Aircrafts Aerodynamics

The fundamentals of aircraft controls are explained in flight dynamics. This article centers on the operating mechanisms of the flight controls. The basic system in use on aircraft first appeared in a readily recognizable form as early as April 1908, on Louis Blériot's Blériot VIII pioneer-era monoplane design.

Aerodynamics is the study of forces and the resulting motion of objects through the air. The basic aircraft's parts that involve in the aerodynamics are the following

·            Fuselage

·            Wings

·             Flap

·            Aileron

·            Empennage

·            Stabilizers

·            Rudder

·            Elevator

   

 

Studying the motion of air around an object allows us to measure the forces of lift, which allows an aircraft to overcome gravity, and drag, which is the resistance an aircraft “feels” as it moves through the air. Everything moving through the air (including airplanes, rockets, and birds) is affected by aerodynamics.

Basic concept of Aerodynamics

Formal aerodynamics study in the modern sense began in the eighteenth century, although observations of fundamental concepts such as aerodynamic drag have been recorded much earlier. Most of the early efforts in aerodynamics worked towards achieving heavier-than-air flight, which was first demonstrated by Wilbur and Orville Wright in 1903.Aerodynamics is a sub-field of fluid dynamics and gas dynamics, and many aspects of aerodynamics theory are common to these fields. The term aerodynamics is often used synonymously with gas dynamics, with the difference being that "gas dynamics" applies to the study of the motion of all gases, not limited to air.

Since then, the use of aerodynamics through mathematical analysis, empirical approximations, wind tunnel experimentation, and computer simulations has formed the scientific basis for ongoing developments in heavier-than-air flight and a number of other technologies. Recent work in aerodynamics has focused on issues related to compressible flow, turbulence, and boundary layers, and has become increasingly computational in nature.

 

FLIGHT BEGINS WITH AIR IN MOTION

As an airplane moves through the air, its wings cause changes in the speed and pressure of the air moving past them. These changes result in the upward force called lift. To understand lift, you first have to understand how air (a gas) behaves under certain conditions. So here we will start by Bernoulli principle: 

“The Bernoulli principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in the pressure exerted by the fluid. When a fluid flowing through a tube reaches a constriction or narrowing of the tube, the speed of the fluid passing through the constriction is increased and its pressure is decreased”

HOW DOES THIS CREATE LIFT?

              A wing is shaped and tilted so the air moving over it moves faster than the air moving under it. As air speeds up, its pressure goes down. So the faster-moving air above exerts less pressure on the wing than the slower-moving air below. The result is an upward push on the wing

Now we have the factors that effects the lifting:

 WHAT FACTORS AFFECT LIFT?

The size and shape of the wing, the angle at which it meets the oncoming air, the speed at which it moves through the air, even the density of the air, all affect the amount of lift a wing creates. Let’s begin with the shape of a wing intended for subsonic flight.

WHY DOES A WING HAVE A ROUNDED FRONT?

Air divides smoothly around a wing’s rounded leading edge, and flows neatly off its tapered trailing edge. You might think a sharp leading edge would be better. However, air cannot turn a sharp corner, so tilting a sharp wing even slightly would disrupt the smooth airflow over the wing. This would cause a loss of lift and increase drag. A rounded leading edge divides the airflow smoothly, even as the wing is tilted up or down.

WHY DOES A WING HAVE A SHARP REAR EDGE?

If the trailing edge were rounded, the higher-pressure air flowing along the lower side would try to follow the rounded surface and spill upward into the lower-pressure air above the wing. A sharp trailing edge prevents this upward spill, because air cannot make a sharp turn. Instead, the air flowing off the top and bottom surfaces rejoins smoothly.

HOW DOES TILTING A WING AFFECT THE AIR FLOWING OVER IT?

Tilting the wing upward increases lift—to a point. If you tilt it too much, the airflow pulls away from the upper surface, and the smooth flow turns turbulent. The wing suddenly loses lift, a condition known as a stall. You can reestablish a smooth airflow by tilting the wing back to a more level position.

 

 

Air flowing past an object pushes harder against the front than the back. This difference creates a backward force called pressure drag.

DOES DRAG INCREASE WITH SPEED?

     As an aircraft's speed increases, drag on the aircraft generally increases much faster. Doubling the speed makes the airplane encounter twice as much air moving twice as fast, causing drag to quadruple. Drag, therefore, sets practical limits on the speed of an aircraft.

HOW DO YOU REDUCE PRESSURE DRAG?

     The air pressure against the leading side of an object is higher than the pressure in the randomly churning eddies of the wake on the other side of it. Streamlining reduces this pressure difference.

 

Friction is the resistance that happens when two things rub together—like air against an airplane. Friction is partly what causes drag.

Air friction, or air drag, is an example of fluid friction. Unlike the standard model of surface friction, such friction forces are velocity dependent. The velocity dependence may be very complicated, and only special cases can be treated analytically. At very low speeds for small particles, air resistance is approximately proportional to velocity and can be expressed in the form

where the negative sign implies that it is always directly opposite the velocity.

 For higher velocites and larger objects the frictional drag is approximately proportional to the square of the velocity: 

where ρ is the air density, A the cross-sectional area, and C is a numerical drag coefficient.

 

The spirals of air that trail off the tips of an airplane’s wings also contribute to drag. These wing tip vortices steal energy from the motion of the airplane, creating vortex drag.

HOW DO WING TIP VORTICES AFFECT AN AIRPLANE?

The pressure imbalance that produces lift creates a problem at the wing tips. The higher-pressure air below a wing spills up over the wing tip into the area of lower-pressure air above. The wing’s forward motion spins this upward spill of air into a long spiral, like a small tornado, that trails off the wing tip. These wing tip vortices create a form of pressure drag called vortex drag.

Vortices reduce the air pressure along the entire rear edge of the wing, which increases the pressure drag on the airplane. The energy required to produce a vortex comes at the expense of the forward motion of the airplane.

Improvements in aerodynamics also hold great potential. Take sharklets for example: At a height of 2.4 metres, the latest generation of these curved wingtips reduce fuel consumption by around 3.5 per cent. They are used within the Airbus A320 family and its successor generation, the A320neo. German airlines have ordered 70 aircraft with this wingtip modification. Some older aircraft can also be retrofitted with these sharklets.

 Tilting the airplane’s wings upward makes the vortices stronger and increases vortex drag. Vortices are especially strong during takeoff and landing, when an airplane is flying slowly with its wings tilted upward.