Fundamentals
• NACA Airfoils – Ever wondered looking at an
aircraft, what enables it to fly in the air. Let’s
explore the cross-sectional shape of the wing
i.e. NACA Airfoils
• National Advisory Committee For Aeronautics
What is an airfoil?
• Any section of the aircraft wing cut by a plane
parallel to the xz plane is known as an airfoil
or in simple words, it is the cross-sectional
shape of a wing. It is the shape that provides
ideal aerodynamic conditions for an aircraft to
fly smoothly in the air.
How airfoil generates Lift?
An airfoil produces lift by exerting
a downward force on the air as it
flows past. According to Newton's
third law, the air must exert an
equal and opposite (upward) force
on the airfoil, which is lifted. The
airflow shifts direction as it crosses
the airfoil and pursues a path that
is curved downward.
Airfoils produce flow rate
differences across their top
and bottom surfaces. The
flow rate difference across
an airfoil produces a
pressure gradient, resulting
in lift.
Airfoil Nomenclature
• The straight line connecting the leading edge and trailing edge
is called the chord line.
• The locus of the points halfway between the upper and lower
surfaces, is called the mean Camber line.
• The most forward and rearward point of the camber line are
the leading edge and trailing edge.
• Camber is the maximum distance between the mean camber
line and the chord line, measured perpendicular to the chord
line.
Nomenclature of NACA airfoils
• National Advisory Committee for Aeronautics
has developed various airfoil profiles that can
be used in aircraft wings depending upon their
application.
• The shape of the airfoil is described by the
digits followed by the NACA. For example
NACA0012,
NACA4412,
NACA24012,
NACA641-212a.
NACA four-digit series
• The first digit denotes the maximum camber as a
percentage of the chord.
• The second digit denotes the position (distance) of
the maximum camber from the leading edge in
tenths of the chord.
• The last two digits denote the maximum thickness
of the airfoil as a percent of the chord.
• For example, NACA2414 airfoil has a maximum
camber of 2%, located 40% from the leading edge
with a maximum thickness of 14 % of the chord.
• For symmetrical airfoil, like NACA 0012, it has
zero camber with a 12 % thickness of the cord.
NACA five-digit series
• This series is designed to locate the maximum camber
closer to the leading edge of the airfoil. There was an
increase in the coefficient of lift as the maximum camber
location was shifted forward.
• The first digit when multiplied by 0.15 yields the theoretical
lift coefficient.
• The second digit when divided by 2, gives the position of
maximum camber in tenths of the chord.
• The third digit represents whether it is a reflex (1) or a
simple (0) camber.
• The last 2 digits give the maximum thickness in the
percentage of the chord length.
For example, NACA 24012 has a maximum thickness of 12 %
of the chord, a design lift coefficient of 0.3, and a maximum
camber located at 0.2 or 20 % chord and has a simple camber.
NACA Six- digit series
The series emphasizes maximizing laminar flow with the hope of reducing the
skin friction drag.
• The number “6” denotes the series.
• The second digit gives the location of the minimum pressure area in the
tenths of the chord.
• The subscript denotes the range of lift coefficient in which favorable
pressure gradients exist on both surfaces.
• The digit after the hyphen gives the design lift coefficient in tenths.
• Last two digits describe the maximum thickness as a percentage of the
chord.
• The alphabet at the end gives the fraction of the chord over which laminar
flow is maintained. a=1, if no value is given.
For example, NACA641-212a airfoil where 6 denote the series located at a
minimum pressure area of 0.4c where low drag is maintained at lift
coefficients 0.1 above and below the design lift coefficient 0.2 with a
maximum thickness of 12 % where a=1 which means distribution is constant
over an airfoil.
NACA 7 digit series
It is an advancement in airfoil in order to maximize laminar flow
achieved by separately identifying the low-pressure zones on upper and
lower surfaces respectively.
• The number ‘7’ represents the series.
• The second digit represents the distance of the minimum pressure
area on the upper surface in tenths of the percentage of the chord.
• The third digit denotes the position of the minimum pressure area on
the lower surface in tenths of the percentage of the chord.
• Alphabet refers to a standard profile from the earlier NACA series.
• The fourth digit indicates the lift coefficient in tenths.
• The last 2 digits give the maximum thickness as a percent of chord.
Consider, the NACA 727A215 has the area of minimum pressure of
20% of the chord back on the upper surface and 70% of the chord back
on the lower surface, uses the standard ‘A’ profile, has a lift coefficient
of 0.2, and has a maximum thickness of 15% of the chord.
NACA 8 digit series
• The 8 digit series or ‘Supercritical’ airfoils are
designed for flight at supersonic speed and the
goal is to maximize laminar flow.
• Nomenclature of 8- digit series airfoil is the same
as that of 7 digit airfoil except it starts with 8
which denotes the series it belongs to.
For example, the NACA 837A215 has an area of
minimum pressure of 30% of the chord back on the
upper surface and 70% of the chord back on the
lower surface, uses the standard ‘A’ profile, has a lift
coefficient of 0.2, and has a maximum thickness of
15% of the chord.
Symmetrical and Unsymmetrical (Cambered)
Airfoils
Typical Airfoils
Angle of Attack, Lift and Drag
• Angle of Attack
– Angle between relative wind direction and chord line.
• LIFT
– Component of aerodynamic force perpendicular to the wind
direction.
• DRAG
– Component of aerodynamic force parallel to the wind direction.
LIFT, DRAG and MOMENT RELATIONS
L = (½)ρV²SCl
D = (½)ρV²SCd
M = (½)ρV²ScCm
Where ρ = free-stream density
V = free-stream velocity
S = reference area
c = wing chord
Cl = lift coefficient
Cd = drag coefficient
Cm = moment coefficient