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Mark Twain Bombsight

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  • Guest

    #1

    Mark Twain Bombsight

    Can someone check my judgement for me please

    Im trying to build this for a B-25B

    Mid-Atlantic Air Museum - Primitive bombsight used for Doolittle raid | Flickr - Photo Sharing!

    To replace a Norden bombsight.

    The B-25B Doolittle bombers had to remove the Norden bombsights as they did not want to risk them falling into enemy hands. In any case the raids were planned to take place at below 1.500 feet and the Norden was useless below 4,000 feet.

    This bombsight was designed by Captain C Greening. This was called the Mark Twain as Twain spent most of his adult life in Elmira, NY, where he wrote most of his short stories. This was also the home of the Rand Corp. makers of the Norden Bombsight.

    These sights cost about 20 cents to build.

    (Thought Id add that lovely little snippet)

    Anyway. The picture has no reference points in which to get dimensions from.

    Now Ive judged the washer in the middle to be 1 inch across. On my tiny netbook it measures an actual 5mm. This makes he whole thing 85mm across, or 17 inches.

    From there Ive got the platform as being 17" x 5". The semi circle bit will be 7" x 6" with the rounded bit starting about 3" up.

    The crosshairs are about 2" x 1"

    Scaled down 1/48 this makes it as follows

    Platform - 9mm x 2.6mm

    Back Plate - 3.7mm x abt 3mm

    I think I can build this from various bits of plastic I have. It wont need to be exact as its going in the nose to be covered by a glass canopy but Id like to have a go.

    Do the measurements feel right?
  • Guest

    #2
    Based on the glass shelf most likely being 1/4 plate, I would agree that the washer is 1" diameter. From this, on my screen it measures exactly 1/2' using my software on screen rulers so giving me a 50% image size. from that, the back plate, which to me looks taller than it is wide actually measures at 7" wide by 6 3/4" high. By rotating the image to get the 'table' horizontal, the measured distance between the tip of the sighting point back to the top of the 'V' notch is 10.625 (times two as it is 50% )making it 21 1/4" long. The width of the table is harder to calculate due to perspective and my total ignorance of geometry but I would think it is around 5 or 6 inches

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    • Guest

      #3
      Originally posted by \
      Based on the glass shelf most likely being 1/4 plate, I would agree that the washer is 1" diameter. From this, on my screen it measures exactly 1/2' using my software on screen rulers so giving me a 50% image size. from that, the back plate, which to me looks taller than it is wide actually measures at 7" wide by 6 3/4" high. By rotating the image to get the 'table' horizontal, the measured distance between the tip of the sighting point back to the top of the 'V' notch is 10.625 (times two as it is 50% )making it 21 1/4" long. The width of the table is harder to calculate due to perspective and my total ignorance of geometry but I would think it is around 5 or 6 inches
      Awesome stuff, cheers. Now all I have to do is build it. OMG - What have I started!!!!

      Comment

      • Guest

        #4
        To get it nice and thin, try cutting a Coke (other types of carbonated soft drinks are available) can and using the thin aluminium sheet, easy to work with (cuts with nail scissors and bends easily) and not over thick for scale. Glue with thin superglue.

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