Structure of an aeroplane (2)

by alan200994 Thu Nov 06, 2008 9:22 pm

ANGLE OF ATTACK
Page 1-11

Structure of an aeroplane (2) Angleofattack

Angle of attack is a term used to express the relationship between an airfoil's chord and the direction of its encounter with the relative wind. Unlike the angle of incidence, an airfoil's angle of attack can change during flight, most often in response to changes in airspeed. As the bottom row in the picture above shows, angle of attack expresses only the angle between the airfoil's chord and the relative wind without regard to the direction of the flight path (climbing, level flight, or descending) of the aircraft.

LIFT
Page.1-11,1-12

Induced Lift is an increase in velocity that reduces the pressure on the top of the wing; therefore, lift is induced. It is also called airfoil lift or Bernoulli's lift.

Dynamic Lift is the pressure of the air impacting against the lower surface of an airfoil.

Drag
Page 1-15, 1-16

Drag is caused by the resistance of the air to any aircraft surface that deflects or interferes with the smooth airflow around the airplane.

Drag is present all the time and is defined as the force which opposes thrust.

Induced drag is the unavoidable by-product of lift and increases as the angle of attack increases.
Parasite Drag is all drag other than induced drag. This type of drag includes skin-friction drag, friction between the outer surfaces of the aircraft and the air through which it moves, and form drag, resistance to the air to the shape of the aircraft. Form drag can be reduced by streamlining the aircraft shape.

AXES OF ROTATION
Page 1-16, 1-17 & Figure 1-22

All maneuvering flight takes place around one or more of three axes of rotation.

Longitudinal axis extends lengthwise from the nose through the tail. Movement about the longitudinal axis is called roll. Roll is controlled by the ailerons.

Lateral axis extends crosswise from wingtip through wingtip. Movement about the lateral axis is called pitch. Pitch is controlled by the elevator.

Vertical axis passes vertically through the center of gravity (when the aircraft is in level flight). Movement about the vertical axis is called yaw. Yaw is controlled by the rudder.

BASIC FLIGHT MANEUVERS
Page 1-21& 1-22

Basic flight maneuvers include climbs, descents, turns, and combinations of these.

In straight-and-level flight, the wings are kept level and the altitude and heading are constant.
(Note: The FAA considers straight and level flight to also be a basic flight maneuver.)

Climbs result from up elevator or an addition of power.

Descents result from down elevator or a reduction in power.

Turns can be gentle, medium, or steep depending on the amount of bank used. They can be made when climbing, descending, or in level flight.

LANDING
Page 1-22

Steps involved in landing a light airplane:

Approach
"Roundout" (level off at start of the flare)
Flare (slowing down while increasing the angle of attack)
Touchdown (on main gear)

STALLS
Page. 1-22

Sufficient airspeed must be maintained in flight to produce enough lift to support the airplane without requiring too large an angle of attack. At a specific angle of attack, called the critical angle of attack, air going over a wing will separate from the wing or "burble" causing the wing to lose its lift (stall). The airspeed at which at which the wing will not support the airplane without exceeding the critical angle of attack is called the stalling speed. This speed will vary with changes in wing configuration (flap position) and load factors (Gs). For example, an aircraft that stalls (exceeds the critical angle of attack) in straight and level flight with flaps retracted at 60 MPH, will stall at 40 MPH with full flaps extended. An aircraft in a level steep-banked turn will stall at a higher airspeed than it would in straight and level flight. The stalling speed varies with conditions, but a stall will occur only when the wing's critical angle of attack is exceeded.

Increasing the Angle of Attack to the Stall Point

The picture above shows a normal airfoil during a typical cruise profile. The angle of attack (denoted between the arrows) is small and the airflow over the wing is smooth, producing lift. No stall condition exists.

In the picture above, the angle of attack has been increased and is now closer to/approaching the critical angle of attack. Airflow above the wing is becoming uneven. However, the angle is still less than the critical angle, so lift is still being produced by the wing. No stall condition exists.


In the picture above, the wing has now exceeded its critical angle of attack. The uneven airflow over the top of the wing has broken into a swirling air mass that can not produce lift. The wing (airfoil) is "stalled".

Relationship Between the Flight Instruments
Page 1-23, 24 &25

The altimeter tells how high (above sea level) the aircraft is flying.

The turn-and-slip indicator tells the pilot the direction, rate, and quality of the turn.

The vertical speed indicator (VSI) shows the pilot the rate of speed the airplane is climbing, descending.

The attitude indicator is a gyroscopic instrument that provides a horizon that moves about so that it always shows the relationship of the horizon to the pitch (nose up and down) and the bank (wing high, level or low) of the aircraft .

The airspeed indicator tells the pilot the speed of the aircraft as it travels through the air.

ENERGY
Page 1-26

Energy is "the capacity for doing work and overcoming resistance. "

Potential energy is stored energy.
Kinetic energy is active energy.

When potential energy is released from its source and causes movement of an object, it becomes kinetic energy.