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Help On Calculating Course  
User currently offlinewardialer From United States of America, joined Sep 2001, 1182 posts, RR: 0
Posted (9 months 4 days 5 hours ago) and read 2524 times:

I have this Flight Planning software which is not too accurate and I only use it to plan my navigations.
But one issue is this.

When planning my route, for example, the Course on the GPS device shows as 72.5 True along with the distance and so on. Thats fine.
But, the software does not show it as exactly being 72.5.

So in this case, what should I enter as course? 72 or 73?

Or for example, if the course shows as 72.6, then how should I round it off?
Would I enter it as 73 or 72?

Please help.

12 replies: All unread, jump to last
 
User currently offlineLONGisland89 From United States of America, joined Jan 2006, 709 posts, RR: 0
Reply 1, posted (9 months 4 days 4 hours ago) and read 2499 times:

To answer your example, If it was 72.6, I would round to 73. Rule of thumb when I was in school was to round up anything .5 or higher. Besides, it really doesn't matter too much. You have to travel over 100nm to be 1nm off course if you are .5 degrees off the whole time.

User currently offlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4183 posts, RR: 37
Reply 2, posted (9 months 4 days 4 hours ago) and read 2497 times:

Try each one. Whichever is closer, use that one.


Chicks dig winglets.
User currently offlinewardialer From United States of America, joined Sep 2001, 1182 posts, RR: 0
Reply 3, posted (9 months 4 days 4 hours ago) and read 2493 times:

So what if it shows 90.5?
Should I use 90 or 91?

Or what if it shows 90.4, then should I use 90 instead?


User currently offlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4183 posts, RR: 37
Reply 4, posted (9 months 4 days 4 hours ago) and read 2488 times:

.4 is closer to 0, so you round down. .5 traditionally goes to round up to the next whole even though its exactly in the middle.

I would just input in each whole number, look at the result, and see which is actually closer.



Chicks dig winglets.
User currently offlinewardialer From United States of America, joined Sep 2001, 1182 posts, RR: 0
Reply 5, posted (9 months 4 days 3 hours ago) and read 2484 times:

Well heres the issue. Software tool uses a Tiros 500-Meter map. So its not like Google Earth were I can zoom-in entirely to the exact point of destination.

So with this, I cannot zoom-in any closer.

So just to verify, if my GPS output planning route was shown as 90.5 T, then I would enter 91?

[Edited 2013-07-19 23:00:58]

User currently offlineStarlionblue From Greenland, joined Feb 2004, 16908 posts, RR: 67
Reply 6, posted (9 months 4 days 3 hours ago) and read 2469 times:

Quoting wardialer (Reply 5):
So just to verify, if my GPS output planning route was shown as 90.5 T, then I would enter 91?

Yes you would. As mentioned above though, half a degree is well within any en route navigation standard. Half a degree is 1 mile off in 120.

AFAIK you don't even need to be accurate to half a degree on a precision approach.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinewardialer From United States of America, joined Sep 2001, 1182 posts, RR: 0
Reply 7, posted (9 months 4 days 2 hours ago) and read 2462 times:

I guess and would think that it also depends on the type of mapping tool.
For example as mentioned, mapping tool uses only a zooming of max. 500 meter Tiros.
Google Earth uses way more zooming down to the street level.

So, my point is this:

If one would need to use pin-point accuracy like for example 90.555 even, then I would guess a 500 meter map zoom would not be suited for this type of accuracy. So then it would be best to use Google Earth then.

But this is an example though.

But this mapping tool of mine does not let me enter .5 or even .555
Only whole numbers.


User currently offlinezeke From Hong Kong, joined Dec 2006, 8643 posts, RR: 75
Reply 8, posted (9 months 4 days 2 hours ago) and read 2458 times:

Quoting wardialer (Thread starter):

If you are using it to plan your VFR navigation exercises, forget it, just use the closest degree, and turn your GPS/VOR off.

Learn to navigate by looking out the window for your track and other traffic. Look for features a long way in front of the aircraft. Learn how to correct your track by visually being able to tell if you are off track, and then perform a heading correction.

Light aircraft are incapable of being flown to the accuracy of 1 degree by following the instruments alone, planned speeds are normally out by a fraction, winds are out, instrument errors etc.

Wanting to achieve better than 500 m accuracy in a light aircraft is setting an unrealistic goal for yourself.



We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
User currently offline26point2 From United States of America, joined Mar 2010, 786 posts, RR: 0
Reply 9, posted (9 months 3 days 19 hours ago) and read 2385 times:

Oh my....are you using this to plan an actual flight or is this some sort of FlightSim exercise?

What happened to the tried-and-true method of using a map? Why does it matter if you're 1/2 mile of course? Will you then be lost?

Planning software is nice and all but if you can't navigate VFR using pilotage and a map you are doomed.

To add....GPS has evolved during my flying career. 20 years ago we used VLF Omega to find Hawai'i...that's 2200NM without a nav aid. When the OGG VOR came to life after 5 hours we could have been 5 miles off course but we still managed to find the islands. It wasn't a miracle. My advice...put down your gadgets and look out the window.

[Edited 2013-07-20 07:37:18]

User currently offlinevikkyvik From United States of America, joined Jul 2003, 9400 posts, RR: 27
Reply 10, posted (9 months 3 days 4 hours ago) and read 2240 times:
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Quoting wardialer (Reply 7):
So then it would be best to use Google Earth then.

I'm no pilot, but do you know what the positional error tolerance in Google Earth is?

Cause I sure don't.



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offlineskyhawkmatthew From Australia, joined Oct 2005, 135 posts, RR: 0
Reply 11, posted (9 months 1 day 1 hour ago) and read 2085 times:

Just round it to the nearest degree. It won't make a jot of difference in the air. Plus, you still need to apply the magnetic variation and that is never going to be a whole number either.

Being one or two degrees out will have absolutely no effect on the outcome of your navex.



Qantas - The Spirit of Australia.
User currently onlineSAAFNAV From South Africa, joined Mar 2010, 254 posts, RR: 0
Reply 12, posted (9 months 20 hours ago) and read 2052 times:

Quoting wardialer (Thread starter):

Or for example, if the course shows as 72.6, then how should I round it off?
Would I enter it as 73 or 72?
Quoting LONGisland89 (Reply 1):
So what if it shows 90.5?
Should I use 90 or 91?
Or what if it shows 90.4, then should I use 90 instead?

I'm sorry to be so blunt, but if you struggle to round of 2-digit numbers while on the ground, you should maybe consider another hobby.

If, I hope, you ask for perfection's sake, ask yourself, in how many instances in daily life do you need to use such perfect values and not round off? I can't really think of anything where it makes any noticeable difference.

Quoting LONGisland89 (Reply 1):
To answer your example, If it was 72.6, I would round to 73. Rule of thumb when I was in school was to round up anything .5 or higher. Besides, it really doesn't matter too much. You have to travel over 100nm to be 1nm off course if you are .5 degrees off the whole time.

As said above. Anything below .5, round down. .5 and up, round up.
Also, with the 1-in-60 rule, if you were 1° off course, you will be 1nm off track after 60nm of travel. If you are not able to distinguish any ground feature at 1nm, it means either you are not reading the map correctly, or that you are in inadvertent IMC. Both of which presents way bigger problems than the 1nm off course.

The point of dead-reckoning/map reading is to actually allow yourself to drift off course, pinpoint yourself, calculate your track error, get back to track, and then also be able to calculate the wind to keep you on track until the next major wind change.

There will always be a slight difference between different methods of planning. Even if you do everything on printed maps, slight variations, accuracy of your own plotting or the printers would induce errors.
When you work on a Lambert's Conical Projection Map, you should draw the track and measure the course about midway. There will be a difference between different points on the map. The exact point you use as your reference will create a difference to what someone else will measure.

Some Flight Planning Software systems use scanned copies of topographical maps with a WGS84 overlay. Google Earth can easily display your co-ordinates slightly away from their co-ordinates when you plot positions. The angles and distances will be correct but displaced from yours.

As said above, get your head out of the cockpit, navigate by ground features, and don't worry too much about being exactly overhead the waypoint. Rather get the big picture right, and precision navigation will come later, especially with IF ratings.

Erich



On-board Direction Consultant
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