PPRuNe Forums What is a rhumb line?

 Professional Pilot Training (includes ground studies) A forum for those on the steep path to that coveted professional licence. Whether studying for the written exams, training for the flight tests or building experience here's where you can hang out.

 29th Jul 2012, 10:35 #1 (permalink) Join Date: Jun 2010 Location: Belfast Age: 23 Posts: 98 I thought this website was about helping people out when your stuck? I dont understand it i have tried to, if you don't want to help why post i don't want to start an argument
 29th Jul 2012, 10:49 #2 (permalink) Join Date: Aug 2009 Location: Bangkok Age: 32 Posts: 198 The use of English on this site is absolutely appalling.
 29th Jul 2012, 10:51 #3 (permalink) Join Date: Jun 2010 Location: Belfast Age: 23 Posts: 98 What is a rhumb line? Definition- Rhumb lines are tracks with a constant track direction between two points on a sphere and therefore must be a longer distance than a great circle track Why are rhumb lines a constant track direction and great circles always changing direction? and why is a rhumb track a greater distance than a great circle?
 29th Jul 2012, 10:55 #4 (permalink) Join Date: Sep 2010 Location: England Posts: 1,135 Do you always get other people to do your homework for you?
 29th Jul 2012, 16:35 #5 (permalink) Join Date: Nov 2000 Location: Wycombe Air Park Age: 61 Posts: 2,254 "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.
 29th Jul 2012, 16:36 #6 (permalink) Join Date: Jun 2010 Location: Belfast Age: 23 Posts: 98 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
 29th Jul 2012, 20:27 #7 (permalink) Join Date: Sep 2006 Location: Delsey Posts: 527 You do read manuals and ATPL notes, don't you? Aerodynamics Aerodynamics What is a great circle track? http://www.pprune.org/professional-p...1727-5-rs.html Speed stability differences between a jet aircraft and a propeller-driven aircraft And you have a CPL? 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'. Look here http://www.freelancepilot.nl/ATPL%20summary.pdf You say you are reading Ace the Tech pilot int. on another thread you started. Be very wary of that book, there are many inaccuracies. I am gobsmacked at the lack of knowledge displayed here, however. Last edited by 500 above; 31st Jul 2012 at 05:51.
29th Jul 2012, 20:59   #8 (permalink)

Join Date: Apr 2012
Location: UK
Posts: 11
Quote:
 I am gobsmacked at the lack of knowledge displayed here, however.
Well what do u expect when students memorize the question bank. I have done my ATPLs and I never learnt the answers. Thus my marks varied from 75% to 98%

I did badly in my class according to the results BUT I am sure that I know more than them!

 29th Jul 2012, 21:05 #9 (permalink) Join Date: Sep 2006 Location: Delsey Posts: 527 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?
 29th Jul 2012, 21:09 #10 (permalink) Join Date: Apr 2012 Location: europe Age: 44 Posts: 40 rhum line?? i scored an average of 80% and failed 2 tests,I was one of the best in my class. now guys score over 90%-100% and don't fail any test. how fair is that?, when you can run android or bristol software, and repeat tests until you get 100%. JAA=lifescrewers !!!! Last edited by a320renewal; 29th Jul 2012 at 21:38.
 30th Jul 2012, 03:34 #11 (permalink) Join Date: Apr 2012 Location: UK Posts: 11 I am the same more or less. Meh such is life
 30th Jul 2012, 04:44 #12 (permalink) Join Date: Nov 2000 Location: Wycombe Air Park Age: 61 Posts: 2,254 When somebody asks you whether the radio altimeter works on QFE or QNH you know it's time to cull the herd.......
 30th Jul 2012, 08:48 #13 (permalink) Join Date: Nov 2005 Location: uk Posts: 115 Convergence 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. It helped me understand it...
 30th Jul 2012, 09:25 #14 (permalink) bristol.gs   Join Date: May 1999 Location: Bristol, England Age: 54 Posts: 1,086 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.
 30th Jul 2012, 09:44 #15 (permalink) Join Date: Jun 2010 Location: Belfast Age: 23 Posts: 98 a320renewal I also learned the ATPL theory, i set my exams back in 2009 as some of the information naturally enough i have forgot and am now trying learn again. Last edited by akafrank07; 30th Jul 2012 at 09:45.
 30th Jul 2012, 09:53 #16 (permalink) Join Date: Jun 2010 Location: Belfast Age: 23 Posts: 98 Alex Whittingham Thanks for the help Alex that explanation is very good and has helped me understand the concept of rhumb line
 30th Jul 2012, 09:57 #17 (permalink) Join Date: Jun 2010 Location: Belfast Age: 23 Posts: 98 SARowl Cheers i have did that, and that cleared things up Last edited by akafrank07; 30th Jul 2012 at 09:57.
 31st Jul 2012, 00:59 #18 (permalink) Join Date: Jul 2012 Location: To the West! Posts: 68 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?' I nearly fell off the the couch laughing. Some things never change. Last edited by bluecode; 31st Jul 2012 at 01:03.
 31st Jul 2012, 07:29 #19 (permalink) Join Date: May 1999 Location: Quite near 'An aerodrome somewhere in England' Posts: 20,216 Average track for a Great Circle between LAX and London Airport is 041°T, whereas the Rhumb Line track is 078°T. Great Circle distance is 4722 nm, whereas the Rhumb Line distance is 11% greater at 5244 nm.
 31st Jul 2012, 08:32 #20 (permalink) bristol.gs   Join Date: May 1999 Location: Bristol, England Age: 54 Posts: 1,086 What do you mean by 'average' great circle track, Beags? Initial gc track is 034°, final gc track is 131°.

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are Off Refbacks are Off Forum Rules

All times are GMT. The time now is 06:00.