CHT's when running LOP
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Hello Nick!
I've been doing a lot of testing out various leaning parameters in the Bonanza, and I've found what appears to be an issue with the modeling of CHT response to LOP vs ROP conditions. From my real world experience, as well as general knowledge shared amongst real world pilots, CHT's should generally be lower when running an engine LOP, as the power generated is reduced. In the real world in a 172SP, I've seen CHT's around 320 when running LOP vs the same cylinder running around 350-360 when running the engine ROP.
When testing this in the Bonanza, I have found no change in CHT when running ROP vs. LOP. This particular test was done around 12,000ft over New Mexico. When running 25 degrees LOP, my cylinder 4 CHT was about 395 (quite high for 19" MP and cruise speeds, but it was hot out). When running 75 degrees ROP at the same altitude and engine parameters, the CHT was... 395. I only gained about 5 knots of speed, so I'm pretty sure that additional airflow wasn't responsible for the ROP CHT's running at the same temp.
Everything that I know about this subject suggests that this behavior is inaccurate. Now, whether or not this behavior is subject to MSFS limitations... I don't know, nor am I aware of if running CHT's high (but under the max limit) matters in this addon. Also, if I'm missing something, I'd love to hear your thoughts. Keeping CHT's low is a major part of real world engine management, as you no doubt know, so I figured I'd bring this up. Love this addon and I will continue to fly it, even with the questionable CHT's.
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After watching videos you should be running at least 50 degrees LOP for safe operations. So you're technically not leaning the mixture enough, you'll lose roughly almost 10 knots running LOP if doing correctly. https://www.youtube.com/watch?v=h3bATVXMHQg
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After watching videos you should be running at least 50 degrees LOP for safe operations. So you're technically not leaning the mixture enough, you'll lose roughly almost 10 knots running LOP if doing correctly. https://www.youtube.com/watch?v=h3bATVXMHQg
@Turbinepilot2 You're right... sometimes. There's significant nuance to how LOP ops go and I don't think they can simply be reduced to a single temperature that's always best to run. Again, having real world experience with this (albeit in a Cessna, but the physics are the same), as well as having watched that video MANY times (Martin is great), sometimes 50 deg LOP is best, sometimes 25 is best. If I'm at a lower altitude and making near or above 65% power, I would absolutely target 50 deg LOP, and would make an attempt to get there quickly, spending as little time in the "red box" as possible. However, in a Bonanza at 12,000ft making 19" of MP, that falls well below 65% power and really there isn't a mixture setting that could hurt the engine as the pressures in the cylinders aren't high enough for detonation. I will acknowledge that this is a contentious topic, but the physics of what's happening support that statement, as well as real world evidence.
So, typically, I'll run closer to 25 deg LOP when I'm above 10,000 (in MSFS, I've never seen 10,000 in the Cessna lol), as the MP is already low, and I don't want to trade too much power for better fuel economy. If I'm below 10,000, or in the turbo Bonanza, I'll run 50 deg LOP to ensure I stay away from the "danger zone".
Regardless of all of this, whether at 25 or 50 deg LOP, you should see a reasonable reduction in CHT's when operating LOP. I flew a flight tonight using 50 deg LOP and was getting 369 deg on cylinder 4. When switching to 50, 75, and 100 deg ROP, the CHT's actually got cooler, but only by 3 degrees, so not enough to really show any change to CHT. If there is a change, it's in the wrong direction. In fact, it seems that CHT's are seemingly barely affected by mixture setting much at all, at least when leaned inside of the "normal" envelope.
Man, I sound like such a pedantic nerd.
. I acknowledge that to most, this won't matter at all, but it is a detail that I noticed and perhaps others might as well. Perhaps it's due to a MSFS limitation. Given how many of those there are, I wouldn't be surprised. -
@Turbinepilot2 You're right... sometimes. There's significant nuance to how LOP ops go and I don't think they can simply be reduced to a single temperature that's always best to run. Again, having real world experience with this (albeit in a Cessna, but the physics are the same), as well as having watched that video MANY times (Martin is great), sometimes 50 deg LOP is best, sometimes 25 is best. If I'm at a lower altitude and making near or above 65% power, I would absolutely target 50 deg LOP, and would make an attempt to get there quickly, spending as little time in the "red box" as possible. However, in a Bonanza at 12,000ft making 19" of MP, that falls well below 65% power and really there isn't a mixture setting that could hurt the engine as the pressures in the cylinders aren't high enough for detonation. I will acknowledge that this is a contentious topic, but the physics of what's happening support that statement, as well as real world evidence.
So, typically, I'll run closer to 25 deg LOP when I'm above 10,000 (in MSFS, I've never seen 10,000 in the Cessna lol), as the MP is already low, and I don't want to trade too much power for better fuel economy. If I'm below 10,000, or in the turbo Bonanza, I'll run 50 deg LOP to ensure I stay away from the "danger zone".
Regardless of all of this, whether at 25 or 50 deg LOP, you should see a reasonable reduction in CHT's when operating LOP. I flew a flight tonight using 50 deg LOP and was getting 369 deg on cylinder 4. When switching to 50, 75, and 100 deg ROP, the CHT's actually got cooler, but only by 3 degrees, so not enough to really show any change to CHT. If there is a change, it's in the wrong direction. In fact, it seems that CHT's are seemingly barely affected by mixture setting much at all, at least when leaned inside of the "normal" envelope.
Man, I sound like such a pedantic nerd.
. I acknowledge that to most, this won't matter at all, but it is a detail that I noticed and perhaps others might as well. Perhaps it's due to a MSFS limitation. Given how many of those there are, I wouldn't be surprised.@DangerZoneDmo that’s a great post. LOP wasn’t talked about much when I flew GA aircraft back in the day. I don’t think I flew with any planes with Gami injectors so we just flew ROP. Now I just fly the bit metal tubes so my knowledge is just from watching YouTube videos or magazine. I’m guessing it’s a MSFS limitation because the mixture adjustment in general is very incorrect on most planes in MSFS. Maybe Blacksquare can do some tweaking in the future though to get it closer to your points.