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Aviation History
1946
1946 - 1483.PDF
AUGUST IST, 1946 FLIGHT Deeca Navigator Southern England Chain of Transmitters Noiv Operational T-J* order to provide Government and Service authorities I with the means of making extensive trials of the Decca -*- Navigator system, a chain of stations sited in the South of England has been built. Three of these stations are now operational and the fourth is nearing completion. All have been built since the war, and the introduction of this new method of navigation shows considerable enter- prise and has created wide interest in air and marine circles in this country and America. The Decca Navigator system employs the same basic principle as the wartime navigational aids Gee and Loran. However, whereas these two systems required rather com- plex receiving equipment and specially trained operators, the Decca system employs simple radio receiving equip- ment, and the results are indicated on three dials which can be read after a few minutes' explanation. The dials or meters give a reading in figures which refer to lattice lines on a chart of the area. Accuracy within yards is attainable with the Decca system and position can be fixed with increasing precision as the range is decreased. The effective range is at least 300 miles in any direction from London, and during day- light hours transmissions can be recorded and used as a navigational aid up to a distance of 1,000 miles from the stations. The master station is sited at Buntingford in Hertfordshire and the two operational slave stations known as the red and the green slaves are at Stokeholy Cross, near Norwich, and East Hoathly, near Lewes, in Sussex. The purple slave will be at Wormleighton, Warwickshire. This English chain of Decca Navigation stations was officially declared operational by the Admiralty and Ministry of Transport at 08.00 hours on July 18th. Principal features of each station are the aerial system which is hung on a steel mas"; 325 feet in height, and two prefabricated main buildings. The master station consists Master and slave stations tor a Decca chain each comprise a325ft steel mast and a transmitter building. The second hut may house either a reserve power unit for the master or an automatic phase control unit for one of the three slaves buildirof mast, transmitter building and reserve power building, while in the case of the slave stations the transmitter build- ing is replaced by one housing the automatic phase control units. By means of this control a very high degree of synchronization is maintained between transmitters. To ensure a reliable 24-hour navigational service, ex- treme precautions have been taken that no failure, either in power supply or radio equipment, shall interrupt the radio transmissions from the stations. SELF-CORRECTING ALTIMETER *N interesting and useful development in instrumentation/•* is announced by the American Square D Company, X. ^ Kollsman Instrument Division As is well known, theconventional sensitive altimeter is an aneroid device which records the Obtaining barometric pressure relative to a pre-setdatum pressure. As a consequence, it is possible in abnormal barometric conditions for an altimeter to register a figurewhich might be as much as 1,oooft out and, of course, when flying in the vicinity of high ground in blind conditions sonii-considerable risk may be involved. At present it is necessary for a pilot to depend upon audiblecontact with ground stations in order that he may reset his altimeter every 100 miles or so as pressure changes occur, bu'this new development, identified as Automatic Altimeter SettMp^eliminates the potentially dangerous sources of errotin t]fie'"!Tses of the conventional altimeter. It also removes the work-load on the pilot, control tower operators and otheioperating personnel. In the new Kollsman device a ground altimeter continuouslysends out its own altimeter setting in the form of a coded radio signal. This is received in the aircraft by compactlightweight radio sets which are self-operative and can easily be combined with existing radio range stations. An automatic-cut-out device prevents confusion when an aircraft is flying within the signal range of two ground stations; the deviceautomatically cuts out the weaker signal. When the coded signal is received, it is automatically decoded and the alti-meters in the aircraft automatically reset themselves accordingly. Two provisions are made for the pilot to make sure thedevice is operating properly. First, he may manually set his altimeter to any arbitrary figure, and il the device is workingcorrectly the altimeter then immediately returns itself Ho its original setting. Secondly, he can feed into his own altimetera coded signal which represents " 29.2 " the setting lor standard or average atmospheric conditions. If the device isfunctioning properly, the altimeter immediately sets itself to " 29.2 " then, when the pilot ceases to give the check signal,returns to the correct reading in accordance with the nearest ground station.The method selected ior the coded signals is to transmit an audible sound of definite frequency; that is, a musicalnote of a definite pitch, with each altimeter setting accorded a specific note. The altimeters fitted in the aircraft containa frequency analyzer, which measures precisely the pitch ot the incoming signal and so causes each altimeter to set itself'in tune" with the ground barometric condition locally. ANNULAR COMBUSTION CHAMBER Concluded from page 112)ciency, 92-95 per cent and maximum to mean temperature ratio 1.2: 1. The temperature distribution at the nozzle endof the combustion chamber was quite good as may be seen from Kg- 3- It has been tevealed that while this combustion chamberproved fairly good as an initial model, several characteristics required improvement. The circumferential temperature dis-tribution was not entirely satisfactory, the space between the burner cone and the small internal cone surrounding the fuelspray was apt to become completely blocked with carbon, the blow-out characteristics at altitude were unsatisfactory and itwas not possible to restart the unit above 12,000ft.
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