iFly GPS Forum

If you have played with the measuring tool any, you have discovered, I'm sure, its great value in determining distances on charts. I use it all the time while planning fuel stops on long X-countries. Another great feather in this tool is its mag heading. However, I think it is important that ever one understands exactly what this information (mag heading) means. The value in this text box is not the initial heading for the course line shown. Let me explain with an example:

On your iFly device, make a flight plan going from Sacramento (SMF) to Washington DC (DCA). Now, using the measuring tool, measure the distance from SMF to DCA. Distance is 2063nm and the heading is 90 degrees. (Brian is going to fix the 180 degrees difference.) But now go to the flight planning page and you will see that the mag heading is 62 degrees! What??? Well, tap 'Done' and go back to the chart. Now zoom all the way out and you will see what is going on. The flight plan course line is the Great Circle route. The measuring tool line is the Rhumb line. This is great for pilots like me who's airplane autopilot is tied to its DG. This means that I can set my heading to the Rhumb line (not counting wind drift) and then not have to be constantly adjusting the heading as I do when flying the Great Circle.

Some notes: (1) In North America the difference between the Great Circle and the Rhunb line is greatest when flying East or West. i.e. There is no difference when flying North or South. (2) Flying the Rhumb line will be a few miles longer than the Great Circle. But very few - From SMF to DCA the G.C. distance is 2063nm. The Rhumb line distance is 2084nm. Brian very wisely chose to display the G.C. distance on the measuring tool. Otherwise, a straight line on the chart would show to be longer than a curved line. That would confuse most of pilots. I don't know why Rhumb line navigation isn't taught in aviation classes.

Sorry for the dissertation. It is raining/snowing today and I can't fly nor work on my homebuilt.

Jim Williams

Okay, I will bite. How do I use the measuring tool? I have been using my 740 for a bit now, and I know it has this feature... but how?

Matt

Matt - On tablets you can also get the measuring tool by placing two fingers on the screen. After the measuring line pops up, you can move each end with one finger to more precisely position the end points. I think this should work on the 740 also. - Jim Williams