Drag is resistance of air to the shape of the aircraft. From
drag can be reduced by streamlining the aircraft shape.
Aerodynamics is the study of how air flows over objects and
the forces that the air and objects exert on each other. Drag is the force of
wind or air resistance pushing in the opposite direction to the motion of the
object, in this case, the cyclist of air.
An Aerodynamic force.
Resists forward motion.
Increases with the square of speed.
D=CD *1/2 p*A*V2
Different types of Drag.
There are different types of drag for an aircraft.
Skin friction drag
v Pressure drags.
Pressure drag is the drag on a body moving through
a fluid as a result of shape of the body. It can also be considered as the
force created by the pressure difference between the front and the rear of the
the fluid flows into the solid object, eddy currents are formed and there is no
longer a smooth flow line. An extreme example of this resistance is the flat
plate at right angles to the wind. The resistance is very large and almost
entirely due to the formation of the turbine. On the contrary, the friction is
negligible. Experiments show that the pre-plate pressure greater than
atmospheric pressure, back pressure less than atmospheric pressure. This
creates a “sucking” effect on the plate.
Airflow in different shapes of objects can
be observed under pressure. Plate pressure is very high. If we replace the
plate with a ball of the same diameter, the pressure resistance is much lower
(about 50%). This is because the separation of the air in the front of the ball
is smoother (air deceleration). In addition, the air separates the rear
slightly along the surface of the sphere prior to separation. As a result, the
turbulent wake region is much narrower than behind.
If the aerodynamic shape of the air flow
with the same frontal area is placed at the same rate of air flow at said air
flow, the resistance is lower than the resistance of the sphere. This is due to
the fact that the tapering cone of the tail almost separates until it reaches
the rear edge before it is detached. This gives a very low resistance and an
pressure drag can be considerably reduced by streamlining”
v Skin Friction Drag.
Between the outer surfaces of the aircraft and the air through which it
moves. Reduced by using glossy, flat finish on surfaces.
Friction between air and the surface of the
aircraft results in frictional resistance to the skin. The airflow decelerates
near the surface and the relative air velocity of the particles is almost zero.
The air layer whose velocity varies from zero to a constant free flow is called
the boundary layer. This is due to the viscosity of the air, which means
shearing or rubbing when moving between adjacent air particles at different
Resistance to surface friction also depends
on the aerodynamic surface smoothness.
For rough surfaces, the frictional
resistance is usually higher than the normal frictional resistance. In addition,
the rough surface will cause an earlier smooth transition to turbulence,
thereby increasing the resistance. The harshness of already disrupted areas can
also lead to increased resistance.
The resistance caused by the laminar
boundary layer is lower than the resistance of the turbulent flow. Therefore,
it is highly desirable to lay the boundary layer on as many surfaces as
possible to achieve low resistance.
Moreover, if the pressure gradient is
favorable, the laminar flow can be kept at a greater distance. As the air flow
passes the maximum curvature point on the upper surface of the airfoil, the
dynamic pressure starts to drop and the static pressure increases. As
hydrostatic pressure increases further along the wing, air flow is destroyed
and turbulence is created, increasing the thickness of the boundary layer. This
is the so-called “reverse pressure gradient.”
v Profile drags
v Parasite Drag.
Parasite drag is the function of skin friction which is depends of wing
chord. All non-lifting part of the resistance caused by the parasitic
resistance caused. Parasite drag is caused by any aircraft surface that
deflects on interferes with smooth airflow around airplane. For example, a
vertical stabilizer or landing gear is a parasitic drag element.
v Induced Drag.
When the wing generates lift, the additional resistance is also
proportional to the lift produced. This resistance is called “inducing
Induced drag is the unavoidable by-product of lift and increases as the
angle of attack increase.
The induction resistance is related to the tip of the tip due to the
pressure difference between the upper and lower surfaces of the blade. This
pressure differential causes air to flow at the edge of the wing. The presence
of a turbine indicates energy loss as turbulence is created on the turbine. So
the additional resistance is related to bubble formation. If the resulting
elevator increases (due to the large difference in pressure between the top and
bottom surfaces), a stronger vortex will result. The intensity of the expansion
current and the associated sensing resistance caused by the vortex are
proportional to the lift.
v Aeroplane Drag:
v Wave Drag:
If the aircraft’s flight speed
exceeds the critical Mach number, additional wave drag will appear. The
critical Mach number is the speed of the aircraft, and although the speed of
the aircraft remains below the critical speed of the Mach (1), the airstream on
the main shaft reaches the speed of sound.
If the airplane’s speed exceeds the
critical Mach number, the air flow in the wing will further accelerate and will
reach faster than the sonic velocity (ultrasonic flow). But then he returned to
the wing, sending a shock wave when the air suddenly became suspicious.
Resistance increases because of this drag coefficient. This extra drag is
called wave drag.
(Critical Mach<1) v Total Drags.