CHAPTER 5 WING DESIGN Mohammad Sadraey Daniel Webster College Table of Contents Chapter 5 ................................................................................................................................................... 1 Wing Design ............................................................................................................................................. 1 5.1. Introduction ................................................................................................................................ 1 5.2. Number of Wings ...................................................................................................................... 4 5.3. Wing Vertical Location ............................................................................................................ 5 5.3.1. High Wing............................................................................................................................. 7 5.3.2. Low Wing .............................................................................................................................. 9 5.3.3. Mid Wing ............................................................................................................................. 10 5.3.4. Parasol Wing ..................................................................................................................... 10 5.3.5. The Selection Process ................................................................................................... 11 5.4. Airfoil ........................................................................................................................................... 11 5.4.1. Airfoil Design or Airfoil Selection .............................................................................. 11 5.4.2. General Features of an Airfoil .................................................................................... 14 5.4.3. Characteristic Graphs of an Airfoil ........................................................................... 17 5.4.4. Airfoil Selection Criteria ................................................................................................ 23 5.4.5. NACA Airfoils ..................................................................................................................... 24 5.4.6. Practical Steps for Wing Airfoil Section Selection .............................................. 32 5.5. Wing Incidence ........................................................................................................................ 37 5.6. Aspect Ratio .............................................................................................................................. 39 5.7. Taper Ratio ................................................................................................................................ 45 5.8. The Significance of Lift and Load Distributions ........................................................... 48 5.9. Sweep Angle ............................................................................................................................. 52 5.10. Twist Angle ............................................................................................................................. 65 5.11. Dihedral Angle ....................................................................................................................... 69 5.12. High Lift Device ..................................................................................................................... 73 5.12.1. The Functions of High Lift Device .......................................................................... 73 Wing Design i 5.12.2. High Lift Device Classification ................................................................................. 75 5.12.3. Design Technique ......................................................................................................... 79 5.13. Aileron....................................................................................................................................... 84 5.14. Lifting Line Theory ............................................................................................................... 84 5.15. Accessories ............................................................................................................................. 89 5.15.1. Strake ............................................................................................................................... 89 5.15.2. Fence ................................................................................................................................. 90 5.15.3. Vortex generator .......................................................................................................... 91 5.15.4. Winglet ............................................................................................................................. 91 5.16. Wing Design Steps ............................................................................................................... 92 5.17. Wing Design Example ......................................................................................................... 93 Problems ............................................................................................................................................ 103 References ........................................................................................................................................ 107 Wing Design ii CCHHAAPPTTEERR 55 WWIINNGG DDEESSIIGGNN 5.1. Introduction In chapter 4, aircraft preliminary design – the second step in design process – was introduced. Three parameters were determined during preliminary design, namely: aircraft maximum takeoff weight (WTO); engine power (P), or engine thrust (T); and wing reference area (Sref). The third step in the design process is the detail design. During detail design, major aircraft component such as wing, fuselage, horizontal tail, vertical tail, propulsion system, landing gear and control surfaces are designed one-by-one. Each aircraft component is designed as an individual entity at this step, but in later design steps, they were integrated as one system – aircraft- and their interactions are considered. This chapter focuses on the detail design of the wing. The wing may be considered as the most important component of an aircraft, since a fixed-wing aircraft is not able to fly without it. Since the wing geometry and its features are influencing all other aircraft components, we begin the detail design process by wing design. The primary function of the wing is to generate sufficient lift force or simply lift (L). However, the wing has two other productions, namely drag force or drag (D) and nose-down pitching moment (M). While a wing designer is looking to maximize the lift, the other two (drag and pitching moment) must be minimized. In fact, wing is assumed ad a lifting surface that lift is produced due to the pressure difference between lower and upper surfaces. Aerodynamics textbooks may be studied to refresh your memory about mathematical techniques to calculate the pressure distribution over the wing and how to determine the flow variables. Wing Design 1 Basically, the principles and methodologies of “systems engineering” are followed in the wing design process. Limiting factors in the wing design approach, originate from design requirements such as performance requirements, stability and control requirements, producibility requirements, operational requirements, cost, and flight safety. Major performance requirements include stall speed, maximum speed, takeoff run, range and endurance. Primary stability and control requirements include lateral-directional static stability, lateral-directional dynamic stability, and aircraft controllability during probable wing stall. During the wing design process, eighteen parameters must be determined. They are as follows: 1. Wing reference (or planform) area (SW or Sref or S) 2. Number of the wings 3. Vertical position relative to the fuselage (high, mid, or low wing) 4. Horizontal position relative to the fuselage 5. Cross section (or airfoil) 6. Aspect ratio (AR) 7. Taper ratio () 8. Tip chord (Ct) 9. Root chord (Cr) 10. Mean Aerodynamic Chord (MAC or C) 11. Span (b) 12. Twist angle (or washout) (t) 13. Sweep angle () 14. Dihedral angle () 15. Incidence (iw) (or setting angle, set) 16. High lifting devices such as flap 17. Aileron 18. Other wing accessories Of the above long list, only the first one (i.e. planform area) has been calculated so far (during the preliminary design step). In this chapter, the approach to calculate or select other 17 wing parameters is examined. The aileron design (item 17) is a rich topic in wing design process and has a variety of design requirements, so it will not be discussed in this chapter. Chapter 12 is devoted to the control surfaces design and aileron design technique (as one control surface) will be presented in that chapter. Horizontal wing position relative to the fuselage will be discussed later in chapter 7, when the fuselage and tail have been designed. Thus, the wing design begins with one known variable (S), and considering all design requirements, other fifteen wing parameters are obtained. The wing must produce sufficient lift while generate minimum drag, and minimum pitching moment. These design goals must be collectively satisfied throughout all flight operations and missions. There are other wing parameters