|
2high2fastagain
|
|
|
Group: Forum Members
Posts: 43,
Visits: 98
|
This is a really interesting problem. Timothy's map intrigued me and so I assumed I could buy a monster ferry tank and have a go at that Atlantic trip. The straight line in the pic below is the Skydemon 'direct' routing from East Midlands to Bangor Maine which looks like a rhumb line. The curved line is the GC route, crudely copied from Google Earth a few degrees latitude at a time. The GC distance is 2,617nm and the rhumb line is 2,707nm. Fascinatingly, the two lines are more than 5 degrees apart in the middle. Is that 300nm? But the distance flown by the rhumb line is only 3.04% longer. I think that to all practical purposes, the rhumb line is fine and if you ever attempted the Atlantic crossing in a single, it could be from airport to airport anyway.
|
|
|
|
|
Timothy
|
|
|
Group: Forum Members
Posts: 23,
Visits: 150
|
if you ever attempted the Atlantic crossing in a single, it could be from airport to airport anyway. Eh? Run that past me again? 
But actually distance flown isn't the issue.
If you flew across the Atlantic (and I seriously considered Iqaluit - Shannon, which I could just make, with my 600 litre ferry tank) you would definitely fly using the plumbed in GPSs. That means that if you had your SD on your lap, you would be, by your calculation, 300nm off track. Not a great back up if the electrics failed!
|
|
|
|
|
ckurz7000
|
|
|
Group: Forum Members
Posts: 538,
Visits: 2.2K
|
Excuse me but this discussion is largely theoretical.
1) In 99.9% the difference between rhumb line and GC track is not an issue.
2) In those cases where it might be you can always put intermediate points on the GC track and approximate the GC course by several rhumb line legs.
So we are talking about the 0.1% cases for which the work-around solution is impractical.
-- Chris.
|
|
|
|
|
Timothy
|
|
|
Group: Forum Members
Posts: 23,
Visits: 150
|
I agree it is theoretical. It's just a question of industry standard, how aeroplanes fly, how radio aids propagate and how all aviation GPS' are designed. For example, SD could never be RNP certified, for exactly the reason 2high2fastagain gives.
There are more important things for Tim to focus on, such as getting all the airway centrelines in the system, even 3D SIDs and STARs, but that doesn't mean that it shouldn't be mentioned, just to sit on the back burner and simmer.
|
|
|
|
|
2high2fastagain
|
|
|
Group: Forum Members
Posts: 43,
Visits: 98
|
Timothy - LOL - I'm sure you know what I mean! Try 'short hops from airport to airport anyway' instead. In terms of that big crossing, I'd concede it would cost a few bob to hire the two Queen Elizabeth aircraft carriers (when they are finished) and to strategically position them as refueling stations for that weekend trip to Bangor Maine (and we'd be the only aircraft on them LOL) Yes, this is a theoretical thread and I completely agree there are more important things for Tim D to do, but nonetheless it's still interesting. The thread drew my attention as I would like to attempt the Atlantic Crossing one day (perhaps to fly into Oshkosh). Timothy, I'd go via Iqaluit as well with a thumping great ferry tank in the C182, though my routing would be Wick, Reykjavik (BIRK), Kulusuk, SondreStrom, Iqaluit and then down through Canada. Having worked in Greenland and seen the spectacularly rapid weather changes, my criteria would be that I would like to have enough fuel to go back to where I came from or even further back if the fog rolled in (I'm a project manager not an adventurer). But that discussion is one for another forum.
In terms of constructive advice for Tim D. Perhaps if someone puts in a very very very long track, a gentle warning that you are getting a rhumb line would be an ample response from Skydemon, but I wouldn't stick it at the top of any lists.
|
|
|
|
|
Timothy
|
|
|
Group: Forum Members
Posts: 23,
Visits: 150
|
2high2fastagain (07/11/2012)
I'm sure you know what I mean! Try 'short hops from airport to airport anyway' instead.I think you are missing my point. How many airports are there on either of the tracks you have drawn?
My longest single flight not passing a single airport was 1385nm, though it has to be said that the GC coincided with the rhumb on that one 
|
|
|
|
|
2high2fastagain
|
|
|
Group: Forum Members
Posts: 43,
Visits: 98
|
None of course, which is why I at least, would take short hops across the northern route in a single.
|
|
|
|
|
Richard747
|
|
|
Group: Forum Members
Posts: 37,
Visits: 115
|
I would like an option for SD to display the GC, the Plog to show Initial True/Mag Track and a changing en-route track required to follow the GC. Thanks.
|
|
|
|
|
Tim Dawson
|
|
|
Group: Forum Members
Posts: 8K,
Visits: 9.1K
|
I've been toying with the idea of showing the GC from takeoff to landing if (for example) its length deviates from the rhumb line length by a certain amount. Would that be useful?
|
|
|
|
|
Richard747
|
|
|
Group: Forum Members
Posts: 37,
Visits: 115
|
Yes, that would be a step in the right direction - thanks.
|
|
|
|