Review of Basic Aerodynamics

As an instrument pilot, you must understand the relationship and differences between the aircraft's flight path, angle of attack, and pitch attitude. Also, it is crucial to understand how the aircraft will react to various controls 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 and Newton's laws.


The Four Forces
The four basic forces acting upon an aircraft in flight are lift, weight, thrust, and drag. The aerodynamic forces produced by the wing create lift. A by-product of lift is induced drag. Induced drag combined with parasite drag (which is the sum of form drag, skin friction, and interference drag) produce the total drag on the aircraft. Thrust must equal total drag in order to maintain speed.

Lift must overcome the total weight of the aircraft, which is comprised of the actual weight of the aircraft plus the tail down force used to control the aircraft's pitch attitude. Understanding how the aircraft's thrust/drag and lift/weight relationships affect its flight path and airspeed is essential to proper interpretation of the aircraft's instruments, and to making proper control inputs.

Tag: Flying instrument, instrument flight, aviation, piloting, instrument rating, instrument flying training, instrument flight rating, instrument rating requirement, instrument rating regulation, aircraft, aero plane, airplane, and aeronautical knowledge.

Newton's First Law
Newton's First Law of Motion is the Law of Inertia, which states that a body in motion will remain in motion, in a straight line, unless acted upon by an outside force. Two outside forces are always present on an aircraft in flight: gravity and drag. Pilots use pitch and thrust controls to counter these forces to maintain the desired flight path. If a pilot reduces power while in straight-and-level flight, the aircraft will slow. A reduction of lift will cause the aircraft to begin a descent. [Figure 2-1: Newton's first law of motion]

Newton's Second Law
Newton's Second Law of Motion is the Law of Momentum, which states that a body will accelerate in the same direction as the force acting upon that body, and the acceleration will be directly proportional to the net force and inversely proportional to the mass of the body. This law governs the aircraft's ability to change flight path and speed, which are controlled by attitude (both pitch and bank) and thrust inputs. Speeding up, slowing down, entering climbs or descents, and turning are examples of acceleration that pilots control in everyday flight. [Figure 2-2: Newton's second law of motion]

Newton's Third Law
Newton's Third Law of Motion is the Law of Reaction, which states that for every action there is an equal and opposite reaction. As shown in figure 2-3: Newton's third law of motion, the action of the jet engine's thrust or the pull of the propeller led to the reaction of the aircraft's forward motion. This law is also responsible for a portion of the lift that is produced by a wing, by the downward deflection of the airflow around it. This downward force of the relative wind results in an equal but opposite (upward) lifting force created by the airflow over the wing.

Tag: Flying instrument, instrument flight, aviation, piloting, instrument rating, instrument flying training, instrument flight rating, instrument rating requirement, instrument rating regulation, aircraft, aero plane, airplane, and aeronautical knowledge.

Flight path: The line, course, or track along which an aircraft is flying or is intended to be flow.

Angle of attack: The acute angle formed between the chord line of an airfoil and the direction of the air that strikes the airfoil.

Induced drag: Caused by the same factors that produce lift, its amount varies inversely with airspeed. As airspeed decreases, the angle of attack must increase, and this increases induced drag.

Parasite drag: Caused by the friction of air moving over the structure, its amount varies directly with the airspeed. The higher the airspeed, the greater the parasites drag.

Relative wind: The direction from which the wind meets an airfoil.