I've been thinking about this but have been afraid to attempt it. I still use full rich. Here's a scenario:
Suppose you have landed at a dirt airstrip at 8000 ft elevation. The runway is long enough to take off normally but the air temperature today is 85F. I suspect that a leaned mixture would produce more power than an overly rich mixture. Would you lean? If so, how would you decide how much to lean?

Let the discussion begin!

Turbo or Non Turbo motor????

I wouldn't lean... But only because my plane does not have mixture control. :-p

You shouldn't suspect - leaning WILL yield a lot more power. I would lean for sure. If you are landing and taking off at 8k with more than 9k density altitudes you are really pushing your luck by not leaning.

Do a runup - rolling if you have to and lean for max rpm the enriched a bit. You should practice at long paved runways before trying on dirt or off strip. If you are familiar with your plane you can probably predict the settings closely enough without need for a protracted static runup.

I think this one will be controversial, I was taught by one old dude with a bazillion hours in the same engine as my plane, continental 0-520, to never lean for takeoff regardless of elevation.

Then another old dude with a bazillion hours who I spend more time with told me to always do it above 6,000.

I've been leaning for years in the skywagon whenever I am in Durango or above (listened to the second old dude), but I've been reading more and more about my engine from lots of sources and I am not so sure anymore what is the right answer.

I'll be interested to see what the brain trust comes up with.

Brad

Assuming it's naturally aspirated, here's how I do it with a 182. I usually do a rolling mag check on the way out with the mix at least a full knuckle and a half out at that altitude. As I give it the onion on takeoff, I'll screw the mix out some more, when it burbles, I twist it in half a turn, glance at the egt's and usually rotate about then. There's a good vid on here somewhere of a Stinson taking off full rich only to crash into trees.

I lean it at 4500'! The engine runs better with the correct mixture. When your doing your runup just lean for best RPM. The richen it a little. If your trying to go straight up you might want to give it a little more fuel to help cooling but I like all the power I can get when taking off.

I absolutely lean my o-470 for takeoff anytime I'm not near sea level, unless it's cold enough to bring the DA down below 3000 ft.

I use the "finger measure" method to set mixture for takeoff, based on testing done at various DA's with a qualified instructor. I also have a CHT gauge.

No two engines/installations are the same though, so figure out what works for you, ideally with someone who has experience in your particular aircraft type.

Full rich @ 8000' and 85 degrees would be like me taking off at 4500 with my carb heat on. That doesn't work so well, I know.

The PPL study materials teach "always lean for maximum RPM/power on the ground prior to takeoff above 5000ft".
They go on to stress that failure to do so can have drastic consequences (think that Stinson crash video).

I can quote that verbatum because I am helping the Mrs study for her PPL, and read it last night

skypony wrote:I've been thinking about this but have been afraid to attempt it. I still use full rich. Here's a scenario:
Suppose you have landed at a dirt airstrip at 8000 ft elevation. The runway is long enough to take off normally but the air temperature today is 85F. I suspect that a leaned mixture would produce more power than an overly rich mixture. Would you lean? If so, how would you decide how much to lean?

Let the discussion begin!

With naturally aspirated engines that have carburetors, I usually lean until the power starts to taper off during runup, then give it a little extra fuel. I pay really close attention to how it's running when I advance to full power to make sure that it's not too lean. I watch the temperatures closely. This is not a very measurable method, but I have run engines beyond TBO with good vitals using this approximate method. I'm not sure that old carbureted GA engines are too sensitive to this. Most certified installations seem to run pretty cool even on hot days. The FAA cooling requirements are pretty demanding. I have also leaned out a lot, and forgotten to push it in some after a long low power descent to a lower elevation field, then had the engine fall on it's face when I powered up to control my rate of sink on short final.

Also keep in mind that at the elevation and temperature you are talking about here, your true airspeed will be about 20% higher than ISA at sea level, so if you land at 55 mph indicated down low, expect 66 mph zero wind ground speed up there on the hot day, plus your control surfaces don't produce near the energy as they do down low. I encountered a situations in my old C170 where the runway was plenty long, I rotated 800 ft in to my ground roll but I couldn't climb at all. Nearly put it in the trees at 1230 ft msl when I hit a down draft on climb out.

I once saw a 65 horse Ercoupe with two big men on board takeoff, then fly a pattern back to landing in ground effect. Good thing that there were no high features or structures close by!

I don't think there is an answer for every NA engine, but my only question is..."why not lean?"

The DA you describe is approaching the service ceiling of many small planes, and the engine is only making 60% to 70% of rated HP. Up high in the 182, leaning out yields some extra airspeed. If your engine is certified to operate at those power settings continuously at peak egt, or at max power (a bit richer), why not take off that way?

Everyone I knew at GJT was taught to lean there as well...

hell I lean to taxi and I'm here at sea level.. mine is fuel injected though and I've found plugs get a bit fouled if I taxi a long way full rich.. anyway at altitude strips I lean till it starts to quit on runup then richen it a half turn and go.. seems to have worked well all these years...continental IO360

Full rich at 8000ft for takeoff ? Are you kidding?

Battson wrote:The PPL study materials teach "always lean for maximum RPM/power on the ground prior to takeoff above 5000ft".
They go on to stress that failure to do so can have drastic consequences (think that Stinson crash video).

I can quote that verbatum because I am helping the Mrs study for her PPL, and read it last night

I'm not certain that the Stinson would have blasted up out of the hole had he leaned properly. There were four adult men on board and the DA was over nine thousand. There are conditions under which a plane just won't climb, regardless of mixture setting. This pilot found those conditions.

Leaning will save fuel and help to prevent excessive (detonation causing) carbon build up in the combustion chamber, which are very good reasons to lean the mixture. It will give a little more power, but probably not much more than about 3-5 percent in the best case, so don't expect any magic.

I'm @ 3660' on floats, running an 0320. I lean to the first knuckle on warmup (still a bit on the rich side) & then lean for cruise alt. (500-1000'). I burn 5.5-6 US gph & temps are fine.

In my case, an IO-520D, which is a high compression engine (8.5 to 1), detonation is a consideration.
It is wise to take off and climb with the Exhaust Gas Temperatures between 1250 and 1300 degrees.
This range will result in the best combination of power produced and temperature control of the Cylinder Heads.

What I did to get an idea of where to adjust the mixture for takeoff, for example at 5000', was at 5000' slow to 60Kts, apply full power, takeoff RPM, and adjust the mixture to achieve 1250 to 1300 degrees, and note the approximate position of the mixture.
So now when I am departing a high altitude airport, I have an idea where to put the mixture, so it will only take a minor adjustment while taking off to achieve adequate power and CHT control (1/2", 5/8", etc).
I also use the 1250 to 1300 EGT climbing at a reduced RPM and full throttle. In this engines case between 2550 and 2750 RPM where Takeoff RPM is 2850.

Another example if you don't have an engine analyzer, and for a high compression engine, is with full power note what your Maximum EGT is while leaning at say 5000', then subtract 200 to 250 degrees and use that as a target for best power and cooling for takeoff.

I am by no means an expert, but the engine in my plane is the most important part so I treat it like I want it to get me home!
I also believe the best money spent on an airplane is an engine analyzer, whether Carbureted or Fuel Injected.
Especially if Fuel Injected!
Get one and learn how to use it You won't regret it.

My $.03.... adjusted for inflation
Mark

With my O-300, I verify correct leaning in-flight by pulling on carb heat periodically and verifying appropriate RPM drop. So, when I land, I figure that I'm already leaned more-or-less appropriately for the elevation of the landing site. (Especially with most of my higher 7K'-8K' landings, which are often on glaciers, and therefor have flat approaches.) So, unless the temperature changes significantly during my time on the ground, I note the mixture setting before engine shut down, and I recreate it when I'm ready to take off again. Then verify it prior to takeoff by changing up the mixture slightly, and watching the RPMs.

-DP

If you're landing at high DA (remember, the Mel doesn't have to be high if its hot out) you can lean for altitude prior to landing, land and shut down with the ignition...leave the mixture set. Or,as was previously mentioned, note approximate mixture position, then set that for takeoff.

Bear in mind that a normally aspirated engine (which includes fuel injection) at 5000 feet density altitude can make only 75 % rated power.

ALWAYS lean for takeoff at high DA.

MTV

I start feeling slight roughness ( 0-360 C/S prop ), at 3000 DA. Which reminds to start a gradual lean. I don't fly LOP. LOP is hard to predict where I fly, Wx, traffic, terrain keeps me changing altitude to much. Unless I have a computer controlled engine I stay away from LOP. I lean during run up for a reasonable rise in engine RPMs if the DA is a factor on taken off. I stilL watch EGT, FF, CHT on climbout just in case sometime goes wrong with the fuel, then I promptly re-adjust.

Note: on the OTHER side of the world my Honda BF150 runs at 41 degree BTC, lean over peak, and has variable value timing. The computer changes these variables 160 times per second. I can't do that and still fly an airplane!

I always lean the engine as soon as I start up for taxi, then again during run up, during climb (if its a big change in altitude) and once again at cruising altitude. I learned to fly at an airport based at 5000 msl and the density altitude in the summer often gets to 8 or 9000. If I don't lean as soon as I start up, during the mag check it is easy to tell that the plugs are a bit fouled. The engine is noticeably smoother when leaned. My dad always says that up here you fly more with the red nob than the black one.

mtv wrote:Bear in mind that a normally aspirated engine (which includes fuel injection) at 5000 feet density altitude can make only 75 % rated power.
MTV

I was taught that a normally aspirated engine loses about 3% power every 1000 feet above sea level...which would make 5000 feet density altitude about 85%, still a significant power loss that need to be accounted for