D/F Tower

[John Cooper]

One from Tony Hawes site RAF Negombo 1956-57 in colour

http://images.theveryoldvic.multiply...nmid=131027812

[P Bellamy]

Sorry Richard, I'm struggling to find any illustrations that match the cabin as yet, but CR/DF seems to have come in during the 1950s.

All the best,
PB

[John Cooper]

On Wheels at RAF Gan 1958 by Tony again in colour

http://tonyhawesraf.multiply.com/pho..._1958#photo=14

[norwichpaul]

Well done Paul/ This is taken from my CT book, refering to Manby 1950-1960s:

In heavy cloud or poor visibility the Approach Controller ensured that aircraft were separated by 1,000ft vertically (2,000ft above 29,000ft) or horizontally where possible by positioning over a radio beacon or other reporting points.

Aircraft requiring assistance to navigate to the airfield and descend through cloud to reach a position where they could continue visually to the runway and land were given a QGH approach, also known as a controlled descent through cloud.

The aircraft was homed to the airfield initially at a height predetermined by the Controller to ensure vertical separation from other aircraft with reference to the QGH procedure. The radar used, ACR7C, had a range of 20 miles and aircraft direction was controlled by means of a CRDF. When the aircraft transmitted on R/T a beam of light (or trace) was indicated on the display showing the heading to be flown to reach the overhead, where the signal was weakest, referred to as the cone of silence. This information was passed to the pilot by the controller, who interrogated the pilot at intervals until the trace shortened or disappeared, showing that the overhead had been reached. The Controller then dispatched the aircraft on the outbound leg of the procedure, instructing the aircraft to call turning inbound towards the airfield at a height based on the commencing height.

The pilot was given instructions by the Controller on the heading to be flown both inbound and outbound based on the Controller's interpretation of the movement of the 'trace' on the CRDF. On turning inbound the pilot continued his descent to a height known as the 'Break off Height', which was based on obstacles such as high ground on the descent track. At this height the pilot hoped to see the airfield and therefore continue visually and land. If not he would not descend any further and would clear the area.

This method of recovery was useful, but relied on frequent checks on the trace, and if the frequency was busy with other aircraft calling for assistance the aircraft could wander off course. Therefore the area covered to decide the Break off Point had to be large and could encompass many obstacles which a more precise approach would miss.

This was where the Radar Controller came into operation. He was able to see the precise position of the aircraft on the radar screen accurate to 0.25 mile and + or – 2 degrees to the approach to the runway marked on the screen. The pilot was informed of his position continuously as well as the height he should be at for each range to maintain a 3 degree glide path, e.g. 4 miles 1250ft, 3 miles 950ft. This sort of accuracy demanded total commitment and only one aircraft could be controlled at a time. If the weather did not permit an aircraft to land from a QGH approach a landing was often possible from a radar approach and efficient co-ordination between the Approach and Radar Controllers enabled the aircraft to home to the overhead and hold to await its turn to commence a QGH/Radar approach.

[Richard Drew]

Paul the D/F at Martlesham & Ibsley are surely wartime?

[norwichpaul]

Yes off course Richard, the only post-war bit so far is the Exeter CRDF and this is now part of the thread as it was a post-war version.

[PETERTHEEATER]

Peter the D/F tower was never on top of the brick structure, more inside with the brick walls surrounding at its lower level. The timber frame is fixed (bolted) to a hexagonal concrete curb, if you look closely at Richard's picture you can just see part of through the opening. Not all D/F towers had the brick blast wall surround, like the Lakenheath example above and another I have seen at Cranfield. Richard's drawing shows the tower too tall I think.

Thanks Paul, I understand.

Richard's sketched in superstructure is just notional.

[Carnaby]

As mentioned earlier Thornaby had the tall hexagonal wooden hut, on the site plan as HF D/F station. It was about 400 yards off the airfield. Not shown on the 1945 plan, but found on a drawing c.1955 was a small single-storey (rendered-brick?) hut with door and windows, located in the very middle of the airfield. It was entitled VHF D/F and had a typical aerial system on its roof. Hullavington had an identical one until recently but it was some distance north of the airfield. Wondered what frequencies were used for HF and VHF as the two aerial systems seemed similar in size?

Graham

[Jim Hope]

NP,
Your photos are of an RV 105 CRDF. Last time I saw one in use was at Salalah in 1971.

[norwichpaul]

Thanks Jim, what can you tell us about it, what is the alien thing and the triangular contraption in the cabinet?