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DMH in HUD


dcs76

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I recently stumbled upon something we could not explain: The wind corrected Desired Magnetic Heading indicator in the HUD (below the heading band) is a little mistery to us.

 

I originally thought that whenever the FPM is alligned with the steerpoint on the HUD, the heading "needle" should be aligned with the DMH as well. This is only the case, however, if there is no cross wind. When I align heading indicator and DMH while having a cross wind component, the steerpoint is not centered in the HUD. Yes the FPM is to the side as I would expect it, but the steerpoint is to the other side - not centered. Maybe this is a bug in the A-10C and the DMH is not correctly calculated. I found an old bug report in the forum, which might be related.

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  • 10 months later...

DMH error.png

I Think this is the same issue. I've been digging deeper into the CDU recently. Screen grab shows navigating to Kobuleti: Bearing 252, Desired Magnetic Heading (DMH) showing as 255 in the CDU. Marker on HUD is showing the same. However, wind is at 173 i.e. left to right, so surely i should be steering a heading less than the bearing not greater. Velocity marker in HUD is showing drift to the right which is as expected with wind at 173 and is showing SP to left of centre as expected when steering DMH255 to a steerpoint that is at 252. I think there is a bug where the DMH calculation has a sign error maybe. 

 

Edit: So flying on from this point if you steer to the marker you are constantly having to adjust to the left. If you of set your course the same amount the other way the FPM and SP mark align and you flight straight there with no adjustment needed. 


Edited by stuart4544
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