Lean for rpm increase while taking off

[k9medic]

I happened upon something new this weekend.

My plane has an o-540 with a CS prop.

While leak checking it after an oil change I leaned the mixture about 5 turns and saw the rpm increase.

I know the relationship between leaning and rpm and altitude but in Florida why would it do this at sea level?

POH says full mixture until through 5000’ on climb out.

Perhaps I’m robbing the engine of some power by running to rich?


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[Dan Thomas]

I happened upon something new this weekend.

My plane has an o-540 with a CS prop.

While leak checking it after an oil change I leaned the mixture about 5 turns and saw the rpm increase.

I know the relationship between leaning and rpm and altitude but in Florida why would it do this at sea level?

POH says full mixture until through 5000’ on climb out.

Perhaps I’m robbing the engine of some power by running to rich?


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According to Precision Airmotive, Lycoming specified the carb with that amount of richness even at sea level. I had called them (at least ten years ago) to complain about the large mag drops in the runup that were much improved if the engine was leaned out, and they told me that Lyc wanted things that way. It might show up in the POH, too, under the runup procedure.
This was in an R182 (O-540-J3C5D). The engine would stumble with the carb heat on and mix full rich, so I started telling the students and instructors to lean it on downwind if it did that. Too much fuel can be as bad as not enough. Airport elevation there was 2975 ASL and on warm days the DA could easily be above 5000.

We had one student go back to an airport he'd just left because the engine was running rough in the climb and there was black smoke behind it. He was at full rich in the climb at 7000'. That behavior is to be expected with that engine and carb. Lean it if it's rough.

 

[Jmcmanna]

My engine runs slightly rough at idle and full rich. I lean it way back when taxiing....almost to cut-off. At full power and full rich, my cylinders are getting a lot of fuel which helps keep them cool. If, during a run up, I needed to lean slightly because of a high DA to get a smooth engine, I would do so because the engine can’t produce enough power to damage anything that high.

In OPs case, if the engine ran smoothly at full rich at takeoff power, then I would go full rich. You are giving up a bit of power in exchange for engine longevity. If it’s not smooth at takeoff power, lean it just enough to get a smooth engine, which should still be mostly full rich.

 

[Stewartb]

Full rich at full power is designed to provide cooling and to prevent detonation. Many of us lean aggressively for ground ops. There’s no threat of damage at low power settings. Just remember to enrich before you go full throttle.

 

[Clip4]

Leaning the Normally Aspirated Engines

• Use full-rich mixture during takeoff or climb. Careful observation of engine temperature instruments should be practiced to ensure the limits specified in Lycoming Operator’s Manual are never exceeded. Refer to the aircraft POH (Pilot’s Operating Handbook) or AFM (Aircraft Flight Manual) for more specific instructions.
• For 5,000 feet density altitude and above, or high ambient temperatures, roughness or reduction of power may occur at full rich mixture. The mixture may be adjusted to obtain smooth engine operation. For fixed-pitch propellers, lean to maximum RPM at full throttle prior to takeoff where airports are at 5,000-feet density altitude or higher. Limit operation at full throttle on the ground to a minimum. For direct-drive and for normally aspirated engines with a prop governor, but without fuel flow or EGT, set throttle at full power and lean mixture at maximum RPM with smooth operation of the engine as a deciding factor.
• For cruise powers where best power mixture is allowed, slowly lean the mixture from full rich to maximum power. Best power mixture operation provides the most miles per hour for a given power setting. For engines equipped with fixed-pitch propellers, gradually lean the mixture until either the tachometer or the airspeed indicator reading peaks. For engines equipped with controllable pitch propellers, lean until a slight increase of airspeed is noted.
• For a given power setting, best economy mixture provides the most miles per gallon. Slowly lean the mixture until engine operation becomes rough or until engine power rapidly diminishes as noted by an undesirable decrease in airspeed. When either condition occurs, enrich the mixture sufficiently to obtain an evenly firing engine or to regain most of the lost airspeed or engine RPM. Some engine power and airspeed must be sacrificed to gain a best economy mixture setting. NOTE: When leaned, engine roughness is caused by misfiring due to a lean fuel/air mixture which will not support combustion. Roughness is eliminated by enriching slightly until the engine is smooth.
• The exhaust gas temperature (EGT) offers little improvement in leaning the float-type carburetor over the procedures outlined above because of imperfect mixture distribution. However, if the EGT probe is installed, lean the mixture to 100˚ F on the rich side of peak EGT for best power operation. For best economy cruise, operate at peak EGT. If roughness is encountered, enrich the mixture slightly for smooth engine operation.
• When installing an EGT probe, the probe must be installed in the leanest cylinder. Contact the airframe or kit manufacturer for the correct location. In experimental or custom applications, multiple probe instrumentation is required, and several power settings should be checked in order to determine the leanest cylinder for the specific application.
• During normal operation, maintain the following recommended temperature limits:
  • Cylinder head temperature – limit listed in the Lycoming Operator’s Manual.
  • Oil temperature – limit listed in the Lycoming Operator’s Manual.
  • For maximum service life, maintain the following recommended limits for continuous cruise operation:
  • Engine power setting – 65% of rated or less.
  • Cylinder head temperatures – 400˚ F. or below.
  • Oil temperature – 165˚ F. – 220˚ F.

 

[k9medic]

Thanks All

I have a Jpi fuel flow meter, a CHT and an EGT for each cylinder so I run pretty lean in Cruise flight.

This just had me scratching my head.


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[Dan Thomas]

Page 4-17 of the R182 POH says that the engine may be leaned in the climb above 3000 feet. It's an indication of the richness of the system in that particular installation. In any case, the POH recommends leaning to get smooth operation. In this airplane, as with many others, the rote teaching of full rich for takeoff and climb is mistaken and can result in some headaches far beyond fouled plugs. A hot day in the circuit at 4000 feet with full rich and carb heat could flood that engine enough that it stumbles badly or quits on final or in the aborted landing. The R182's HA-6 carb is a horizontal-draft affair mounted on the aft face of the engine, and fuel can puddle in the bottom of the manifold and get sucked in all at once when you open the throttle. You drown the engine.

 

[Matthew Rogers]

What about an O-200 in winter or summer? Sometimes in the C150, every bit of power is needed to get over the trees, so finding any extra HP on the takeoff roll is better than crashing. I assume that just reducing power a tiny bit at 500-1000 would be sufficient to allow for best power takeoff without cooking the cylinders in a sustained beat power climb.

I only have a crappy oil temp gauge and it only gets to “normal” temps in a long sustained full power climb in winter. So at least the oil always stays very cold in winter. Summer it will gradually get hot in a long climb like that, but never seen it get into the danger zone so far.

With that said, my POH lists an RPM range for full power on the takeoff roll, but no static maximum RPM that I can check on the ramp. 1966 C150F. I have heard that making sure the prop is pitched as fine as possible is good to make sure that it will produce maximum HP (max static RPM).

 

[Kenny Phillips]

Note that the carb is designed to supply a proper mixture at the most extreme limits of operation. At sea level, or below, in cold air (say, 35°F in Death Valley), you'd need a bunch of fuel. It would be too rich at Montgomery Field, near sea level, in July.
On super hot days where density altitude was 2K over field elevation we'd lean out the old Skyhawk, just to get moving more quickly. Gotta watch the engine temps, but with an O-300, not much to worry about.

 

[Dan Thomas]

What about an O-200 in winter or summer? Sometimes in the C150, every bit of power is needed to get over the trees, so finding any extra HP on the takeoff roll is better than crashing. I assume that just reducing power a tiny bit at 500-1000 would be sufficient to allow for best power takeoff without cooking the cylinders in a sustained beat power climb.

I only have a crappy oil temp gauge and it only gets to “normal” temps in a long sustained full power climb in winter. So at least the oil always stays very cold in winter. Summer it will gradually get hot in a long climb like that, but never seen it get into the danger zone so far.

With that said, my POH lists an RPM range for full power on the takeoff roll, but no static maximum RPM that I can check on the ramp. 1966 C150F. I have heard that making sure the prop is pitched as fine as possible is good to make sure that it will produce maximum HP (max static RPM).

The Type Certificate Data Sheet for you model will specify the max/min Static RPM for whatever propeller is installed. Here:
http://rgl.faa.gov/Regulatory_and_G...ffa7b7d8625816900659753/$FILE/3A19 Rev 50.pdf

Scroll down to the 150D/E/F. Look up your prop model in your logs and see what the TCDS says for the static RPM range. That's the range the engine should run on the ground at full throttle with the brakes locked on a standard day. You can't reduce the pitch of a fixed-pitch prop to get redline RPM (which is where full power is generated) for takeoff or you'll be over redline not long after you start moving and would have to reduce the throttle, and it would climb poorly and cruise even worse. A fixed-pitch prop is a compromise, and if you want max power on takeoff you need at least a constant-speed prop, which means a more expensive airplane. Much more expensive. You're stuck with second gear, while a constant-speed prop gives you all the gears except reverse.

Reducing power even 50 RPM will hurt the performance in the climb. Try it sometime. If you're having high temps in the climb on the little O-200, you might need to get the temp instruments checked for accuracy and see that the baffle seals are in good shape and that none of the baffling is broken or missing. I've seen that too often.

For getting out of small fields with obstacles, pay attention to the POH information, including the type of surface (pavement/grass/dirt) and wind and temperature. It all makes a big difference, and those that just hope to get over the trees usually eventually end up in them. You can get a bit more power for takeoff in high-DA situations by leaning to max static RPM before you release the brakes; that will be in the POH, too. Once clear of the obstacles you can slowly push the mixture to rich. Slowly so that you stop pushing if the engine starts getting rough.

 

[Clip4]

What about an O-200 in winter or summer? Sometimes in the C150, every bit of power is needed to get over the trees, so finding any extra HP on the takeoff roll is better than crashing. I assume that just reducing power a tiny bit at 500-1000 would be sufficient to allow for best power takeoff without cooking the cylinders in a sustained beat power climb.

I only have a crappy oil temp gauge and it only gets to “normal” temps in a long sustained full power climb in winter. So at least the oil always stays very cold in winter. Summer it will gradually get hot in a long climb like that, but never seen it get into the danger zone so far.

With that said, my POH lists an RPM range for full power on the takeoff roll, but no static maximum RPM that I can check on the ramp. 1966 C150F. I have heard that making sure the prop is pitched as fine as possible is good to make sure that it will produce maximum HP (max static RPM).

You might want to consider some performance calculations.

 

[Skip Miller]

What about an O-200 in winter or summer? Sometimes in the C150, every bit of power is needed to get over the trees, so finding any extra HP on the takeoff roll is better than crashing. I assume that just reducing power a tiny bit at 500-1000 would be sufficient to allow for best power takeoff without cooking the cylinders in a sustained beat power climb.

Be careful with that. I am not sure which carb you have on the O-200, but many carbs have a “power enrichment circuit” that adds more fuel at wide open throttle. So without an all-cylinder temperature device installed, your “reducing power a tiny bit” may close the power enrichment circuit leaving your mixture dangerously lean in a prolonged climb.

-Skip

 

[Dan Thomas]

Be careful with that. I am not sure which carb you have on the O-200, but many carbs have a “power enrichment circuit” that adds more fuel at wide open throttle. So without an all-cylinder temperature device installed, your “reducing power a tiny bit” may close the power enrichment circuit leaving your mixture dangerously lean in a prolonged climb.

-Skip

The MA-3SPA in that installation doesn't have any enrichment circuit. It's a pretty crude affair that doesn't carburate as well as my old (1946) Stromberg carb did.

But then, funny things can happen. We had a 172 that I'd installed a new engine in, complete with new carb (MA-4), and that engine ran a little rough on the climbout, and leaning didn't help. Pulling the throttle back a hair got a few extra RPM and the engine smoothed out. I couldn't find anything wrong with the carb or linkages, so I figured that the fuel nozzle in that unit was less than perfect and didn't atomize the fuel properly. Closing the throttle plate a little made the fuel stream strike it and break it up better. Precision had a series of ADs in the '90s regarding the two-piece venturi. The single-piece that replaced it caused all sorts of troubles so they issued another AD requiring a cross-drilled nozzle which caused a different set of troubles in a few cases, so they issued yet another AD allowing the reinstallation of the old parts as long as the venturi was inspected for looseness every 100 hours.

 

[Skip Miller]

Thanks, Dan. -Skip

 

[Matthew Rogers]

The MA-3SPA in that installation doesn't have any enrichment circuit. It's a pretty crude affair that doesn't carburate as well as my old (1946) Stromberg carb did.

I just remember hearing that the O-200 really did not make enough power or heat to cause problems in all but the worst cases. Maybe that is not correct. Since most C150s lack any form of temp gauge other than an oil temp gauge, I wonder how many people have any clue of what cylinder head temps result from different settings and situations. In winter, my oil temp only gets to “normal summer cruise temps” after a sustained full power Vy climb for 20+ minutes. Otherwise the oil is “cold-ish” (bottom of the green) the whole time. Does my oil temp actually have any correlation to my cylinder head temps?

But like all GA aircraft, simply flying the plane every week makes it last longer than anything else.

 

[Snowmass]

I have a IO-520 which is of course fuel injected. It is normal for power to increase at idle by leaning because the injection is deliberately set too rich to aid in starting in colder WX (no choke). If, at full throttle, you can get more RPM (CS prop) by leaning then lean at any altitude during your take off run to clear obstacles with max safety. You can then run rich of max power in climb if needed for cooling. I climb about 200 degrees ROP for cooling in climb. Since I rarely cruise over 60% for economy I have found that leaning to just before roughness works just fine without even looking at EGT even with fuel injection and GAMI injectors just like with a carburetor.

 

[Snowmass]

But like all GA aircraft, simply flying the plane every week makes it last longer than anything else.

Is this a totally rational statement? While your airplane might last more flight hours you are also putting more hours on it so unless you just want to fly for some other purpose this does not make sense to me. And flying every week just to "make the plane last loner" is the most dangerous flying of all: take off, flying in airport traffic and landing.

 

[Dan Thomas]

I just remember hearing that the O-200 really did not make enough power or heat to cause problems in all but the worst cases. Maybe that is not correct. Since most C150s lack any form of temp gauge other than an oil temp gauge, I wonder how many people have any clue of what cylinder head temps result from different settings and situations. In winter, my oil temp only gets to “normal summer cruise temps” after a sustained full power Vy climb for 20+ minutes. Otherwise the oil is “cold-ish” (bottom of the green) the whole time. Does my oil temp actually have any correlation to my cylinder head temps?

But like all GA aircraft, simply flying the plane every week makes it last longer than anything else.

The O-200 doesn't have an oil cooler in most installations, including the 150. There's a spot on the case for one, but I've never seen one anywhere. There is a baffle duct along the bottom of the crankcase that takes cooling air from under the prop and scoots it along the case, soaking up heat, and dumps that air onto the oil tank to soak up some more.

Cessna's mechanical oil temp gauges are rudimentary devices that can be inaccurate. The check is to take the bulb out of the screen housing and put it into a can of hot water and heat the can further with a heat gun or small torch (carefully!!!) until the water boils. The gauge should still be in the green but close to the redline. The O-200-A's redline oil temp is 225°F, not far above the boiling point of the water.

CHTs on most engines are more dependent on baffling and baffle seals. Old, tired, hard, torn, cracked seals are bad. BAD. Loose baffling is bad. Missing baffling is really bad. I have found intercylinder baffles missing altogether. Those are underneath the cylinders and direct the cooling air into the cylinder and head fins and keep it there until it exits at the bottom center. They're a pain to remove and install, which is probably why some mechanics seem to think they're not important. But nothing an engineer designs into an airplane is unimportant unless it's a cigarette lighter or coffee cup holder. There are usually wires that keep the front and rear baffles tight against the cylinders for the same reasons intercylinder baffles are there. They're often gone, too. On various Cessna models there was a plastic baffle and seal around the air filter, and that's usually busted or missing. It was incorporated in the late 1960s to improve cooling by preventing prop blast into the lower cowl. Such air entry reduces the pressure differential between the top and bottom of the engine, and that differential is what drives the cooling air.

 

[Dan Thomas]

Is this a totally rational statement? While your airplane might last more flight hours you are also putting more hours on it so unless you just want to fly for some other purpose this does not make sense to me. And flying every week just to "make the plane last loner" is the most dangerous flying of all: take off, flying in airport traffic and landing.

Airplanes and their engines rot whether they're flown or not, and ground-running or short flights introduce moisture from combustion into the crankcase that doesn't have enough time to get "boiled" out before shutdown. A cold air-cooled engine has large clearances that let plenty of blowby gases past the rings, and water vapor is one of those gases. It condenses in the case, mixes with the oil, and reacts to form acids that eat that engine. Start the engine, fly for a half-hour, and park it. The damage starts and continues quietly while you think your bird is safe. Or just start it and ground-run it; that's even worse. We replaced the engine in a 277-hour C172S because the owner had ground-run it, thinking he was helping things last longer. Doesn't work that way. The cylinders were shot. Accessory case gearing was rusty. Aircraft engines don't have the tight clearances you car's engine does, and they don't have any positive crankcase ventilation (PCV) systems like your car does, either. So water and corrosive gases get in there and only lengthy heat (not an engine heater) drives out the worst of it.

 

[Snowmass]

I understand the above but, of course, much also depends on the humidity in one's area and I am in Arizona. In 7000 hours on various engines (A-65 up) I have never experienced ANY corrosion which I would noticed since I do all my major and top overhauls myself. I only fly to go somewhere so my planes can sit months or just days.

However, I shy away from "conventional wisdom" and am always skeptical (as an engineer) and want some form of scientific testing. The only benefit I can see from a ground run up is to splash oil on corrosion prone parts so I propose the following experiment. Run up an engine just enough to splash on corrosion prone surfaces and no longer which I am guesstimating to be 2 minutes at 1700 RPM. To test this take an oil sample just before and after each 2 minute run up and have these lab analysed and see if there is any difference in noxious chemicals due to just 2 minutes of operation. This part is simple and cheap but what is more involved would be to see what it takes to get good oil re-coating. I am doing this now every few weeks but I do not think I will get much improvement since I never have any corrosion to begin with.

 

[Dan Thomas]

I understand the above but, of course, much also depends on the humidity in one's area and I am in Arizona. In 7000 hours on various engines (A-65 up) I have never experienced ANY corrosion which I would noticed since I do all my major and top overhauls myself. I only fly to go somewhere so my planes can sit months or just days.

However, I shy away from "conventional wisdom" and am always skeptical (as an engineer) and want some form of scientific testing. The only benefit I can see from a ground run up is to splash oil on corrosion prone parts so I propose the following experiment. Run up an engine just enough to splash on corrosion prone surfaces and no longer which I am guesstimating to be 2 minutes at 1700 RPM. To test this take an oil sample just before and after each 2 minute run up and have these lab analysed and see if there is any difference in noxious chemicals due to just 2 minutes of operation. This part is simple and cheap but what is more involved would be to see what it takes to get good oil re-coating. I am doing this now every few weeks but I do not think I will get much improvement since I never have any corrosion to begin with.

It's a lot more complex than that. I have run up engines before inspections first thing in the morning, then found water inside the rocker covers when they were removed for various reasons. In our colder climate we normally find the oil on the dipstick looking like foamy coffee with cream after a shorter flight, and that's the oil/water emulsion that results from crankcase moisture accumulating and mixing with the oil on short flights.

The rest of it is chemistry. Water provides oxygen and hydrogen. Oil supplies sulfur, chlorine and nitrogen, as do the other blowby gases. The metals in the engine--aluminum, iron, copper, zinc and tin--act as catalysts. Leave them sitting together and over time we get sulfuric, hydrochloric and nitric acids, and none of those are friendly to engines. Hydrobromic acid can be formed when engines are run on leaded fuels. These reactions also form sludges. These are some of the major reasons we change oil periodically. Just coating the engine parts with oil will do little good if there's water in there, too. Water mixes with the oil during operation, and when the engine is shut down it's left in places like the lifter bodies, oil galleries in the case and crank, in the accessory case and between the pistons and cylinder walls. I have pulled cylinders off after a short runup and found water droplets in there.

You have experience with one or two airplanes. Licensed mechanics get many years of experience with hundreds of airplanes representing a wide range of aircraft and engines, owners and their various habits and levels of care, the conditions they're operated and stored in and other factors, and we learn what to look for. There are preservative storage oils like Aeroshell Fluid 2F that are put into engines and run for a while to get them all through the engine, and then the oil is also sprayed into the cylinders to coat the upper end as well. Preservative oils neutralize the acids.

Arizona is not immune to corrosion. Most of the water comes from the combustion process, not the environment.

 

[Matthew Rogers]

So the flights that I take just to see how high my 150 can go do a lot of good. Full power climb for 30 minutes in the winter. Get the engine hot enough for long enough to drive off any water. Last one I hit 13,600 (18 degrees F up there, 18 F on the ground too!), got carb ice at the top.

 

[N1120A]

Note that the carb is designed to supply a proper mixture at the most extreme limits of operation. At sea level, or below, in cold air (say, 35°F in Death Valley), you'd need a bunch of fuel. It would be too rich at Montgomery Field, near sea level, in July.
On super hot days where density altitude was 2K over field elevation we'd lean out the old Skyhawk, just to get moving more quickly. Gotta watch the engine temps, but with an O-300, not much to worry about.

At 437' and 20-25, like MYF is so much of the time, one of our club's R182s hates being run up full rich. Those 182 carbs are massive and, like mentioned, will pool gas and flood like nobodies business. My Tiger likes being run up full rich there, but my Bonanza actually doesn't like being full rich till it gets a bit of manifold pressure pushed in before take off.

 

[Snowmass]

It's a lot more complex than that.
Arizona is not immune to corrosion. Most of the water comes from the combustion process, not the environment.

I proposed a simple TEST to see the effect of re-coating oil via a very short run up, on engines that sit, in my case, months without being flown. The oil sample before and after the 2 minutes will show if noxious chemicals have been created in the ultra short time. As we always said where I worked, Hughes Aircraft engineering laboratory, "ONE TEST IS WORTH A THOUSAND OPINIONS"

 

[bnt83]

Dad had a huge habit of leaning for takeoff pretty much all the time without consideration of engine, fuel system, airplane or prop combinations. In this case an o-470R in a 182. Still leaning it out like he would for an o-300 powered 172 like he used to do at Stapleton airport.

Then he flew it with a CGR-30P engine monitor and complained that CHTs were to high, flying from 1,300 MSL in South Dakota.

My response was “leave it full rich or burn it up during takeoff and climb to 5k, you choose.”

problem solved

 

[Dan Thomas]

I proposed a simple TEST to see the effect of re-coating oil via a very short run up, on engines that sit, in my case, months without being flown. The oil sample before and after the 2 minutes will show if noxious chemicals have been created in the ultra short time. As we always said where I worked, Hughes Aircraft engineering laboratory, "ONE TEST IS WORTH A THOUSAND OPINIONS"

Do it, but let that engine sit for a month before taking any oil samples. The acids take time to form. And then get back to us with the results.

Aircraft engine overhaul shops don't have to do such tests. They already know all about it. And so do the engine manufacturers. They know that the worst of the moisture gets in there in the first few minutes after startup. That's when clearances are the biggest.

https://www.lycoming.com/content/frequency-flight-and-its-affect-engine

 

[Tantalum]

POH says full mixture until through 5000’ on climb out.

Perhaps I’m robbing the engine of some power by running to rich?

(1) that POH was probably written by Dwight Eisenhower was president and before Sputnik was launched

(2) stoichiometrically speaking, you are right, the engine is probably a little bit too rich.. don't forget that running rich also helps cool the engine.. and up until "recently" it was a preference to be on the rich side of the curve.. and the safer choice

 

[timwinters]

I don't think anyone has mentioned yet...

If you have an engine monitor. The GAMI boys recommend paying attention to your EGT's during a full power run-up and take-off on a standard day at sea level. In my case, I was at CGI, elevation is only 342, and I tested numerous times on days when the density altitude was 0, or very close to it.

Then they recommend that you lean to replicate those EGT's as closely as possible on all take-offs.

 

[Salty]

(1) that POH was probably written by Dwight Eisenhower was president and before Sputnik was launched

(2) stoichiometrically speaking, you are right, the engine is probably a little bit too rich.. don't forget that running rich also helps cool the engine.. and up until "recently" it was a preference to be on the rich side of the curve.. and the safer choice

And the engine hasn’t changed how it reacts one bit since then.

 

[kgruber]

I always "Lean Forward" on takeoff!!

 

[Tantalum]

And the engine hasn’t changed how it reacts one bit since then.

Nope, the chemistry doesn't change, but we have fancier tools now to monitor these things and dial them in better. Some of the club planes I've rented that only had 1 EGT dial were definitely dialed wayyyyy too rich.. when you go full rich the engine would sound like it's dying.. the local "experts" would just have you lean it a little.. ofcourse then they'd be mad at the renters for fouled plugs... *sigh*

To the OP's point as well, a lot of people are just trained "go full rich for take off!" without being taught the chemistry of what's happening in the cylinder, etc.

 

[Dan Thomas]

To the OP's point as well, a lot of people are just trained "go full rich for take off!" without being taught the chemistry of what's happening in the cylinder, etc.

Younger folks, in general, have no frame of reference to understand the engine. Most of them have never seen any engine apart, or studied diagrams or animations, or have any idea of the rapidity with which things are happening in there. When I taught aircraft systems I had to start with some pretty basic stuff first.

Can't blame them, really. They are 40 years too young to have owned an old car that needed persuading to get started and kept running. Even an "old" car now doesn't need a lot of fooling with. And our bubble-wrap culture keeps kids off homemade go-karts and minibikes and the like.

At least we can show them stuff like this:

 

[flyingron]

Continental has a pretty solid answer: Once you're at or below max continuous power, you can do anything you want with the mixture from full rich to lean misfiring without worrying about damaging the engine. So if you're at DAs of 5000' in a non-turbo'd engine, even with all the knobs pushed in you're not over max continuous. Why not lean for best power. It was standard procedure when I learned to fly at BJC. At lower elevations I use full rich for the takeoff and initial climb, but I bring the mixture back slightly at the first power reduction.

 

[N1120A]

I'm a little surprised people still don't know about leaning, given all the stuff out there about density altitude and the like. Some airplanes cool better than others, so you can lean earlier, but you always need to lean for altitude - especially on departure.

 

[Tantalum]

Younger folks, in general, have no frame of reference to understand the engine. Most of them have never seen any engine apart, or studied diagrams or animations, or have any idea of the rapidity with which things are happening in there. When I taught aircraft systems I had to start with some pretty basic stuff first.

Can't blame them, really. They are 40 years too young to have owned an old car that needed persuading to get started and kept running. Even an "old" car now doesn't need a lot of fooling with. And our bubble-wrap culture keeps kids off homemade go-karts and minibikes and the like.

At least we can show them stuff like this:

Luckily I grew up with a dad who liked fixing things and both brother and dad where mechanical engineers so I have seen many a motorcycle, lawnmower, outboard, '79 Dodge Dart, etc., engines taken completely apart

But even if people don't understand the mechanics of how an engine works I think that's fine, what they should understand though is how combustion itself works.. why air density matters, etc. Fuel / air mixtures.. and the like

You can see people really glaze over on this when they move to complex planes and get introduced to MP.. and glaze even more over when turbos are introduced..

 

[Pilawt]

I know the relationship between leaning and rpm and altitude but in Florida why would it do this at sea level?

What temperature? Density altitude may be considerably higher than sea level.

If you have an engine monitor. The GAMI boys recommend paying attention to your EGT's during a full power run-up and take-off on a standard day at sea level. In my case, I was at CGI, elevation is only 342, and I tested numerous times on days when the density altitude was 0, or very close to it.

Then they recommend that you lean to replicate those EGT's as closely as possible on all take-offs.

That’s exactly what I do, with my carbureted O-360. Taking off on a standard day at S.L. with full rich mixture my #3 (hottest) cylinder stabilizes at around 1350 F. So after every takeoff, regardless of elevation or temperature, I lean to that value and keep it at that “happy place” all the way up in the climb, CHT permitting.

 

[David Megginson]

I happened upon something new this weekend.

My plane has an o-540 with a CS prop.

While leak checking it after an oil change I leaned the mixture about 5 turns and saw the rpm increase.

I know the relationship between leaning and rpm and altitude but in Florida why would it do this at sea level?

POH says full mixture until through 5000’ on climb out.

Perhaps I’m robbing the engine of some power by running to rich?


Sent from my iPhone using Tapatalk

Yes, you're robbing it of power, and that's a good thing. If you're operating your normally-aspirated engine above normal cruise power, then near sea-level density altitude you will produce dangerously-high CHTs and internal pressure at the mixture that gives you max power (about 100°F rich of peak EGT), and your engine could start into pre-detonation. Running full rich—deliberately less efficiently—keeps the CHTs (and pressures) in a safe range at full power.

As you climb higher, your normally-aspirated engine is producing less power, so it's safe to start leaning. And in cruise, operating at 75% power or below, you can lean really far to the other side of peak EGT, to get the same cool temps with a lot less gas (assuming your engine runs smoothly lean of peak EGT). But that doesn't apply to take-off/climb power, until your density altitude is at least a few thousand feet.

 

[Dan Thomas]

You can see people really glaze over on this when they move to complex planes and get introduced to MP.. and glaze even more over when turbos are introduced..

And then constant-speed props. And--oh boy--electricity. Can't see it so can't understand it. Plenty of misunderstandings there.

 

[MooneyDriver78]

After a flight I pull the dipstick out to let the water vapor escape, don’t know if it helps but figure it can’t hurt.


Tom

 

[midlifeflyer]

And the engine hasn’t changed how it reacts one bit since then.

No, but we know more about it.