ESTIMATION OF PITCHING MOMENT OF A HYBRID LIFTING FUSELAGE - DISGUISED AS HULL OF AN AIRSHIP

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1 Asian Research Publishing Netork (ARPN). All rights reserved..arpnjournals.com ESTIMATION OF PITCHING MOMENT OF A HYBRID LIFTING FUSELAGE - DISGUISED AS HULL OF AN AIRSHIP Anar Ul Haque 1, Waqar Asrar 1, Ashraf Ali Omar 2, Erin Sulaeman 1 and JS Mohamed Ali 1 1 Department of Mechanical Engineering, International Islamic University Malaysia, Kuala Lumpur, Malaysia 2 Department of Aeronautical Engineering, University of Tripoli, Libya aqar@iium.edu.my ABSTRACT Munk-Multhop s method is usually used for estimation of pitching moment of fuselage of conventional aircraft but application of the same for hybrid lifting fuselage had not been earlier explored. CFD methods can also be applied for the said purpose but it is difficult to separate out the portion of the moment caused by the fuselage, since the ing and fuselage affect each other. In the present ork, a hull disguised as hybrid lifting fuselage of a hybrid buoyant aircraft as taken as a test case. Slope of the pitching moment obtained from the Munk-Multhop s method as further corrected to account for the effect of slenderness ratio. Good agreement of results as found after defining the camber profile of the hybrid lifting fuselage and applying the said correction. The location of the ing relative to the fuselage and lift curve slope of ings has a dominant role in estimation of pitching moment coefficient of the fuselage. Keyords: munk-multhop s method, zero lift pitching moment coefficient, pitching moment coefficient, hybrid lifting hull. INTRODUCTION The concept of hybrid lifting fuselage is derived from lighter than air aircraft (LTA), hich get aerostatic lift due to buoyancy effect of lifting gas and aerodynamic lift generated by the aerodynamic profile of fuselage. The static longitudinal stability characteristics of airships is estimated by applying the methods either derived from the ind tunnel testing or by using the potential flo theory. Results of previous ork related to stability analysis of airships (Acanfora and Lecce, 2011; Moutinho and Azinheira, 2005; Wang, 2012) have shon that static stability criteria for aircrafts is not applicable for airships. This is perhaps due to the fact that airships donat have a ing attracted to it and that is the reason the airships do not have negative value of slope of the pitching moment coefficient as function of angle of attack, ( Carichner and Nicolai, 2013). Due to the absence of a comprehensive databank of (A&S) parameters, advanced design and analysis methods for such aircrafts are not yet fully established. In this regard an analytical effort as done in present research ork to use computational fluid dynamics and lo fidility tools to evaluate the applicability of Munk-Multhop s method. For hybrid lifting hull ith small ings attached to it; analytical relationship of pitching moment coefficient of fuselage at zero lift, and the slope of the pitching moment coefficient as function of angle of attack are shon belo as Equation. (1), taken from reference (Gudmundsson, 2013) and Equation. (2), derived from the Munk-Multhop s method to cater the effect of the shape, respectively. These equations contain the constant 36.5, hich facilitate the conversion of the angle (, i ) and slope C ZL f L from per radian to per degree, respectively. (1) (2) In Equation. (1-2), terms C ref and S ref are the reference dimensions for the chord length and reference area, respectively. Complete derivation of Equation. 2 is beyond the scope of this ork. It is important to note that in Equation. (2) the ing lift curve slope is in per degree; alloing the use of in per degree. dback x ( ) d back d front x ( ) d front and are upash gradient before the ind and donash gradient after the ing, respectively. The integrals in Equation (2) can be solved by using Simpson s rule or any other quadrature formula. Equation. (1-2) are no applied on a generic model of hybrid lifting hull of the hybrid buoyant aircraft. MATERIALS AND METHODS Fuselage used in the present study as taken from a recent ork by reference (Haque et al. 2014), hich has fineness ratio equal to 5.5 and internal volume of 535 m 3. Profile as obtained by using standard airfoils Eppler-1200 and S-1016 till 80 percent of chord length i.e. 2217

2 Asian Research Publishing Netork (ARPN). All rights reserved..arpnjournals.com in side vie, this lifting hull has a shape of Eppler-1200 airfoil and it is S-1016 as the top/plan vie. The extended version of Munk-Multhop s method (Equation. (1-2)) as then applied hich accounts for the effect of ing upash and its donash effects. Figure-1 shos the major dimensions of the fuselage used in the numerical integration ork. The fuselage as divided into 13 planes in lateral direction and slices their mid sections as are shon in the Figure-2. Figure-1. Implementation of Munk-Multhop method for estimating the and. Figure-2. Mid-sectional vie of the fuselage of hybrid lifting hull. Nose of the fuselage as defined as the datum/reference point. Sign convention used to define i is the same as that used in reference f (Gudmundsson, 2013), Figure-3. Effect of as included by estimating its valve using XFLR softare. Although the geometry of the fuselage as also modeled alongith ith that of the ing; but due to knon constrains of modeling, this analytical tool could not predict the aerodynamic forces acting on the voluminous fuselage. Therefore, only the ing as considered here for the analysis ork and for cruise flight condition; as estimated to be equal to (/degree) and is shon here as Figure-4. ANSYS-FLUENT, a commercial CFD analysis softare as used to obtain the aerodynamic properties of the fuselage. Numerical simulations ere run by employing the Menter Shear Stress Transport (MSST) turbulence model for cruise velocity, V cruise equal to 100 km/hr. No-slip all condition is employed at the surface of the fuselage. Figure-3. Fuselage camber incidence angle, i. f 2218

3 Asian Research Publishing Netork (ARPN). All rights reserved..arpnjournals.com Figure-4. Plot to get the slope of. (d) Variation in pitching moment coefficient of fuselage ith different reference areas. (a) Computational Grid. (e) Trendline of lift produced by the lifting fuselage. (b)surface Grid. (f) Plot used to find the C m (/degree). Figure-5. CFD results of fuselage alone case at V=100 km/hr (Haque et al. 2015). (c) Sectional vie of the grid and contours of total prssure on the surface of fuselage. In the simulation ork, steady-state condition is considered and a pressure-based solver; SIMPLEC as used. The C-O computational grid type used in this numerical ork is shon in Figure-5(a) and surface grid is given in Figure-5(b). Fully structured grid is generated so that the flo is aligned ith the grid. Sectional vies of the grid are shon in Figure-5(c). Grid independence study as also carried out by changing the number of grid points in the circumferential and axial direction. Grid 2219

4 Asian Research Publishing Netork (ARPN). All rights reserved..arpnjournals.com skeness as also checked before defining the properties of the boundary conditions. as estimated for different available options of reference area S ref and it as found that slope of decreases ith increase fus in its value, Figure-5(d). For the present study, similar to conventional aircraft S ref as taken equal to the total platform area of ing, equal to m 2. as fus also plotted as Figure-5(e) hich as further utilized to get the plot of C m vs C L. Plot shon in Figure-5(f) had provided the value of C m equal to -0.6, here lift becomes equal to zero. Moreover, it can be observed from Table-3 that ithout correction for slenderness ratio k 2 k 1, in comparison ith CFD result; the values of m as over predicted by the Munk-Multhop s C fus method. It can be observed from this table that although the CFD ork did not include the upash and donash fus effects due to the ing, but overall the results are quite in agreement ith those obtained from extended version of Munk-Multhop s method. It is cited in reference that the pitching moment contribution of the fuselage can also be approximated by Equation. (3), taken from a NACA Reprt (Gilruth and White, 1941). In this relationship; W f is the maximum idth of the fuselage and L f is the length. Figure (16.14) of reference (Raymer, 2012) provides the empirical pitching moment factor K f. fus 2 K f W f L f CS fus, perdeg (3) value obtained by using Equation. (2) for lifting fuselage under study as almost double than that predicted by CFD and Munk-Multhop s method and its value is equal to fus and Table-1. Implemntation of Munk s Multhop matrix to find C for ing location at m, including the sensitivity analysis for. ZL m BACK FUSELAGE FRONT FUSLEAGE ID Ii Dx x c i fi x dβ/dα 2 Δ 2 Δ Δ 2 Δ i ii iii iv i ii iii iv i ii iii iv WING W Table-2. and fus for ing at m. Table-3.Comparison of results. ID Ii Dx x c i fi x dβ/dα 2 Δ 2 Δ BACK FUSELAGE FRONT FUSLEAGE WING W The difference beteen the CFD and analytical results may not be treated as error because ( Multhop. H., 1936) mentioned that so far based on the comparison study, the Munk s correction for slenderness ratio had little effect on longitudinal motion of fuselage. 2220

5 Asian Research Publishing Netork (ARPN). All rights reserved..arpnjournals.com But hen his theory is applied for the lift producing fuselage than a need is perceived to cater the effect of the slendernss ratio. The forces and moments due to upash and don effects of the presented ing have a small influence on the values of and C m, but may have a much fus greater effect on very large fuselages. Boundary layer separation and vortex flo at aft body are the potential reasons of small difference beteen the results for C m. For accurate estimation of C m, value of should be defined ith accuracy for knon value ZL of zero lift angle attack of ing. Based on the comparison of analytical and computational results, correction to account the effect of the slenderness ratio is suggested. CONUSIONS In this analytical and numerical study, Multhop's method hich is based on Munk's ork on the pitching moment of airships as evaluated for its potential usage for hybrid lifting fuselage. Correction had been applied in C m and C m to account for the effects of fineness fus ratio. If the correction to account the shape/slenderness ratio effects is not included, then in comparison ith CFD results, existing Munk-Multhop's method for conventional aircraft has over-predicted the slope of pitching moment coefficient for a hybrid lifting fuselage. ACKNOWLEDGEMENTS The support of the Ministry of Science, Technology and Innovation (MOSTI), Malaysia, under the grant SF0189 is gratefully acknoledged. Special thanks to Professor Snorri Gudmundsson for useful discussions during the course of this research ork. [4] Grant E Carichner and Leland M Nicolai. (2013). Fundamentals of Aircraft and Airship Design: Volume II, Airship Design. (J. A. Schetz, Ed.). American Institute of Aeronautics and Astronautics,AIAA. [5] Gudmundsson, S. (2013). General Aviation Aircraft Design: Applied Methods and Procedures. Butterorth-Heinemann. [6] Haque, A. U., Asrar, W., Omar, A. a., Sulaeman, E., & Ali, J. M. (2014). Conceptual Design of a Winged Hybrid Airship. 21 st AIAA Lighter-Than-Air Systems Technology Conference, doi: / [7] Moutinho, A., & Azinheira, J. R. (2005). Stability and robustness analysis of the AURORA airship control system using dynamic inversion. In Robotics and Automation, ICRA Proceedings of the IEEE International Conference on (pp ). [8] Multhop. H., (1941). The Aerodynamics of Fuselage, NACA Technical Report. [9] Raymer, D. (2012). Aircraft Design: A Conceptual Approach. (J. A. Schetz, Ed.) (Fifth Edit.). Washington, DC: American Institute of Aeronautics and Astronautics, Inc. doi: / [10] Wang, X. L. (2012). Computational Fluid Dynamics Predictions of Stability Derivatives for Airship. Journal of Aircraft, 49(3), doi: /1.c REFERENCES [1] Acanfora, M. and Lecce. L, (2011) On the Development of the Linear Longitudinal Model for Airships Stability in Heaviness Condition, Aerotecnica Missili & Spazio, The Journal of Aerospace Science, Technology and Systems. Aerotecnica, 90(1), (2011) [2] Gilruth, R., R. and White, M., D., (1941), "Analysis and prediction of longitudinal stability of airplanes", NACA Report No: NACA-TR-711. [3] Haque, A. U., Asrar, W., Omar, A. A., Sulaeman, E., and Ali, JS. M., (2015), Poer-off static stability analysis of a clean configuration of a hybrid buoyant aircraft, 7 th Ankara Internatıonal Aerospace conference, September METU, Ankara Turkey. 2221