Leaning in the Climb

[Ironflight]

OK, let me set one rule - this is NOT an LOP thread - OK? You can start your own thread to argue that topic, if you are tired of the old ones....

This is about leaning in the climb...

Most of us probably learned to fly in simple planes with minimal engine instrumentation. Since there were no EGT's or CHT's, we were taught some basic rules of thumb:

1) in cruise, below 75%, lean to roughness, then enrichen until smooth.
2) Don't lean at full power (greater than 75%) below 5,000 - above that altitude, lean until smooth.

These rules were no doubt designed to protect the engine from folks who had no instrumentation, and therefore no better insight into engine operation.

Now let me ask a question about the second rule, and hopefully some knowledgeable engine guys (Mahlon?),will chime in. What exactly, does this rule protect? Is it keeping cylinder head temperatures below limits? Is it to keep EGT's reasonable? To stop from overheating valves? Prevent detonation?

The reason that I ask is that many of us are now flying heavily instrumented aircraft with real-time graphs and alarms for many of the parameters. Given this additional insight, is it, for instance, OK to lean, as long as we keep the temps in limits? 5,000' and 70% power seem like very arbitrary numbers (kind of like the mystery of running "square" or "oversquare" - both of which are really accidents of the units being used...), yet I find myself still sticking to them - even though the engine seems very happy in climb when I do break the rules.

Anyone want to take the first swing at this topic? I am truly curious, as an engineer, if we can manage the systems differently with better instruments!

Paul

[Yukon]

Originally Posted by Ironflight

OK, let me set one rule - this is NOT an LOP thread - OK? You can start your own thread to argue that topic, if you are tired of the old ones....

This is about leaning in the climb...

Most of us probably learned to fly in simple planes with minimal engine instrumentation. Since there were no EGT's or CHT's, we were taught some basic rules of thumb:

1) in cruise, below 75%, lean to roughness, then enrichen until smooth.
2) Don't lean at full power (greater than 75%) below 5,000 - above that altitude, lean until smooth.

These rules were no doubt designed to protect the engine from folks who had no instrumentation, and therefore no better insight into engine operation.

Now let me ask a question about the second rule, and hopefully some knowledgeable engine guys (Mahlon?),will chime in. What exactly, does this rule protect? Is it keeping cylinder head temperatures below limits? Is it to keep EGT's reasonable? To stop from overheating valves? Prevent detonation?

The reason that I ask is that many of us are now flying heavily instrumented aircraft with real-time graphs and alarms for many of the parameters. Given this additional insight, is it, for instance, OK to lean, as long as we keep the temps in limits? 5,000' and 70% power seem like very arbitrary numbers (kind of like the mystery of running "square" or "oversquare" - both of which are really accidents of the units being used...), yet I find myself still sticking to them - even though the engine seems very happy in climb when I do break the rules.

Anyone want to take the first swing at this topic? I am truly curious, as an engineer, if we can manage the systems differently with better instruments!

Paul

Gosh, Paul, with all those caveats, I hesitate to reply, but I'm certain even
Mahlon will agree.........excess fuel at high power settings provides a buffer against detonation.

[L.Adamson]

Originally Posted by Ironflight

2) Don't lean at full power (greater than 75%) below 5,000 - above that altitude, lean until smooth.

Out here in the mountain west at 4600' msl, we'll assume you're going to lean the engine, everytime, before the takeoff roll.

If you don't, you'll loose a good percentage of takeoff power before ever leaving the ground. This has also been cited as contributing cause in numerous departure accidents around here.

Those from "sea-level" cities along the U.S. coast and places such as U.K., seldom seem to believe, will once and a while argue, but it's a fact! -LEAN BEFORE TAKEOFF-

P.S. --- there is one guy around here, who claims he needs full rich in his factory airplane; but we know he has screwed up cables!

[flyeyes]

Originally Posted by Ironflight

OK, let me set one rule - this is NOT an LOP thread - OK? You can start your own thread to argue that topic, if you are tired of the old ones....

This is about leaning in the climb...

<snip>
Given this additional insight, is it, for instance, OK to lean, as long as we keep the temps in limits? 5,000' and 70% power seem like very arbitrary numbers <snip>
I am truly curious, as an engineer, if we can manage the systems differently with better instruments!

Paul

Hi Paul.

I'm not an engineer, but unless my understanding of this is deeply flawed, this one is pretty simple.

First, you have to make sure your engine is set up properly (many aren't). This means that each cylinder, at sea level and full power under standard conditions, is at least 200 degrees rich of peak EGT. This is very important, and if your engine isn't set up this way, fix it. A little too rich at WOT is OK, a little too lean isn't, even if it's only one cylinder. You can figure this out in a single flight by noting the EGTs just after takeoff, and finding peak EGT after the power is below 75%. Do it more than once to check your numbers.

One you have established that you are rich enough, the takeoff EGT at sea level is your target EGT in the climb. In other words, as you climb (without changing the mixture) the EGTs will gradually fall as the MP drops. It is OK to lean to maintain the EGT you had at takeoff, as long as it's 200 below peak.

In the past couple of weeks, I have made high density-altitude takeoffs (leaving GCN and AEG) and it is very helpful to know, on the takeoff roll, what target EGT to lean to for max performance.

As an example, the first cylinder to peak in my RV-8 peaks consistently (with both ignitions firing) at about 1320 indicated EGT. In the climb, I just ensure that it remains at or below 1100 or so. I probably tweak the mixture every 1000-1500 feet.

I'm sure Walter or somebody with a deeper understanding of this will jump in, but this seems to be working well for me.

James Freeman

[n468ac]

We lean as follows - assumes going to 6000' or higher and climbing at 135 to 140 kts...

Start leaning once you get to pattern alt. - we can pull the mixure a 1/2" out before the EGT shows any changes.

Lean to EGT is 1390 on the hotest cyn
Lean during the climb to keep the hotest EGT to 1390
Once at flight alt lean to 50 ROP

[AlexPeterson]

My method is to keep full rpm/throttle until about at 1000 agl. I then pull the MAP to about 23 or so, and the rpm to 2400 (usually brings the MAP up to about 24). I then pull the mixture from full rich to around 8 gph, which is lean of peak. I watch the CHT's fairly closely, and lower the nose (from normal climb of 120 kt) if any cylinder thinks about going over 400. If cylinder temps don't behave, I'll put full rich back in (about 11 or 12 gph), and that will promptly cool things down significantly. Power will be less, of course.

Deakin recommends keeping the mixture full rich on the way up to keep things cool, but he also writes that it is generally ok to lean below 75% power, given one stays out of the "red zone" between, I think, 100F ROP and 50F LOP.

What say you, Mr. Atkinson?

[dan]

I lean as aggressively as possible while still keeping CHTs stable. My mixture control is my CHT control. If I see CHTs dropping, I lean further. If I see CHTs rising, I enrich. This "policy" assumes constant airspeed in the climb and ROP.

This is with fuel injection. YMMV.

[fodrv7]

Morning Paul and all,
For you and others who have GRT engine monitor (or similar) if you accept the Deakin advice to lean on the climb to manitain Take-off EGT, then shortly after TO select 'NORMAL' on the Engine Monitor. As you climb the engine monitor will display degrees Rich from the Take-off EGT and you can simply lean back until the difference is zero.
This method, which came to me one night at 3am (sorry 0300hr), has two advantages.
1/. You don't have to memorise the T/O EGT.
2/. Instead of using an arbitary figure of say 1400 degrees, you are using the figure for the conditions of the day.

Pete.
PS. By the way, here is a page from the Lycoming maual that graphically displays what happens to Mixture and fuel flow when you lean below about 80%.
P.

[penguin]

Originally Posted by AlexPeterson

Deakin recommends keeping the mixture full rich on the way up to keep things cool, ...

Pelican's Perch #64 is the relevant reading material here, http://www.avweb.com/news/columns/182176-1.html. Although this is written for a Continental fuel injected engine, the principle is the same. Deakin advocates maintaining the EGT you had at (about) 1000' using the mixture control.
Pete

[n468ac]

[quote=fodrv7]Morning Paul and all,
For you and others who have GRT engine monitor (or similar) if you accept the Deakin advice to lean on the climb to manitain Take-off EGT, then shortly after TO select 'NORMAL' on the Engine Monitor. As you climb the engine monitor will display degrees Rich from the Take-off EGT and you can simply lean back until the difference is zero.
This method, which came to me one night at 3am (sorry 0300hr), has two advantages.
[quote]

THANKS! ... I never though about.