AIAA.1977.High.lift.Cardinal

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250 J. AIRCRAFT VOL. 16, NO. 477-1217

Flight Test Results for an AdvancedTechnology Light AirplaneDavid LKohlman*University of Kansas, Lawrence, Kansas

A single-engine light airplane wa s modified by the installation of a wing with reduced area, Fowler flaps,Kruger flaps, and spoilers. Flight test results show that zero-lift drag was reduced 13.8% and a trimmedmaximum lift coefficient of 2.73 wa s achieved. Gust response wa s significantly reduced an d excellent roll controlwachieved with spoilers. Several design features employednhnwwings have excellent potentialoncorporationnfuture l ight airplanes.

NomenclatureA =aspect ratiob =wing spanc=mean aerodynam ic chordCD = airplane drag coefficientCD() =zero lift drag coefficientGI = rolling moment coefficientC /g = roll power dCf/ddsCfS = roll damping coefficientC[ = airplane l i f t coefficiente = induced drag efficiency factorp = roll rateSw = wing areaTH P = thrust horsepowerTH Pe = equivalent thrust horsepowerVe=equivalent velocityVT true airspeedW gross weight0 = sideslip angledf = Fowler flap deflection5k=Kruger flap deflectionds = spoiler deflection0=roll anglePo = standard sea-level dens itya =density rat io, p/p ()

IntroductionT HIS paper reports th e final results of flight tests of amodified Cessna 1 Cardinal a ircraf t .T purpose othis programwo evaluate h effectsoa research wingincorpo rating increased wing loadin g and severalaerodynamic featuresnordinarily foundo light aircraft.Tchanges incorporated nhnwwinga1wing areareducedb 37%,2 thickness ratio reduced,3 Fowlertrailing-edge flaps installed, 4) Kruger leading-edge flapsinstalled,a5spoilers installedoroll control.T basic design philosophy involvedh improvement ocruise performanceb increasing wing loading.Aauxi l iarybenefit is a considerable improvement in r ide quality inturbulence. T main tain acceptable s tall speeds imp rovedtrailing-edge flaps were employed along with Kruger leading-edge flaps. Spoilers for roll control were also investigated

Presenteda Paper 77-1217ah AIAA Aircraft Systems &Technology Meeting, Seattle, Wash. , Aug. 22-24, 1977; submittedFeb. 14 , 1978; revision received Sept. 7, 1978. Copyright AmericanInst i tute of Aeronautics an d Astronautics, Inc. , 1977. All r ightsreserved.Index categories: Co nfig urat ion Design; General Av iat ion ; Per-formance.*ProfessoroAerospace Engineerin g. Associate Fellow A I A A .

because they ca n permit the use of full-span flaps. Details ofthdesign philosophy, parametric studies, wind-tunnel tests,flight simulator studies, an d preliminary performanceestimates were presentednRefs. 1-4.It should be emphasized that the modified Cardinal, hereinreferred to as the Redhawk, is strictly a research vehicledesigned o investigate several different aerodynamicmprovements which might be applied to the design of generalaviat ion aircraf t . The constraint of mounting the new wingson an existing fuselage an d wing carry-through structurecompromised the design in several respects; thus , theRedhawk shouldnbconsidered aaprototype airplaneoproposed modification to the Cessna Cardinal.Prioromodifyinghtest airplane,aextensivesobaseperformance datawobtained throug h flight testing. 5 Thesedata are used in this paper for comparison. The same instru-mentation system used for the base data flight tests was usedfo r these tests. Details of the system are reported in Ref. 5.

Airplane ConfigurationA three-view of the Redhawk an d relevant geometric data,compared withhoriginal Cardinal,a presentedn Fig.1a Table 1.T ailerons a available onlyaa backup rollcontrol system aa connectedohcontrol wheelohr ight side. The spoilers ar e connected to the l e f t control wheel.This independent arrangement made in-fl ight comparisonsbetween ailerona spoiler roll control characteristics veryconvenient .Both leading-edge an d traili ng-e dge flaps were driven in -dependently by standard Cessna Cardinal flap motors. Other

than the wings, no other changes were made to theaerodynamic configurationo engineohstandard CessnaCardinal.LiftaDrag Characteristics

T l i f ta drag characteristicsoh Redhawk weredetermined froma serieso steady, level f l i gh t data pointsconducted at two pressure al titu des , 2500 ft and 7500 ft .Engine brake horsepower was determined from enginemanifold pressure, rpm , pressure alt i tu de, ambient tem-perature, ah power chart suppliedbh enginemanufacturer . The power predicted from th e engine chart wasthen reducedb5%o accounto losses from inlet tem-perature rise and miscel laneou s losses.Thrust horsepower was determined from brake horse-power, propeller rpm,adensi ty, true airspeed,a propellerperformance char ts .T actual calcu lations were performedwith the aid of a computer program supplied by CessnaAircraft Company.Weight was determined fo r each point by p lo t t i ng th eapproximate fuel consumed vs t ime using th e known f u e l


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APRIL 1979 FLIGHT TEST RESULTSFOA D V A N C E D LIGHT AIRPLANES 251consumption characteristicsa approximate power settings,and the initial an d final weight of the airplane. Dragcharacteristics were determineda follows. Assuming thatdrag cbrepresented bastandard parabolic drag polar,

CD = CDo+C2L/irAethen thrust horsepower may be expressed in the followingmanner :

1100TH P

275veAp0SwyeW2

1100 = K1V4e+K2Thus, if TH Pe ( V e ) is plotted as a function of V4e, a normaldrag polar will appear as a straight line an d CD() an d e can bedetermined from th e slope, ( K t ) and intercept (K2) of theline. Ve n miles p hour , Swn f t 2 ,a p0 ns lug / f t3 , then

Kj348.4 W2e = 403.4vAPoSwK2Figure 2 presents typical flight test data corrected to astandard gross weight of 2500 Ib . Complete data for allconfigurat ions are available in Ref. 6. A summary of theRedhawk drag characteristics aa comparison withhCardinal are presented in Table 2. Note tha t since the dragcoefficients a basedow different areas,h quanti tyCDSW,h equivalent flat plate f ronta l area, should bcompared odetermine relative amounts oactual drag.Several significant results appear in Table 2. First , th ereduced wing area of the Redhawk results in a 13.8%reduct ion in zero l i f t drag. As shown in the power-velocity

curves o Fig.3 that producesa increased maximum air-speedoapproximately 3o6m p h , dependingoalt i tude.The induced drag efficiency factor for the Redhawk is veryclose to that of the Cardinal except for the 10-deg Fowler flapsetting. T improved efficiencyo this condi t ion believedto be the result of reduced separation at the wing-body at -t achment area. Note that e accounts for all drag cont r ibut ionswhich are a function of angle of a t t ack , inc luding t r im drag;the values of e in Table 2 are representative of this class ofairplanes .T total zero l i f t dragoh Redha wk only slightlylarger than that oh Cardina loh f u l l flaps landingconfigura t ion. The very small increase in CD() due to Krugerflaps with 6f = 40 deg is probably a result of designing theKruger flaps to be most effective with th e 40-deg Fowler flapposit ion. The large leading-edge upwash in this condi t ionresults in very little separation from the undersurface of theKruger flap compared with th e d f = 10-deg c onf igura t i on .Tratiooinduced dragohRedhawk a Cardinal aagiven airspeed in the cruise configura t ion is(SwARe)Cardlna

' ) Cardinal (S wARe )R&= 1.34

If h span oh Cardinal h been retained ohRedhawk, with no change in Redha wk wing area, CD() and e,the increase in maximum speed at 7500 ft would be ap-proximately86m p h ,a shown nFig.3becausehincreasein induced drag ohRedhawk wouldbel iminated.Figure4presents h t r immed l i f t curves oh Redhawk.TFowler flaps provide asubstant ia l AC Zawella increasein CLT Kruger flaps provide virtuallyn increasenCLat constant a but extend th e l i f t curve to a higher stall anglean d a higher C,L-max

Fig. 1 Three-view com-parison o RedhawkaCardinal configurations.

12

10

0102030Ve4x IO "8 ~MPH 4

Fig.2 Level f l ight power requirements , cruise configuration.

Table 1 Geometric properties of the Cardinal and Redhawk wings

Gross weig h t , N, (Ib)Wing area , m 2 ( ft 2 )Wing loading, N/m - , (psf)Span,m( f t )Aspect ra t ioTaper rat ioTwist, degDihedral , de gAirfoi l sectionInboa rdOutboardTrai l ing-edge flapTypeSpan , percentArea (both) , m 2 , ( f t 2 )Leading-edge flapSpan, percentDeflection, de gAileronTypeCh o r d , percentSpan , percentSpoilerCh o r d ,cm( in . )SpanInboar d , percentO u t b o a r d , percent

Cardina l11,120, (2500)16. 23 , (175)648, (14.3)10. 82, (35. 5)7. 2

0.73.01.5N A C A 6 4 A 2 1 5N A C A 6 4 A 2 1 2

Single Slot532.74, (29.5)

Frise4133

Redhawk11,120, (2500)10.21, (110)1089, (22.7)9.58, (31.4)

9.00.53.03.0

N A C A 2 4 1 2N A C A 2409Fowler472. 93 , (31. 5)Kruger83135

Round nose243610.16(4)

28.532


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25 2 D.L. KOHLMAN J. AIRCRAFTTable 2 Comparison odrag characteristicsdetermined from flight test

Redhawk

Cardinal

Cruise6 /=10deg, 6 ^ = 0 d6 /=10deg, 6^ =1 35dfly = 4 0 deg, 6^=0 deg^ = 40 deg, 6^ = 1 35 deg

CruiseFull flaps

0.03660.05460.07700.07460.07520.02670.0462

4.0266.0068.478.218.274.678.08

0.550.670.6850.580.590.5640.545

140 r

120

100

80

60

4

CARDINAL CRUISE.REDHAWK CRUISE.REDHAWK WITH CARDINAL SPANREDHAWK LANDING^ CONFIG.GROSS \WT = aSOO LB

Table3 Comparisono stall speedsamaximum l i f t coefficients3

60 80 IOO 120 140 160

Fig. 3 Power required and available for the Redhawk and Cardinal.

2.5

- 2 0 2

Fig. 4 Trimmed l i f t curves for the Redhawk.468 10

CX~D

Configurat ion

CruiseKruger flaps onlyFowler flaps1dFowler flaps1dan d Kruger flapsFowler flaps4d(30 deg for Cardinal)Fowler flaps4da Kruger flaps

Redhawk CardinalK , m p h C , K, mp h C,^ m a x . s ^max.79.669.871.262.864.457.0

1.40 64.71.821.752.25 . .2.14 55.02.73

1.35

1.84

aGross weight =2500 Ib ; Redhawk e.g. location 7.2% m.a.c. (109 in.), Car-dinal e.g. location 19% m.a.c. (109.3 in.).

Fig. 5 Cross section of wing in landing configuration.

-10 r

*A

Fig. 6 Longitudinal trim data for the Redhawk.

Stall PerformanceThe greatly reduced wing area of the Redhawk necessitatedthe use of very effective high l i f t devices to obtain takeoff andlanding performance comparable oh original Cardinal .Extensive use of available NASA data an d two-dimensionalwind-tunnel tests at the Univers i ty of Kansas 7 contr ibuted to

th e design of the Fowler flaps an d Kruger flaps. A crosssection ohairfoila flapsshownnFig.5Stalls were conducted b establishing equilibrium levelflight approximately 10 to 15 mph above the anticipated stallspeed. Power was then reduced such that the airplanedecelerated approximately 1 knot /s at constant alt i tude unt i l a

stall occurred. Power was generally very close to idle by thet imeh airplane stalled. Stall speed w definedahm i n i m um airspeed recorded during th e stall maneuver .Data oh stall performance a presentedn Table3Whileh Redhawk cruise configurat ion ha relatively highstall speed,h maximum l i f t coefficient exceeds thatohCardinal, probably due to the higher aspect ratio. Use ofFowler and Kruger flaps almost doubles the maximum l i f tcoefficient of the clean conf igurat ion, producing a t r immedl i f t coefficient a stallo 2.73aastall speed wi th inwmof the Cardinal . Use of f u l l span trailing-edge flaps wouldreduce Redhawk stall speed at landing below that of theCardinal.


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A P R I L 1979 FLIGHT TEST RESULTS FOR A D V A N CE D LIGHT A I R P L A N E S 253- 4.0"-

Fig. 7 Redhawk spoil-er cross section.

STEADY STATEROLL RATE, p-DEG/SEC 20

10

-3 0

-4 0

20 4O 6O~ DEG RIGHT

O CRUISE CONFIG.V = 120 MPH

n LANDING CONFIG.V ^ 80 MPH

Fig. 8 Redhawk spoiler roll rate data.

Figure 7 shows the spoiler cross section. There is a 0.4-in.gbetween hhingeline a leading edge ohspoiler, bno direct venting from the undersurface of the wing to thespoiler cavity.Tentire span ohroll spoilersnfrontoa fixed aileron with the Fowler flap completely inboard of thespoiler. Roll performance w determined b initiatingsteady-state roll rates with many different valueso stepspoiler inputs with a clean conf igurat ion and with full Fowlerflap and Kruger flap deflections.Figure8presentsh flight test resultsoh Redhawkntermso roll rateaa functiono spoiler deflection. Figure9converts th e roll rate data to roll helix angle, pb/2VT. Figure10 shows time histories of both low- and high-speed rollresponse.Several characteristics are apparent. Roll rate is very nearlya linear function of spoiler deflection. Roll rates are adequatefo r good handling qualities, even though only a relativelysmall spoiler span is used. There is no perceptible yawingmoment produced b spoiler deflection. Pilots reported thattherewnan rolling moment followinga step spoilerinput . Therea decreasen roll helix angle, pb/2VT, whenflapsa deployed, primarily becauseohinboard shiftoth e l i f t distr ibution, giving th e spoilers a smaller fraction ofth e total l i f t to spoil.A series of design charts to predict spoiler effectiveness ispresented in Refs. 8 and 9. Although aspect ratio and taperratio were not exactly matched, the similar l i f t distr ibutionsfo r straight tapered wings should give reasonably closeresults. Tsteady-state roll equation

2V\C,

The f u l l span Kruger leading-edge flaps are particularlyeffective, producing approximatelya 10-mph reductionnstall speed when deployed with an y Fowler flap deflection.The AQ due to Kruger flaps is 0.59 with full 40-degFowler flap deflection.Stall characteristics were acceptable na conf igurat ions,bhuo Kruger flaps greatly improved h con-t rol labi l i ty and gentleness of the stall. Spoiler roll control iseffective th roughout the stall maneuver .

Longitudinal TrimLongitudinal t r im data a presented n Fig.6 Severalcharacteristics a apparent . Fowler flap deployment causesaa shiftnhneutral point , increasing h static stabil i ty .It also results in a mild nose-up pi tching m om e nt . Thus ,t rans i t ion from pattern speed to f inal approach is verycomfor table with only modera te trim wheel inputs r equ i r ed .Kruger flap dep'oyment causes vir tual ly no t r im change. Theonly noticeable effect dur ing Kruger flap actua t ion is a slightbuffe taaKruger angleoabout9deg.

Spoiler Roll CharacteristicsAlthough ailerons were installed on the Redhawk as analternate means of roll control, spoilers are the primary rollcontrol surfaces.T spoilersa actuatedbacmapushrod l inkage which deflects one spoiler while holding theotherna fixed posit ion.Tcmconnectedbcable ohpilot 's control wheel. T spoiler segmentsa provided oeach wing,h inboard segment extending from3%o63.5% semispan,ah outboard from 64.5% o 96.5%semispan. Ini t ia l ly, both inboarda outboard spoilers wereused fo r roll control . However, after extensive flight testing

aa mechanical modif icat iono permit greater spoilerdeflection, became apparent that adequate control couldbachieved using th e outboard segments only, and controlforces due to friction and spoiler weight could be reduced.The data reported herein are for outboard spoiler segmentsonly .

w usedo determine C, from flight test data with C/s Pdetermined analytically from Ref. 10 .T resultsa presentedn Table 4 There goodagreement ohclean wing, whilehwind-tunnel data witha straight taper overpredicts hflaps-down roll powerohairplane because oh inboard shiftnloading caused bhFowler flaps.T rolling m o m en t characteristics ohRedhawk spoilersa similar nnature ohdata reportedbW e n t z1 1 from wind-tunnel tests of an unvented spoiler on aclean wing with a GA(W)-1 airfoi l .Nwheel force data wererecordedoh Redhawk; however ,a pilots repor tedapositive centering force for the spoilers under all f lightcondit ions.

Dynamic StabilityDynamic stabili ty da ta were recorded o determine whetherth e decreased wing area had a significant effect on thedynamic flight characteris t ics .

LongitudinalLongi tudina l dynamic data were taken in the followingm an n er .T airplane w stabilizeda t r immedn levelfl ight.T elevator wdeflected o providea longi tudina ldis turbance, then returned to the original t r immed posit ion.T resul t ing phugoid mode wallowed o oscillate t h roughseveral cycles. Lateral i npu t s were made as required to keepthwings level.

Table 4 Summary of (he lateral control power fo r th e Redhawk

Clean win g Full flaps deployedFlight test results using s teady- 0.042 ra d 's ta te ro ll approx ima t ionPredieted from w i n d - t u n n e l 0.042d a t a 8

0.025 rad

0.037


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254 D.L. KOHLMAN J. AIRCRAFTTable 5 Phugoid mode characteristics, W= 2500 Ib

Redhawk

Cardinal

Configurat ionCleanCleanClean6/ = 40 deg5k -135 deg

5,= 30 deg

mph1201201208080808080

Frequency, up,rad/s0.2260.2250.2250.2590.2700.2530.3390.324

Damping rat io,0.10970.07460.07460.13360.13360.12450.0450.044

-.06 L

Fig. 9 Steady-state roll helix angle with spoilers.

LEFT ROLL

Fig.1 Roll time historiesfohRedhawk.

1 2 3 4TIME~S

b) LEFT ROLLVQ = 120 MPH

T I M E - S E C

T resultsa summarizedn Table 5 Frequency adamping ratios were determined from analysisohoscillographic time historyopitch angle assumingastandardsecond-order dynamic system model. The short period modeha d such a high frequency and damping ratio that nomeaningful quanti tat ive data could bobtained.No Cardinal data were taken at 120 m p h . In the landingmode,a8 m p h ,h Redhawkha decreased phugoidfrequency but a significantly increased damping ratio. Thiscan be attr ibuted to the lower l i f t /drag ratio of the Redhawkcompared to the Cardinal in the landing conf igurat ion.Lateral-Directional

As is usually th e case with light, single-engine aircraf t , theDutch roll mode w highly damped.T maneuverwinitiated by inducing a large side-slip angle with th e rudder ,then centering h rudder a spoiler quickly while allowingth e oscillationo d am p .T high damping ratio makes extremely difficult o extract accurate quant i ta t ive resultsfrom hdata ,bh frequency appears obapproximately2.57 rad/sahdamping ratio d0.22 a1mHAS.Although it was not possible to obtain quanti tat ive data,th e spiral mode appeared to be stable for all airspeeds an dconf igura t ions . This was a design objective achieved by in-creasing dihedral from 1.5dohCard inalo3dohRedhawk. This causeda obvious increase n roll sensit ivityto rudder input and decreased the Dutch roll damping ratio at12 0m from about04oh Card inalo 0.22 ohR e d ha w k .

ConclusionsQuant i t a t ive flight da taa test pilot evaluationsohRedhawk have demonstrated the fol lowing:1. Ride q u a l i t y in t u rbu l enc e is s ignif icant ly improved dueto the higher wing loading .2. Zero-lift drag was reduced 13.8%.3Tcombined Fowlera Kruger flap system provides at r immed ma x imum l i f t coefficient o 2.73.4 Spoilers provide adequa te roll accelerationa veryfavorable roll control characteris t ics , part icular lyhel iminat ion of adverse yaw.5 Althoughh Kruger flapsa probab lyo heavyacomplex fo r very l ight a i rcraf t , they are very effective high-l i f tdevices an d provide very favorable stall characteris t ics .6. The Fowler flaps an d spoilers ar e simple , l ightweightsystems which couldb easily incorporated n l ight aircraftdesigns .In summa ry , t he rea s ignif icant advantageso increasingth wing loading o typical l igh t a i r c r a f t .T high- l i f tdevices, and possibly spoilers, required to employ higher wing

loading, represent a well-developed technology which can bereadily appliedohnext generat ion o l ight a i r c r ta f t .Acknowledgment

This research was supported by the NASA LangleyResearch Center unde r Grant No. N C R 17-002-072.


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APRIL 1979 FLIGHT TEST RESULTS FOADV AN C E D LIGHT AIRPLANES 255References

' Roskam,a Kohlman, D.L.,"A Assessmento Per-formance, Stability,a Control ImprovementsoGeneral AviationAircraft," SAE National Business Aircraft Meeting, Paper 700240,Wichita, Kansas, March 1970.2Kohlman, D.L.a Roskam, J., "A Review ohUniversityoKansas Light Airplane Research Program,"S National BusinessAircraft Meeting, Paper 710379, Wichita, Kansas, March 1971.3Crane, H.L., McGhee, R.J. , an d Kohlman, D.L., "Applicationsof Advanced Aerodynamic Technology to Light Aircraf t ," SA ENational Business Aircraft Meeting, Paper 730318, Wichita, Kansas,April 1973.4Kohlman, D.L., "Drag Reduction Through Higher WingLoadings," NASA-Industry-University Drag Reduction Workshop,University of Kansas, Lawrence, Kansas, July 14-16, 1975.5Kohlman, D.L., "Flight Test Data for a Cessna Cardinal,"NASA CR-2337, Jan. 1974.

6Kohlman, D.L., "Flight Evaluation of an Advanced TechnologySingle-Engine Airplane," Universityo Kansas Centero Research,Inc., Rept. No. KU-FRL 204, Dec. 1976.7Garrett , R.B., "Experimental Investigation of High Lift Devicesfo r a Light Aircraft," M.S. Thesis, University of Kansas, Lawrence,Kansas, 1969.8Sapp, C.W., "Application o Spoilerso Light Airplanes," M.S.Thesis, University of Kansas, Lawrence, Kansas, 1968.9Agler, R.D., "Experimental Investigation of the Influence ofWing Geometryo Spoiler Effectivenesso Light Aircraft ," M.S.Thesis, University oKansas, Lawrenc e, Kansas, 1970.10 Roskam, J., Methods for Estimating Stability Derivatives ofConventional Subsonic Airplanes, Publishedbh author ,Lawrence, Kansas, 1971.11 Wentz, W .H. , Jr. and Volk, C.G., Jr., "Reflection-Plane Testsof Spoilers on an Advanced Technology Wing with a Large FowlerFlap," NASA CR-2696, 1976.

From theAIAA Progress in Astronautics and Aeronautics SeriesALTERNATIVE HYDROCARBON FUELS:COMBUSTION AND CHEMICAL KINETICSv. 62

A Project SQ U I D Wo r k s h o pEdited by Craig T. Bowman, Stanford UniversityaJ&rgen Birkeland, Departmento Energy

T current generationo internal combustion enginesh resultoa extended period o simultaneous evolutionoengines and fuels. During this period, th e engine designer wa s relatively free to specify fuel properties to meet engine per-formance requirements,ahpetroleum industry respondedbproducing fuels withhdesired specifications. However,today's rising cost of petroleum, coupled with th e realization that petroleum supplies will not be able to meet the long-termdemand,h st imulateda interestn al ternat ive l iquid fuels, part icular ly those t ha tcb derived from coal.Awidevariety of l iquid fuels can be produced from coal, and from other hydrocarbon and carbohydrate sources as well, rangingfrom methano l to high molecular weight , lo w volati l i ty oils. This volume is based on a set of original papers delivered at aspecial workshop calledbh Depar tmento Energyah Depar tmento Defense oh purposeo discussinghproblemso switching o fuels producible from such nonpetroleum sourcesoun automotive engines, aircraftgturbines,a stationary power plants.Tauthors were asked alsoo indicatehwresearchnhareasocombustion, fuelchemistry,a chemical kineticscb directed toward achieving a t imely t rans i t iono such fuels, should becomenecessary. Research scientists in those fields, as well as development engineers concerned with engines and power plants , willfind this volume a useful up-to-date analysis of the changing fuels picture.

463pp.,6x9iilus., $20.00Mem., $35.00List

TO ORDER WRITE: Publications Dept., AIAA, 1290 Avenue of the Am ericas, New York, N. Y. 10019

AIAA.1977.High.lift.Cardinal

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