Wing Design II Lift surfaces/devices Control surfaces Ailerons Leading-edge slats Vertical Stabilizer Rudder Spoilers Elevators Flaps Horizontal Stabilizer Wing Wing-tip device Basic Configuration Choices Wing planform span taper ratio sweep Wing airfoil geometry airfoil sections twist & incidence thickness
Basic Configuration Choices Vertical wing placement Control surface placement Empennage Fuselage shape Definition of Sideslip and Yaw +n V +β Wing Taper Ratio 2
Wing Taper Ratio Reduces the wing-root bending moments by moving the center of lift inboard Thicker inboard sections allow for lighter, more rigid structures Allows for reduction of inboard airfoil thickness for transonic drag reduction Must keep room for ailerons, etc. Wing Incidence Incidence Angle Wing Incidence Allows a lower rotation angle on take-off Permits the airplane to be lower to the ground May increase the lower fuselage size, and therefore increase drag
Wing Airfoil Sections The tip should have a high maximum lift coefficient and gradual stalling characteristics The inboard section should have a high maximum lift coefficient with flaps extended Wing Thickness Distribution Thicker wings increase fuel volume Thicker wings are structurally lighter Thick wings will increase transonic drag penalty Best to add thickness near the root to balance these requirements Wing Twist
Wing Twist Spanwise distribution of airfoil chord lines are not in the same plane Used to maintain desired pressure and lift distribution Wash-out: decrease incidence near the tip to avoid stall in the region of ailerons Wing Dihedral The angle between a horizontal plane containing the root chord and a plane midway between the upper and lower surfaces of the wing Dihedral: the wing plane lies above the horizontal plane Anhedral: the wing plane lies below the horizontal plane Wing Dihedral
Wing Dihedral Positive sideslip (nose left) creates an upward velocity on right wing and downward velocity on left wing Equivalent of downwash Increases angle of attack over right wing, decreases angle of attack over left wing Results in a rolling moment to the left Adverse Yaw When the aircraft rolls to the left, the drag of the right wing is increases increased induced drag increased drag of ailerons The plane will tend to yaw to the right! This is an example of cross coupling Wing Sweep & Dihedral Already discussed Mach effects Sweep also affects dihedral
Wing Sweep & Dihedral Wing Sweep & Dihedral Positive sideslip increases velocity over the right wing and decreases velocity over the left wing The right wing will have more lift than the left wing The wing will roll left Vertical Wing Placement Low wing Mid wing High wing
Vertical Wing Placement & Dihedral The vertical placement of the wing affects dihedral as well Each wing placement type has different characteristics Vertical Wing Placement Vertical Wing Placement & Dihedral Positive sideslip over high wing aircraft increases angle of attack of right wing and decreases angle of attack of left wing The right wing has more lift than the left wing The plane will roll left The affect is opposite for a low wing aircraft
Low Wing Flaps Low Wing Easier landing gear stowage Ground clearance difficulty Decreases roll stability (dihedral effect) Mid Wing Flaps
Mid Wing Provides the lowest drag Allows for better clearance than low wing Structural carry-through a problem High Wing Flaps High Wing Allows for placing the fuselage close to the ground Allows clearance for engines/props Possible structural weight savings Increases roll stability (dihedral effect)
Stability Coupling We have seen that the aircraft geometry has a large affect on the stability, control, and handling qualities of the aircraft In general, there are two types of affects: directly coupled cross coupled Stability Coupling The affect of the elevator on pitch moment is an example of direct coupling The affect of roll attitude on yaw moment is an example of cross coupling In general, direct coupling is an order of magnitude larger than cross coupling