AE317 Aircraft Flight Mechanics & Performance UNIT B: Wings and Airplanes ROAD MAP . . . B - 1: Wings, H - L Devices, & Whole Aircraft B - 2: Mach - Number Effects & Lift/Drag B - 3: Advanced Subjects & An Exercise Brandt, et.al., Introduction to Aeronautics: A Design Perspective Chapter 4: Wings and Airplanes 4.1 Design Motivation 4.2 Wings 4.3 High - Lift Devices 4.4 Whole Aircraft Lift 4.5 Whole Aircraft Drag and Drag Polar Unit B - 1: List of Subjects Wing Geometry Wing Tip Vortices & Downwash Induced Drag Winglets & Tip Plates High - Lift Devices
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AE317 Aircraft Flight Mechanics & Performance
UNIT B: Wings and Airplanes
ROAD MAP . . .
B-1: Wings, H-L Devices, & Whole Aircraft
B-2: Mach-Number Effects & Lift/Drag
B-3: Advanced Subjects & An Exercise
Brandt, et.al., Introduction to Aeronautics: A Design Perspective
A wing with a rectangular planform, a NACA 2412 airfoil, a span of 5 m, and a chord of 2 m is operating in standard sea-level atmospheric condition at a freestream velocity (magnitude) of 42 m/s and an angle of attack of 8 degrees. If the wing’s span efficiency factor is 0.9, how much lift and drag is it generating?
Example 4.1
Page 8 of 10 Unit B-1
Trailing-Edge Flaps
• Plain Flap: changes camber to increase lift; effect is limited by additional flow separation.
• Split Flap: deflects only the underside of the trailing edge; it avoids the flow separation of upper
surface (slightly greater lift than plain flaps).
• Slotted Flap: has a gap or slot to allow faster-moving air from the lower surface to flow over the
upper surface; the higher energy air delays flow separation of upper surface. A single, double, and
triple slotted flap designs exist.
• Fowler Flap: moves the surface aft to increase the wing area before deflecting downward to increase
camber. Fowler flaps usually have one or more slots to increase effectiveness.
Effects of Trailing-Edge Flaps
• Increase camber, moving the lift-curve up and to the left.
• (Except Fowler flaps) the lift-curve slope is unchanged.
• Zero-lift angle of attack ( )0L = is shifted to more negative.
• Drag is increased at lower lift condition, and minimum drag coefficient will become higher.
Strakes and Leading-Edge Extensions (LEX)
• Strakes (F-16) and Leading-Edge Extensions, or LEXs (F-18) prevents flow separations at high
angles of attack. The device generates strong leading-edge vortices with intense low-pressure field
that help supporting the lift.
High-Lift Devices (1)
Page 9 of 10 Unit B-1
Leading-Edge Flaps and Slats
• Plain Leading-Edge Flap: deflects to increase wing camber; and to move the point of minimum
pressure farther aft on the upper surface of the airfoil at high angles of attack.
• Fixed Slot: can be used to admit higher-speed air onto the upper wing surface to re-energize the
boundary layer and to delay separation.
• Slat: is a leading-edge flap that, when it is extended, opens up a slot as well.
• Boundary-Layer Control: boundary-layer separation over the upper surface of a wing can be
prevented by either "removing" (suction) or "re-energizing" (tangential blow of bleed air).
Powered Lift and Vectored Thrust
• Internally Blown Flap (Jet Flap): bleed air directed onto its leading edge and upper surface from
the rear of the wing; the high-velocity air delays separation and increases lift.
• Externally Blown Flap / Upper Surface Blowing: exhaust can be directed at the leading edge of a
flap, or at the wing and flap's upper surface.
• Vectored Thrust: the engine nozzle can also be movable to redirect or vector the engine exhaust
downward; re-orients the engine thrust vector.
Whole Aircraft Drag and Drag Polar
• The whole aircraft's drag polar can be represented as: 0
2
D D LC C kC= + (4.15)
( )01k e AR= (4.16): 0e is called Oswald's efficiency factor ( )0 : for whole aircrafte e
The Avro Vulcan jet bomber aircraft is nearly an all-wing aircraft, with only a small fuselage section sticking forward of its large triangular-shaped (or delta) wing. Its wing uses a thin NACA 0009 airfoil and has a wingspan of 111 ft and planform area of 3,964 ft2. Assume that it’s flying in standard 5,000 ft atmospheric condition at a true airspeed of 300 ft/s and an angle of attack of 8 degrees. Its is 0.009, its span
efficiency factor is 0.9, its Oswald’s efficiency factor is 0.7, and its average wing chord length is 36 ft. Estimate how much lift and drag it is making for these conditions.