Too rich?

[Nova]

I’m a student pilot. I have a question about the 172 I’m learning to fly in. I’ll ask my instructor but not gonna see him for awhile thought I’d ask here. Is it possible to kill the engine by mistake by going full rich?? I know on the ground at takeoff its set full rich. But if you were to go to say 8000 feet and not lean it out at all could you ‘choke’ aka over rich it to the point it quits? Would it be obvious it’s way too rich long before it would die? Also.. if you had an engine failure would one of the first things you’d do is turn on the electric fuel pump? Check the fuel selector? Make sure it’s on both? Then try and start it? If one tank is dry one is 1/2 full and it’s on both will it suck air? Just trying to understand it all %100. Better to learn now. Thanks

 

[Capt. Geoffrey Thorpe]

Too rich to run. No.
Too rich for max efficiency, yes.
Engine failure, first thing is fly the airplane.
If you have time, carb heat first, fuel pump, change selectors, diddle mag switch. But you still need to fly the airplane.

 

[sarangan]

I’m a student pilot. I have a question about the 172 I’m learning to fly in. I’ll ask my instructor but not gonna see him for awhile thought I’d ask here. Is it possible to kill the engine by mistake by going full rich?? I know on the ground at takeoff its set full rich. But if you were to go to say 8000 feet and not lean it out at all could you ‘choke’ aka over rich it to the point it quits? Would it be obvious it’s way too rich long before it would die? Also.. if you had an engine failure would one of the first things you’d do is turn on the electric fuel pump? Check the fuel selector? Make sure it’s on both? Then try and start it? If one tank is dry one is 1/2 full and it’s on both will it suck air? Just trying to understand it all %100. Better to learn now. Thanks

Unless you’re flying at very high altitudes like 12,000 ft, running full rich won’t usually kill the engine, but you’ll lose so much power that it can feel almost like the engine’s dead anyway.

 

[Nova]

Too rich to run. No.
Too rich for max efficiency, yes.
Engine failure, first thing is fly the airplane.
If you have time, carb heat first, fuel pump, change selectors, diddle mag switch. But you still need to fly the airplane.

Yes... find the spot your gonna try and land start the controlled decent... THEN everything else. Carb heat.. hadn't thought of that one.

 

[455 Bravo Uniform]

If one tank is dry one is 1/2 full and it’s on both will it suck air?

No.

 

[asicer]

I know on the ground at takeoff its set full rich. But if you were to go to say 8000 feet and not lean it out at all could you ‘choke’ aka over rich it to the point it quits?

Fly to 8000 feet and not lean it out, no. Land at an airport situated at 8000 feet, the mixture is full forward, the throttle is all the way back, the plugs haven't been cleaned in a while, the carburetor is less than perfectly adjusted, the airplane is on the ground and it's not moving then yes

If you have time, carb heat first, fuel pump, change selectors, diddle mag switch. But you still need to fly the airplane.

A 172 with a fuel pump generally means an IO-360 (172SP), no carb heat.

 

[Salty]

I’ve seen engines with improperly set idle mixture that would absolutely shut off when full rich at low rpm.

 

[asicer]

I’ve seen engines with improperly set idle mixture that would absolutely shut off when full rich at low rpm.

But in the air at altitude, the windmilling action is usually enough to keep the prop moving and the engine available.

 

[Domenick]

Might be a good time to mention high altitude takeoffs. Think about it. If running too rich at the very least reduces power, what would happen if you took off from a mile-high airport at full rich? The point is for high-altitude takeoffs, lean for best performance.

Personally, I'm not sure why that is not the SOP at all altitudes. Potential detonation when the engine can produce 100% power?

 

[455 Bravo Uniform]

Also.. if you had an engine failure would one of the first things you’d do is turn on the electric fuel pump? Check the fuel selector? Make sure it’s on both? Then try and start it?

Next time you’re at the plane, look at the emergency procedure (checklist) for engine failure. Then point to or touch everything that it calls for, in order.

Does it seem smooth or contrived?

Next, instead, visually go from left to right then down (or up and from right to left) on the panel including the floor & engine gauges, to everything the checklist asked for - not in the checklist order, but rather in a left/right and up/down “flow”. Does that seem any better?

If so, then the thing to do is look and touch everything in a panel-geographic sense, THEN follow it up with the checklist to confirm you didn’t miss anything.

Of course all of this occurs AFTER you’ve implemented Airspeed at best-glide, and then found the Best field. A, B, C, right?

Note that I am NOT a flight instructor.

 

[MRC01]

I’ll ask my instructor but not gonna see him for awhile thought I’d ask here. Is it possible to kill the engine by mistake by going full rich??

Yes, but you have to be pretty high DA for that to happen. Below 5,000' DA it won't happen directly, but it could happen indirectly as being so rich can foul the plugs in flight which can cause rough running and loss of power.

Also.. if you had an engine failure would one of the first things you’d do is turn on the electric fuel pump? Check the fuel selector? Make sure it’s on both? Then try and start it? If one tank is dry one is 1/2 full and it’s on both will it suck air? Just trying to understand it all %100. Better to learn now. Thanks

It depends on the airplane, so follow the POH procedures for engine failure in flight. If the engine fails in flight you don't know the cause - could be too much fuel, could be too little, could be loss of spark (bad plug or magneto), could be a bird stuffed itself into the air intake. Or 100 other things.

It's worth mention that the ONLY time to use full rich is when using full power at sea level. Or more generally, when using 70+% power (even that doesn't require full rich, but just rich of peak power). As soon as you pull the power back you can lean it. And you should! Even at sea level. If you don't, all you're doing is wasting gas, creating unnecessary pollution, gunking up the spark plugs and valves.

... The point is for high-altitude takeoffs, lean for best performance.
Personally, I'm not sure why that is not the SOP at all altitudes. Potential detonation when the engine can produce 100% power?

Good question. Here's my take on it:

With common standard performance engines that are correctly timed, detonation is not a big risk. Consider that for most of these engines, the STC to run 87 or 91 octane mogas is either paperwork only, or modifications that reduce the risk of vapor lock. Nothing about detonation, so these engines don't need anywhere near 100 octane gas.

The main reason we don't lean for peak RPM at sea level, and when at high DA we set mixture for peak RPM and then a few turns rich of that, is cooling. These engines are primarily air cooled. When climbing, there is less airflow through the cowl because the airspeed is slower than cruise and the angle of the cowl to the air is subobtimal. Yet we're at full throttle producing max power and heat. So we run a bit rich of peak power to have a little extra fuel to help with cooling. When you level off for cruise it resolves both problems, airflow should be sufficient, and you don't need the extra fuel anymore.

 

[Dan Thomas]

Beware. Some engines have manufacturer specifications for richer mixes at full rich that other engines. The Lyc O-540-J3C5D in the R182 is an example. Pulling carab heat on downwind, especially on a warm day, can produce some very rough running. The engine almost wants to die on final. We had a student that returned to a departure airport because the engine was shaking and leaving black smoke behind the airplane. He was a full rich at 7000 feet. I called Precision Airmotive and complained about their carb, but they told me that Lycoming specified those metering jets and that's what they wanted. Couldn't change it. And sure enough, the POH tells the pilot to lean above 3000' DA to smooth the engine.



During runup, one even has to lean the engine to avoid excessive mag drops.

 

[midlifeflyer]

Is it possible to kill the engine by mistake by going full rich?? I know on the ground at takeoff its set full rich. But if you were to go to say 8000 feet and not lean it out at all could you ‘choke’ aka over rich it to the point it quits

Yes, it will quit. I've actually watched it happen twice. Once was a lesson I gave at Leadville, CO (I let it happen to the pilot). The other was at KAPA in metro Denver when a Cherokee cleared for takeoff added power to taxi onto the runway and went forward about 3 feet.

Will you catch it? Maybe. Like too lean, the engine will stumble before it quits. How quickly do you notice? How quickly do you correct?

 

[MRC01]

The Lyc O-540-J3C5D in the R182 is an example. ... the POH tells the pilot to lean above 3000' DA to smooth the engine.

That's not unusual. The POH for my 1980 Cessna 172N (Lyc O-320) says the same thing (lean above 3000') under section 4 Normal Procedures. Some airplanes using the same engine say to lean above 5000'. It depends not only on the engine, but also on the airplane where it's installed, since that affects fueling & cooling.

 

[brcase]

Generally a carbureted normally aspirated engine it is going to be very difficult to kill it by being to rich.
I have had primer come loose and start pumping/draining excess fuel into the intake causing the engine to run very poorly.
The fuel injected 172XP I fly even at 2500 feet will barely idle with the fuel pump on and full rich. As I recall it runs better but still poorly at full power with the low fuel pump and and full rich.
I have read about a turbocharged engine failing at altitude when the turbo charger duct came loose effectively disabling the turbo charger and the engine dying because it was to rich. I don't recall if it started running when he got lower or not. I seem to recall it fouled the plugs so badly that lower altitude didn't help and he ended up making power off or low power emergency landing.

Brian

 

[Clip4]

I’m a student pilot. I have a question about the 172 I’m learning to fly in. I’ll ask my instructor but not gonna see him for awhile thought I’d ask here. Is it possible to kill the engine by mistake by going full rich?? I know on the ground at takeoff its set full rich. But if you were to go to say 8000 feet and not lean it out at all could you ‘choke’ aka over rich it to the point it quits? Would it be obvious it’s way too rich long before it would die? Also.. if you had an engine failure would one of the first things you’d do is turn on the electric fuel pump? Check the fuel selector? Make sure it’s on both? Then try and start it? If one tank is dry one is 1/2 full and it’s on both will it suck air? Just trying to understand it all %100. Better to learn now.

Have you read the AFM for the aircraft?

 

[Clip4]

Beware. Some engines have manufacturer specifications for richer mixes at full rich that other engines. The Lyc O-540-J3C5D in the R182 is an example. Pulling carab heat on downwind, especially on a warm day, can produce some very rough running. The engine almost wants to die on final. We had a student that returned to a departure airport because the engine was shaking and leaving black smoke behind the airplane. He was a full rich at 7000 feet. I called Precision Airmotive and complained about their carb, but they told me that Lycoming specified those metering jets and that's what they wanted. Couldn't change it. And sure enough, the POH tells the pilot to lean above 3000' DA to smooth the engine.

View attachment 144972

During runup, one even has to lean the engine to avoid excessive mag drops.

The O-540J3C5D is D rated to 235 HP. This means at sea level the engine is already producing less (90%) of it normally rated HP.

I own an R182 and have flown 6 other R182s. I don’t have to lean for runup.



The carb is also side draft vs up draft and the engine tends to run rich. In you mags aren’t cutting through a Rich mixture at with a DA below 3000, it is an indication of an improperly maintained R182.Having a good AP to adjust the carb and keeping the plugs cleaned and gapped results in not needing to lean during runup.

 

[Dan Thomas]

In you mags aren’t cutting through a Rich mixture at with a DA below 3000, it is an indication of an improperly maintained R182.Having a good AP to adjust the carb and keeping the plugs cleaned and gapped results in not needing to lean during runup.

I did the 500-hour mag inspections always. On time. As per the manual. And it still needed leaning for runup, particularly on warm days. Our airport was at 2975' ASL.

And it did this one two separate engines, the original engine and the second engine with a new carb and freshly overhauled magneto on a fresh Lycoming factory overhaul.

I am a Canadian AME, the equivalent of the US A&P/IA.

 

[DCR]

Might be a good time to mention high altitude takeoffs. Think about it. If running too rich at the very least reduces power, what would happen if you took off from a mile-high airport at full rich? The point is for high-altitude takeoffs, lean for best performance.

Personally, I'm not sure why that is not the SOP at all altitudes. Potential detonation when the engine can produce 100% power?

Been wondering about this lately...

When I lean for taxi (172N), I spin the knob counterclockwise until the engine stumbles, then quickly add a 5 clockwise flicks (which is about 1 and a quarter full turns) to smooth it out. This is plenty of fuel to taxi but if I add takeoff power at this setting the engine will stumble again.

So, how exactly do you lean for a high DA takeoff? Do you set takeoff power during your run-up and lean it there? Lean at 1700 RPM during your mag check? Seems hard to get right unless you add a good amount of throttle.

Edit: just went to the POH (of course, after I posted the question) and apparently the answer is to set full throttle during your run-up in order lean.

 

[MRC01]

So, how exactly do you lean for a high DA takeoff? Do you set takeoff power during your run-up and lean it there? Lean at 1700 RPM during your mag check? Seems hard to get right unless you add a good amount of throttle.

Edit: just went to the POH (of course, after I posted the question) and apparently the answer is to set full throttle during your run-up in order lean.

Yep. Find a spot that doesn't have gravel, sand or other debris on the ground because a full power runup will pick it up and scratch the prop. Make sure you're not blasting anything behind you with the airstream, then apply brakes, then full power, and start leaning. As you lean, the RPM will slowly increase, then keep leaning and it will decrease. As soon as the RPM starts to drop, enrich back to peak RPM, then enrich a couple of turns from there (you want to be just rich of peak RPM). Then go back to idle and do the rest of your normal pre-takeoff procedures.

Do this entire process as quickly as possible because running full power on the ground can heat up the engine and ding up the prop. But don't rush it, take the time to do it right.

Also: when you rotate and take off at high DA, fly the indicated airspeeds (Vy or Vx as appropriate). That means keeping the nose down and climbing at a shallower angle than you're used to at sea level. It will also seem faster than you're used to, because the airspeed reads low at high DA. But that's OK, you need to fly the indicated speed because it represents your "aerodynamic" speed in the thinner air.

 

[Nova]

Have you read the AFM for the aircraft?

No it’s a rented airplane I’m gonna find out the exact year and model next lesson and look that up

 

[Nova]

Been wondering about this lately...

When I lean for taxi (172N), I spin the knob counterclockwise until the engine stumbles, then quickly add a 5 clockwise flicks (which is about 1 and a quarter full turns) to smooth it out. This is plenty of fuel to taxi but if I add takeoff power at this setting the engine will stumble again.

So, how exactly do you lean for a high DA takeoff? Do you set takeoff power during your run-up and lean it there? Lean at 1700 RPM during your mag check? Seems hard to get right unless you add a good amount of throttle.

Edit: just went to the POH (of course, after I posted the question) and apparently the answer is to set full throttle during your run-up in order lean.

Aren’t you suppose to look at exhaust temperature for best mixture? Although I’m not sure the 172 I’ve been training in even has that. On the pre flight check list the company who owns the plane came up with they say to set the mixture about 1/4” in from full rich and it’s never touched after that at least not in my 1 hour lesson at around 3-4 thousand feet most of the time. And my location is about 750 above sea level just fyi. I was just wondering if you took off and went up pretty high without remember to lean it out could you kill the engine. Sounds like from most replies it’s possible but you’d probably hear and feel it’s not running right long before it actually died. But I certainly don’t have the experience to know. I have a whopping 4.5 hrs of air time so far.

 

[midlifeflyer]

Edit: just went to the POH (of course, after I posted the question) and apparently the answer is to set full throttle during your run-up in order lean.

You can. It can also cause issues with more powerful aircraft where the brakes are not necessarily going to hold. SOP for the locals is to lean at runup power and add mixture to compensate for the extra needed for full power and cooling. One alternative I’ve used at very high DAlt is runup power leaning with a short full power check on the runway.

But for transients who have not been taught how the technique applies to their airplane, or when in doubt, full power is best.

 

[Domenick]

No it’s a rented airplane I’m gonna find out the exact year and model next lesson and look that up

Here is the 1998 version of the C172 POH. I'm guessing it's good enough.

Dropbox

www.dropbox.com

...On the pre flight check list the company who owns the plane came up with they say to set the mixture about 1/4” in from full rich and it’s never touched after that at least not in my 1 hour lesson at around 3-4 thousand feet most of the time.

Not unusual for a school particularly from a low elevation field. There is no necessity to lean at the typical training altitudes from low elevation fields.

Way back in my training at sea level we never addressed leaning until I asked about it based on threads in various forums. After asking, my CFI was quite forthcoming on the subject and we leaned from then on. Since then I've been an aggressive leaner on the ground and in the air. On the ground to keep the plugs clean. In the air, to save fuel, keep the plugs clean, and improve performance.

I have a whopping 4.5 hrs of air time so far.

Wait until you are comfortable in the plane and have acquired the muscle memory to unconsciously control the plane, much like driving a car, before you address leaning. At this point in your training keep it simple, but your question shows good awareness. Good luck in your training. Do not become discouraged/frustrated when you hit training plateaus. You will. We all did.

 

[midlifeflyer]

Wait until you are comfortable in the plane and have acquired the muscle memory to unconsciously control the plane, much like driving a car, before you address leaning

It kind of depends where you are training, no?

Definitely agree that at a lowland airport where you are maybe going to 3000 AGL for maneuvers it can probably wait although I have seen spark plug fouling at fairly low altitudes in the summer. That's probably what @Nova's school is trying to address with that 1/4".

If it's that simple, doing it is just a matter of inserting it into the checklist. I'm sure if the full leaning procedure can be "mastered" by a presolo student in Denver by the 2nd or third lesson with no more than "Mixture...Adjust" as a checklist item , so can 1/4" lean.

 

[MRC01]

Definitely agree that at a lowland airport where you are maybe going to 3000 AGL for maneuvers it can probably wait although I have seen spark plug fouling at fairly low altitudes in the summer. That's probably what @Nova's school is trying to address with that 1/4".

It sounds like that's what they're trying to address, but incorrectly. Pulling mixture back 1/4" doesn't do much of anything and teaches students incorrect procedures. With a fixed pitch prop, proper leaning means you have a goal: either rich of peak RPM (for max power), or lean of peak RPM (for max efficiency).

Leaning to rich of peak RPM is described above. Leaning to lean of peak RPM is also called "rich of rough" and that phrase means set the mixture to the leanest setting it will take before it runs rough. To do this, lean the engine until it gets slightly rough. Normally, before any roughness sets in, as you lean you'll get a slight RPM drop and hear a change in the tone & pitch of the engine. But you might not in some airplanes. Either way, when it is lean to the point of a slight roughness, enrich a half turn or whatever small amount is needed to restore smooth operation. This "rich of rough" is the normal mixture setting for cruise operations below 75% power - even at sea level.

As @Domenick suggests, this is simpler than it sounds and after a few hours of flying you can do this entirely by feel, one-handed, while keeping your eyes out the window and flying the airplane. But if you fly near sea level this can wait until you've mastered basic maneuvers, to avoid excessive workload and distraction.

 

[DCR]

Aren’t you suppose to look at exhaust temperature for best mixture? Although I’m not sure the 172 I’ve been training in even has that.

That's kind of a big can worms and I'm not really the one to answer it, but a few considerations:

1: Many older aircraft don't have exhaust gas temperature (EGT) gauges like you mentioned. My main rental aircraft does not.

2: EGT can vary significantly on each cylinder, especially in a carbureted engine. To lean by referencing EGT I think it's best to at least have a probe on each cylinder. Better would be that plus fuel injection. Best would be all that plus computer controlled fuel mapping. In the carbureted engine you might starve one cylinder to get another just right, so you will never get it spot on.

3: Leaning for cruise flight I would be ok operating on the edge a little. If the engine starts to stumble you just re-lean. For takeoff and low altitude ops I want as close to a 0% chance of the engine hesitating as possible, so I'll add a little extra juice if I'm not sure.

Even in the other 172N I rent which does have a single EGT gauge - I never use it to lean. I just looked up the POH and there is a procedure for leaning with and without the EGT gauge, I can't say how much difference it makes (maybe someone else knows). I also don't pay for the fuel so...

 

[Albany Tom]

When I read the title, I thought "nope, it's not possible for a person to be too rich to fly. But maybe it's possible to be too rich to fly well."

I lean by the roughness, as per the POH. With most PA-28's it's easy to get an idea of where that should roughly be based on knob position.

Most on here have flown a lot more planes than I have. The only time I've had an engine want to die being too rich was a cub that was jetted incorrectly. No mixture in that plane, but full carb heat would cause it to stumble and sometimes die, and the culprit turned out to be a very wrong mixture adjustment on the too rich side.

I have had lead fouling from running too rich, though, detected on run-up when one mag didn't work. Wondering if OP's facility's use of limited leaning is just related to that, keeping it just lean enough to stop fouling. That's a complete guess.

 

[Racerx]

Dad's pa32 was was getting a 350-400 rpm gain during ground leaning. He had never leaned on the ground before. Finally was able to convince him it wasn't right by referencing the Lycoming manual and showed him the idle mixture...which he was unaware of. Any more than 50 rpm increase and your idle mixture is too rich...dude, you're way beyond that!

When I first started flying it more (before I knew better), on a hot humid day I pulled power to idle over the numbers. Could hear it almost die on roll out and I had to advance the throttle to keep it going. So yeah. You can be so rich dies.

Now that the idle mixture got set properly, I don't even need to ground lean unless it's a high DA day/airport.