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"Why are rhumb lines a constant track direction and great circles always changing direction?"
Because your definition already says it - rhumb lines are lines of constant direction therefore they cut all meridians at the same angle. Try it on your globe - you will see that they spiral towards the Poles. Lines of latitude are also rhumb lines. The Equator is a rhumb line and a Great Circle. All combinations of meridians and anti meridians are Great Circles.
Look at your globe from the top and try to go between two points using a constant direction and going directly via Great Circle - you will see the rhumb line is longer. However, on shorter journeys it is more convenient to fly one heading and accept the longer distance travelled.
Hi cityflyer i suppose your right i guess i thought it could just be easily explained, what it is i dont understand is; Ok a rhumb line track has a constant direction, between 2 points on a sphere? would i be right in saying that rhumb lines can only be done over short distance, because as say LA to London would not be possible with a constant track? (as that would take you somewhere into greenland as the initial heading is approx NE) Cheers
About akafrank07 Licence Type (eg CPL. Pilots only) CPL/IR Current a/c Type (eg B737. Pilots only) N/A Location Warrenpoint
You appear to be a lazy type without the gumption or drive to self study. Pay for a full ground school course, it's peanuts compared to the 320 rating you will inevitably pay for after asking others on here where to 'buy it'.
This is appalling though. Not knowing what a GC or a RL is, let alone not knowing what an SOP is or compressibility effects... It shows you the system is flawed, if indeed the OP isn't a 12 year old with no more than MSFS time. Which licensing authority issued his CPL I wonder?
1. Go to a good toystore. 2. Buy a reasonable globe (of the Earth that is). 3. Sellotape a piece of string over London. 4. Use the string to find the shortest route to your destination - over the pole to China/Japan is good 5. This is the Great Circle Route. Look how the 'string' is a straight line on the Earth's surface but its bearing changes with regard to the lines of longitute it crosses.
Aircraft used to fly rhumb line tracks in the days before they had global navigation systems like FMS, IRS/INS and GPS linked in to the autopilot. They had to do this because their heading reference was either a DI or a compass or a combination of the two and to fly a great circle track, the shortest route, would require a constantly changing track direction which would be extremely hard to manage manually. You still do this today for shorter legs in light aircraft, you draw a line on the chart and either measure track in the middle or measure it at both ends and take the average. The difference isn't much but by doing that you are flying the rhumb line, which is approximately half way between the initial and final great circle track.
In the old days long tracks were achieved by approximating the great circle track, which in its simplest way involved a rubber band on the globe as described above, then flying a series of rhumb line tracks between waypoints to approximate to the great circle. In the example you quote for LA to London the great circle track would take you near Greenland, and you would fly a series of airways, direct tracks and NAT tracks to approximate to it, either flying rhumb lines with old navigation kit or great circles with modern kit. The single rhumb line track would go much further south, and never go north of London's latitude, but you would never fly a single rhumb line track of that length, the route has always, even in the earliest days of navigation, been broken down into a series of shorter tracks from waypoint to waypoint so that you can assess your progress and tracking.
A few years ago. I was watching the TV series Hornblower. At one point our eponymous hero, Hornblower was up for promotion. He found himself up for the board of the admiralty hoping for promotion to Lieutenant. Remember this was set at the beginning of the nineteenth century.
I laughed and turned to my girlfriend of the time and said. I'll bet they'll ask similar questions they ask us pilots. The first question: 'What's a Rhumb line?'