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    Re: Visiting local museum and CN-items
    From: David Pike
    Date: 2019 Dec 19, 09:15 -0800

    Here are some clearer pictures. https://picclick.com/Calculator-Device-Flight-Computer-Russian-Aviation-Navigator-SLIDE-312540569194.html#&gid=1&pid=1  The velocity triangles left by the previous owner show the method of use similar* to the one I suggested.  The main difference is the ruler means you don’t need to use your imagination to form the triangle.  The disc slides up and down so that some part of the ruler can be over the centre of the disc.  The speed circles can be any of four values.  In the pictures given, there is a choice of four speed ranges.  Because the ruler speed by the centre of the disc is never zero or even end in 0 or 00, you’d have to be good at arithmetic to mark speed vectors directly from the ruler, or you could transfer speeds using dividers. 

    I’m not sure what the little aluminium cursor on the outside of the disc is for; perhaps it’s just a reminder of the track required, wind direction, or heading.  The highest speed range suggests the device in the link above was being produced until quite recently. 

    The device in the museum has speeds on the disc suggesting a single speed range, so perhaps it is quite old going back to a time when aircraft didn’t exceed 150 km/hr.  Whilst the ruler is helpful and adds to accuracy, by 1920s standards, you could probably manage without.  It would appear the device has evolved slowly over time like the Dalton.  * I say similar, because the triangle shown could only have been used given TAS, Hdg, Trk & GS to get W/V.  For anything else, you’d apply W/V first at the centre.  To get wind speed, you could probably wiggle everything to lie the wind vector against some part of the ruler.  To get wind direction you’d have to rotate the disc until the wind vector stood up and down parallel to the centre line, so a certain amount of imagination would still be needed.  DaveP


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