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7.Обучение чтению литературы на английском языке по специальности «Аэродинамика». Часть 2.

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UNIT I
1. Learn the new words and word combinations.
draw v
estimate v
%, *
steadily adv
, airfoil n
+) *
derivative n
, *
appropriate adj (=, *)=
frequency n
transducer n
*', strain gage
*)<), >%
thermistor n
, *
tuft n
*
dye n
, )= =
sophisticated adj <
straightener n
*)
vane n
>(, 7, *
honeycomb adj ), regain v
*
', strut n
*, rectangular adj *)
rough adj
, 7
tolerance n
*
consideration n '<
affect v
(), )
negligible adj
, * 2. Read and analyze the text, answer the questions.
TEXT IA
WIND TUNNELS
Wind Tunnel is a tube like structure where wind is produced usually by a large fan to flow over the test object. The object is connected
to instruments that measure and record aerodynamic forces that act
upon it.
Wind tunnels are usually designed for a specific purpose and speed
range. There are special tunnels for propulsion, icing research, sub4
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sonic, supersonic and hypersonic speeds. According to its basic architecture a wind tunnel may be open and draw air from the room into the
test section, or the tunnel may be closed with the air recirculating
around the circuit. Wind tunnels may be classified according to the air
pressure (atmospheric, variable-density), or their size (ordinary ones or
full-scale). There are numbers of wind tunnels (meteorological tunnel,
shock tunnel, plasma-jet tunnel, hot-shot tunnel, water tunnel) that fall
in a special category of their own.
The wind tunnel is the most lasting contribution of the Wright
brothers to the science of aerodynamics. It is estimated that it took the
Wright Brothers less than 20 hours of wind tunnel testing to produce
their successful Flyer (although their empirical research was a life time
achievement).
The Douglas DC-3, perhaps the most successful commercial aircraft ever built, required about 100 hours of wind tunnel testing. Wind
tunnel time has been steadily increasing (and so have the costs) since:
the Boeing 747 required over 1000 tunnel hours; the Space Shuttle
nearly 10 years of time.
Wind tunnel testing is the technical support of any major development process involving aerodynamics. It is used for aircraft, helicopters, cars, trains, and laboratory research.
Some operations ordinarily performed in the wind tunnel are the
following.
 Drag/Lift measurements on aircraft, helicopters, missiles, racing cars.
 Drag/Lift/Moment characteristics of airfoils and wings.
 Static stability of aircraft and missiles
 Dynamic stability derivatives of aircraft
 Surface Pressure distributions on nearly all systems.
 Flow visualizations (with smoke, oil, talcum).
 Propeller performances (torque, thrust, power, efficiency, etc.).
 Performances of air-breathing engines.
 Wind effects on buildings, towers, bridges, automobiles, etc.
 Heat transfer properties of engines, aircraft, etc.
Measurement equipment and testing procedures are topics on their
own. They include instrumentation for the measurement of pressure,
temperature, forces, moments, turbulence intensity, etc.
The progress in electronics has widened the market of instrumentation
for wind tunnel measurements. For pressure measurements systems that
convert pressures into electric signals of appropriate frequency (trans5
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ducers, strain gages. etc.) are used. Measurements of temperatures, temperature gradients and heat transfer are made with thermocouples, thermistors, resistance sensors. Turbulence levels are measured with laser systems
(LDA, Laser Doppler Anemometry), particle tracking systems (PIV, Particle Image Velocimetry), hot wires, thermal anemometers. Analysis of flow
direction (streamlines) can be made with a very simple technique, consisting in placing tufts on the surface of the models. Also used are dyes and
oils (for surface streamlines and turbulence) and smoke (for field streamlines). For shock wave visualizations, the Schlieren photography has been
used for many years. Other methods include the shadowgraph technique
and optical interferometry. For the highest speeds absorption methods are
used.
The most up-to-date wind tunnels have now sophisticated computer
controls. Main components of a tunnel are: entrance cone, test section,
regain passage, propeller/motor, return passage. Flow straighteners,
corner vanes, honeycomb layers for reduced turbulence, air exchangers
and diffusers are other common features.
The test section is where the model is placed and held with appropriate struts. The section is generally rectangular (sometimes the test
section is an open jet). The longitudinal dimension is about twice the
maximum dimension of the section. Very seldom the models tested in a
wind tunnel are in true size. Most likely they are scaled. Models on
scale are hard to build and generally very expensive (just think of the
surface roughness, tolerances, small details, etc.) To simulate the real
conditions the aerodynamicist must keep the dimensionless parameters
constant. For example, a model 1:4 must be tested at four times the real
speed. Hence the smaller the model, the higher the speed in the test section, the other parameters being constant (this limitation can be removed in a pressurized wind tunnel).
The researcher must find a compromise between model's size and
wind tunnel size. The decision is generally dictated by cost considerations. When the real Reynolds and Mach numbers cannot be reproduced, the experimental data are affected by the so-called scale effect.
Extrapolation to real scale depends on the type of experiment performed and the range of Reynolds and Mach numbers tested. Sometimes the scale effects are negligible, sometimes (like transonic flows,
low speeds) they are not.
The test conditions are never the same as the operational conditions.
Among the most well known effects there are the scale effects, the flow
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blockage, due to the presence of the model in the test section and wall
boundary layers. Other effects are dependent on the type of experiments
performed, for example angle of attack corrections for a wing, due to
induced downwash. Wind tunnel correction requires special analysis
and processing techniques.
3. Answer the questions.
1. What are the purposes wind tunnels are designed for?
2. Why is it necessary to measure and record aerodynamic forces
that act upon the object?
3. How is wind produced in a wind tunnel?
4. How may wind tunnels be classified?
5. What categories do wind tunnels fall in?
6. What are brothers Wright famous for?
7. What is wind tunnel testing important for?
8. What operations performed in wind tunnels do you know?
9. Why is it important to mention the measurement equipment
speaking about wind tunnels?
10. What systems, techniques or methods are used in complex wind
tunnel measurements?
11. How much computers play in wind tunnels?
12. Why are models tested in a wind tunnel seldom in true size?
13. What do you know about the scale effect?
14. Why are the test conditions never the same as the operational
conditions?
4. Complete the sentences.
1. Wind tunnels are usually designed …
2. According to its architecture a wind tunnel may …
3. Twenty hour wind tunnel testing is …
4. For pressure measurements systems that …
5. To simulate the real conditions …
6. The smaller the model, the higher …
7. The decision is generally dictated by …
5. Make up full sentences with the list of wind tunnel operations
given in Text IA.
x Drag/Lift measurements on aircraft, helicopters, missiles, racing cars.
x Drag/Lift/Moment characteristics of airfoils and wings.
x Static stability of aircraft and missiles
x Surface Pressure distributions on nearly all systems.
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x Flow visualizations (with smoke, oil, talcum).
x Propeller performances (torque, thrust, power, efficiency, etc.).
x Performances of air-breathing engines.
x Wind effects on buildings, towers, bridges, automobiles, etc.
x Heat transfer properties of engines, aircraft, etc.
6. Match a word in column A with a word in column B.
A
B
longitudinal
model
tested/experimental
parameters
reduced
component
surface
roughness
real
cone
main
size
entrance
exchanger
appropriate
effect
constant
streamline
negligible
dimension
turbulence
level
7. Make up sentences with word combinations from ex. 4. Add the
following words where possible.
Hard, lasting, successful, generally, so-called, well known, special,
involved, maximum, processing, induced.
8. Make up questions to each part of the sentence.
1. The wind tunnel is the most lasting contribution of the Wright
brothers to the science of aerodynamics.
2. Models on scale are hard to build and generally very expensive.
3. The progress in electronics has widened the market of insteuments for wind tunnel measurement.
9. Try to find out what these prominent persons are famous for.
The Wright brothers, Mach, Reynold, Doppler, Douglas.
10. Answer the questions.
1. What types of wind tunnels do you know?
2. Why do scientists need different types of wind tunnels?
3. Could you specify problems concerning wind tunnels?
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11. Read the text with a dictionary.
TEXT IB
A FEW TYPES OF MODERN WIND TUNNELS
Hotshot Wind Tunnels
Hotshot tunnels are designed to operate at the highest speeds (up to
M = 27), for analysis of flows past ballistic missiles, space vehicles in
atmospheric entry and plasma physics, heat transfer at high temperatures. It runs intermittently, like other high speed tunnels, but it has a
very low running time (one second or less). The mechanism of operation is based on a high temperature/ pressure gas (air or nitrogen) produced in an arc-chamber and a near-vacuum in the remaining part of
the tunnel. Pressure in the arc-chamber can reach several MPa, while
pressures in the vacuum chamber can be as low as 0.1 Pa (pressure ratios
of the order of 10 million); temperatures of the hot gas are up 5,000 K.
The high pressure gas is separated by the vacuum chamber by a diaphragm that breaks down as its resistance is exceeded.
Pressurized Wind Tunnels
In a pressurized wind tunnel experiments can be performed at flow
densities different (generally higher) from the atmospheric pressure. A
model on scale 1:4 should be tested at four times the operational speed
in an atmospheric wind tunnel. By increasing the density to four times
the atmospheric pressure keeps the Reynolds number constant at the
operational speed. This type of tunnel has its own peculiar problems.
Meteorological Wind Tunnels
These are tunnels used to study effects on suspension bridges, highrise buildings, towers, dispersals of pollutants from factories, etc. They
often require a special sizing, but they are characterized by the long test
sections. Unlike most wind tunnels, it is important to simulate the effects of the boundary layers (atmospheric boundary layer). The test section is generally very large. Testing of elastic structures (bridges) requires lengthy preparation of the model.
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Tunnels with Moving Ground
Wind tunnels with moving ground are used by the automobile industry, by racing cars teams, by the truck industry and for high-speed
trains. A moving belt is used to simulate the road conditions. The belt
moves with autonomous motor synchronized with the tunnel speed.
Simulating a road vehicle in a wind tunnel presents peculiar problems
related to the presence of the ground boundary layer, the ground effect
and the rotating wheels. There are several approximations of the road
conditions, some of which are sketched in Fig. 1. The most accurate
approach consists in having a moving belt on the wind tunnel floor.
(Other methods include vertical suction, tangential blowing, boundary
layer removal ahead of the model, etc.)
Fig. 1. Car in a wind tunnel
Having rotating or non-rotating wheels in the test facility makes a
considerable difference in the resulting drag coefficient. Measuring
aerodynamic lift and drag is quite elaborate, because of the struts interference and because of the rolling resistance of the tires, which depend
on the vertical load.
Vertical Wind Tunnels
A vertical wind tunnel (VWT) is a wind tunnel which moves air up
in a vertical column. It is a recreational wind tunnel, frequently
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advertised as ‘indoor skydiving’ or ‘bodyflight’. It is also a popular
training tool for athlets.
Vertical wind tunnels enable human beings to fly in air without
planes or parachutes, through the force of wind being generated
vertically. Wind moves upwards at approximately 120 mph, the
terminal velocity of a falling human body belly-downwards, although
this can vary from person to person.
Bodyflight, or ‘body flight’, is the art of ‘flying your body’ in a
controlled manner. This includes turns, rolls, lateral movement, fall rate
control, and other acrobatics in the air. Bodyflight is accomplished via
increasing/decreasing the drag of your body, using arms and legs as
rudders for bodyflight motion control, as well as other techniques
similar to that of an airplane.
Various propellers and fan types can be used as the mechanism to
move air through a vertical wind tunnel. Motors can either be dieselpowered or electric-powered and typically provide a vertical column of
air between 6 and 16 feet wide. A control unit allows for air speed
adjustment by a controller in constant view of the flyers. The controller
can turn the air up for extra lift or down for less lift depending on the
size, skill level and needs of the tunnel flyer.
The first human to fly in a vertical wind tunnel was Jack Tiffany in
1964 at Wright Patterson Air Force Base. The first recreational vertical
wind tunnel was developed by a Canadian company named Aerodium
in Quebec. It was developed and patented as the ‘Levitationairum’ by
Jean St-Germain in 1979.
An important milestone in vertical wind tunnel history was ‘Wind
Machine’ at the closing ceremonies of the 2006 Torino Winter Olympics.
This was an Aerodium unit custom built by Aerodium Canada and
Aerodium Latvia for the sole purpose of the closing ceremony. Many
people had never seen a vertical wind tunnel before, and were fascinated
by the flying humans with no wires to keep them aloft.
12. Answer the questions.
1. What are the differences in operation of various wind tunnels?
2. What mechanisms move air though wind tunnels?
3. What properties of an object are measured in wind tunnels?
4. Which type of a wind tunnel would you prefer to design and
construct?
5. Would you like to make experiments in wind tunnels? What for?
Where?
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13. Prepare and make a mini-presentation of any type of a wind
tunnel. Draw pictures, schemes to visualize your speech. Use words
for the beginning:
Today I would like to …
Let me just start by introducing myself. My name is …
In my presentation I would like to report on …
The topic of today's presentation is …
I’ve divided my presentation into three(main) parts …
I’ll focus on three major issues.
First of all, I'll be looking at …, second …, and third …
Finally, I'll offer some solutions.
Then I'll move on to the problem …
Feel free to ask questions at any time … (after my presentation) …
Now, I'd like you to take a look at this next slide … (graph) …
which shows.
14. Round-table talk. Play roles of specialists in various industrial
fields. Say which type of a wind tunnel you need to conduct experiments
at your enterprise, plant, factory etc. Use words and phrases.
Would you mind telling us whether … ?
Could you be a bit more specific?
I'm afraid I don't catch you … (understand) …
I'd like to draw your attention to the latest figures.
So, just how good are the results?
It would be completely wrong to change our strategy at this point.
We compared the two offers and found the first one totally unacceptable.
I think this fact is extremely important.
15. Read the text and answer the questions.
TEXT IC
HOW WIND TUNNELS WORK
Air is blown, sometimes even sucked through a tunnel containing
any object that one wants to test. Typically, the air is moved through
the tunnel using fans. For large wind tunnels, a single fan is not sufficient, so instead a series of multiple fans are used to provide sufficient
airflow. Due to the sheer volume and air speed required, turbofans and
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not electrical motors may power the fans.The airflow created by the
fans is highly turbulent because of the fan blade motion and so is not
useful for accurate measurements. For accurate measurements, the
airflow has to be turbulence-free and laminar, which means that the
airflow has to flow in parallel layers, with no disruption between the
layers. To correct that problem, a row of closely placed vertical and
horizontal air vanes are used to smooth out the turbulent airflow.
That way, the air would be laminar by the time it reaches the testing
object.
The inside walls of a wind tunnel are typically very smooth, since
ragged edges could create turbulence. Otherwise, the accuracy of the
testing would be disturbed. Even smooth walls create some drag in the
airflow, so the object being tested is usually placed near the center of
the tunnel.
Lighting is normally recessed into the circular walls of the tunnel
and shines through windows. If the light were to be mounted on the
inside surface of the tunnel, the light bulb would generate turbulence
when the air blows around it. Similarly, observation is usually done
through transparent portholes in the walls of the tunnel. Rather than
flat windows, the observation windows may be curved to match the
overall shape of the inner surface of the tunnel. That is to reduce turbulence created by the window. Because air is transparent, it is difficult to observe the airflow itself. Instead, smoke or mist is sprayed
into the tunnel ahead of the testing object. That way it is possible to
see the airflow with the bare eye. Another simple way to test the airflow is to put thin strips on the testing object's surface and see how
much they move.
16. Answer the questions.
1. What mechanisms are used to provide sufficient airflow through
a tunnel?
2. What is the drawback of airflow in a wind tunnel?
3. What kinds of measurements do scientists need for their work?
4. Why is the object being tested placed near the center of the tunnel?
5. What difficulties were overcome to observe the object in the tunnel?
6. What methods to observe the object in the wind tunnel could you
suggest?
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17. Could you describe the experiment with any object inside a
wind tunnel?
What methods would you apply to measure the airflow?
What difficulties could you predict in observing the object?
Why is it especially important to have accurate experiment measurements?
18. Ask your friend about his experiment with an object in a wind
tunnel.
19. Read the text, use a dictionary and answer the question: What
do you know about the computer control in aerodynamics?
TEXT ID
COMPUTER CONTROLS AND DATA ACQUISITION
Aerodynamicists look forward to the future; they now speak of
electronic wind tunnels. What they really mean is that aerodynamic
theory has improved considerably and electronic computers have
more than kept pace so that the mathematical prediction of the performance characteristics of aircraft and their components is much
more accurate.
The hallmark of modern scientific research is the computerization
of all measuring devices, the direct analysis of the data gathered and the
automatic display of digested information in forms palatable to human
observers. The Wrights were able to make do with the visual observation of test airfoils mounted on a bicycle, but aerodynamic research depends more and more heavily on computers so much that a wind tunnel
must now shut down when its computer falters. Computers not only
collect, process, store and reduce large volumes of experimental data
but they also control the tunnel itself. With appropriate software, it is
possible to control a wide range of parameters in real-time, to visualize
the progress of the test with the tunnel running, start and stop the process. This is now the norm, not an extreme example of computerization.
The National Transonic Facility typifies the modern trend toward
tunnel / computer symbiosis. Four computers handle the functions of
data acquisition and display, data base management, process monitoring and communication, and tunnel and model control. Tunnel control
means just that. The various aspects of tunnel operation are monitored
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continuously and automatically. When these parameters stray too far
from the norm, the computer sounds the alarm and takes appropriate
remedial action, even shutting the tunnel down when personnel and
equipment are in danger.
A test in the tunnel can be completely programmed from tunnel
startup to shutdown. Changes in Mach number, air temperature, altitude
and configuration of the model are also brought under the jurisdiction
of the computers.
At the behest of the test operator, various plots and displays can be
generated almost instantaneously for real time evaluation. Parameters
being measured can be compared within 2 seconds with theoretical expectations or with data from previous runs by calling in information
stored in memory banks.
Old timers in wind tunnel research can recall how, back in the
1920s, the two engineers with the sharpest eyes would peer through
tunnel observation ports, read the balance scales, and call out their readings to the recorder. It would be days, sometimes weeks, before the data
were processed. Of course, there were computers of sorts in those days,
but they were slow, error prone, and also went out to lunch.
The control room of a big, up to date wind tunnel resembles that
of an electric power plant-buttons, lights, switches, and displays
everywhere. Bit by bit, though, the computer is taking over the
monitoring of displays and the pushing of buttons. Today, the impact of the marriage of the wind tunnel and computer is largetomorrow it will be profound. As Leo Cherne has asserted, ‘The
computer is incredibly fast, accurate and stupid. Man is unbelievably
slow, inaccurate and brilliant. The marriage of the two is a force beyond comprehension.’
With extensive computerization, self streamlining walls, laser based
instrumentation, cryogenic operation and magnetic model suspension,
wind tunnel technology is unquestionably keeping pace with the rapidly
advancing state of the art in scientific research.
The basic engineering mission of the wind tunnel will remain the
same as it has been for a century: pioneering aerodynamic research followed by performance validation of new aircraft designs and subsequent refinement of configurations. In addition, wind tunnel validation
of new theoretical concepts will always be part of aerodynamic progress.
Through the years, wind tunnels have always been able to respond
quickly to unexpected problems.
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20. Comment on the following.
1. Computers not only collect, process, store and reduce large volumes of experimental data but they also control the tunnel itself. Do
you think it is possible? How?
2. Tunnel control means just that. What? Do you know?
3. As Leo Cherne has asserted, ‘The computer is incredibly fast,
accurate and stupid. Man is unbelievably slow, inaccurate and brilliant.
The marriage of the two is a force beyond comprehension.’ What does
it mean?
4. Wind tunnel validation of new theoretical concepts will always
be part of aerodynamic progress. Why?
UNIT II
1. Learn the new words and word combinations:
hurling adj
''
hurl v
', , 7)
rifle n
( )
forensic adj '
firearms n
<
bullet n
*
)
barrel n
, , '', , %
projectile n
), *
)
impart v
*, ), *, '=
to be aware v , , ' curve n
), '
retardation n *, <, **)
assumption n **<, *
=
subtle adj
, , yaw n (v)
, ; bore n
, '
shallower adj , *, *
hollow n
*, *, *
taper n
, ** <, <)
crimp v
>, dispersion n , *)
shift n
*=, , , *'
erratic adj
*, *)
deceleration n 7 , '; 16
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flesh n
plotted adj
equalized p.p
elevation n
ambient n
*
, , '
7)
7)) , <(= *
2. Match Russian and English equivalents.
, ) *
), , ) <(= , ') +*, ) ,
) (
) ', * *
, * <(= .
Flight characteristics of the bullet, ambient conditions, line of sight,
ambient air density, hunting bullet, square of velocity, rifling in a barrel, curvilinear, forensic science.
3. Translate the following sentences paying attention to contextual meanings of the vitalized words.
1. Examinations involve analyzing firearm, ammunition, and tool
mark evidence in order to establish whether a certain firearm or tool
was used in the commission of a crime.
2. Over long periods of flight, these forces have a major impact on
the path of the projectile, and must be accounted for when predicting
where the projectile will travel.
3. At extremely long ranges, artillery must fire projectiles along
trajectories that are not even approximately straight.
4. When the straight path of the projectile is plotted in the rotating
coordinate system that is used, then this path appears curvilinear.
4. Read the text without a dictionary.
TEXT IIA.
BALLISTICS
Ballistics (gr. ba'llein, ‘throw’) is the science of mechanics that
deals with the motion, behavior, and effects projectiles, of especially
bullets, gravity bombs, rockets, or the science or art of designing and
hurling projectiles so as to achieve a desired performance.
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Overview
A ballistic body is a body which is free to move, behave, and be
modified in appearance, contour, or texture by ambient conditions, substances, or forces, as by the pressure of gases in a gun, by rifling in a
barrel, by gravity, by temperature, or by air particles.
Firearm ballistics information can also be used in forensic science.
Separately from ballistics information, firearm and tool mark examinations involve analyzing firearm, ammunition, and tool mark evidence in
order to establish whether a certain firearm or tool was used in the
commission of a crime.
Ballistics is sometimes subdivided into:
x internal ballistics, the study of the processes originally accelerating the projectile, for example the passage of a bullet through the barrel
of a rifle;
x transition ballistics, (sometimes called intermediate ballistics)
the study of the projectile's behavior when it leaves the barrel and the
pressure behind the projectile is equalized;
x external ballistics, the study of the passage of the projectile
through space or the air; and
x terminal ballistics, the study of the interaction of a projectile with
its target, whether that be flesh (for a hunting bullet), steel (for an antitank round), or even furnace slag* (for an industrial slag disruptor).
A ballistic missile is a missile designed to operate in accordance
with the laws of ballistics.
External ballistics is the part of the science of ballistics that deals
with the behaviour of a non-powered projectile in flight. External ballistics is frequently associated with firearms, and deals with the behaviour of the bullet after it exits the barrel and before it hits the target.
When in flight, the main forces acting on the projectile are gravity and
air resistance.
Forces acting on the projectile
Gravity imparts a downward acceleration on the projectile, causing
it to drop from the line of sight, and the air resistance decelerates the
projectile with a force proportional to the square of the velocity (or
cube, or even higher powers of v, depending on the speed of the projectile). Over long periods of flight, these forces have a major impact on
the path of the projectile, and must be accounted for when predicting
where the projectile will travel.
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Target shooters must be very aware of the external ballistics of their
bullets. When shooting at long ranges, bullet drop can be measured in
tens of feet within the accurate range of many rifle cartridges, so
knowledge of the flight characteristics of the bullet and the distance to
the target are essential for accurate long range shooting. At extremely
long ranges, artillery must fire projectiles along trajectories that are not
even approximately straight; they are closer to parabolic, although air
resistance affects this. For the longer ranges and flight times, the
Coriolis effect becomes important. In the case of ballistic missiles, the
altitudes involved have a significant effect as well, with part of the
flight taking place in a near-vacuum.
External factors
Wind. Wind has a range of effects the first being the effect of
making the bullet deviate to the side. From a scientific perspective,
the ‘wind pushing on the side of the bullet’ is not what causes wind
drift. What causes wind drift is drag. Drag makes the bullet turn into
the wind, keeping the centre of air pressure on its nose. This causes
the nose to be cocked (from your perspective) into the wind, the base
is cocked (from your perspective) ‘downwind.’ So, (again from your
perspective), the drag is pushing the bullet downwind making bullets
follow the wind. A somewhat less obvious effect is caused by head or
tailwinds. A headwind will slightly increase the relative velocity of
the projectile, and increase drag and the corresponding drop. A tailwind will reduce the drag and the bullet drop. In the real world pure
head or tailwinds are rare, since wind seldom is constant in force and
direction and normally interacts with the terrain it is blowing over.
This often makes ultra long range shooting in head or tailwind conditions hard. Wind also causes a Magnus effect, whereby the sideways
component of the wind combined with the spin of the bullet creates a
force acting either up or down, perpendicular to the sideways vector
of the wind.
Ambient air density. Air temperature, pressure, altitude and
humidity variations make up the ambient air density. Decreased air density will result in a decrease in drag, and increased air density will result in a rise in drag. Humidity has a counter intuitive impact. Since
water vapor has a density of 0.8 grams per litre, while dry air averages
about 1.225 grams per litre, higher humidity actually decreases the air
density, and therefore decreases the drag.
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Vertical angles. The vertical angle (or elevation) of a shot will also
affect the trajectory of the shot. Ballistic tables for small calibre projectiles (fired from pistols or rifles) assume that gravity is acting nearly
perpendicular to the bullet path. If the angle is up or down, then the
perpendicular acceleration will actually be less. The effect of the path
wise acceleration component will be negligible, so shooting up or
downhill will both result in a similar decrease in bullet drop.
Long range external factors. The coordinate system that is used to
specify the location of the point of firing and the location of the target
is the system of latitudes and longitudes, which is in fact a rotating coordinate system, since the Earth is rotating. For small arms, this rotation is generally insignificant, but for ballistic projectiles with long
flight times, such as extreme long-range rifle projectiles, artillery and
intercontinental ballistic missiles, it is a significant factor in calculating
the trajectory. During its flight, the projectile moves in a straight line
(not counting gravitation and air resistance for now). Since the target is
co-rotating with the Earth, it is in fact a moving target, relative to the
projectile, so in order to hit it the gun must aim slightly ahead of the
target, the gun must be aimed to a point where the bullet and the target
will arrive simultaneously.
When the straight path of the projectile is plotted in the rotating coordinate system that is used, then this path appears curvilinear. The fact
that the coordinate system is rotating must be taken into account, and
this is achieved by adding terms for a ‘centrifugal force’ and a ‘Coriolis
effect’ to the equations of motion. When the appropriate Coriolis term
is added to the equation of motion the predicted path with respect to the
rotating coordinate system is curvilinear, corresponding to the actual
straight line motion of the projectile.
* furnace slag – *.
5. Agree or disagree with the statements.
1. Ballistics is subdivided into internal ballistics and external ballistics.
2. External ballistics is frequently associated with firearms.
3. Air temperature isn’t important for ambient air density.
4. A tailwind will slightly increase the relative velocity of the projectile.
5. Water vapor has a density of 0.8 grams per litre.
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6. Answer the following questions to the text.
1. What long range external factors do you know ?
2. How is ballistics subdivided ?
3. Which forces act on the projectile ?
4. What is the consequence of the using of the rotational coordinate
system ?
7. Translate sentences paying attention to the highlighted words.
1. In physics, Coriolis effect is an apparent deflection of moving objects when they are viewed from a rotating reference frame.
2. A ballistic coefficient, or BC, combines the air resistance of the
bullet shape and its sectional density.
3. The BC gives the ratio of ballistic efficiency compared to the
standard projectile.
4. The effect of gravity on a projectile in flight is often referred to
as bullet drop.
5. Sectional density grows linearly with bore diameter.
8. Make sentences with the word combinations from Ex. 7.
9. Translate the text with a dictionary.
TEXT IIB.
DRAG RESISTANCE MODELLING AND MEASURING
Mathematical models for calculating the effects of air resistance are
quite complex and for the simpler mathematical models not very reliable beyond 500 m (500 yd), so the most reliable method of establishing trajectories is still by empirical measurement.
Fixed drag curve models generated for standard-shaped projectiles
Use of ballistics tables or ballistics software based on the
Siacci/Mayevski G1 drag model, introduced in 1881, are the most
common method used to work with external ballistics. Bullets are described by a ballistic coefficient, or BC, which combines the air resistance of the bullet shape (the drag coefficient) and its sectional density
(a function of mass and bullet diameter).
The deceleration due to drag that a projectile with mass m, velocity v,
and diameter d will experience is proportional to BC, 1/m, v ² and d ².
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The BC gives the ratio of ballistic efficiency compared to the standard
G1 projectile, which is a 1 pound (454 g), 1 inch (25.4 mm) diameter
bullet with a flat base, a length of 3 inches (76.2 mm), and a 2 inch
(50.8 mm) radius tangential curve for the point.
Sporting bullets, with a calibre d ranging from 0.177 to 0.50 inches
(4.50 to 12.7 mm), have BC’s in the range 0.12 to slightly over 1.00,
with 1.00 being the most aerodynamic, and 0.12 being the least. Sectional density is a very important aspect of a bullet, and is the ratio of
frontal surface area (half the bullet diameter squared, times pi) to bullet
mass. Since, for a given bullet shape, frontal surface increases as the
square of the calibre, and mass increases as the cube of the diameter,
then sectional density grows linearly with bore diameter. Since BC
combines shape and sectional density, a half scale model of the G1 projectile will have a BC of 0.5, and a quarter scale model will have a BC
of 0.25.
Since different projectile shapes will respond differently to
changes in velocity (particularly between supersonic and subsonic
velocities), a BC provided by a bullet manufacturer will be an average
BC that represents the common range of velocities for that bullet. For
rifle bullets, this will probably be a supersonic velocity, for pistol bullets it will be probably be subsonic. For projectiles that travel through
the supersonic, transonic and subsonic flight regimes BC is not well
approximated by a single constant, but is considered to be a function
BC(M) of the Mach number M; here M equals the projectile velocity
divided by the speed of sound. During the flight of the projectile the
M will decrease, and therefore (in most cases) the BC will also decrease.
Most ballistic tables or software takes for granted that one specific
drag function correctly describes the drag and hence the flight characteristics of a bullet related to its ballistics coefficient. Those models do
not differentiate between flat-based, spitzer, boat-tail, very-low-drag,
etc. bullet types. They assume one invariable drag function as indicated
by the published BC. These resulting drag curve models are referred to
as the Ingalls, G1 (by far the most popular), G2, G5, G6, G7, G8, GI
and GL drag curves.
10. Complete each sentence with an appropriate ending.
1. Bullets are described by
a ballistic coefficient which
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2. During the flight of the projectile the Mach number
3. Most ballistic tables or software takes for granted that
4. Since different projectile
shapes will respond differently to the changes in velocity
hence the flight characteristics of
a bullet related to its BC.
B. a ballistic coefficient provided
by a bullet manufacturer will be
an average BC.
C. Combines the air resistance of
the bullet shape and its sectional
density.
D. will decrease and the BC will
also decrease.
11. Translate the text with a dictionary.
TEXT IIC
MORE ADVANCED DRAG MODELS
Pejsa model. Besides the traditional Siacci/Mayevski G1 drag
model other more advanced drag models exist. The most prominent
alternative ballistic model is probably the model presented in 1980 by
Prof. Arthur J. Pejsa. Mr. Pejsa claims that his method was consistently
capable of predicting rifle bullet trajectories within 2.54 mm (0.1 in)
and bullet velocities within 0.3048 m/s (1 ft/s) out to 914.4 m (1000 yd)
when compared to dozens of actual measurements.
The Pejsa model is an analytic closed-form solution that does not
use any tables or fixed drag curves generated for standard-shaped projectiles. The Pejsa method uses the G1-based ballistic coefficient as
published, and incorporates this in a Pejsa retardation coefficient function in order to model the retardation behaviour of the specific projectile. Since it effectively uses an analytic function (drag coefficient modelled as a function of the Mach number) in order to match the drag
behaviour of the specific bullet the Pejsa method does not need to rely
on any prefixed assumption.
Besides the mathematical retardation coefficient function, Pejsa
added an extra slope constant factor that accounts for the more subtle
change in retardation rate downrange of different bullet shapes and
sizes. It ranges from 0.1 (flat-nose bullets) to 0.9 (very-low-drag bullets). If this deceleration constant factor is unknown a default value of
0.5 will predict the flight behaviour of most modern spitzer-type rifle
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bullets quite well. With the help of test firing measurements the slope
constant for a particular bullet can be determined. These test firings
should preferrably be executed at 75% to 80% of the supersonic range
of the projectiles of interest, staying away from erratic transonic effects. With this the Pejsa model can easily and accurately be tuned for
the specific drag behaviour of a specific projectile, making significant
better ballistic predictions for ranges beyond 500 m (546.7 yd) possible.
Degrees of Freedom (6 DOF) model. There are also advanced
professional ballistic models available. These are based on 6 Degrees of Freedom (6 DOF) calculations. 6 DOF modelling needs
such elaborate input, knowledge of the employed projectiles and
long calculation time on computers that it is unpractical for nonprofessional ballisticians. 6 DOF is generally used by military organizations that study the ballistic behaviour of a limited number of
(intended) military issue projectiles. Calculated 6 DOF trends can be
incorporated as correction tables in more conventional ballistic
software applications.
Doppler Radar-Measurements
For the precise establishment of BC's or maybe scientifically better
expressed drag coefficients Doppler radar – measurements are required.
The normal shooting or aerodynamics enthusiast however has no access
to such expensive professional measurement devices. Doppler radars are
used by governments, professional ballisticians, defence forces and a few
ammunition manufacturers to obtain exact real world data of the flight
behaviour of projectiles of their interest.
12. Answer the questions.
1. What advanced drag models do you know?
2. Does Peisa model use any tables?
3. What are Doppler radar measurements used for?
4. Why is the use of 6 DOF model limited?
13. Speak on the topic ‘Drag resistance modelling and measuring’.
14. Read text IID without a dictionary and speak about same applications of the ballistic science.
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TEXT IID
FORENSIC BALLISTICS
In the field of forensic science, forensic ballistics is the science of
analyzing firearm usage in crimes. It involves analysis of bullets and
bullet impacts to determine the type.
Rifling, which first made an appearance in the 15th century, is
the process of making grooves in gun barrels that imparts a spin to
the projectile for increased accuracy and range. Bullets fired from
rifled weapons acquire a distinct signature of grooves, scratches, and
indentations which are somewhat unique to the weapon used.
The first firearms evidence identification can be traced back to
England in 1835 when the unique markings on a bullet taken from a
victim were matched with a bullet mold belonging to the suspect. When
confronted with the damning evidence, the suspect confessed to the
crime.
The first court case involving firearms evidence took place in 1902
when a specific gun was proven to be the murder weapon. The expert in
the case, Oliver Wendell Holmes, had read about firearm identification,
and had a gunsmith test-fire the alleged murder weapon into a wad of
cotton wool. A magnifying glass was used to match the bullet from the
victim with the test bullet.
Calvin Goddard, physician and ex-army officer, acquired data from
all known gun manufacturers in order to develop a comprehensive database. With his partner, Charles Waite, he catalogued the results of
test-firings from every type of handgun made by 12 manufacturers.
Waite also invented the comparison microscope. With this instrument,
two bullets could be laid adjacent to one another for comparative examination.
In 1925 Goddard wrote an article for the Army Ordnance titled ‘Forensic Ballistics’ in which he described the use of the comparison microscope regarding firearms investigations. He is generally credited
with the conception of the term ‘forensic ballistics’, though he later
admitted it to be an inadequate name for the science. In 1929 the first
independent scientific crime detection laboratory was opened in the
United States.
15. Give examples of using of the forensic ballistics.
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UNIT III
1. Learn the new words and word combinations
insect n
airborne adj
* * , (=
curvature n
', , smoke trail
wisp v
tether adj
*)
wingspan n
vortice n
downstroke n
whirling arm
=(=)) 7
spin v
=)
glider n
*
harness n
*), <
free-spinning adj
' =(=)
unobtrusively adv
), remote control
% *
hurdle n
*, *, **)
seize up v
, flex v
, '
whirlwind n
, 2. Match Russian and English equivalents.
?< < , '-<
, ', 7 , =.
Airborn creatures, insect's complex wing form, tiny whirlwinds,
hummingbird-sized, robobugs.
3. Read and analyze the text.
TEXT IIIA (PART I)
MOTH IN A WIND TUNNEL
It was not until the late 1990s that researchers finally discovered
how insects fly. Until then, aerodynamic theory could not explain how
insects' small wings create enough lift to get the creatures airborne. As
conventional wisdom had it, lift is a result of lower-pressure air flowing
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over the top of a wing, thanks to the differing curvature of its upper and
lower surfaces and the wing's angle relative to the airflow. Yet insects
somehow produce up to three times more lift than this model suggests.
There had to be something else going on.
In December 1996, a team led by Charles Ellington, a zoologist at
the University of Cambridge, found out what it is. Using high-speed
video in a wind tunnel, they filmed smoke trails as they wisped over the
wings of a tethered hawkmoth*, which has a 10-centimetre wingspan.
This showed that the insect's complex wing motion – beating down and
forward, then rotating back and upward – was generating tiny whirlwinds that moved along the leading edge of each wing.
After further experiments with a 10-times life-size mechanical
model of the moth, they found that these vortices were being created
on the downstroke and producing a low-pressure area above the
wing that can give up to 50 per cent more lift than is needed to loft
the creature.
* hawkmoth – '< ().
4. Make five questions on the text.
5. Read more about robots-insects.
TEXT IIIA (PART II)
FLOAT LIKE A ROBOT BUTTERFLY
In 1804 the English aviation pioneer George Cayley installed a bizarre* machine at the top of his staircase. He attached wings of various
shapes to a whirling arm atop the device, and as it spun the wings
would either climb or descend depending on their ability to generate
lift. This helped Cayley to develop the aerodynamic theories that led to
his successful manned glider flights, and ultimately to the Wright
brothers' powered aircraft.
More than two centuries later, a whirling arm is once again being
used to prepare the next revolution in flight technology: micro-aircraft
that harness the complex aerodynamics and navigation techniques of
insects. In his lab at the University of California, Berkeley, microsystems engineer Ronald Fearing fixes each new version of the mechanical
insect he is developing to the tip of a 30-centimetre free-spinning arm
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he calls a ‘flight mill’. Like Cayley's machine, this allows him to measure how much lift his creation can generate, and to test different ways
of controlling it.
Mechanical insects could prove far more maneuverable than microsized versions of conventional aircraft or helicopters. The insect-like
craft could fly unobtrusively** around buildings, zipping*** into open
windows, for example. When equipped with different kinds of sensors,
they could be used as miniature spy drones, security guards and pollution monitors.
The military in particular are interested. The Pentagon's Defense
Advanced Research Projects Agency is developing four flying
‘robobugs’, weighing up to 10 grams each and with wingspans of up to
7.5 centimetres. It is challenging work. If micro-aircraft like Fearing's
are ever to fly, they will not only need to generate lift in a similar way
to insects, but also mimic the way bugs sense their environment to allow them to maintain stability and land safely. Recent developments in
wing mechanics and control systems mean that researchers are now
getting close.
The first hurdle for engineers like Fearing is to develop mechanisms that will generate enough lift. Insects do this by rapidly beating
their wings down and forward, and then rotating them back and upward. Andrew Conn at the University of Bristol in the UK unveiled a
hummingbird-sized wing mechanism driven by a pair of motorized
aluminium cranks that reproduce a typical insect wingbeat: one beats
the 7.5-centimetre wing up and down, while the other rotates it. This
current design's wing motion is adjustable and should allow more maneuverability in the air.
However, the scientist has found that friction in the mechanism is
slowing the wing’s beating. The device is also currently too heavy to
take off, so the researchers plan to replace as much metal as possible
with carbon fiber.
These problems come as no surprise to the entomologists at Michael Dickinson's lab at the California Institute of Technology in Pasadena, where they study fly and honeybee wing dynamics. Anyone attempting to mimic insect wing motion using such complex machined
gearing may be wasting their time, they say. As the Bristol team is finding, friction dominates at such small scales, so micro-sized versions of
conventional gears and pulleys can sometimes seize up. Dickinson's
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team reckons success is much more likely to come by emulating the
way an insect uses muscles to flex its whole thorax, which in turn
moves the wings.
Generating lift is only half the problem, though. The micro-aircraft
will also need precision 3D flight control once in the air. Remote control is one option, but they will be more useful if they can be autonomous, and for this they will need to mimic another part of the insect's
repertoire.
Insects navigate by monitoring the way surfaces around them –
most obviously the ground – sweep backwards in their field of vision as
they fly forward. This ‘optical flow’ provides cues about their airspeed
and height that are crucial for landing safely, avoiding obstacles and
navigation in general. The bug can be sure it is hovering, for instance,
when it senses no optical flow. When flying forwards at a steady speed,
the insect ‘knows’ that if optical flow decreases, its altitude must have
increased. When it comes in to land, a bug slows down safely as it approaches the ground by ensuring the flow rate stays steady. Fearing
plans to recreate this ability to sense optical flow by adding a fisheye
lens above a light-sensing chip that will feed optical flow data to the
machine's microchip brain.
If robotic insects do fly, Fearing believes they will quickly become
cheap and commonplace. ‘Something that weighs less than a tenth of a
gram will sell for less than a buck’, he says.
*bizarre – , '.
**unobtrusively – ), .
***zip – *) .
6. Answer the questions.
1. Whose experience in aerodynamic testing was used by Microsystems engineer Ronald Fearing?
2. Why is it interesting to make a mechanical insect?
3. What are the main problems with small insect-like aircraft?
4. How were these problems solved?
7. Read and analyze the first part of the text ‘On the End of a
Whirling Arm’ from English into Russian.
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TEXT IIIB (PART I)
ON THE END OF A WHIRLING ARM
The utility of wind tunnel is obvious today, but it was not the first
aerodynamic test device. Early experimenters realized that they needed
a machine to replace nature's capricious winds with a steady, controllable flow of air. They recognized, as Leonardo da Vinci and Isaac Newton had before them, that they could either move their test model
through the air at the required velocity or they could blow the air past a
stationary model. Both approaches were employed in the early days of
aeronautics.
First, relatively steady natural wind sources were searched out.
Models were mounted above windswept ridges and in the mouths of
blowing caves. Even here, the perversity of nature finally forced experimenters to turn to various mechanical schemes for moving their test
models through still air. the simplest and cheapest contrivance for moving models at high speeds was the whirling arm – a sort of aeronautical
centrifuge.
Benjamin Robins (1707–1751), a brilliant English mathematician,
was the first to employ a whirling arm. His first machine had an arm 4
feet long. Spun by a falling weight acting on a pulley and spindle arrangement, the arm tip reached velocities of only a few feet per second.
Robins mounted various blunt shapes – pyramids, oblong plates,
etc. – on the arm tip and spun them in different orientations. He concluded that ‘all the theories of resistance hitherto established are extremely defective.’ Different shapes, even though they presented the
same area to the airstream, did not always have the same resistance or
drag. The manifestly complex relationship between drag, model shape,
model orientation, and air velocity defied the simple theory propounded
earlier by Newton and made ground testing of aircraft all the more important to the infant science of flight.
8. Translate from Russian into English the sequel of the text ‘On
the End of a Whirling Arm’ using a dictionary and the useful vocabulary.
Airfoil, tip speed, heavier-than-air, square feet, triplane glider, flapping wings.
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TEXT IIIB (PART II)
?+ !<< " (1773–1857) < * =(=
() 7
, ' * *€
( , (= (= .  =(=)) 7
5 >
% 10–20 >
. 4
< + *, " *
*, , ), ' * ** )< . 4 1852 "
* *
*) * *=(
200 >
. " 1852 %( * > *, ' , 7 )< '
*) *
) *).
‚) " * < + +* * (=) +*, < ( * ' >>) ). ! " , ) < *€
( ** * , + ( *% . " : «D * < , *< *) ». !
, *
, ' * < *, * +
<( *€
( ') ). <) * <) , *, '
(%. 7 < ' ** (= )! @ .
9. Speak on the topics.
First aerodynamic testing devices.
Benjamin Robins.
George Cayley.
10. Fill in the gaps in the text ‘Aerodynamics’ with the words
from the box.
Heavier-than-air, Much number, temperature, forces, subsonic,
velocity, lift, density, shock waves, supersonic.
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Aerodynamics
Aerodynamics (shaping of objects that affect the flow of air, liquid
or gas) is a branch of fluid dynamics concerned with the study of forces
and gas flows. The solution of an aerodynamic problem normally involves calculating for various properties of the flow, such as
_________, pressure, __________, and ____________, as a function of
space and time. Understanding the flow pattern makes it possible to
calculate or approximate the _________ and moments acting on bodies
in the flow. This mathematical analysis and empirical approximation
form the scientific basis for ___________________ flight.
Aerodynamic problems can be classified in a number of ways.
The flow environment defines the first classification criterion. External aerodynamics is the study of flow around solid objects of
various shapes. Evaluating the __________ and drag on an airplane,
the ____________ that form in front of the nose of a rocket or the
flow of air over a hard drive head are examples of external aerodynamics. Internal aerodynamics is the study of flow through passages
in solid objects. For instance, internal aerodynamics encompasses
the study of the airflow through a jet engine or through an air conditioning pipe.
The ratio of the problem's characteristic flow speed to the speed
of sound comprises a second classification of aerodynamic problems. A problem is called ______________ if all the speeds in the
problem are less than the speed of sound, transonic if speeds both
below and above the speed of sound are present (normally when the
characteristic speed is approximately the speed of sound),
____________ when the characteristic flow speed is greater than the
speed of sound, and hypersonic when the flow speed is much greater
than the speed of sound. Aerodynamicists disagree over the precise
definition of hypersonic flow; minimum ________________ for hypersonic flow range from 3 to 12. Most aerodynamicists use numbers between 5 and 8.
The influence of viscosity in the flow dictates a third classification. Some problems involve only negligible viscous effects on the
solution, in which case viscosity can be considered to be nonexistent. The approximations to these problems are called inviscid flows.
Flows for which viscosity cannot be neglected are called viscous
flows.
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11. Read the text and tell about the conservation laws.
TEXT IIIC
CONSERVATION LAWS
Aerodynamic problems are solved using the conservation laws, or
equations derived from the conservation laws. In aerodynamics, three
conservation laws are used.
Conservation of mass: Matter is not created or destroyed. If a certain mass of fluid enters a volume, it must either exit the volume or increase the mass inside the volume.
Conservation of momentum: Also called Newton's second law of
motion.
Conservation of energy: Although it can be converted from one
form to another, the total energy in a given system remains constant.
All aerodynamic problems are therefore solved by the same set of
equations. However, they differ by the assumptions made in each problem. The equations become simpler as assumptions are made.
12. Students A, B and C read their texts and tell the partners what
the texts are about. Make up 5 questions to the text.
Student A
Subsonic Aerodynamics
In a subsonic aerodynamic problem, all of the flow speeds are less
than the speed of sound. This class of problems encompasses nearly all
internal aerodynamic problems, as well as external aerodynamics for
most aircraft, model aircraft, and automobiles.
In solving a subsonic problem, one decision to be made by the
aerodynamicist is whether or not to incorporate the effects of compressibility. Compressibility is a description of the amount of change of
density in the problem. When the effects of compressibility on the solution are small, the aerodynamicist may choose to assume that density is
constant. The problem is then an incompressible problem. When the
density is allowed to vary, the problem is called a compressible problem. In air, compressibility effects can be ignored when the Mach number in the flow does not exceed 0.3. Above 0.3, the problem should be
solved using compressible aerodynamics.
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Student B
Transonic Aerodynamics
Transonic aerodynamic problems are defined as problems in which
both supersonic and subsonic flow exist. Normally the term is reserved
for problems in which the characteristic Mach number is very close to
one.Transonic flows are characterized by shock waves and expansion
waves. A shock wave or expansion wave is a region of very large
changes in the flow properties. In fact, the properties change so quickly
they are nearly discontinuous across the waves.
Transonic problems are arguably the most difficult to solve. Flows
behave very differently at subsonic and supersonic speeds, therefore a
problem involving both types is more complex than one in which the
flow is either purely subsonic or purely supersonic.
Student C
Supersonic Aerodynamics
Supersonic aerodynamic problems are those involving flow speeds
greater than the speed of sound. Calculating the lift on the Concorde
during cruise can be an example of a supersonic aerodynamic problem.
Supersonic flow behaves very differently from subsonic flow. Fluids react to differences in pressure; pressure changes are how a fluid
is ‘told’ to respond to its environment. Therefore, since sound is in
fact an infinite small pressure difference propagating through a fluid,
the speed of sound in that fluid can be considered the fastest speed
that ‘information’ can travel in the flow. This difference most obviously manifests itself in the case of a fluid striking an object. In front
of that object, the fluid builds up a stagnation pressure as impact with
the object brings the moving fluid to rest. In Gas traveling at subsonic
speed, this pressure disturbance can propagate upstream, changing the
flow pattern ahead of the object and giving the impression that the
fluid ‘knows’ the object is there and is avoiding it. However, in a supersonic flow, the pressure disturbance cannot propagate upstream,
akin to the case of a man walking 10 km/h backwards in a train moving 50 km/h forwards. Thus, when the fluid finally does strike the object, it is forced to change its properties – temperature, density, pres34
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sure, and Mach number – in an extremely violent and irreversible
fashion called a shock wave. The presence of shock waves, along with
the compressibility effects of high-velocity (see Reynolds number)
fluids, is the central difference between supersonic and subsonic aerodynamics problems.
13. Read the text and give the title to it.
TEXT IIID
Automotive aerodynamics is the study of the aerodynamics of
road vehicles. The main concerns of automotive aerodynamics are reducing drag, reducing wind noise, and preventing undesired lift forces
at high speeds. For some classes of racing vehicles, it may also be important to produce desirable downwards aerodynamic forces to improve
traction and thus cornering abilities.
An aerodynamic automotive will integrate the wheel and lights in
its shape to have a small surface. It will be streamlined, for example it
does not have sharp edges crossing the wind stream above the windshield and will feature a sort of tail called a fastback. It will have a flat
and smooth floor to support the Venturi effect and produce desirable
downwards aerodynamic forces. The air rams into the engine bay, is
used (cooling, combustion, and for passengers), reaccelerated by a nozzle and then ejected under the floor.
Automotive aerodynamics differs from aircraft aerodynamics in
several ways. First, the characteristic shape of a road vehicle is bluff,
compared to an aircraft. Second, the vehicle operates very close to the
ground, rather than in free air. Third, the operating speeds are lower.
Fourth, the ground vehicle has fewer degrees of freedom than the aircraft, and its motion is less affected by aerodynamic forces.
Automotive aerodynamics is studied using both computer modelling and wind tunnel testing. For the most accurate results from a wind
tunnel test, the tunnel is sometimes equipped with a rolling road. This is
a movable floor for the working section, which moves at the same
speed as the air flow. This prevents a boundary layer forming on the
floor of the working section and affecting the results.
Total aerodynamic drag = Cd multiplied by the frontal area. The width
and height of curvy cars lead to gross overestimations of frontal area.
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14. Speak on the topic ‘My future specialism’ using information
from Units II and III.
SUPPLEMENTARY TEXTS
TEXT 1
HISTORY OF KITES
Kites have been around for thousands of years and they are a part of
many different cultures around the world. There is a lot of information
available on the web concerning the history of kites, so we will not duplicate that information here. We suggest that you use your favorite
search engine to find this information. (Search on the phrase ‘History of
Kites’). From an aerodynamics point of view, two of the most important users of kites were the Wright brothers. In 1899, as they were developing their theories for the control of an aircraft by using wing
warping, they built a small maneuverable kite to verify their ideas. Between 1900 and 1903 they would often fly their gliders as unmanned
kites at Kitty Hawk, North Carolina. These experiments led directly to
their successful 1903 aircraft.
Types of Kites
A wide variety of kite kits and kite accessories are available at department, hobby, and toy stores. You can even design and build your
own kites. This slide shows some of the more popular types of kites.
(The names for the various kites are not standardized - what I call a
diamond kite may be called a two-stick kite at another site, and my
‘Delta’ kite may be called a ‘bat’ somewhere else.) Once again, there
is a lot of information available on the web concerning kite design and
purchase. (Search on the phrase ‘Kite Design’ with your search engine).
Forces on a Kite
Each of the kites on this slide looks different than another kite, but
the forces acting on all the kites is exactly the same. In fact, with the
exception of thrust, the forces acting on a kite are also the same forces
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which act on an airliner or a fighter plane. Like an aircraft, kites are
heavier than air and rely on aerodynamic forces to fly. Gas balloons and
bubbles, on the other hand, are lighter than air and rely on buoyancy
forces to fly. Like an aircraft, kites have a solid frame normally made of
wood or plastic, and this frame is covered by a paper, plastic, or cloth
‘skin’ to generate the lift necessary to overcome the kite's weight. A
kite must be made as light as possible for good performance, yet be
strong enough to withstand high winds. Determining the forces on a
kite can be difficult, so we have prepared a kite simulator to let you
study these forces. You can use KiteModeler to design your own kites.
You can then build a kite based on your design and compare the results
with the computer program.
Flying
While the forces on all kites are the same, each kite flies a little differently. Some kites are highly maneuverable and some kites are very
stable. There are kites with multiple control lines that can perform
stunts, while other kites can be flown to high altitudes. We can use
math techniques that you learn in school to determine the altitude of a
kite graphically. With a little more knowledge of mathematics, you can
actually calculate the altitude at which the kite is flying.
Regardless of the type of kite, the flyer must always fly safely for
the protection of others, to protect property, and to insure that the kite
can be flown again.
Have Fun!
TEXT 2
THE ROLE OF THE WIND TUNNEL
FOR AUTOMOBILE DESIGN
Racing teams have been devoting more and more time to the development of the aerodynamics of their cars. They have done so (and they
still do it) with track and wind tunnel testing. Track testing is widely
recognized for being too expensive and dependent on many casual
events. The advantage, of course, is that the car is tested in its actual
configuration in a real world situation.
The wind tunnel is the technical answer of the aerodynamic engineers. The wind tunnels are nowdays very sophisticated, and allow a
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wide range of studies, including modeling of the car in compete configuration, ground plane simulation, etc.
Tunnels with Moving Ground
One major advancement has been promoted by the use of moving
ground planes (previously not used in other branches of aerodynamics).
When in the 1970s it was discovered that downforce can be created by
means of ground effect, it became essential to simulate the effect of the
track on the car performance (on underbody, side pods, exposed
wheels, wings).
In a wind tunnel with a stationary ground plane a boundary layer
build up under the car, and can interfere with the boundary layer of the
lower components. Such a case cannot give the correct answer.
There are several ways to remove the ground boundary layer, but
the most effective method is to use a moving belt, with the wheels rotating with the belt. The simulation of rotating wheels could not be
more effective. The importance of the exposed wheels in Indy and
Formula 1 has been widely recognised, and neglecting this effect may
have a large effect on the overall performances.
Racing for Land Speed Records
Running fast is an old occupation, and sometimes a risky one. One
of the most fascinating pursuits is the land speed record by vehicles that
now resemble rockets on wheels, rather than cars. This record has now
surpassed Mach 1 (i.e. the sonic speed).
We report here a few basic aerodynamic considerations. Torda and
Morel (1971) pointed out that at high subsonic to low supersonic speed
the vehicle generates shock waves that are reflected from the ground.
These shock reflections cause a pressure build-up below the vehicle
that have an effect dependent on the speed: at subsonic speed shock
wave interference produces additional downforce; at transonic speeds
the problem is further complicated by the vehicle clearance; at supersonic speeds the interaction may result in reversal of direction of the lift
force.
Since these vehicles are rockets, transonic drag rise can be reduced
by increasing the finess ratio. Nose design is also critical. For example,
a von Karman ogive is known for having minimum wave drag at transonic speeds.
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1. Write an essay of the text.
2. State the main idea of each passage of the text.
TEXT 3
ADVANCED WIND TUNNELS
By the late 1940s, aircraft were becoming increasingly expensive to
develop and the costs of designing an unsuccessful aircraft were also
growing. As a result, aircraft designers sought to model mathematically
and to simulate as much of an aircraft's performance as they could
without having to build the airplane itself. This, combined with the increasing speed of aircraft, created a great demand for new and more
sophisticated wind tunnels. In particular, supersonic wind tunnels were
in great demand during the post-World War II period.
Supersonic tunnels work in a way that seems contrary to logic. As
the throat of a wind tunnel constricts, one expects the velocity of the air
rushing through it to increase. It therefore seems logical that a model
should be placed at the constricted part of such a tunnel in order to take
advantage of the high-velocity airflow. But the reality is that as the airspeed approaches Mach 1, the air compresses and also heats up as it
piles up at this constricted part. Only when the air gets past this constriction does it actually move faster than Mach 1, as the energy stored
in both the compression and in the heat of the air converts to kinetic
energy. Put another way, all of this stored energy has to convert to another form and this form consists of large amounts of air moving very
fast through the wind tunnel. This is how a supersonic wind tunnel
works, with the model placed in a section of the tunnel where the throat
actually expands.
Numerous small supersonic tunnels were in use by the 1940s, but
aircraft designers wanted bigger tunnels for their models. By 1948, the
National Advisory Committee for Aeronautics (NACA) began operating a 4-foot by 4-foot (1.2-meter by 1.2-meter) supersonic tunnel at
Langley, Virginia, on the Atlantic coast. Another NACA facility,
Ames, located in California, also began operating a slightly larger and
more sophisticated supersonic wind tunnel around this time. Because
even the slightest imperfection in the tunnel walls would cause the air
to pile up and create shock waves, supersonic tunnels require very
smooth interior surfaces.
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Many of the same principles used in supersonic tunnels were also
used in hypersonic tunnels to explore speeds greater than Mach 5. But
several other problems occur in these types of tunnels. One is that the
power requirements to accelerate the air are tremendous, so most hypersonic wind tunnels do not operate continuously but store up tremendous amounts of compressed air and release it in a brief burst. This is
why many hypersonic tunnels have large storage tanks for holding
compressed air. Another problem is that as the air moves out of the
constriction chamber it cools as its heat energy is converted to kinetic
energy. In a hypersonic tunnel, the air can cool so much that it actually
liquefies. This is not simply a case of the moisture in the air condensing. The air itself turns to liquid. In order to prevent this from happening, the air is deliberately heated as it is compressed in a ‘settling
chamber’ before being released. In a Mach 10 wind tunnel, for example, air is heated to 3,000 degrees Fahrenheit (1649 degrees Celsius) so
that it does not liquefy when it is released.
Another method of obtaining high velocities is to fire models out of
the barrel of a gun inside of a supersonic wind tunnel. In this way, the
speed of the model combines with the speed of the moving air to produce a greater simulated velocity. The models are photographed as they
streak by. Because the air itself is not moving at hypersonic velocities,
this does not create any of the problems associated with liquefication of
the air, but the models are destroyed in the process of testing them.
A major development during this period was the slotted wall wind
tunnel. A big problem with wind tunnels is that the air flowing off a
model can hit the tunnel wall, and flow back toward the model and/or
interfere with the test measurements. Ray Wright, a researcher at Langley, proposed putting slots in the walls of a wind tunnel so that the air
could move more freely around the model. Another group of aerodynamicists, led by John Stack, applied this technique to the transonic
wind tunnel, which instantly solved many of the problems that they
were encountering as air speeds approached Mach 1. As a result, in
1951 Stack and his group were awarded the Collier Trophy, which
honors the most important advance in aeronautics for the year.
In addition to being used to design new planes, wind tunnels are
also used to solve many other problems that affect existing aircraft once
they become operational. One problem that plagues aircraft that fly in
cold temperatures is ice. Ice builds up on propellers and on aircraft surfaces, particularly wings, and can affect performance in dangerous
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ways. Ice buildup on wings is particularly bad, for it can destroy lift and
cause the plane to lose altitude and crash, or can block control surfaces
and make it impossible for the pilot to fly the plane.
Icing tunnels were developed beginning in the 1940s to study this
problem. They are similar to conventional subsonic wind tunnels but
are equipped with refrigeration systems that can cool the air to well below freezing. Water droplets are then sprayed into the airflow so that
they can freeze on aircraft surfaces. Engineers monitor the buildup of
ice on the aircraft. Anti-icing devices such as electric heaters or pipes
containing a heated liquid such as alcohol are installed in the parts of
aircraft that generate the most ice. When ice begins to build up on a
model in the icing tunnel, the heaters are turned on and researchers then
study how effective they are at stopping the buildup of ice.
There are many other different kinds of wind tunnels. There are
‘spin tunnels’ that test how aircraft behave when they fly out of control
and start spinning, a situation that is commonly referred to by pilots as
‘departure from controlled flight.’ These tunnels test whether the pilot
can recover in this situation or needs to parachute out of the airplane.
There are ‘free flight’ tunnels where models are actually ‘flown’ by
remote control by a pilot sitting in a control booth and sending signals
to the model through a wire tether. There are also blast-furnace-type
tunnels for testing how spacecraft and missiles act in high temperature
airflows such as they encounter when reentering the Earth's atmosphere. And there are magnetic tunnels, where the model is held stable
inside the tunnel by powerful magnetic fields so that more accurate
measurements can be taken.
Before the 1950s, most of the wind tunnels operated in the United
States were run by the NACA. But in 1946, a study of American wind
tunnels resulted in a recommendation that industry and universities play
a greater role in operating wind tunnels. This led to the National Unitary Wind Tunnel Plan Act of 1949. The Act established new supersonic wind tunnels at the three major NACA facilities, but also pushed
for the creation of supersonic wind tunnels at universities. The development of a university wind-tunnel base was important both to serve as
a check on NACA research and to train new aeronautical engineers.
The NACA tunnels were also directed to perform more industry research, symbolizing a decreased emphasis on government-sponsored
wind tunnel research.
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For years wind tunnels represented a less expensive way of testing
an airplane than building the full-size vehicle. But wind tunnel research
was and still is expensive. Testing a new airplane design in a wind tunnel costs millions of dollars. As a result, aircraft designers have increasingly shifted to computers and a method called computational fluid dynamics (air, after all, is a fluid, like water), which simulates airflow
entirely within a computer. Computing power is relatively cheap, and
computer models can be changed much more easily than physical models made of plastic, metal, and wood.
Today, wind tunnels are used less and less and the giant wind tunnels that dominated so many aeronautical research centers starting in
the 1930s and 1940s are now often called upon only to serve as backups
to the computer simulations, to prove that their predictions are sound.
In several important cases, however, aircraft designers have had to use
wind tunnels to test their designs after computer simulations have
proven inadequate. For example, the Pegasus XL air-launched rocket
suffered an in-flight aerodynamic failure that was not predicted by a
computer-generated aerodynamic model. But in a matter of years, most
of the large NACA-built wind tunnels may become totally silent, their
roar replaced by the hum of a supercomputer.
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'&*'+ /*:;<:$<= * '>:
Macmillan English Dictionary for Advanced Learners: International Student Edition. Macmillan Education, London, 2006.
Longman Dictionary of Scientific Usage. The Reprint Edition. Moscow,
1987.
Hornby F.S. Oxford Advanced Learner's Dictionary, 7th ed. Oxford: Oxford University Press, 2006.
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* .
7 -
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), 1987.
.. $ *: &' ), * * - . 2- .,
*'. *. .: $. 4, 2006.
!"# .$. * - : ˆ- *. .: #?, 2003.
www.en.wikipedia.org/wiki/Aerodynamics
www.grc.nasa.gov
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CONTENTS
@ .......................................................................................... 3
Unit I ....................................................................................................... 4
Text IA. Wind Tunnels ............................................................................ 4
Text IB. A Few Types of Modern Wind Tunnels .................................... 9
Text IC. How Wind Tunnels Work ......................................................... 12
Text ID. Computer Control and Data Acquisition ................................... 14
Unit II ..................................................................................................... 16
Text IIA. Ballistics .................................................................................. 17
Text IIB. Drag Resistance Modelling and Measuring ............................. 21
Text IIC. More Advanced Drag Models .................................................. 23
Text IID. Forensic Ballistics ................................................................... 25
Unit III .................................................................................................... 26
Text IIIA (part I). Moth in a Wind Tunnel .............................................. 26
Text IIIA (part II). Float Like a Robot Butterfly ..................................... 27
Text IIIB (part I). On the End of a Whirling Arm ................................... 30
Text IIIB (part II). Sir George Cayley ..................................................... 31
Text IIIC Conservation Laws .................................................................. 33
Text IIID .................................................................................................. 35
Supplementary Texts ............................................................................ 36
Text 1 ............................................................................................... 36
Text 2 ............................................................................................... 37
Text 3 ............................................................................................... 39
?* ................................................................ 43
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