Warbird compasses wrong by +10 or more degrees

[RodBorza]

On 9/25/2021 at 2:09 AM, Nealius said:

 

Then something's not right with the master compass, then. After setting the master compass on the Mosquito it still does not show correct variation at Batumi. Is there any way to adjust the master compass on the Mustang or the Axis planes? They're showing incorrect declination as well. 

 

I also recently was told the Channel map does not yet have declination modeled at all, and yet the compasses are 10+ degrees off.......None of it is making any sense.

Hey Nealius,

 

I'm following various of your posts, and I am noticing the same problem.

 

The directional gyros need to be set with the engine revved, to ensure proper suction (as you did with the German plane)

Pure magnetic compasses, on P-51, P-47, Spitfire and Mosquito work as they should, showing proper declination (6 degrees in case of the Caucasus)  

The Remote Indicator Compasses on P-51 and Mosquito are broken, for whatever reason, I find the same 20 degrees of error between them and the pure magnetic compasses.

[RodBorza]

On 9/24/2021 at 7:20 AM, Nealius said:

I noticed something weird with the compass repeaters in some of the warbirds and checked all of them (except Dora and I-16) out. I found that they have a +10 degree discrepancy from both the info bar heading and the heading indicated by the gyrocompass or any other cockpit compass. 

 

Method: 

1. Hot start aircraft on ramp at High Halden (magnetic declination +0.69)

2. Run engines up to 1,100 or 1,200rpm for vacuum pressure and electric power to give proper compass readings

3. Cross-check compasses with info bar (I did not check the big Brit compass in the Mossie or Spit)

 

Results:

Aircraft	Infobar heading	Directional Gyro	Compass (Magnetic)
Bf 109 K4	011	NA	022
Fw 190 A8	012	NA	025
P-47D-40	013	014	013
P-51D-25	012	014	024
Spitfire	012	013/014	NA
Mosquito	012	013/014	022

 

The P-47 is the only one with correct compass readings. The directional gyros in the aircraft that have them are okay, but the magnetic compasses/compass repeaters (manuals are inconsistent in naming) are off by 10 or more degrees. In the Kurfurst and Anton particularly you will have to subtract 10~13 degrees to find your actual heading becuase you don't have a directional gyro. Even if the infobar heading is True and not Magnetic, the decllination of Kent is less than one degree, which appears to be corroborated on the directional gyros. 

Compass.trk 86.13 kB · 5 downloads

 

After much testing and fiddling around with .LUA files, I got to this conclusion:

 

The Remote Indicator Compass only works as it should if you are perfectly straight and level. From what I've read, you use the gyro compass for navigation most of the time. Even if drifts. 

On the ground, you rev up the engine, set the right heading and disregard the Remote Indicator Compass. It does not work well on the ground because the aircraft is inclined, thus the equipment is not at its optimal position. 

Once you are in the air, trim the aircraft straight and level. 

 

If you are having trouble trimming the warbirds, check this post:

 

Once trimmed and in level flight, you can use the Remote Indicator Compass to check/calibrate the Gyro Compass (every 15 minutes or so). The Remote Indicator Compass won't work fine while banking or making turns. 

 

I tested it in the P-51 and it works fine.  On the Mosquito I still get the 20+ degrees of error. Don't know why.

 

Modern aircraft like F-5 and the Huey which have the Remote Compass do not have this problem because they are sitting more or less level with the ground while on the ground. Also, as being more modern, DCS lua files uses a error factor (K_deviation) of 0.9 instead of 0.74627 as it is used in warbirds.

 

If you want to check it out the files are located on: 

P-51D

[Your Drive]:\Eagle Dynamics\DCS World OpenBeta\Mods\aircraft\P-51D\Cockpit\Scripts\RemoteCompass_AN5730

 

UH-1H

[Your Drive}:\Eagle Dynamics\DCS World OpenBeta\Mods\aircraft\Uh-1H\Cockpit\Scripts\RemoteCompassTransmitter