Annual completed. Do you agree?

[Clark1961]

-- air density is the real driver, not air pressure

Now there is a classic one.

density=MW*Pressure/(ZRT)

MW = molecular weight, 28.97 for air IIRC
Z = compressibility factor
R = gas constant
T = absolute temperature, degrees Fahrenheit + 460

So density varies directly with pressure and indirectly with temperature

At 50 degree change in temperature is about a 10% change in density for temperatures we normally operate in.

A 1,000 ft elevation change is inconsequential so pick a number for altitude and stick with it. Normally that number is in the 3,000 to 5,000 ft range.

 

[Bill]

A 1,000 ft elevation change is inconsequential so pick a number for altitude and stick with it. Normally that number is in the 3,000 to 5,000 ft range.

So my choice of 5000msl was fairly logical after all. B)

 

[poadeleted20]

I agree it's not necessary but it's not going to "shock cool" or otherwise harm the engine.

It won't cause "shock cooling", but whether it causes harm depends on whether you consider fouling the plugs and creating lead deposits to be "harm", because that's what happens when you pull the throttle back and push the mixture forward.

 

[poadeleted20]

Re: leaning during climb.

I apply the philosophy of determining your plane's full power EGT at sea level on a standard day (if you have an engine monitor like I do then pick a cylinder, I use #1).

Then lean to that EGT before take-off and slowly dial out the mixture as you climb to maintain that EGT.

That comes from either Mike Busch or the Ada boys, I don't recall which.

AFAIK, Walt Atkinson is the one who started saying that, but I think he also said you shouldn't do it without all-cylinder CHT instrumentation. See rbridges' comment about how fast the CHT's run up when he leans in the climb. And you need all cylinder EGT, too, lest you find one uninstrumented cylinder spiking while the instrumented cylinder reads what you want, e.g., my #3 is usually the high EGT, but in climb, #2 is higher, and that can drive the #2 CHT highest on the engine in climb.

 

[poadeleted20]

I don't want to derail this, but how do you determine whether the engine is running "rough." There's obvious roughness, and there's the subtle sensation that the engine isn't quite as smooth as it was before reducing richness. The first is something you hear, and the second is something you feel (feel implies something obvious - I mean something really subtle.)

I think that's a matter of demonstration rather than something you can put into words, so get someone who knows what it is to fly with you and demonstrate.

 

[Bill]

Who climbs to 5,000'? Some days I fly 1,000' off the deck for hours and never go higher. Lean all the time except for take off.

Not me, usually climb 8-10k for most trips longer than an hour.

 

[poadeleted20]

That procedure sounds like it requires a full power run up each flight(?).

The procedure Walt recommends is primarily for leaning in the climb, but it can be applied to high DA takeoffs, where with a fixed pitch prop a full power run to lean to peak RPM is necessary anyway. However, most c/s prop aircraft come with some sort of recommendation on how to do this, usually by fuel flow rather than EGT.

 

[Bill]

Note however, that doesn't mean you should not enrichen the mixture on most engines when coming down in a descent.

Yeah, the Mooney has a high redline, I normally leave cruise power set and dial in a 500fpm decent. I get 180-185kts on the downhill, which makes up some for the climb. I have to keep an eye on EGT and enrichen as we come down.

 

[steingar]

Is there a salient reason to not lean below 5k feet? If it boosts RPM, why not?

 

[timwinters]

I never see a CHT over 350.

Regarding shock cooling by going full rich...

I find the opposite to be true. When I get to cruise altitude (and I've been slowing leaning as I climb) if I don't wait about 5 minutes before "doing the big pull" then I will set off my shock cool alarm which is set at 35df/min.

If I wait about five minutes to let things "settle in" on their own and then do "the big pull", the alarm never goes off.

 

[poadeleted20]

So my choice of 5000msl was fairly logical after all. B)

I've seen DA's more than 3000 feet different than the MSL altitude. I'll stick with doing it by DA.

 

[poadeleted20]

Is there a salient reason to not lean below 5k feet? If it boosts RPM, why not?

Because it can drive CHT's beyond their design limits. The biggest reason for running full rich (which is significantly overrich) on takeoff and during climb is to prevent overtemping. Your engine's cooling system is designed to keep it properly cool at normal cruise power, normal cruise speed, and appropriate cruise mixture setting per the POH. In a climb, you're developing more power and getting less airflow through the engine compartment than is necessary to keep it cool unless you lower the combustion temps by running way rich. If you have an engine analyzer, this is easy to demonstrate.

 

[comanchepilot]

No. There isn't any legal fixed pitch prop installation which is going to redline at climb speed. Just make sure when you're transitioning from cruise to climb that you are raising the nose to climb attitude while you advance the throttle so you slow to climb speed as power comes up, and you'll be fine.

We are only talking about climbs? You are right Ron but redline is an issue and during descent . . . and redline is a red line . . . do not exceed.

 

[poadeleted20]

I never see a CHT over 350.

Good. In your 182 with its Continental engine, you really want to keep it there. Continentals generally have much lower CHT limits than Lycomings, and what is acceptable in a Lycoming can cook a Continental in relatively short order.

 

[poadeleted20]

We are only talking about climbs? You are right Ron but redline is an issue and during descent . . . and redline is a red line . . . do not exceed.

The post to which I was responding did indeed only cover climbs, and the poster said he didn't lean during climb because he was afraid the engine RPM would rise above redline. For cruise and descent with a fixed-pitch prop, you'd better keep the throttle back to stay under redline RPM because you have no idea what bad things might happen if you don't. However, even there, I don't see riching the mixture as an appropriate means to keep RPM under redline -- that's what the throttle is for, and riching the mixture is only going to foul the plugs and lead up the engine.

 

[Bill]

Because it can drive CHT's beyond their design limits. The biggest reason for running full rich (which is significantly overrich) on takeoff and during climb is to prevent overtemping. Your engine's cooling system is designed to keep it properly cool at normal cruise power, normal cruise speed, and appropriate cruise mixture setting per the POH. In a climb, you're developing more power and getting less airflow through the engine compartment than is necessary to keep it cool unless you lower the combustion temps by running way rich. If you have an engine analyzer, this is easy to demonstrate.

If he is at, say 3000msl, and pulls the black knob back such that power is <=75%, could he not lean then? I lean all the time at 3k for short trips, but am at significantly less than full power. (more like 55%)

 

[poadeleted20]

If he is at, say 3000msl, and pulls the black knob back such that power is <=75%, could he not lean then?

Maybe, but not certainly unless he is at cruise speed. As I said, the engine cooling system is not designed to provide adequate cooling for continuous operation even at 75% power when leaned below 5000 DA. Without all-cylinder CHT, you're shooting in the dark if you lean more aggressively than the POH suggests, especially in a climb (which is what we were discussing).

I lean all the time at 3k for short trips, but am at significantly less than full power. (more like 55%)

55% in level cruise flight? Not a problem at 3000 MSL regardless of OAT/actual DA.

 

[murphey]

I think that's a matter of demonstration rather than something you can put into words, so get someone who knows what it is to fly with you and demonstrate.

Come on up to Colorado, we'll take a run up to Leadville and will demonstrate leaning to rough engine.

MSL - 9934
DA in the summer - easily over 12K

 

[timwinters]

What works on one engine might destroy the next one. You guys can't discuss this topic with a "this will (or won't) work on every engine out there" approach.

My engine typically cruises with CHTs about 320 (and #6 at 290). I have to climb very aggressively on a hot day to get the CHTs over 350.

What I can do to/with my engine is completely different than what someone who struggles to keep CHTs below 400 can do.

In fact, I can do just about anything to my engine without too much concern for its health. Many cannot.

 

[Clark1961]

What works on one engine might destroy the next one. You guys can't discuss this topic with a "this will (or won't) work on every engine out there" approach.

What are you talking about? I take off full rich every time no matter what altitude so every engine should be able to do the same. [stamps foot]

 

[Shawn]

I have not been leaning for taxi

I too never leaned for taxi...until one day the engine started sputtering at 500' on climbout!...EEEEEEEK!...can you say pucker factor! Well, had a whole lotta fouled up plugs on the bottom of the jugs that didn't get caught in the run up. After cleaning all the plugs, A/P suggested to lean aggressively for taxi and run up to 1500 RPM before pulling mixture for shut down to keep any build up on the plugs burned off.

Now I lean for taxi!

 

[SixPapaCharlie]

and run up to 1500 RPM before pulling mixture for shut down to keep any build up on the plugs burned off.

I've not been doing that. I just pull the mixture at whatever RPM I am at when parking the plane.

 

[brcase]

<snip>
and I generally go full rich as soon as I am about 8-10 miles out from my destination. I have a bad habit of trying to make the first turn off so I guess that is killing the brakes.

I actually think this is a good technique. Lean it to about the setting you are going to land with, 4 or 5 minutes before you enter the pattern. This will start pre-cooling the engine before you reduce power on downwind. When you have an engine monitor that shows cooling rate you can really see how this gradually brings your engine temperature down in preparation for landing.

I agree you almost can't hurt an O-320 with anything you do but it is still a good habit and arguably better for your engine.

Worst case is enter the pattern go full rich and reduce power to a landing descent power setting at the same time. Which is probably the scenario you mechanic is concerned about.


Brian

 

[poadeleted20]

...and run up to 1500 RPM before pulling mixture for shut down to keep any build up on the plugs burned off.

That's close to Lycoming's recommendation:

9. Prior to engine shut-down the engine speed​

should be maintained between 1000 and 1200​

RPM until the operating temperatures have​

stabilized. At this time the engine speed should be​

increased to approximately 1800 RPM for 15 to 20​

seconds, then reduced to 1000-1200 RPM and​

shut-down immediately using the mixture control.

See Lycoming Service Letter L192 for more details. This is especially important if your engine was originally designed to run on 80/87 or 91/96 avgas, since even "low lead" 100LL has 2-4 times the tetraethyl lead as those fuels had.

 

[SixPapaCharlie]

Adding that to my checklist.
Thanks Ron!

 

[comanchepilot]

That's close to Lycoming's recommendation:
See Lycoming Service Letter L192 for more details. This is especially important if your engine was originally designed to run on 80/87 or 91/96 avgas, since even "low lead" 100LL has 2-4 times the tetraethyl lead as those fuels had.

everyone forgets this one - its been on the checklist for a while - also - lean it pretty good whilst running it up - don't let it backfire but lean it out - such will increase the combustion temps and burn some off too . . .

 

[comanchepilot]

I too never leaned for taxi...until one day the engine started sputtering at 500' on climbout!...EEEEEEEK!...can you say pucker factor! Well, had a whole lotta fouled up plugs on the bottom of the jugs that didn't get caught in the run up. After cleaning all the plugs, A/P suggested to lean aggressively for taxi and run up to 1500 RPM before pulling mixture for shut down to keep any build up on the plugs burned off.

Now I lean for taxi!

you should be so lean that the motor wlll run at taxi rpms but the moment you increase power for take off - it sputters from a lack of fuel. Then its leaned right since you will not be able to take off without increasing mixture

 

[flyingron]

you should be so lean that the motor wlll run at taxi rpms but the moment you increase power for take off - it sputters from a lack of fuel. Then its leaned right since you will not be able to take off without increasing mixture

If you don't lean that much, you're not doing anything anyhow. The idle loop keeps a pretty high mixture until you get the knob pretty close to cutoff.

 

[flyingron]

you should be so lean that the motor wlll run at taxi rpms but the moment you increase power for take off - it sputters from a lack of fuel. Then its leaned right since you will not be able to take off without increasing mixture

If you don't lean that much (with a carb), you're not doing anything anyhow. The idle loop keeps a pretty high mixture until you get the knob pretty close to cutoff.

 

[Shawn]

you should be so lean that the motor wlll run at taxi rpms but the moment you increase power for take off - it sputters from a lack of fuel. Then its leaned right since you will not be able to take off without increasing mixture

That sputter was from the fouled plugs while full rich, not forgetting to enrichen after taxi...but that is a great tip so I don't have another sputter at 500' from forgetting to enrichen the mixture before departure!

 

[comanchepilot]

That sputter was from the fouled plugs while full rich, not forgetting to enrichen after taxi...but that is a great tip so I don't have another sputter at 500' from forgetting to enrichen the mixture before departure!

I understood that- but the ground lean, like Ron mentions, in a carb'd motor needs to be really lean before it matters. . .

 

[paflyer]

Who climbs to 5,000'? Some days I fly 1,000' off the deck for hours and never go higher.

Look where you live.

 

[Fearless Tower]

Re: leaning during climb.



I apply the philosophy of determining your plane's full power EGT at sea level on a standard day (if you have an engine monitor like I do then pick a cylinder, I use #1).



Then lean to that EGT before take-off and slowly dial out the mixture as you climb to maintain that EGT.



That comes from either Mike Busch or the Ada boys, I don't recall which.

Pretty sure it comes from Deakin, although his recommendation is to note your EGT at 1000' AGL and use that as the reference to lean to.

 

[Fearless Tower]

I've not been doing that. I just pull the mixture at whatever RPM I am at when parking the plane.

If you own the airplane or are the only person flying it, set your RPM to your normal starting RPM (typically between 800-1200 RPM), then pull the mixture to shutdown and leave the throttle alone. If you do that, you'll avoid being the guy who starts the engine and RPM goes up to 2000+ right off the bat.

 

[Bill]

If you own the airplane or are the only person flying it, set your RPM to your normal starting RPM (typically between 800-1200 RPM), then pull the mixture to shutdown and leave the throttle alone. If you do that, you'll avoid being the guy who starts the engine and RPM goes up to 2000+ right off the bat.

Depends. On our fuel injected engine, I use a different throttle setting for prime vs. starting.

 

[Fearless Tower]

Depends. On our fuel injected engine, I use a different throttle setting for prime vs. starting.

What engine? I have IO-470s and I use the same.

 

[SixPapaCharlie]

Got the plane this evening. First flight since the annual (showroom clean and that was a nice surprise). Dad and I flew to dinner. And then relocated to our new home at KDTO.

 

[JimNtexas]

I figure if aerobraking is good enough for the F-15, it's good enough for me.

 

[RickG]

you should be so lean that the motor wlll run at taxi rpms but the moment you increase power for take off - it sputters from a lack of fuel. Then its leaned right since you will not be able to take off without increasing mixture

This is the procedure I follow (O-300) while taxiing before takeoff.

Q: After landing, do you lean again for ground ops while taxiing to hangar / tie down / parking spot? Or do you leave the mixture rich so the fuel helps with the engine cool down?

 

[Bill Watson]

That's close to Lycoming's recommendation:
See Lycoming Service Letter L192 for more details. This is especially important if your engine was originally designed to run on 80/87 or 91/96 avgas, since even "low lead" 100LL has 2-4 times the tetraethyl lead as those fuels had.

When I went to Lycoming engine school, the instructor commented on how important this issue is in terms of reducing lead deposits. He said he was surprised to see how much and how quickly lead was deposited if temperatures were allowed to fall before shutdown. Even a few seconds would start the process. It's all about keeping temps up.

you should be so lean that the motor wlll run at taxi rpms but the moment you increase power for take off - it sputters from a lack of fuel. Then its leaned right since you will not be able to take off without increasing mixture

That's what I do and it works real well.

If you don't lean that much, you're not doing anything anyhow. The idle loop keeps a pretty high mixture until you get the knob pretty close to cutoff.

I had no idea what this was about until engine school but I get it now.