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MaxGM

Mixture adjustments

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Hello everyone.

 

As I am digging into BoS, I was wondering about mixture management, and I have a few questions for the in game experience as well as out of sheer curiosity.

I have tried google and the forum search engine, but didn't find the grail.

 

First, what does the mixture % displayed by the technical chat represent ? 0% is lean and 100% rich I figured by stalling engines and by the blue flames (complete combustion = less gas). But what does the percentage represent ? 0% seems to be close to actual 0% gas in the mixture, or, at least enough to stop combustion in the engine even when the propeller is rotating, but, what about 100% ? Is it linked to the properties of each carburettor/injectors ? All I know is it does not represent a fixed A/F ratio since adjustment is required with altitude, but I still wonder what it is exactly.

 

Then, and the answer to the first question might be the key for this one : how to optimally use mixture adjustments to save fuel during cruise ? The only interests I see would be : 

a: of course, not flying richer than the stoechiometric ratio, as the cooling the unburnt fuel provides is useless at low power outputs 

b: engine load could be (partially at least) managed with the mixture instead of the airflow, thus we can get rid of some of the air intake friction losses.

 

And to finish I was wondering how pilots were managing this (except the Germans and their fully automated stuff ofc :P ). Experience and "cuisine recipes" kind of tricks, or engineering sourced datas ?

 

I thank you guys in advance for your enlightments.

 

 

 

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Almost each plane with manual mixture in the game is controlled differently and has different settings..

Eg,
i16 The mixture set to 100% = Full Auto Rich and reducing it will only lower mixture for economy.
IL2 The mixture set to 50% = Full Auto mode and it will adjust safely from Ground to Service ceiling
Mig3 The mixture set to 50% = Full Auto mode and it will adjust safely from Ground to Service ceiling (manual leaning below 50%)
Spitfire The mixture on 100% = Full Auto rich and 0% = Full Auto Lean (you can adjust within that range if you really wanted to)


Its so varied


 

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My understanding is that any technochat %s do not represent real physical variables - such as the actual ratio of gasoline to air - but simply represent the % of travel on the axis between the two ends.

 

When the developers do the engine model, they will try to fix the two ends to correspond to the settings in the actual plane, in so far as the complex engine management actually includes the physical variables, but as the above poster points out, these vary from plane to plane.

 

I terms of actual use, the best bet is to read the Tech Specs or actual Pilot's Notes for the type, and see how the actual controls were intended to be used for that specific plane type.  This will (almost always ?) give sensible in-game results.  You can use the feedback from your instruments to fine tune once you have a clear idea of how your current ride performs.  

 

Practically speaking I would bet that less than 0.0001% of sorties in BoX (or other CFSs) ever attempt to conserve fuel by using mixture, especially in MP.  If they were going to do that, they would not all be taking off with 50% fuel loads!  Even in SP, it is very rare to get a mission designed so that fuel economy is ever an issue, unless you get an actual fuel leak, in which case looking for a place to land is more of a priority. So leaning for economy cruise is a topic hardly ever discussed...    Generally people are just trying to get maximum performance, and again, given that the vast majority of flights and fights take place at low altitudes, most people can fly at full rich or auto rich almost all the time without worrying.  

 

This may change if we get to the Pacific, although I would not bet on it. 

Edited by unreasonable

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on warbirds, it's not very common to lean for performance - usually for that you'd just blast it full open for that, and leaning is used mainly to save fuel whenever you're not about to die in a violent fireball...

 

there is one plane which has a rather unique feature for mixture control - and it seems to be properly modelled too:  the Pe2 series 35.   it has a very curious pair of gauges atop the right side, marked only with a lower-case alpha - those are actually air/fuel ratio indicators

 

this is quite unusual, as most planes don't have this gauge at all (I had never seen it before this)

 

 

some research suggests best performance is (perhaps) achieved at .8~.9 indicated ratios - or something....

 

yet I don't really know what exact method the gauge uses to calculate this ratio, as you can see in the link above, there's more than one way to get there - and that would very much change what readings you'd want for best performance.... 

 

 

 

I'm also not sure if those gauges do anything more than visually indicate what should be happening in the engine...   maybe they just "fake it" - while the engines themselves use a more simplistic model in practice (like our oil/fuel pressure gauges will do)

 

 

but that can only be answered by devs, I think.... 

 

I also don't know what exact method the gauge uses to calculate this ratio, as you can see in the link above, there's more than one way to get there

Edited by 19//Moach

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Well, after having tested a bit, it is really hard to find the sweet spot for the perfect mixture.

 

I did some experiments on the La-5(did I mention I love radials ? :D ). What I usually do is leaning while watching my RPMs, when they start to noticeably drop (by that I mean that you can see it on the meter, not 100RPM, so when the needle starts to "really move"), that is usually the moment when the flames go from yellow to blue. Now adjusting on the M82 is not particularly usefull since mixture 100% = automatic. But it can allow some savings during cruise.

 

That mixture control skill seems (on paper at least) to be way more important in the klimovs who don't have any automated regulation. 

Thus I checked the Pe-2 with the alpha gauges (figured an instrument to match engine behavior with displayed A/F ratio would be more useful than testing it blind on a yak), and frankly it intrigued me.

I know the oxygen sensor we use in the car industry were designed somewhen around the 60's, so I am really curious about how those 1940's A/F gauges worked. My instincts tell me it was a flow measurements comparison. Assuming they work perfectly, it seems that the klimovs are really gas thirsty since when the needle gets close while still being inferior to 1 (theoretically a bit rich, close to the stoechiometry), engines lose power perceptibly. An engine should not lose much power with a mixture close to the stoechiometry normally, especially a rich one, so I was wondering if these gauges were accurate, or if this a mixing issue (ie not homogeneous mixture in the chamber that would have lean spots and dampen flame propagation).

EDIT 1: after further testing, the RPM starts to drop a bit (which is what I observed) when closing to 1 on the alpha gauge, but it does not result in a perceptible loss of speed, so I am actually not too bugged by this. It is basically a behavior similar to the one I observed on the shvetsov M82.

 

EDIT 2 : some numbers added : Moreover, after a climb on the peshka, alt ~5000m, supercharger on 2nd gear, I set the mixture to get lambda around 0.9. Throttle down to get ~700mmHg of manifold pressure. The lambda ratio seems to be conserved. Now, with the same mixture lever position, I go full throttle, switch the supercharger to 1st gear (to simulate an increase of altitude without having to climb), get ~700mmHg of manifold pressure, but I see my lambda drop (to around 0.7-0.8).

 

Thus I don't get how the mixing work. My idea of a basic carburettor is that the mechanical flow of air, goes through a venturi which results in a proportional pressure loss that sucks fuel in, and thus mixture is basically adjusted with air flow, so why do we have to adjust in this case ? Is the injection happening before the supercharger in this case ?

In short, I don't really understand the Klimovs so far  :wacko:

 

To conclude I'm in the market for some books about WW2 engines. Especially these Klimovs with their early lambda gauge, and the BMW 801 fully automated controls, so if anyone knows some good references, I'm interested. I soon will have quite some time to kill, and having a "productive" way to do so is appealing  :lol:

Edited by MaxGM

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I'm a newbie in mixture control too. I don't know if there is tutorial missions or videos, but each time I'm flying I put everything at 100% and no problem... (Flying LaGG3 mostly).

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I had wondered the same thing about those "lambda gauges" myself

 

but it's worth pointing out, these gauges are really marked with what looks like a lower-case A, or "alpha" - or maybe something else that looks quite a lot like it, the "" proportionality indicator

 

 

I have not come across any clear definition of how exactly those gauges work, but "lambda" was my first guess as well (why does it read "α" or "∝" then?)

 

 

so, according to wikipedia, one could expect to get best performance at around .7~.9 indicated... assuming of course, this is really λ that's being measured here 

 

 

Ideal-stoichiometry.jpg

 

but I don't really think that's the case, seeing how the gauges appear to function I'm more inclined to say this isn't really lambda at all being shown.

 

this gauge shows most likely something else, I think...  something kinda like λ, but not λ exactly...  

 

 

 

I have not yet figured out exactly what that is, though - does anyone have a clue? either historically or mathematically guessing?

 

 

I would very much like to see some official (dev) confirmation of this, and a more thorough description of just how this whole thing is implemented - I still can't tell if those gauges actually show real simulation parameters, or if they simply "fake it" like our fuel and oil pressure indicators do.

Edited by 19//Moach
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