| Aerodynamics Glossary
Wing Design Tip
A most difficult aspect of wing design can be choosing the correct
airfoil cross sectional shape. Although most airfoil shapes can support
flight, only the right one will save thousands of dollars in operational
costs over the life of the aircraft. MultiSurface Aerodynamics is a digital
wind tunnel that can compare the performance of many airfoil shapes to make
the airfoil selection process easy.
Please Click
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Aerodynamic Center
The aerodynamic center is a point along the airfoil or wing about which the
moment coefficient does not vary with an angle of attack change.
Use VisualFoil to compute the moment about
the aerodynamic center of airfoils. Use
MultiSurface
to compute the location of and the moment about the aerodynamic center for
tapered sweptback wings.
Airfoil
An airfoil is the cross section of a wing. The airfoil shape and variations
in angle of attack are primarily responsible for the lift and profile drag
of the wing.
VisualFoil allows you to generate NACA airfoils
and contain libraries of over 1000 different shapes. You can even analyze
your custom airfoil.
Angle of Attack
The angle of attack is defined as the angle between the plane of the wing
(airfoil chord) and the direction of motion (free stream velocity). The angle
of attack can be varied to increase or decrease the lift acting on the wing.
An increase in lift often results in an increase in drag.
VisualFoil and
3DFoil allow you to vary the angle of attack of
airfoils and wings. The software will output the lift coefficient and
corresponding drag coefficients.
Center of Pressure
A point along the airfoil about which the moment due to the lift is zero,
i.e., it is the point of action of the lift. The center of pressure will
change its position when the angle of attack changes.
Use VisualFoil to compute the location of
the center of pressure of an airfoil. The programs can also illustrate the
pressure distribution along the airfoil and in the flow field using innovative
color graphics.
Chord
The chord is the dimension of the airfoil from its leading edge to trailing
edge.
Use VisualFoil to analyze airfoils of various
chord lengths in nondimensional form. Use 3DFoil
to analyze tapered wings where the chord length varies from the root to the
tip of the wing.
Circulation
Circulation is a measure of the vorticity in the flow field. For an inviscid
flow field, the lift is equal to the product of the circulation about the
airfoil, the density and the velocity.
Use 3DFoil to compute and graph the circulation
distribution along the span of a tapered wing. Compare the distribution at
various angles of attack and taper ratios.
Computational Fluid Dynamics (CFD)
Computational fluid dynamics is the term given to a variety of numerical
mathematical techniques applied to solving the equations that govern fluid
flows and aerodynamics.
Modern CFD results can rival the accuracy of wind tunnels in testing airfoils,
wings and entire airplanes for certain test configurations.
VisualFoil and 3DFoil
are examples of CFD software. Please click here
to compare the results of VisualFoil with wind tunnel data.
Density
The mass of a substance contained in a given volume divided by the volume.
For a incompressible fluid, the density is considered to be constant throughout
the flow field. However, for a compressible fluid, the density can vary from
one location to the next in the flow field. The speed of sound in a fluid
depends on the ratio of pressure changes to density changes in the fluid.
VisualFoil and 3DFoil
use built in tools to compute the density as a function of altitude. The
programs also allow you to select the density of water for marine
applications.
Drag
Drag is an aerodynamic force opposing the direction of motion. Drag can be
due to surface viscosity (friction drag), pressure differences due to the
shape of an object (form drag), lift acting on an finite wing (induced drag)
and other energy loss mechanisms in the flow such as wave drag due to shock
waves and inefficiencies in engines.
Use VisualFoil to compute the profile drag
for airfoils. Use 3DFoil to compute the total drag
(induced and profile) for the entire 3-D wings.
Drag Coefficient
The drag coefficient is defined as the drag/(dynamic pressure * reference
area). The reference area is usually the plan-form or flat projection (the
wing's shadow at noon) area of the wing.
Use 3DFoil to automatically compute the drag
coefficient of general wings. Simply enter the wing span, root chord and
tip chord. Learn why two airfoils can have different drag values.
Click here.
Dynamic Pressure
The dynamic pressure is defied as the product of the density and the square
of the velocity divided by two. The dynamic pressure has units of pressure,
i.e. Force/Area. The dynamic pressure is used to non-dimensionalize forces
and pressures in aerodynamics.
VisualFoil and
3DFoil internally compute the dynamic pressure
when calculating the aerodynamic coefficients.
Flap Deflection Angle
The flap deflection angle is the angle between the deflected flap and the
chord line. The angle is positive for a downwards deflection of the flap.
Deflect the flap downwards to increase the airfoil's lift.
Use VisualFoil to compute the lift and drag
developed with a negative or positive flap deflection.
Lift
The lift is a force acting perpendicular to the direction of flight. The
lift is equal to the fluid density multiplied by the circulation about the
airfoil and the free stream velocity. In level flight, the lift developed
by an airplane's must be equal to the weight of the entire airplane.
Use VisualFoil to compute the lift developed
by airfoils. Use 3DFoil to compute the lift developed
by a tapered sweptback wing.
Lift Coefficient
The lift coefficient is defined as the lift/(dynamic pressure * reference
area). The reference area is usually the plan-form area of a wing or horizontal
projection of the wing.
VisualFoil and
3DFoil will automatically compute the lift coefficients
for airfoils and 3-D wings respectively.
Mean aerodynamic chord
This chord is located along the wing and has the aerodynamic property of
the two-dimensional wing.
Use 3DFoil to compute the length of the mean
aerodynamic chord for a tapered swept wing. WingAnalysis can also compute
the Reynolds number based on the mean aerodynamic chord.
NACA Airfoils
NACA airfoils are wing cross section designs
invented by the NACA organization. NACA eventually became NASA (National
Aeronautics and Space Administration). Here are a few popular airplanes that
have NACA airfoil wings:
| Airplane |
Root Airfoil |
Tip Airfoil |
| Beech 50 Twin Bonanza |
NACA 23014.1 |
NACA 23012 |
| B-17 Flying Fortress |
NACA 0012 |
NACA 0010 |
| Cessna 152 |
NACA 2412 |
NACA 0012 |
| Cessna 172 1973-later |
NACA 2412 |
NACA 2412 mod |
| Cessna 550 Citation II |
NACA 23014 |
NACA 23012 |
| Douglas DC-3 |
NACA 2215 |
NACA 2206 |
| Fairchild A-10 Thunderbolt II |
NACA 6716 |
NACA 6713 |
| Sikorsky S-61 SH-3 Sea King |
NACA 0012 |
NACA 0012 |
VisualFoil and 3DFoil
can generate and test NACA airfoils for your specific project
requirements.
Panel Method
This numerical method places singularities along the airfoil. In the case
of VisualFoil or
3DFoil , the singularities are vortices. The
vorticity is distributed linearly along the panel.
Use VisualFoil to compare the lift computed
using a vortex panel method and thin airfoil theory.
Plain Flap
A plain flap is a hinge attachment near the trailing edge of an airfoil.
The length of the flap is measured as a percentage of the chord and the
deflection is measured in degrees.
Use VisualFoil compute the lift and drag acting
on airfoils with when the length and deflection of the flap are varied.
Pressure Coefficient
The pressure coefficient is a non-dimensional form of the pressure. It is
defined as the difference of the free stream and local static pressures all
divided by the dynamic pressure.
Use VisualFoil to compute and graph the pressure
distribution along the upper and lower surfaces of an airfoil. The data is
also available in tabular form.
Reynolds Number
The Reynolds number is a non-dimensional parameter that compares the inertia
to viscous forces. If the Reynolds number is low, then viscosity plays an
importatant part in the simulations.
More information about Reynolds Number can be found
here.
Stall
At low angles of attack, the lift developed by an airfoil or wing will increase
with an increase in angle of attack. However, there is a maximum angle of
attack after which the lift will decrease instead of increase with increasing
angle of attack. This is know as stall. Knowing the stall angle of attack
is extremely important for predicting the minimum landing and takeoff speeds
of an airplane.
VisualFoil uses a tested theoretical model
to predict the onset of stall for airfoils. 3DFoil
uses a proprietary method and classical wing theory to predict the maximum
lift and angle of attack for maximum lift for your wing.
Streamlines
Contours in the flow field that are tangent to the velocity vector.
Use VisualFoil to graph the streamlines for
airfoils at various angles of attack.
Wing Loading
The total weight of the airplane divided by the planform area of the wing.
Use 3DFoil to compute the wing area given the
span, root chord, tip chord and sweep angle.
Wing Span
The span is the total length of the wing.
Use 3DFoil to compute the lift and drag acting
on a finite wing when the span is varied.
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About Dr. Hanley
Dr. Patrick E. Hanley,
is the owner and founder of Hanley Innovations, a small business specializing
in the development of aerodynamics and fluid dynamics simulation software
for education and industry. Dr. Hanley earned his B.S. degree (summa cum
laude) in aerospace engineering from Polytechnic Institute of New York
and his S.M. and Ph.D. degrees from the department of Aeronautics and
Astronautics of Massachusetts Institute of Technology (MIT). He also completed
a minor in the area of management of innovation and technology at MIT's Sloan
School of Management.
After graduating from MIT, Dr. Hanley joined the Mechanical Engineering
faculty at the University of Connecticut where he formulated and taught
courses in aerodynamics, compressible fluids, introductory fluid mechanics
and heat transfer. As a faculty member, he won the highly competitive National
Science Foundation Research Initiation Award, the NASA-ASEE Summer Faculty
Fellowship and three consecutive research awards from NASA Lewis Research
center to study compressible viscous flows in turbomachinery using pseudospectral
methods. This research led to the successful education of four (4) Ph.D students
and four (4) Masters degree students. In addition Dr. Hanley can be credited
with a number of publications including the pioneering work in multi-domain
pseudospectral methods for compressible viscous flows entitled "A Strategy
for the Efficient Simulation of Viscous Compressible Flows using a Multi-domain
Pseudospectral Method" which can be found in Journal of Computational Physics,
Vol 108, No. 1, pp. 153-158, September 1993.
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