Wing Design II

Wing Design II
Lift surfaces/devices
Ailerons
Control surfaces
Leading-edge slats
Vertical Stabilizer
Rudder
Spoilers
Flaps
Wing
Wing-tip device
Elevators
Horizontal Stabilizer
Basic Configuration
Choices
• Wing planform
– span
– taper ratio
– sweep
• Wing airfoil geometry
– airfoil sections
– twist & incidence
– thickness
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Basic Configuration
Choices
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•
•
•
Vertical wing placement
Control surface placement
Empennage
Fuselage shape
Definition of Sideslip
and Yaw
+n
V∞
+β
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
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