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Thread: Use of Gee

  1. #1
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    Default Use of Gee

    I would like to understand Gee in "layman's terms" and I wondered if anyone could provide me with a walkthrough of how a navigator would utilise it.

    Thinking aloud....

    Did he have to manually send a signal (or were the signals constant)?
    If he did have to manually send a signal, did he have to send two, one to each ground station?
    What information did he receive in the return signal?
    What did he have to do with that information to establish the aircraft's position?
    Were the same two ground stations always used or did these vary?
    Did different Gee maps have to be used depending on which stations were in use?

    My objective is to have a paragraph or two which assumes I am a navigator explaining how he utilised Gee (a kind of "Gee for Dummies").

    Any help, even if it is a link to an article which achieves my objective, would be much appreciated.

    Regards

    Pete
    Main areas of research:

    - CA Butler and the loss of Lancaster ME334 (http://rafww2butler.wordpress.com/ )
    - Aircrew Training (Basic / Trade / Operational / Continuation / Conversion)
    - The History of No. 35 Squadron (1916 - 1982) (https://35squadron.wordpress.com/)

    [Always looking for copies of original documents / photographs etc relating to these subjects]

  2. #2
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    Pete,
    The Wiki bit (https://en.wikipedia.org/wiki/Gee_%28navigation%29) seems fairly good. Ian The Radar may cavil with some bits - but not, I think, too many!!
    HTH
    Peter Davies
    Meteorology is a science; good meteorology is an art!
    We might not know - but we might know who does!

  3. #3
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    Pete

    My understanding was that GEE in the aircraft was a receive only apparatus. The signals were transmitted by ground stations and triangulated by the set in the aircraft.

    A receiver in the aircraft received signals transmitted by two or three ground stations, which were situated in known locations, one of these stations was the master station and triggered the transmission from the other stations. These pulse signals were displayed on a cathode ray tube in the aircraft. By noting the time that the signals were received and using a set of tables the position could be triangulated and then plotted onto maps held by the navigator which had an overlay of hyperbolic lines.

    I have just found this which might explain it better:

    "Consider two transmitters located some eighty miles apart that alternately transmit pulses spaced exactly one millisecond apart. If the navigator on an aircraft receives those pulses and they are still exactly one millisecond apart, then the aircraft must be the same distance from each transmitter, irrespective of how far the aircraft is away from the transmitter. This can be shown on a chart as a straight line drawn from the centre of a line joining the two transmitters and at at right angles to that adjoining line. Other lines can be dawn on the chart where there is constant time difference between the two received two pulses that may be less or more than one millisecond depending whether the aircraft is nearer to one transmitter rather than the other. However in these cases the lines are no longer straight but are hyperbolic in shape and where the focal points of the two sets of hyperbolic lines are the at transmitters

    If the navigator measures the time delay between these received pulses and refers to the lines drawn on his Gee map which are marked with numbers relating to the delay time, he does at least know he is somewhere along that line.

    Given another pair of transmitters set up at an angle to the first pair, another set of lines are then available and another measurement can be taken. Referring to the two measurements and the two set of lines on the Gee chart, his position will be where the two lines cross.

    In practice there are only three transmitters needed as one, denoted as the A transmitter can be used for both pairs where the other two transmitters are defined as B and C and are given different colours on the Gee chart issued to the navigator. Four pulses are then transmitted in the sequence A, B, A, C, and in order to identify which A pulse is which, the second A pulse is doubled every fourth transmission and is referred to as a ghost pulse." More info can be found here, http://www.pitstonemuseum.co.uk/myweb/gee.htm

    HTH

    Daz

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    Thanks for the feedback. I recognise that it is a complicated subject (and the articles prove how complicated it is!)

    If I try and take it step by step, I will then be able to build up some text which makes some sense to me:

    Before setting off on a sortie, would I need to know what Gee Chain was being utilised (were there different Gee maps depending on the Gee chain being used?)

    Step One: Gee Chains set up in the UK (and on the continent, in the latter years of the war?) sent a constant stream of signals
    Step Two: These signals would appear on my Indicator Unit Type 62A throughout the sortie which looked like this [need to add a diagram of the signal]
    Step Three: When I needed to establish the position of the aircraft (how often would I do this?) I would watch the signals on the unit (for how long?) and it would ..... tell me what?
    Step Four: To interpret the information and mark it on the map (and presumably in the navigation log) I would .....................

    ... still lots of questions, so any further help would be welcome

    Regards

    Pete
    Last edited by PeteT; 18th May 2017 at 13:55.
    Main areas of research:

    - CA Butler and the loss of Lancaster ME334 (http://rafww2butler.wordpress.com/ )
    - Aircrew Training (Basic / Trade / Operational / Continuation / Conversion)
    - The History of No. 35 Squadron (1916 - 1982) (https://35squadron.wordpress.com/)

    [Always looking for copies of original documents / photographs etc relating to these subjects]

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    I am interviewing a 78 Sqn Wireless Operator next week, and although it wouldn't have been his job I'll ask him if he can add anything. He is 97 years young and his memory is as sharp as a razor. His sense of humour is brilliant, last week he was telling me about a recent trip to hospital where the nurse asked him to tell her everything that was wrong with him when he finished she said 'is there anything you haven't got' to which his reply was "yes rigor mortis". Ive also got some Navigator course notes which I'll look through.


    regards
    Daz

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    Thanks Daz; I look forward to hearing his views.

    In the mean time, if anyone can fill in some (or all) of the blanks, I would be most grateful

    Regards

    Pete
    Main areas of research:

    - CA Butler and the loss of Lancaster ME334 (http://rafww2butler.wordpress.com/ )
    - Aircrew Training (Basic / Trade / Operational / Continuation / Conversion)
    - The History of No. 35 Squadron (1916 - 1982) (https://35squadron.wordpress.com/)

    [Always looking for copies of original documents / photographs etc relating to these subjects]

  7. #7
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    Hi Pete,

    There's a good account in ‘Snaith Days’, by Keith Ford, which includes:

    Specialist nav briefing would precede the main briefing and other specialist briefings would follow (Bombing, Flight Engineer and Signals Leaders may hold these). W/Ops would pick up their ‘goodies bags’ from one of the WAAF clerks in the Signals Section (containing flimsies, Q codes, pliers, screwdriver and torch.) Navigators would pick up their nav bags from the Nav Section, containing log sheets (F441), nav tables, flight plans, Dalton computer and all the necessary charts. Their navigation planning meeting would generally last an hour and be led by the Station Navigation Officer or his nominated deputy. The Lat and Long of each turning point would be read out and reference letters allocated to them. Tracks and distances for all leg would be given. The navigators would then draw these in on their charts, possibly in red or blue (out) and green (back). Gee charts would be checked to see which chains could be used and their frequencies noted. Plots would be made for diversion airfields and beacons close to track that could be used for emergency fixes. Unambiguous H2S identification features would be marked and again, allocated reference letters. Window dropping start and finish points were marked. So too were positions for switching Nav lights and IFF on and off, altering VSC on DRC and bomb jettison areas. Potential hazards such as shipping convoys and heavily defended areas were marked up. The navigators would draw up a small plotting chart of turning points, heights to fly, true course, air speed and distance between turning points. They would also draw a table of Adiabatic Lapse Rate variation against ICAN standard to allow more accurate altimeter reading. If there was time before main briefing, the navigators would turn their charts face down and leave the briefing room for a leg stretch, SPs locking and guarding the door.
    Navs could obtain Gee fixes in an arc from UK out to the Elbe, Hanover, Kassel and Mannheim, although jamming could reduce this. The Nav would decide which Gee chain to use, fitting the appropriate RF unit (type 24, 25 or 27) to set the equipment to the correct frequency. Gee worked on a master transmitter and two or three slave stations (ground transmitters were designated Type 7,000 Stations). The Master transmitter sent out a pulsed signal that activated a slave (in sequence e.g. ABACAD). The receiver in the aircraft measured the time difference in the transmissions (microseconds), producing for one slave station a hyperbola showing possible positions that the aircraft could be at for that time difference. The Gee charts showed the hyperbolic curves for the B slave station in red, C in green and D in purple. It could take an average of 4 and a half minutes for the Nav to adjust the signal on the screen, plot the co-ordinates on the Gee chart, note Lat and Long, work the fix on the plotting chart, put in air position and work out wind speed and direction. He would also need to issue a course correction to the pilot if off track.

    When Gee began to be interfered with by jamming, the anti-jamming selector switch would be set to the appropriate position. Under jamming, the green Gee signal ‘stalks’ would be joined by dozens of others, hence the interference was named ‘grass’. If the Nav or B/A could monitor the true stalks closely they could still be differentiated from the spurious signals, but this required constant attention and was easier if the B/A was available to allow the Nav to focus on all his other tasks.
    Worth getting Keith Ford's book as the Gee diagrams are very good. Looking in the Spilsby Operations Log book for e.g. Berlin, 29/30 Dec '43, HQ 5 Group broadcast navigation details for the night ahead at 1300 hrs, which included:

    Target Whitebait Chart Series (11)
    X.F on Eastern Chain
    RF 25/3/1 from Z-90 to Z+120
    There will be transmissions on RF 24/4 merely as a spoof and is not to be used.
    AIR14/499 Navigational Training - Operational Procedures includes the following from an Op Nav procedure published during the Berlin period:

    9. Within GEE range fixes should be taken averaging on the exact minute and at 6 minute or 12 minute intervals over this country and 12 minutes over the early part of the North Sea. These fixes should be used to obtain track and ground speed winds. Towards the end of GEE range fixes should be taken at frequent intervals. Single fixes should not be used [but] by readings taken half a minute before, exactly on, and half a minute after the time required . . . the readings [can be] averaged and the fix plotted. Ground speed checks between thse fixes worked out after GEE has faded will enable the Navigator to select the last reliable GEE fix.

    10. He has now achieved his great object with GEE - a fix as far as possible from base with accurate 'Met' information for the future.

  8. #8
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    Thanks for all the feedback, both here and offline.

    My understanding is now at the point where the navigator receives calculated figures from Gee which he could transfer onto the Gee Chart. If anyone has any examples of the calculated figures and how these related to the chart, then I think I am almost there.

    Regards

    Pete
    Main areas of research:

    - CA Butler and the loss of Lancaster ME334 (http://rafww2butler.wordpress.com/ )
    - Aircrew Training (Basic / Trade / Operational / Continuation / Conversion)
    - The History of No. 35 Squadron (1916 - 1982) (https://35squadron.wordpress.com/)

    [Always looking for copies of original documents / photographs etc relating to these subjects]

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