The Physics of Flight T here are four basic forces at work when an aircraft is in flight: Lift Thrust Gravity Drag Of these four forces, only gravity is constant (unchanging), the remaining three forces can be altered or affected by the pilot.When an aircraft is flying level at a constant speed, all four of these forces are in balance or equilibrium. Lift Lift is achieved through the cross-sectional shape (airfoil design) of the wing. As the wing moves through the air, the airfoil's shape causes the air moving over the wing to travel faster than the air moving under the wing. The slower airflow beneath the wing generates more pressure, while the faster airflow above generates less. This difference in pressure results in lift. Lift will vary dynamically depending on the speed an aircraft is traveling at.
T here are four basic forces at work when an aircraft is in
flight:
Lift
Thrust
Gravity
Drag
Of these four forces, only gravity is constant (unchanging),
the remaining three forces can be altered or affected by the
pilot.When an aircraft is flying level at a constant speed, all
four of these forces are in balance or equilibrium.
Lift Lift is achieved through the cross-sectional shape (airfoil
design) of the wing. As the wing moves through the air, the
airfoil's shape causes the air movingoverthe wing to travel faster
than the air movingunderthe wing. The slower airflow beneath the
wing generates more pressure, while the faster airflow above
generates less. This difference in pressure results inlift .
Liftwill vary dynamically depending on the speed an aircraft is
traveling at.
2. Angle of Attack
The angle at which the airfoil meets the airflow also greatly
affects the amount of lift generated. This angle is known as
theAngle of Attack(AoA). It is commonly thought that AoA is the
angle of the aircraft relative to the ground - this isincorrect .
The AoA is the angle of thewingrelative toairflow , which can be a
very different angle, depending on the attitude of the
aircraft.
For example, if you are flying at 300 mph on a level course,
your AoA is normally close to zero (actually about 5) since your
wing is pointed in the same direction as your mass is traveling.
Picture an aircraft on a landing glide. The pilot maintains a
nose-up attitude to help slow the aircraft, while the actual
direction the aircraft is traveling is in a slope down toward the
runway.
Thus AoA is the angle between where the wing is pointed and the
glide slope the plane is on.
Why is AoA important?Angle of Attack is critical to all planes
because the AoA greatly effects the flow of air across the wings.
Since planes have different wings, planes also have different AoA
limits that they must fly within. If you exceed your maximum AoA,
you interrupt the flow of air over one or both wings and you induce
a stall. This is NOT just at low speeds. The Focke-Wulf Fw 190
series were well known to be susceptible to high speed stalls if
the AoA was exceeded. Despite flying at 300 mph, you can pull the
aircraft into a turn which interrupts airflow and will quickly
cause a dangerous stall.
3. Thrust When the propeller on the aircraft engine rotates, it
pulls in air from in front of the aircraft and pushes it back
towards the tail. The force generated by this isthrust . Thrust
gives the aircraft forward momentum, and in turn, creates lift on
the lifting surfaces (mainly the wings). Generally, the greater the
thrust, the greater the airspeed. Thrust is controlled by raising
or lowering the revolutions-per-minute (rpm) of the engine by using
the throttle. Drag As an aircraft is propelled forward by thrust,
an undesirable effect is also created: resistance. When the
aircraft travels through the air, its frontal area pushes against
the air in front of it, and air flowing over the aircraft causes
friction. This is known asdrag . For any given aircraft, drag can
be increased and decreased depending on the conditions. For
example, a more streamlined aircraft will reduce drag, while other
factors may increase drag. These include increased AoA, lowering
flaps and/or landing gear, and carrying external stores, such as
bombs and rockets Altitude Air density varies with altitude; at
lower altitudes, it is thicker, while higher up, the air is
thinner. The density of the air directly affects drag and thrust.
For example, at lower altitudes the thicker air increases thrust by
supplying the propeller with more mass to move. However, that mass
also increases drag. The lesser amount of oxygen associated with
the thinner atmosphere of higher altitudes reduces the power output
of the engine, thereby reducing thrust. However one benefit of
thinner atmosphere is that it creates less drag. G-Forces Gravity
effects all objects within the Earth's gravitational field -G-force
. When a person is standing still on the earth, they are
experiencingOne G(one times the force of gravity). When a pilot in
an airplane changes its orientation rapidly (tight turns, loops,
etc.), the aircraft will undergo additional G-forces. These may
bepositiveornegativeG-forces.
4.
Positive G-Forces
Positive G's are generated when an aircraft pitches upwards
(the nose pulls up). For example, when the aircraft turns quickly
or pulls up sharply. A World War II fighter may be capable of
generating 7 G's or more. The physical effect of Positive G's on a
pilot is a possibleblackout , usually preceded bygreyout(a less
severe effect).This is caused by the increased effort the heart
must generate to counter the G-forces and still supply the brain
with sufficient blood. When the G-forces are too great, the pilot
will slowly lose vision due to this lack of blood supply. When
prolonged, the blackout can cause a loss of consciousness.
Negative G-Forces
Negative G's are generated when an aircraft pitches downwards
(the nose goes down). For example, a sharp dive or similar maneuver
thatunloadsthe aircraft of the force of gravity. Excessive Negative
G's will cause a pilot tored out .This is the effect of excessive
blood being pumped to the pilot's brain, causing distorted vision.
Red out is usually preceded bypink out . This signals the onset of
excessive negative G's.
Compressibility
When an aircraft approaches the speed of sound, the airflow
over the wings of the aircraft can actually exceed the speed of
sound. This transonic airflow creates a shockwave and a barrier
that disrupts the flow of air over the control surfaces. This
causes a dramatic loss in control efficiency and is known
ascompression . Compression usually occurs between Mach 0.7 to 0.9.
Mach 1.0 is the speed of sound. The actual speed of sound varies at
different altitudes, depending on air density.
The practical effect of compression on an aircraft is a lack of
control. The ailerons and/or elevators seem to lock up, and moving
the joystick has little effect on the aircraft. If you experience
compression in a dive, you may not be able to recover.
For a World War II aircraft to attain these speeds, a
high-speed dive would be required. To counter compression, speed
must be reduced. Increasing drag and decreasing thrust will slow
the plane. Once the aircraft slows, control will be regained.
Note that some aircraft compress at slower speeds, such as the
A6M Zero and Messerschmitt Bf 109. These aircraft are lighter than
most others, and sustained high speeds in level fight can begin to
compress their control surfaces.
5. Aircraft Control Surfaces
An aircraft maintains control in flight with its control
surfaces (see the illustration below with its color coded control
surfaces). These are:
TheAileronsthat controlRoll
TheRudderthat controlsYaw
TheElevatorsthat controlPitch , and to a somewhat lesser
degree,
The Flaps which provideextra Lift and Drag
We also mention theLanding Gearwhich changes the airflow around
the aircraft when it is lowered.
Each of these primary control surfaces controls one set of
primary aircraft movements (roll, pitch, or yaw). Coordinated use
of these control surfaces allows you to perform complex
maneuvers.
6. Primary Control Surface Function Ailerons (Roll) TheAilerons
, located on the outer part of the trailing edge of the wings,
control therollor bank of the airplane. The two ailerons (one on
each wing), work in opposite directions to each other. When the
left one is raised, the right one is lowered. The roll/bank of the
aircraft is controlled by the side to side movement of the joystick
Elevator (Pitch) The pitch , or the up and down movement of the
aircraft is controlled by theElevator . It is located on the
trailing edge of the horizontal tail assembly and is controlled by
the forward and backward movement of the joystick. Pulling the
joystick back will move the elevator up, causing the nose of the
aircraft to point up. Similarly, pushing the joystick forward will
move the elevator down and pitch the nose down.
7. Control Surface Function
Rudder (Yaw)
On the trailing edge of the vertical stabilizer is theRudder .
This controls theyawor the left/right sliding movements of the
aircraft. On a real aircraft, this is controlled by the foot
pedals. War birds supports the use of rudder pedals, but for those
who don't have pedals, the rudder may be manipulated with the
following keys:Awill move the rudder left, causing left yaw
forces,Dwill move the rudder right initiating right yaw force,
andSwill center the rudder
Flaps The Flaps are located on the underside of the trailing edge
of the wings, inboard of the ailerons. This set of control
surfaces, when lowered, changes the cross sectional shape (airfoil)
of the wing. By lowering the flaps, more surface area on the wing
is created, thus increasing lift. This enables you to lower
yourstallspeed and increase yourAngle-of-Attack(AoA). However, the
flaps also increase the drag on the aircraft, which reduces speed.
Flaps are most commonly used for take off and landing.
8. Un conventional Control surfaces FLAPERON:is a type of
control surface that combines aspects of both flaps and ailerons.
In addition to controlling the roll or bank of an aircraft like
conventional ailerons, both flaperons can be lowered together to
function much the same as a dedicated set of flaps would. Both
ailerons could also be raised, which would give spoilerons. The
pilot has separate controls for ailerons and flaps. A mixer is used
to combine the separate pilot input into this single set of control
surfaces called flaperons. The use of flaperons instead of separate
ailerons and flaps can reduce the weight of an aircraft. The
complexity is transferred from having a double set of control
surfaces (flaps and ailerons) to the mixer. Certain aircraft use
different kinds of surfaces, such as a V-tail/ruddervator,
flaperons, or elevons, to avoid pilot confusion the aircraft will
still normally be designed so that the yoke or stick controls pitch
and roll in the conventional way, as will the rudder pedals for
yaw. V-TAIL/RUDDERVATOR: In aircraft, aV-tail(sometimes called
aButterfly tail ) is an unconventional arrangement of the tail
control surfaces that replaces the traditional fin and horizontal
surfaces with two surfaces set in a V-shaped configuration when
viewed from the front or rear of the aircraft. The rear of each
surface is hinged, and these movable sections, sometimes called
ruddervators, combine the tasks of the elevators and rudder.
Advantages:With fewer surfaces than a conventional three-aerofoil
tail or a T-tail, the V-tail is lighter, has less wetted surface
area, and thus produces less drag (disputed). In modern day light
jet general aviation aircraft such as unmanned aerial drone Global
Hawk .the power plant is often placed outside the aircraft to
protect the passengers and make certification easier. In such cases
V-tails are used to avoid placing the vertical stabilizer in the
exhaust of the engine Disadvantages:Combining the pitch and yaw
controls is difficult and requires a more complex control system.
The V-tail arrangement also places greater stress on the rear
fuselage when pitching and yawing ELEVONS:On an aeroplane, elevons
are a single control surface which combines the function of the
elevators and ailerons in one. They are usually seen on delta-wing
aircraft
9. In addition to the primary flight controls for roll, pitch,
and yaw, there are often secondary controls available to give the
pilot finer control over flight or to ease the workload. The most
commonly-available control is a wheel or other device to control. A
few of the most common Secondary control Surfaces are as follows
SLATS: Slats are aerodynamic surfaces on the leading edge of
the wings of fixed-wing aircraft which, when deployed, allow the
wing to operate at a higher angle of attack. A higher coefficient
of lift is produced as a product of angle of attack and speed, so
by deploying slats an aircraft can fly more slowly or take off and
land in a shorter distance. They are usually used while landing or
performing maneuvers which take the aircraft close to the stall,
but are usually retracted in normal flight to minimize drag.
Secondary control Surfaces SPOILER: (sometimes called alift dumper
) is a device intended to reduce lift in an aircraft. Spoilers are
plates on the top surface of a wing which can be extended upward
into the airflow andspoilit. By doing so, the spoiler creates a
carefully controlled stall over the portion of the wing behind it,
greatly reducing the lift of that wing section. Spoilers differ
from airbrakes in that airbrakes are designed to increase drag
while making little change to lift, while spoilers greatly reduce
lift while making only a moderate increase in drag. Spoilers are
sometimes used when descending from cruise altitudes to assist the
aircraft in descending to lower altitudes without picking up speed.
the real gain comes as the spoilers cause a dramatic loss of lift
and hence the weight of the aircraft is transferred from the wings
to the undercarriage, allowing the wheels to be mechanically braked
with much less chance of skidding. Reverse thrust is also often
further used to help slow the aircraft on landing. AIR
BRAKES:Inaeronautics,air brakesare a type of flight control used on
an aircraft to reduce speed during landing. Air brakes differ from
spoilers in that air brakes are designed to increase drag while
making little change to lift, whereas spoilers greatly reduce the
lift-to-drag ratio and a higher angle of attack required to
maintain lift, resulting in a higher stall speed.
10. Secondary control Surfaces Elevator trim:The most
commonly-available control is a wheel or other device to control
elevator trim, so that the pilot does not have to maintain constant
backward or forward pressure to hold a specific pitch attitude
(other types of trim, for rudder and ailerons, are common on larger
aircraft but may also appear on smaller ones) Trim tabs are small
surfaces connected to the trailing edge of a larger control surface
on aircraft. The angle of the tab relative to the larger surface
can be adjusted to null out hydro- or aero-dynamic forces and
stabilize the boat or aircraft in a particular desired attitude
without the need for the pilot to constantly apply a control force.
Many airplanes also have rudder and/or aileron trim systems. When a
trim tab is employed, it is moved into the slipstream opposite to
the control surface's desired deflection.
11. Major Systems/Parts of Aircraft Fuselage: The fuselage is
that portion of the aircraft that usually contains the crew and
payload, either passengers, cargo, or weapons. Most fuselages are
long, cylindrical tubes or sometimes rectangular box shapes. All of
the other major components of the aircraft are attached to the
fuselage.Empennageis another term sometimes used to refer to the
aft portion of the fuselage plus the horizontal and vertical
tails.Landing Gear : The Under Carriage/ landing gear is used
during takeoff, landing, and to taxi on the ground. Most planes
today use what is called a tricycle landing gear arrangement. This
system has two large main gear units located near the middle of the
plane and a single smaller nose gear unit near the nose of the
aircraft.They are eitherretractableorfixed .
12. The wing is the most important part of an aircraft since it
produces the lift that allows a plane to fly. The wing is made up
of two halves, left and right, when viewed from behind. These
halves are connected to each other by means of the fuselage. A
wingproduces liftbecause of its special shape, a shape called an
airfoil. If we were to cut through a wing and look at its
cross-section, as illustrated below, we would see that a
traditional airfoil has a rounded leading edge and a sharp trailing
edge.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 theleading edge ; the back of the wing
(at the top) is called thetrailing edge . The distance from the
leading edge to the trailing edge is called thechord , denoted by
the symbolc . The ends of the wing are called thewing tips , and
the distance from one wing tip to the other is called thespan ,
given the symbols . The shape of the wing, when viewed from above
looking down onto the wing, is called aplan form . In this figure,
the plan form is a rectangle. For a rectangular wing, the chord
length at every location along the span is the same. For most other
plan form ,the chord length varies along the span. Thewing area,
A,is the projected area of the plan form 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. Thetotal surface
areaincludes both upper and lower surfaces. The wing area is a
projected area and is almost half of the total surface area. Aspect
ratiois a measure of how long and slender a wing is from tip to
tip. TheAspect Ratioof a wing is defined to be the square of the
span divided by the wing area and is given the symbolAR . 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 / cHigh aspect ratio wings have long spans
(like high performance gliders), while low aspect ratio wings have
either short spans (like the F-16 fighter) 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. wing
Continue
13. Engine :The other key component that makes an airplane go
is its engine, or engines. Aircraft use several different kinds of
engines, but they can all be classified in two major categories.
Early aircraft from the Wright Flyer until World War II used
propeller-driven piston engines, and these are still common today
on light general aviation planes. But most modern aircraft now use
some form of a jet engine. Many aircraft house the engine(s) within
the fuselage itself. Most larger planes, however, have their
engines mounted in separate pods hanging below the wing or
sometimes attached to the fuselage. These pods are callednacelles
.PROPULSION The key to making a jet engine work is the compression
of the incoming air. If uncompressed, the air-fuel mixture won't
burn and the engine can't generate any thrust. Most members of the
jet family employ a section of compressors, consisting of rotating
blades, that slow the incoming air to create a high pressure. This
compressed air is then forced into a combustion section where it is
mixed with fuel and burned. As the high-pressure gases are
exhausted, they are passed through a turbine section consisting of
more rotating blades. In this region, the exhausting gases turn the
turbine blades which are connected by a shaft to the compressor
blades at the front of the engine. Thus, the exhaust turns the
turbines which turn the compressors to bring in more air and keep
the engine going. The combustion gases then continue to expand out
through the nozzle creating a forward thrust. The above explanation
describes a simple turbojet, as illustrated Here Diagram of an
axial-flow turbojet The term "jet engine" is often used as a
generic name for a variety of engines, including the turbojet,
turbofan, turboprop, and ramjet. These engines all operate by the
same basic principles, but each has its own distinct advantages and
disadvantages. All jet engines operate by forcing incoming air into
a tube where the air is compressed, mixed with fuel, burned, and
exhausted at high speed to generate thrust.
14. The turbojet (and the turbofan) can also be fitted with
anafterburner . An afterburner is simply a long tube placed in
between the turbine and the nozzle in which additional fuel is
added and burned to provide a significant boost in thrust. However,
afterburners greatly increase fuel consumption, so aircraft can
only use them for brief periods. Turbofan: A further variation on
the turbojet is the turbofan. Although most components remain the
same, the turbofan introduces a fan section in front of the
compressors. The fan, another rotating series of blades, is also
driven by the turbine, but its primary purpose is to force a large
volume of air through outer ducts that go around the engine core.
Although this "bypassed" air flow travels at much lower speeds, the
large mass of air that is accelerated by the fan produces a
significant thrust (in addition to that created by the turbojet
core) without burning any additional fuel. Thus, the turbofan is
much more fuel efficient than the turbojet. In addition, the
low-speed air helps to cushion the noise of the jet core making the
engine much quieter. Turbofans are typically broken into one of two
categories--low-bypass ratio and high-bypass ratio--as
illustrated.The bypass ratio refers to the ratio of incoming air
that passes through the fan ducts compared to the incoming air
passing through the jet core.In a low-bypass turbofan, only a small
amount of air passes through the fan ducts and the fan is of very
small diameter. The fan in a high-bypass turbofan is much larger to
force a large volume of air through the ducts. The low-bypass
turbofan is more compact, but the high-bypass turbofan can produce
much greater thrust, is more fuel efficient, and is much
quieter.Turboprop: A concept similar to the turbofan is the
turboprop. However, instead of the turbine driving a ducted fan, it
drives a completely external propeller. Turboprops are commonly
used on commuter aircraft and long-range planes that require great
endurance. The turboprop is attractive in these applications
because of its high fuel efficiency, even greater than the
turbofan. However, the noise and vibration produced by the
propeller is a significant drawback, and the turboprop is limited
to subsonic flight only. In a typical turboprop, the jet core
produces about 15% of the thrust while the propeller generates the
remaining 85%.
15. Ramjet: Another noteworthy variation on the turbojet is the
ramjet. The idea behind this type of engine is to remove all the
rotary components of the engine (i.e. fans, compressors, and
turbines) and allow the motion of the engine itself to compress
incoming air for combustion. However, the price of this simplicity
is that the ramjet can only produce thrust when it is already in
motion. Instead of using a compressor to draw in air and compress
it for combustion, the ramjet relies on the motion of the aircraft
to ram air into the engine at high enough speed that it is already
sufficiently compressed for combustion to occur. Since ramjets
typically cannot function until reaching about 300 mph (485 km/h)
at sea level, they have been rarely used on manned aircraft.
However, the ramjet is more fuel efficient than turbojets or
turbofans starting at about Mach 3 making them very attractive for
use on missiles. Such missiles are typically launched using rocket
motors that accelerate the vehicle to high-subsonic or
low-supersonic speeds where the ramjet is engaged. CONCLUSION :(
Interactive) Classification of Aircraft ,Discuss What are the
control surfaces used for Take off and Landing of an Aircraft ?
Sequence of operation ?Discuss
16. GLOBAL NAVIGATION SYSTEM
Global Navigation Satellite System( GNSS ) is the standard
generic term forsatellitenavigation systems that provide autonomous
geo-spatial positioning with global coverage. early predecessors
were the ground based DECCA, LORAN and Omega systems, which used
terrestrial longwave radio transmitters instead of satellites.
These positioning systems broadcast a radio pulse from a known
"master" location, followed by repeated pulses from a number of
"slave" stations. The delay between the reception and sending of
the signal at the slaves was carefully controlled, allowing the
receivers to compare the delay between reception and the delay
between sending. From this the distance to each of the slaves could
be determined, providing a fix.
Satellite navigation systemsallows small electronic receivers
to determine their location (longitude, latitude, and altitude) to
within a few meters using time signals transmitted along a
line-of-sight by radio from satellites. Receivers on the ground
with a fixed position can also be used to calculate the precise
time as a reference for scientific experiments. The first satellite
navigation system wasTransit,a system deployed by the US military
in the 1960s. Transit's operation was based on the Doppler effect:
the satellites traveled on well-known paths and broadcast their
signals on a well known frequency. The received frequency will
differ slightly from the broadcast frequency because of the
movement of the satellite with respect to the receiver. By
monitoring this frequency shift over a short time interval, the
receiver can determine its location to one side or the other of the
satellite, and several such measurements combined with a precise
knowledge of the satellite's orbit can fix a particular
position.
GNSS classification
GNSS that provide enhanced accuracy and integrity monitoring
usable for civil navigation are classified as follows:
GNSS-1is the first generation system and is the combination of
existing satellite navigation systems (GPS and GLONASS),
withSatellite Based Augmentation Systems(SBAS) orGround Based
Augmentation Systems(GBAS). In the United States, the satellite
based component is theWide Area Augmentation System(WAAS), in
Europe it is theEuropean Geostationary Navigation Overlay
Service(EGNOS), and in Japan it is theMulti-Functional Satellite
Augmentation System(MSAS). Ground based augmentation is provided by
systems like theLocal Area Augmentation System(LAAS).
GNSS-2is the second generation of systems that independently
provides a full civilian satellite navigation system, exemplified
by the European Galileo positioning system. These systems will
provide the accuracy and integrity monitoring necessary for civil
navigation. This system consists of L1 and L2 frequencies for civil
use and L5 for system integrity. Development is also in progress to
provide GPS with civil use L2 and L5 frequencies, making it a
GNSS-2 system.
17. LAAS/GBAS :Local Area Augmentation System is the ICAO
definition ground based augmentation for Satellite Navigation.
Ground Based Augmentation System is the European application of
LAAS. SBAS:SBAS is a generic term for GPS and GLONASS augmentations
such as WAAS, EGNOS and MSAS, which use geostationary satellites to
broadcast information to users over a large Geographical service.
SBAS uses the transmission of a GPS look-alike signal from the SBAS
geostationary satellite to further augment the GPS system
performance. WAAS :WAAS consists of two basic elements. The first
is a network of differential ground-stations that receive the GPS
signals and calculate differential correction signals. 35 ground
stations are required to cover the USA. These differential
corrections are then transmitted to the second element of the
system, which are WAAS transponders on a number of Inmarsat
geostationary communications satellites. The differential signals
are then transmitted from the communication satellites to the
aircraft. In addition, the communication satellites also transmit
integrity information about the performance of the GPS satellites
and a signal similar to a GPS satellite. This GPS type signal is
used for navigation and gives the appearance of an additional GPS
satellite being present.This situation highlights the importance of
the GNSS receiver in the aircraft being able to detect faulty
satellites and discard them from the position calculation .
MSAS:Japan is implementing the Multi Satellite-based Augmentation
System (MSASJapanese Definition) that will provide correction to
GPS only. The SBAS system planned by Japan. Differential Global
Positioning System(DGPS) is an enhancement to GPS that uses a
network of fixed, ground-based reference stations to broadcast the
difference between the positions indicated by the satellite systems
and the known fixed positions. These stations broadcast the
difference between the measured satellite pseudo ranges and actual
(internally computed) pseudo ranges, and receiver stations may
correct their pseudo ranges by the same amount. Correction signal
is typically broadcasted with in-build UHF band radio modem
As of 2009 the United States NAVSTAR Global Positioning System
(GPS) is the only fully operational GNSS. The Russian GLONASS is a
GNSS in the process of being restored to full operation. China has
indicated it will expand its regional Beidou navigation system into
the global COMPASS navigation system by 2015. The European Union's
Galileo positioning system is a GNSS in initial deployment phase,
scheduled to be operational in 2013.
GlobalSatellite Based Augmentation Systems(SBAS) such as
Omnistar andStarFire.
Regional SBAS including WAAS(US), EGNOS (EU), MSAS (Japan) and
GAGAN (India).
Regional Satellite Navigation Systems such a QZSS (Japan),
IRNSS (India) and Beidou (China).
Continental scaleGround Based Augmentation Systems(GBAS) for
example the Australian GRAS and the US Department of Transportation
National Differential GPS (DGPS) service.
Regional scale GBAS such as CORS networks.
18. ABAS : Aircraft-based augmentation system (ABAS-ICAO
definition) augments and/or integrates the information obtained
from the GNSS elements with other information available on board
the aircraft. The aim is to enhance the overall performance of the
GPS equipment on board in terms of integrity, (continuity),
availability and (accuracy) Frequency spectrum VHF datalink appear
better than satellite communications Switching between ground-based
VHF and satellite-derived datalink for CNS/ATM operations can be a
seamless procedure, according to tests carried out by the Dutch
National Laboratory NLR and ARINC. In general, the ground-based
system proved faster and broader than the satellite link.EGNOS:The
space-borne segment of EGNOS will initially be composed of
navigation transponders carried on two satellites owned by the
International Maritime Satellite Organization (Inmarsat).These are
Inmarsat-3 series satellites that are positioned above the Indian
Ocean at 64 East, and over the Atlantic Ocean at 15.5 West. The
Inmarsat-3 satellites operate from geostationary orbits at 36,000km
above the Equator. Since their orbit speed matches that of the
Earths rotation, the spacecraft appear to be stationary above the
same area of Earth at all times. The EGNOS ground network will
provide the backbone for three navigation services: ranging,
integrity monitoring and wide-area differential corrections. The
ranging service will enable the EGNOS transponders to broadcast
GPS-like navigation signals. As a result, these satellites become
two more sources of space-based navigation data for users. This is
important because neither the GPS or GLONASS systems can guarantee
that the minimum number of six satellites required for
safety-critical applications, like aircraft navigation, is in view
at all times and all locations world-wide. The EGNOS integrity
service will enable users to know within 10 seconds (or 6 secs?)
whether a navigation satellite signal is out of tolerance, allowing
action to be taken before any critical situation arises. The third
function of EGNOS is known as the wide-area differential service,
which broadcasts correction signals to improve the precision of
satellite navigation. With the wide-area differential service, the
satellite navigation precision will dramatically increase to 5 or
10 metres well above the approximately 100 metres for the currently
available non-encrypted signals from GPS
19. Current global navigation systems GPS The United States'
Global Positioning System (GPS), which as of 2007 is the only fully
functional, fully available global navigation satellite system. It
consists of up to 32 medium Earth orbit satellites in six different
orbital planes, with the exact number of satellites varying as
older satellites are retired and replaced. Operational since 1978
and globally available since 1994, GPS is currently the world's
most utilized satellite navigation system. GLONASS The formerly
Soviet, and now Russian,GLObal'naya NAvigatsionnaya Sputnikovaya
Sistema , or GLONASS, was a fully functional navigation
constellation but since the collapse of the Soviet Union has fallen
into disrepair, leading to gaps in coverage and only partial
availability. The Russian Federation has pledged to restore it to
full global availability by 2010 with the help of India, who is
participating in the restoration project. Compass China has
indicated they intend to expand their regional navigation system,
calledBeidouorBig Dipper , into a global navigation system; a
program that has been calledCompassin China's official news agency
Xinhua. The Compass system is proposed to utilize 30 medium Earth
orbit satellites and five geostationary satellites. Having
announced they are willing to cooperate with other countries in
Compass's creation, it is unclear how this proposed program impacts
China's commitment to the internationalGalileoposition system
Galileo The European Union and European Space Agency agreed on
March 2002 to introduce their own alternative to GPS, called the
Galileo positioning system. the system is scheduled to be working
from 2012. The first experimental satellite was launched on 28
December 2005. Galileo is expected to be compatible with the
modernized GPS system. The receivers will be able to combine the
signals from both Galileo and GPS satellites to greatly increase
the accuracy. Other regional navigation systems Beidou navigation
system Chinese regional network to be expanded into the global
COMPASS Navigation System. Till 2007, the resolution of Beidou
navigation system already reached as high as 0.5m, thus China
became the second country after USA which achieved