Radio beacons: Difference between revisions

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Radio beacons (view source)

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[[HSI]] [[Primary flight display]]
[[HSI]] [[Primary flight display]]


==Radio navigation==
Kapstok For the main article. Think that is the correct title.
===Introduction===
Going from one place to another is not difficult, we do it every day. We look around and go from one place to another. We see and recognise the landscape and landmarks around. We are familiar with where we are so it is easy to find our way around.


If we go to a place we are not familiar with we would buy (download) a map to find our way around. There are street names and specific buildings we can orientate ourselves with. On our Swiss knife we have a mini compass we sometimes use to orientate the map North.
Visual navigation is possible when we are low enough and when the weather allows it. To orientate ourselves we use a map and a compass. Movement goes a lot faster as walking so to see where we are we have to update our position on the map often or else we would get lost quick.
When there are not enough visual clues to know where we are we will have to rely on our equipment on-board to navigate. Lucky there is a rack of tools in our aircraft to help us find our way, even at night and high up in the sky. We just have to know how to use it.
Instead of relying on visual landmarks (roads, rivers, churches, towns) radio navigation relies on radio beacons. Radio beacons can be seen with the right equipment, from far away and independent of the weather. The position of radio beacons is clearly marked on navigation maps. Radio beacons are placed near airports, can be aligned with runways and can be placed in remote areas so to mark a route over them.
The time that a pilot had to fly with the yokes in it's hands all the time has long been passed. Our aircraft have an autopilot and radio beacons are ideal for automated flight. With a NDB station we use the heading bug, with a VOR station we select the radial to use and the autopilot keeps us on that course.
Some wise words about GPS.
DR nav, beacon-to-beacon, wind
===Basic techniques===
====Pitfall====
Often there are radio stations near each other that transmit on the same frequency. Our equipment will tune into the signal that is strongest. The strongest signal is not always the nearest. Always be sure you know the identity of a station before using it.
====Dead reckoning====
[http://en.wikipedia.org/wiki/Dead_reckoning Dead reckoning ('''DR''')] is a technique you use every day in many situations. If you know where you are and how fast you move you can predict where you will be after some time. If you have a good compass and know your (ground) speed well you can even do some navigation with this method. Even with the navigational tools that are available today you will rely on this method without knowing it. For long tracks without radio beacons nearby (and no GPS) it is the only way to navigate.
====Position finding====
We always start from an airport, we know where it is on the map. Going further on the way it is possible to get lost so it is important to figure out where we are if we get lost. Lucky most radio beacons tell their identity, in Morse code or in other ways. That identity gives a good clue where we are on the map but we have to pinpoint our position before we can navigate any further. (images needed)
:*We need tune in to just one VOR-DME to pinpoint our position. It gives the radial we are crossing and the distance to the station. From that we use the map, a compass rose and a ruler to pinpoint the position.
:*With two VOR stations we receive two radials. With two NDB stations we have to bearings on the compass. On the map we draw the two radials from the station to find our position at the cross point.
====Go from====
Starting from a runway or passing over a radio station we know where we are and where we want to go. We set the radio beacon in our equipment and we add or subtract 180 from the course we want to fly. The result is the position where the NDB should be on the compass rose or the radial we have to select from the VOR station. With a NDB we set the heading bug and with a VOR we pick the radial to fly. The big problem with this course it it's increasing inaccuracy. The wind will place us at a complete different point as expected. The radial of a VOR station should compensate for winds but with some winds you will discover how inaccurate a VOR radial can be. FROM navigation should be avoided but if needed it can work for a 100 miles or so.
====Go to====
As soon as we pick up a signal from a radio beacon we can easy navigate towards it. With a NDB we set the heading bug, with a VOR we select the radial.
*A VOR radial will bring you with high accuracy in a straight line over the radio station.
*Setting the heading bug on the bearing of the NDB once will not bring you there. The wind will blow you off course and you will see the bearing of the NDB drift slowly over the compass rose. If you bring the heading bug back each time you will have flown a long wide curve instead of a straight line. (image on wikipedia?) You should set the heading bug ''over'' the bearing of the NDB towards the wind direction so to compensate for the wind. It's a bit of a guess on how much that compensation should be.
====Go in between====
On maps there are '''fixes'''. A fix is a place that is crossed by two or more ''easy'' radials from a VOR or bearings from a NDB. Typically the ''easy'' bearings are 45 degrees intervals on a compass rose, but there are plenty of fixes that use other intervals. It's a bit of guessing what beacons should used for a fix but it can assume the two nearest ones. Navigating Fix to Fix is not practical. In between navigation is only done for approach or to identify a place where to change course (to start an approach) since there are runways without beacons.
===Planning===
[[File:VOR route.png|right|400px|Red = straight line between take-off and landing Green= individual legs Compass rose= record heading of TO Circle= range of VOR station Hexagon = VOR station]]
Know the requirements and limitations of the aircraft. Does it need tarmac, an ILS, how much runway? Etc. Not any airfield is suited for landing of just any aircraft. Examine the airfield before deciding to go there. What is the cruising altitude of the aircraft? Can it fly over mountains or should it fly around them? Can it cross areas where there are no beacons? What is the range of the aircraft, when does the fuel run out?
From the requirements and limitations we can plan our route.
To plan a route we begin with a map, a ruler and a compass rose. On the map we draw a straight line between take-off and landing. For longer routes a string and a globe is used. The straight line is the fastest route. Unfortunately that route is almost impossible to navigate. The route must be divided in '''legs''', each leg begins on a radio beacon and ends on a radio beacon.
Near the straight line identify the VOR stations. A typical VOR station has a range of about 100 NM AGL. To prevent FROM navigation the legs should be less then 50 NM in length. To prevent continues tuning of your radio receiver and ever changing course the legs should be above 25 NM in length. If possible prevent NDR stations since they need continues attention. Prevent legs longer as 100 NM.
Draw a line from station to station, each line is a leg of the route. Calculate the length of each leg. From the length of the leg and ground speed calculate the time for each leg. Use a compass rose to read the heading of each leg (True North or Magnetic North). Identify name, type, location and frequency of the stations.
The result should be a sheet listing the legs of the planned route.
{| border="1" cellpadding="10"
|Name of station || Type ||Latitude  ||Longitude || Frequency || Heading || Distance || Time
|}
The first line will be the airfield with a "0" heading and a "0" distance. The headings on the list will be the heading towards the identified station.
Calculate from the cruising altitude, the sink rate (feet per minute) and the average sink speed (ground speed during descend) the distance the aircraft needs to reach the height of the landing runway. Add this point as a separate leg.
*Or use [[Kelpie Flight Planner]].
===Principles===
erm.
===Equipment===
====Radio rack====
Typically in FlightGear we have two VOR receivers, one NDB receiver and one DME. The frequencies can be set either in the Equipment=>Radio (F12) window or using the radio rack in the 3d cockpit.
The 3d-rack and window look a bit like this:
{| border="2" cellpadding="15"
|'''Type''' || '''Active frequency''' || <='''Swap'''=> || '''Input frequency''' || '''Radial''' ||'''Input knob '''
|-
|Window    ||Window - 3d            || Window - 3d      || Window - 3d          || Window      ||3d
|}
:Type= NAV1 and NAV2 are the VOR stations; ADF is the NDB station; DME is the DME station
:Active frequency= this is the frequency the radio is tuned to
:Swap= make the input frequency the active frequency
:Input frequency= this shows the frequency that is being set
:Radial= the selected radial for a VOR station or bearing of the NDB compass rose
:Input knob= turn the knob to select the input frequency, outer ring for big steps, inner ring for small steps
*Some "cells" are not available for each type of station. Some "cells" that appear are not functional.
*The ADF is a sensitive piece of equipment and often is retracted into the aircraft to protect it. It often needs to be extended before it works.
*DME tuning often is automatic on NAV1 and NAV2
#We turn the '''Input knob''' till the '''Input frequency''' matches the station we want to use or we use the '''Input frequency''' window.
#For a VOR station we enter the '''Radial''' or turn the knob on the HSI.
#Press the '''Swap''' button to activate the '''Input frequency''' (towards the '''Active frequency''').
====Indicators====
The equipment that displays the received information varies from aircraft to aircraft.
The ADF that tunes to the NDB station is the most basic. Typically it's an arrow on a compass rose. Sometimes you can turn the compass rose. Sometimes the compass rose is combined with the compass (and the heading bug). Sometimes the ADF is combined with the VOR receiver. One way to display the NDB is the [http://en.wikipedia.org/wiki/Radio_direction_finder#Radio-magnetic_indicator_.28RMI.29 Radio Magnetic Indicator ('''RMI''')].
VOR stations are mostly used for automated flight so most, if not all, receiving equipment (on NAV1) can be linked with an autopilot.
Receiving the radial from the VOR station has many variations. The most basic is a compass rose and a vertical line, named the VOR indicator. If the vertical line is in-centre the top of the rose identifies the radial combined with a TO indicator. If the FROM indicator is shown the radial is the bottom of the rose. This setup is often combined with an ILS giving also a horizontal line.
Similar in setup but a bit more modern is the [http://en.wikipedia.org/wiki/Course_Deviation_Indicator Course Deviation Indicator ('''CDI''')].
More common these days is the Horizontal Situation Indicator '''([[HSI]])''' that is also described on [http://en.wikipedia.org/wiki/Horizontal_situation_indicator Wikipedia].
and since it's often compined with the autopilo
, ranging from a simple VOR indicator, a CDI, a HSI to a PFD.
http://en.wikipedia.org/wiki/VHF_omnidirectional_range#Using_a_VOR
VOR indicator
HSI
CDI
PFD
RMI
===Navigation===
===further reading===
IFR
VFR


<nowiki> [[Category:Navigation]] </nowiki>
<nowiki> [[Category:Navigation]] </nowiki>
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