investigating Bug: HUD terrain elevation display not right

[N22YF]

In the unguided bomb delivery modes, the manual says the HUD shows the terrain elevation under the selected weapon type (in the data block in the lower left corner). However, the number here appears to be MSL+AGL (in feet), instead of terrain elevation which would be MSL-AGL. Without a target locked, this readout is MSL+AGL of the aircraft at the moment; with a target locked, it changes to (current MSL) + (current MSL - target elevation).

 

Here are some screenshots - you can see radar altitude = 1733 ft and altitude MSL = 4000 ft. Without a target locked, the "terrain elevation" readout is 5731 which is roughly 4000+1733:

 

(You can also see this on the HUD image on page 50 of the DCS A-10A manual: the MSL altitude is 1812 ft, the radar altitude is 1795 ft, and the "terrain elevation" readout is 3608, which is roughly 1812+1795.)

 

When I lock on the ocean ahead, the "terrain elevation" readout changes to 7998, which is roughly 4000 (MSL) + 4000 (AGL):

 

In rockets and gun modes, this second line correctly shows terrain elevation (MSL-AGL) instead of MSL+AGL. However, while my understanding of the manual is that this number should be the terrain elevation where the weapon pipper is pointed, it's actually the terrain elevation underneath the aircraft. See this screenshot - I'm at 4000 ft MSL and the radar altimeter is reading 1733 ft. While the weapon pipper is pointing at the ocean (elevation of 0), the second line reads "2263" which is roughly 4000-1733 - that is, the terrain elevation below me. This issue also applies to the unguided bomb delivery modes described above, when no target is locked (that is, in that case, this second line is also being computed at the aircraft's position rather than at the location of the pipper).

 

(The target elevation readout does appear to be correct in AGM-65 mode: it shows the terrain elevation for the point the reticle is over.)

 

Finally, in a related issue, the third line of this data block, the slant range, is given in meters (e.g., 8208m in the above screenshot). This should probably be in feet since the other distance readouts on the HUD (distance to the next waypoint and the range numeric under the reticle) are in nautical miles; my understanding is, in the real-life A-10A, these can be selected to be either all in meters and kilometers, or all in feet and nautical miles, but not a combination. However, I don't think a slant range readout even exists there in the real-life A-10A's HUD - maybe better to just remove it?

 

 

So to sum up, the issues are:

1. In the unguided bomb modes, the target elevation is wrongly calculated as MSL+AGL instead of MSL-AGL.
2. In rocket mode, gun mode, and bomb mode without a target locked, the target elevation is calculated using the aircraft location instead of the location at the pipper.
3. The slant range on the third line of this data block should probably be given in feet (or just removed).

 

(I'm running 2.5.5.41371.1 stable.)

Edited December 4, 2020 by N22YF

[randomTOTEN]

Bump!

[BIGNEWY]

Hi, we will investigate it, however it maybe intended.

 

The A-10A we have is based on as close to LASTE 6 avionics suite and we need to check our design document and other sources. 

 

thanks

[N22YF]

9 hours ago, BIGNEWY said:

Hi, we will investigate it, however it maybe intended.

 

The A-10A we have is based on as close to LASTE 6 avionics suite and we need to check our design document and other sources. 

 

Thank you - so glad to hear this will be investigated!

 

Regarding issue #1, I would be shocked if this were intended - I cannot imagine any situation where the value of MSL+AGL would be chosen to be displayed to the pilot, instead of the target elevation. But I've never flown a real A-10, so perhaps there's some peculiarity that I'm not aware of.

 

Regarding issue #2, my understanding of the real-life LASTE 6 A-10A behavior (which could be wrong, again given that I haven't flown an A-10 in real life) is that the target elevation (for all weapons, including Mavericks) can be chosen in a few ways, including: the pilot can manually input a value; the elevation of the current waypoint can be used; or the pilot can press a button which records the terrain elevation under the aircraft at that instant as the target elevation. (This target elevation value is then used for all targeting calculations, such as where the CCIP pipper is positioned.) While the current DCS behavior is somewhat similar to the third method described above, I don't think it's in the spirit of the actual behavior, which is to record a value to use for later targeting rather than to continuously show the terrain elevation under the aircraft (which will not necessarily be the target's elevation when the target is being engaged.) To my understanding, to be more realistic, any or all of these three methods should be implemented (that would be awesome ) - maybe the easiest for y'all would be to simply use the elevation of the current waypoint. I was comparing the current behavior to the DCS A-10A manual which reads, "The second line indicates the barometric elevation, in meters, of the terrain below the weapon pipper." The current DCS behavior (i.e., continuously displaying the elevation of the terrain under the aircraft) matches neither the description in the DCS A-10A manual nor my understanding of actual LASTE 6 A-10A behavior.

 

Regarding issue #3, my understanding of the real-life LASTE 6 A-10A behavior is that slant range is not displayed there in the first place, but I could be wrong.

[randomTOTEN]

I'm mostly concerned about the AGL+MSL readout. I'm fine with the current FC3 magic pipper, and just a readout of ground elevation below the aircraft. Don't really have an opinion on the use of meters.

Thanks for looking into it!