Drag in Aviation: Factors and Effects
Aviation Meteorology
Third Stage
The second lecture
DR.IQBAL KHALAF khames
D
r
a
g
When the airplane moves through the air, there is another aerodynamic
force present
•
Drag
•
Drag is generated by every part of the airplane
(even the
engines
).
•
Drag
acts in the direction opposed to the motion.
•
And directed
along and opposed
to the flight direction.
•
There are many
factors
that affect the
magnitude
of the drag force
including the
1-
shape
of the aircraft
2- the
"stickiness"
of
the air
3-the
velocity
of the aircraft
.
•
Drag acts
through
the aircraft center of pressure( C
p
)
.
•
Factors that affect drag
•
There are many factors that affect drag. We can group these factors
into:
•
(
a
) Those associated with
the airplane
•
(
b
) Those associated with the
motion of the
airplane
through the air
•
(
c
) Those associated with
the air itself
A
:
Those associated with
the
airplane
•
The drag
depends:-
•
linearly
on the
size
of the
airplane
moving through the air.
•
The cross-sectional
shape
of an
airplane
determines the
form
drag
created by the
pressure variation
around the
airplane
.
•
If
the
drag as aerodynamic friction
•
The amount of drag depends on the;
1-
surface roughness of the aircraft.
2-
A smooth surface produces less drag than a roughened
surface
.
This effect is called
surface
friction
and is usually included
in the measured
Drag coefficient
(C
d
)of the
aircraft
.
B
:
Those associated with the
motion of the
airplane
through the air
•
Drag is associated:
with the movement of the aircraft through the air,
So drag depends on the
velocity
of the air
.
•
Drag actually varies with the
square
of the
relative velocity
between
the surface of aircraft and the air.
The slope of an airplane's wing affects the flow, which affects the
amount of drag an airplane produces
•
If the
aircraft
moves through the air at speeds near the
speed of
sound
,
shock waves
are formed on the
aircraft
which create an
additional drag component called
wave drag
.
•
The motion of the aircraft through the air also causes
boundary
layers
to form on the aircraft surface .
•
A boundary layer:- is a region of very low speed flow near the surface
which contributes to the surface friction
.
C
:
Those associated with
the air itself
Drag depends directly on the
mass
of the flow going past the aircraft.
The drag also depends in
other
properties
of the air:-
1-
viscosity
of the air
2-
compressibility
of the air .
all of this information
on the factors that affect drag into a single
mathematical equation called the
Drag Equation.
With the drag equation
we can predict how much drag force is generated
by a given aircraft surface moving at a given speed through a given air
.
Drag Equation
D = C
d
x A x 0.5 x ρ x V
2
T
y
p
e
s
o
f
D
r
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g
•
There are many different types of drag. The most commonly
encountered are:
•
Parasite Drag
•
Form Drag
•
surface Friction Drag
•
Interference Drag
•
Induced Drag
•
Wave Drag
.
P
a
r
a
s
i
t
e
D
r
a
g
•
Parasite
(
Parasitic
)
Drag
(D
P
):- is defined as all
drag
that is not
associated with the production of
lift
•
Parasite Drag is caused by moving aircraft through a fluid medium. In
aerodynamics, the fluid medium concerned is the
atmosphere
.
•
The principal components of Parasite Drag are
Form Drag
,
Friction
Drag
and
Interference Drag
.
F
o
r
m
D
r
a
g
•
Form Drag
, also known as
Pressure Drag
or
Profile Drag
•
Form Drag
:-
is the
drag
caused by the separation of the boundary
layer from a surface and the wake created by that separation.
•
Form Drag
is primarily
dependent upon
the
shape
of the aircraft and
how that shape
interacts
with the airflow.
s
u
r
f
a
c
e
F
r
i
c
t
i
o
n
D
r
a
g
•
Surface Friction Drag
, also known as
Skin Friction Drag
•
Surface Friction Drag:-
is
drag
caused by
1-the friction of a fluid against the surface of an aircraft that is moving
through it.
2-caused by rough spots on the surface of the aircraft.
•
Surface Friction Drag :-
is directly proportional to the
area
of the
surface in contact with the fluid and
increases
with the
square of the
velocity.
•
Common sources of this type of surface friction drag are:-
1- snow
2-dirt
3- dead insects
4-and other debris
that accumulates on the airframe
•
surface friction drag is one of the reasons why
airplane deicing
is a
crucial step before you take off during winter weather conditions.
I
n
t
e
r
f
e
r
e
n
c
e
D
r
a
g
•
Interference Drag
:-is
drag
that is generated by the mixing of airflow
streamlines between airframe components such as the wing and the
fuselage, the engine pylon and the wing.
•
In the case of a military or other special purpose aircraft, between
the airframe and attached external stores such as fuel tanks, weapons
or sensors.
•
Interference drag is greatest in areas with
sharp angles
like where:-
1-the wing strut meets the fuselage
2-the wings themselves attach to the fuselage.
I
n
d
u
c
e
d
D
r
a
g
•
When higher pressure air from underneath the wings flows up and
over the top of the wing, this is a source of induced drag.
•
The ratio between the
width
of the wing and the
height
of the wing is
important in this type of induced drag.
•
The
lower this ratio
, the
greater the induced drag force
and vice
versa.
W
a
v
e
D
r
a
g
•
Is a component of the
drag
on aircraft wings and fuselage moving
at
supersonic
speeds, due to the presence of
shock waves
•
Wave drag:-
1- is independent of
viscous effects
of air
2- tends to present itself as a sudden increase in drag as the aircraft
increases speed to the
critical Mach number
.
critical Mach number
•
In aerodynamics, the critical
Mach Number
(M
cr
or M
crit
) of an aircraft
is the lowest Mach number at which the airflow over any part of the
aircraft reaches the speed of sound.
•
There is a critical Mach number, which will depend on
the slowest
part of the local flow velocity across the body of an aircraft
.
P
r
o
f
i
l
e
D
r
a
g
•
Both form drag and interference drag relate to:-
•
The size of aircraft
•
The design of aircraft
•
The configuration of the aircraft.
•
Sometimes both types of drag are considered together as the overall
profile drag of the airplane.
•
The profile drag:-
is the amount of form drag plus the amount of
interference drag.
D
r
a
g
a
n
d
A
i
r
s
p
e
e
d
•
Drag increases with the square of the airspeed, while induced drag,
being a function of lift, is greatest when maximum lift is being
developed, usually at low speeds. The diagram below shows the
relationship of parasitic drag and induced drag to each other and to
total drag.
Relationship of Drag with Airspeed
•
There is an airspeed at which drag is minimum, and in theory, this is
the maximum range speed; however, flight at this speed is unstable
because a small decrease in speed results in an increase in drag, and a
further fall in speed. In practice, for stable flight, maximum range is
achieved at a speed a little above the minimum drag speed where a
small speed decrease results in a reduction in drag.
•
Drag in aviation is the aerodynamic force that opposes an aircraft's motion through the air. It is generated by every part of the airplane and depends on factors like the shape of the aircraft, surface roughness, and velocity. Drag is influenced by the size of the airplane, cross-sectional shape, and surface friction. Factors affecting drag can be categorized into those associated with the airplane, motion through the air, and the air itself. Understanding these factors is crucial for efficient flight performance.
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Presentation Transcript
Aviation Meteorology Third Stage The second lecture DR.IQBAL KHALAF KHAMES
Drag Drag When the airplane moves through the air, there is another aerodynamic force present The air resists the motion of the aircraft and the resistance force is called Drag Drag is the Aerodynamic force that opposes an aircraft's motion through the air.
Drag Drag is generated by every part of the airplane (even the engines). Drag acts in the direction opposed to the motion. And directed along and opposed to the flight direction.
There are many factors that affect the magnitude of the drag force including the 1-shape of the aircraft 2- the "stickiness" of the air 3-the velocity of the aircraft. Drag acts through the aircraft center of pressure( Cp ).
Factors that affect drag There are many factors that affect drag. We can group these factors into: (a) Those associated with the airplane (b) Those associated with the motion of the airplane through the air (c) Those associated with the air itself
A : Those associated with the airplane The drag depends:- linearly on the size of the airplane moving through the air. The cross-sectional shape of an airplane determines the form drag created by the pressure variation around the airplane.
If the drag as aerodynamic friction The amount of drag depends on the; 1-surface roughness of the aircraft. 2- A smooth surface produces less drag than a roughened surface. This effect is called surface friction and is usually included in the measured Drag coefficient (Cd )of the aircraft.
B: Those associated with the motion of the airplane through the air Drag is associated: with the movement of the aircraft through the air, So drag depends on the velocity of the air. Drag actually varies with the square of the relative velocity between the surface of aircraft and the air.
The slope of an airplane's wing affects the flow, which affects the amount of drag an airplane produces If the aircraft moves through the air at speeds near the speed of sound, shock waves are formed on the aircraft which create an additional drag component called wave drag.
The motion of the aircraft through the air also causes boundary layers to form on the aircraft surface . A boundary layer:- is a region of very low speed flow near the surface which contributes to the surface friction .
C: Those associated with the air itself Drag depends directly on the mass of the flow going past the aircraft. The drag also depends in other properties of the air:- 1- viscosity of the air 2-compressibility of the air .
all of this information on the factors that affect drag into a single mathematical equation called the Drag Equation. With the drag equation we can predict how much drag force is generated by a given aircraft surface moving at a given speed through a given air.
Drag Equation ? ?2 2 ? = ?? ? = ??*? ?2*0.5*A *A Where ??:- drag coefficient ?:- Density ?:-velocity A:- Area
Types of Drag Types of Drag There are many different types of drag. The most commonly encountered are: Parasite Drag Form Drag surface Friction Drag Interference Drag Induced Drag Wave Drag .
Parasite Drag Parasite Drag Parasite (Parasitic) Drag (DP):- is defined as all drag that is not associated with the production of lift Parasite Drag is caused by moving aircraft through a fluid medium. In aerodynamics, the fluid medium concerned is the atmosphere. The principal components of Parasite Drag are Form Drag, Friction Drag and Interference Drag.
Form Drag Form Drag Form Drag, also known as Pressure Drag or Profile Drag Form Drag:- is the drag caused by the separation of the boundary layer from a surface and the wake created by that separation. Form Drag is primarily dependent upon the shape of the aircraft and how that shape interacts with the airflow.
surface Friction Drag surface Friction Drag Surface Friction Drag, also known as Skin Friction Drag Surface Friction Drag:- is drag caused by 1-the friction of a fluid against the surface of an aircraft that is moving through it. 2-caused by rough spots on the surface of the aircraft. Surface Friction Drag :- is directly proportional to the area of the surface in contact with the fluid and increases with the square of the velocity.
Common sources of this type of surface friction drag are:- 1- snow 2-dirt 3- dead insects 4-and other debris that accumulates on the airframe surface friction drag is one of the reasons why airplane deicing is a crucial step before you take off during winter weather conditions.
Interference Drag Interference Drag Interference Drag :-is drag that is generated by the mixing of airflow streamlines between airframe components such as the wing and the fuselage, the engine pylon and the wing. In the case of a military or other special purpose aircraft, between the airframe and attached external stores such as fuel tanks, weapons or sensors. Interference drag is greatest in areas with sharp angles like where:- 1-the wing strut meets the fuselage 2-the wings themselves attach to the fuselage.
Induced Drag Induced Drag When higher pressure air from underneath the wings flows up and over the top of the wing, this is a source of induced drag. The ratio between the width of the wing and the height of the wing is important in this type of induced drag. The lower this ratio, the greater the induced drag force and vice versa.
Wave Drag Wave Drag Is a component of the drag on aircraft wings and fuselage moving at supersonic speeds, due to the presence of shock waves Wave drag:- 1- is independent of viscous effects of air 2- tends to present itself as a sudden increase in drag as the aircraft increases speed to the critical Mach number.
critical Mach number In aerodynamics, the critical Mach Number (Mcror Mcrit) of an aircraft is the lowest Mach number at which the airflow over any part of the aircraft reaches the speed of sound. There is a critical Mach number, which will depend on the slowest part of the local flow velocity across the body of an aircraft.
Profile Drag Profile Drag Both form drag and interference drag relate to:- The size of aircraft The design of aircraft The configuration of the aircraft. Sometimes both types of drag are considered together as the overall profile drag of the airplane. The profile drag:- is the amount of form drag plus the amount of interference drag.
Drag and Airspeed Drag and Airspeed Drag increases with the square of the airspeed, while induced drag, being a function of lift, is greatest when maximum lift is being developed, usually at low speeds. The diagram below shows the relationship of parasitic drag and induced drag to each other and to total drag.
Relationship of Drag with Airspeed There is an airspeed at which drag is minimum, and in theory, this is the maximum range speed; however, flight at this speed is unstable because a small decrease in speed results in an increase in drag, and a further fall in speed. In practice, for stable flight, maximum range is achieved at a speed a little above the minimum drag speed where a small speed decrease results in a reduction in drag.
