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the Angle of Incidence. This angle in a given aircraft never changes. It is fixed by the construc tion of the
aircraft.
l   Angle Of Attack
As the aircraft passes through the air it traverses a particular line of flight. The air passing by the surfaces
of the aircraft in the opposite direction of travel is called the Relative Wind. The angle which the wing
chord makes with this Relative Wind is called Angle of Attack. An increase in angle of attack increases
both lift and drag. If the angle becomes to great, it will pass the Critical Angle of Attack. This is a point
where the airflow over the wing becomes so disturbed that the wing ceases to produce lift. The wing then
enters into a Stalled condition. Stalls will be described more fully later in this chapter.
l   Center of Pressure
Even though the lift of an airfoil is distributed along its surface, the resultant force of all the lift forces
can be considered to be at single point along the wing known as the Center of Pressure.
l   Center of Lift
The Center of Lift( shown as CL in the diagram) is the same point as the Center of Pressure. You can
think of all the lift of the wing as being a single force concentrated at this point on the wing.
l   Dihedral
When you stand in front of an aircraft, looking toward the tail, the wings are usually higher at the wing
tips than at the wing root (where the wing attaches to the fuselage). This upward angle from wing root to
tip is called DIHEDRAL.
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On an aircraft with dihedral, when one wing drops, it will produce slightly greater lift than the other
wing. The aircraft tends to return to a level status providing lateral stability to the aircraft.
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Aerodynamics
Principles of Aerodynamics
Flight involves a balance of forces. These forces are THRUST, DRAG, LIFT and WEIGHT.
When Thrust and Drag are equal, the speed of the
aircraft through the air (airspeed) will remain
constant in smooth air. When Lift and Weight are
equal, the aircraft will neither ascend or decend.
Attitude
The Attitude of an aircraft refers to it's relationship to the ground. When in a level attitude, the
longitudinal centerline of the aircraft is approximately paralell to the earth's surface. In this attitude, the
horizon will appear to be just about on the nose of the aircraft( i.e. the top of the engine cowling is
approximately aligned with the horizon).
When the nose of the aircraft is above the horizon, this is called a nose high attitude. If the nose is below
the horizon, the aircraft is in a nose low attitude.
Center Of Gravity
The weight of the airplane, pilot and
passengers, fuel and baggage is distributed
throughout the aircraft, as shown by the small
downward arrows in the diagram. However,
the total weight can be considered as being
concentrated at one given point, shown by the
larger downward arrow. This point is referred
to as the Center of Gravity. If the plane were
suspended by a rope attached at the center of
gravity ( referred to as the CG) it would be in
balance.
The Center of Gravity (CG) is affected by the
way an aircraft is loaded. For example, if in a
4 place aircraft, there are 2 rather large
individuals in the front seats, and no rear seat passengers or baggage, the CG will be somewhat toward
the nose of the aircraft. If however, the 2 front seat passengers are smaller, with 2 large individuals in the
rear seats, and a lot of baggage in the rear baggage compartment, the CG will be located more aft.
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Every aircraft has a maximum forward and rearward CG position at which the aircraft is designed to
operate. Operating an aircraft with the CG outside these limits affects the handling characteristics of the
aircraft. Serious "out of CG" conditions can be dangerous.
Aircraft Balance
An aircraft in straight and level flight is similar to a childs "teeter-totter". There is a balance point in the
middle (called a fulcrum), with weight on both sides of the fulcrum. For the "teeter-totter" to be in
balance, the downward forces on both sides of the fulcrum must be equal.
In the diagram at right, the fulcrum of an aircraft in
flight is the center of lift. Generally the CG is
forward of the Center of Lift, causing the aircraft to
naturally want to "nose down". The elevator located
　
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