Technology Foundations

Stuarts Draft High School
Technology Foundations
Trim Action
For an aircraft to remain aloft, the lift from the wings must counter the downward pull of
gravity. The Sum of the lift that develops over the wings can be considered to act at a single
point along the fuselage called the center of lift (CL) position. Likewise the weight of an
aircraft can be considered to act through a single point called the center o gravity (CG)
position. When the center or lift from the wings aligns with the center of gravity of weight,
and the forces balance, level flight can be maintained.
Neutral Balance
The horizontal stabilizer in the tail functions to hold an aircraft stable at a given pitch so that
the wings maintain the correct amount of lift and do not stall. If an air disturbance causes an
aircraft to pitch up or down, it will change the angle of attack (AOA) of the wings and tail and
cause a lifting force to develop in the tail that will act against any pitch change. This tail force
will remain as long as the aircraft is rotated out of position. As the restoring actions in the tail
rotate the aircraft back to proper pitch, the restoring forces in the tall will diminish and
Unstable Balance
If a plane is properly balanced, the center of gravity (CO) may end up being behind the center
of lift (CL). In order for an aircraft to balance and fly' when this happens the horizontal
stabilizer must also be positioned to develop lift. With this balance or forces the aircraft is
much less able to keep itself stable and level in air turbulence because the restoring action of
the tall will be canceled by the changes in the lever action of lift in the wings as the pitch
Stable Balance
In most gliders and airplanes, the center of gravity is kept positioned forward of the center of
lift of the wing to ensure the aircraft remains stable. In this configuration a downward lift
force is needed in the tail to balance the forces. The horizontal stabilizer is given an angle of
attack that develops a downward force that balances the aircraft for flight. This is called
trimming an aircraft.
Flight Vocabulary Terms
The study of the forces acting upon an object in motion through an
A movable hinged section on the trailing edge of an airplane's wing
used to control rolling movement.
The cross-section shape of a wing taken at right angles to the wingspan.
A self-propelled, lighter-than-air craft, which can be steered.
The speed of an aircraft relative to the air rather than to the ground.
A device for measuring the relative altitude of an aircraft by measuring
atmospheric pressure.
Angle of Attack
The angle at which a wing strikes the air stream.
Angle of Incidence
The angle of the wing in relation to an arbitrary line fore and aft in the
Aspect Ratio
The relationship of the wingspan to the wing chord, expressed
numerically by the number of times the span can be divided by the
An airplane which flies by virtue of freewheeling rotating wings set
windmill fashion above the fuselage
A turn made in flight with one wing tip lower than the other.
The curvature of the wing from the leading edge to the trailing edge.
An airplane designed to fly tail first.
Center of Gravity
Center of Lift
Center of Pressure
The point through which the resultant forces of gravity act no matter
how the body is oriented.
The point at which the average of all lifting forces act.
The intersection of the resultant force with the plane of the chord of the
lower surface. This center varies with the angle of incidence in a
characteristic manner for every wing shape. The center is located for a
given angle of incidence by giving its distance from the leading edge in
percent of the chord length.
The width of a wing from leading edge to trailing edge.
The difference between the angles of incidence of the wing and the
The up tilt of wing panels toward the tips to increase stability in the roll
The hinged control section of the stabilizer used to induce a change in
The fixed forward portion of the vertical tail.
A form for holding parts together for assembly.
The body of an airplane.
Sustained forward flight in which speed is maintained only by the loss
of altitude.
Ground Speed
The speed of an aircraft relative to ground.
Induced Drag
The resistance of a wing to forward movement due to disturbance of the
surrounding air and related to the lift produced by the wing.
The quantity of matter in a body.
Moment Arm
The distance from the center of gravity at which a force is applied.
Motor Stick
A strong wooden strip, often serving as a fuselage, used to support the
rubber motor of a model airplane.
An airplane that flies by flapping its wings in a bird-like fashion.
Parasitic Drag
Resistance to forward movement caused by non-lifting components of
an airplane.
An airplane with itas wings mounted above the fuselage by struts or a
Pitch-Diameter-Ratio The relationship between the propellet pitch and diameter, expressed as
a mathematical proportion.
Propeller Pitch
The distance theoretically traveled by a propeller in one revolution.
Propeller Torque
The reactive force generated by a revolving propeller that tends to rotate
an airplane in the direction counter to the direction or the propeller's
The moving part of an airplane's vertical tail used to control movement
on the yaw axis.
A prolonged stall in which an airplane rotates about its center of gravity
while it descends.
The tendency of an airplane to return to level flight after having been
disturbed by some force.
The complete loss of lift resulting from too steep an angle of attack.
A rising column of relatively warm air.
Tip Loss
The reduction of lift near the tips of wings due to the leakage of highpressure air from beneath to the low-pressure area above.
The concave curve on the underside of some airfoils.
Wing Loading
Ratio of lifting efficiency; weight of airplane / area of the wings.