Cary wrote:
That works for the area in which you live, but not for high elevation take-offs. You need to lean for take off to an approximate best power setting at higher elevation air strips, or your engine won't develop good take off power--it'll be too rich.

Cary

what is the procedure to do this? just in case i ever make it out west

doc_dyer wrote:what is the procedure to do this? just in case i ever make it out west

First install a multi-probe engine analyzer if you don't already have one... Leaning for take-off can create freaky-high temperatures in one or more cylinders, and without a analyzer you'll never know it. It's a lot different than leaning in cruise, since you're not red-lining the RPM's in cruise, and a lot more air is flowing over the cylinders.

Regardless of density altitude, if I'm going to lean for take-off I don't put the throttle all the way in. By backing it off exactly one fingers' width, the enrichment valve stays closed and the #3 cylinder doesn't skyrocket into melt-down temperatures, which it does if I firewall the throttle. It's just one of those quirks.

My procedure is to lean to a rough estimate based on previous experience, then when I apply power I monitor the EGT/CHT along with everything else as I'm building speed. Adjust mixture as necessary in the ground roll. Assuming it's high enough to warrant leaning to begin with, you should have ample time to adjust the mixture to a very close approximate before getting airborne.

It's not difficult, but it does require an understanding of your engine and its quirks, which you'll only get with the engine analyzer.

Halestorm wrote:
If you're worried about forgetting the position of the mixture control your friends "CIGAR" and "GUMP" should help you remember where it is...

I've always found when I lean for taxi, any attempt at takeoff power would cause the engine to die at the advancement of the throttle.

hotrod180 wrote:All knobs forward except cowl flaps.

If you got any significant DA, that's bad news bears

Hammer wrote:

doc_dyer wrote:what is the procedure to do this? just in case i ever make it out west

First install a multi-probe engine analyzer if you don't already have one... Leaning for take-off can create freaky-high temperatures in one or more cylinders, and without a analyzer you'll never know it. It's a lot different than leaning in cruise, since you're not red-lining the RPM's in cruise, and a lot more air is flowing over the cylinders.

Regardless of density altitude, if I'm going to lean for take-off I don't put the throttle all the way in. By backing it off exactly one fingers' width, the enrichment valve stays closed and the #3 cylinder doesn't skyrocket into melt-down temperatures, which it does if I firewall the throttle. It's just one of those quirks.

My procedure is to lean to a rough estimate based on previous experience, then when I apply power I monitor the EGT/CHT along with everything else as I'm building speed. Adjust mixture as necessary in the ground roll. Assuming it's high enough to warrant leaning to begin with, you should have ample time to adjust the mixture to a very close approximate before getting airborne.

It's not difficult, but it does require an understanding of your engine and its quirks, which you'll only get with the engine analyzer.

In the grand scheme of things, engine analyzers are relative newcomers, but we were leaning for take-off long before they became available. Here's the method I was taught back in 1973 when I moved to Laramie (elev. 7377'), and which I later taught my students, which is done at normal run-up rpm: start with the mixture control at full rich and slowly lean while watching the tach. It will gradually show an increase in rpm, and then it will start to decrease. Move the mixture control back to where the rpm peaked. Then move it further rich about half an inch of movement. This works whether it's a push-pull control, or a "console" lever a la later PA28s, twins, etc. It works whether the prop is fixed pitch or constant speed, and whether the engine is carbureted or fuel-injected. CAUTION; do NOT lean for take-off with a turbo-charged engine--the POH should be consulted, but generally speaking, full rich is used with turbo-charged engines regardless of the airstrip elevation.

There are some who think leaning for take-off should be done not at run-up rpm but at full throttle, otherwise using the same method, because as Hammer indicates, that opens the enriching valve, which will be open on take-off. I've found that the end results are virtually the same, but by doing it at the lower run-up rpm, there's less chance of picking up FOD with the prop. So I don't do it at a full throttle.

Now that I have an analyzer (Insight G1), I can confirm with it that the time-honored method works just fine. So although I think engine analyzers are wise investments, if you don't have one, you can still properly lean for take-off.

Next question: what about when you're on an unimproved strip? Or for that matter, on a high elevation lake with a seaplane? It's just another step in the run-up process. I always do rolling run-ups on gravel/dirt strips--every seaplane pilot does "rolling" run-ups. It takes a little practice to be able to do a rolling run-up without drifting off the strip, so like anything new, I recommend practicing it on a wide area, like a 150' wide runway, before doing it for real on a 20' wide gravel strip with trees and ditches on either side. It's sort of like learning to back a boat trailer--better to practice in an empty Safeway parking lot than on a long boat ramp that is only 2' wider than the trailer's tires.

Cary

Lots of things were done before engine analyzers came along, but that doesn't mean they were good for the engine.

I was taught the same procedure for leaning for take off, and that procedure will put my #3 cylinder into very unhealthy temperatures in less than half a minute. I understand that's just a quirk of my particular engine, but every engine has its quirks. Will a couple minutes at 450 degrees ruin the #3 cylinder? Not immediately, but its not a temperature anybody would want their cylinders to ever reach. It's only 50 degrees from metal failure, if I recall correctly.

I personally would not use the aforementioned procedure with my airplane. That it doesn't cause a problem with your airplane is great, but completely antidotal. I can't think of a single other procedure that has the potential to overheat an engine in a short amount of time. An engine analyzer is so cheap compared to the components it's monitoring...

Cary's post above aligns with what I was taught. I learned to fly in a spot where 9000' DA is common. Leaning for max RPM during the run up was part of the checklist. We did the mag check at 1700 and then the leaning for power at 2000. We leaned for max and then richened for a 50 rpm drop; about a half an inch.

When I'm on a rough strip at high DA in the 185 I do what the POH recommends: "mixture should be adjusted during the takeoff roll to the fuel flow corresponding to the field elevation." It adds....."the power increase is significant above 3000' and this procedure should always be employed for field elevations greater than 5000."

Bill

Hammer wrote:.... Will a couple minutes at 450 degrees ruin the #3 cylinder? Not immediately, but its not a temperature anybody would want their cylinders to ever reach. It's only 50 degrees from metal failure, if I recall correctly....

Don't know about your engine (O-360 Lyc?), but FWIW the TCDS for the Continental O470 lists CHT redline at 525 degrees (for all but the G & N models) when using a sparkplug gasket type probe,

I think what Hammer's talking about is the report that aluminum loses about half it's tensile strength at 400 deg F. I heard that on a Mike Busch webinar.

I keep mine below 400 as well, 500 is the Lycoming red line.

I think CamTom is correct... 500 degrees is the red line for Lycoming. The jugs should stay on, but it's not like RPM red line...it's where really bad stuff starts to happen, fast.

My personal red line is 400 degrees. I've gotten one cylinder five-degrees above that a couple times...didn't bother me per se, but I don't like going there.

Another fifty-degrees beyond that...Nope...not my idea of good engine management. Especially at 10,000 DA with nothing but trees to land in.

It's REALLY easy to get to those temperatures with ham-fisted "leaning for takeoff". If that doesn't bother you then ok... Not for the likes of me though.

Really, the method I described isn't "ham fisted". Approximate, yes. Ham fisted, no. I still do it the same as I always did, but for the last several hundred hours, I've confirmed its "accuracy" with my G1 analyzer on my Lycoming O-360. My engine isn't anything special, and I suspect it's representative of just about every other carbureted O-360 out there.

Full disclosure: I did have to have some cylinder work done on my #3 this year--compression was just a few pounds under Lycoming's specs. Both #3 and #4 have run hot since the engine was built. But it has nothing to do with leaning for take off.

Cary

Seems like a lot of people have induction leaks that are not fixed too. Makes a cylinder temperature anomaly pretty fast, even in a few short seconds i.e. leaning for takeoff.

delete

Induction Leak test link:

https://www.youtube.com/watch?v=CfG4QGv-r64


One of my concerns is also how do we/you test/certify accuracy of instruments.

I spent over a decade in the business with AMPEX Corp.
Repaired and calibrated all sorts of instruments. We would pull analog movements out if they displayed any out of balance characteristics and balance them before calibrating the instrument they went back into. Most analog meters are most accurate around their 75% of scale.

Most digital units displayed a sampling average of 10 to 100 samples before averaging a reading to be displayed.

Sample:
An analog Simpson 261 model would let you see low frequency <60hz ripple where a digital meter left having to use a scope.

Just adding the calibration info as reference because the aviation environment is a lot tougher than an engineering lab. Cept. for the shaker table building.

Photo of cylinder induction gaskets replacement. Blue stains were noticed, especially after priming. Roughness (1100 - 2000 RPMs), uneven EGT/CHTs were noticed and fixed.

Engine TT400 SN, parts = $10.00 (including shipping)

I learned the same as Cary. I did it quickly. Later I began to lean Lycoming O-540, 0-320, and 0-360 engines that way regardless of DA. They ran better. Even later I found Aerial Patrol companies requiring the same. I never had an analyser. All four of the pipeline patrol engines I flew behind got three thousand hours without cylinder changes.

hotrod180 wrote: I've heard some people say that leaning on the ground doesn't really do anything, that the idle circuit (which isn't affected by the mixture knob) is what's in play below about 1200 rpm or so. My experience seems to bear this out.

Partly correct - the idle circuit is in play up to 1200 rpm but the mixture knob definitely controls the mixture at all RPM ranges otherwise how can it shutdown the engine? If you are not seeing the 50RPM rise on shutdown, then your idle mixture is too lean. If your idle mixture is set slightly rich, then as you pull the mixture knob, the mixture goes from slightly rich to peak RPM (50 RPM rise) and then too lean to run and it quits.

We just broke in our Pponk and we have the idle mixture set way too rich. Given our Colorado density altitudes of 7000'+ we definitely have to lean on the ground and we see a huge improvement in idling. Before run-up, I'll push the knob full rich, run the engine up to 1700 RPM, then lean for peak. That knob position is slightly richer than the position for smooth idling (but it depends on the day).

Hammer wrote:, but it's not like RPM red line...it's where really bad stuff starts to happen, fast.

I've run an O-200 at 4300 RPM and an O-360 at 3500 RPM. The O-360 has over 1000 hours on it and is as tight as a new engine with 15 years of oil analysis showing no bearing wear. With a little bit of balancing, these engines run fine above red line. And they sound even better from the ground!

Ace007 wrote:.. If you are not seeing the 50RPM rise on shutdown, then your idle mixture is too lean. If your idle mixture is set slightly rich, then as you pull the mixture knob, the mixture goes from slightly rich to peak RPM (50 RPM rise) and then too lean to run and it quits.....

Double-checked the idle-cutoff behaviour yesterday, got a very slight rise then the engine quit. Checked my early Cessna series 100 manual-- it calls for a 20 rpm increase, which is about what I saw.

Now here's a (dumb?) question: why set the mixture rich, then always have to lean it? Why not set it slightly lean instead? After all, common wisdom is that you can't lean it enough to hurt it at ground-appropriate rpms.

hotrod180 wrote:

Ace007 wrote:.. If you are not seeing the 50RPM rise on shutdown, then your idle mixture is too lean. If your idle mixture is set slightly rich, then as you pull the mixture knob, the mixture goes from slightly rich to peak RPM (50 RPM rise) and then too lean to run and it quits.....

Double-checked the idle-cutoff behaviour yesterday, got a very slight rise then the engine quit. Checked my early Cessna series 100 manual-- it calls for a 20 rpm increase, which is about what I saw.

Now here's a (dumb?) question: why set the mixture rich, then always have to lean it? Why not set it slightly lean instead? After all, common wisdom is that you can't lean it enough to hurt it at ground-appropriate rpms.

Guessing: probably won't start if it's too lean.

Cary

Cary wrote:

hotrod180 wrote:

Ace007 wrote:.. If you are not seeing the 50RPM rise on shutdown, then your idle mixture is too lean. If your idle mixture is set slightly rich, then as you pull the mixture knob, the mixture goes from slightly rich to peak RPM (50 RPM rise) and then too lean to run and it quits.....

Double-checked the idle-cutoff behaviour yesterday, got a very slight rise then the engine quit. Checked my early Cessna series 100 manual-- it calls for a 20 rpm increase, which is about what I saw.

Now here's a (dumb?) question: why set the mixture rich, then always have to lean it? Why not set it slightly lean instead? After all, common wisdom is that you can't lean it enough to hurt it at ground-appropriate rpms.

Guessing: probably won't start if it's too lean.

Cary

This!

These engines are set up rich to help with cold starts, works a lot like a choke. After it warms up and it will run you lean it out, a lot like a choke.