how to set course correctly in HSI

[whaaw]

Hi again, Whaaw,

 

I'm not sure how to attach a file for you, but I copied the page out of the Pilot's Handbook of Aeronautical Knowledge, FAA-H-8083-25B, that explains/discusses magnetic variation. However, you don't need me to attach since you can go here and find the manual:

 

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/

 

Find the Pilot's Handbook of Aeronautical Knowledge, FAA-H-8083-25B and go to Chapter 8, page 8-24.

 

There's other good stuff there, too, for pilots such as the Instrument Flying Handbook, etc.

 

Hope this was helpful!

 

All my best,

Rob

 

very helpful, thank you!

[Ramsay]

Normally, a positive or negative sign is not given for variation. It's either East or West.

 

+ve variation is East, -ve variation is West. For clarity I used +6° East, the sign comes from the definition of MV

 

MV = True - Magnetic = 126°T - 120°M = +6° for Batumi RWY 13

 

[Ramsay]

now im a bit confused, isnt caucasus -6°?

 

The magnetic variation in the Caucasus map is approx. +6° (East) ...

 

(1) MV = True - Magnetic = 126°T - 120°M = +6° for Batumi RWY 13

 

Many players get confused by the signage of Easterly magnetic variation as, in DCS we often want to convert F10 (True) bearings to Magnetic.

 

Rearranging equation (1) for magnetic bearings ...

 

(2) Magnetic = True - MV = 126°T - (+6°) = 126°T - 6° = 120°M for Batumi RWY 13

 

So although MV in the Caucasus map is +6°, you still subtract it from the F10 (True) bearings to derive the correct Magnetic bearings for ILS, BRC, FB, etc.

 

Because we often subtract these Easterly (positive) variations, it's often assumed the variation is negative, when it's not the case.

 

i watched the grimreapers youtube video for the harrier, and he did ILS landing and did the curse -6° and it was spot on.

 

The maths does not change, subtracting 6° from the F10 (True) bearing, as shown in the Grim Reaper video is the correct procedure to find the equivalent Magnetic bearing.

[RobfromME]

Hi Ramsay,

 

You're quite correct in the concept and the math. But, due to just this confusion, the method I shared and the mnemonic are typically taught to prevent just the confusion that whaaw had. You're absolutely correct, however. It's just that the pilot typically (at least in the old days...) had True heading and the local variation as knowns and had to solve for his magnetic heading which is what was important to him as he didn't have a True north indicator in the cockpit.

Thus, the variation for pilots is most often given as East and West, without a negative. Other disciplines and organizations (NOAA) may use other means as you've shown that are more suited to their needs.

 

The same information, packaged for a different user. I often have to change my "delivery" of information depending on if I'm speaking to a test pilot with an engineering degree or a line pilot. Very different individual methods of thinking, but what I tell the line pilot, the test pilot understands as well for the same reasons.

 

Just wanted to clarify that I wasn't implying your information was inaccurate, only more complicated than what whaaw was looking for based upon his replies.

 

All my best,

Rob

Edited April 23, 2019 by RobfromME

[Backy 51]

The confusion might be resulting from Ramsay's post showing "In the Caucasus map, magnetic variation is approx +6E". Normally, a positive or negative sign is not given for variation. It's either East or West. Notice that he does do the correct thing when finding magnetic, he subtracts the value.

 

Remember the mnemonic "East is least, West is best" when converting TRUE to MAGNETIC. Thus, when going from a True direction to a Magnetic direction, East is subracted and West is added to the true value.

 

If converting from Magnetic to True, the opposite is the case. However, normally we get true from charts and convert, thus using the mnemonic.

Using sectional charts here in the US, you find the true heading using your protractor on the chart, then add or subtract variation per the "East is least, West is best" mnemonic to find the magnetic heading you'll use on your HSI (or whiskey Compass if we don't have an electrical system in our airplane...i.e. Taylorcraft!)

 

All my best,

Rob

 

Tried and true by Hercules Magellan himself! East is LEAST and West is BEST! ;)