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