(Aeronautical Engineering)

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???? (Aeronautical Engineering) NASA National
Aeronautics and Space Administration NACA
National Advisory Committee for Aeronautics TEXT
Aircraft Flight 2nd Ed. by R. H. Barnard D.
R. Philpott ??? ??? ????
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CH.1 Lift(??)

• 1./ Lift
• - Forces on an aircraft in steady level flight(??
  ????)
• Fig. 1.1 (p1) ? Lift Weight, Thrust
  Drag
• - Direction of the aerodynamic forces Fig. 1.2
  (p2)
• Lift a force at right angles to the direction
  of flight
• 2./ Conventional (Classical) Wing
• 3./ Moving Aircraft and Moving Air
• 4./ Generation of Lift

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????? ??
1. ????? ??? ???? ??? ??? ???? ??? ????, ??? A?
?? ? ?? ??? ??? ??? ??? ????? ??? ?? ?(??) ????
??? ??? ??? ????.  ?? B? ?? ? ??? ?? A ?? ? ?
???? ?? A? ??? ????? ??? ??? ?? C? ?? ? ??? ???
??? ???? ? ?, ? ??? ?? ?? ?? ?? ???? ???
????(airfoil, ??) ? ??? ???? ???? ??. ?, ??? ????
??? ??? ???(???? lt ????)? ?? ??? ? ??? ????? ????
?? ?? ???? ?? ? ?? ??(lift)??.
??  ???? ??? ?? ?? ??
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2. The lift is defined as the force normal to the
free-stream direction and the drag parallel to
the free-stream direction. For a planar airfoil
section operating in a perfect fluid, the drag is
always zero no matter what the orientation of the
airfoil is. This seemingly defies physical
intuition and is known as D'Alembert's paradox.
It is the result of assuming a fluid of zero
viscosity. The components of the static-pressure
forces parallel to the free-stream direction on
the front surface of the airfoil always exactly
balance the components of the pressure forces on
the rear surface of the airfoil. The lift is
determined by the static-pressure difference
between the upper and lower surfaces and is zero
for this particular case since the pressure
distribution is symmetrical. If, however, the
airfoil is tilted at an angle to the free stream,
the pressure distribution symmetry between the
upper and lower surfaces no longer exists and a
lift force results. This is very desirable and
the main function of the airfoil section. 3.
Kutta Condition  
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5./ Aerofoil Section

• - ????(airfoil)??, ??? ?? ??? ??? ???? ??(wing),
  ???(aileron), ???(elevator), ???(rudder)? ?? ??
  ??(section)? ???. ???? ??? ???? ????? ??? ?? ????
  ??, ? ??? ?? ??? ?? ????? ????.  ??? ?? ?? ???
  ????? ??? ??? ??? ?? ???? ?? ????? ??.
• - ?? ??? (Mean Camber Line)  ? ??? ?? ??? ?????
  ??? ?????. ?? ???? ??? ??(??, leading edge), ? ??
  ??(??, trailing edge)?? ???.
• ?? ?? ?? ?? (Camber or Maximum Camber)  ????? ??
  ?????? ?? ??
• ?? (Chord)  ??? ??? ?? ??.  ?? ???? ??.
• ?? (Thickness)  ???? ?????? ? ??? ?????? ??.  ?,
  ????? ?? ??.

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• ??  ????? ??
•      ?? ??? (Leading Edge Radius)  ???? ?? ????
  ???? ?? ???? ??? ??? ?? ??? ??? ?? ???
• ?? ?? (Lower Camber)  ??????? ???(lower
  surface)??? ??
• ? ?? (Upper Camber)  ??????? ??(upper
  surface)??? ??

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- ???(?? ???) ( angle of attack)??, ????(??
????)? ???(chord line)? ??? ???.  ???? ????
????(?? ????? ??)? ??? ???. ??? ????????
??(gust)? ?? ??? ??? ?? ???? ??? ?? ????
????.   -??? ???? ?? ???. ???? ????? ????? ?????
??? ??? ???? ??. ??? ?? ???? ????? ???? ??? ?????
???? ???? ??? ??? ??? ??(separation)?? ??(eddy)?
???? ??? ???. ???? ?? ???? ???? ????? ?? ??? ????
??? ????? ??? ???? ? ??? ??? ???? ?? ??? ?? ???
???? ??? ??? ? ?? "bubble point"? ??? ? ?? ????
?? ???(critical angle of attack)?? ??.  ? ?? ???
???? ??? ???? ??? ??? ??? ??? ??? ???? ??? ??
??(stall)????.
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10./ Wing Circulation
6./ Air Pressure Density and Temperature 7./
Pressure and Speed 8. / Dynamic Pressure 9./
Unexpected Effects 10./ Wing Circulation -
Circulation - Kutta-Joukowski Theorem The
faster the flight speed(at a fixed altitude), the
less will be the circulation required to generate
a given amount of lift.
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11./ Wing-Bound Vortex
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12./ Magnus Effect
Any object rotated so as to produce a vortex or
circulation, will generate lift when placed in a
stream of air. This is known as the Magnus effect.
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13./ Air Flow around an Aerofoil Section
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14./ Stagnation
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15./ Pressure and Lift
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17. Lift Coefficient
16. Direction of the Resultant Force due to
Pressure 1. where flight speed,
wing plan area lift
coefficient 2. Lift force is directly related
to the dynamic pressure. 3. Lift a measure of
the lifting effectiveness of the wing lift
f wing planform, section shape, angle of attack,
compressibility, viscosity
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18. Variation of Lift with Angle of Attack and
Camber

• curve (Fig. 1.17)
• The influences of angle of attack and camber are
  largely independent that is, the increase in
  lift coefficient due to camber is the same at all
  angles of attack.
• zero-lift angle
• - stall angle

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19. Variation of with Flight Conditions

• - In landing and take-off where the speed, and
  thus dynamic pressure, are low, a large value
  is required. As the flight speed increases, the
  lift coefficient required reduces.
• As the flight speed increases, the lift
  coefficient required reduces.
• - Most aircraft are designed to fly in a near
  level attitude at cruise, and must therefore
  adopt a nose-up attitude on landing and take-off.
  (see Fig. 1.20)
• - Most modern aircraft have a less cambered wing
  section that is optimized to produce low drag at
  cruising speed.

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20. Stalling

• - The stalling characteristics of an aircraft
  wing depend not only on the aerofoil section
  shape, but also on the wing geometry, since not
  all of the wing will stall at the same angle of
  attack.
• Stalling occurs when the air flow fails to
  follow the contours of the airfoil and becomes
  separated.(Fig. 1.18, 1.19)
• - Once the flow separates, the leading-edge
  suction and associated tangential force
  components are almost completely lost. Therefore,
  the resultant force due to pressure does act more
  or less at right angles to the surface, so there
  is a significant rearward drag component. The
  onset of stall is thus accompanied by an increase
  in drag. Unless the thrust is increased to
  compensate, the aircraft will slow down, further
  reducing the lifting ability of the wing.
• - After the stall has occurred, it may be
  necessary to reduce the angle of attack to well
  below the original stall angle, before the

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lift is fully restored. An aircraft may lose a
considerable amount of height in the process of
recovering from a stall, and trying to prevent
its unscheduled occurrence is a major concern of
both pilots and aircraft designers.
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