Looking for a real Mosquito compass deviation card, anyone?

[Lau]

Folks,

I have been testing the DCS Mosquito compass deviation and would like to just have a look at a real Mosquito deviation card to see the deviation pathern. I realize results will vary from one bird to the other. but still.

If anyone have access to the real bird or already have a picture available that would be awesome!

You can also share your results here, so hopefully we also get a compass deviation card in our virtual Mosquito (topic will later be moved to the whish list).

To start off, here is what I actully see in DCS:

MOSQUITO FB VI		Date
Aircraft		JUNE 6TH 1944
Cmp
C to M		M to C
+1°00'	000°	-1°00'
0°00'	10° - 20°	0°00'
-2°00'	30°	+2°00'
-1°00'	40°	+1°00'
-2°00'	50°	+2°00'
-1°00'	60° - 80°	+1°00'
0°00'	90°	0°00'
-1°00'	100° - 120°	+1°00'
+1°00'	130°	-1°00'
0°00'	140° - 170°	0°00'
+1°00'	180° - 200°	-1°00'
-2°00'	210°	+2°00'
-1°00'	220°	+1°00'
0°00'	230°	0°00'
-2°00'	240°	+2°00'
0°00'	250°	0°00'
-1°00'	260°	+1°00'
0°00'	270° - 290°	0°00'
+1°00'	300°	-1°00'
0°00'	310° - 320°	0°00'
-1°00'	330°	+1°00'
0°00'	340°	0°00'
+1°00'	350°	-1°00'

Cheers,

Lau

Edited November 9, 2023 by Lau

[Skewgear]

There already is a deviation card in the Mosquito cockpit. Left sidewall, in line with the port engine oil pressure warning light.

[Lau]

What you are referencing is unfortunately the radio signal direction finder calibration table. A compass deviation card could be added in the same place with the possibility to flip from one card to the other by a simple mouse click. Dreams cost nothing 

If you want to play with the compass deviation you can use the card I provided in my initial message and let us know if you find any discrepancies.

More to the point, with the results I gathered it seems that compass deviation is not simulated by ED in the Mosie, this is why it would be interesting to see a real Mosquito compass deviation card, ideally from an airframe with a close enough cockpit configuration. Even with a wooden airframe there might be enough deviation by the gear set in the cockpit?

Best,

Lau

Edited November 10, 2023 by Lau

[stuart666]

Ive seen nothing like that, and Ive looked. It might be worth asking on https://ww2aircraft.net/forum/ and see if anyone has one. I would suppose there would be some difference between a BIV and a FBVI just to the close proximity of the guns. I suspect its a tall order.

I believe there is an example deviation card in in the 1944 Air Ministry Air Navigation manual but, unhelpfully, its of an Avro Manchester...

https://play.google.com/store/books/details/Great_Britain_Air_Ministry_Air_Navigation?id=WbJ8AAAAIAAJ

I think you are right, other than the magnetic deviation, I dont believe they model individual aircraft compass deviation. Whats even stranger, when I create a scenario on channel map, I believe sometimes says 9 degrees deviation on the rose, and other times 8.9. Maybe they are modelling compass deviation via random event, instead of modelling the aircrafts personal compass deviation?

 

Edited November 15, 2023 by stuart666

[Skewgear]

Declination (edit, not individual compass deviation, see below) is modelled according to mission date and variation rate over time. Check the mission editor compass rose for the default June 2016 date when you open the editor, and then check what it says after you change the date to July 1944.

Individual airframe speed variation definitely seems modelled in the Mossie (try flying close formation on a Channel transit with other players). As mentioned, my belief is the card we see on the left sidewall (I.e. Next to the pilot's compass) is the mag dev card. Placing the RDF deviation card there would make even less sense than placing the main compasses out of sight of the navigator...

Edited November 15, 2023 by Skewgear

[some1]

12 minutes ago, Skewgear said:

Deviation is modelled according to mission date and variation rate over time. Check the mission editor compass rose for the default June 2016 date when you open the editor, and then check what it says after you change the date to July 1944.

That's magnetic declination (aka magnetic variation).

Compass deviation is from the interference from metal aircraft structure and other equipment surrounding the compass. It's unique to the aircraft, not mission date.

[Skewgear]

3 hours ago, some1 said:

That's magnetic declination (aka magnetic variation).

Compass deviation is from the interference from metal aircraft structure and other equipment surrounding the compass. It's unique to the aircraft, not mission date.

Bah. Yes I meant declination, not deviation!

[Lau]

On 11/15/2023 at 11:48 AM, stuart666 said:

Ive seen nothing like that, and Ive looked. It might be worth asking on https://ww2aircraft.net/forum/ and see if anyone has one. I would suppose there would be some difference between a BIV and a FBVI just to the close proximity of the guns. I suspect its a tall order.

I believe there is an example deviation card in in the 1944 Air Ministry Air Navigation manual but, unhelpfully, its of an Avro Manchester...

https://play.google.com/store/books/details/Great_Britain_Air_Ministry_Air_Navigation?id=WbJ8AAAAIAAJ

I think you are right, other than the magnetic deviation, I dont believe they model individual aircraft compass deviation. Whats even stranger, when I create a scenario on channel map, I believe sometimes says 9 degrees deviation on the rose, and other times 8.9. Maybe they are modelling compass deviation via random event, instead of modelling the aircrafts personal compass deviation?

 

 

@stuart666

Hi Stuart, thanks for your irterest with compass deviation. Magnetic Variation is indeed simulated throughout time in DCS, info is provided from the compass rose that can be moved  around as stated. As with individual compass deviation for each aircraft, I believe ED is moving in that direction since, I get different results for the Spitfire, P51D and Mosquito. Please refer to my other posts in relevant threads for the compass deviation cards I provided with what I actually see in game. It is easy to mix deviation and variation but they are not the same as stated by other members.

Thanks for the links I will check them out.

On 11/15/2023 at 1:02 PM, Skewgear said:

Declination (edit, not individual compass deviation, see below) is modelled according to mission date and variation rate over time. Check the mission editor compass rose for the default June 2016 date when you open the editor, and then check what it says after you change the date to July 1944.

Individual airframe speed variation definitely seems modelled in the Mossie (try flying close formation on a Channel transit with other players). As mentioned, my belief is the card we see on the left sidewall (I.e. Next to the pilot's compass) is the mag dev card. Placing the RDF deviation card there would make even less sense than placing the main compasses out of sight of the navigator...

 

@Skewgear

Thanks for shimmying in this conversation about compass deviation. 

I am not sure as to what you mean by "individual airframe speed variation seems modelled in the Mossie" Do you mean that speed variation affects the compass stability as do any other movements like yaw, roll? They do, but for only a brief period of time, once the plane stops jerking the compass becomes stable allowing for accurate readings. That is not compass deviation as stated by @some1

About the card you are referencing on the left wall, unless you have a different version than the latest beta available to us customers, then I do not agree. I have attached a screenshot of the card I see. If you have the same, how would you effectively use this card as a compass deviation card? it's not even displaying relevant information for 360 deg of bearings. You can sure do better as a beta tester than just say it is a compass deviation card and not even read the nicely made Chuck's Guide for the Mosquito page 28. 

Best,

Lau

 

[stuart666]

18 hours ago, Lau said:

@stuart666

Hi Stuart, thanks for your irterest with compass deviation. Magnetic Variation is indeed simulated throughout time in DCS, info is provided from the compass rose that can be moved  around as stated. As with individual compass deviation for each aircraft, I believe ED is moving in that direction since, I get different results for the Spitfire, P51D and Mosquito. Please refer to my other posts in relevant threads for the compass deviation cards I provided with what I actually see in game. It is easy to mix deviation and variation but they are not the same as stated by other members.

Thanks for the links I will check them out.

@Skewgear

Thanks for shimmying in this conversation about compass deviation. 

I am not sure as to what you mean by "individual airframe speed variation seems modelled in the Mossie" Do you mean that speed variation affects the compass stability as do any other movements like yaw, roll? They do, but for only a brief period of time, once the plane stops jerking the compass becomes stable allowing for accurate readings. That is not compass deviation as stated by @some1

About the card you are referencing on the left wall, unless you have a different version than the latest beta available to us customers, then I do not agree. I have attached a screenshot of the card I see. If you have the same, how would you effectively use this card as a compass deviation card? it's not even displaying relevant information for 360 deg of bearings. You can sure do better as a beta tester than just say it is a compass deviation card and not even read the nicely made Chuck's Guide for the Mosquito page 28. 

Best,

Lau

 

Thanks Lau. I admit im very new to this stuff, so Im talking very much from a position as an amateur, so apprecate you not ripping me a new one.

Speaking of Links, I notice Greg of Gregs Airplanes and Automobiles has done a video on navigation, and its his opinion that individual aircraft magnetic variation, at least in the ones he has flown, does not exist. That of course doesnt make him right, but I find it interesting he has come to the conclusion it is so.

As he points out, if they did, they would have to vary it for every aircraft that spawned, which I suppose to prove awkward.

[JBDCS]

I looked at this a long time ago, not for the Mosquito but for the FW-190D9 IIRC, but the setup is the same for all modules I think.

The per-aircraft compass deviations are set up and working in game (or at least they were, not looked at them recently), but they are really than per-type rather than per-individual aircraft.

In the Cockpit/Scripts directory under each module (most of them at least), there will one one or more .lua files containing a table and variable

deviation = {
...
}
K_deviation = ...

where the deviation table contains the deviation figure for each angle from 0 to 360 degrees.  The bit of code after that multiplies the deviations by the K_deviation factor, so that can be used to adjust the deviation strength for all angles.

Eg. for the Mosquito there are two files containing this table, compass_device.lua and repeater_compass_device.lua, presumably for two different instruments (I've not flown the Mossie for a long time and can't remember what instruments it has). [Edit: Just had a look at the manual and they are the main Magnetic Compass and the R.I. Compass Repeater.]

However, the deviation table always contains the same figures (on all modules I've looked at at least), and the K_deviation factor is usually the same too (0.74627), so it looks like they just use a generic deviation table across all modules, but you could edit the tables to create per-type deviations (though not for individual aircraft).

To see that this is working you can edit these .lua tables and see the effect in the cockpit.  Eg. if you add 10 to each of the right-hand figures in the deviation table, you should see the compass direction moved by 10*0.74627 = approx 7.5 degrees the next time you use that aircraft type.  If you add 10 to the figures for a range of angles and leave the others as they are, the compass will read 7.5 degrees differently from standard when you're in that range of magnetic heading angles, but the same as standard otherwise.  If you just change one of the two files, the two instruments will read differently where you've changed the values in one.

 

And back to the OP, it would be very interesting to see an original deviation card, and to set something similar up in game.

Edited November 23, 2023 by JBDCS

[Lau]

@JBDCS Thanks a bunch for taking the time to explain your findings, by the sound of it, there is a light of hope that we can implement a little MOD for the compass deviation once we are happy with the figures we want to integrate in the SIM. Good Stuff !

Best,

Lau

[stuart666]

I should add, thats the only WW2 deviation card I can find right now, thats from the Air Ministry Navigation manual. I will post up if I find any more. Not the most immediately useful source (or aircraft come to that...) but at least its something to experiment with.

[JBDCS]

Okay thanks stuart666, so if I'm interpreting it correctly that is showing the method the ground crew would use to set up the compass so the deviations were minimal, then the remaining deviations (which we would set up in game) are the figures in column vi of the second table.

PS. Is that Air Ministry Navigation Manual online somewhere?  Sounds interesting.

Edited November 27, 2023 by JBDCS

[stuart666]

On 11/27/2023 at 10:51 AM, JBDCS said:

Okay thanks stuart666, so if I'm interpreting it correctly that is showing the method the ground crew would use to set up the compass so the deviations were minimal, then the remaining deviations (which we would set up in game) are the figures in column vi of the second table.

PS. Is that Air Ministry Navigation Manual online somewhere?  Sounds interesting.

 

Yeah, here you go. You need a google account, but you can read it for free there.

https://play.google.com/store/books/details/Great_Britain_Air_Ministry_Air_Navigation?id=WbJ8AAAAIAAJ

I actually bought a 1944 copy on Amazon, wasnt very expensive. Little above my head though, but its making me think I should probably input wind corrections into my Mosquito scenarios.

[Lau]

On 11/27/2023 at 11:51 AM, JBDCS said:

Okay thanks stuart666, so if I'm interpreting it correctly that is showing the method the ground crew would use to set up the compass so the deviations were minimal, then the remaining deviations (which we would set up in game) are the figures in column vi of the second table.

PS. Is that Air Ministry Navigation Manual online somewhere?  Sounds interesting.

 

@JBDCS 

Affirmative for column VI. If we do not find a real mosquito compass deviation card, I am happy to at least have some sort of realistic deviation added to the compass so we can play with the mechanics of air navigation in DCS. It's healthy for the brain!

I am happy to provide the deviation cards with the values we will agree for the Mosquito, P51D and Spitfire, could you add them in game with the process you have described earlier?

Then we could also add the compass deviation card to at least the pilot documents in game even if I normally have it on my tablet within a navigation spreadsheet taking in to account variables (variation, deviation, wind and so forth...). I promise I will move to paper and pencil only once we are done with the testing part of things.

The idea is to introduce a slight error if pilots do not take in to account compass deviation, I understand DCS maps are small but it is nice to know the SIM can take in to account this factor. That being said even with DCS as is, a pilot not taking in to account variation + deviation + wind vector can lead to an interesting navigation offset error.

 

Just now, stuart666 said:

Yeah, here you go. You need a google account, but you can read it for free there.

https://play.google.com/store/books/details/Great_Britain_Air_Ministry_Air_Navigation?id=WbJ8AAAAIAAJ

I actually bought a 1944 copy on Amazon, wasnt very expensive. Little above my head though, but its making me think I should probably input wind corrections into my Mosquito scenarios.

@stuart666Thanks for the link I always like offline versions since I am most of the time offline, here is one in pdf and other formats out of interest 

Manual of Air Navigation, Volume 1

If you guys find volume 2, please let me know. 

I currently use the US version also covering astronomical navigation, but before we ask for air sextant to ED, lets wait for the "drift meter" which is easy to implement in game and already 3D modeled. Some variants of the Mosquito where also equipped with a glass nose and a bombsight. That could be a good introduction for the tech required for a B17 but I am way out of the OP with my digression. 

Best,

Lau

[JBDCS]

29 minutes ago, Lau said:

Affirmative for column VI. If we do not find a real mosquito compass deviation card, I am happy to at least have some sort of realistic deviation added to the compass so we can play with the mechanics of air navigation in DCS. It's healthy for the brain!

I am happy to provide the deviation cards with the values we will agree for the Mosquito, P51D and Spitfire, could you add them in game with the process you have described earlier?

Thanks both of you for those links.

Lau, yes I could have a go at setting up any deviation figures in the set up files.

I was actually thinking of trying to set something up based on that Manchester card for testing to try out their calibration procedure, ie. set it up so that the compass gives the readings listed on the card, then make the adjustments step by step as they do, by adding/subtracting from the figures in the deviations setup .lua file, to get to the final deviations in column vi.

One complication which I haven't mentioned yet, is the way DCS handles the magnetic inclination (rather than declination), ie. the vertical component of the magnetic field.  Because taildragger aircraft are always pitched up when on the ground, if the compass is fixed in the aircraft this component will also affect the compass reading except when the aircraft is pointed to magnetic north or south.  In practice I think the compass usually has a gimbal or a floating needle to handle this and read correctly for small pich/roll angles, but the last time I looked at it (a few years ago admittedly) they seemed to be reading as if fixed.  This complicates things a lot when testing the compass on the ground.  I'll have to have another look at it sometime.

Not sure when I'll get time to look at this though.  Hopefully fairly soon.

[JBDCS]

1 hour ago, Lau said:

Thanks for the link I always like offline versions since I am most of the time offline, here is one in pdf and other formats out of interest

Looks like you can download an offline PDF of stuart666's 1944 manual here, in case you haven't found this yourself:

https://www.google.co.uk/books/edition/Air_Navigation/WbJ8AAAAIAAJ?hl=en&gbpv=0

Not spotted any volume 2 though I'm afraid.

Some different contents in this 1944 copy from the 1935 copy you linked to by the look of it.  Thanks again to both of you for the links anyway, I've got lots to read now.  I found this one by browsing the search results for Great Britain. Air Ministry in Google Books, lots of interesting stuff there (from the book link above, pick 'Search on Google Books' under the Author on the right).

[stuart666]

The ONLY place ive noticed a reference to volume 2 is on the Australian war memorial, which sadly doesnt host a copy online. So it clearly exists, but doesnt seem to have been much issued for whatever reason.

https://www.awm.gov.au/collection/LIB118151

[average_pilot]

One further problem regarding dead reckoning navigation in DCS, if you allow me since the topic is being touched here, is that geographic north doesn't seem to align with longitude lines. You can use the ruler in the F10 map and lay a line on top of a longitude line and it won't show 0/180 degrees for true heading. That only happens if you align the ruler with the up/down direction of the screen. I thought that was going to be fixed with the introduction of the compass rose, but no, still true north is the screen-space up/down direction. I don't know if that's a limitation of the F10 map or the terrains in DCS (since they are flat AFAIK) or something else that I'm missing.

I'm mentioning because even taking into account wind component, compass deviation and magnetic declination, as is standard technique in dead reckoning, we can't still fly in the right direction because of the disparity between where the geographic coordinates say the true north is and where DCS says it is. It's my understanding that true heading in DCS is warped as a result of imposing geographic coordinates that refer to positions on a sphere on top of flat terrains and assigning the true north to the up/down direction of the flat terrain as displayed in the F10 map through all the terrain from east border to west border.

[JBDCS]

@average_pilot Yes I think I see what you mean, and it's one of the quirks of DCS terrain maps.

The maps are set up on a rectangular grid, as usual in real maps, which doesn't necessarily align with true north (again as in real life).

In our case the map north, which I call Grid North, as indeed they do on UK Ordnance Survey maps is the equivalent to our x and z coordinates in-game (y is the "up" coordinate, x is north and z is east).  This is the grid and coordinates on the F10 map.

The latitude/longitude lines can be shown/hidden in Mission Editor by going into the map options and toggling Geographical Grid, and from those you can see that the geographical (ie. true) north is aligned differently from grid north to different degrees at different points of the map.  The ruler in Mission Editor and (I guess though not checked) the F10 map is simply based on the grid coordinates.

The magnetic declination will also vary across the map.  These can be obtained from a magdecl lua library, which will calculate and cache the magnetic declination and inclination for  all latitudes/longitudes at any date, based on magnetic field models.

I think in real life (though see note below) magnetic declinations are normally given relative to true north, but in game I'm pretty sure they're applied to the grid north.  This means that if you fly a long way west-east or vice versa, true north in game will shift significantly, but the in-game grid north will not change and the magnetic declination will only change slightly.  In real life, the magnetic declination would be applied relative to true north, so that would also shift in the same direction, which does not happen in game.

Note 1: I just checked a UK OS map which was to hand (1:50,000) and in that case the magnetic declination IS given relative to grid north.  However that's a walking map rather than a flying one, and the relative movement of true north across the map is likely very small, as opposed to a map covering hundreds of km / nm.  When I get time I'll have a look at OS maps of different areas for the same date and see how they vary.  The map key gives details of true north vs grid at each corner (in this case, grid north aligned with true on the western edge, and just under half a degree difference (true W of grid) at the eastern edge).

Note 2: I need to do some experiments in game to check out the above claims - as I've said I experimented with various compass bearing tests in he past but not recently.

I think it may be a good idea to start a new thread in a general section for discussions like this about magnetic compass navigation, where we can share info on how things work in real life and in game (but keep it free of various ADF/radio navigation info), because we're getting fairly off-topic I guess. Hopefully in the next few days I'll get chance to experiment and confirm (or otherwise) what I found last time I looked, and will maybe start a new thread and if so will post a link here.

I guess (at least hope) this kind of thing is a big part of the projected 'Whole World Map'.  Which makes me think of note 3 below:

Note 3: I haven't tried any navigation stuff out in the southern hemisphere yet, eg. the South Atlantic map - got the map but hardly dare trying navigation out!  Then there's the upcoming Kola Peninsula map for higher latitudes northern navigation.

Edited November 30, 2023 by JBDCS
Typos

[JBDCS]

Okay I've started a bit of testing now with the Mosquito on the ground.  Not got as far as playing with compass deviations yet - I've got them set to zero for testing in my compass_device.lua script - but been investigating my comments a few posts up about how pitch and bank affect the compass.  I'm glad to say that I was wrong in saying that the game works as if the compass was fixed in the airframe rather than floating - from testing with the Mosquito it looks like the pitch and bank do not affect the compass reading for small enough angles, so things are working as they should.

This is controlled by another setting in compass_device.lua, max_pitch_bank = math.rad (10), which tells it the the first 10 degrees of pitch and bank are handled by the compass needle levelling, so should not affect the reading.

However, the Mosquito on the ground is pitched up at 11.1 degrees, so there is still an effect seen on the ground when not aligned to magnetic north or south.  I'll put some details of my testing in a spoiler below so people who are interested can have a look, but the short advice for Mosquito navigation based on the results is that you should only take note of the compass readings when you're within 10 degrees of level flight. 

It's good that DCS models the compass in this kind of detail.

Spoiler

Details of what I did to test out this effect:

1. Edited compass_device.lua and set K_deviation = 0 to get rid of any compass deviations.

2. Set up a snap view which looks directly down on the compass, to make reading it and taking screenshots easier and consistent.

3. Set up a simple mission at Anapa with a Mosquito set up on a parking area but with waypoint type set to Take off from ground (so that the heading can be set).

The mission date was left as default (June 2016) and the magnetic declination there is 7.025 deg East, as can be found out by setting up a hook script to export the data (either by the difference of Export.LoGetMagneticYaw() and Export.LoGetSelf().Heading, or from the magvar library).  The incination is 63.224 deg (this one can only be found out from the magvar library I think).

4. Ran the mission with the aircraft at different headings, to align with magnetic N, E, S and W, ie. with headings 007, 097, 187 and 277.  In each case, took a screenshot of the compass when the aircraft was settled on the ground, with the info bar shown to see the details of the heading and pitch, etc.

The results are below.  The screenshots with the aircraft heading to magnetic north and south align exactly as expected, but with the aircraft heading east or west the vertical component of the field (down) pulls the compass north towards the rear of the aircraft since it's pitched nose-up at more than 10 degrees.

Heading North (007):

Heading East (097):

Heading South (187):

Heading West (277):

5. After that I edited compass_device.lua again and changed the max_pitch_bank figure from 10 degrees to 12 (the pitch angle on the ground is just over 11 degrees).  When the test mission was rerun with heading 097 (East), the compass now aligns exactly since the device will handle that pitch angle now:

Viewed from the side, you can see how the compass needle is levelled to keep it reading correctly (this view at heading 007):

 

 

Edited December 2, 2023 by JBDCS
Fixed missing text and jumbled images

[Lau]

@JBDCS

Good evening Sir,

On 11/30/2023 at 11:38 AM, JBDCS said:

Thanks both of you for those links.

Lau, yes I could have a go at setting up any deviation figures in the set up files.

I was actually thinking of trying to set something up based on that Manchester card for testing to try out their calibration procedure, ie. set it up so that the compass gives the readings listed on the card, then make the adjustments step by step as they do, by adding/subtracting from the figures in the deviations setup .lua file, to get to the final deviations in column vi.

Thanks a lot for taking the time to investigate the way DCS works in order to integrate the compass deviation to our simulated flights.

On 11/30/2023 at 10:45 AM, Lau said:

@JBDCS 

Affirmative for column VI.

I may have answered to fast your question about column « vi ». The Manchester Swing Card deals with magnetic fields which we fortunately do not have in DCS. In DCS we only crunch numbers. We are therefore only interested in the difference from the Actual "Course Magnetic" (ii)  to the "Aircraft Compass Reads" (iii) and that result is given in column IV Deviation (ii - iii) not column VI as I previously stated, sorry for that.  You may have realized this after my answer, but I just thought it would be good to clarify this point for good measure.

 Compass deviation is well explained in page 197 of the RAF Air Navigation Manual Vol 1. While I am at it, here is the link to the USAF WW2 Air Navigation Manual that I previously stated. The topic about compass deviation starts at page 145 of the manual. What I like about this manual is that everything about the 40s Air Navigation is included and more!

USAF Air Navigation Manual WWII

Now the tedious part is to find the numbers that need to be devided by the K_deviation factor "0.74627" so the compass is able to take in to account the deviation we would like to add or subtract but also, smooth out the magnetic influence throughout the 360 deg range to avoid big bumps in deviation over just a couple of degrees. This is why compass deviations can be represented by a sinusoidal curve.

Therefore and taking an example so I can also hopefully understand how it will work in the lua file but also to make things simple without taking in to account coefficients or residual deviations since we do not need them in DCS (please refer to the attached spreadsheet).

Considering for example that we choose to implement:

For a magnetic heading of 10°

Deviation from the Compass to the Magnetic Heading = +3°

Deviation from Mag Hdg to  the Compass = -3°

Then to get to a Mag Hdg of 10° we must be able to steer with the compass to approx -3°00', hence  7 deg on the compass.

To get that 7 deg (10° - 3°) reading in the compass we write approx -4.02 deg (-3.00 / 0.74627) to the lua file for Mag Hdg of 10°. Here I am just trying to follow your explanation on how the lua works.

Rinse and repeat across the whole range for maybe every 10 degrees of magnetic course change.

Most compass deviations have a mix of negative and positive values accross the sinusoid, interesting to see that the Manchester compass deviation only uses positive values. For training purposes, I suggest that we also add negative values to make the navigation exercise more interesting. According to ED there is almost no deviation in the default lua file, which seems odd considering all the gear and armament installed in a Mosquito at that time.

Page 202 of the vol 1 mentions the conditions where deviation might change beyond what the compass deviation card states (e.g. Bombs, jet fuel tanks, etc…). The standard flights will take off with a bomb load and jet fuel tanks, accomplish the mission and then RTB clean. The ideal would be to be able to have two separate deviation profiles. One for a fully loaded airframe and a second one for a clean configuration. The tricky part would be to script the moment when the SIM switches from one profile to the other after dropping bombs for instance. If we could find a way to script this, then nothing would prevent us from adding several profiles to match the airframe state. In real life crews would have different compass deviation cards taking this different states in to account. Just thoughts.

This bring us to the actual compass deviation card which should contain only the edges or most predominant deviations, a summary of what is in the lua file. I am also including the data for every 10 deg to be entered in the lua. The below profile which we could initially use is for a Mosquito fully loaded to the teeth. The bigger the deviation the more important it will be for crews to consider it to avoid ending in the wrong place and perhaps overfly a dangerous area, or simply miss the next turning point, the joys of DCS. More importantly, I believe that as a pilot anyone using this little mod will be well acquainted with the effect and interpretation of deviation during navigations, hence a better virtual pilot.

The attached compass deviation card is admittedly a USAF type format, feel free to give it a RAF style or even a graphical interpretation as on vol 1.

I noticed in the lua file that "K_deviation = 0.74627 -- 2.5 degrees max". I hope this will not be a problem for deviations larger than 2.5 degs.

The test bed you have setup with the possibility of a top down view on the P8 looks very good. I understand that you prefer to make all your testing on the ground, it can be a challenge to fly the Mosquito and read the compass at the same time. Now that you found a way to remove the condition that affected the precision of the compass on a pitched aircraft over ground you should hopefully get very precise results.

I’ll be happy to work on more profiles if we manage to script the process either via the mission editor or via some xml within the Mosquito module.

In real life, the compass can be a very unreliable peace of gear that needs to be closely monitored by the navigator.

May the force be with ED (they sure have the solution to this) and with you for entering all these numbers : ))

Best,

Lau

 

Mosquito Compass Deviation Data and card.xlsx

Edited December 4, 2023 by Lau

[JBDCS]

4 hours ago, Lau said:

Page 202 of the vol 1 mentions the conditions where deviation might change beyond what the compass deviation card states (e.g. Bombs, jet fuel tanks, etc…). The standard flights will take off with a bomb load and jet fuel tanks, accomplish the mission and then RTB clean. The ideal would be to be able to have two separate deviation profiles. One for a fully loaded airframe and a second one for a clean configuration. The tricky part would be to script the moment when the SIM switches from one profile to the other after dropping bombs for instance. If we could find a way to script this, then nothing would prevent us from adding several profiles to match the airframe state. In real life crews would have different compass deviation cards taking this different states in to account. Just thoughts.

Okay not read you full post properly yet (will do tomorrow), but unfortunately I don't think anything like the above paragraph is possible in game (if anyone can correct me, please do).

The deviations are, I think, baked into the .lua scripts for the aircraft and loaded at mission start, so will be constant through the mission, and unchanged by dropping ordnance etc.

As I say, I'd be happy to be proved wrong.

4 hours ago, Lau said:

I noticed in the lua file that "K_deviation = 0.74627 -- 2.5 degrees max". I hope this will not be a problem for deviations larger than 2.5 degs.

No, no problem at all.  That just means that with the generic profile it looks like they're using, the maximum compass deviation is 2.5 deg.  You can make it as big or small as you want.

[JBDCS]

4 hours ago, Lau said:

I may have answered to fast your question about column « vi ». The Manchester Swing Card deals with magnetic fields which we fortunately do not have in DCS. In DCS we only crunch numbers. We are therefore only interested in the difference from the Actual "Course Magnetic" (ii)  to the "Aircraft Compass Reads" (iii) and that result is given in column IV Deviation (ii - iii) not column VI as I previously stated, sorry for that.  You may have realized this after my answer, but I just thought it would be good to clarify this point for good measure.

Sorry to correct your correction, but I think I was right in my guess, though it was just that at the time.  I've had a bit of a look at that section of the 1944 RAF manual, and this covers it I think:

"(a) From these eight deviations , calculate coefficient A. Loosen the compass fixing screws , and remove A by rotating the whole compass that number of degrees in the appropriate direction (clockwise if A is +, and vice-versa) . Re -tighten the screws.
Coefficient A should be corrected only if of the order of 1 1/2° or more , and then only on the authority of the responsible navigation officer."

So in their example, coefficient A is +3 so should be corrected by a compass rotation, to leave the column vi figures.

[Lau]

@JBDCS

Thanks, I'll wait that you have the time to read my full post properly including the spreadsheet with the figures that could be added to the Lua file. I look forward to understand how your interpretation of column VI will play with the figures I have suggested.

Best,

Lau

PS: I am mixing a little bit things in this message. Agree, there are two separate things. 1) The understanding of the compass swing card provided by Stuart for the Manchester and 2) The process of adding the correct figures to the LUA file in order to have a deviation card that will allow the pilot to steer the correct magnetic heading.

Edited December 9, 2023 by Lau