This slide gives technical definitions of a wing's geometry, which
is one of the chief **factors** affecting
airplane lift and drag.
The terminology is used throughout the airplane industry and is also
found in the FoilSim program
developed here at NASA Glenn. Actual aircraft wings are complex
three-dimensional objects, but we will start with some simple
definitions. The figure shows the wing viewed from three directions;
the upper left shows the view from the top looking down on the wing,
the lower left shows the view from the front looking at the
wing leading edge, and the right shows a side view from the left
looking in towards the centerline. The side view shows an airfoil
shape with the leading edge to the left.

__Top View__

The top view shows a simple wing geometry, like that
found on a light general aviation aircraft. The
front of the wing (at the bottom) is called the **leading edge**;
the back of the wing (at the top) is called the **trailing
edge**. The distance from the leading to trailing edges is called
the **chord**, denoted by the symbol **c**. The ends of the wing are called the **wing
tips**, and the distance from one wing tip to the other is called
the **span**, given the symbol **s**. The shape of the wing, when viewed from above
looking down onto the wing, is called a **planform**. In this
figure, the planform is a rectangle. For a rectangular wing, the
chord length at every location along the span is the same. For most
other planforms, the chord length varies
along the span. The **wing area, A,** is the projected area of the
planform and is bounded by the leading and trailing edges and the
wing tips. **Note:** *The wing area is NOT the total surface
area of the wing. The **total surface area**
includes both upper and lower surfaces. The wing area is a projected
area and is almost half of the total surface area.*

**Aspect ratio** is a measure
of how long and slender a wing is from tip to tip.
The **Aspect Ratio** of a wing is defined to be the square of
the span divided by the wing area and is given the symbol **AR**.
For a rectangular
wing, this reduces to the ratio of the span to the chord length as shown
at the upper right of the figure.

AR = s^2 / A = s^2 / (s * c) = s / c

High aspect ratio wings have long spans (like high performance gliders), while low aspect ratio wings have either short spans or thick chords (like the Space Shuttle). There is a component of the drag of an aircraft called induced drag which depends inversely on the aspect ratio. A higher aspect ratio wing has a lower drag and a slightly higher lift than a lower aspect ratio wing. Because the glide angle of a glider depends on the ratio of the lift to the drag, a glider is usually designed with a very high aspect ratio. The Space Shuttle has a low aspect ratio because of high speed effects, and therefore is a very poor glider. The F-14 and F-111 have the best of both worlds. They can change the aspect ratio in flight by pivoting the wings--large span for low speed, small span for high speed.

__Front View__

The front view of this wing shows that the left and right wing do not
lie in the same plane but meet at an angle. The angle that the wing
makes with the local horizontal is called the **dihedral angle**.
Dihedral is added to the wings for roll stability; a wing with some
dihedral will naturally return to its original position if it encounters
a slight roll displacement. You may have noticed that most large
airliner wings are designed with diherdral. The wing tips are farther
off the ground than the wing root. Highly maneuverable fighter planes,
on the other hand do not have dihedral. In fact, some fighter aircraft
have the wing tips lower than the roots giving the aircraft a high roll
rate. A negative dihedral angle is called ** anhedral **. **Historical Note:**
* The Wright brothers designed their 1903
flyer
with a slight anhedral to improve the aircraft
roll
performance. *

__Side View__

A cut through the wing perpendicular to the leading and trailing
edges will show the cross-section of the wing. This side view is
called an **airfoil**, and it has some geometry definitions of its
own as shown at the lower right. The straight line drawn from
the leading to trailing edges of the airfoil is called the **chord
line**. The chord line cuts the airfoil into an upper surface and a
lower surface. If we plot the points that lie halfway between the
upper and lower surfaces, we obtain a curve called the **mean camber
line**. For a **symmetric airfoil** (upper surface the same
shape as the lower surface) the mean camber line will fall on top of
the chord line. But in most cases, these are two separate lines. The
maximum distance between the two lines is called the **camber**,
which is a measure of the curvature of the airfoil (high camber means
high curvature). The maximum distance between the upper and lower
surfaces is called the **thickness**. Often you will see these
values divided by the chord length to produce a non-dimensional or
"percent" type of number. Airfoils can come with all kinds of
combinations of camber and thickness distributions. **NACA** (the
precursor of NASA) established a method of designating classes of
airfoils and then wind tunnel tested the
airfoils to provide lift coefficients and
drag coefficients for designers.

Navigation..

- Beginner's Guide to Aerodynamics
- Beginner's Guide to Propulsion
- Beginner's Guide to Model Rockets
- Beginner's Guide to Kites
- Beginner's Guide to Aeronautics

Go to...

- Beginner's Guide Home Page

*byTom
Benson
Please send suggestions/corrections to: benson@grc.nasa.gov *