Wondering if there’s typos in the test section of my book.
Posted by 2-4-Dinitro_penis@reddit | flying | View on Reddit | 9 comments
Here's an example of something I thought sounded off:
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True or false? The extra fuel in a rich mixture causes extra heating in the cylinders by its evaporation.
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True.
Everything else I read in this chapter lead me to think that running the mix richer lead to more COOLING, not more heating.
Is this just a typo or am I fundamentally misunderstanding things?
PullDoNotRotate@reddit
False. In fact, takeoff mixtures are almost always deliberately over-rich (via power enrichment) to provide that extra cooling when the most power is required.
flyingron@reddit
Evaporation of anything causes cooling. However, that's not what is happening with a rich mixture anyhow. The main reason why a rich mixture is cooler is because you are generating less power when you get away from the peak (stoichiometric point).
So, the question is false for a number of reasons.
3minence@reddit
I don't see how this can be correct. I can't seem to find an interpretation of the question that makes that answer make sense.
If we are saying more fuel = more evaporation, then by the process of phase change liquid to gas, the fuel is absorbing heat to do that, cooling the cylinder.
More fuel = hotter if you were running lean past peak egt, so then more fuel means hotter, but you are in rough running there, which is both impractical and dangerous.
Any more or less fuel than what you get at peak egt (or the optimal stoichiometric ratio of fuel and air) will cool the engine, not heat it.
2-4-Dinitro_penis@reddit (OP)
I think it’s a typo. Which is strange because it’s not the first version of this book iirc.
This is from “The pilot’s manual- ground school”.
That question goes against what the author said in the chapter as well.
I’m wondering if I should switch study material. This book is… okay. But the way he writes seems to needlessly over complicate things.
Sometimes he includes multiple overcomplicated graphs, often with unlabeled axis, and when I finally figure it out it’s like..: oh…. He could have done this with just one line and a 20 word explanation.
youngbus1141@reddit
What book?
OriginalJayVee@reddit
That doesn’t sound accurate to me. For a given ideal mixture setting at a given altitude, increasing the mixture would reduce the temperature though not solely because of any “cooling effect” of the excess fuel, more because it’s not burning efficiently and therefore not producing its peak combustion temperatures.
This may help: https://www.reddit.com/r/flying/comments/yz3zc3/mixture_and_engine_cooling/
TheAntiRAFO@reddit
Peak heat/temperature will happen at the ideal ratio between fuel and air. Running with more OR less fuel will decrease heat.
More fuel-less air-less compression heating.
Less fuel -more air, not a lot of chemical energy is going into the cylinder which turns into less heat/mechanical motion
In short, you are correct, and to my limited knowledge, it seems a lot of indie test prep content will miss this concept and switch it around
NlCKSATAN@reddit
I would tend to agree with you, based on my experience with working on carbed motorcycles. There might be something I’m missing though.
rFlyingTower@reddit
This is a copy of the original post body for posterity:
Here's an example of something I thought sounded off:
True or false? The extra fuel in a rich mixture causes extra heating in the cylinders by its evaporation.
True.
Everything else I read in this chapter lead me to think that running the mix richer lead to more COOLING, not more heating.
Is this just a typo or am I fundamentally misunderstanding things?
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