EDM-760 - small bug with relative EGT +/- sign
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This is something I've briefly noticed a few times but didn't really understand, and thought I might have been imagining things, but on my last flight, investigated further and now I believe I understand what's happening.
You'll have to bear with me for the explanation, but in summary, I believe the +/- symbol on the EGT scale, relative to peak EGT, is based on instantaneous mixture lever position, rather than the actual EGT at that moment. It looks like a bug, and I'll try to explain how to make it show...
Normal/expected behaviour:
- Start 'Lean Find' mode (in ROP) and lean your mixture until you reach peak EGT.
- Continue to lean the mixture (or overshoot slightly) and the EGT value will increase positively - lean of peak.
- Begin to increase mixture and the value will decrease, eventually going negative once rich of peak.
Actual behaviour:
- As you enrich the mixture faster, the negative sign will appear before the EGT value has reduced to zero and gone in the other direction. The faster you increase the mixture, the sooner the negative sign shows up.
It seems to me that the final/target value of the EGT is known by the mixture lever position, and this is reflected in whether you see a +/- value. However, the actual numerical value takes time to get there.
Going from lean of peak, increasing mixture to rich of peak, the EDM-760's values (on both engines) might go:
10, 9, 8, 7, 6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5...
The values marked in bold should clearly be positive, but the minus sign shows up too soon.If you repeat but move the mixture levers forwards faster, the relative EGT values might go like this instead:
10, -9, -8, -7, -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5...If this is correct behaviour (possible but unlikely), I unreservedly apologise for wasting your time!
Edited to add: This is in MSFS 2020 with the post-release 1.1 patch applied.
Regards,
Martyn -
Hi Martyn. I just wanted to give you a quick reply since you took the time to write this out. I have also intuitively noticed this behavior with my own software, and I did investigate what was causing it at one point. This was several years ago, but I believe there was a fuel-flow-based simplification that I made that was likely the cause. Unfortunately, I didn't see a clean way of fixing this at the time. I suspect this behavior might go away when I start using some new fuel flow calculations available in the sim (2020 & 2024) courtesy of Working Title. If it still persists, then I will revisit the cause and see if I can come up with a solution after sitting it on it for a couple years. Thanks for your thorough explanation!
