Engine Shutdown Question...

[trafficinsight]

Leaning for a 20-50 RPM rise (at 1000 RPM) is pretty standard at my school. I tend to lean really aggressively, and when I've been running the mixture I've never experienced a fouled plug. I've had 2 or 3 foul when students forgot to lean.


:yeahthat:
Question for the other guy-how exactly does leaning in taxi damage an engine? You are not producing anywhere near enough power to damage the engine, no matter what the mixture setting is. Unless you habitually taxi at 85% power. Watch the CHTs-they will stay well cool of any danger zone no matter how you lean on taxi.

Why don't you lean to peak EGT in flight? It's the same on ground, with less cooling airflow. Again, I think it'd have to be a hot day and long ground run, followed by a long climb to altitude to do any damage, and that's if you lean way more than the 1" that's on all those checklists.

Fouled plugs from ground running 99% of the time are carbon fouled and can be burned off during the runup. Lead fouled plugs can't be burned off no matter how hard you lean. Once the lead is on the plug it's not going anywhere.

Also, If you lean and see a 50 rpm rise then your idle mixture is set too rich anyway, when shutting the engine down if you pull the mixture knob out slowly you should see a 25 rpm rise, followed by a drop to idle cutoff. I'd hazard a guess and say that there are a lot of airplanes out there where this is not the case.

I think I may have only had a fouled plug once that wouldn't burn off, and that was after power on and power off landings at a NIFA event. I never lean on the ground. The 152's foul sometimes but they do pattern work all day with the mixture full rich... so I clean the lower plugs at the 50 hour, haven't had one come back for a fouled plug since I started doing that.

If I don't aggressively lean during taxi in my Swift (HIO-360 engine), I can guarantee I will see more than a 150rpm drop on a mag check. Without leaning the mixture, my fowl will be fouled.

Your Swift has an HIO-360? is that a conversion or something?

 

[Roger, Roger]

Why don't you lean to peak EGT in flight? It's the same on ground, with less cooling airflow.

Also, If you lean and see a 50 rpm rise then your idle mixture is set too rich anyway, when shutting the engine down if you pull the mixture knob out slowly you should see a 25 rpm rise, followed by a drop to idle cutoff. I'd hazard a guess and say that there are a lot of airplanes out there where this is not the case.

I will lean to peak EGT in flight, or lean of peak. But only at lower power settings. Again, the power (and therefore heat and pressure in the cylinder) produced in ground running is SO LOW that unless you are running some ungodly hot turbocharged engine you will have trouble even getting close to preignition or detonation. Even with the mixture full rich for takeoff, you get hotter CHTs in the climb than on the ground.

*note: all of this is directed to small, low-horsepower, normally aspirated engines. So if you are flying a Duke or something like that and have no CHT installed to monitor the situation, I can see being wary of doing anything that might reduce cooling.

Also, about the idle cutoff RPM rise-when we check that for mx runs, we check it with the throttle at dead idle (~600 RPM IIRC). Normally when sitting stopped (such as immediately after starting) we open the throttle to about 1000 to keep annoying things like low volts annunciators from dinging at us, get the battery charging, etc. So when the mixture is set for the right rise at ICO, we get a significantly higher rise when leaning at about 1000 RPM.

You're right, though, about a lot of airplanes having incorrect idle RPM rise. In the defense of A&Ps everywhere, it is a pretty finicky and subjective adjustment to make and can change depending on the temperature and pressure of the day.

 

[nosehair]

If you lean and see a 50 rpm rise then your idle mixture is set too rich anyway, when shutting the engine down if you pull the mixture knob out slowly you should see a 25 rpm rise, followed by a drop to idle cutoff.[/ quote]
Haven't been flying any old rental beaters lately, have you?

Yeah, they are more often than not, set too rich. If you don't lean while taxiing, the mag check won't pass - in some engines - and at some density altitudes.

I/we find it a good habit practice for the professional life where you encounter many different engines and conditions and being subject to specific departure and arrival times.

 

[Orange Anchor]

Your Swift has an HIO-360? is that a conversion or something?

Swifts are like snowflakes.. no two the same. My engine came out of a helicopter. Rated 210HP on the helicopter but since I can't pull the RPMs, it is officially rated at 180HP. Still more than enough to give me 1500-1800fpm on takeoff and 135KTAS in cruise at 9GPH.

 

[Hacker15e]

What is the reason for wanting to lean on the ground?

 

[tgrayson]

What is the reason for wanting to lean on the ground?

John Deakin goes into great detail on the how's and why's:

http://www.avweb.com/news/pelican/182045-1.html

 

[HeyEng]

Now THIS is why I joined JC!!! Damn good discussion about AIRPLANE STUFF. Not Obama. Not Union. Not gas prices!!!

Of course, controversy. Now I am wondering if I should be leaning during taxi...anic:

This hobby is expensive enough without tearing up the engines!!!

 

[Roger, Roger]

John Deakin goes into great detail on the how's and why's:

All hail tgrayson for invoking the name of John Deakin!

I knew he addressed it somewhere, I was just too lazy to look.

 

[tgrayson]

Now I am wondering if I should be leaning during taxi...

The only person who questioned it was TrafficInSight and he admitted he didn't have any evidence to back up his view. Most experienced pilots acknowledge the virtues of leaning during taxi. The only slight risk is taking off with it partially leaned. Deakin (and others) advocate leaning almost to the point of the engine quitting, so that if you advance full throttle, the engine *will* quit before it hurts anything.

Don't let someone make you paranoid without good evidence.

 

[HeyEng]

The only person who questioned it was TrafficInSight and he admitted he didn't have any evidence to back up his view. Most experienced pilots acknowledge the virtues of leaning during taxi. The only slight risk is taking off with it partially leaned. Deakin (and others) advocate leaning almost to the point of the engine quitting, so that if you advance full throttle, the engine *will* quit before it hurts anything.

Don't let someone make you paranoid without good evidence.

Oh yes...I am one of those dudes that is always saying "can you show me that in writing?"

The Deakin article was quite enlightening. Looks like I have many other articles to read that he has up there too!!! So much information, so little time.

I tend to think that if you are using the checklist, then you are going to enrichen the mixture anyway, or at least catch it on the "clean-up".

Speaking of flying...it is too nice out there to hang around on the computer. Time to go cruise around the windsock for a bit...later, gator!!! :nana2:

 

[Old Pete]

Leaning for Ground Operations is in the Cessna Pilot Information Manual.

a. set throttle to 1200rpm
b. lean mixture for maximum rpm
c. set throttle to rpm appropriate for ground operations (800-1000)

While I haven't seen the "run-up to 1800rpm before shut down" on a check list or in a manual recently, I remember being taught that procedure when I first started flying.

 

[Lee D]

Speaking from my own experience; I think it is more important to consider leaning during taxi at higher altitude airports, especially on the high density altitude days. I suspect some engines are more prone to this than others, namely the larger ones.

I flew a Cessna 210 from time to time. (It had a Contintental engine. . . 285 HP if I remember correctly.) If you did not lean during taxi you got bigger drops during the mag check and had to burn off the plugs. Had similar issues with a Piper Comanche 250, a Cessna 310 and a Turbo Lance. (All larger engines, all while in the Salt Lake area.) I don't remember it being such a problem in the smaller 172's, Warriors etc.

 

[HeyEng]

Also, If you lean and see a 50 rpm rise then your idle mixture is set too rich anyway, when shutting the engine down if you pull the mixture knob out slowly you should see a 25 rpm rise, followed by a drop to idle cutoff. I'd hazard a guess and say that there are a lot of airplanes out there where this is not the case.

So after flying today, I gave this a try. I brought it to 1,000 RPM and leaned it out pretty slow. If there was a rise AT all, it was very slight. This would lead me to believe that leaning during taxi doesn't do a whole lot anyway, at least on my plane...but that is just an assumption, so I will continue to lean for taxi.

 

[Hacker15e]

Interesting article, thanks for the link.

 

[trafficinsight]

Swifts are like snowflakes.. no two the same. My engine came out of a helicopter. Rated 210HP on the helicopter but since I can't pull the RPMs, it is officially rated at 180HP. Still more than enough to give me 1500-1800fpm on takeoff and 135KTAS in cruise at 9GPH.

I think that holds true for all old airplanes I'd never heard of them doing that before.

I like Swifts, and I totally would love to have a Swiftfury someday

 

[trafficinsight]

The only person who questioned it was TrafficInSight and he admitted he didn't have any evidence to back up his view. Most experienced pilots acknowledge the virtues of leaning during taxi. The only slight risk is taking off with it partially leaned. Deakin (and others) advocate leaning almost to the point of the engine quitting, so that if you advance full throttle, the engine *will* quit before it hurts anything.

Don't let someone make you paranoid without good evidence.

Nobody has evidence, just opinion, nothing wrong with that. I agree with Deakin on a lot of points and happen to disagree with him on this one.

No reason to result to veiled insults.

 

[Orange Anchor]

I think that holds true for all old airplanes I'd never heard of them doing that before.

I like Swifts, and I totally would love to have a Swiftfury someday

The Swift Fury is really a completely different machine with a different wing. It looks like a Swift and I sure hope they sell lots because that will pull the value of the original Swifts up.

Some are not aware that some guys that worked on the Curtiss P-40 (Flying Tigers' fame) worked on the Swift. Here is an image of the two machines.

 

[Orange Anchor]

Nobody has evidence, just opinion, nothing wrong with that. I agree with Deakin on a lot of points and happen to disagree with him on this one.

For my engine, I know that if I don't lean while taxiing (my airport is 1200ft MSL) I will foul the plugs. Twice I forgot and I had them load up enough that i had to pull them and clean them. Not a good way to start a trip.

 

[mjg407]

Same for my weee-bity Cheetah with the O-320 HC engine. Don't lean, stand by.

 

[CoffeeIcePapers]

Fouled plugs from ground running 99% of the time are carbon fouled and can be burned off during the runup.

Let me get this straight... You think running the engine at 1000RPM with a lean mixture causes more heat and more damage than running the engine at 1500-2000RPM with a lean mixture to burn it off? How does this make any sense at all?

Not trying to take a shot at you, just trying to follow our logic.