Sunday, April 19, 2015

Navigation and Guidance

Introduction:-

Navigation and Guidance:-

Navigation is the term which is used for the determination of position or velocity basically it gives us the idea of the vehicle's location at a given time while Guidance is the term which is referred to our desired Destination from vehicles present location to a designated target.

Types of Navigation:-

Navigation is divided into two types.

 1- Positional Navigation.
2- Dead Reckoning.

Positional Navigation:-

Positional Navigation is something which can be done with the help and guidance of some one. i.e Satellites,Radio etc.


Positional navigation is divided into further three categories.
1- Radio Navigation
2- Celestial Navigation
3- Mapping Navigation

Radio Navigation :-

Radio navigation is the application of radio frequencies to determine a position on the Earth. Like radio location, it is a type of radio determination. directions, e.g. by bearing, radio phases or interferometry, distances, e.g. ranging by measurement of travel times.



Celestial Navigation:-

Celestial Navigation is the navigation which is performed through stars. it uses sights or angular measurements taken between a celestial body ( the sun, the moon or a planet or a star). 

Mapping Navigation:-

Mapping navigation is performed through the maps which tells us the distances and location of our desired places.

Dead Reckoning:-

Dead reckoning is something which is always done or performed without help and guidance of some one.


Dead reckoning is divided into further two categories.
1- Inertial Navigation
2- Doppler Navigation

1- Inertial Navigation:-

An inertial navigation system (INS) is a navigation aid that uses a computer, motion sensors (accelerometers) and rotation sensors (gyroscopes) to continuously calculate via dead reckoning the position, orientation, and velocity (direction and speed of movement) of a moving object.



2- Doppler Navigation:-

A Doppler Navigation system uses the Doppler principle to measure an Aircraft’s ground speed and drift. The Doppler radar functions by continuous measurement of Doppler shift and converting the measured values to ground speed and drift angle.





Uses of Navigation in Military:-

1- Interdiction is the term which is used in military navigation it means destroy your enemy before he destroy's you in war.

2- Preemptive attack is another term usually used in military Navigation an attack initiated on the basis of incontrovertible evidence that an enemy attack is imminent which means kill your enemy before getting killed.

3- Close air support (CAS) is also the part of military navigation it is defined as air action by fixed or rotary-winged aircraft against hostile targets that are close to friendly ground or naval forces, and which requires detailed integration of each air mission with fire and movement of these forces.


                                                                 CAS

4- Short take off is another term used in Military navigation A short takeoff and landing (STOL) aircraft is an aircraft with short runway requirements for takeoff and landing. Many STOL-designed aircraft also feature various arrangements for use on runways with harsh conditions (such as high altitude).





Marker Beacons:-

Marker Beacons tells us that how far we are away from Runway There are three types of marker beacons that are installed as part of their most common application.

1- Inner marker beacon.
2- Middle marker beacon.
3- Outer marker beacon.

Inner marker beacon:-

 It is located at the beginning (threshold) of the runway on some ILS approach systems (usually Category II and III) having decision heights of less than 200 feet (60 m) AGL. It is of white colour and it Triggers a flashing white light on the same marker beacon receiver used for the outer and middle markers; also a series of audio tone 'dots' at a frequency of 3,000 Hz in the headset.

Middle marker beacon:-

It is normally positioned 0.5 to 0.8 nautical miles (1 km) before the runway threshold. it is of Amber colour (yellow) When the aircraft is above the middle marker, the receiver's amber middle marker light starts blinking, and a repeating pattern of audible morse code-like dot-dashes at a frequency of 1,300 Hz in the headset.

Outer marker beacon:-

The Outer Marker which normally identifies the final approach fix (FAF) it is of Blue colour and is situated on the same course/track as the localizer and the runway center-line, four to seven nautical miles before the runway threshold.

Bearing and Fix:-

Bearing in Navigation stands for Direction while Fix is your destination.

Navigation Instruments in Aircraft:-

1- ADF:-

ADF (Automatic Direction Finder) is the radio signals in the low to medium frequency band of 190 Khz. to 1750 Khz. it is also known as RBI (Relative bearing indicator) It was widely used today. It has the major advantage over VOR navigation in the reception is not limited to line of sight distance.

ADF consists of three parts.
1- Fixed card
2- Moving card
3- RMI (Radio Magnetic Indicator)

Fixed Card:-

It is fixed to the face of instrument and cannot rotate. 0 degree is always straight up as the nose of aircraft.

Moving Card:-

It tells us about Magnetic bearing and  the dial face of the instrument can be rotated by a knob. By rotating the card such that the Magnetic Heading (MH) of the aircraft is adjusted to be under the pointer at the top of the card.

MB=MH+RB

MB= Magnetic bearing
MH=Magnetic heading
RB=Relative bearing

RMI:-

RMI stands for Radio magnetic indicator The dual needle RMI is similar to single needle RMI except that it has a second needle. The first needle indicated just like single needle. in the picture , the yellow needle is a single which indicate the Magnetic Bearing to the NDB station.The second needle is the green needle in the picture.


2- ELT:-

ELT is Emergency locator transmitter which is used to transmit electric signals in emergency ELT is a life saver.


3- DME:-

DME is distance measuring equipment it tells us how far we are away from destination it is used in aviation for navigation purposes. The DME system consists of an interrogator on board an aircraft and a DME station on the ground.


4- VOR:-

VOR stands for Very high frequency omni range it is used to avoid CB clouds VOR is always CDI (course deviation instrument).




VOR is divided into two types CVOR and DVOR.

CVOR:-

it is Conventional Very high Omni range.It has 1 ground antenna.



DVOR:-

DVOR stands for Doppler Very high Omni range.It has 52 antennas.


5- CDU:-

It is the major component of Inertial navigation system The Control Display Unit (CDU) is the interface device unit used to access the Flight Management Computers (FMC), the main computers and software of larger aircraft. CDU's are mostly seen on airliners.





TCAS:-

A traffic collision avoidance system or traffic alert and collision avoidance system (both abbreviated as TCAS, and pronounced tee-kas) is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft. It monitors the airspace around an aircraft for other aircraft equipped with a corresponding active transponder, independent of air traffic control, and warns pilots of the presence of other transponder-equipped aircraft which may present a threat of mid-air collision(MAC).




The main purpose of TCAS is to avoid traffic collision between aircrafts TCAS operates independently of Air Traffic Control (ATC) by communicating with other transponder-equipped aircraft to build a 3-dimensional map of aircraft in the same airspace. By extrapolating the current range and altitude difference to anticipated future values, TCAS determines the potential of a collision threat.


TCAS Versions:-

There are following TCAS Versions.
1- TCAS I
2- TCAS II
3- TCAS III
4- TCAS IV

TCAS I:-

  • Less expensive and less capable than TCAS II and TCAS III
  • Designed primarily for general aviation use
  • Displays the approximate bearing and relative altitude of all transponder-equipped aircraft within a range of approximately 40 miles. Figure 1 shows a TCAS display (Traffic Advisory).

TCAS II:-

  • More comprehensive than TCAS I
  • Used in the majority of commercial aviation aircraft
  • Operates the same as TCAS I but has greater range and bearing accuracies than TCAS I and a Resolution Advisory (RA) function
  • In the event of a potential collision, TCAS II will issue a Resolution Advisory (RA) to each pilot that consists of direct, vocalised corrective or preventive vertical manoeuvring commands to avoid a collision

TCAS III:-

  • TCAS III offers both vertical and horizontal RAs and TAs. Horizontal directives commanding left or right manoeuvres are beneficial for two conflicting aircraft close to the ground with minimal vertical manoeuvring space.

TCAS IV:-

  • Due to the limited accuracy in using directional antenna for TCAS III, TCAS IV uses information encoded by the aircraft in the Mode S transponder. It will require a reliable source of position (e.g. INS, GPS) in order for the aircraft to be encoded.
References:-

http://aviationknowledge.wikidot.com

http://wiki.flightgear.org
   
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