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Aerodynamics & Performance

Introduction:

  • In order to understand the operation of the major components and subcomponents of an aircraft, it is important to understand basic aerodynamic concepts
  • Aerodynamics is the branch of dynamics dealing with the motion of air and other gases which give us the performance we need to fly
  • It can be associated with the forces acting on an object in motion through the air or with an object that is stationary in a current of air
  • Several factors affect aircraft performance including the atmosphere, aerodynamics, and aircraft icing
  • Pilots need an understanding of these factors for a sound basis for prediction of aircraft response to control inputs
The Four Forces
Figure 1: Pilot's Handbook of Aeronautical Knowledge,
The Four Forces
Lift/Drag Performance Curve
Figure 2: Lift/Drag Performance Curve

Lift and Basic Aerodynamics:

  • Four forces act upon an aircraft in relation to straight-and level, unaccelerated flight
  • Understanding how these forces are created, and more importantly impact each other, allow us to understand how we manipulate them to control an aircraft in flight
  • These forces, which make up the Principles of Flight, are thrust, drag, weight, and lift: [Figure 1]
    • Thrust:

      • Thrust is the forward force produced by the powerplant/propeller
      • It opposes or overcomes the force of drag
    • Drag:

      • Drag is a rearward, retarding force and is caused by disruption of airflow by the wing, fuselage, and other protruding objects
      • Drag opposes thrust and acts rearward parallel to the relative wind
    • Weight:

      • Weight is the combined load of the aircraft itself, the crew, the fuel, and the cargo or baggage
      • Weight pulls the aircraft downward because of the force of gravity
    • Lift:

      • Lift opposes the downward force of weight, is produced by the dynamic effect of the air acting on the wing, and acts perpendicular to the flight path through the wing’s center of lift (CL)
  • An aircraft moves in three dimensions and is controlled by moving it about one or more of its axes:
    • The longitudinal, or roll, axis extends through the aircraft from nose to tail, with the line passing through the CG
    • The lateral or pitch axis extends across the aircraft on a line through the wing tips, again passing through the CG
    • The vertical, or yaw, axis passes through the aircraft vertically, intersecting the CG
    • All control movements cause the aircraft to move around one or more of these axes and allows for the control of the aircraft in flight [Figure 3]
  • Aircraft Components and Structure
  • Stanford - Aircraft Design: Synthesis and Analysis
  • NASA - Aerodynamics Index
Aircraft Axis
Figure 3: Aircraft Axis

Performance:

Aerodynamics & Performance Overview: