Hi ChristiaanJ,
You are absolutely correct, that's the reason why I stated no correction for longitude when flying northbound or southbound.
Made my life easy...
You can also view it as follows, but the calculation is more approximate than plotting a position with GPS: As you mentioned, we'll take the speed of earth rotation over the equator as an example, since we all know how to calculate the difference for other latitudes. Take 1000 MPH, that's about 14.5 NM per minute. Then take your own speed and do the same, eg. 0.8M is roughly 8 NM per minute( let's keep it real, 0.1M difference gives us something like 10seconds difference over a mile) remember, this is only if you fly due east/west, otherwise you have to correct by the cosine of the angle as well to get you speed in relation to a meridian (eg. fly Hdg 150 is 60 degrees off the 090, then it's 8(NM/min)xcos60=4). Pick a point far enough so you know the sun at that point has not risen yet and find the rising time from the almanach, then plot what was you position at the same time. Add up or subtract (depending if you fly east or west) the calculated speed in NM/min (like a collision course or take over from 2 airplanes, for example flying due east will give us 14.5+8=22.5NM/min. You can deduct at what time you will reach the horizon together, we will have to apply the previous method to correct for altitude.
This becomes waaayyy too inaccurate in the end and waaaayy too little time to work out if you realised you wanted to know the time only a few minutes before the sun rises. But I guess on long haul, with a nice big calculator and a lot of willpower...
In the end, you divide the inaccurate by the square root of roughly, and we should get there in no time...
Any other ideas, maybe more practical?
Cheers,
Flex