (Fig. 7) approximately two months after the initial test (Test 179).

Figure 6. Comparison of induced twist measurements from Test179 (DLR model with unexpected behavior) and immediatelypreceding Test 178 (also a transport model, but with expectedbehavior) at η ≈ 0.95.

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The two digital cameras located on thenearside test section wall that were used forTest 179 were recalibrated for camerapointing angles and location since thecameras had been repositioned after Test179. Other camera parameters such asdistortion, camera constant, andphotogrammetric principal distance wereunchanged from the original test 179. A pairof similar digital cameras was installed onthe farside test section wall to enablemeasurements on the left wing forcomparison to the right wing (Fig. 5). Acommercially available digitalphotogrammetric system was used tomeasure the 3D locations of targets on bothwings and fuselage. The 3D target locationswere then used to establish locations andpointing angles in the tunnel coordinatesystem for the camera pairs that observedthe right and left wings. Since illuminationof the left wing produced objectionableglints on the right wing, the right and left wing data were not taken simultaneously, but instead taken as separateruns within a few minutes of each other.

For the static loading experiment the model was oriented at approximately 0° angle-of-attack. A 4 ft × 4 ftoptical table breadboard was placed beneath the model on hardwood blocks and leveled to provide a stable and rigidmounting surface for digital indicators mounted to contact the lower wing surfaces and body. These indicators wereused to measure vertical deflection of the most outboard target nearest the TE at η = 0.95 on both wings as well as tomeasure deflection of the centerline of the body. The optical breadboard also served as a stable base location forsmall screw jacks used to apply vertical upward loads near the wingtips of each wing. Small metal pads werebonded to the lower surface of the wings where the screw jack ball tips would contact the wings and to the uppersurfaces where the point load of the weight hangers would contact the wings. Precision accelerometers from threesets of Angle Measurement Systems (AMS)13 were also bonded to the lower surface of both wings at the three mostoutboard semispan stations (η ≈ 0.56, 0.73, and 0.95), at the centerline of the body, and to the optical table, alloriented with their primary sensitive axes parallel to the flow direction. (The AMS is a portable, accurate, threeangle measurement system consisting of a notebook computer that is attached via cable to an instrument packagethat houses three precision servo-accelerometers.) The accelerometers on the body and optical table were multiplesensor units that measured both roll and pitch. Note that polyimide film tape was placed on the wings under allbonding to protect the wing surfaces. The digital indicators had anuncertainty of better than 0.001 inch. The uncertainty of the AMSangle measurements was better than 0.005°. Alignment andplacement errors of the digital indicators and accelerometers (whichhad to be aligned to the targets on the upper wing surface frombeneath the wing) likely degraded the reference accuracy from thebest-case values listed above. Several series of screw jack andweight hanger loadings were applied to each wing. Equal amountsof deflections (for upward deflection) or weights (for downwarddeflection) were applied to each wing. The maximum induceddeflection when using screw jacks for upward deflection waslimited to 0.15 inch at η = 0.95, which was close to that expected from the Re = 3 × 106 wind-on runs at M = 0.75and pitch angle near zero. Weights applied for downward deflection were limited to 16 lbs for each wing. Theranges of induced deflection and twist for the static loading experiment are shown in Table 1 where ∆Z0.95 and ∆θ0.95

are the deflection and twist at η = 0.95, and ∆θ0.73 and ∆θ0.56 are the twist at η = 0.73 and η = 0.56 respectively.Table 2 lists the bias error observed during the static loading test. The various cameras are labeled as either right

wing (RW) or left wing (LW) as shown in Fig. 5. Camera RW1, the primary camera used for the single-view

Figure 7. Static loading setup in NTF test section.

Table 1. Minimum and maximum ofinduced deflection and twist during staticloading experiment.

min max∆Z0.95, inch -0.072 0.150∆θ0.95, deg -0.334 0.158∆θ0.73, deg -0.161 0.078∆θ0.56, deg -0.095 0.047

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technique, is located behind a window viewport on the nearside test section wall (wall closest to control room) atapproximately the model center of rotation and 34 inches above the tunnel centerline. Camera RW1 views the uppersurface of the right wing (Fig. 5). Note that since camera RW1 is located on the left test section wall (lookingupstream), the right wing tip is farther from thecamera than the fuselage. Camera RW2 is alsolocated behind the nearside test section wall atthe same height above centerline as cameraRW1, but is located 36 inches downstreamfrom camera RW1. The Cam designation RW1+ RW2 in Table 2 indicates two-viewphotogrammetry using cameras RW1 and RW2.Similar designations are used for the camerasmounted on the farside test section wall thatview the left wing. The bias errors presented inTable 2 were determined by subtracting thereference values from digital indicators andprecision inclinometers from thephotogrammetrically measured values of the load-induced deflection and twist. The bias error was taken as themaximum error encompassing 95% of the data points. The values in Table 2 under the label ∆Z0.95 represent themeasured deflection error of the most-outboard aft target located at η = 0.95. The values in Table 2 under the labels∆θ0.95, ∆θ0.73, and ∆θ0.56 represent the bias error in measuring the induced twist under static load compared toprecision inclinometers. The values under Ndata represent the number of data points for each case of the camerameasurements. Note that while the bias error for the two-view photogrammetry is marginally better for deflection,twist angle measurements are generally very slightly worse than for the single-view technique. Based on the resultsof this very limited sample, one can conclude that the single-view and two-view techniques were not substantiallydifferent in terms of bias error for the static loading test.

The optically measured deflection at the most outboard semispan station η = 0.95 versus the reference measureddeflection based on digital indicators is presented in Fig. 8 for primary camera RW1. Similar plots of the opticallymeasured induced twist versus the reference measured twist from inclinometers for the most outboard semispanstations at η = 0.95, 0.73, and 0.56 are presented in Figs. 9 – 11. In these figures the red lines represent where thedata would fall if in perfect agreement with the reference values. Similar trends are observed for the other camerasand for the two-view photogrammetric results.

Table 2. Bias error encompassing 95% of error duringstatic loading experiment.

inch deg deg degCam(s) ∆Z0.95 ∆θ0.95 ∆θ0.73 ∆θ0.56 NdataRW1 0.0032 0.033 0.034 0.016 53RW2 0.0037 0.053 0.043 0.017 64RW1 + RW2 0.0025 0.065 0.043 0.023 53LW1 0.0022 0.055 0.014 0.031 75LW2 0.0026 0.081 0.016 0.030 79LW1 + LW2 0.0021 0.059 0.015 0.023 75

Figure 8. Optically measured deflection of trailing-edge outboard target (η = 0.95) versus referencemeasurement based on digital indicator duringstatic loading experiment. Red line representsperfect agreement with reference.

Figure 9. Optically measured induced twist of mostoutboard station (η = 0.95) versus referencemeasurement based on inclinometer during staticloading experiment. Red line represents perfectagreement with reference.

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2. PrecisionThe precision of individual data points is determined by computing the 95% precision prediction intervals of the

original and repeat wind-on runs (three runs from each test) from Tests 179 and 186 separately as well as combinedbased on third-order polynomial least squares fits. The results for Re = 3 × 106, M = 0.75, and q = 832 psf arepresented in Table 3 for deflection and Table 4 for flow-induced twist at the 5 η-stations on the wing. (The intervalspresented are the maximumof the computed values ofthe prediction intervals thatoccur at the extremes of therange of angle-of-attack,generally < -3.5° or > 1°.Slightly lower values of 5 to10% are computed over themidrange of angle-of-attackfrom -3.5° to 1°.) The labelsT179 and T186 represent three repeat runs each during Tests 179 and 186 whereas label T179 + T186 represents thecombined results of the six runs from both tests. The column Ndata contains the number of data points used in thecomputation of the prediction interval.

Note that the precision prediction interval for deflection is approximately four times the bias error observedduring the static loading test for the most outboard η-station. Thus the precision component of the uncertaintydominates. For instance, the RSS of the bias and precision for camera RW1 at the most outboard semispan station atη = 0.95 is 0.0126 inch compared to the precision interval alone of 0.0122 inch. It is expected that the bias errordecreases as η decreases (moves toward fuselage) due to the smaller range of inboard deformation so that theprecision will also likely dominate the uncertainty of deflection measurements at all η-stations. Unlike fordeflection, the precision predictionintervals for twist are generallymarginally smaller than the bias errorsfound in the static loading test.

If least squares curve fits are used todescribe the data then it is moreappropriate to use the confidenceinterval of the curve fit as a measure ofthe precision of the fit rather than theprediction interval. The 95% confidence

Figure 10. Optically measured induced twist atη = 0.73 versus reference measurement based oninclinometer during static loading experiment.Red line represents perfect agreement withreference.

Figure 11. Optically measured induced twist atη = 0.56 versus reference measurement based oninclinometer during static loading experiment.Red line represents perfect agreement withreference.

Table 3. Precision prediction intervals (95%) when measuring flow-induced deflection during wind-on testing at 3-million Reynolds number.

inch inch inch inch inch∆Z0.95 ∆Z0.73 ∆Z0.56 ∆Z0.45 ∆Z0.28 Ndata

T179 0.0122 0.0094 0.0074 0.0060 0.0043 73T186 0.0083 0.0062 0.0049 0.0041 0.0030 47T179 + T186 0.0115 0.0081 0.0063 0.0052 0.0043 120

Table 4. Precision prediction intervals (95%) when measuringflow-induced twist during wind-on testing at 3-million Reynoldsnumber.

deg deg deg deg deg∆θ0.95 ∆θ0.73 ∆θ0.56 ∆θ0.45 ∆θ0.28 Ndata

T179 0.030 0.016 0.011 0.012 0.012 73T186 0.033 0.028 0.019 0.015 0.009 47T179 + T186 0.032 0.024 0.017 0.015 0.013 120

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intervals for deflection andtwist are presented in Tables5 and 6 for the same data asthe previous two tables. (Theintervals presented are themaximum of the computedvalues of the confidenceintervals that occur at theextremes of the range ofangle-of-attack, generally < -3.5° or > 1°. The confidence levels are reduced by more than one-half over the midrange of angle-of-attack from -3.5° to 1°.) When using least squares curve fits the bias error and precision for deflection are comparable, whereasthe bias component dominates the twist uncertainty.

3. UncertaintyThe estimated uncertainties for the primary camera RW1 at Re = 3 × 106 are plotted in Figs. 12 and 13 versus η

for cases when either individual data points, or least squares curve fits are used to describe the data. The uncertaintycomputations are based on theRSS of the bias errors determinedfrom the static loading experimentand the precision as determinedfrom repeat runs. Since deflectionbias error was only determined forthe most outboard semispanstation, that value of bias (0.0032inch) was used for the mostinboard stations as well. The biaserrors for twist for semispanstations at η = 0.45 and 0.28 were taken to be equal to the bias error of 0.016° found at η = 0.56 during the staticloading experiment.

It should be noted that for the uncertainties shown in Figs. 12 and 13 the bias component is based on the staticloading experiment. Even though the ranges of deflection and twist were similar to that experienced during thewind-on runs (at Re = 3 × 106) and the experiment was conducted in the NTF test section, there are a number ofdifferences between the static experiment and the wind-on runs. For instance, during the static loading experimentthe temperature varied between 66 and 70° F, whereas the wind-on runs are conducted at 40° F. The static

Table 5. Confidence intervals (95%) when measuring flow-induceddeflection during wind-on testing at 3-million Reynolds number.

inch inch inch inch inch∆Z0.95 ∆Z0.73 ∆Z0.56 ∆Z0.45 ∆Z0.28 Ndata

T179 0.0049 0.0038 0.0030 0.0024 0.0017 73T186 0.0039 0.0029 0.0023 0.0019 0.0014 47T179 + T186 0.0040 0.0028 0.0022 0.0018 0.0015 120

Table 6. Confidence intervals (95%) when measuring flow-inducedtwist during wind-on testing at 3-million Reynolds number.

deg deg deg deg deg∆θ0.95 ∆θ0.73 ∆θ0.56 ∆θ0.45 ∆θ0.28 Ndata

T179 0.012 0.006 0.004 0.005 0.005 73T186 0.015 0.013 0.009 0.007 0.004 47T179 + T186 0.008 0.008 0.006 0.005 0.005 120

Figure 13. Estimated uncertainty in inducedtwist for primary camera used in single-viewtechnique based on static loading and repeat wind-on runs at Re = 3 × 106.

Figure 12. Estimated uncertainty in deflectionfor primary camera used in single-view techniquebased on static loading and repeat flow runs at Re= 3 × 106.

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experiment was conducted at ambient pressure in air, whereas the flow runs were conducted at a total pressure of upto 41 psia in nitrogen. Also note that possible additional bias errors caused by flow field optical effects would likelyinflate the bias errors from that observed during the static loading experiment, especially for tests with cryogenicoperation at very low temperatures and high pressure. The constant and relatively mild temperature of 40° F for themodel deformation data presented here reduces potential error sources that are dependent on temperature-extremesthat may be present in full cryogenic tests. For such tests, with an operating range from above ambient down tocryogenic temperatures (temperature change of over 350° F), the uncertainty would likely increase from the valuespresented here.

B. Comparison of Single-View and Two-View Photogrammetry ResultsA comparison of right-wing results from single-view and two-view photogrammetry for the static loadingexperiment is presented in Table 7. The means and standard deviations of the differences between the twotechniques for 53 data points are presented. Similar wind-on data for 69 data points at Re = 3 × 106, M = 0.75, and q= 832.3 psf are presented in Table 8 for flow-induced twist and Table 9 for deflection. For both the static loadingand wind-on repeat runs, the differences between the two techniques is generally less than the uncertainty of eithertechnique.

V. Model Deformation Results

A. Re = 3 × 106 Deformation ResultsFlow-induced twist versus CL is presented in Fig. 14 for Re = 3 × 106 at the five semispan stations η for three

runs of the wing/body configuration. The Mach number M was 0.75 and the dynamic pressure q was 832.2 psf. Thethree runs presented in Fig. 14 were from the first test 179. (Repeat data for this same configuration and conditionsare presented in section C entitled “Comparison of Right-Wing and Left-Wing Deformation”.) Note that the inboardη-stations exhibit the expected behavior of more negative induced twist as CL increases, but that the outboard η-stations exhibit unusual behavior. For the most outboard station at η = 0.95, the induced-twist is relativelyindependent of CL, which was not expected. This troubling behavior of the outboard η-stations repeated throughoutTest 179 as well as for the repeat Test 186 conducted two months later. The corresponding wing deflection along thetrailing edge is presented in Fig. 15 for the same three runs used for Fig. 14. The wing deflection behavior is typicalof that seen for transport models. It is unclear why the wing deflection exhibits expected behavior while the induced-twist data does not.

Table 7. Differences in single-view and two-view photogrammetry for induced deflectionand twist during static loading experiment.

mean std dev∆Z0.95, inch 0.0001 0.0006∆θ0.95, deg 0.009 0.031∆θ0.73, deg 0.005 0.015∆θ0.56, deg 0.001 0.009

Table 9. Differences in flow-induced deflection, ∆Z, between single-view and two-view photogrammetryduring wind-on testing for 69 points at 3-million Reynolds number.

inch inch inch inch inch∆Z0.95 ∆Z0.73 ∆Z0.56 ∆Z0.45 ∆Z0.28

mean 0.0013 0.0012 0.0008 0.0008 0.0002std dev 0.0058 0.0045 0.0036 0.0030 0.0022

Table 8. Differences in flow-induced twist, ∆θ,between single-view and two-view photogrammetryduring wind-on testing for 69 points at 3-millionReynolds number.

deg deg deg deg deg∆θ0.95 ∆θ0.73 ∆θ0.56 ∆θ0.45 ∆θ0.28

mean 0.002 0.001 0.010 0.006 0.010std dev 0.008 0.014 0.064 0.007 0.010

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Flow-induced twist and deflection versus η at four values of CL are presented in Figs. 16 and 17 for one of thethree runs (run # 51) plotted in Figs. 14 and 15. The solid lines through the data are based on cubic splineinterpolation of the five data points for each CL. Note the possible discrepancy between the deflection and twist datafor CL = -0.014 where it was expected that the slightly negative deflection at this CL would correspond to a slightlypositive rather than negative induced wing twist. Further computational analyses are needed to either explain orcontradict this unexpected behavior at low values of CL.

The 95% confidence intervals for twist and deflection for the three runs plotted in Figs 14 and 15 are presentedin Figs. 18 and 19. The confidence intervals were computed using third-order polynomial least squares fits to thedata versus CL. These intervals represent the precision of the least squares curve fit. Any unknown bias errors are, ofcourse, unaccounted for. See Tables 5 and 6 for numerical values (maximums) of the confidence intervals.

Figures 20 and 21 present comparisons of three of the configurations tested at Re = 3 × 106 in terms of inducedtwist and deflection versus CL. These three configurations were wing/body (WB), wing/body/fairing (WBF), andwing/body/pylon/nacelle (WBPN) with M = 0.75 and q = 832.3 psf. The line plots are based on third-order leastsquares fits to the data from three repeat runs at each configuration. Although very little difference is noted inboard

Figure 14. Flow-induced twist at Re = 3 × 106

and M = 0.75 for various semispan stations, η(three runs of wing/body configuration).

Figure 15. Flow-induced wing deflection at thetrailing edge at Re = 3 × 106 and M = 0.75 forvarious semispan stations, η (three runs ofwing/body configuration).

Figure 16. Flow-induced twist versus η at Re = 3× 106 and M = 0.75 for the single run 51 of thewing/body configuration during Test 179 for fourvalues of CL. The solid lines through the data arebased on cubic spline interpolation of the five datapoints for each CL.

Figure 17. Flow-induced deflection versus η atRe = 3 × 106 and M = 0.75 for the single run 51 ofthe wing/body configuration during Test 179 forfour values of CL. The solid lines through the dataare based on cubic spline interpolation of the fivedata points for each CL.

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for the three configurations, the WB configuration does exhibit slightly more induced-twist at the most outboard η =0.95. The WB and WBF configurations have nearly identical deflection, with the WBPN configuration differing byaround 0.02 inch at low values of CL.

B. Re = 5 × 106 Deformation ResultsData from six repeat runs at Re = 5 × 106 for the wing/body configuration are presented in Figs. 22 and 23 versus

CL for five η-stations with M = 0.75 and q = 1389 psf. (This data set is compared to the 3-million data set in sectionD where the Re = 3 × 106 data set is scaled for comparison by the ratio of q for the 5-million data over q for the 3-million data.) Note that, very much like the 3-million data, the more inboard η-stations of the 5-million data exhibitexpected behavior of more negative induced twist as CL increases, while the more outboard η-stations exhibit theunusual behavior noted earlier. Again, like the 3-million data, the wing deflection behavior of the 5-million data istypical of that seen for transport models. It is unclear why the wing deflection exhibits expected behavior while the

Figure 18. 95% confidence intervals for flow-induced twist from three runs at Re = 3 × 106

number and M = 0.75 for various semispanstations, η (wing/body configuration).

Figure 19. 95% confidence intervals for flow-induced wing deflection at the trailing edge fromthree runs at Re = 3 × 106 and M = 0.75 for varioussemispan stations, η (wing/body configuration).

Figure 20. Least-squares curve fits (three runseach) for flow-induced twist at Re = 3 × 106 and M= 0.75 for various semispan stations, η comparingwing/body (WB), wing/body/fairing (WBF), andwing/body/pylon/nacelle (WBPN) configurations.

Figure 21. Least-squares curve fits (three runseach) for flow-induced wing deflection at thetrailing edge at Re = 3 × 106 and M = 0.75 forvarious semispan stations, η comparing wing/body(WB), wing/body/fairing (WBF), andwing/body/pylon/nacelle (WBPN) configurations.

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induced-twist data does not. Further studies are needed to determine if the unexpected behavior for induced twist hasa physical explanation (other than unexplained bias error in the induced-twist measurements at low values of CL).

Flow-induced twist and deflection versus η at four values of CL are presented in Figs. 24 and 25 for one of thesix runs (run # 106) plotted in Figs. 22 and 23. The solid lines through the data are based on cubic splineinterpolation of the five data points for each CL. Note that similarly to the 3-million Reynolds data there is a possiblediscrepancy between the deflection and twist data for CL = -0.005. For this value of CL it was expected that theslightly negative deflection would correspond to a slightly positive rather than negative induced wing twist. Again,further computational analyses are needed to either explain or contradict this unexpected behavior at low values ofCL.

Figures 26 and 27 present induced twist and deflection comparisons of the two configurations tested at Re = 5 ×106. The two configurations presented are the wing/body (WB) and wing/body/fairing (WBF) with M = 0.75 and q =1389 psf. The line plots are based on third-order least squares fits to the data from 6 repeat runs at eachconfiguration. Very little difference is noted at the most inboard and outboard stations, with the WBF configuration

Figure 22. Flow-induced twist at Re = 5 × 106

and M = 0.75 for various semispan stations, η (sixruns of wing/body configuration).

Figure 23. Flow-induced wing deflection at thetrailing edge at Re = 5 × 106 and M = 0.75 forvarious semispan stations, η (six runs of wing/bodyconfiguration).

Figure 24. Flow-induced twist versus η at Re = 5× 106 and M = 0.75 for the single run 106 of thewing/body configuration during Test 179 for fourvalues of CL. The solid lines through the data arebased on cubic spline interpolation of the five datapoints for each CL.

Figure 25. Flow-induced deflection versus η atRe = 5 × 106 and M = 0.75 for the single run 106 ofthe wing/body configuration during Test 179 forfour values of CL. The solid lines through the dataare based on cubic spline interpolation of the fivedata points for each CL.

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exhibiting slightly more induced-twist at η = 0.45, 0.56, and 0.73. The WBF configuration appears to have slightlymore deflection.

C. Comparison of Right-Wing and Left-Wing DeformationComparisons of the induced twist at Re = 3 × 106 for the right and left wings versus CL are presented in Figs. 28 -

31 for the various η-stations. The right wing data is indicated in blue and the left wing data in red. Right wingdeformation data from Test 179 (same data as Fig. 14) is indicted with blue circles. Right wing data from Test 186,which occurred two months after the conclusion of Test 179, are indicated with blue squares. Thus Figs. 28 - 31 alsoshow the test-to-test precision in addition to the right/left wing comparison. The left wing data from Test 186 isindicated with red squares. All data are for the WB configuration at M = 0.75 and q = 832.2. The left wing data weretaken with the same type camera, view geometry, and procedures used to measure the right wing. All data presentedin Figs. 28 - 31 were reduced using the single-view photogrammetry technique. (Two-view photogrammetry of bothwings during Test 186 compared well with the single-view technique, with data scatter of the two techniques withinnearly the same 95% prediction intervals.) The three runs for Test 179 contained nearly twice as many data points asthe Test 186 set of three runs. Due to differences in illumination requirements, the right and left wing data runs fromTest 186 were taken separately within a few minutes of each other. Note that the left wing exhibits less induced-twist at all η-stations (except for the most outboard station) for CL less than the maximum. At the maximum CL theleft and right wing have nearly the same induced-twist for all η-stations except for the most outboard station wherethe induced-twist of the left wing is greater than the right wing. The largest differences in induced-twist occur at CL

near zero. For the most outboard station at η = 0.95, the induced-twist for the left wing is equal to that of the rightwing at a CL around 0.3. The twist of the left wing is greater than the right wing by about 0.05° at maximum CL andless than the right wing by about 0.14° at the lowest value of CL for the most outboard station. While the left wing iscloser to the expected behavior than the right wing, the left wing still does not fully exhibit the expected behavior.For instance, typically the induced-twist would reduce to zero near CL = 0. (Note that zero induced twist would notnecessarily occur precisely at CL = 0 since the total load may be zero, but the distributed varying load on the wingcould still cause spanwise deformation.) Even though the left wing is significantly closer to the expected behaviorfor induced twist than the right wing, its behavior is still at odds with experience since the induced-twist at CL = 0 israther large at -0.25°.

Similar comparison data for the right and left wings for deflection are presented in Figs. 32 – 36 for the samedata set as for Figs. 28 – 31. The left wing exhibits less deflection as CL increases for all η-stations, with themaximum difference of 0.05 inch at the most outboard η-station at CL = 0.6. In terms of deflection, the left wingappears stiffer than the right wing for all η-stations of the wing.

Figure 26. Least-squares curve fits (six runseach) for flow-induced twist at Re = 5 × 106 and M= 0.75 for various semispan stations, η comparingwing/body (WB) and wing/body/fairing (WBF)configurations.

Figure 27. Least-squares curve fits (six runseach) for flow-induced wing deflection at thetrailing edge at Re = 5 × 106 and M = 0.75 forvarious semispan stations, η comparing wing/body(WB) and wing/body/fairing (WBF) configurations.

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Figure 28. Comparison of right (blue) and left(red) wing flow-induced twist at Re = 3 × 106 andM = 0.75 for η = 0.28 and η = 0.45. Data fromthree runs each of Tests 179 and 186 right wingand Test 186 left wing of wing/body configuration.

Figure 29. Comparison of right (blue) and left(red) wing flow-induced twist at Re = 3 × 106 andM = 0.75 for η = 0.56. Data from three runs eachof Tests 179 and 186 right wing and Test 186 leftwing of wing/body configuration.

Figure 30. Comparison of right (blue) and left(red) wing flow-induced twist at Re = 3 × 106 andM = 0.75 for η = 0.73. Data from three runs eachof Tests 179 and 186 right wing and Test 186 leftwing of wing/body configuration.

Figure 31. Comparison of right (blue) and left(red) wing flow-induced twist at Re = 3 × 106 andM = 0.95. Data from three runs each of Tests 179and 186 right wing and Test 186 left wing ofwing/body configuration.

Figure 32. Comparison of right (blue) and left(red) wing flow-induced deflection at TE at Re = 3× 106 and M = 0.75 for η = 0.28. Data from threeruns each of Tests 179 and 186 right wing and Test186 left wing of wing/body configuration.

Figure 33. Comparison of right (blue) and left(red) wing flow-induced deflection at TE at Re = 3× 106 and M = 0.75 for η = 0.45. Data from threeruns each of Tests 179 and 186 right wing and Test186 left wing of wing/body configuration.

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D. Verification with Additional End-On Wingtip (η = 1.00) ViewsAs an additional verification of the outboard twist measurements, two digital cameras were installed for an end-

on view of each wingtip for the repeat wind-on Test 186 (for a total of six digital cameras for that test) as shown inFig. 37. The 0.1 inch diameter targets for each wingtip, separated by 1.5 inch, were applied with black marking penon a painted white background as shown for the right wingtip in Fig. 38 where the flow is from right to left. Thecamera that was used to measure the right wingtip was located behind a centerline viewport on the farside testsection wall nearest the right wingtip. The camera viewed the right wingtip slightly from above (due to the DLRmodel being located below the centerline of the test section). The camera that viewed the left wingtip was similarlylocated on the opposite nearside test section wall closest to the left wingtip. These cameras were calibratedindividually with a small 2-step optical calibration fixture (consisting of a set of targets at known locations) placedin near contact with each wingtip and aligned with its coordinates parallel to the tunnel coordinate system. The twowingtip-view cameras required a third set of runs (1 set for right wing, 1 set for left wing, 1 set for wingtip views) toavoid interference from illumination for the right and left wing camera pairs that viewed the whole wing. Theseparate wingtip runs were made within a few minutes of the whole-wing right and left run sets. The image datafrom the wingtip-view cameras (Fig. 38) were degraded in contrast considerably compared to the whole-wing (Fig.3) due to inability to ideally illuminate the wingtip targets. This was also the first time that this technique had beentried at the NTF. Measurements for the wingtips show considerably more scatter than the whole-wing data and arenot considered as reliable. Their main use was to independently verify the unexpected trends for induced twist notedoutboard for low values of CL.

Figure 34. Comparison of right (blue) and left(red) wing flow-induced deflection at TE at Re = 3× 106 and M = 0.75 for η = 0.56. Data from threeruns each of Tests 179 and 186 right wing and Test186 left wing of wing/body configuration.

Figure 35. Comparison of right (blue) and left(red) wing flow-induced deflection at TE at Re = 3× 106 and M = 0.75 for η = 0.73. Data from threeruns each of Tests 179 and 186 right wing and Test186 left wing of wing/body configuration.

Figure 36. Comparison of right (blue) and left (red) wing flow-induced deflection at TE at Re = 3 × 106

and M = 0.75 for η = 0.95. Data from three runs each of Tests 179 and 186 right wing and Test 186 leftwing of wing/body configuration.

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Right-wing flow-induced twist from a wingtip camera (red symbols representing data at η = 1.00) overlaid ondata from the primary camera acquired for two runs during the repeat wind-on Test 186 is presented in Fig. 39. Theblue symbols (data at η = 0.95) represent three runs each of Test 179 and Test 186 (same data as for Fig. 31, butwithout the left wing data). The conditions were Re = 3 × 106, M = 0.75, and q = 832 psf for the wing/bodyconfiguration. The change in twist for the wingtip data was computed as the tip angle (with calibration based on twowind-off polars that bracketed the wind-on runs) minus the pitch angle from the onboard inertial sensor. The wingtipdata shows less induced twist by up to 0.1° at a CL near 0.4, but generally shows the same trend with CL that thewhole-wing data shows. A similar wingtip overlay for the left wing is presented in Fig. 40 for the same conditions asFig. 39. Figure 40 only shows Test 186, and not Test 179 data, since the left wing was not measured in Test 179.Much larger differences are noted compared to η = 0.95 (especially at high values of CL), but the general trend ofsignificant induced twist at low values of CL is still seen in the data for the left wingtip.

E. Comparison of q-scaled 3-million and 5-million Reynolds Number Deformation DataIf the 3-million and 5-million Reynolds Number data sets differ only because of the difference in dynamic

pressure and if the Re = 3 × 106 data is properly scaled for q, the two data sets should coincide. Any differencesbetween the q-scaled 3-million and 5-million data would then be either Reynolds number effects or experimentalbias error that is a function of q (or Re). The q-scaled 3-million induced-twist data along with the original 5-million

LW1, LW2

Farwall

Flow outNearwall

RW1, RW2

RtipLtip

LW1, LW2

Farwall

Flow outNearwall

RW1, RW2

RtipLtip

Figure 37. Sketch of additional right (Rtip) andleft (Ltip) wingtip camera locations used duringTest 186 (looking upstream).

Figure 38. Image from right wingtip camera.Flow is from right to left.

Figure 39. Right-wing flow-induced twist from awingtip camera (red symbols at η = 1.00) from tworuns overlaid on data from the primary cameraconsisting of three runs each of Test 179 and Test186 (blue symbols at η = 0.95) at Re = 3 × 106 andM = 0.75 for the wing/body configuration.

Figure 40. Left-wing flow-induced twist from awingtip camera (red symbols at η = 1.00) for tworuns overlaid on data from the primary cameraconsisting of three runs from Test 186 (bluesymbols at η = 0.95) at Re = 3 × 106 and M = 0.75for the wing/body configuration.

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data are plotted versus CL in Fig. 41. Third order least square fits to the data are presented in Fig. 42. The 5-milliondata are the same 6 repeat runs plotted in Figs. 22 and 23. The 3-million data is the same three repeat runs plotted inFigs. 14 and 15. The induced-twist and deflection data from Re = 3 × 106 has been scaled by the ratio of q for the 5-

million data over q for the 3-million data, or 1388.6 / 832.2 = 1.669. The Re = 5 × 106 data are plotted as bluecircles. The q-scaled Re = 3 × 106 data are plotted as red squares and labeled on the plots as “3×106(q)”. Excellentagreement within 0.01° occurs at the most inboard η-stations at η = 0.28 and η = 0.45 for induced-twist. Systematicdifferences around 0.03° which are greater than the 95% prediction intervals are noted for η = 0.56, with morevariation at higher values of CL. Differences increase to about 0.04° for η = 0.73 at mid-range values of CL.Differences approach 0.07° for the most outboard η = 0.95 at CL ≈ 0.1, but are in good agreement at CL ≈ 0.5. It is

Figure 41. Comparison of 5-million (blue circles,six runs) and q-scaled 3-million (red squares, threeruns) Reynolds number data for flow-induced twistat M = 0.75 for the η-stations (wing/bodyconfiguration). Data from 3-million Reynolds havebeen scaled by the ratio of q at 5-million over q at3-million.

Figure 42. Comparison of 5-million (blue, sixruns) and q-scaled 3-million (red, three runs)Reynolds number curve fits to the data for flow-induced twist at M = 0.75 for the η-stations(wing/body configuration). Data from 3-millionReynolds have been scaled by the ratio of q at 5-million over q at 3-million.

Figure 43. Comparison of 5-million (blue circles,six runs) and q-scaled 3-million (red squares, threeruns) Reynolds number data for flow-induceddeflection at M = 0.75 for the η-stations (wing/bodyconfiguration). Data from 3-million Reynolds havebeen scaled by the ratio of q at 5-million over q at3-million.

Figure 44. Comparison of 5-million (blue, sixruns) and q-scaled 3-million (red, three runs)Reynolds number curve fits to the data for flow-induced deflection at M = 0.75 for the η-stations(wing/body configuration). Data from 3-millionReynolds have been scaled by the ratio of q at 5-million over q at 3-million.

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unclear if the differences seen in the induced-twist comparisons are due to true Reynolds number effects or are aresult of experimental error.

Differences in deflection for the same data sets are shown in Figs. 43 and 44. Differences in deflection are not asevident as for twist except for the most outboard η-station near low values of CL where differences approach 0.04inch. Differences in deflection for CL > 0.2 range from less than 0.005 inch at the most inboard to about 0.02 inchoutboard.

VI. ConclusionUnexpected behavior of flow-induced twist prompted a static loading experiment and repeat limited wind-on

testing to be conducted in the NTF two months after the completion of the original test. The static loadingexperiment validated and established wind-off bias errors for the experimental techniques used to measure modeldeformation. Bias errors found from the static loading test were combined with precision determined from repeatwind-on tests to give estimates of the uncertainty of the experimental techniques. In addition, results from the staticloading experiment and wind-on tests comparing the single-view and two-view photogrammetric techniques werefound to be within the uncertainty of either technique. The unexpected behavior of flow-induced twist outboard onthe right wing remains perplexing since experimental validation based on independent reference sources seemed toverify proper operation (wind-off) and a repeat wind-on test showed nearly identical unexpected behavior. While theoutboard induced twist of the left wing was found to behave closer to the expected result than the right wing, itsbehavior is still at odds with past experience with transport models. Additional independent measurements ofinduced twist for both wingtips during the repeat wind-on test showed similar unexpected behavior at low values oflift coefficient. Further computational analyses are needed to either explain or contradict the unexpected behavior ofthe induced twist measured outboard on the wings at low values of lift coefficient.

AcknowledgmentsGreg Gatlin, NASA Langley, and Ralf Rudnik, DLR, are acknowledged for many discussions involving the

model deformation data, comparison to computational predictions, and the unexpected behavior of the induced-twistmeasurements. Danny Barrows, NASA Langley, is acknowledged for assistance with camera calibrations anddiscussions about the data. The operations and supporting staff at the NTF are acknowledged for technical assistancewith the original wind-on test and follow-up static loading experiment and repeat wind-on test.

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12Burner, A. W., Liu, T., DeLoach, R., “Uncertainty of Videogrammetric Techniques used for Aerodynamic Testing,” AIAA-2002-2794, 22nd AIAA Aerodynamic Measurement Technology and Ground Testing Conference, Saint Louis, MO, June 2002.

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