1.5.4 Compass no longer takes geographic grid into accound

[Ramsay]

Prior to 1.5.4 DCS level modules took the geographic grid into account when displaying heading and bearing information i.e. NDB direction, RSBN radials and values were close to those measured in google earth.

 

In 1.5.4, game grid/F10 map = true north and magnetic declination adjustments are applied to the F10 value for western aircraft, etc.

 

Near Batumi, bearings are 7° lower than they should be i.e. Batumi to Tbilisi should read 88° T / 82° M but reads 75° magnetic.

 

Prior to 1.5.4, I flew several navigation missions in the L-39C between Maykop and Smolenskaya NDB on the Maykop RSBN 276° radial as this was required to follow a direct ground track as viewed in tacview, the required RSBN radial has changed to 272° in 1.5.4

 

Example

 

Batumi, lines of longitude run at 353°, so true = F10+7°

 

The bearing from Batumi to Senaki is measured as 21° in the F10 map, so true = 21°+7° = 28°. In 1.5.4, true = F10 = 21°, which is incorrect.

 

A A-10C at Batumi reads Senaki TACAN course bearing as 15° magnetic (no HSI deviation)

 

Instruments effected: magnetic compass, HSI/RMI, ADF, TACAN, RSBN

Test aircraft: A-10C, SA-342M/L and L-39C

 

Related Gazelle thread.

[MikeMikeJuliet]

Seems like a lot of things were broken by this update. Interesting findings...

[Ramsay]

Compass reads the same in 1.2.16

 

Seems like a lot of things were broken by this update. Interesting findings...

 

It seems NOT, I've just checked the A-10C in version 1.2.16.43180 and the Batumi to Senaki TACAN bearing reads the same.

 

 

 

I always thought the compass in full DCS modules took the geographic grid into account, seems it's only used for Lat. and Long, coordinates ?

[gospadin]

An actual magnetic compass doesn't know its grid. Only an INS would know how to adjust a compass-provided value.

 

Actual VORs and VORTACs are calibrated to magnetic headings every 15-20 years, but you have to know on a per-VOR basis what *that* specific VOR wants you to fly, relative to the others. This information is on charts and in the AF/D or Chart Supplements, updated every 56 days.

Edited July 14, 2016 by gospadin

[Ramsay]

An actual magnetic compass doesn't know its grid. Only an INS would know how to adjust a compass-provided value.

Compass

 

• 
  
• A magnetic compass aligns with the earths magnetic field, no INS needed.
  
• At the other end of the technology spectrum, the A-10C EGI system uses GPS satellites, gyros, magnetic sensors and/or declination tables to align it's HSI.
  

Declination

 

• 
  
• Magnetic declination describes how the local direction of magnetic north compares to true north (the lines of longitude on the geographic grid).
  
• It's used when transferring compass directions to a map, or vice versa
  
• The declination in the DCS Caucus map is approx. +6° E (0° magnetic = 6° true)
  
• AFAIK the DCS data base holds fractional data to an accuracy of 0.1 or 0.01 degrees.
  

So I expected the latitude and longitude projection and aircraft compass bearings to be pretty accurate.

 

Error

 

• 
  
• However the aircraft compass and the geographic grid use different frames of reference/projections i.e. 7° difference at Batumi
  
• The error pretty much cancels it's self out as every compass, instrument, TACAN, VOR, etc. has the same error.
  
• But the instrument values will differ from the real world i.e. google earth.
  

Creating Target Waypoints in the Gazelle

 

• 
  
• I've seen people wonder why they had large (400m) waypoint errors when using their own coordinates and a target bearing/distance to calculate it's lat. and long. This *may* be why.
  

Actual VORs and VORTACs are calibrated to magnetic headings every 15-20 years, but you have to know on a per-VOR basis what *that* specific VOR wants you to fly, relative to the others. This information is on charts and in the AF/D or Chart Supplements, updated every 56 days.

This is out of scope and not really relevant to inconstancies in DCS. Edited July 15, 2016 by Ramsay