The Airplane - Introduction

Private Pilot License (PPL) Notes

This section introduces the basic principles of flight, the airplane's controls, and the aerodynamics that make it fly.

The Four Forces of Flight:

• Thrust: The forward force, equal to drag plus the component of weight along the flight path.
• Drag: The resistive force opposite to thrust.
• Lift: The upward force generated by the wings, perpendicular to the direction of flight.
• Weight: The gravitational force pulling the aircraft down. The weight has two components in a climb: one along the flight path (W sin α) and one perpendicular to the flight path (W cos α).

Lift is less than weight during a climb.

• Thrust = Drag + W sin α
• Lift = W cos α (where α is the angle of climb)

How Lift is Produced:

• Bernoulli's Principle
  • Increasing the speed of a fluid decreases its pressure.
• Wing Shape
  • Upper surface is curved (camber); lower surface is relatively flat.
  • Airflow over the top speeds up, decreasing pressure and creating lift.
• Newton's Third Law
  • Action-reaction principle.
  • Air striking the bottom of the wing is deflected downward.
  • The wing pushes air down; air pushes the wing up.
• Total Lift
  • Combination of decreased pressure on top and increased pressure below the wing.
• Key Wing Parts
  • Leading Edge: Front of the wing.
  • Trailing Edge: Back of the wing.
  • Chord Line: Imaginary line from leading to trailing edge.
  • Upper Camber: Top curve of the wing.
  • Lower Camber: Bottom curve of the wing.

Axes of Flight and Movements:

• Longitudinal Axis (Roll)
  • Runs lengthwise through the fuselage.
  • Movement around this axis is called roll or bank.
• Lateral Axis (Pitch)
  • Passes through the wings, side to side.
  • Movement around this axis is called pitch.
• Vertical Axis (Yaw)
  • Runs vertically through the center of gravity.
  • Movement around this axis is called yaw.

Primary Flight Controls:

• Elevator
  • Controls pitch (movement around the lateral axis).
  • Operated by pushing or pulling the yoke.
  • Pulling back moves the elevator up, pitching the nose up.
  • Pushing forward moves the elevator down, pitching the nose down.
• Ailerons
  • Located at the outboard ends of the wings.
  • Control roll (movement around the longitudinal axis).
  • Operated by turning the yoke left or right.
  • Turning yoke right raises right aileron, lowers left aileron; airplane banks right.
  • Turning yoke left raises left aileron, lowers right aileron; airplane banks left.
• Rudder
  • Controls yaw (movement around the vertical axis).
  • Operated by pressing the rudder pedals.
  • Pushing right pedal moves rudder right, yawing nose right.
  • Pushing left pedal moves rudder left, yawing nose left.
  • Used primarily to counteract adverse yaw during turns.

Adverse Yaw and Coordination:

• Adverse Yaw
  • Occurs when deflecting ailerons during turns.
  • Down aileron increases lift and drag on that wing.
  • This causes the airplane to yaw opposite the turn direction.
• Coordination with Rudder
  • Rudder input counters adverse yaw.
  • Ensures smooth, coordinated turns.

Additional Control Surfaces:

• Trim Tabs
  • Used to relieve control pressure on primary control surfaces.
  • Attached to trailing edge of elevator, sometimes rudder.
  • Elevator trim adjusted in flight; rudder trim often ground-adjustable.
• Flaps
  • Located on the inboard trailing edge of wings.
  • Both flaps extend and retract simultaneously.
  • Lowering flaps increases wing chord and camber.
  • Increases both lift and drag.
  • Allows for steeper, slower approaches during landing.
  • Can be used to shorten takeoff distance.

Understanding these principles and how to control the airplane is essential for safe and efficient piloting. The natural forces acting on an airplane must be either utilized or counteracted during flight.