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I don't mean to be a naysayer, but that doesn't work. I've laid out the 160 bearing line (340 to) LAY separately from both the DME and the NDB at Islay and the lines coincide nearly perfectly and don't come close to intersecting the 167 radial from TIR.

Laying out the same bearing line on the nearby RN NDB produces a line that is visibly non-parallel (slightly more westerly) with the one from LAY. It looks to me as if there is an error (or a radical difference) in the magnetic variation of the two locations LAY and RN.

John

Leg4Waypoint2.jpg

EDIT:

Here's another look...

EDIT EDIT: The choice of 155/335 has nothing to do with the waypoints per se; I just chose it to get the lines from the two VORs to lie close to one another for easy visual comparison. Anyway, this second image makes if clear that the fault lies with the magnetic variation at LAY. It's lying within the triangle formed by the other three and should have a very similar magvar value.

Leg4Waypoint2-002.jpg

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Hi John,  it should look like this.                                                 (I use 100nm radial lines so disregard the extended lines :) )

 

Map.jpg~original

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Oops, your right John, I had to go out and was making the map as fast as I could while my honey pie was giving me the foot tap. :D  The radial lines on the map are correct but I typed in the wrong OB radial for the VOR, it was supposed to be 167* as you pointed out.

 

Try doing it yourself again and zoom into the LAY NDB until all you see is the airport. The DME and NDB should not be touching when you try to use the Show Radial option. Trust me. ;)

 

Believe it or not there is something to see there at the intersecting point that is hard to see on the map.

 

Here's the edited map.

MapA.jpg~original

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This whole thing has got me scratching my head. I'm having a hard time figuring out how people can plot the same radials and bearing lines in Plan-G and get different results.

Is anyone by chance using the Magnetic variation update (a replacement magdec.bgl) by Hervé Sors? That's going to make their radials look different from those with the stock FSX version of the file.

John

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Try doing it yourself again and zoom into the LAY NDB until all you see is the airport. The DME and NDB should not be touching when you try to use the Show Radial option. Trust me.

That's not how it works on my Plan-G map. The DME and the NDB are virtually on top of one another on the map. See image below...

Leg4Waypoint2-003.jpg

Here's the stock airport in ADE - the two navaids are within a few feet of one another. I do note that the navaids are shown in a different location on the field between Plan-G and the FSX version shown in the ADE screenshot.

Leg4Waypoint2-004.jpg

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Before using the Show Radial, hover your cursor over them until the little popup shows the NDB in the box. That will make the show radial option use that signal.

 

From what I have seen so far the radials in PlanG are either not that totally accurate, could be the map or caused by changing zoom level or even screen resolution. Maybe Tim can enlighten us on this phenomenon.

 

When I make my Leg flight plans for MEBAR I also use the QDM to check my ranges from my last waypoint to the next, according to the Event & Flight Briefing distances given. This gives me a general idea of what Andrew is trying to make our flight path look like too.

 

Here is my airport zoomed in all the way.

MapB.jpg~original   

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John,

 

As I am responsible for the mayhem, let me try and explain the possible causes for this situation.  I haven't been able to identify a single cause, therefore, it is highly probable multiple factors are the cause.

 

For convenience, please excuse my use of dot points:

  1. FSX was used for the planning, as FSX is the predominant FS in use;
  2. the planning was done using a default install of FSX data;
  3. the detailed planning was done on a very large scale map (high zoom level) using Plan-G and the "QDM: Range and Bearing" function;
  4. subsequent investigation has revealed a minor variance in plots using the Plan-G "QDM: Range and Bearing" function and "Show Radial" function;
  5. Points 3 and 4 can be influenced by the accuracy of the placing of the mouse pointer when using the two aforementioned functions in Plan-G, this is why a very large scale map was used in the planning;
  6. the waypoints were plotted in reverse during planning;
  7. plotting bearings to two NAVAIDs which are on similar bearings and reciprocals produces a fine error margin which thereby increases the magnitude of any error;
  8. a variation of one degree can represent a large variation in the plotted line on the map and this variation is magnified further in instances from Point 7;
  9. there are variations in NAVAID locations between FS9 and FSX;
  10. there are possible differences in magnetic variation between FS9 and FSX data, notwithstanding any add-ons which users have installed and have introduced further changes; and
  11. possible plotting error due to misreading the bearing TO and bearing FROM instructions.
Having said all that, the accuracy of radio NAV instruments in the aircraft are incapable of the same level of accuracy to which the waypoints were plotted.
 
It is accepted the navigation instructions are challenging and additional information could be provided.  However, an additional point for consideration in flight planning, which I suspect is possibly being overlooked, is the distance for each sub sector, i.e. waypoint to waypoint.  When combined with the bearing information it provides a third element.
 
Finally, as with previous events, there is a theme to the MEBAR 2014 route and certainly by Flight Leg 4 it should be obvious - otherwise they "haven't seen the light".  A little extra research will show the waypoint is the Dubh Artach Lighthouse on Dhu Heartach skerry.
 
Cheers
Andrew
 
P.S.  Brett's plot is the same plot I got during the planning, allowing for some minor variance due to the above noted causes.
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Andrew and Brett,

Thanks for the info. You guys are, of course, correct. Using your latest posts here's what I've come up with....

I guess the biggest part of the problem was using the Plan-G "Show Radial" function instead of the "QDM: Range and Bearing" function. As we're all aware by now, the ISY DME and the LAY NDB are pretty much co-located on the airport at Islay. There seems to be something funky with the ISY DME. By the way, I wasn't using FS9 at all for any of this.

If I suppress the ISY DME by turning off VORs on the map, the "Show Radial" function produces a correct 340 line that passes west of Tiree and does intersect the TIR 167 radial. If I don't suppress ISY, I get a line that is about 6 degrees too far east and which is almost parallel with the TIR 167 radial, so no intersection occurs. The two lines from Islay, one correct and one incorrect, are about six miles apart at Tiree.

Not having the Lat/Long coordinates of the derived waypoint (the lighthouse) and indeed, not even knowing about it, it seemed as if using the "Show Radial" function to lay out lines on the map off LAY and TIR was the easier way to go since that function produces persistent lines on the map and both radials can be drawn and seen simultaneously. Using the "QDM: Range and Bearing" function only gives one line at a time and it's dynamic, i.e. follows the mouse pointer.

Anyway, an unexplained skewing effect of ISY, along with using the "Show Radial" function is the culprit. If the 340 radial is drawn from LAY/ISY with ISY showing, the line produced by the "Show Radial" function is, for reasons I don't understand, about 6 degrees too far east, passing east of Tiree instead of west. Drawing the 340 line with ISY suppressed (VORs off on the map) produces a correct line.

I appreciate the detailed information. There were a few key points in there that finally helped me figure this out even though I still don't understand the skewing effect of ISY on the "Show Radial" function. In the future, I'll turn off co-located Navaids when establishing bearing lines.

Thanks for the lesson.

John

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If I suppress the ISY DME by turning off VORs on the map, the "Show Radial" function produces a correct 340 line that passes west of Tiree and does intersect the TIR 167 radial. If I don't suppress ISY, I get a line that is about 6 degrees too far east and which is almost parallel with the TIR 167 radial, so no intersection occurs. The two lines from Islay, one correct and one incorrect, are about six miles apart at Tiree.

 

John,

 

This point is strange, but I have now successfully replicated this situation.

 

At lower zoom levels, where the NAVAIDs appear co-located / overlayed, using the "Show Radial" function defaults the drawn bearing to the VOR or DME.

 

During planning and when I use the "Show Radial" function, I have zoomed to Zoom Level 17 in Plan-G so both NAVAIDs, LAY NDB and ISY DME, are clearly separated.  I then place the mouse cursor over the centre dot of the LAY NDB and plot the radial using the "Show Radial" function.  For absolute accuracy, I do the same for the TIR VOR.  When I zoom out to a smaller scale view the intersected plot is as I anticipate it to be.

 

From my experience in using Plan-G, especially for planning such events, the accuracy in plotting bearings is in how accurate you position the mouse cursor over the centre dot of the NAVAID and using the largest scale map (Zoom Level 17) for this purpose is best.

 

Cheers

Andrew

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Andrew, did what you said and also unchecked NDB's and got the intersection. Maybe I should have done this on previous legs as I found some of the waypoints strange? Still enjoying the legs could have done without the constant rain leg 3 though, I started to get tunnel vision. Ha Ha!

 

Michael.

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