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Flaps are usually deployed in "degree" increments. In small aircraft deployment is usually in 10 degree
increments from zero degrees (non-deployed) to 40 degrees maximum. Larger or more sophisticated
aircraft may have a different range of settings. Normally, the flaps operate electrically through a 4 or 5
position switch located on the instrument panel. In earlier aircraft the flaps were operated using a manual
flap handle.
Deployment of flaps increases both the lift and drag of the wing. Flap activation increases the angle of
attack across the wing / flap section. At 10 degrees, more lift than drag is produced. As the flap angle is
increased more drag and less lift is produced for each increment of deployment.
The primary use of flaps is in landing. They permit a steeper decent without increase in airspeed. Flaps
may be used in certain take-off situations(usually 10°) on short or soft fields.
Dynamics of Flight
Drag
Just as wind friction causes drag in an automobile, aerodynamic friction and displacement of air during
flight creates aerodynamic DRAG. Drag occurs any time that air is displaced from its normal stable
condition. Air has density and weight, and although compressible, it still requires energy to displace.
l INDUCED DRAG occurs as a by-product of lift.
l PARASITE DRAG results from friction with surfaces and appendages, and impact with structures
Aerodynamics
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such as struts, landing gear, antennas, etc..
Induced Drag
Induced drag results from the creation of lift. The amount of drag depends on the airfoil design of the
wing, its camber and angle of attack. Also due to the way the air flows across the wing during flight,
vortices are generated at the wing tips which add to the induced drag component. .
Parasite Drag
Parasite drag is an unwanted resistance of the air to an object traveling through e air. The 3 types of
parasite drag are Form, Skin and Interference as demonstrated below.
Form Drag
The form of the
object and the
effective frontal
surface it
presents to the
air has a
significant effect on the amount of drag generated. As shown in (A), a surface such as shown would
present much more "frontal" drag than it would is it were rotated 90 degrees as in (B). Drag can be
reduced in the aircraft design by streamlining objects such as wing struts to minimize the frontal
appearance to the air flow.
Skin Friction
Even though the form in (A) above is re-oriented to shape (B), there is still some form drag. In addition,
there is friction between the skin of the surface and the air flow. It is obvious that if the surface is dirty,
has frost, ice or other obstructions, that drag will increase. Effects of skin drag can be reduced by smooth
surfaces and flush riveting in the design, and by keeping the surface clean and waxed by the owner.
Interference Drag
Surfaces at angles to each other as in (C) create turbulence in the region of the joint. This occurs most
frequently at the intersection of the fuselage and wing
Pitch, Power and Performance
The amount of lift that a wing generates is a function of it's design (camber, area, etc.), speed through the
Aerodynamics
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air, air density, and angle of attack. The effects of air density will be treated in more detail in a later
chapter.
The three aircraft
shown above can
all be in constant
altitude flight, but
at different
airspeeds. Maintaining a fixed altitude at a given airspeed requires the pilot to control two factors; (1)
Angle of Attack and (2) Power. The angle of attack is controlled by the up, neutral, or downward trim
position of the elevators. The power, is controlled by the "power setting" of the engine and propeller. For
a "fixed pitch" propeller, this means adjusting the engine RPM. For a variable pitch propeller, this means
adjusting both the throttle and the propeller pitch control.
The left aircraft could be at a 10 degree nose-up attitude with an indicated airspeed of say 70 nautical
miles per hour (knots). The center aircraft could be at cruise with a 0 degree attitude and 110 knots. The
right aircraft could be in a slightly high speed decent at minus 3 degrees of pitch and an indicated
airspeed of 140 knots (abbreviated kts).
The pilot can control the Pitch, Power and Performance of the aircraft and can fly at a considerable range
of attitudes, speeds and power settings.
Lift versus Drag
An aircraft with a given total gross weight can be operated in level flight over a range of power settings
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