Mixture Issues with Prop Planes

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141

Disclaimer : I’m a software developer, neither a pilot or engine specialist.

Short answer: by treating 91% FS mixture as the “full rich” value: pretty much, yes.

Long answer now …
Your graph does not show fuel flow but I think you’ll agree that (at least on the right half), fuel flow should only go up as the mixture gets richer ?

Let me use my elite drawing skills to show you how I think MSFS works, and how it doesn’t contradict your graph at all.

As MSFS mixture goes past 91%, the quantity of oxygen in the mixture is so low that the engine is now losing a lot of power, the prop can not sustain its required RPM even at finest pitch and starts slowing down. This inevitably reduces fuel flow !

fuel3
fuel3734×696 154 KB

So I’m not saying the mixture system MSFS is great; it isn’t.

I’m saying that should Asobo recalibrate the internal FS code to map the old 0-91% range to be the new 0-100% (should be a pretty simple fix), our main problem with mixture disappears as the right side of my graph will be “cut out”.

Until then, mapping my throttle so it sends 91% (at sea level, ISA conditions) when fully forward is achieving the same result from the “outside”, and I don’t consider mixture an issue any more.

I’ve done more testing, here are some FS values to get maximum power on take-off :
1000 ft - 83%
2000 ft - 75%
3000 ft - 68% etc… and for 9000 ft - 43%.

I doubt this curve is right, the leaning needed seems high to me as altitude increases. But here again, it’s a “setting the curve / calibrating” issue, not a “it does not work” one.

What I’m curious about : in a real GA plane, if you’re doing the run-up on the parking at Leadville, CO (9900ft), engine at full power (terrible idea), what happens as you push the mixture fully forward ?

  • does the RPM & therefore fuel flow go down as you go very rich, as it does in MSFS ?
  • or is there is a limiting system in the engine to prevent over-richness so RPM and fuel flow stay at their max values ?
142

Hey, oh my God, yes, no, you’ve got it totally bass-ackwards…

By the way, I’m a software developer and a pilot… and I’ve read the entire “Engines” book by Mike Busch, which makes me a decent engine “conaisseur”, maybe :joy:

In “my” graph (it’s not mine, it’s from Lycoming, the engine manufacturer), mixture is pretty much the same as fuel flow, and percent power is the same as RPM.

So as fuel flow goes DOWN, RPM initially goes UP, even if you are putting less fuel into the engine. That’s why at high density altitude airfields you “lean” (less fuel) to peak RPM (max RPM). The fuel/air ratio for best power is 1:12.5 as I mentioned above. So if you put more fuel into it, you’ll get less RPM. They’re not directly tied together.

So, in short, it seems Asobo has it pretty much totally wrong and it’s not a calibration issue at all, right?

PS: If we talk about a constant-speed prop, then best power is at peak MP (as far as I know… I fly a constant-pitch…)

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143

It’s not that Asobo got it wrong, it’s that they’re way overdoing the effect. Normally you wouldn’t lean under 6000ft, but in MSFS you need to start leaning from pretty much above 1000ft. The effect is the same as the real deal, it just starts way earlier, and you need to lean way more.

144

Please check the following masterclass very closely.

TL:DR - Lycoming now recommends leaning for climb above 3000ft. Leaning for cruise at any altitude.

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145

Yeah I think you’re recommended to lean any time below 3k feet when you’re in a reduced power setting

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146

In fact, the “formal” recommendation is to lean anytime you’re under 75% power, simply because under this power setting you will probably not get the engine hot enough to damage it. The rule of thumb was to lean for cruise above 3000, and lean for climb above 5000. That’s where the value 3000 ft is coming from. Lycoming is basically now telling us to forget that old rule of thumb and now lean for climb above 3000, and lean for cruise at any altitude.

In reality, if you have a CHT gauge you can forget all of the above, and simply lean whenever you have some “room” on the CHT. You should keep your CHT between 350 and 380, round about. Too hot and your engine will melt. Too cold and you’ll get sticky valves.

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147

Yup. In fact for max power in FS you have to lean even at ground level ! Weird that no one in the Asobo dev team rang a bell about it … But it might be that this part of the code was inherited from older FS versions, and they didn’t challenge it at all. Anyway, we’ll see what the next update will bring.

148

I know who Lycoming is, thanks. I’ve seen such graphes from them (and from Continental), I’ve used them to code MFD leaning pages. I obviously meant “your” as “the one in your post” to avoid confusion with the one in mine (not as obvious as I thought, then, sorry).

Yes as mixture increases, so does the fuel flow. Exactly as the blue line shows on my graph for the “real life” mixture range. But in MS it doesn’t any more after the 91% richness line, which is one of the symptoms of the issue.

Ok so you’d rather talk about a fixed pitch prop. In this case, we can replace my green RPM curve (meant for constant-speed) with the “Percent Power” curve, it is similar to RPM. Use your imagination to extend it to the right ; see what it looks like in the 91-to-100% MSFS mixture zone ? Exactly like my green curve : a slow but increasing downward curve. So we agree here too.

No one said they were, indeed most of the time,they’re not. But MSFS allows us to go into an “overrich” zone where the RPM goes down as mixture gets richer because there is less and less oxygen. In these condtions, the slower the engine goes, the less fuel it can process. The percentage of fuel in the mixture still goes up, but not as fast as the RPM goes down, so the fuel flow goes down. Remember, I’m talking MSFS, not real life.

So … as you haven’t shown any argument in contradiction with my theory on how the MSFS mixture works, I’d say you’ve pretty much failed to understand anything about it. Which is probably my fault, as I’m neither a graph pro (hard to believe I know) or a native english speaker. I guess we’ll better leave it at this then, we’re both wasting our time.

Which reminds me of a joke I read on a John Deakin article. How you start a fight in a pilot bar ? Ask any question out loud about flying procedures or engine management …

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149

Hey man, don’t take offense. As we are writing and not really “listening” to each other, I’m used to so many sarcastic and provocative “your graph” replies, that I might have gone into a defensive mode.

But in my eyes it’s quite simple. I would be fine with accepting the explanation of MFS simply allowing too much fuel, but, if I recall correctly, peak RPM was at peak fuel flow also, which is totally wrong. And I don’t even remember what the EGT was doing anymore, but I remember it as being completely all over the place.

I cannot go and check at the moment as my game pass expired (I’m not paying 10 bucks a month for that), and honestly I’m not convinced on the sim as it is now. Maybe if they will show a properly working mixture, I might get it. Yes, this is such a big deal for me.

So, as fuel flow decreases, I would expect at some point a peak RPM, followed by peak CHT, and followed by peak EGT, in that order. Ideally, after peak EGT, we should also have best economy (max range).

They don’t need to be perfectly modeled, exactly the correct temperatures, exactly at the right fuel/air ratios, etc. But I do expect to see those key points in the correct order! Anything else, and they are unflyable to me, and I will just wait until there’s a decent add-on for the trainers (C152, C172).

Cheers.

150

Yup, got a bit frustrated as one gets when he can not convey his point, sorry about that. :slight_smile:

In MSFS, peak EGT (or TIT in turbos) is as it should left of peak RPM, but I have my doubts about peak CHT, I fear peak CHT & peak EGT occur at the same mixture level.

Anyway moot point as they’re about to change things up, we’ll see what the forecoming “mixture update” will bring, I’ll try to test things properly then and bring some feedback.

Cheers.

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151

That would be great, I’m really interested in seeing the result. It will have a great impact on me deciding whether to get the standard version… the premium deluxe… or nothing at all :smiley:

152

So I’m super excited for this as the baron is by far my favorite. I am anxiously awaiting proper mix, cowl effects and hopefully someday the compression/egt and the cabin heat controls.

One thing I did notice is at launch she was only ever powerful enough to get 1500-2000 fpm climb. In the the last update or two I was able to get 2-3500 at sea level up to 10k. That was exciting but I think she was still doing a baked in automix. Weird but ill take it.

Still super excited.

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153

Should we ask what ever happened to the mixture in the new dev Q&A?

154

One of the community managers stated that it was pushed back to a later (next?) update, because they wanted to make sure the fix will not introduce new issues.

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155

Jayne already said it was pushed back to the next update to make sure it didn’t cause bugs

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156

I hope the new mixture update also models the interaction with turbocharged engines correctly.

In FSX/P3D this was completely wrong. Whilst manifold pressure would remain constant in the climb until reaching critical altitude, mixture required leaning as if it was a naturally aspirated engine.

We can only hope they take the time to get it right.:crossed_fingers:

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157

The way I “read” that information, is that they found bugs and need to fix it some more… or they found out that the logic needs to be properly redesigned.

I hope it makes it into the next update… I’m waiting for this to decide weather I buy the premium deluxe (to get the default steam gauge C172), or if I just get the standard version and buy a decent add-on with the money savings.

As it stands now, I would not have fun flying the steam gauge C172, if setting the mixture for cruise would be totally off from its real life counterpart.

Cheers.

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158

I dunno, is that the only reason you’d be buying the Premium? I’m regretting it, a little.

  1. You only need the Deluxe for the C172 Classic
  2. In general, All of the planes in MSFS aren’t really much better than FSX default planes. Ok, yes, they’re better than that, but not relatively so. The performance mods have MADE this sim for me. We can’t edit the Premium/Deluxe planes to make them better, at least not yet… so… this is a HUGE check mark against them as far as I’m concerned.
  3. I will rarely, if ever, fly into any of the Premium or Deluxe airports. I’m an East Coast US GA flyer.
  4. In FSX, you needed Deluxe to get the SDK, so that was huge to me. Not so here.
  5. I don’t think we’ll be getting any more content associated with Premium/Deluxe versions, so I’m not sure what advantage I’m getting out of having purchased it?

Were I to do it over again, I might only have chosen deluxe for the Classic 172, or… more likely, like you said, spent the money on addons.

Granted, it’s only $60, so not a huge loss, so I’m not really that sad; but, knowing what I know now, there’s not much advantage to Deluxe or Premium to me now. Even just trying to use the Premium/Deluxe Liveries that are out there crash the sim for me, and I haven’t bothered to take the time to figure out why. But, on the flip side, I’m happy to have supported further development of the sim, so there’s that. That adds value.

I really purchased Premium for the SR22. That alone could have justified it for me if it flew ok. But… not so much, I haven’t flown it since I bought the sim, the modded planes just fly so much nicer too me. The Classic C-172 does flies ok, and it does have the GNS530 which does get replaced by the mod, so I did have fun with it for a while. But, now, instead, I’m flying the Mooney and PA44 which both also use the 530 and are steam gauge, too, and more my style of plane. (the plane I rent has a 530, so that’s important to me as I need to learn how to better use it).

I hope they open access to the Premium/Deluxe planes someday so people can make them flyable. I mean, for the casual simmer/gamer/person being introduced to flying, they’re probably great. I was looking for a bit more.

Don’t get me wrong, I love the sim as is, and what’s planned has me even more excited. You just triggered a Premium/Deluxe rant to come out… :slight_smile:

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159

Anyone tried out the latest update yet? Says the SR22 mixture was fixed but doesn’t say anything about the others.

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I’m interested to know if any improvements have been made too.