1. Kwanjung Yee Pusan National University Aircraft Conceptual Design Copyright © 2009 by Kwanjung Yee

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3. - 2 - Scope of this Chapter

4. - 3 - The output of the configuration layout → design drawings and geometric information Design layout process begin with conceptual layouts → aerodynamic concept/internal components location Used to discuss novel ideas before the layout Once the design has been iterated → “Inboard profile” : more detailed than the initial layout → “Inboard isometric” drawing : prepared by art group for the purpose of illustration and briefing End Products of Configuration Layout

5. - 4 - “Lofting” : the process of defining the external geometry of the aircraft “Production Lofting” : most detailed form of lofting → exact, mathematical definition of the entire aircraft → accurate within a few hundredth of an inch over the entire aircraft “Lofting” gets its name from ship building → the hull shape was defined in the loft over the shipyard “Conic lofting” : lofting method based on a mathematical curve form / used first time on P-51 Mustang → wide variety of curves and easy to use A conic is 2 nd degree curve whose family includes circle, ellipse, parabola and hyperbola → its shape depends upon the angle of the cut through the cone Explanation of the figure above Conic Lofting

6. - 5 - To create a smoothly lofted fuselage using conics, the points A,B,C and S in each of cross sections can be connected longitudinally by a smooth line → Longitudinal Control Lines (A, B, C, S) While this procedure seems complicated at first, with a little practice a good designer can construct an accurate conic in less than a minute Conic Fuselage Development

7. - 6 - The new cross section is created by measuring, from the LCLs, the positions of the A,B,C and S points at the desired location of the new cross section For point A, each point is defined by two measurements, one from side view and one from top view “Control Stations” : the original cross sections that are used to develop the longitudinal control lines Typically, 5~10 control stations will be required to develp a fuselage that meets all geometric requirements Five control stations are used to define fighter fuselage Station 120 : approx. circular → used for cockpit Station 240 : side-mounted inlet Station 370 : similar to station 240, relatively square cross-sectional shape Station 500 : circular cross section → connection with a round exhaust nozzle The canopy, inlet duct and inlet duct fairing would be lofted in a similar fashion Side and Top view of longitudinal control points Conic Fuselage Development

8. - 7 - In the design evaluation, one should evaluate the design layout to ensure that the cross sections are smooth longitudinally In shipbuilding, the smoothness of hull contour is evaluated by “waterline” For aircraft, it is more common to use vertically oriented cuts known as “buttock-plane cuts” “Buttock-plane” cuts from the intersection of the aircraft with vertical planes defined by their distance from the center Fuselage Loft Verification

9. - 8 - Amount of compound-curvature in lofting → Cost driver “ Flat-wrap” : surface with curvature in only one direction → a surface can be constructed by wrapping a flat sheet → far cheaper and easier than other construction technique Constant cross section shape Linearly scaled section shape If the fuselage surface is smooth, then the longitudinal lines for the different butt-planes will all be smooth Buttock-plane cuts can also be used to generate new cross sections Flat-Wrap Fuselage Lofting

10. - 9 - The geometric dimensions necessary for layout of the reference wing or tail are given in the figure above The spanwise location of the mean aerodynamic chord(MAC) can be determined by a quick graphical method shown above The wing is initially located on the aircraft that some selected percent of the MAC is aligned with aircraft C.G. → First estimate of the wing position to attain the required stability characteristics Wing/Tail Layout and Loft

11. - 10 - Wing/Tail Lofting The reference wing is defined to the aircraft centerline and is based on the projected area Actual, exposed wing begins at the side of the fuselage and includes the effect of the dihedral upon the true-view area “ Leading-edge extension(LEX)” increases lift for combat maneuvering Highly blended wing/body is used to minimize the transonic and supersonic shocks Once the actual wing planforms are settled, they are required to verify that there is sufficient room for the fuel tanks, landing gear, spars etc. For initial design, it is assumed that the airfoil coordinates are smoothly loffed → Simplifying the generation of cross sections

12. - 11 - The wetted area of the fuselage is initially estimated using just the side and top views of the aircraft by the method shown above Aircraft wetted area(S wet ) : the total exposed surface area → the area of the external parts that would get wet if it were dipped into water : major contributor to friction drag The wing and tail wetted area can be approximated from their planforms → true view exposed plnform area * a factor based on the wing or tail thickness ratio The wing/tail wetted area is estimated using the relations shown in the figure Wetted Area Determination

13. - 12 - Aircraft internal volume is used as a measure of the reasonablensss of a new design Aircraft internal volume is estimated in a similar fashion to the wetted area estimation A more accurate estimation of internal volume can be obtained by graphical integration process much like that usd for wetted area determination A more accurate estimation of wetted area can be obtained by graphical using a number of fuselage cross sections Volume Determination

14. - 13 - Overall Design Layout Steps