TACAN
DESCRIPTION
TACAN (TACtical Air Navigation) is a radio navigation aid, used to find a distance (slant range) and bearing from a ground beacon. The ground beacon transmits "radials" which can be received by the aircraft and interpreted to find which radial the aircraft is passing or flying along. Slant range to the beacon; as TACAN operates by direct line of sight, altitude will add to the range measurement.
Some aircraft such as the Victor K2 tanker also carried TACAN transmitters to aid locating in flight, however, this is configured for range finding only, as the aerials required for radials are physically too large to carry, but Violet Picture UHF homing can be used for direction finding, in conjunction with TACAN for range.
126 channels were originally available, which are set via the TACAN control unit, each corresponds to a different VHF frequency. Around 1967, the number of channels was doubled, the original 126 now being named "X", and the new 126 named "Y".
SYSTEM COMPONENTS
TACAN Display
| Manufacturer: | SMITHS |
The indication of the TACAN system is displayed on the navigation display as a series of concentric rings for range and a bearing line. An additional counter also displays range.
Navigation display in TACAN mode.
Displaying a homing point 140 NM away at a bearing of 30°
TACAN Control Unit
| Manufacturer: | Standard Telephones and Cables (STC) |
The TACAN control unit allows the aircrew to set different TACAN channel numbers, which controls the operating frequency of the transmitter / receiver unit. Each ground or airborne beacon is allocated a channel number different to others in the locality.
TACAN control unit.
TACAN Offset Computer
| Manufacturer: | SMITHS |
A TACAN offset computer can be used to set up a homing point remote to the beacon for navigation to anywhere within a 195NM radius of a beacon. A destination point is found on a map, the bearing and distance from the closest TACAN beacon are measured, these are input to the offset computer, and as long as the aircraft stays within range of the beacon, the TACAN system guides the pilot to the remote location. Genius.
TACAN Coupler Indicator
| Manufacturer: | SMITHS |
This unit converts the TACAN receiver output signals from synchro to resolver (sine and cosine) signals for use with the offset computer and display. It is located in the port side of the spine, so the indicators are only used for system testing and calibration purposes.
Typical TACAN coupler indicator unit.
This example is from a Belfast aircraft, but is very similar to the Lightnings' unit.
TACAN T/R Unit
| Manufacturer: | Standard Telephones and Cables (STC) |
The ARN-72 TACAN T/R unit is indicated below. When it was designed in the early 60's only the original 126 TACAN channels were in use globally. Around 1967 the number of TACAN channels in use was doubled (ref: IMSM/18/67), and the original 126 became labelled "X" channels and the new channels being labelled "Y" channels, but the RAF Lightnings did not receive an upgrade and remained only capable of the original (now "X") 126 channels. It is worth noting that the UK only has TACAN beacons on X channels anyway, so an upgrade to as Y channels would not have been necessary for UK flying.
ARN-72 TACAN transmitter/receiver unit shown the
port "elephant's ear" of T Mk.5, XS458 22-04-2006
As well as bearing and range information, the T/R unit also receives a Morse code signal from the transmitting beacon. The code spells out three letters associated with the location of the transmitting beacon, such as "VYL" for Valley as shown below. The Morse code tone volume is set on the control unit by the "VOL" knob, and fed through to the aircrew headsets.
ADVERTS
These adverts are useful for dating the beginnings of the use of TACAN.
STC advert - TACAN at the 1955 Farnborough SBAC show
Published: Flight, 09-09-1955
Source: Aviation Ancestry↗
STC advert - TACAN
Published: Aeroplane, 16-12-1955
Source: Aviation Ancestry↗
STC advert - STARN21 TACAN, and P1 Lightning
Published: Aeroplane, 06-09-1957
Source: Aviation Ancestry ↗
REFERENCES
F Mk. 3, T Mk. 5 and F Mk. 6 aircrew manual:
A.P.101B-1003, 5 & 6A, Part 1, Chapter 7, A.L.2, Nov 84 - Instruments - Paragraph 28
T Mk.5 electrical "Vol. 1":
AP4700E, Vol.1, Book 2, Sect.9, Chap.1, A.L.1, Nov 64, TACAN
T Mk. 5 wiring diagrams:
AP101B-1005-10, Sheet 37, A.L.3, Nov 1981, Cabin Lighting, Starboard
AP101B-1005-10, Sheet 55, A.L.3, Nov 1981, VHF, UHF, Intercommunication and Telebriefing
AP101B-1005-10, Sheet 56, A.L.3, Nov 1981, Radio and Radar Installations - Fig 3, TACAN
Flying manual:
A.P.129, Vol.1 Sect.2, Chap.5, 6th Edition, Feb. 1962 - TACAN
NATO Memorandum - TACAN (source: archives.nato.int↗)
SGM/226/64, TACAN, 22 June 1964
NATO Memorandum - TACAN Channel Doubling (source: archives.nato.int↗)
IMSM/18/67, TACAN Channel Doubling, 14 March 1967
EXTERNAL LINKS
TACAN information:
vintageavionics.nl↗