Aerodynamic Characteristics of Canard-ForwardSwept Wing Aircraft Configurations

G. Q. Zhang∗ and S. C. M. Yu†

Nanyang Technological University, Singapore 639798, Republic of Singapore

A. Chien‡

University of California, Los Angeles, California 90095

and

S. X. Yang§

Beijing Institute of Technology, 100081 Beijing, People’s Republic of China

DOI: 10.2514/1.C031740

The aerodynamic characteristics between the canard and wing of the Canard-forward swept wing aircraft

configurations have been investigated numerically at low Reynolds number. The variation of the aerodynamic

characteristics at different canard positions is the focus of the present investigation. The aerodynamic interference

and the mutual coupling effect between the canard and wing will have great influences on the lift, drag, and sideslip

characteristics of the whole aircraft. The canard-generated vortex can induce a favorable interference onto the main

wing, controlling the onset of the boundary layer separation from the leading edge. At small angles of attack (α <10 deg the aerodynamic characteristics are sensitive to the relative position of the canard and the wing, but at high

angles of attack (α > 20 deg they are not only related to the orientationof the canard (forwardorbackward), but alsothe features of the vortices generated above the canard and the wing, including their strength and location.

Nomenclature

Cd = drag coefficientCL = lift coefficientCP = pressure coefficientCX = Yawing moment coefficientCY = rolling moment coefficientc = chord length, mL = fuselage length, mR = radius of the frontal nose, mRe = Reynolds number, Uc∕γα = angle of attackβ = angle of sideslipδXW = Wing deflection angle at x axisδYC = canard deflection angle at y axis

I. Introduction

W ITH the advancement of the aviation technology theaerodynamic performance for modern fighter aircrafts has

become more demanding [1–3]. Even the overload stall charac-teristics have now become one of their basic features [4,5]. There aretwo main advantages of employing canard in the aircraft design.Firstly, lower trim drag; in contrast to tail-wing configuration wheretail wing contributes to the nose-up with its negative lift to trim pitchby providing positive lift, the presence of the canard can affect thelongitudinal lift load distribution of the aircraft. It can lead to sonicboom reduction while achieving higher lift to drag ratio due to lowertrim drag under constant lift conditions. Secondly, potential for lower

sonic boom intensity; the installation of the canard can mitigateconcentration of equivalent area distribution at the most concernedmain-wing portion. The up/down-wash due to the tip-vortex of thecanard surface also influences the main-wing lift load distributionfavorably.Yoshimoto and Uchiyama [6] focused on the advantages of

optimized canard surface positioning for supersonic aircraft in termsof sonic boom reduction and improvement in lift to drag ratio. Theresults revealed that amongmany chosen design variables, the settingangle was the most sensitive to the two objective functions; sonicboom intensity and lift to drag ratio. Skujins and Cesnik [7] inves-tigated the canard’s effect on the flow over the elevon controlsurfaces. The computed results showed that the slipstream behind thetrailing edge of a canard did in fact have an impact on the controleffectiveness of the elevon. Preliminary experiments further showedthat the slipstream’s effect on the elevon diminished with increaseddistance from the canard. Soltani et al. [8] conducted a series of wind-tunnel tests to study the effects of a canard and its position on thedownstream flowfield over the wing surface. The wing-surfacepressure was measured for both canard-off and canard-on config-urations. The results showed that a remarkable increase in the wingsuction peak was found for the canard-on configurations. At low tomoderate angles of attack the mid-canard configuration developed ahigher suction region on the wing. Whereas at high angles of attack,the upper-canardwas found to induce themost favorable flowfield onthe wing.Ma and Liu [9] conducted wind-tunnel tests to investigate the

effect of thewing’s and canard’s sweep angles on lift enhancement ofa delta-wing/canard configuration at low to high angle of attack(AOA). The results showed that when AOA was less than a certaincritical value, no lift enhancement occurred at any canard config-urations. When AOA was more than the critical value, the canardconfigurations of the 40 deg swept wing were the first to have a lift-enhancement effect. As the wing sweep of canard configurationsbecame larger, the AOA at which lift enhancement occurred becomelarger correspondingly. Schmid and Breitsamter [10] conductedwind-tunnel tests to measure the turbulent flowfield above the wingof a delta-canard-configuration at moderate (α � 15 deg) and high(α � 24 deg) angle of attack by hot-wire anemometry. The resultsshowed that at high angle of attack the flow always separated at theleading edge for both the nondeflected and deflected leading-edgecases. For the latter case of the deflected leading edge, the interaction

Received 9 November 2011; revision received 24 August 2012; acceptedfor publication 24August 2012; published online 30 January 2013.Copyright© 2012 by the American Institute of Aeronautics and Astronautics, Inc. Allrights reserved. Copies of this paper may be made for personal or internal use,on condition that the copier pay the $10.00 per-copy fee to the CopyrightClearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; includethe code 1542-3868/13 and $10.00 in correspondence with the CCC.

*Research Fellow, Aerospace EngineeringDivision, School ofMechanicaland Aerospace Engineering.

†Associate Professor, Aerospace Engineering Division, School ofMechanical and Aerospace Engineering.

‡Assistant professor, Division of Interventional Neuroradiology, Depart-ment of Radiological Sciences.

§Professor, Aircraft Design Division, School of Aerospace Engineering.

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between the inboard wing vortex and leading-edge vortex resulted indecreasing downstream expansion of the burst vortex and therebyreducing turbulence intensity levels. Heron and Myose [11]investigated the effect of a canard on a 70 deg swept main delta wing.Dye flow visualization was used to observe the vortex breakdownlocation during dynamic pitch-up and pitch-down motion withdifferent pitching rates. The results showed that compared to the no-canard configuration there was a delay in the vortex breakdown. Themost favorable delay was obtained when the canard was locatedclosest to the main delta wing or when the model was pitched up at afast rate or pitched down at a slow rate. Chang et al. [12] alsoconducted the water-tunnel experiment to test the flow visualization,normal force, and pitch moment of the NASATP-1803 strake-wingmodel at high attack angles. The results show that as the pitch-reduced frequency increases the wing vortices sustain longer flowlines and provide more normal force during pitch-up motion.Bergmann andHummel [13] carried out experiments to investigate

a close-coupled canard-wing-body combination in symmetrical flow.The configuration consisted of a delta canard, a deltawing and a bodyof revolution as fuselage. The results showed that the aerodynamiccharacteristics of this configuration were governed by the inter-ference between the vortex generated by the canard and wing and bytheir breakdown. The vortex breakdown for the canard vortex hadbeen kept away from the canard due to the favorable accelerationeffect from the wing, even up to very high AOA. This had led to highmaximum lift for high-canard positions (above the wing). Sohn andChung [14] investigated the effects of a strake planform change on thevortex characteristics of double-delta wings through wing-surfacepressure measurements and the off-surface flow visualization of thewing-leeward How region. The results show the double-delta wingconfiguration with the 79 deg sweep single-delta shape strake canproduce a more concentrated vortex system at upstream locations.However, the concentrated vortex system for the double-delta wingconfiguration with the 79 deg sweep single-delta shape strake tended

to diffuse and breakdown much faster than the other two config-urations as the flow proceeded downstream. The test results revealedthat strake modification can greatly alter the vortex flow patternaround a double-delta wing.Our preliminary studies [15] mainly focused on the longitudinal

characteristics for the forward swept wing (FSW) aircraft config-urations but without considering the vertical fin. It was discoveredthat the canard also plays many important roles in the FSW aircraftand the interference of vortices generated by the canard and the wingmay lead to better lift characteristics. The canard vortex can effec-tively control separation of the boundary layer at the leading edge ofthe main wing. Nevertheless, the yawing and rolling characteristicsbetween the canard and the FSW aircraft configurations have notbeen fully understood. With these issues in mind, this article hasmodified the previous geometry, and introduced the vertical fin intothe aircraft such that the corresponding lift, drag, pitching, yawing,and rolling characteristics can be investigated in greater details.Section II will describe the computational approach including theflow configurations. Results will be presented and discussed inSec. III. The paper ends with concluding remarks in Sec. IV.

II. Flow Configurations and Computational Method

A. Forward Swept Wing Configuration

First, the design for the FSW configurations is described asfollows. As shown in Fig. 1a, No. 1 corresponds to the no-canardcase. In the back-sweep canard (BSC) configurations, No. 2represents the length from the leading edge of the canard to the noseaccounting for 42% of the length of the fuselage while No. 3 is for17%. In the forward-sweep canard (FSC) configuration, No. 4, 5, and6 represent 54%, 42%, and 17% of the fuselage length, respectively.The high canard is located at �1∕6 of the radius of the frontal nosewhile the low canard is at −1∕6 of the radius (see in Fig. 1b).The geometric parameters of the FSWmodel considered have been

listed in Table 1, including the wing and canard. The length of the

Fig. 1 Different views of the generic FSW aircraft model.

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FSWmodel fuselageL is 0.5 m, and the radiusR of the frontal cross-actual area is 0.024 m. The NACA0012 airfoil is used as both thecanard and wing. The reference area for the wing and canard is 0.056and 0.0068 m2, and the corresponding span of thewing and canard is0.438 and 0.189m, respectively. The aspect ratioAR for thewing andcanard is 5.12 and 4.73, respectively. The forward- and backward-swept angles for the wing are−21 deg and−34 deg, with respect tothe canard is 46 and 26 deg, respectively. The FSC is basically theinverted shape of the BSC.

B. Computational Method

The simulation is conducted using the ANSYS/FLUENTV.6.3.26. When modeling the whole aircraft, the results will besignificantly affected by the quality of the mesh. As shown in Fig. 2,during meshing for the wing and the canard, the method of sizefunction is adopted to improve the mesh quality. The radial length ofthe computational domain is 30 times the cross-section of thefuselage. The computational domain is divided into 24 subregions togenerate structural mesh, concentrating on the regions close to thebody surface. The whole mesh has been smoothed and swapped,which can rebuild the nodes, modify the connectivity of units, andimprove the accuracy of the calculation.The freestream velocity considered is at 20 m∕s and the

corresponding Reynolds number (Re) is based on 1.6 × 105. In thenumerical simulation the couple-implicit solver is used. SIMPLEiteration is adopted with the wall functions.

III. Results and Discussion

A. Comparison of the Simulation and Experimental Results

First, the reliability of the numerical methodmust be verified.Withall the computational region parameters of the model being the sameas the FSW aircraft simulation compared with the wind tunnel testperformed by Scharpf and Muellert [16]. As shown in Fig. 3a, thethree main factors affecting the performance of a closely coupleddual-wing system with the same airfoil shape and equal chords arestagger St the longitudinal separation of the wings. Gap G is thevertical distance between the wings. Decalage δ (δc, δw) is the angleof the canard andwingwith respect to theX andY axis. BothSt andGare measured from 1∕4 chord point to 1∕4 chord point andnondimensionalized with respect to chord length c. Both the wingand the canard are FX63-137 airfoils with chord length of 6 in. andaspect ratio of 2.67. The Reynolds number (Re) is about 1 × 105. The

lift and drag characteristics of the tandem case at different angles forthe canard and wing δ (δXC, δXW) are compared.As shown in Fig. 3b, it can be seen that numerical results are

in excellent agreement with the wind-tunnel experimental data,showing the accuracy of the present CFD approach.

B. The Longitudinal Characteristics of Forward Swept Wing

1. Effects of Longitudinal Positions of the Backward-Sweep Canard

The vortex interferences around the canard and the wing actuallyfall into two broad categories: swirling and inducing. The swirling isa direct interference, which occurs between two relatively closevortices, and is generated through the shear layer. The other inter-ference is the indirect inducing, which occurs between two relativelyfar away vortices and is irrelevant to the shear layer. Figure 4 showsthe lift and drag characteristics at different longitudinal positions forthe BSC, and the canard is positioned middle of the fuselage.As shown in Fig. 4a, compared with No. 1 (the noncanard case),

the corresponding lift characteristics for No. 2 and No. 3 have beenimproved significantly. The CL at α � 40 deg in particular hasincreased by about 47.27% and 37.37%, respectively, whereasCLmax

has increased by about 44.69% and 35.45%, respectively. It showsthat the aerodynamic interference and mutual coupling between thecanard and wing have actually enhanced the lift characteristics of thewhole aircraft.In contrast, as shown in Fig. 4b, the drag characteristics do not

show any clear difference when α � 10 deg. On one hand, thecanard-FSW configuration can enlarge the surface area of the entireaircraft to a certain extent, but it can also increase the correspondingfriction drag. On the other hand, the dynamic pressure of the flowaround themainwing after passing the canardwill become lower thanthatwithout passing the canard, and the effective angle of attack of themain wing will also be reduced owing to the downwash effect. Thesetwo effects cancel each other and render the overall drag to be almostunchanged. However, with the further increase in angles of attack,the rise of lift-related drag becomes more dominating and thiscan eventually produce larger net drag when α � 10 deg. Whenα � 10 deg, the change of canard longitudinal position fromNo. 2 toNo. 3 has little effect on the lift characteristics of the whole aircraft.At small angles of attack the vortices above the canard and wing areunable to be generated effectively. When the canard is moved closerto the wing the downwash effects will become stronger, therebyreducing the effective angle of attack to the main wing. This willeventually postpone the generation of vortex over the main wing.However, the upwash effect that the wing exerts on the canard willalso become stronger. The net effect results in almost absence of anyobvious change in the lift characteristics.However, at α � 10 deg, as shown in the Figs. 5ai and 5biii, we

can see that a stronger and concentrated vortex is generated abovethe surface of themainwing. The vortex induces negative pressure onthe upper surface of the main wing, which can provide substantialvortex lift. These contributions can account for a very largeproportion of the total lift force and the corresponding lift curvesshownonlinear trend. If theBSC ismoved closer to themainwing the

Fig. 2 Decomposition of the computational domain.

Table 1 Summary of the FSW geometry

Geometric parameters FSW FSC & BSC

Reference Areas, m2 0.056 0.0068Span, m 0.438 0.189Root Chord, m 0.115 0.06Tip Chord, m 0.056 0.02Aspect Ratio 5.12 4.73Taper Ratio 0.487 0.333Forward/backward swept angle, deg −21, −34 46, 26

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upwash effects on the canard created by the wing will becomestronger. From Figs. 5aii and 5biv, we can see that the streamlineshave induced the secondary clockwise-vortices (No. 2) above thecanard. This can make the corresponding lift characteristics benefitfurther from the so-called canard-wing interference. Moreover, thesecondary vortex of No. 2 is about two times stronger than No. 3.It also reveals that the close-coupling configuration has enhanced thelongitudinal dynamic characteristics further.

2. Effects of Vertical Positions of Backward-Sweep Canard

Figures 6a and 6b show the lift and drag characteristics at differentvertical positions of BSC-FSW, and Fig. 7 shows the correspondingstreamlines at different vertical positions of BSC-FSW. For all theangles of attack considered, the lift characteristics of high canard aregenerally better than those at the low canard combination.Whenα ≤ 10 deg, thevortices are unable to generate alone the top

surfaces of the canard and wing, so the “conventional” flow patternmakes the lift and drag characteristics insensitive to the verticalposition of the canard. However, when α > 10 deg, as shown inFig. 7aii, the No. 2 high canards had created its ownvortex. However,compared with the middle position (Figs. 5aii and 5biv), vortex (1)and (2) for the high canard begins tomove closer andmergewith eachother. The corresponding vortex lift force will therefore be greatlyreduced. Close to the upper surface of the No. 2 wing shown inFig. 7ai, we can also see that a secondary clockwise-vortex has alsobeen generated. This will also make some contributions to the vortexlift force for the high BSC-FSW configuration.In addition, the effects on the wing vortices created by the low

canard are relatively weaker (Fig. 7bi), which in turn enable theboundary layer to separate earlier and the lift created by the vortexdrops sharply. If the canard is moved closer to the wing, thecorresponding downwash created by the low canard will becomestronger, and the effective angles of attack of the wing will decrease

and the corresponding “enhanced” lift with respect to the vortex willalso decrease eventually. Consequently, at all attack angles, the liftcharacteristics with the high canard are generally better than thosewith the low canard. Although the drag characteristics show thesimilar trend as the lift, due to the presence of canard, there areinsignificant changes because the friction drag plays a dominant partunder the high attack angles.

3. Effects of Longitudinal Positions of the Forward-Sweep Canard

In FSC-FSW configuration, the lift and drag characteristics aregiven in Fig. 8, and the streamlines plotting at selected cross-sectionplanes are shown in Fig. 9. The canard is also positionedmiddle of thefuselage.Comparing Fig. 8 with Fig. 4, the aerodynamic characteristics of

the FSC configuration are significantly different from that of the BSCconfiguration. At all angles of attack considered, when the canard ismoved closer to the wing, the corresponding lift characteristics willnot be improved. However, there is a transition position for the FSCNo. 5 (at about 42% of the fuselage). After this position both theclose-coupled and farther-lower positions have shown better aerody-namic characteristics, for example No. 4 (54% of the fuselage) andNo. 6 (17% of the fuselage). This is mainly due to the opposite trendof the surface flow pattern for the FSC and BSC. The flow around theFSC is always deflected towards the symmetry plane of the wing,whereas the coming air from the front canard will concentrate on theinside of the main wing, near the root separation zone of the mainwing. The vortex created by FSC appears earlier, which also breaks

b) Drag characteristics

a) Lift characteristics

Fig. 4 Comparison of the lift and drag characteristics at differentlongitudinal positions of BSC.

b) Variation of lift characteristics

a) The parameter definition of the canard and wing

Fig. 3 Lift characteristics of tandem wing compared with wind-tunnel

test data.

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a) Lift characteristics b) Drag characteristicsFig. 6 Comparison of the lift and drag characteristics at different vertical positions of BSC.

Fig. 5 Streamlines perpendicular to the body axis at different longitudinal positions of BSC (Ma � 0.06, α � 20 deg).

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down earlier. The corresponding vortex lift force will thereforedecrease, which will speed up the boundary-layer separation at theroot of the wing. In the FSC configuration the downwash on thewing imposed by the canard will occupy a dominating position.Consequently, as the canard is moved closer to the wing (from No. 6toNo. 5 position), the stronger downwash effect will become, and theworse the longitudinal characteristics will become.As a result, the liftcharacteristics of No. 6 FSC is better than No. 5 FSC.However, when the canard is moved beyond the transition position

(about 42% of the fuselage), the upwash on the canard created by thewing will be recovered. This will enable the root of the wing to befreed from separation and thereby, improving the flow pattern near

the root wing. The relatively better aerodynamic characteristics suchas No. 4 (54% of the fuselage) can be obtained in the close-coupledposition.As shown in Figs. 9a and 9b, both No. 4 (54% of the fuselage) and

No. 5 (42% of the fuselage) have formed their own vortex. But thevortex strength for No. 4 is found to be stronger than No. 5, and thevortex center is also closer to the surface of wing. The vortex hasoccupied more than 60% span length of wing. The control over theflow of wing has therefore been strengthened. However, the vortexcenter for No. 5 is further away from the surface of the wing, and theability to control the airflow of the wing surface is weaker than thatof No. 4.

b) Drag characteristicsa) Lift characteristics

Fig. 8 Comparison of the lift/drag characteristics at different longitudinal positions of FSC.

Fig. 7 Streamlines perpendicular to the body axis at high and low BSC-FSW (Ma � 0.06, α � 20 deg).

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4. Effects of Vertical Positions of Forward-Sweep Canard

In FSC configuration, Fig. 10 shows the lift and drag charac-teristics for the canard at different vertical positions and the corre-sponding vortex structures are also shown in Fig. 11.As shown in Fig. 10, the lift characteristics of the FSC are also very

different from those of the BSC. One can see that in the close-coupleposition, the lift characteristics of the high canard are obviously betterthan the low canard. Although the canard vortex breaks down earlier,the obvious vortex has also generated on the upper surface of No. 4high layout. This can create the relatively larger vortex lift force. ForNo. 4 low layout, the vortex breaks down earlier. Hence, at all theangles of attack, the lift characteristics of No. 4 high position showsbetter than No. 4 low position.However, for No. 6, after passing a certain angle of attack

(α � 20 deg), No. 6 low canard will become better than the highcanard. This may be attributed to the difference in the flow pattern. Inthe FSC configuration, the canard vortex breaks down earlier and theforce to control thewing vortex will becomeweaker. This means thata large proportion of the vortex-induced lift will be lost, but thedownwash on the wing made by the canard would convert into thefavorable interference. The downwash on the wing made by the lowcanard will become stronger than that of the high canard. Although

the effective angles of attack of the wing decreases, the root of thewing has become cleaner and the flow pattern of the root wing hasbeen improved. The upwash on the canard made by the wing thusbecomes stronger. The net effects produce better lift characteristicsfor No. 6 low canard than No. 6 high canard.

C. The Yawing and Rolling Characteristics of Forward Swept Wing

1. Backward-Sweep Canard

In order to investigate the yawing and rolling characteristics ofCanard-FSWaircraft configuration, we choose eight selected modelsto investigate further. They are No. 2 high and low BSC, No. 3 highBSC, No. 4 high and low FSC, No. 6 high and low FSC, as well asNo. 1 noncanard.As shown in Fig. 12a, at β > 15 deg, for the No. 2 high and low

BSC and No. 3 high BSC, when the canard is added, the corre-sponding yawing- and rolling-moment curves have been changed.However, compared with the rolling moment, the yawing moment isnot so sensitive to the presence of the canard.Figure 12b shows that both the No. 2 and No. 3 high BSC have

made contributions to the rolling stability of the whole aircraft. Inaddition, the No. 2 high BSC shows better rolling characteristics than

Fig. 9 Streamlines perpendicular to the body axis at different longitudinal positions of FSC (Ma � 0.06, α � 20 deg).

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the No. 3 high BSC. But for the No. 2 low BSC, the correspondingrolling-moment curve has moved up, indicating that the No. 2 lowBSC has created unstable rolling moment.For the No. 2 and No. 3 high BSC, the right sliding can reduce the

back sweep angles of the left wing. The aspect ratio would increase,but the right wing will have the opposite trends. The correspondinglift force created by the left wing should be relatively bigger than theright wing. In addition, due to the fact that the canard is placed at ahigher position, the fuselage can create the additional asymmetricdistribution of angles of attack on the left and right canard. Positive

angle of attack is created on the left canard, whereas at the rightcanard it becomes negative, both these two factors could create anoverall stable rolling moment.However, forNo. 2 lowBSC, due to the presence of the low canard,

it can create extremely stronger downwash effects on the rear wing.The left wing is affected by the leading-edge vortex of low BSC, andthe corresponding vortex is relatively weaker than that of the right

a) Lift characteristics

b) Drag characteristics

Fig. 10 Comparison of the lift and drag characteristics at differentvertical positions of FSW.

Fig. 11 Streamlines perpendicular to the body axis at high FSC-FSW (Ma � 0.06, α � 20 deg).

b) Rolling moment characteristics

a) Yawing moment characteristics

Fig. 12 The yawing- and rolling-moment of BSC-FSW.

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wing and is located nearer to the wing root. Due to the slidingeffect, the downwash effects can improve the flow pattern of the rightwing,with an extended boundary-layer separation. Both these factorsmake the differences of lift force on the left and right wing decreased.Consequently, the rolling stability drops.

2. Forward-Sweep Canard

As shown in Fig. 13a, different from that of BSC, both the yawingand rollingmoments have shown changes at different positions of theFSC.ComparingNo. 6 high and lowFSCwith theNo. 4 high and lowFSC, the positions of canard have made no difference on the yawingmoment. It also shows that the rolling characteristics of the highposition of FSC are better than the low position arrangement.The difference can also be attributed to the flow pattern between

BSC and FSC. Both the canard and wing will create their ownleading-edge vortex at certain angles of sideslip. The vortex of FSC isrelatively smaller and breaks down earlier than in the case of BSC, sothevortex of FSCwill not have good control over the flow of themainwing. It appears that all the changes have to attribute to the positionof FSC.As shown in Fig. 13b, the rolling characteristics of high FSC are

better than the low FSC configuration. It is mainly due to the fact thatthe vortex created by the FSC is weaker and also breaks down earlier,so the vortex effect is not fully exploited. The downwash effects havebecome dominating in this period. The effective angles of attack onthe left wing suffer a decrease. Consequently, the differences of

the asymmetric lift force on the right and left wing will decrease. Sothe curves for lowFSChavemoved up, and are not any better than thehigh FSC configuration.

IV. Conclusions

Compared with the noncanard configuration, the introduction ofthe canard can fundamentally change the flow pattern of the mainwing. The aerodynamic interference and mutual coupling betweenthe canard andwing can actually enhance the lift characteristics of theforward swept wing (FSW) aircraft.At small angles of attack (α < 10 deg), the aerodynamic charac-

teristics of canard-FSW configuration mainly depend on the geom-etry shapes of the canard (forward or backward swept) as well as therelative positions of the canard and wing; at high angles of attack(α > 20 deg), the aerodynamic performance of the configuration isnot only related to the shape of the canard (forward or backward) butalso the features of the vortices generated above the canard and thewing, including their strength and location.At high angles of attack, due to the difference in the flow pattern

between backward swept canard (BSC) and forward sweep canard(FSC) configurations, it is easier to create the secondary vortex onthe upper surface of BSC than the FSC, which can also provide asubstantial vortex lift force.In the BSC configuration, the yawing moment is not sensitive

to the introduction of the canard. Both the low BSC and FSCconfiguration can make the corresponding rolling-moment curvesmove up in the positive direction. It also reveals that the low-positioncanard can reduce the rolling stability.

References

[1] Tu, E. L., “Vortex-Wing Interaction of a Close-Coupled CanardConfiguration,” Journal of Aircraft, Vol. 31, No. 2, 1994, pp. 314–321.doi:10.2514/3.46489

[2] Howard, R. M., and O’Leary, J. F., “Flowfield Study of a Closed-Coupled Canard Configuration,” Journal of Aircraft, Vol. 31, No. 4,1994, pp. 908–914.doi:10.2514/3.46578

[3] Lee, J.W., Jeon,K. S., Kim,M. J., Byun,Y.H., Kim,C. J., andYu,Y.H.,“Rotor Design for the Performance Optimization of Canard Rotor/WingAircraft,”Computational Science and Its Applications, Vol. 3984, 2006,pp. 932–941.doi:10.1007/11751649_102

[4] Montalvo, C., and Costello, M., “Effect of Canard Stall on ProjectileRoll and Pitch Damping,” Journal of Aerospace Engineering, Vol. 225,No. 9, 2011, pp. 1003–1011.doi:10.1177/0954410011403578

[5] Kim, C., and Lee, J., “Hub Drag-Reduction Strategies of Canard Rotor/Wing Unmanned Aerial Vehicles,” Journal of Aircraft, Vol. 44, No. 4,2007, pp. 1388–1391.doi:10.2514/1.24395

[6] Yoshimoto, M., and Uchiyama, N., “Optimization of Canard SurfacePositioning of Supersonic Business Jet for Low Boom and Low DragDesign,” AIAA Paper 2003-3576.

[7] Skujins, T., and Cesnik, C.E.S., “Canard–Elevon Interactions on aHypersonic Vehicle,” Journal of Spacecraft and Rockets, Vol. 47, No. 1,2010, pp. 90–100.doi:10.2514/1.44743

[8] Soltani, M.R., Askari, F., Davari, A.R., and Navebzadeh, A., “Effects ofCanard Position on Wing Surface Pressure,” Scientia Iranica

Transaction B: Mechanical Engineering, Vol. 17, No. 2, 2010,pp. 136–145.

[9] Ma, B.F., and Liu, P.Q., “Effects of Wing and Canard Sweep on LiftEnhancement of Canard Configurations,” Journal of Aircraft, Vol. 41,No. 6, 2004, pp. 1521–1523.doi:10.2514/1.8707

[10] Schmid, A., and Breitsamter, C., “Experimental Study on the Flowfieldof a Delta-Canard-Configuration with Deflected Leading Edge,” New

Results in Numerical and Experimental Fluid Mechanics V, Vol. 92,2006, pp. 94–102.doi:10.1007/978-3-540-33287-9_12

[11] Heron, I., andMyose, R. Y., “DeltaWingVortex-Burst Behavior under aDynamic Freestream,” Journal of Aircraft, Vol. 46, No. 5, 2009,pp. 1500–1512.doi:10.2514/1.36697

a) Yawing moment characteristics

b) Rolling moment characteristics

Fig. 13 The yawing- and rolling-moment of FSC-FSW.

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[12] Chang, L.M., Lee, H. J., Huang, C.M., Chuang, S. H.,Wang, S.W., andChen, K. T., “Static and DynamicAerocharacteristics Testing of Strake-Wing Aerial Vehicle in Water Tunnel,” Transactions of the Japan

Society for Aeronautical and Space Science, Vol. 53, No. 180, 2010,pp. 91–98.doi:10.2322/tjsass.53.91

[13] Bergmann, A., and Hummel, D., “Aerodynamic Effects of CanardPosition on a Wing Body Configuration in Symmetrical Flow,” AIAAPaper 2001-0116.

[14] Sohn, M. H., and Chung, H. S., “Effects of Strake Planform Change onVortex Flow of a Double-Delta Wing,” Journal of Aircraft, Vol. 44,

No. 6, 2007, pp. 1842–1848.doi:10.2514/1.30261

[15] Zhang, G. Q., Yang, S. X., and Xu, Y., “Investigation of VortexInteraction in Canard-FSW Configurations Based on the NumericalWind Tunnel Method,” Chinese Journal of Aeronautics, Vol. 23, No. 3,2010, pp. 312–319.doi:10.1016/S1000-9361(09)60221-1

[16] Scharpf, D. F., and Muellert, T. J., “Experimental Study of a LowReynolds Number Tandem Airfoil Configuration,” Journal of Aircraft,Vol. 29, No. 2, 1992, pp. 231–236.doi:10.2514/3.46149

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