*So what is the overwhelming reason for Australia to do something different? * * Mike*
A compass needle aligns with the magnetic field lines of the Earth - it does not point necessarily to the North pole. A compass needle requires to be weighted differently in the Northern and Southern hemisphere to counteract the magnetic inclination. That's why we have "Northern" and "Southern" Hemisphere magnetic compass' in our gliders. A "Northern" hemisphere's compass needle end (or disk vector) would just have the Southern end pointing down until it touches its casing - it won't work! However, ASI's will still work in the "Northern" and "Southern" hemisphere. The influences are more subtle. The Winter company builds precision instruments for sailplanes. The number built is rather small compared to car speedometers (just ask Mike how many varios he sells!) Winter would have to built ASI's that spin anti-clock wise but the production run is too small - there a lots more sailplanes in the Northern hemisphere compared to the Southern hemisphere. The requirement to counteract the Coriolis force acting differently here in the Southern hemisphere is overcome by the requirement to extend the ASI's range 20 knots past VNE. Anything is possible - that's why I bought a lottery ticket. I reckon I would look good in a 31! :-) E On Tue, Sep 10, 2013 at 2:39 PM, Mike Borgelt < mborg...@borgeltinstruments.com> wrote: > Here's the relevant part of CS22 regarding airspeed indicators: > > CS 22.1323 Air-speed indicating system > (a) The air-speed indicating system must be > calibrated to indicate true air-speed at sea-level > in standard atmosphere with a maximum pitot- > static error not exceeding ± 8 km/h or ± 5% > whichever is greater, throughout the following > speed range 1·2 VS to VNE, and with wing-flaps > neutral and air brakes closed. > (b) Calibration must be made in flight. > (c) The air-speed indicating system must be suitable for speeds between > VS0 and at least 1·05 times VNE > > So a glider like that ASH31Mi with a Vne of 152KIAS needs an ASI capable > of reading to at least 159.6 KIAS so the standard Winter ASI which reads to > 160 knots would be adequate. > > So what is the overwhelming reason for Australia to do something > different? > > Mike > > > >
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