Review of Basic Aerodynamics

The instrument pilot must understand the relationship and differences between several factors that affect the performance of an aircraft in flight. Also, it is crucial to understand how the aircraft reacts to various control and power changes, because the environment in which instrument pilots fly has inherent hazards not found in visual flying. The basis for this understanding is found in the four forces acting on an aircraft and Newton’s Three Laws of Motion.

Relative Wind is the direction of the airflow with respect to an airfoil.

Angle of Attack is the acute angle measured between the relative wind, or flight path and the chord of the airfoil. Flight path is the course or track along which the aircraft is flying or is intended to be flown.


The Four Forces
The four basic forces [Figure 2-3] acting upon an aircraft in flight are lift, weight, thrust, and drag.


Lift
Lift is a component of the total aerodynamic force on an airfoil and acts perpendicular to the relative wind. Relative wind is the direction of the airflow with respect to an airfoil. This force acts straight up from the average (called mean) center of pressure (CP), which is called the center of lift. It should be noted that it is a point along the chord line of an airfoil through which all aerodynamic forces are considered to act. The magnitude of lift varies proportionately with speed, air density, shape and size of the airfoil, and angle of attack. During straight-and-level flight, lift and weight are equal