On 3.4.17 22:32, Martin Gregorie wrote:
> On Mon, 03 Apr 2017 19:47:12 +0300, Tauno Voipio wrote:
>
>> On 3.4.17 17:29, Martin Gregorie wrote:
>>
>>> Nope - I wouldn't have a clue about my weight and height in Imperial
>>> units, but then NZ went metric before the UK did - and did it faster,
>>> cheaper and with a lot less hassle than happened here. It was quite a
>>> shock to arrive here and have go back to using outdated Imperial units.
>>>
>>> Small side note: actually, I do use some of the old units due to the
>>> pervasive ICAO influence on aviation. As a glider pilot I measure speed
>>> and rate of climb in knots, altitude in both feet and meters and
>>> distance in km (because the Silver, Gold and Diamond badges measure
>>> distance in km and height in meters).
>>
>> In aviation, there is some sense in distances in nautical miles (1 arc
>> minute on great circle) and speeds in knots.
>>
>> Altitudes are measured in feet. The explanation was that on the
>> altimeter 1000 m / revolution was too coarse and 100 m / revolution too
>> fast.
>>
>> Vertical speeds are measured in feet/minute.
>>
> I know that are - in powered aircraft, but the variometers in UK gliders
> are always calibrated in knots because it simplifies calculation:
> dividing sinking speed by airspeed (ASIs are also calibrated in knots)
> gives glide ratio without needing conversion factors - something you need
> to know when calculating a final glide home.
>
> By contrast, all European gliders are metric - rates of climb and height
> in metres, speed in km/h, distances in km, which makes the glide ratio
> calculation a bit harder.
>
> OTOH all European powered civil aircraft use nautical miles, feet and
> knots in conformity with ICAO conventions.
>
>> As a born metric system user, I see aviation as a huge mess of all kinds
>> of units, especially as American made aircraft have the manuals in
>> inches and pounds.
>>
> Yes, you're right, but it can get even worse, with older American
> aircraft often have airspeeds measured in miles per hour rather than
> knots.
>
> I think the ICAO approved units is a left-over from the aftermath of WW2.
> The ICAO was set up in 1944 with 52 countries signing the convention, so
> my guess is that the use of nautical miles, knots, feet and pressures
> stated as mm of mercury rather than bars dates from about then and which
> countries had operating civil airlines at the time, and so, with air
> traffic control needing the use a single system worldwide and the
> immediate post war dominance of US and British civil aircraft makers that
> seemed like the most sensible approach. And, once set, why change? Look
> up the "Gimli Glider" incident to see the problems you can get from
> changing measurement units!


Right. The point with the altimeter scale is moot, as current
IFR aircraft are quickly having glass cockpits with band-style
altimeter and airspeed indicators.

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-TV (CPL(A), ME IR)

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