Mechanical Questions 101
- Thread starter LifeAsBen
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Aztec Flyer
You are leaning as you increase altitude. The air density change that an airplane is subject to is much greater than in a typical trip in a car. Once you start leaning an aircraft piston engine below peak in cruise the output of the engine decreases. The CHTs will drop and the engine is actually running cooler.
An auto engine will do the same thing. Provided you can run it at a constant load, at a constant RPM at a constant altitude. Good luck with that.
LifeAsBen
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LifeAsBen
I get that, but it heats up a lot at peak, correct? I don't know but I imagine cars are never leaned to peak. I'm simply curious if maybe the pistons in aviation are able to withstand higher temps.
Subsea
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Subsea
Excessive leaning (near peak EGT or leaner) will only cause a problem at high power levels...usually above 75% of the rated HP of the engine. When you go up in altitude, there is physically less air available (unless you are turbo charged), so it's difficult to get above 75% of the rated power, or you can just pull the throttle back at a lower altitude.
You can lean a gasoline engine all day long at a low power setting and it will do no damage (there are varying opinions on this matter, but no one had burned a hole in a piston, they may have had to change out their cylinders at 1900 instead of 2000 hrs). Screw the power to it and go lean, and you're asking for it.
If you are driving a car up the mountains, it will lean itself utilizing the oxygen content of the exhaust to guess current mixture. Cars are run rich of peak for performance and smooth operation.
You can lean a gasoline engine all day long at a low power setting and it will do no damage (there are varying opinions on this matter, but no one had burned a hole in a piston, they may have had to change out their cylinders at 1900 instead of 2000 hrs). Screw the power to it and go lean, and you're asking for it.
If you are driving a car up the mountains, it will lean itself utilizing the oxygen content of the exhaust to guess current mixture. Cars are run rich of peak for performance and smooth operation.
I would venture to guess that cars are indeed leaned to peak, when running in closed loop.
Capt. Geoffrey Thorpe
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Light and Sporty Guy
Yup. That's just about exactly where they run most of the time. But, at least some will go rich when run at very high power levels for an extended time.
If you need to go rich to reduce temperatures under certain conditions, then you need to run rich. However, if there is no need, say at 60% power, then running rich is just ****ing gas out the exhaust.
bflynn
Final Approach
The answer on leaning is the cylinders get hotter and can get hot enough to damage them if you let them. But you're also going a lot faster than a car and hopefully cooling them more efficiently. So you either monitor the cylinder head temperatures or you don't push operations that might get them into elevated ranges - super lean operations, extended slow flight etc.
A question I didn't see answered is about what's under the hood. As I'm sure you remember, there are regulations related to who can work on an airplane and limits on what they can do. A pilot can do very little and that's good because you don't want a bunch of other goofballs tinkering with the engine that you're flying behind. If you own the aircraft you can do a little more, change the oil, service the spark plugs, etc. 14 CFR Part 43, Appendix C, section (c)(30) tells you what an owner can do, which is basically the items listed in section (c). Some very capable owners develop a good relationship with their A&P mechanic and do work under supervision with the mechanic inspecting and certifying the work performed. Other than that, you need to be a certified mechanic to work on airplanes.
Speaking off spark plugs and fouling, they shouldn't. Fouling indicates running too rich. They should be a nice dusty grey color.
A question I didn't see answered is about what's under the hood. As I'm sure you remember, there are regulations related to who can work on an airplane and limits on what they can do. A pilot can do very little and that's good because you don't want a bunch of other goofballs tinkering with the engine that you're flying behind. If you own the aircraft you can do a little more, change the oil, service the spark plugs, etc. 14 CFR Part 43, Appendix C, section (c)(30) tells you what an owner can do, which is basically the items listed in section (c). Some very capable owners develop a good relationship with their A&P mechanic and do work under supervision with the mechanic inspecting and certifying the work performed. Other than that, you need to be a certified mechanic to work on airplanes.
Speaking off spark plugs and fouling, they shouldn't. Fouling indicates running too rich. They should be a nice dusty grey color.