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jolly_magpie
11-23-2009, 09:46 AM
What is actually involved in this and why is it done in RL?? Googled it but only found some really technical explanations, could someone please describe it in plain english?

For tailsitters it seems to involve jacking up the tail so the A/C is level, sometimes it is on a large, rotatable platform that can turn the whole kite, in an area of the airfield free of ferrous metals. AFAIK the V1 flying bomb had this done before deployment in a special area of the launching site too.

Thanks in advance...

Crash_Moses
11-23-2009, 10:36 AM
Because true North isn't the same as magnetic North the magnetic compasses need to be calibrated. If I recall correctly from my days in the Marines magnetic North is off from true north by roughly 3 degrees.

Most airplane compasses include small ferrous plates that allow one to adjust where the compass points. Swinging the compass is simply adjusting it to point as close to true North as possible (or at least in relation to local airports).

BTW, love www.worldworksgames.com (http://www.worldworksgames.com). I've bought tons of models from there.

general_kalle
11-23-2009, 10:41 AM
aktually the earth's innner magnet is slowly turning upside town (very very very sloooooooowly) and so in some years the magnetic poles will be at equator and in many many years north will be south and south will be north.

dahoyle
11-23-2009, 10:58 AM
It is a really simple concept, as Crash pointed out. There are essentially three norths. True, grid and magnetic. It is often forgotten in this day of GPS and such, but for those of us with old time navigation experience, you will remember that there is a declination diagram at the bottom of most real navigational maps, which shows what it is.

Unfortunately, it isn't quite as simple in one way. The magnetic north varies by location, sometimes east, sometimes west, and by varying amounts. Additionally, the magnetic north pole, is not in the same place as the true north pole, topographically speaking.

here is a link that demonstrates that quite clearly, and shows that the actual differences can be quite significant, in many cases, much more than 3 degrees.

http://www.dauntless-soft.com/...8-2_files/fig8-6.jpg (http://www.dauntless-soft.com/PRODUCTS/Freebies/Library/books/AK/8-2_files/fig8-6.jpg)

PF_Coastie
11-23-2009, 11:11 AM
Yes, but you guys are talking about "Variation" which changes and is usually updated with each addition of a chart/map. The change is calculated by location as said. So this a relative constant.

Swinging a compass has to do with "Deviation" which is the influence of magnetic objects around a magnetic compass. The deviation will vary with every course change therefore the compass needs to be "Swung" to cover this. It is then recorded on a deviation Table for quick reference. The deviation is minimized by using magnets to keep the deviation at minimal levels.

I am going by memory here, but just trying to put it in Laymans terms for easy understanding. Hope this helps.

BSOCRenegade
11-23-2009, 02:48 PM
Originally posted by dahoyle:
It is a really simple concept, as Crash pointed out. There are essentially three norths. True, grid and magnetic. It is often forgotten in this day of GPS and such, but for those of us with old time navigation experience, you will remember that there is a declination diagram at the bottom of most real navigational maps, which shows what it is.

Unfortunately, it isn't quite as simple in one way. The magnetic north varies by location, sometimes east, sometimes west, and by varying amounts. Additionally, the magnetic north pole, is not in the same place as the true north pole, topographically speaking.

here is a link that demonstrates that quite clearly, and shows that the actual differences can be quite significant, in many cases, much more than 3 degrees.

http://www.dauntless-soft.com/...8-2_files/fig8-6.jpg (http://www.dauntless-soft.com/PRODUCTS/Freebies/Library/books/AK/8-2_files/fig8-6.jpg)


Indeed, the term for that is the G-M Angle (G-M being Grid-Magnetic). In California the G-M Angle is (if I remember correctly) 14 degrees or so. At Benning I think it was 0, which is great for navigation.

Choctaw111
11-23-2009, 08:09 PM
Originally posted by Crash_Moses:
If I recall correctly from my days in the Marines magnetic North is off from true north by roughly 3 degrees.

.

That depends on your location.
In the bottom portion of every military map there is a section devoted totally to Magnetic North, Grid North, True North and the deviation (in degrees) between Grid and Magnetic North.
Here on the East Coast of the US, the deviation is about 3 degrees as you already mentioned, but at FT Lewis, Washington, the deviation is around 15 degrees (I cannot remember exactly).
Here is a good illustration.
Keep in mind that Grid North and True North will usually be very close, but Magnetic North will vary greatly depending on location as the compass will always point to the Hudson Bay.
Imagine being stationed at Ft Wainright, Alaska. Grid North and True North are very similar, but Magnetic North is due East on the Map.
http://www.athro.com/geo/topo/compass.jpeg

Zeus-cat
11-23-2009, 08:33 PM
This sounds like a topic for raaaid.

dahoyle
11-23-2009, 08:43 PM
Originally posted by BSOCRenegade:

Indeed, the term for that is the G-M Angle (G-M being Grid-Magnetic). In California the G-M Angle is (if I remember correctly) 14 degrees or so. At Benning I think it was 0, which is great for navigation.

-8-9 degrees at Bragg,
+10 at Carson.

I've spent many a night with a map, compass, and a ruck. Have the scarred shins to prove it. Nothing like night land nav at Camp McCall, with 3 percent illumination. So much for using the stars....

PF_Coastie
11-23-2009, 09:35 PM
You guys are still getting the terms mixed up. The Variation is the difference between true north and magnetic north. Here in Portsmouth, Va it is 10D 30' with a 30" annual increase.

Deviation is different for every magnetic compass on every heading. When someone swings a compass, they usually record every 15 degrees.

In short, If I plotted a course in "true" of 180 degrees and I wanted to follow that course with a magnetic compass on a boat. I would look on the Chart/map for the local Variation which would be 10.5 degrees West. I would then look at the annual increase (30 seconds) and see when the chart was printed. Let's say it is an old one and was printed in 1999. This is really insignificant because it is only about a tenth of a degree. So for simplicties sake we will round up to 11 degrees variation. Using the formula T-V-M-D-C +W we will add 11 degrees to our 180 degrees true to give us 191 degrees Magnetic.
Now we have to look at our Deviation table and find the deviation for 191 degrees. Lets say it is 3 degrees E. We then subtract 3 from 191 Magnetic and we come up with 188 degrees "COMPASS". So, 188 is what we would have to steer to follow our plotted course(not taking into account Set and drift of course).

Get it? Got it?......Good! http://forums.ubi.com/images/smilies/blink.gif

erco415
11-23-2009, 09:41 PM
Originally posted by PF_Coastie:
You guys are still getting the terms mixed up. The Variation is the difference between true north and magnetic north. Here in Portsmouth, Va it is 10D 30' with a 30" annual increase.

Deviation is different for every magnetic compass on every heading. When someone swings a compass, they usually record every 15 degrees.

In short, If I plotted a course in "true" of 180 degrees and I wanted to follow that course with a magnetic compass on a boat. I would look on the Chart/map for the local Variation which would be 10.5 degrees West. I would then look at the annual increase (30 seconds) and see when the chart was printed. Let's say it is an old one and was printed in 1999. This is really insignificant because it is only about a tenth of a degree. So for simplicties sake we will round up to 11 degrees variation. Using the formula T-V-M-D-C +W we will add 11 degrees to our 180 degrees true to give us 191 degrees Magnetic.
Now we have to look at our Deviation table and find the deviation for 191 degrees. Lets say it is 3 degrees E. We then subtract 3 from 191 Magnetic and we come up with 188 degrees "COMPASS". So, 188 is what we would have to steer to follow our plotted course(not taking into account Set and drift of course).

Get it? Got it?......Good! http://forums.ubi.com/images/smilies/blink.gif

An easy way to remember the above formula is

True Virgins Make Dull Company

To further complicate things, deviation can be affected by various equipment in the aircraft being on/off. Things like electrically heated windshields, airconditioning, etc, can make for a large change in compass reading. In some aircraft it's so bad that the compass is placarded as 'unreliable' with the offending equipment on.

Choctaw111
11-23-2009, 09:45 PM
Originally posted by dahoyle:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BSOCRenegade:

Indeed, the term for that is the G-M Angle (G-M being Grid-Magnetic). In California the G-M Angle is (if I remember correctly) 14 degrees or so. At Benning I think it was 0, which is great for navigation.

-8-9 degrees at Bragg,
+10 at Carson.

I've spent many a night with a map, compass, and a ruck. Have the scarred shins to prove it. Nothing like night land nav at Camp McCall, with 3 percent illumination. So much for using the stars.... </div></BLOCKQUOTE>

Now that's what I'm talking about. Night land nav with no moon and a loaded ruck.
It takes special people to want to do that kind of stuff http://forums.ubi.com/images/smilies/16x16_smiley-happy.gif

jolly_magpie
11-24-2009, 12:46 AM
Yow, wotta canna woims.

So...each aircraft has different arrangements of ferric items that affect how north shows on the compass, and swinging it compensates for it, am I reading this right? And there are little magnets that are moved around to actually make the adjustments?

I know of true north, the actual "top" of the planet, magnetic north which is the point that compasses are attracted to, that wanders a bit but VERY slowly, but what is grid north? Does this relate to the particular projection of the map?

Different A/C have different equipment, thus needing different compass adjustments...so can the adjustment be applied across the board for the same model? For example, once you figure out the adjustment for a B-17G, can you apply that to ALL B-17Gs? Or does each airframe require it to be done individually?

On a side note THANK YOU for buying our model sets, it is GREATLY appreciated! I am working on a new sci-fi set right now, it's my best yet.

erco415
11-24-2009, 06:16 AM
Each individual aircraft needs it's compass swung. Not only that, but each aircraft needs it's compass swung as part of regular maintenance every so often.

I have no idea how you would swing a compass on an aircraft carrier.

PF_Coastie
11-24-2009, 06:36 AM
I have no idea how you would swing a compass on an aircraft carrier.

Ships use a Gyro Compass which is a complicated piece of equipment that always points to true north. I would imagine that a carrier has several of these Gyro's and repeaters on board. Not sure whether they would still maintain magnetic compasses, but maybe they do as an emergency back-up.

You would swing this compass while underway and simply steer the ship on each 15 degree heading while the compass is being adjusted.

AndyJWest
11-24-2009, 07:46 AM
You would swing this compass while underway and simply steer the ship on each 15 degree heading while the compass is being adjusted

I'd have thought it would be easier to keep the ship on a constant heading and turn the plane. Only snag is, you are adjusting the compass while sitting on a large lump of metal. Any swell will complicate things too.

AndyJWest
11-24-2009, 07:52 AM
Now that's what I'm talking about. Night land nav with no moon and a loaded ruck.
It takes special people to want to do that kind of stuff
I thought the idea was to pretend you didn't like it, Choctaw? Dragging yourself through swamps and nettle patches is no fun unless you can have a good moan about it afterwards. At least, from the few squaddies I've known (mostly TA), that is the way it works. The British soldier is only happy when he's got something to complain about (we have lots of happy soldiers).

I can only navigate at night when drunk, though I have had my compass go wrong on occasion even then.

dahoyle
11-24-2009, 01:28 PM
Originally posted by AndyJWest:

I thought the idea was to pretend you didn't like it, Choctaw? Dragging yourself through swamps and nettle patches is no fun unless you can have a good moan about it afterwards.



NO, No.

You have it all wrong. It's all about faulty memory. Somehow, three days, and several beers later, you manage to convince yourself and your buds, that it was actually an exciting adventure. The fact that you almost drowned when you tripped over a cyprus knee, and your ruck was shoving your face in the mud, somehow seems like something that should be repeated at a later day. Never mind "floaties". Filling your canteen at three in the morning, only to find it half filled with algae clumps and water beetles, the next time you take a strong pull from it. Thats livin'

erco415
11-24-2009, 07:22 PM
Thanks Coastie- I was thinking about swinging the aircraft's compass whilst sitting upon a huge metal thing.

Many of the aircraft I fly have a flux gate mounted out near the wingtip (as far as possible from large ferrous bits) for the magnetic sensing to the gyro, perhaps something similar on the ships?

Choctaw111
11-24-2009, 08:02 PM
Originally posted by dahoyle:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by AndyJWest:

I thought the idea was to pretend you didn't like it, Choctaw? Dragging yourself through swamps and nettle patches is no fun unless you can have a good moan about it afterwards.



NO, No.

You have it all wrong. It's all about faulty memory. Somehow, three days, and several beers later, you manage to convince yourself and your buds, that it was actually an exciting adventure. The fact that you almost drowned when you tripped over a cyprus knee, and your ruck was shoving your face in the mud, somehow seems like something that should be repeated at a later day. Never mind "floaties". Filling your canteen at three in the morning, only to find it half filled with algae clumps and water beetles, the next time you take a strong pull from it. Thats livin' </div></BLOCKQUOTE>


He He. I guess not many here can relate to that too well.
We have a few sailors, some Marines, even Air Force and the Army guys here are mostly legs.

Kettenhunde
11-24-2009, 08:36 PM
night land nav at Camp McCall


Still have the bridge between the N and the E?

Waldo.Pepper
11-24-2009, 10:19 PM
Originally posted by jolly_magpie:
What is actually involved in this?



Some details of compass swinging here.

http://www.spitfiresite.com/photos/historic/uploaded_images/spitfire-i-compass-swinging-721083.jpg

http://www.spitfiresite.com/ph...n-compass-swing.html (http://www.spitfiresite.com/photos/historic/2009/03/spitfire-mk-i-on-compass-swing.html)

http://img.photobucket.com/albums/v516/WaldoPepper/book/88-2.jpg

http://img.photobucket.com/albums/v516/WaldoPepper/book/88.jpg

http://img.photobucket.com/albums/v516/WaldoPepper/book/Dscn0736.jpg

http://img.photobucket.com/albums/v516/WaldoPepper/book/Ju52onkompansierswageb.jpg

I think you get the idea by now.

jolly_magpie
11-25-2009, 12:50 AM
Great pics, thanks!

Waldo.Pepper
11-25-2009, 12:58 AM
Originally posted by jolly_magpie:
Great pics, thanks!

Pics are nice and all ... but the text in the link is what I was getting at.

Reproduced here...

Compass swinging was a rather time-consuming task which could be simplified considerably by placing an aircraft on a rotating platform such as this. With a fitter sitting in the cockpit and the aircraft in flight-ready configuration, the engine was started and then the platform aligned so that the aircraft faced the 0 degree (north) heading. Then the fitter would check if the aircraft magnetic compass was in alignment with the magnetic north. If not, he would adjust the compensator screws with a non-magnetic screwdriver until the compass read 0 degrees. Then the procedure would be repeated for the 90-degree (east), 180 (south) and 270-degree (west) headings.

After these adjustments the compass was checked once again by turning it around stopping at each 30-degree heading and recording the compass readings, fine-tuning the compensator screws to ensure that there was no more than a few degrees difference between any of the indicated headings on the compass and the actual heading.

jolly_magpie
11-25-2009, 01:10 AM
Ok, gotcha.

So, the platform was handy but if you did not have one you could grab onto the tailwheel and pull it around so it faced each direction. This would be a hassle with the engine running, I can see, as well as the advantage of tricycle gear.

Do contemporary A/C need this done to them?

Gumtree
11-25-2009, 03:27 AM
Where ever a magnetic compass is installed it needs to be swung to read accurately. This also should be done at regular intervals and especially after some changes to the ships / plane's structure are made.

The different magnetic fields of any changes or additions all affect the compass. I use to drive my crew crazy by placing metal objects near a compass then telling them to steer a course, once they were settled on their course I would remove the object and wind the helmsmen up about not being able to steer a simple compass course.

Man it got boring on long trips hehe.

Kettenhunde
11-25-2009, 05:38 AM
Do contemporary A/C need this done to them?

Yes, there is a compass rose at most fields.

Choctaw111
11-25-2009, 10:03 AM
There are some great photos in here. Thank you for sharing them.

jolly_magpie
11-25-2009, 11:17 AM
Excellent info all around, are you sure this IS the Zoo??

Taylortony
11-25-2009, 12:35 PM
Aircraft Compass bases are getting rarer these days with commercial pressures on space, they are built and check calibrated to ensure any metal in them does not effect the readings, the reason you swing the compass is to correct it's reading as you are mounting it in a bloody big metal box that will effect it, UK wise we swing them every 3 years and I for my sins am licenced to do it........

Kettenhunde
11-25-2009, 01:08 PM
I love the US....

I don't need an A&P signoff to check the compass or adjust it.

Waldo.Pepper
11-25-2009, 05:01 PM
I would have thought that today in our comparatively modern times the compass in an aircraft (perhaps not a light aircraft but a large commercial carrier) would be made to not need this done. I am thinking of a compass as an all digital affair rather that say a hatpin in a cork.

AndyJWest
11-25-2009, 05:03 PM
Even with modern GPS and the like, a magnetic compass will be useful as a backup. Apart from anything else, it needs no power supply.

Waldo.Pepper
11-26-2009, 01:57 AM
Originally posted by AndyJWest:
Apart from anything else, it needs no power supply.

Right of course. But wouldn't the magnetic compass be slaved to the gps (or whatever) and then be self correcting/adjusting? Thus eliminating the need to go through the laborious procedure of being swung?

Kettenhunde
11-26-2009, 05:15 AM
http://www.aircraftspruce.com/menus/in/compasses.html

http://www.chiefaircraft.com/a...mpasses-Airpath.html (http://www.chiefaircraft.com/airsec/Aircraft/FlightInstruments/Compasses-Airpath.html)

Taylortony
11-26-2009, 05:59 AM
Originally posted by Kettenhunde:
I love the US....

I don't need an A&P signoff to check the compass or adjust it.

Actually yes you do and no you cannot, same as EASA here it's a licenced engineer or an ATPL, for over there see

http://www.pilotsofamerica.com...d.php?t=10906&page=2 (http://www.pilotsofamerica.com/forum/showthread.php?t=10906&page=2)

Andy,

GPS is not allowed as a primary means of navigation here on the lighter side, it is only a back up, needs to be in case you loose GPS for a myriad of reasons.
Nothing is slaved to the magnetic compass, it has power to it for its built in light. you use a remote compass for that.

Kettenhunde
11-26-2009, 06:39 AM
Actually yes you do and no you cannot,


Nope...I don't need an A&P. I love America...

In fact, I don't need an A&P to overhaul my engine. If I did not know what I was doing, it would be stupid. It is nice to know that I have the freedom to be as stupid as I wanted to be though.

They even address it in that thread. I know some of those guys in that thread. Small world, huh?

AndyJWest
11-26-2009, 06:43 AM
Yes, TT, thinking about it, I'm sure you are right. I seem to remember reading in one of the aviation magazines about some halfwit trying to navigate a light aircraft across the channel using GPS, and nearly killing himself in the process. No flightplan, no contact with the airfield he was trying to reach, and generally no clue about what the heck he was doing. I fly like that myself on MS flight sims (arguably on IL-2 as well), but not clever in real life. Apart from anything else, aircraft GPS systems are sufficiently complex to cause confusion if you are trying to reprogram them in midflight, while dealing with other things.

Thinking about it, GPS doesn't give a direct compass bearing anyway - it tells you where you are, not which way you are pointing.

Kettenhunde
11-26-2009, 06:59 AM
On this airplane, I could not adjust the compass....

http://img256.imageshack.us/img256/8222/rallyec.jpg (http://img256.imageshack.us/i/rallyec.jpg/)


I sold it and got one that has much higher performance and I can work on myself.

DrHerb
11-26-2009, 07:20 AM
Your new plane is in the Experimental class then? Apparently the owner can preform their own maintainance work if its in that class, or so Ive read

Kettenhunde
11-26-2009, 08:15 AM
Exactly I will never go back to certified for my personal airplane.

http://img204.imageshack.us/img204/1551/whitelightening.jpg (http://img204.imageshack.us/i/whitelightening.jpg/)


There is the magic words across the back seats that free the wallet....

http://img204.imageshack.us/img204/9146/backseat.jpg (http://img204.imageshack.us/i/backseat.jpg/)