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Thread: D.F. indicator

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    Default D.F. indicator

    Hi,

    a Wellington instrument panel had a D.F. indicator. One can see it in this illustration (second from the right showing an L and R):

    http://www.avsim.com/pages/0409/FCS/Wellington-Instrument-Panel.jpg

    Can anybody explain to me what this was for?

    Thanks.

    Marcel

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    Not D/F but Bomb Steering Indicator

    See

    "
    Paragraph 50 – Pilot’s steering indicator. The steering indicator (33) at the port side of the instrument panel is employed in conjunction with the course-setting bomb sight (CSBS) and indicates to the pilot the angular divergence of the aeroplane’s course relative to the target. The indicator also possesses red and green coloured signalling lamps illuminated by separate push-switches at the bomb-aiming station."

    from this thread on the forum
    http://www.rafcommands.com/forum/sho...rom-Wellington

    Ross
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    Hi Ross,

    my information came from A.P. 1578C. In these Pilot's Notes is the image of the one of the website I refered to. No 21, the one showing L + R, is described as a D.F. indicator. And I wonder what this is.

    Best.

    Marcel

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    Marcel,
    The set of Wellington Pilot's Notes in my possession (AP 1578A, Vol I, Sect I, for Wellington I, IA and IC aeroplanes) have this instrument described more fully as the D F loop scale setting indicator, which should give you a whole lot more to chew on as regards its actual function. It is also made clear in this publication (under paragraph 8) that the D/F equipment was located in the "Wireless compartment" and therefore came under the purview of the wireless operator. However as the indicator is located in the pilot's compartment, he also seems to have a legitimate reason for having an interest in the setting of this equipment too. The D/F (Direction Finding) loop was of course mounted in the roof of the aircraft on the centre line at approximately the wireless operator's normal station, and in early aircraft the loop was enclosed in a streamlined (tear-drop shaped) fairing, but later aircraft often had a larger, fully exposed (unfaired) loop. I will leave the rest to the experts.
    David D

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    Hi,

    thanks also to David. My Pilots notes are for Wellington III, X, XI, XII, XIII and XIV.

    So we talk about the same indicator, very nice. Yes, the Wellington IIIs seem to have had the exposed aerials. The indicator belongs therefore to the D.F. loop aerial.

    Can anybody explain what the indicator actually has shown? Left or right ...

    Thanks.

    Marcel

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    Different beasts.

    The one L and R scaled 0 to 35 degrees with the two indicator lights is the Bomb Steering indicator and driven by the CSBS,
    No. 7 in this pilots notes piccy for the Halifax
    http://forum.keypublishing.com/attac...1&d=1314118210

    The one L and R only with no scaling is the Visual Indicator or D/F Loop and driven from the R1155 wireless receiver.
    http://www.chavfreezone.me.uk/ad8882b9.html

    Both types can be seen in the clearer pilots notes for the Halifax. (7 and 12)

    I'll take a picture tomorrow of the Bomb Steering Indicator on my Halifax Panel tomorrow so you can compare it to the image from the Wellington Notes,

    Oops just realised I was looking left instead of right as you directed. Visual indicator on right, bomb steering on left in the wellington notes.

    Ross
    Last edited by Ross_McNeill; 3rd October 2016 at 20:39. Reason: Oops added with face palm
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    Default

    HI,

    thanks to both of you.

    As you may have seen, the image of the Wellington instrument panel shows the indicator of Ross' second link. Nice to see such an indicator. So as a most rough description the D.F. indicator helps the pilot the stay on the correct course. The information came from the wireless operators equipment which used the information from the D.F. loop antenna, correct?

    Marcel

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    The D/F equipment needed a radio signal emitter (beacon) which was omni directional.

    The relationship of aircraft equipment is shown on this pictorial diagram
    http://www.vk2bv.org/archive/radio/r...les/charta.jpg

    Two basic ways to operate.

    1. WOp use to get bearing for passing to Nav

    The WOp would set his receiver typically R1155 to the frequency then using the handwheel controller and indicator type E2 would rotate the aerial loop to get the best signal (either strongest signal or aural null depending on the beacon type). He could use either headphones or the visual indicator (magic eye on R1155 set) to listen to the signal and determine the loop position for required max or null signal.

    2 WOp set up for pilot to fly bearing to.

    Again the WOp sets the frequency but instead of rotation of loop for bearing he sets the loop for fore/aft axis of aircraft.

    Having done this the pilot can use his visual indicator to fly left or right as directed by the needles to home in on the beam to the beacon.

    Couple of things needed care in operation.
    1. Two max signal and two null signal points on the 360 degrees transmission of the beacon signal. They needed a rough expected bearing to the beacon so that they could make sure that a reciprocal course to that required was not flown.
    2. The beam did not contain any height information so care to maintain safe terrain avoidance was needed.
    3. When D/F in use the receiver could not be used to receive any other signal via aircraft fixed HF aerial or MF trailing aerial. Also no "tune" of T1154 transmitter could be done so no ability to transmit on any frequency that had not been preset on the click stop knobs.

    Ross
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    Ross’ explanation is how it should have worked. And on most occasions that was how it did work! But I think another ‘cautionary note’ might be added to Ross’ list. A lot of successful radio propagation/reception at these frequencies depends upon whether the F1, F2, and/or (sporadic) E layers are behaving themselves. These, in turn, are heavily dependent upon day/night, summer/winter, St Elmo’s Fire, and sunspot activity, etc, etc.
    Sod’s Law of Natural Cussedness dictates that every time you practiced taking, naving, or flying, by D/F bearings it was perfect. But (perhaps returning from ops with damaged aircraft/crew) when you really needed that bearing, the above would militate against you. T’was always thus in the arcane world of the “wiggly amps”.
    HTH
    Peter Davies
    Last edited by Resmoroh; 4th October 2016 at 12:36. Reason: QSD
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    Hi Marcel and Ross,

    One other thing the w/Op needed to be careful of was flying the reciprocal. The 'R.R.R' rule applied: the W/Op read off the bearing to the signal on the LOOP scale, He then Reduced the reading of the LOOP scale (eg wound the loop aerial from 270 degrees down to 250 degrees). If the needles moved to the Right, the sense was Right. If the needles moved to the left, he would rotate the loop aerial through 180 degrees before using the bearing.

    The whole M/F D/F and H/F D/F organisation reached a peak in 1942 when under 'average' conditions each bomber typically called for around four fixes on an operation. The usual sequence was for an aircraft to obtain 2 or 3 M/F fixes over the North Sea, then to switch to the home station H/F D/F for final homing.

    By mid-1942, the Command was growing too fast for the organisation to keep up. However, GEE was also coming in, which largely replaced the fix/homing requirement. The M/F D/F sections continued after that primarily because they were an important part of emergency ASR procedures, whilst H/F continued primarily for short range voice traffic during landing procedures and for the Darky organisation.

    Bomber Command also used M/F Beacons, and could broadcast details during an operation to allow crews to use German beacons over the continent (with the risk of deception). Broadcasts were required because German codes would have to be broken for the beacons in operation on any given night. Each side worked hard to jam the opposition's M/F beacons, so much so that the system became virtually unusable for RAF and GAF alike. Bomber Command stopped trying to use and/or jam German M/F beacons once GEE was established.

    The last of the non-radar aids to navigation was the Jay Beam system, which was originally introduced to mask the adoption of GEE. Jay Beams worked on the SBA system (so didn't use the D/F indicator) and provided 'homing lines' across the North Sea. Again, all but two were discontinued in late 1943 due to the availability of GEE.

    Cheers,

    Richard
    Last edited by Richard; 4th October 2016 at 12:40.

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