wing design ii - california polytechnic state universityrcumming/wing_design_ii.pdf1 wing design ii...
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Wing Design II
Leading-edge slatsAilerons
Elevators
Rudder Spoilers
Flaps
Horizontal Stabilizer
Vertical Stabilizer
Wing-tip device
Wing
Lift surfaces/devices Control surfaces
Basic Configuration Choices
• Wing planform– span– taper ratio– sweep
• Wing airfoil geometry– airfoil sections– twist & incidence– thickness
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Basic Configuration Choices
• Vertical wing placement • Control surface placement• Empennage• Fuselage shape
Definition of Sideslipand Yaw
V∞β+
n+
Wing Taper Ratio
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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
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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
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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
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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
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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
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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
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Low Wing
Flaps
Low Wing
• Easier landing gear stowage• Ground clearance difficulty• Decreases roll stability (dihedral effect)
Mid Wing
Flaps
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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)
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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