Auto-rich mixture question

[Zergling924]

Quick q about how the auto-rich mixture works in general (asking in context of flying La-5 but my question applies to any other aircraft with auto mixture settings as well). For the La-5, how close do I have to be to 100% mixture to get it into auto-rich mode, does it have to be exactly 100%? E.g. if it's 99% then it won't be auto-rich anymore? Or is there some wiggle room? Visually I see that there's a "slot" that the mixture lever settles into at 100%, is this the indicator I should be going by?

 

And a follow-up question: if I want maximum engine cooling with rich mixture, then should I take the mixture out of auto rich and put it as high as possible without engaging auto rich? Assuming that the auto mixture feature might automatically lean out the mixture more than I would otherwise want for max cooling effect.

 

Thanks! Couldn't find a straight answer to this after searching on Google for a bit.

[=MERCS=JenkemJunkie]

I don't remember the min/max details, but it's easy to test for yourself. Just fly in auto level in a quick match and wait for your max speed and your temps to stabilize. Then play with the mixture and see what changes it gives to your speed and temps, and there's your answers. Do it at x8 speed.

Edited April 21 by =MERCS=JenkemJunkie

[Zergling924]

Good suggestion! I went ahead and tested it today. In short, I'm not sure if the auto mixture feature on the La-5 does anything, at least in my hands. Here are the tests I did and the results. Long post I know, but wanted to put it in detail in case anyone else came across this same question.

 

All of the below testing was done with the La-5 series 8 in quick mission mode in the summer Stalingrad map. I tested 100% mixture which should enable auto mixture (where the mixture lever is definitely settled into the physical maximum position slot) vs 95% mixture which should not engage auto mixture (where the lever is just disengaged from this same physical slot). There is no indication in technochat whether auto mixture is enabled or not, so I am assuming it's engaged only if the mixture lever is settled into the maximum position slot.

 

For reference, this is what it looked like for me at 95% mixture:

 

And 100% mixture:

 

Test 1: how does auto-mixture impact engine cooling?

Auto-mixture (at least to my understanding) should choose an optimal mixture given a plane's altitude, so in theory, auto-mixture is probably going to choose a mixture less than 100% for most altitudes. Therefore, I expected that auto-mixture would lead to less efficient cooling than manually keeping a rich mixture, all other things equal.

 

Test conditions:

- 15% outlet cowl
- 50% oil radiator
- modified engine M-82F (for unlimited boost)
- boost on

- 100% RPM (~2400 RPM)
- 100% fuel capacity (unlimited fuel enabled)

- autolevel enabled at 1500 m altitude

 

I tested 100% mixture vs 95% mixture, letting everything settle out at 8x speed until equilibrium.

 

I found that at 100% mixture (the auto-mixture setting), the oil temperature settled around 97-98. At 95% mixture, the oil temp settled around 100.
 

So if anything, 100% mixture behaves as if it's still putting in more fuel than at 95%, as far as engine cooling.

 

Test 2: does auto-mixture actually conserve fuel?

If auto-mixture chooses a mixture that is significantly less than 100%, then it should conserve fuel compared to something like 95% mixture.

 

For this test, most of the conditions were the same, except I used the minimum fuel and counted how many seconds it took for the engine to stop from running out of fuel.

 

Test conditions:

- 100% outlet cowl
- 100% oil radiator
- stock engine
- boost off

- 100% RPM (~2400 RPM)
- 60L fuel (minimum capacity)

- autolevel enabled at 1500 m altitude

 

At 100% mixture, the engine lasted for 6m2s (362 s), and at 95% mixture, it lasted for 6m22s (382 s).
 

This corresponds to 9.94 L/min fuel consumption (100% mixture) vs 9.42 L/min (95% mixture).

 

These two fuel consumption rates almost match perfectly what would be expected for running at 95% vs 100% (true) mixtures. So it doesn't look like the 100% mixture setting actually leans out the fuel at all, at least under my test conditions.

 

Test 3: does the auto-mixture setting visibly lean the mixture at higher altitudes?

I thought maybe I was at too low an altitude to kick in the "automated" part of the auto-mixture, so I took the plane up to 4000 m altitude to visually confirm if the mixture leaned out at all. There didn't seem to be any visual change in the engine flame color between 100% and 95% mixture settings (both were deep orange). This was a qualitative experiment though, so not necessarily the most conclusive.

 

Overall, this suggests that at least under the conditions I tested, there is no automatic mixture management in the La-5 in the game. I'm not sure at this point exactly what the "auto" part refers to. At the end of the day though it seems like there's not a huge difference between the 100% auto-mixture setting and the 95% "manual" mixture setting, and if you want max cooling then 100% is still better.

Edited April 21 by Zergling924
clarification

[=MERCS=JenkemJunkie]

You've been busy. The 1C pilot note says "It is possible to manually lean the mixture by moving the mixture control to less than maximum." but nothing about making it richer. So it's possible the auto mode at 100% decides the maximum richness, and your only option is to make the mixture leaner than that automated maximum by going under 100%. You'd have to go digging through manuals if you care to find the real world answer though. But yeah, for in-game it doesn't really matter though, just leave at 100% unless you want to save fuel.