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Thread: QDM question

  1. #1
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    Default QDM question

    Hi all,

    I would like to ask for help with radio telegraphy question - I have following record for one Wellington returning to Honington:

    QDM
    Abing
    QTG
    225
    02.50

    QDM
    Abing
    090
    03.01

    As far as I know:
    QDM = what is the magnetic course to steer with zero wind to reach you (from plane)
    QTG = Send call followed by dash so I may take bearing (from ground)

    So I suppose that at 02.50 plane sent QDM do D/F station in Abington which asked QTG and finally sent course 225.
    At 03.01 plane asked again QDM and got course 90.

    Is my deduction correct?

    It seems to me quite strange that the plane was wandering so far inland and finally landed at 04.40 in Grantham instead of Honington!

    Was it common of just an example of poor navigator skill?

    Any comments appreciated.

    TIA

    Pavel
    Czechoslovak Airmen in the RAF 1940-1945
    http://cz-raf.webnode.cz

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    Default

    Pavel, Hi,
    What date was this? The weather may have had some bearing (no pun intended!) on the location of this a/c.
    Assuming that the ground D/F station is the Abington near Northampton then the first QDM (225) would place the a/c southwest of the D/F station. The next (090) would place the a/c to the east of the D/F station. But in only 10 mins flying time the a/c must have been very close to the D/F station - and on a northeasterly(?) course. This would take it nearer Peterborough/Grantham than Honington. If we know the airspeed of the a/c we can work out how long the flight track is from a QDM of 225 to a QDM of 090 and get fairly near an estimate of the ground track. Or have I got my QDMs the wrong way round? We need a Coastal Command Signaller to advise!
    Incidentally, QDM on its own is a statement. The 'question', in Morse procedures, would be QDM IMI. The IMI is the question mark!
    HTH
    Peter Davies
    Meteorology is a science; good meteorology is an art!
    We might not know - but we might know who does!

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    Default

    Hi Peter,
    thanks for comments.
    It was on 1st/2nd July 1941 when returning from Brest.
    It seems to me you are right. My opinion is that they by mistake probably flew over Coventry too where they got into balloon barrage.
    Unfortunately no other info including the speed is not recorded as the plane not landed at home base.
    BTW Wellington maximum speed was 378 km/h or if you want 235 mph, so they were flying something less.

    Pavel
    Czechoslovak Airmen in the RAF 1940-1945
    http://cz-raf.webnode.cz

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    I think Peter is right. From the few times I received bearings from a ground station in flight (done by radar these days), a sudden and large change like that indicates you are very close to the station. It can take you a few seconds to figure this out, and my first reaction was to think that something must be terribly wrong.

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    Default

    Pavel/Bill,
    There is something not quite right here!
    Let us take this one step at a time and use reason and logical argument.
    No problem with the weather except, possibly, a bit of mist/fog at the Base airfields.
    First, is the ground D/F station the Abington slightly to the northeast of Northampton? If so, then therefore (3-dots!) -
    Pavel says a QDM at 0250 of 225.
    Pavel says a QDM at 0301 of 090.
    Let us assume that this Wimpy was doing 200 mph at this point (you can insert whatever units you like, but I don’t think it will affect the final argument!).
    At 200 mph this equates to 3.33 miles per minute. Given 11 minutes from QDM 225 to QDM 090 gives us a track length (between QDMs) of 36.66 statute miles.
    If the a/c was at 225 from the D/F station at 0250, and if it was at 090 at 0301 then it must have been somewhere over the Oxford area at 0250, and directly east of Abington (only just) at 0301. One can play with 36.66 track lengths on Google Earth such that they fit reasonably well.
    This means that the a/c was on a northeasterly course as it passed Abington.
    If it did not land until 0440 then 1hr 39 mins elapsed from being “abeam Abington” to its supposed ATA. If it had continued on the same (possible) course after being abeam Abington then it would have come down somewhere in the North Sea!! Don't fit!
    We must check Time Zones.
    A northeasterly course would have taken it nowhere near Honington.
    Just where the possible Coventry balloon-barrage fits in I can't begin to work out! Coventry is 30 statute miles northwest of Northampton at - disturbingly - about 90 degrees to our supposed northeasterly track!!!
    As I understand it 0440 GMT was 7 minutes before sunrise on 1/2 Jul 42. Again, need to check Times Zones.
    Request immediate arrival of (a) hairy old Navigator, and (b) hairy old BC Brass-Pounder.
    HTH (but I doubt if it will!!).
    This has now gone beyond my expertise! HELP!!!!
    Peter Davies
    Last edited by Resmoroh; 15th March 2009 at 19:15.
    Meteorology is a science; good meteorology is an art!
    We might not know - but we might know who does!

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    Hi Peter,

    many thanks for your interest in this problem!
    To be honest my navigation skill is limited to map reading so I really appreciate your help.

    As the plane landed not on home base, the landing time 04.40 was written by hnad into ORB later, also one book states the landing was at 04.28.

    Anyway I suppose that the navigator was totally lost and maybe he also do not trust to obtained courses so he was directing the Wellington all ober the east and central England...

    I will try to check all document once more if there is no more information which may help us to solve the little mystery.

    Pavel
    Czechoslovak Airmen in the RAF 1940-1945
    http://cz-raf.webnode.cz

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    Peter, I think your argument falls down at the point "continued on the same (possible) course". I think the nav realized he was somewhat confused, that is why he was asking for 2 DFs in a short time. Maybe he sorted it out from those (to some extent anyway), and would have altered course shortly after.

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    Bill (and for Pavel)
    I think you mistake me. I did not mean to give the impression that they had just flogged on on that course, but to indicate that 'Grantham' (and I assume that means RAF Spitalgate?) is only 50 miles from Abington (Northampton). They might have expected to cover that distance in around 15 minutes. We still have 1hr 29mins of airborne time to account for!!! At the end of a night bombing mission they must have been fairly short of "gravy". What were they doing? Blundering about in the dark until dawn when they could all map-read to find out where they were?
    Interesting little problem!!
    HTH
    Peter Davies
    Meteorology is a science; good meteorology is an art!
    We might not know - but we might know who does!

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