A Critical Assessment Of UH-60 Main Rotor Blade Airfoil Data
NASA Technical Memorandum 103985A Critical Assessment of UH-60Main Rotor Blade Airfoil DataJoseph TotahSeptember 1993N94-32063(NASA-TM-103985)A CRITICALASSESSMENT OF UH-60 MAIN ROTORBLADE AIRFOIL DATA(NASA. AmesResearch Center) 24 pUnclasG3/02NASANational Aeronautics andSpace Administration0005471
NASA Technical Memorandum 103985A Critical Assessment of UH-60Main Rotor Blade Airfoil DataJoseph Totah, Ames Research Center, Moffett Field, CaliforniaSeptember 1993NASANational Aeronautics andSpace AdministrationAmes Research CenterMoffett Field, California 94035-1000
SummaryMany current comprehensive rotorcraft analyses employlifting-line methods that require main rotor blade airfoildata, typically obtained from wind tunnel tests. In order toeffectively evaluate these lifting-line methods, it is of theutmost importance to ensure that the airfoil section dataarc free of inaccuracies. A critical assessment of theSCI095 and SC1094R8 airfoil data used on the UH-60main rotor blade was performed for that reason. Ninesources of wind tunnel data were examined, all of whichcontain SCI 095 data and four of which also containSC1094R8 data. Findings indicate that the most accuratedata were generated in 1982 at the 11-Foot Wind TunnelFacility at NASA Ames Research Center and in 1985 atthe 6-inch-by-22-inch transonic wind tunnel facility atOhio State University. It has not been determined if datafrom these two sources are sufficiently accurate for theiruse in comprehensive rotorcraft analytical models of theUH-60. It is recommended that new airfoil tables becreated for both airfoils using the existing data. Additional wind tunnel experimentation is also recommendedto provide high quality data for correlation with these newairfoil tables.Symbolscorrelation parameter for QJ at lowsupersonic speedsKcorrelation parameter for airfoil sectiondrag due to liftLp/cairfoil perimeter/chord(lVD)maxmaximum lift-to-drag ratioLlift, IbMMach numberMIMach number at which the slope of C/achanges from " " to "-"MODdrag divergence Mach numberPerrormeasured pressure transducer steadybias error, psiaP/lower surface pressure, psiaPuupper surface pressure, psiat/cthickncss-to-chord ratioSAmean value of airfoil pressurecoefficientfree-stream Reynolds numberReynolds number in drag correlationvfree-stream velocity, ft/saangle of attack, dcg or radzero-lift angle of attack, dcg or radbwind tunnel model span, ftcwind tunnel model chord, ft1/PCdsection drag coefficientC/Q gradient at speeds greater than M]Csection drag coefficient at zero liftCd0 gradient at speeds greater thanCfmean skin friction coefficientQsection lift coefficientCmaximum section lift coefficientd0/maxC/a"max'"min"recovereddC//da average section lift curveslope at zero liftmaximum value of C/a at M 1.0minimum value of C/at M 1.0recovered value of C/a at 1.0 M 1.1form drag/friction dragwind tunnel test section height, ftMODYratio of specific heats, 1 .4 for airPdensity, slugs/ft3IntroductionNASA, in cooperation with the U.S. Army Aviation andTroop Command (ATCOM), is engaged in a program toprovide and validate the technology and methodologyrequired to improve the performance, dynamics,acoustics, handling qualities, and cost of civil and militaryrotorcraft. A major element of this program, the UH-60Phase II Airloads Program, consists of ground based andflight research of the UH-60 Blackhawk helicopter with a
pressure instrumented blade and a full suite of otherinstrumentation.NASA and ATCOM arc currently preparing for rigorousanalysis methodology validation using high quality datagenerated from the UH-60 Phase II Airloads Program.Analysis methodology validation involves assessing andimproving state-of-the-art comprehensive analyticalmodels through exhaustive correlative studies inperformance, dynamics, and rotor structural loads andairloads. In order to assess and improve the theories andassumptions employed in comprehensive analyticalmodels, accurate vehicle representations must beestablished.The main rotor blade airfoil section characteristics arcamong the most important parts of the vehicle representation. The airfoil sections on the UH-60 Blackhawkhelicopter are the SCI095 and SC1094R8 utilized on themain rotor blade shown in figure 1. The profiles of theseairfoils are shown in figure 2.Sikorsky Aircraft, a Division of United TechnologiesCorporation, was tasked to provide NASA with allknown steady, 2-D wind tunnel data on the SC1095and SC1094R8 airfoils. Nine data sets (refs. 1-9) wereidentified and provided to NASA, all of which containedSCI 095 data and four of which contained SC1094R8data. This report documents an assessment of that data forboth airfoils.An effort similar to the UH-60 Phase II Airloads Programwas performed on an H-34 helicopter by Scheiman in theearly 1960s. That experiment has long been a standard forrotor airloads data, but it did not include high speeds.Furthermore, rotor systems have evolved dramaticallyfrom the early 1960s. The UH-60 Phase II AirloadsProgram will consider high speeds and will gather data atmuch higher sample rates. The U.S. rotorcraft industryhas played a key role in defining the requirements for thisprogram to ensure it meets their needs. Also, a formalrecommendation resulting from a peer review of theprogram in 1990 was a primary motivator for the workpresented in this report.I would like to acknowledge and thank Mr. RobertFlemming from Sikorsky for his thorough review of thedata and for his comments, all of which have beenincorporated in this report.Description of DataNine sets of UH-60 airfoil data have been considered.The sources of these data sets which contain SCI 095 andSC1094R8 airfoil data are listed in table 1. These datasets are identified in table 1 and throughout this report,as Experiment 1, Experiment 2, and so on, throughExperiment 9. Pertinent information about the experiments, the wind tunnel facilities, airfoils, and measurement devices are also noted in this table. Some details ofthese experiments are discussed in this section.The primary objectives of three of the experiments wereto assess current technology airfoils, either stand-alone orcompared with prototypes. Experiments 3 and 8 gatheredsteady, 2-D data on the SC1095 and SC1094R8 airfoilsand compared them to prototype airfoils. Experiment 7gathered SCI095 data for correlation with a computational fluid dynamics code.Evaluation of Experiment 7 data revealed grossdiscrepancies relative to the data from all the otherexperiments. The published report documenting thisexperiment noted that inaccurate tunnel wall correctionswere applied to generate the reported data (ref. 7).Regrettably, appropriate wall corrections are not availableand the tunnel configuration has since been permanentlymodified.Some experiments examined alternate methods of testing.For example, the primary objective of Experiment 2 wasthe testing of a Tunnel Spanning Wing Apparatus (TSWor TSA) which fit inside a wind tunnel test section. TheTSW was evaluated in Experiments 2 and 5, and laterused in Experiment 8. Experiment 2 attributed prc-stall"bumps" in lift coefficient at high angles of attack tomodel flexibility. Experiment 5 gathered data with andwithout a center span device that alleviated the modelflexibility problems noted in Experiment 2. Experiment 5published two sets of SC1095 wake drag data, identifiedas 5a and 5b. The 5a drag data accounted for the difference in static pressures on each side of the wake behindthe airfoil, whereas the 5b drag data did not.The remaining four experiments were primarily concerned with the study of trends. Experiment 1 consideredthe influence of various surface irregularities relative to abaseline SC1095 airfoil. Experiment 4 studied icingconditions relative to baseline SCI095 and SC1094R8airfoil characteristics. This experiment generated relatively small amounts of data under normal, non-icingconditions. Data published from two alternate lift
measurement approaches devised in Experiment 4 werealso evaluated. Experiment 6 studied the effect ofReynolds number on both the SCI 095 and the SC1094R8airfoils. This experiment documented known problems indetermining Q max , and the airfoils used in that experiment were tabbed. The tabs were deflected upwardapproximately 3 degrees. The tabs also changed thethickncss-to-chord ratios to 0.091 and 0.09 for theSCI 095 and SC1094R8 airfoils, respectively. Untabbcdthickncss-to-chord ratios arc 0.095 and 0.094 for theSCI 095 and SC1094R8, respectively. Finally, Experiment 9 measured the effects of dynamic stall relative tobaseline SC1095 steady, 2-D characteristics. Data fromExperiment 9 were limited to speeds less than M 0.3.In summary, although all of the data from these nineexperiments were examined, Experiment 7 and someExperiment 4 results were not published in this report.Experiment 7 results were omitted because of theaforementioned problem with the tunnel wall corrections.Experiment 4 data gathered using the two alternate liftmeasurement approaches were also omitted because noattempt was made to address known anomalies noted atcertain test conditions. In each instance the experimenterwas consulted prior to omitting the results, andconcurrence was obtained.Evaluation MethodologyThe methodology developed by McCroskey (ref. 10) andfirst applied to NACA 0012 data was used to evaluate theSC1095 and SC1094R8 data. This methodology usesspecific criteria to separate accurate data from inaccuratedata. All the data arc then placed into one of four groupsthat further reflect varying levels of accuracy. A shortsummary of the aforementioned criteria, and thedefinitions of the four groups are given in this section.3. PQQ and PC(J0 are slightly dependent on Reynoldsnumber.GroupsFour groups were defined by McCroskey to distinguishvarying levels of accuracy. A graphical approach is usedto place the data into each of these groups. This approachbegins with two plots; PQa versus Re and Cd0vcrsus Refor data less than M 0.6 and between 106 Rc 107.Group 1 quality data should have values for both PQand Cd 0 within 0.0005 and 0.0002, respectively, of alog curve fit approximation of only the accurate dataidentified by the aforementioned criteria. Group 1 qualitydata are of sufficient accuracy for use in comprehensiveanalytical input models. This is further examined in theDiscussion section.Group 2 quality data should have values for both PQand Cd0 within 0.004 and 0.001 , respectively, of thelog curve fit of only the accurate data identified by theaforementioned criteria. It has not been determinedwhether Group 2 data arc sufficiently accurate for use incomprehensive analytical models. This will also beexamined in the discussion section.Group 3 quality data should have values for either PQ aor C(j o within the Group 2 tolerances. Finally, Group 4quality data have values for both PQa and Cc)0 outsidethe Group 2 tolerances.Once the groups have been established, C/ Qj , and(L/D)max are examined throughout the full r"ange of Machnumbers. The trends that these parameters exhibit as afunction of Mach number are characterized by theirinflection points, or the points at which the trendsabruptly change direction. The inflection points ofinterest arc:C/a : C /a max ' C 'a min ' and C/arccovcrcdCriteria2-Generally speaking, for M 0.6 and between106 Rc 107, accurate data is distinguished frominaccurate data if they exhibit the followingcharacteristics:3.(L/D)max: maximum value of (L/D)max4.C/1.0.10 per degree PC/U 2n per radian, whereb Vl - M , 0.10 is a known boundary, and 2n is thetheoretical lift-curve slope.2.pC/a and PC(J0 are independent of Much number.max: maximum value of QmaxThe accuracy with which these inflection points can beestimated, in addition to the continuous and unscattcrcdbehavior of the data between the inflection points, areindications of data consistency.It is important to realize that the groups are defined at lowspeeds for a given range of Reynolds number. This docs
not ensure that the data in any given group will retain thesame accuracy at higher speeds. It is therefore importantto plot all groups throughout the full range of Machnumbers and check the consistency of the data bothwithin the individual groups and among the groupsthemselves.ResultsThe methodology described in the previous section wasapplied to the data from the experiments for both airfoils.The results of the evaluation of the data are presented inthis section. Table 2 lists pertinent information about thewind tunnel facilities used in all nine experiments, tunnelwall corrections, and known accuracies of experimentsthat generated the NACA 0012 data previously evaluatedby McCroskey.SC1095 AirfoilEvaluation of PQa- Figure 3 shows derived PQavalues from the experiments plotted versus log(Rc).Figure 4 shows a log curve fit of the data only between0.10 pC/a 2n, along with Group 1 and Group 2tolerances. Balance data from Experiment 2 and pressuredata from Experiments 3 and 6 values are within theGroup 2 tolerance; however, none of the experiments arcconsistently within the Group 1 tolerance. The implication is that Experiments 2 (balance), 3, and 6 producedGroup 2 quality lift coefficient data because the derivedPQa values are within the Group 2 tolerance.Evaluation of Cd0— Figure 5 shows Q]0 values from theexperiments plotted versus log(Re), along with a logcurve fit of that data, and Group 1 and Group 2tolerances. Wake drag data from Experiments 1, 4, 5a,6, and 8 appear to be within or very near the Group 1tolerances. Wake drag data from Experiments 2, 3, 5b,and 9 are all within the Group 2 tolerances. Theimplication is that all of the experiments produced Group2 quality drag coefficient data because the C{j0 values arcwithin the Group 2 tolerance.Groupings- Based entirely on the above evaluations ofPQQ and Cd0 as presented in figures 3 through 5 thegroupings for the SC1095 data are:Group 1NoneGroup 2Experiments 2 (balance and wake drag), 3,and 6Group 3Experiment 1, 2 (pressure), 4, 5, 8, and 9Group 4NoneResults for C/Q- The variation of C/Q throughout the fullrange of Mach numbers is shown in figure 6, with eachgroup duly noted. An examination of the Group 2 datareveals that there is a smooth and consistent trend in thevariation of C/Q with Mach number up to M 0.84. Thistrend is noticeably different than that exhibited by theGroup 3 data, and less scattered than the Group 3 data aswell. A maximum value of C/a occurs at M 0.84 and aminimum value occurs at M 0.90, with a small recoveryat speeds greater than M 0.95. Maximum, minimum,and recovered values of C/a can be roughly estimatedfrom the data shown in figure 6. The McCroskcy-Smithexpression superimposed on figure 6 will be discussed inthe next section.In summary, no lift coefficient data exist beyondM 1.10, the best lift coefficient data available are foundto be Group 2 quality, and that the data are only consistent at speeds up to M 0.84.Results for Cd0- The variation of C j0 throughout the fullrange of Mach numbers is shown in figure 7, with eachgroup duly noted. There is a consistent trend in thevariation of the Group 2Cd 0 with Mach number up toM 0.80. Experiment 8 balance data appear to be higherthan the established trend beyond M 0.70. A maximumvalue of C(j0 can be roughly estimated at M 0.98. TheMcCroskcy-Smith expression superimposed on figure 7will be discussed in the next section.In summary, no drag coefficient data exist beyondM 1.10, the best drag coefficient data available arefound to be Group 2 quality, and the data arc onlyconsistent at speeds up to M 0.80.Results for (L/D)max and C/max- Figures 8 and 9 showthat (L/D)max and Qdata from Experiments 2(balance and wake drag), 3, and 6 are consistent at speedsbetween 0.50 M 0.84. However, scatter belowM 0.5 is evident. McCroskey showed that good datatend to exhibit high (L/D)max ar d Q m ax va'ucs at 'ovvspeeds. (L/D)max and C/ max data from Experiment 3 datawere noticeably higher at low speeds than the otherexperiments that produced Group 2 quality data. Based onthese figures, it appears that (L/D)max and C/ max occur atroughly M 0.3.
The inflection points of interest for C/a, C(j0, (L/D)max,and C/ max for the SCI095 airfoil data arc given in table 3.lower speeds, regardless of the groupings. The Smithexpression superimposed on figure 13 will be discussed inthe next section.SC1094R8 AirfoilIn summary, no lift coefficient data exist beyondM 0.90, the best lift coefficient data available areGroup 2 quality, and these data are only consistent atspeeds up to M 0.70.Evaluation of pc/a— Figure 10 shows derived PQavalues from the experiments plotted versus log(Re).Figure 11 shows a log curve fit of the data within0.10 PQa 2n, along with Group 1 and Group 2tolerances. Some of the data from each experiment arcoutside the Group 2 tolerances. At least half of thebalance data from Experiment 8 and half of the pressuredata from Experiments 3, 4, and 6 are scattered within theGroup 2 tolerances. None of the experiments are consistently within the Group 1 tolerances. It can be concludedthat all of these experiments produced a certain amount ofGroup 2 quality lift coefficient data because the derivedPQ a values are within the Group 2 tolerance.Evaluation of C,j0- Figure 12 shows C Q values fromall the experiments plotted versus log(Re), along with alog curve fit of that data, and Group 1 and Group 2 tolerances. Most or all of the data from Experiments 3, 6,and 8 arc within the Group 2 tolerances. Data fromExperiment 8 are scattered, with a few points outside theGroup 2 tolerance boundary on the high side. Data fromExperiment 4 were not used in deriving the log curve fitand arc outside of the Group 2 tolerance. The implicationis that Experiments 3, 6, and 8 produced a certain amountof Group 2 quality drag coefficient data because the Cd0values are within the Group 2 tolerance.Groupings- Based entirely on the evaluation of PC/Q andC(jo as presented in Figures 10 through 12 the groupingsfor the SC1094R8 data arcGroup 1NoneGroup 2Experiments 3, 6, and 8Group 3Experiment 4Group 4NoneResults for C/ — The variation of C/ n throughout the fullrange of Mach numbers is shown in figure 13. An examination of the Group 2 data reveals that there arc slightlyconflicting trends in the variation of C/ a with Machnumber. Experiment 6 values tend to be higher thanthe trend established by the other experiments belowM 0.60. A maximum value occurs at M 0.83, but nom i n i m u m or recovered values can be established. Thedata tend to be more scattered beyond M 0.70 than atResults for Cd0- The variation of Cd0 throughout the fullrange of Mach numbers is shown in figure 14. There arcconflicting trends in the variation of Cd0 with Machnumber beyond M 0.70. Wake data from Experiment 6,and to a lesser extent from Experiments 3 and 8, exhibitlower drag values than the balance data from Experiment 8. Figure 14 also shows that some Experiment 8wake drag data arc high at low speeds, and those datapoints correspond to the high drag values noted infigure 12. A maximum value of Cd0 cannot be determined. The Smith expression superimposed on figure 14will be discussed in the next section.In summary, no drag coefficient data exist beyondM 0.90, the best drag coefficient data available arcGroup 2 quality, and the data arc only consistent at speedsup to M 0.70.Results for (L/D)max and Qmax- Figures 15 and 16show (L/D)max and C/ max data, respectively, from all theexperiments. These data arc only consistent at speedsbetween 0.60 M 0.84. Scatter below M 0.6 isevident. Experiment 6 again appears to exhibit a different(L/D)max and C/trend than the other experiments,which all tend to be in better agreement. Experiments 3and 8 exhibit slightly higher values of (L/D)max andC/ max . Based on these figures it appears that (L/D)maxand C/ max occur at roughly M 0.3.The inflection points of interest for C/a, Cd0, (L/D) max ,and C/max for the SC1094R8 airfoil data arc given intable 3.The results of this evaluation show that none of theexperiments produced Group 1 quality data. Some of theexperiments produced Group 2 quality data. Experiment 3produced Group 2 quality data for both the SCI095 andthe SC1094R8 airfoils. Experiment 8 produced Group 2quality data for the SC1094R8 airfoil. The SC1095data was found to be consistent up to M 0.84 for liftcoefficient and M 0.80 for drag coefficient. TheSC1094R8 data was found to be consistent up toM 0.70 for both lift and drag coefficient, exceptfor some scattered drag data at low speeds. Other
P/-P P,crrorexperiments that produced Group 2 quality data werefound to exhibit slightly different trends, inconsistencies,or lower values of (L/D)max and C/ max relative to theaforementioned experiments.During the initial phases of this evaluation, the experimenters responsible for the publication of the SCI 095 andSC1094R8 data were contacted. They were sent somepreliminary results and were asked to comment on thoseresults. The following responses were obtained and werefactored into the results presented in figures 3 through 16.1. In general, at low drag levels, a balance sized to havehigh drag level capability does not give adequate resolution or precision.2. In transonic or rotational flow balance drag data canbe more accurate than the total probes of a wake rakebecause a rake can not capture all of the losses.rPu-P' -P'error-substituting'measuredmeasured2P.error-2P, error(2)(3)errorNote that on the UH-60 Phase II Airloads Programpressure blade, the transducer measurements arc accurateto within 0.1% of their maximum range of 20 psia. Thus,measured3. When experimental angle-of-attack increments aretoo coarse to accurately derive reasonable values for C(j0,assume that QJO Cda Q- Note that the zero-lift angle ofattack for the SCI 095 and SC1094R8 arc -0.3 and -1.4 ,respectively (rcf. 11).4. Integration of surface pressures on a model with alimited number of pressure taps is generally inaccurate.errorequals 0.04 psia.Now, consider the maximum error in the calculation oflift for a given group tolerance, as follows:Croup 1 0.0005JAa-pV2error5. Tunnel wall rporosityJ affects C/*Gtand C/m'max, and isdiscussed in the published report for Experiment 5(rcf. 5).-O.OOOSJAa-pV 2PA L( Group 1DiscussionDiscussion is warranted on the Group 1 and Group 2tolerances relative to accuracies in experimental measurements. To illustrate this, consider the derivation of liftfrom measured data as12Lmcasurcd C/measured PVwhere — fC/measuredg I'(Cp. -C Pr )d\ '/u/Assuming there arc inaccuracies in the pressuretransducer measurements in the form of a simple biaserror, Pcrror. tncn(4)(1) O.OOlAa-pV 2(5) 0.008Aa-pV2(6)errorPA L Group 2errorFigure 17 is a plot of equations (3), (5), and (6) versusairspeed for a nominal anglc-of-attack range of 1.0 . Itcan be seen that a large region exists beyond M 0.40,which indicates that the assumed bias error in liftmeasured by the UH-60 pressure blade is smaller thanthe maximum possible error that can be obtained whencalculating lift using Group 2 wind tunnel data. This isnot the case for Group 1 quality data.The purpose of figure 17 is to show that Group 1 data aresufficiently accurate to use in predicting UH-60 airloads.It is not meant to imply that Group 2 quality data are notsufficiently accurate. Such a determination is dependenton many factors, such as:
1. The desired accuracy of the predictions.2. Aspects of the physical representation of the UH-60that arc inaccurate or cannot be modeled, that overshadowany inaccuracies realized by using Group 2 quality data.3. Limitations of the comprehensive analytical modelthat may overshadow any inaccuracies realized by usingGroup 2 quality data.Until these issues have been resolved, it cannot be determined whether Group 2 data arc sufficiently accurate fortheir intended use in the UH-60 model.This last issue is the primary concern when evaluatinglifting-line methods employed in comprehensive rotorcraft analyses. It is not known if current methodologiesarc sensitive to errors introduced by using Group 2quality data. This question forms the basis for therecommendations discussed in the next section.Also, it should be noted that consistent Group 2 qualitydata do not exist beyond speeds of roughly M 0.70 orM 0.80, depending on the airfoil. The advancing bladeMach numbers for the SC1095 and the SC1094R8 airfoilsarc 1.012 and 0.90, respectively, at the "do not exceed"velocity of 192 knots and 20,000 feet.There are currently many sources of SCI095 andSC1094R8 data circulating throughout the aerospacecommunity in a variety of different formats. Not all thesources of data arc traceable. In fact, many of thosesources may be inaccurate. An easy way to check theaccuracy of those data sets would be to plot the variationof C/Q and Cd0 versus Mach number against the resultspresented in this report for either airfoil. Alternately, theresults presented in this report can be approximated usingsemi-empirical expressions developed by McCroskcy(rcf. 10) for the NACA 0012 airfoil in supersonic flowand by Smith (rcf. 12) for a variety of different airfoils insubsonic flow. Correlation of the semi-empirical expressions with the results presented in this report are shown infigures 6 and 7 for the SC1095 airfoil, and in figures 13and 14 for the SC1094R8 airfoil. The combined, orcomposite, McCroskcy-Smith expressions used togenerate the approximations shown on those figures arcpresented in the appendix.ConclusionsThe primary motivation for this evaluation was to preparefor rigorous analysis methodology validation as part ofthe UH-60 Phase II Airloads Program. Analysis method-ology validation consists of assessing and improvingstate-of-the-art comprehensive analytical models throughexhaustive correlative studies in performance, dynamics,and rotor structural loads and airloads. In order to productively assess and improve the theories and assumptions employed in comprehensive analytical models,accurate vehicle representations must be established. Themain rotor blade airfoil section characteristics arc amongthe most important parts of the vehicle representation.Ultimately, the improvements in analysis methodologyand in vehicle representations will be judged relative toimprovements in the correlation of predictions withexperimental measurements.This report shows that the most accurate data arc Group 2quality. The experiments that generated this quality ofdata were performed in 1982 at the 11-Foot Wind TunnelFacility at NASA Ames Research Center and in 1985 atthe 6-Inch by 22-Inch Transonic Wind Tunnel Facility atOhio State University. It has not been determined whetherGroup 2 quality data arc sufficiently accurate to use incomprehensive analytical models to predict experimentally measured airloads data.Furthermore, the McCroskey methodology used to evaluate the airfoil data tend to work best when there arelarge amounts of data, a significant portion of which areGroup 1 and 2 quality throughout the desired ranges ofMach and Reynolds numbers. Although it can be arguedthat a significant percentage of the data presented hereinare Group 2 quality, they are not nearly as much asdesired, nor are they as consistent as desired. Therefore, itis important that further synthesis and experimentation beperformed in order to generate Group 1 quality data. Thisconclusion warrants specific recommendations, discussedin detail in the next section.RecommendationsThe results presented in this report show that the mostaccurate data arc Group 2 quality. It has not been determined whether this is of sufficient accuracy to use inpredicting UH-60 airloads. If it is determined that theaccuracy is not sufficient, then the following recommendations should be interpreted as requirements.It is recommended that further wind tunnel experimentation be performed to obtain Group 1 quality data, and thatthis effort be preceded by a synthesis similar to thatperformed by Tanner (ref. 13). Candidate facilities forthe experimentation include those shown by McCroskey
to produce Group 1 quality data. However, speed, angle of-attack range, and Reynolds number range should beconsidered before choosing a wind tunnel. It is understood that the aforementioned wind tunnels may not beable to satisfy the high speed requirement, and this shouldweigh heavily in the selection of a wind tunnel facility.Further, large positive and negative angle-of-attack rangesshould be considered in increments small enough toidentify the exact values for C/max and Cdo. It isimportant that both the synthesis and experimentation beperformed for full scale Reynolds numbers. ActualSCI 095 and SC1094R8 contours as measured on thePhase II Airloads Program pressure instrumented bladeshould be used if new wind tunnel models of those airfoilsections arc to be fabricated. Determination of severalcritical parameters should be the priority of both thesynthesis and the experimentation. These parametersinclude, but are not limited to, C/ , Cin . .'«max '«minCin. Mnn, CH , the maximum values of'"recovered" UL" a max'(L/D)max and C/ m , and the Mach numbers at whichwheredC,S--5.4dMand the expression developed by McCroskey for C/Q is0.93 Msl.ll)M2(t/c)] In the M s 0.6 region the log empirical curve fit of theCd0data is given asCdo -0.01 43 -0.001 Olog(R c )(11)The expressions developed by Smith for Cdo arc0 Ma (MDD 0.8)L/cf.Cs \K[(0.01745) aZL ]2-7c\ C F(12) 6x10 wherethey occur.0.455c f - Finally, it is recommended that a methodology bedeveloped to evaluate pitching moment coefficient, andthat the synthesis and additional experimentation treatpitching moment coefficient with the same level of detailas lift and drag coefficient.a2.58ZL-- - 3dc gS A -1.14AppendixcFor the SC1095 airfoil data, the combined, or composite,McCroskey-Smith expressions are superimposed onfigures 6 and 7. In the M s 0.6 region the
NASA Technical Memorandum 103985 A Critical Assessment of UH-60 Main Rotor Blade Airfoil Data Joseph Totah September 1993 (NASA-TM-103985) A CRITICAL ASSESSMENT OF UH-60 MAIN ROTOR BLADE AIRFOIL DATA (NASA. Ames Research Center) 24 p N94-32063 Unclas G3/02 0005471 NASA National Aeronautics and Space Administration
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