Cessna 172 air fuel ratio...

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dtvonly

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dtvonly
Hi. I looked through the 172 poh but did not find, numerically, what the proper air-fuel ratio is. For that matter, is c152 air fuel ratio the same? Thanks.
 
dtvonly said:
Hi. I looked through the 172 poh but did not find, numerically, what the proper air-fuel ratio is. For that matter, is c152 air fuel ratio the same? Thanks.
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How do you intend to use this information in flight?

Besides, the proper air-fuel ratio varies with what phase of flight you're in anyway. As far as I know, the "ideal" number is a function of chemistry, not engine design. Stoichiometric ratio is 14.7:1, but that may not be "proper" depending on what you're doing with the airplane at the time.
 
How are you expecting to measure air/fuel ratio?
 
What difference does it make what the numerical A/F ratio is when you have no instrumentation installed to measure it?
 
In general, the mixture (if you have Exhaust gas temperature sensors) would be set reletive to the "peak" temperature (which is pretty close to the stoichiometric, or chemically correct, ratio). Traditionally, one runs rich of peak because airplanes come from the day when gasoline was dirt cheap and it didn't matter if you **** some out the exhaust. Some individuals advocate running lean of peak when at cruising power to save fuel, reduce the risk of CO poisoning, and otherwise just be sensible. Others, of course, will tell you that running lean of peak will cause your airplane to crash into a school for children of personal injury attorneys. Or something like that.

 
dtvonly said:
Hi. I looked through the 172 poh but did not find, numerically, what the proper air-fuel ratio is. For that matter, is c152 air fuel ratio the same? Thanks.
Click to expand...

It is not in there directly just because it isn't very useful.
Also depends on what you are doing, Maximum Power, Best Economy?

These numbers are in the Power setting charts. a bit of math you could probably figure out the approximate fuel ratios, ie. calculate how much air pumped at an RPM vs the published gallons per hour.

Brian
 
OP if you want numbers, here they are (approximately):
Full rich 10:1 (cools the engine for climbing)
Best power 12:1 (adjust mixture for maximum rpm)
Best Economy 15:1 (adjust mixture for peak EGT)

C152 same as C172 and basically the same for any gasoline powered engine.
 
You didn't say which model of C172, but if it's Lycoming powered, go to the Lycoming website and download the appropriate engine operating manual and it will tell you everything you want to know to figure out the answer to your question. You will need to know what your MP is though...
 
You need to know much more than MP. Restrictive losses through carburetors and throttle bodies can vary and depend on altitude, temperature, humidity, and a zillion other things. Well not a zillion but several other. Most modern EFI cars have mass flowmeters to help control their ECMs.

Stick to the POH if you ain't know better and you can't aks someone.
 
Sac Arrow said:
You need to know much more than MP.
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Sigh... Yep, that's true, but I figured temperature, atmospheric pressure, altitude and RPM were things the average C172 pilot would have available to them. I haven't seen a lot of fixed pitch C172's with MP gauges and that's why I mentioned it...
 
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