research article experimental investigation of a wing-in...

Research ArticleExperimental Investigation of a Wing-in-Ground Effect Craft

M. Mobassher Tofa,1,2 Adi Maimun,1,2 Yasser M. Ahmed,1,2

Saeed Jamei,1,2 Agoes Priyanto,1,2 and Rahimuddin2

1 Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia2Marine Technology Centre, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia

Correspondence should be addressed to Yasser M. Ahmed; [email protected]

Received 3 November 2013; Accepted 23 December 2013; Published 16 February 2014

Academic Editors: K.-M. Chung and J. E. Lamar

Copyright © 2014 M. Mobassher Tofa et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

The aerodynamic characteristics of thewing-in-ground effect (WIG) craftmodel that has a noble configuration of a compoundwingwas experimentally investigated and Universiti Teknologi Malaysia (UTM) wind tunnel with and without endplates. Lift and dragforces, pitching moment coefficients, and the centre of pressure were measured with respect to the ground clearance and the wingangle of attack. The ground effect and the existence of the endplates increase the wing lift-to-drag ratio at low ground clearance.The results of this research work show new proposed design of the WIG craft with compound wing and endplates, which canclearly increase the aerodynamic efficiency without compromising the longitudinal stability. The use of WIG craft is representingan ambitious technology that will help in reducing time, effort, and money of the conventional marine transportation in the future.

1. Introduction

Wing in ground effect is quite a new concept of designingfast ships, which has vast relevance in numerous areas such astransportation of cargo, tourism, rescue operations, and mil-itary functions. WIG craft gives an alternate solution to gainhigher speed [1]. The ground effect (GE) is a phenomenonwhere the lift-to-drag ratio of a body will increase while itis cruising at a very close distance to the surface of wateror ground [2]. Volkov and Russetsky [3] and Hooker [4]widely discussed useful characteristics of WIG craft. Thedevelopment of WIG crafts originated from observationsmade of the landing performance of aircraft in 1920’s. LaterUSA and theUSSR became interested in attempting to exploitthe potential benefits of ground effect. The USA abandonedefforts to produce ground effect craft in the mid 1960’s asthey were more interested in surface effect ship development.Germany began work in the late 1960’s using the designsof Alexander Lippisch. However, USSR was the undisputedleader in research and development of WIG crafts up tothe late 1980’s [5]. Under these circumstances, the Ministryof Science Technology and Innovation (MOSTI) Malaysiaprovided funds to develop a WIG craft here.

The lift and drag that are produced by a wing definethe performance and general attributes of the craft that itsupports. A wing that is moving through the air producesa resultant force. Lift is the component of the resultantforce perpendicular to the velocity vector of the wing. Thecomponent that is resultant force parallel to the velocityvector of the wing is defined as induced drag.There are otherforms of drag, which are collectively known as parasite orprofile drag; this drag is created by the friction of the objectmoving through the air. The total drag of an object movingthrough the air, can be achieved by summing up induceddrag and parasite drag. Both lift and drag are functions ofa number of variables such as the density of the air, thevelocity of the object through the air and the geometry of theobject. Figure 1 depicts the formation of lift (𝐿) and induceddrag (𝐷

𝑖) from the resultant force (𝑅) created by the wing’s

movement through the air. In addition, the previous figureshows that the position of the wing as it moves through theair is characterized by the geometric angle of incidence (𝛼),where the geometric angle of incidence is the angle betweenthe chord line of the wing section and the velocity vectorof the wing [6]. If the wing is designed properly, the liftingsurface near ground generates higher lift at smaller ground

Hindawi Publishing Corporatione Scientific World JournalVolume 2014, Article ID 489308, 7 pageshttp://dx.doi.org/10.1155/2014/489308

2 The Scientific World Journal

Chord line

Veffective

Vfreestream

W

LR

Di

eff

Figure 1: Lift and drag of a wing section [6].

clearances. However, the drag decreases with decreasingground clearance for span-dominated GE.

A properly designed lifting system should increase lift-to-drag ratio and reduce drag for constant lift as the groundclearance reduces [5]. Many experimental and numericalsimulations have been conducted by several researchers tostudy the phenomenon ofGE. Jung et al. [7] conducted exper-imental investigation ofwingwithNACA6409 section.Threedifferent types of endplates were tested in those experimentsat various ground clearances, angle of attacks, and aspectratios. Endplates help to increase the performance of thewingthough moving its center of pressure forward to the leadingedge. Furthermore, it was found that the freestream velocityhas insignificant effect on the wing aerodynamic coefficients.Pressure distribution through the symmetrical airfoil surfaceunder different ground clearances and angle of attack werestudied by Ahmed and Sharma [8]. NACA4412 airfoil sectionwith flap in extreme ground effect were numerically inves-tigated by Ockfen and Matveev [9]. The study consists ofa steady-state, incompressible, finite volume method usingSpalart-Allmaras turbulence model for the turbulent flow.It was found that favorable trailing-edge flap configurationimproves aerodynamic characteristics of NACA4412 wingsection. Chun and Chang [10] numerically analyzed theturbulent flow around two-dimensional WIG with respect totwo ground boundary conditions, that is, moving and fixedbottom boundary. According to this study, the lift force andmoment are not influenced by different bottom conditions,though the drag force simulated by the moving bottom isgreater than that by the fixed one. The influence of theendplates on the aerodynamic characteristics of small aspectratio (AR) wing was studied by Park and Lee [11]. Accordingto their study, the reduction of the tip vortex will developa substantial rise in the lift and lift-to-drag ratio, whichcan be developed by endplate. They claimed endplates alsomade a small deviation of height stability at different groundclearances and angle of attacks, which can reduce the heightstability. Park and Lee [12] demonstrated the optimal profilesof two-dimensional wings to reach a moderate stability andhigh efficiency. In an another research work by Yang et al.[13], it was shown that for three-dimensional wing, end platesactually enhance the height stability at low ground clearance.Kornev and Matveev [14] found that the profiles of tail wingand main wing are the main factors of static height stability.They suggested that for acceptable stability of aWIG craft, the

centre of gravity should be close to the height of aerodynamiccenter (𝑋

ℎ), and it should be between the height of aerody-

namic center and pitch aerodynamic center (𝑋𝛼). Irodov [15]

recommended a height static stability criterion as follows:

HS =𝐶𝑀𝛼

𝐶𝐿𝛼

−𝐶𝑀𝑧

𝐶𝐿𝑧

< 0,

𝑋𝛼=𝐶𝑀𝛼

𝐶𝐿𝛼

,

𝑋ℎ=𝐶𝑀𝑧

𝐶𝐿𝑧

,

(1)

where 𝐶𝑀𝛼, 𝐶𝐿𝛼, 𝐶𝑀𝑧, and 𝐶𝐿

𝑧are derivatives of lift and

moment coefficient with respect to pitching angle and height.In a stable WIG craft, these derivatives usually are 𝐶𝐿

𝑧> 0,

𝐶𝑀𝛼< 0, 𝐶𝐿

𝛼> 0, and 𝐶𝑀

𝑧> 0 [15].

A new configuration of the compound wing was devel-oped in UTM by Jamei et al. [16] to improve the aerodynamicperformance of the wing. The compound wing was dividedinto three parts: the middle part of rectangular wing shapeand the side parts with reverse taper wings with an anhedralangle. The compound wings could create a greater reductionof downwash velocity and modify the pressure distributionon the lower side. The high increment of lift-to-drag ratio forthe present wing in extreme ground effect recognizes a goodefficiency for wing-in-ground (WIG) craft. Furthermore, ithas been found that the performance of the wing improvesnoticeably for a certain total span of compound wing whenthe span of the middle part becomes smaller. It can be seenfrom the literature review that improving the aerodynamiccharacteristics of the wing in proximity to the ground bydifferentmeans, such as the endplates, different configurationof wing is one of the important parameters in designing aWIG craft. The improvement of wing can increase the rangeand endurance of flight and decrease the fuel consumptionandCO

2emission.Therefore, there aremany research articles

dealt with the wing in ground effect, butmost of these articlesfocused on the aerodynamic characteristics of the wing onlyand not the whole WIG craft.

In this research work, the aerodynamic characteristicsand static stability of theWIG craft with the compound wingconfiguration [14] developed at UTM was experimentallyinvestigated with and without endplates.

2. UTM Wind Tunnel

The aerodynamic characteristics, specifically the groundeffect, of the WIG craft with a compound wing were investi-gated in a low speed wind tunnel at the Universiti TeknologiMalaysia (UTM-LST). This wind tunnel was able to delivera maximum air speed of 80m/s (160 knots or 288 km/hr)inside the test section. The size of test section was 2.0meters wide, 1.5 meters height, and 5.5 meters long. Theflow inside the wind tunnel was of good quality, with aflow uniformity

The Scientific World Journal 3

Figure 2: New compound wing configuration designed in UTM[16].

Thewind tunnel is equipped with a 6-component balancefor load measurements. The balance is a pyramidal type withvirtual balance moment at the centre of the test section. Thebalance has a capability to measure aerodynamic forces andmoment in the 3-dimensional. The aerodynamic loads canbe tested at various wind direction by rotating the model viaturntable. The accuracy of the balance is within 0.04% basedon 1 standard deviation.Themaximum load range is ±1200Nfor axial and side loads [17].

3. WIG Craft Model

The experiments were carried out on a WIG craft modelthat used a new compound wing configuration [16] as shownin Figures 2 and 3. The compound wing was composed ofthree parts: a rectangular wing in the middle and two reversetaper wings with an anhedral angle at the sides [16]. TheNACA 6409 airfoil section was selected as a section of thecompound wings.The principal dimensions of theWIG craftare summarized in Table 1.

4. Experimental Procedures and Set-Up

In the wind tunnel, aerodynamic force measurements werecarried out for a range of ground clearances (ℎ/𝑐) and differ-ent angles of attacks (𝛼), from ℎ/𝑐 = 0.18 to ℎ/𝑐 = 0.25 andfrom 𝛼 = 4∘ to 𝛼 = 6∘. Ground clearance (ℎ/𝑐) was defined asthe distance ratio between the wing trailing edge centre andground surface (ℎ) to root chord length (𝑐) of the wing.

In this study, the floor of wind tunnel was used as a fixedflat ground as shown in Figure 4. The WIG craft model wasmounted on the test section of the wind tunnel with a strut asshown in Figure 5.The position of the strut was at the 40% ofchord length from the leading edge of the compound wing.The strut was adjustable and then was fixed at any height.TheWIG craft model could be rotated about an axis at the strutposition.

The frontal area ratio of the WIG craft model and thetest section was small; therefore, the blockage ratio for thewings related to side and roof walls of the wind tunnel canbe neglected. In this study, all experiments were performedwith freestream velocity of 25m/s.

5. Results and Comparisons

The WIG craft model aerodynamic coefficients and centreof pressure were obtained in this study using the followingformulas:

𝐶𝐿=𝐿

0.5𝜌𝑈2𝑆,

𝐶𝐷=𝐷

0.5𝜌𝑈2𝑆,

WIG craft model with endplates

(a)

WIG craft model without endplates

(b)

Figure 3: WIG craft model with compound wing.

Table 1: Principle dimensions of WIG craft.

Scale factor 1 : 6Wing span 83.4 cmWing root chord 66.7 cmMiddle wing span 41.4 cmAspect ratio 1.25Anhedral angle 13∘

Length of WIG craft 1.2mBreadth of WIG craft 0.13mTail wing span 0.78mTail wing chord 0.15m

𝐶𝑀=𝑀

0.5𝜌𝑈2𝑆𝑐,

𝑋𝑐𝑝= 0.4 +

𝐶𝑀

𝐶𝐿cos 𝛼 + 𝐶

𝐷sin 𝛼.

(2)

The lift coefficients of the WIG craft model with and withoutendplates are shown in Figure 6. As expected the lift coeffi-cient of the WIG craft model with endplates was higher thanthe lift coefficient of the WIG craft model without endplates.The lift coefficients of theWIG craftmodel increase up to 42%and 50% for angles of attack of 4∘ and 6∘, respectively. Fromthe previous figure, it is clear for higher angle of attack andlower ground clearance endplates significantly enhanced thelift coefficient.


(a) (b)

Figure 4: Wind tunnel test for WIG craft model: (a) model with endplates and (b) model without endplates.

Inlet

5.5m

Roof

WIG craft

Bottom Strut

1.5m Outlet

AmplifierBalance system

Computer

Figure 5: Experimental setup in the wind tunnel at the Universiti Teknologi Malaysia.

Figure 7 depicts the drag coefficient (𝐶𝐷) of theWIG craft

model with and without endplates. The drag coefficients oftheWIG craftmodel with and without endplates do not showhigh discrepancy for each angle of attack, probably becauseof reduction of induced drag due to the effect of endplates.Thus, the increment of drag can be related only to angle ofattack and ground clearance. For higher angle of attack andground clearance drag coefficient increases up to 11% and 5%,respectively, as shown in the figure.

The performance of an aircraft is defined by its lift todrag ratio (𝐿/𝐷).The comparison of lift to drag ratio betweenthe WIG craft model with and without endplates is shownin Figure 8. For lower ground clearance endplates enhancethe lift-to-drag ratio up to 45%; the lift-to-drag ratio of WIGcraftmodel with endplates decreases sharply compared to themodel without endplates as the ground clearance increases.Augmentation of lift to drag ratio can also be attributed tothe angle of attack, where larger angle of attack amplifies thelift to drag ratio. In addition, 𝐿/𝐷 decreased when the groundclearance was smaller.

The moment coefficients (𝐶𝑀) of the WIG craft model

with and without endplates are shown in Figure 9. Thepitching moments were measured about the point which was40% of the chord length from the leading edge. The 𝐶𝑀

𝑧

being positive for the wing with end plates is consistent withthe prior discussion about stability for a WIG.

The second parameter that hasmain effect on the stabilityof WIG craft is its center of pressure. The distance betweenthe leading edge and center of pressure on the wing isdefined as𝑋

𝑐𝑝. Figure 10 shows the center of pressure for the

WIG craft model with and without endplates. In general, theposition of center of pressure of the WIG craft model shiftedtowards leading edge due to effect of endplates. This effect isexpected as pitching moment reduced due to endplates.

As discussed earlier, static stability depends on the rate ofchange of moment and lift coefficient with respect to angleof attack and ground clearance. The height of aerodynamiccenter (𝑋

ℎ) and pitch aerodynamic center (𝑋

𝛼) of the WIG

craft model with endplates were upstream than that of theWIG craft model without endplates as depicted in Figures 11and 12. The height of static stability (HS) of the WIG craftmodel for both with and without endplates was negative withrespect to ground clearance (Figure 13) that makes the craftstatically stable for both cases [15].

6. Conclusion

This study experimentally investigated the aerodynamic char-acteristics of aWIG craftmodel with a new configuration of acompoundwing. Effect of endplates on the craft aerodynamiccharacteristics was studied and it was found that endplatesincrease the lift and drag ratio of theWIG craftmodel. Finally,


0.4

0.35

0.3

0.25

0.2

0.150.17 0.19 0.21 0.23 0.25 0.27

h/cCL

WIG Withendplate (

WIG Withendplate (

WIG Withoutendplate (


Figure 6: Lift coefficient (𝐶𝐿) of WIG craft model with and without endplates versus ground clearance (ℎ/𝑐) at different angles of attack.

0.062

0.060

0.058

0.056

0.054

0.0520.17 0.19 0.21 0.23 0.25 0.27

h/c

CD

WIG Withendplate (

WIG Withendplate (



Figure 7: Drag coefficient (𝐶𝐷) of WIG craft model with and

without endplates versus ground clearance (ℎ/𝑐) at different anglesof attack.

7

6

5

4

3

2

L/D

0.17 0.19 0.21 0.23 0.25 0.27

h/c

WIG Withendplate (

WIG Withendplate (



Figure 8: Lift-to-drag ratio (𝐿/𝐷) of WIG craft model with andwithout endplates versus ground clearance (ℎ/𝑐) at different anglesof attack.

0.05

0.04

0.04

0.03

0.03

0.02

0.02

0.01

0.01

0.00

CM

0.17 0.19 0.21 0.23 0.25 0.27

h/c

WIG Withendplate (

WIG Withendplate (



Figure 9: Moment coefficient (𝐶𝑀) of WIG craft model with and

without endplates versus ground clearance (ℎ/𝑐) at different anglesof attack.

0.90

0.85

0.80

0.75

0.70

0.65

0.60

Xcp/C

0.17 0.19 0.21 0.23 0.25 0.27

h/c

WIG Withendplate (

WIG Withendplate (



Figure 10: The position of the center of pressure (𝑋𝑐𝑝) of WIG craft

model with and without endplates versus ground clearance (ℎ/𝑐) atdifferent angles of attack.


0.25

0.20

0.15

0.10

0.05

0.00

−0.05

Xh

0.18 0.19 0.2 0.21 0.22 0.23 0.24

h/c

WIG With endplateWIG Without endplate

Figure 11: Height of aerodynamic center (𝑋ℎ) of WIG craft model

with and without endplates versus ground clearance (ℎ/𝑐) at angleof attack of 4∘.

−0.03

−0.05

−0.07

−0.09

−0.11

X𝛼

0.18 0.19 0.2 0.21 0.22 0.23 0.24

h/c


Figure 12: Pitch aerodynamic center (𝑋𝛼) of WIG craft model with

and without endplates versus ground clearance (ℎ/𝑐) at angle ofattack of 4∘.

0.00

−0.05

−0.10

−0.15

−0.20

−0.25

−0.300.18 0.19 0.2 0.21 0.22 0.23 0.24

h/c


HS

Figure 13: Height of static stability (HS) of WIG craft model withand without endplates versus ground clearance (ℎ/𝑐) at angle ofattack of 4∘.

the following points can be concluded from this researchwork.

(i) A new design of WIG craft was presented by com-bining compound wing with new configuration andendplates.

(ii) The aerodynamic performance of the new design wasinvestigated by wind tunnel tests and aerodynamiccoefficients are presented for the new design.

(iii) The static stability of the new design was investigatedand it was found that the newdesign is statically stableenough.

Nomenclature

𝑐: Chord length𝐶𝐿: Lift coefficient𝐶𝐷: Drag coefficient𝐶𝑀: Moment coefficient𝐷: Drag corceℎ: Height of trailing edge above the groundℎ/𝑐: Ground clearanceHS: Height of static ctability𝐿: Lift force𝐿/𝐷: Lift-to-drag ratio𝑆: Planform area of wing𝑋𝑐𝑝: Center of pressure𝑈: Freestream velocity𝛼: Angle of attack, geometric angle of incidence.

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of paper.

Acknowledgment

The authors would like to thank the Ministry of Science,Technology and Innovation (MOSTI) Malaysia, for fundingthis research project.The authors are grateful toDr. S.Mansorand Eng. Abd Basid of UTM aeronautics lab for providingnecessary help and guidance needed to perform this test.

References

[1] K. V. Rozhdestvensky, “Ekranoplans—the GEMs of fast watertransport,” Transactions of the Institute of Marine Engineers, vol.109, no. 1, pp. 47–74, 1997.

[2] J. M. Reeves, “The case for surface effect research, platformapplications and development opportunities,” in Proceedings ofthe NATO-AGARD Fluid Mechanics Panel Symposium in LongRange and Long Range Endurance Operation of Aircraft (FMP’93), pp. 24–27, The Hague, The Netherlands, 1993, Session 1A.

[3] L. D. Volkov and A. A. Russetsky, “Ekranoplans: problems andperspectives,” Sudostroenie Journal, pp. 1–6, 1995.

[4] S. Hooker, Wingships: Prospect for High-Speed Oceanic Trans-port, Jane’s All theWorld’s Surface Skimmers, Jane’s InformationGroup, Coulsdon, UK, 1982.

[5] K. V. Rozhdestvensky, “Wing-in-ground effect vehicles,”Progress in Aerospace Sciences, vol. 42, no. 3, pp. 211–283, 2006.

[6] M. Halloran and S. O’Meara, “Wing in ground effect craftreview,” Contract Report CR-9802, The Sir Lawrence WackettCentre for Aerospace Design Technology, Royal MelbourneInstitute of Technology, Melbourne, Australia, 1999.


[7] K. H. Jung, H. H. Chun, and H. J. Kim, “Experimental inves-tigation of wing-in-ground effect with a NACA6409 section,”Journal of Marine Science and Technology, vol. 13, no. 4, pp. 317–327, 2008.

[8] M. R. Ahmed and S. D. Sharma, “An investigation on theaerodynamics of a symmetrical airfoil in ground effect,” Exper-imental Thermal and Fluid Science, vol. 29, no. 6, pp. 633–647,2005.

[9] A. E. Ockfen and K. I. Matveev, “Aerodynamic characteristicsof NACA 4412 airfoil section with flap in extreme groundeffect,” International Journal of Naval Architecture and OceanEngineering, vol. 1, no. 1, pp. 1–12, 2009.

[10] H. H. Chun and C. H. Chang, “Turbulence flow simulation forwings in ground effect with two ground conditions: fixed andmoving ground,” International Journal of Maritime Engineering,pp. 211–227, 2003.

[11] K. Park and J. Lee, “Influence of endplate on aerodynamic char-acteristics of low-aspect-ratio wing in ground effect,” Journal ofMechanical Science and Technology, vol. 22, no. 12, pp. 2578–2589, 2008.

[12] K. W. Park and J. H. Lee, “Optimal design of two-dimensionalwings in ground effect usingmulti-objective genetic algorithm,”Ocean Engineering, vol. 37, no. 10, pp. 902–912, 2010.

[13] W. Yang, Z. Yang, and C. Ying, “Effects of design parameters onlongitudinal static stability forWIG craft,” International Journalof Aerodynamics, vol. 1, no. 1, pp. 97–113, 2010.

[14] N. Kornev and K. Matveev, “Complex numerical modelingof dynamics and crashes of wing-in-ground vehicles,” AIAA,2003-600, 2003, http://authors.library.caltech.edu/21291/1/Kor-nev N Complex Numerical modeling.pdf.

[15] R. D. Irodov, “Criteria of longitudinal stability of ekranoplan,”Ucheniye Zapiski TSAGI, vol. 1, no. 4, pp. 63–74, 1970.

[16] S. Jamei, A. Maimun, S. Mansor, and N. Azwadi, “Numericalinvestigation on aerodynamic characteristics of a compoundwing in ground effect,” Journal of Aircraft, vol. 49, no. 5, pp.1297–1305, 2012.

[17] Aeronautic Laboratory Universiti Teknologi Malaysia, 2013,http://aerolab.fkm.utm.my/?id=home&pid=523.

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014


Active and Passive Electronic Components

Control Scienceand Engineering

Journal of



RotatingMachinery


Hindawi Publishing Corporation http://www.hindawi.com

Journal ofEngineeringVolume 2014

Submit your manuscripts athttp://www.hindawi.com

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

Acoustics and VibrationAdvances in



Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation http://www.hindawi.com

Volume 2014

The Scientific World JournalHindawi Publishing Corporation http://www.hindawi.com Volume 2014

SensorsJournal of


Modelling & Simulation in EngineeringHindawi Publishing Corporation http://www.hindawi.com Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks


research article experimental investigation of a wing-in...

Documents