Aerodynamics
Several factors affecting on airplane performance. Such as atmosphere, aerodynamics and aircraft icing.
But aerodynamics is most important factor. We knowing about what is aerodynamics? Whats importance of aerodynamics knowledge for pilot?
The Wing
To knowing about aerodynamic forces, a pilot must to understand basic terms related with airfoils.
You know about aerofoil?
The aerofoil have six main parts.
- Leading Edge
- Trailing Edge
- Uper Camber
- Lower Camber
- Maen Camber Line
- Mean Cord Line
Leading Edge:
The front edge of an airplane propeller blade or wing.
Trailing Edge:
The rearmost edge of a moving structure, such as an airfoil. the back edge of a propeller blade or aerofoil Compare leading edge.
Upper/ Lower Camber
The camber of an aerofoil can be defined by a camber line, which is the curve that is halfway between the upper and lower surfaces of the aerofoil.
Chord Line
The chord line is the straight line intersecting the leading and trailing edges of the airfoil, and the term chord refers to the chord line longitudinal length (length as viewed from the side).
Mean Camber Line
The mean camber is a line located halfway between the upper and lower surfaces. Viewing the wing edgewise, the mean camber connects with the chord line at each end. The mean camber is essential because it assists in shaping aerodynamic qualities of an airfoil.
The measurement of the maximum camber; inclusive of both the displacement of the mean camber line and its linear measurement from the end of the chord line, provide properties useful in evaluating airfoils.
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 intrinsic 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.
What is Basic Aerodynamics?
The instrument pilot have to knowing the link and differences between a number of factors that involve the performance of an aircraft in flight. Also, it is vital 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 primary 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 acting upon an aircraft in flight are
- Lift
- Weight
- Thrust
- Drag
Lift
Lift is a factor 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.
Weight
Weight is the force exerted by an aircraft from the pull of gravity. It acts on an aircraft through its center of gravity (CG) and is straight down. This should not be confused with the center of lift, which can be significantly different from the CG. As an aircraft is descending, weight is greater than lift.
Thrust
Thrust is a force that drives an aircraft through the air and can be measured in thrust and/or horsepower. It is a component that is parallel to the center of thrust and overcomes drag providing the aircraft with its forward speed component.
Three rotation axes
All maneuvering takes place approximately three axes of rotation. One way to define these axes is a Cartesian coordinate system with
- An x axis from left to right,
- A y-axis from top to bottom,
- And a z-axis from near to far.
Your viewing angle within this plane is called the heading, whereas an orthogonal angle is called the elevation. But we can also define three axes of rotation referring to our fighter. They are known as the longitudinal axis, lateral axis, and vertical axis. Imagine a coordinate system with the origin at your fighters center of gravity. The center of gravity is the theoretical point where the entire weight of the aircraft is considered to be concentrated.
The lateral axis is an imaginary axis protruding through the side of the aircraft. A rotation around this axis is known as pitching. This pitch movement is produced by the elevators and will affect your heading and elevation. The longitudinal axis is an imaginary axis protruding through the nose of the aircraft. A rotation around this axis is known as a roll. This roll movement is produced by the ailerons. Consider that a roll will not change your heading. And finally the vertical axis is an imaginary axis protruding through the top and bottom of the aircraft. A rotation around this axis is know as yawing. This yaw movement is produced by the rudder.
Drag
Drag is the net aerodynamic force parallel to the relative wind and is generally a sum of two components: induced drag and parasite drag.
Induced drag
Induced drag is caused from the creation of lift and increases with angle of attack. Therefore, if the wing is not producing lift, induced drag is zero. Conversely, induced drag decreases with airspeed.
Parasite drag
Parasite drag is all drag not caused from the production of lift. Parasite drag is created by displacement of air by the aircraft, turbulence generated by the airfoil, and the hindrance of airflow as it passes over the surface of the aircraft or
components. All of these forces create drag not from the production of lift but the movement of an object through an air mass. Parasite drag increases with speed and includes skin friction drag, interference drag, and form drag.
Skin Friction Drag
Covering the entire “wetted” surface of the aircraft is a thin layer of air called a boundary layer. The air molecules on the surface have zero velocity in relation to the surface; however, the layer just above moves over the stagnant molecules below because it is pulled along by a third layer close to
the free stream of air. The velocities of the layers increase as the distance from the surface increases until free stream velocity is reached, but all are affected by the free stream.
The distance (total) between the skin surface and where free stream velocity is reached is called the boundary layer. At subsonic levels the cumulative layers are about the thickness of a playing card, yet their motion sliding over one another creates a drag force. This force retards motion due to the viscosity of the air and is called skin friction drag. Because skin friction drag is related to a large surface area its affect on smaller aircraft is small versus large transport aircraft where skin friction drag may be considerable.
Interference Drag
Interference drag is generated by the collision of air streams creating eddy currents, turbulence, or restrictions to smooth flow. For instance, the airflow around a fuselage and around the wing meet at some point, usually near the wing’s root. These air flows interfere with each other causing a greater drag than the individual values. This is often the case when external items are placed on an aircraft. That is, the drag of each item individually, added to that of the aircraft, are less than that of the two items when allowed to interfere with one another.
Form Drag
Form drag is the drag created because of the shape of a component or the aircraft. If one were to place a circular disk in an air stream, the pressure on both the top and bottom would be equal. However, the airflow starts to break down as the air flows around the back of the disk. This creates turbulence and hence a lower pressure results. Because the total pressure is affected by this reduced pressure, it creates a drag. Newer aircraft are generally made with consideration to this by fairing parts along the fuselage (teardrop) so that turbulence and form drag is reduced.Total lift must overcome the total weight of the aircraft, which is comprised of the actual weight and the tail-down force used to control the aircraft’s pitch attitude. Thrust must overcome total drag in order to provide forward speed with which to produce lift. Understanding how the aircraft’s relationship between these elements and the environment provide proper interpretation of the aircraft’s instruments.
Newton’s First Law, the Law of Inertia
Newton’s First Law of Motion is the Law of Inertia. It states that a body at rest will remain at rest, and a body in motion will remain in motion, at the same speed and in the same direction until affected by an outside force. The force with which a body offers resistance to change is called the force of inertia. Two outside forces are always present on an aircraft in flight: gravity and drag. The pilot uses pitch and thrust controls to counter or change these forces to maintain the desired flight path. If a pilot reduces power while in straight-and-level flight, the aircraft will slow due to drag. However, s the aircraft slows there is a reduction of lift, which causes the aircraft to begin a descent due to gravity. [Figure 2-4]
Newton’s Second Law, the Law of Momentum
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. Acceleration refers either to an increase or decrease in velocity, although deceleration is commonly used to indicate a decrease. 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 accelerations that the pilot controls in everyday flight.
Newton’s Third Law, the Law of Reaction
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 fig the action of the jet engine’s thrust or the pull of the propeller lead 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, from 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.
