Aero Chapter 01, General Aerodynamics Review
T-45 Aerodynamics Student Workbook
If a wing is to have good qualities at
both high and low speeds, it must be
able to change shape in flight. Flaps
and slats are high lift devices used to
Stall
CL
change the shape of the wing and
max
Region
increase CL at low airspeeds.
As angle of attack increases, CL also
increases, providing the boundary
layer is maintained.
CL
As angle of attack increases beyond
the angle where boundary layer can be
maintained, a reduction in CL will occur
as separation of the boundary occurs.
At this point, stall commences
(Figure 3).
AIR DENSITY
Air density (r) is affected by barometric
pressure, temperature, and humidity.
AOA
Pressure altitude is the altitude in the
standard atmosphere corresponding to
Figure 3: AOA VS COEFFICIENT OF LIFT (CL)
a particular altitude. On a standard
day, pressure altitude and altitude
above ground level (AGL) are the
same. On a nonstandard day, altitude
AGL and pressure altitude will not agree.
Simply stated, density will decrease as
pressure altitude, temperature, or humidity
increase. Remember, pressure decreases
as altitude increases. As altitude
increases and pressure decreases, density
decreases. However, with an altitude
increase, temperature decreases. Density
36,000 FT
decreases at a given rate to the altitude
where temperature becomes constant,
approximately 36,000 ft. Without the
favorable temperature offset, density
decreases more rapidly (Figure 4) at
altitudes above approximately 36,000 ft.
Perhaps the more appropriate term for
correlating aerodynamic performance in
the nonstandard atmosphere is density
altitude. Density altitude is the altitude in
the standard atmosphere corresponding to
a particular value of air density. The
ALTITUDE
computation of density altitude involves
pressure (pressure altitude) and
DENSITY
PRESSURE
temperature. Density altitude is pressure
TEMPERATURE
altitude corrected for nonstandard day
temperature. At high field elevations on a
Figure 4: AIR DENSITY
warm day, the density altitude may be
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