NavList:

Tony Oz you ask: How does this minimum speed depend on the circumstances?

Tony

The only way you can keep the Sun’s azimuth constant is if your local time remains constant.  I.e. the westerly component of your groundspeed is 15°longitude/hr.  To have a pre-flight lunch in UK and a post-flight lunch in Canada (on the same day), you need a very fast aeroplane.  450kts groundspeed will do it at 60°N.  However, don’t forget you’re invariably facing a headwind, so you'll probably need more than 450kts airspeed.  Above 60°N you would not need to travel quite so fast, but you’d soon have to change your navigation technique to allow for the convergence of the meridians.  So basically, as Gary says, "Forget it".  With the Vulcan, we never set out to achieve this situation on purpose, it's just that occasionally you'd pre-calculate a sight and you'd suddenly think "Good gracious.  I must have made a mistake.  I've ended up with the same Hc and Azimuth as last time". As far as I remember, we used to track up to Prestwick; then around 315°T to around 60°N; then West to just beyond Greenland; then around 235°T to Goose Bay.  It sounds a crazy route until you look at the great circle.  DaveP