Mixture leaning strategies/thoughts

[Tristar]

As a pilot and even student alike, we are taught that to have the proper air to fuel ratio we were supposed to lean the mixture to a certain amount. Obviously this helps with finding the perfect amount of fuel to a certain amount of air molecules which also depends on temp of that air since hot air has a different density than cold.

In my flight training, I was taught to listen to the engine. We didn't have EGTs and I honestly had never messed with one until my instrument training in college. I still to this day want to twist the red knob back until engine roughness and then twist in about three times. I will admit I'm still learning the best way to lean an engine but my original procedure hasn't failed me. If I understand this right, most people lean above 3,000 ft but you can at any point during your flight. I consider it a good procedure to twist it full rich during final landing preperation but this may not always hold true depending on where your flying.

So after all of my learning up to this point is said and done, I was curious if you would share your thoughts and processes as to your leaning procedures. Maybe what you find works for your aircraft in general or maybe what to watch out for such as detonation and over/under leaning.

Also for you A&P types or just really intellegent pilots, I was curious how much increase does one twist of a mixture knob do and is there a significant difference between an EGT guage and the old "listen and richen" method?

Fly safe,
Tristan

 

[tonycondon]

tristan, in my vast 172 flying experience, ive never noticed much of a difference between listnening for roughness then enrichening till smooth, and setting 75-100 degF rich of peak EGT. This method works good for small non turbo'd engines, IME.

 

[jesse]

I do a full power run up in every airplane I fly. I check all the gauges when it comes up to full power and lean as needed. In the winter it amounts to basically no leaning but in the summer it can be quite a bit for a very noticeable performance increase. You never know when that slight performance edge might save you.

Also for you A&P types or just really intellegent pilots, I was curious how much increase does one twist of a mixture knob do and is there a significant difference between an EGT guage and the old "listen and richen" method?

The effect of one twist of the knob will vary from airplane to airplane. You'll eventually fly some planes that have a lever to slide and no knob to twist.

The gain you get by having an EGT probe on every cylinder along with GAMI injectors is that you can fly the airplane lean of peak for less wear and good economy. You won't be encountering this situation for a very long time. You'll usually find owners with high performance airplanes that run this kind of setup. The amount of money saved is very real for them.

If you just have a single EGT probe on one cylinder (most airplane you fly will be like this). You have no idea what is going on with the other cylinders so I'm pretty hesitant to trust it completely and tend to fly much richer (for good reason) than I would if I had a fuel injected plane with Gamis and a JPI. I take it into consideration for leaning but I don't lean strictly based on it. More or less twist out from rough and look at the EGT to see if it seems reasonable.

Most pilots around the midwest think I'm crazy for leaning on every takeoff. First time I flew with Nick (knows nothing but high density airports) I noticed he was leaning for takeoff.

Mixture comes up to wherever I had it for takeoff. If it's a hot summer day it'll be out quite a bit. If it's winter it's more or less full rich. Prop comes forward on short final. It is part of my verbal before landing CGUMPS check.

 

[HomeatFL250]

Mixture?.......Leaning?.......Whats that? ........J/K

I would agree with Tony. As far as I can remember back in the day, there wasn't much difference between the three turns and the EGT methods. I think I preferd just doing the three turns.

 

[Dave Siciliano]

I'm flying a different plane with different equipment.

My first flying was in turbine helicopters and I don't recall leaning those (maybe we leaned to one side or the other when we turned <g>).

Early on in my fixed wing flying, I always just did what I was instructed to do; leaned until it got a bit rough; then, enrichened a turn or two. No JPI or other engine monitor then.

The graphic engine monitor has completely changed the manner in which I run my plane along with more precision fuel injectors.

Now, in the P-Baron and with the A-36 before that, engine management takes significant attention. I depart full rich (turbo charged) and begin my leaning at one of two place--sometimes in the climb--at other times in cruise.

This time of year, I can climb LOP at about 18.5 gph (v. over 30 full rich) and still climb 600 to 700 fpm. Makes a significant difference in fuel usage and gives me more range. In cruise, I burn about 16.5 gph LOP v. over 20 on the rich side. Still true out about 210 to 220 knots at FL200. All CHTs under 380.

Best,

Dave

 

[AirBaker]

Hi Tristan.

It's really going to depend on what you have available to you in the cockpit. If you've got a good engine analyzer and you're flying behind a big bore engine, you should definitely keep an eye on your CHTs and EGTs.

Most 172s and such just have a single EGT analog gauge. Here, you're not going to get all the info you'd hope for, but you can keep an eye on what gauges you have.

There is the generic answer of 'Check the POH' but those can be a bit conservative.

I wouldn't bother leaning until 3000 MSL, and in general I wouldn't fully lean until in cruise. Once in cruise, I would go for the lean til rough, then richen a tad method. I'd rather burn a few extra gallons of 100LL than a few cylinders.

 

[tonycondon]

I'm flying a different plane with different equipment.

My first flying was in turbine helicopters and I don't recall leaning those (maybe we leaned to one side or the other when we turned <g>).

Early on in my fixed wing flying, I always just did what I was instructed to do; leaned until it got a bit rough; then, enrichened a turn or two. No JPI or other engine monitor then.

The graphic engine monitor has completely changed the manner in which I run my plane along with more precision fuel injectors.

Now, in the P-Baron and with the A-36 before that, engine management takes significant attention. I depart full rich (turbo charged) and begin my leaning at one of two place--sometimes in the climb--at other times in cruise.

This time of year, I can climb LOP at about 18.5 gph (v. over 30 full rich) and still climb 600 to 700 fpm. Makes a significant difference in fuel usage and gives me more range. In cruise, I burn about 16.5 gph LOP v. over 20 on the rich side. Still true out about 210 to 220 knots at FL200. All CHTs under 380.

Best,

Dave

yea dave I didnt figure getting into the Turbo side of things was what Tri was asking about. Im trying to convince my boss (and mostly our old time mechanic) that getting the 421 set up for LOP is a good idea. They are flying 1600 hrs a year or so and would save a ton of money on gas. In the 421 I usually set mixtures for low 1500's EGTs in climb and just under 1600 EGT in cruise. works out to around a 25 gph climb and 20 gph cruise. if CHTs start to creep up in climb it goes richer.

 

[Tristar]

tristan, in my vast 172 flying experience, ive never noticed much of a difference between listnening for roughness then enrichening till smooth, and setting 75-100 degF rich of peak EGT. This method works good for small non turbo'd engines, IME.

Please forgive me if I dont word this quite right or understand it fully.

Tony,
I believe our CFI said that the charts in the POH for cruise power settings is established at max lean during standard conditions. I also understand that we enrichen the mixture to a smooth setting. Does this have any difference on the performance and correctness of these charts because of the three-turn richening method? I'm also wondering if there is a way you can calculate the performance with a given power setting, weather conditions, and possibly mixture? Just pure curiosity.

 

[AirBaker]

Most pilots around the midwest think I'm crazy for leaning on every takeoff.

Every takeoff? Just curious as to why.

 

[AirBaker]

I think the 3-turn method will soon become an old wives tale... You really have no idea where you're parking that mixture. But it's mostly all you've got in some aircraft.

 

[tonycondon]

Please forgive me if I dont word this quite right or understand it fully.

Tony,
I believe our CFI said that the charts in the POH for cruise power settings is established at max lean during standard conditions. I also understand that we enrichen the mixture to a smooth setting. Does this have any difference on the performance and correctness of these charts because of the three-turn richening method? I'm also wondering if there is a way you can calculate the performance with a given power setting, weather conditions, and possibly mixture? Just pure curiosity.

yea the charts for fuel consumption are for a "best economy" lean. but of course the charts for speed are at a 'best power" lean. Basically you should proverbially throw the fuel flow charts out the window. See what you actually get for fuel burn in cruise leaning the way you lean. and then use that. I think the way the generated the charts had something to do with voodoo. I have no idea how they could get the fuel flows as low as they claim.

Every takeoff? Just curious as to why.

because hes crazy of course!

 

[AirBaker]

...something to do with voodoo...

I guess the real question is... how far do we want to take this discussion?

Small engines, big bore/high compression engines, turbo/non...

 

[jesse]

Every takeoff? Just curious as to why.

Better performance. I can climb better. It also gets the leaning procedure in my head as being something I always do. That way when it DOES really matter I won't forget.

I always fly for best performance and assume the engine is going to quit. The airplanes I fly it works out well. Get into some of the bigger stuff and things get hot quick and that changes the game. My flying for best performance has saved me once now. If I wouldn't have did it there is NO way I would of made it back to the airport with the little engine power I had when I glided back.

 

[AirBaker]

Better performance. I can climb better. It also gets the leaning procedure in my head as being something I always do. That way when it DOES really matter I won't forget.

I always fly for best performance and assume the engine is going to quit. The airplanes I fly it works out well. Get into some of the bigger stuff and things get hot quick and that changes the game.

I guess as long as you're keeping the heat thing in mind. There's a guy out here that keeps burning through cylinders in his IO-520 powered 182. Leans for takeoff out of a 2900' MSL airport.

At some point you (the global YOU) are going to make the engine quit because it was leaned instead of keeping it cool.

 

[jesse]

I guess as long as you're keeping the heat thing in mind. There's a guy out here that keeps burning through cylinders in his IO-520 powered 182. Leans for takeoff out of a 2900' MSL airport.

At some point you (the global YOU) are going to make the engine quit because it was leaned instead of keeping it cool.

You can't stop people from being idiots. He is probably leaning way out until he gets best power and rolling with it. I lean until I hit best power and enrichen generously from there. I also watch what the EGT is telling me. Of course it's only one cylinder but it's better than nothing. Sometimes it's almost no difference but on real hot days it matters a LOT.

As I said, the more powerful airplanes you get into the larger the heat danger is.

Another leaning topic. I always lean VERY aggresively after engine start and for taxi.

 

[CJones]

Another leaning topic. I always lean VERY aggresively after engine start and for taxi.

I have put myself in the habit of leaning on the ground in the RV. It's REALLY noticeable in such a small plane when the 'roughness' smooths out during taxi. Plus, I'm the one that has to change the plugs, so I make it a point to prevent fouling as much as possible. Haven't gotten to the point of leaning for takeoff, though.

As for 'general' leaning, I usually start the leaning process once I'm in a stabilized climb. With the E.I. fuel flow gauge and Grand Rapids EGT/CHT on each cylinder, it's possible to really 'dial-in' performance as necessary.

 

[Tristar]

Jesse,

Leaning in different parts of the year is understandable because there are different amounts of "air" depending on the temp.

I don't believe I've ever heard of levers on an airplane for leaning. What types?

If I remember right, in standard airplanes its always a good idea to run a little richer than usual. The 152 POH recommends 25 degrees rich of peak EGT. I'm assuming thats after the drop and also where our 3 turns come from despite some aircraft lacking an EGT guage. Some CFIs or pilots for that matter feel comfortable around 75-100 which I'm still learning the concepts. According to the POH at max leaned (or how they word it as charted "peak EGT") would result in an 8% greater range for the 152. Something does confuse me though. It refers to the "Recommended Lean mixture." Where would you find that or am I missing something?

I don't think your crazy at all for leaning on take off. Actualy pilots that fly out of high altitudes I referred to slightly in my original post. I have not done it myself for two reasons, one I was hoping you'd clearify. Obviously, one, most of my flying was done at sea level so it hasn't occured naturaly and two (which I'm hoping to understand) I'm afraid of leaning too much and the engine failing on take off/climbout. Is that just a paranoya or a justifiable concern?

I also put in full rich every time I land. I wonder if that would be a problem of actualy drowning the engine in some areas such as in the mountains. I'll keep my methods for now because it hasn't failed me, proven otherwise,or flying at high altitude airports currently but it would be good to know.

 

[Tristar]

Dave,

Silly question, I didn't think you leaned Turbine aircraft? If an aircraft is fuel injected especialy, there isn't a leaning method because it does it automaticaly. I could be wrong.

Yes in some aircraft as small as the 152, you might gain a gallon or two per hour savings which is significant in a way considering the amount used but in larger aircraft it can go from 19 down to around 14 or 15 such as a Cessna 206 which can be up around 4-5gph. (very rough estimate, only trying to show the point). Obviously any pilot understands this adds up. Your flight planned fuel range may not be 4:30 but actualy 4:15 or so since those fuel ranges in the POH are ONLY if leaned propperly. Cessna has been sued many times for pilots not reading the POH and assuming a range without leaning propperly.

 

[jesse]

Jesse,

Leaning in different parts of the year is understandable because there are different amounts of "air" depending on the temp.

I don't believe I've ever heard of levers on an airplane for leaning. What types?

Lots of them. The Diamond for example. Some pipers have a lever you will pull out that cannot twist.

If I remember right, in standard airplanes its always a good idea to run a little richer than usual.

You want to be richer than peak. The reason for this is you have no way to deliver consistent fuel flow and no ability to monitor the EGT of each cylinder without GAMI and JPI.

I'm afraid of leaning too much and the engine failing on take off/climbout. Is that just a paranoya or a justifiable concern?

I lean QUITE a bit past what I would normally lean for cruise. EGT always looks good. I've never had a problem. I was taught it by people that *ALWAYS* did it. They never had problems reaching TBO.

I also put in full rich every time I land. I wonder if that would be a problem of actualy drowning the engine in some areas such as in the mountains. I'll keep my methods for now because it hasn't failed me, proven otherwise,or flying at high altitude airports currently but it would be good to know.

I doubt you would get it rich enough to where the engine would quit. But if you are at an airport with a decent elevation on a HOT day. You very well might not have enough power to do a go around. Usually when you go around it's because something bad happened and you generally want to go UP as fast as you can.

 

[AirBaker]

Silly question, I didn't think you leaned Turbine aircraft? If an aircraft is fuel injected especialy, there isn't a leaning method because it does it automaticaly. I could be wrong.

You still do lean fuel injected aircraft for sure.

The lean for max range thing is a bit deceiving. You basically do not want to be at 'peak'. 25 degrees on the rich side isn't all that great for your engine either.

It's all a trade off of heat in the engine, power, and fuel consumed.

 

[jesse]

If an aircraft is fuel injected especialy, there isn't a leaning method because it does it automaticaly. I could be wrong.

The 172R you fly is fuel injected and it must still be leaned. I don't know of a fuel injected certified airplane that will handle the leaning by itself. Actually I think the Diamond TwinStar might do this but I could be wrong Kent!?

Yes in some aircraft as small as the 152, you might gain a gallon or two per hour savings which is significant in a way considering the amount used but in larger aircraft it can go from 19 down to around 14 or 15 such as a Cessna 206 which can be up around 4-5gph. (very rough estimate, only trying to show the point). Obviously any pilot understands this adds up. Your flight planned fuel range may not be 4:30 but actualy 4:15 or so since those fuel ranges in the POH are ONLY if leaned propperly. Cessna has been sued many times for pilots not reading the POH and assuming a range without leaning propperly.

Leaning is important. If you don't you'll have crappy fuel burn, low performance, and fouled up plugs. It gets *REALLY* important in the big planes as fuel burn will be insane without it. In the 172 you fly the best thing you really can do is the lean till rough and 3 twists. In more powerful airplanes the story changes.

 

[Dave Siciliano]

Dave,

Silly question, I didn't think you leaned Turbine aircraft? If an aircraft is fuel injected especialy, there isn't a leaning method because it does it automaticaly. I could be wrong.

Yes in some aircraft as small as the 152, you might gain a gallon or two per hour savings which is significant in a way considering the amount used but in larger aircraft it can go from 19 down to around 14 or 15 such as a Cessna 206 which can be up around 4-5gph. (very rough estimate, only trying to show the point). Obviously any pilot understands this adds up. Your flight planned fuel range may not be 4:30 but actualy 4:15 or so since those fuel ranges in the POH are ONLY if leaned propperly. Cessna has been sued many times for pilots not reading the POH and assuming a range without leaning propperly.

Sorry to go way overboard! I was just focused on leaning in general.

Don't remember leaning the turbines <g>

In fuel injected, turbo charged, especially big bore; leaning is very important. The JPI and better fuel injectors have really made a difference. If we ever link up, I'll try to show you how it works on this plane. After a flight, I can download the data and look at exactly where all cylinders were running.

Best,

Dave

 

[Tristar]

The problem with understanding the performance of your aircraft is although they do give you charts and procedures, they are only for standard perfect conditions. Every flight is different and I know very few pilots that sit down and calculate every last MPH or KTS. Not to mention, as a student, many of us aren't walked through every part of the POH and taught every calculations including the "ifs and onlys." Maybe I was left out of the learning curve but I'm still learning much about the aircraft I fly on a weekly basis. I'm not sure if this is in fault of the instructors aren't clearified on what teach on how in depth for engine operations or that students have so much on thier minds at grasping basics such as landings and stalls that the FAA/CFI alike put no detailed requirements on what we as students need to know other than "lean to roughness and turn in three times." Don't get me wrong, that worked for me during the stress of primary training but it does make me curious and deffinitly defines the idea of a pilots certificate as being a license to learn.

 

[AirBaker]

Tristan, do you have a Fuel Flow gauge in the cockpit?

 

[Tristar]

Tony could you please remind me what the average fuel flow you use for the 152 and possible the 172R. I know I should know this but it seems everyone has different "guesses." I don't believe I've found it but what I saw was NMPG and not MPG. Do I technicaly have to compute this as a rough estimate or is it in the book somewhere? ...or should I just throw it out the window and listen to the CFIs? (no offense, but I will be teaching this one day and I dont want to learn it wrong)

 

[jesse]

Tony could you please remind me what the average fuel flow you use for the 152 and possible the 172R. I know I should know this but it seems everyone has different "guesses." I don't believe I've found it but what I saw was NMPG and not MPG. Do I technicaly have to compute this as a rough estimate or is it in the book somewhere? ...or should I just throw it out the window and listen to the CFIs? (no offense, but I will be teaching this one day and I dont want to learn it wrong)

Fill the tanks up all the way. Go fly around like you usually do. Land and fill them up again. Divide amount of fuel by hobbs hours flown and you now have a good number to use.

172 is usually around 8 gallons. I plan 10 to be safe. 152 is more like 6 or 7. Plan 8 to be safe.

Planning 10 in a 172 gives you four hours of fuel. I hope no pilot tries to fly a 172 on standard tanks past 4 hours. I like to land somewhere between 3 and 3.5.

 

[AirBaker]

I'd plan a flight by the POH... then compare the burn rates to what Jesse suggested.

 

[Tristar]

Better performance. I can climb better. It also gets the leaning procedure in my head as being something I always do. That way when it DOES really matter I won't forget.

I always fly for best performance and assume the engine is going to quit. The airplanes I fly it works out well. Get into some of the bigger stuff and things get hot quick and that changes the game. My flying for best performance has saved me once now. If I wouldn't have did it there is NO way I would of made it back to the airport with the little engine power I had when I glided back.

You do realize there is a requirement for making it back to the airport plus 30 min remaining right? Just pickin on ya!

....although if you're getting down to absolute minimums and only calculate that remaining 30 min, it'd have to be a pretty good calculation considering aircraft and outside forces or a just great estimate I would think. It can almost be scary how little fuel 30 minutes is. Not to mention anything can mess that up such as constant turns in a certain direction can even starve the airplane or even something silly as lacking to remember "unusable fuel" which is rare to my understanding.

I applaued you on the best performance thinking though despite it probably not being comfortable for me. I feel comfortable with an hour of fuel always in the tanks but I know to some people thats not always possible which could be the purpose of the FAA recommendations.

 

[jesse]

You do realize there is a requirement for making it back to the airport plus 30 min remaining right? Just pickin on ya!

Fuel wasn't the problem. I had about 55 gallons of fuel in the plane still.

....although if you're getting down to absolute minimums and only calculate that remaining 30 min, it'd have to be a pretty good calculation considering aircraft and outside forces or a just great estimate I would think. It can almost be scary how little fuel 30 minutes is. Not to mention anything can mess that up such as constant turns in a certain direction can even starve the airplane or even something silly as lacking to remember "unusable fuel" which is rare to my understanding.

IMHO it is foolish to fly an airplane down to 30 minutes left. I've done it once and I won't do it again I thought I had a good reason at the time but the more I think about it now the more I smack myself. I also had been monitoring fuel burn *VERY* closely and checked it on the ground right before that last leg.

I applaued you on the best performance thinking though despite it probably not being comfortable for me. I feel comfortable with an hour of fuel always in the tanks but I know to some people thats not always possible which could be the purpose of the FAA recommendations.

Keeping a hour of fuel in the tanks is a *REALLY* good idea. If you ever go under a hour I will be yelling at you
There is nothing uncomfortable about flying like it matters. Always take off on the centerline. Always land on the centerline. If you miss the centerline go back up and do touch and go's until you hit it. Always pick a spot on the runway to land. Always estimate where you will lift off and see how close you get. Over time you will become very good in the airplane.

 

[Tristar]

No you guys are right. I believe I had it mixed up with something else as far as leaning the R. Blonde moment, hehe.

I cannot remember it exactly but there is a system that actualy slightly keeps the fuel injected aircraft slightly leaned. Am I incorrect on this?

 

[Tristar]

Sorry to go way overboard! I was just focused on leaning in general.

Don't remember leaning the turbines <g>

In fuel injected, turbo charged, especially big bore; leaning is very important. The JPI and better fuel injectors have really made a difference. If we ever link up, I'll try to show you how it works on this plane. After a flight, I can download the data and look at exactly where all cylinders were running.

Best,

Dave

That would be interesting to learn I'm sure!

I'd actualy like to learn how leaning in the turbines works too. I thought by that time it'd be all automatic. I'll leave that for another thread though if we get too off topic.

All of what I'm referring to deals with the 152, 172R, and the 172RG (only because I have the manual for this one.) These aircraft are what I have 99% of my experience in.

 

[Tristar]

Tristan, do you have a Fuel Flow gauge in the cockpit?

I fly 1997/8 172R models. Yes we do. On start up, I look for 3-5 on the fuel flow when I turn the engine pump on. Is there a reason you asked?

 

[tonycondon]

Tony could you please remind me what the average fuel flow you use for the 152 and possible the 172R. I know I should know this but it seems everyone has different "guesses." I don't believe I've found it but what I saw was NMPG and not MPG. Do I technicaly have to compute this as a rough estimate or is it in the book somewhere? ...or should I just throw it out the window and listen to the CFIs? (no offense, but I will be teaching this one day and I dont want to learn it wrong)

6 gph is usually a conservative estimate in a 152. Ive never flown a 172R. Is that 180 hp? If so I would guess its around 10 as a conservative preflight estimate. If its 160 hp then 9 will be a good flight planning number.

In this case I would throw out the book and use the numbers based on yours and others experience in the particular plane you are flying. Its easy to explain this to students (for when you are a CFI) something like "These numbers are not attainable in real life. In real life, we see X.X gph fuel flow. So we will make our flight plan for X.X + 1 gph and then we will have a little extra built in reserve."

 

[AirBaker]

I fly 1997/8 172R models. Yes we do. On start up, I look for 3-5 on the fuel flow when I turn the engine pump on. Is there a reason you asked?

Yep... Find out what the POH says your numbers for cruise should be. Park the mixture there...

 

[jesse]

I fly 1997/8 172R models. Yes we do. On start up, I look for 3-5 on the fuel flow when I turn the engine pump on. Is there a reason you asked?

I suspect you are talking fuel pressure. He's talking fuel flow--Like X gallons per hour being burned.

 

[Tristar]

Jesse,

I must have missunderstood your story. I thought you flew it down to the last 30 minutes of fuel. What were you flying to have 55 gallons "still" in the tanks?

Yes, I haven't flown where there wasn't at least an hours worth of fuel in the tanks on landing.

Boy you really like to pick on me about my centerline take offs and landings. I'm short...I'm working on it! Here's a question for ya which I hope doesn't take us off topic. When ATC says "fly runway heading" does it mean to track runway heading or if the runway is runway 36 you fly straight north on the DG/compass? I always thought it was tracking runway heading so you don't over fly another airplane but a CFI once told me no that it was fly that runways magnetic heading despite the wind because other aircraft will also drift with the wind. I don't believe I believe this but during climb out, I didnt feel like arguing with an ATP instructor....although I found it slightly funny that a few seconds later ATC told us to scoot over which I would have been correct but arguably only when ATC instructed me to do so.

 

[Tristar]

6 gph is usually a conservative estimate in a 152. Ive never flown a 172R. Is that 180 hp? If so I would guess its around 10 as a conservative preflight estimate. If its 160 hp then 9 will be a good flight planning number.

In this case I would throw out the book and use the numbers based on yours and others experience in the particular plane you are flying. Its easy to explain this to students (for when you are a CFI) something like "These numbers are not attainable in real life. In real life, we see X.X gph fuel flow. So we will make our flight plan for X.X + 1 gph and then we will have a little extra built in reserve."

How can you flight plan for that until you're at cruise, leaned out and see the fuel flow?

I was always told 7 for the 152 and 8 for the 172, the 172R I always forget for some reason.

 

[Tristar]

I suspect you are talking fuel pressure. He's talking fuel flow--Like X gallons per hour being burned.

I'll show you the guage this weekend and we can correct it. I thought it was fuel flow.

 

[AirBaker]

How can you flight plan for that until you're at cruise, leaned out and see the fuel flow?

I was always told 7 for the 152 and 8 for the 172, the 172R I always forget for some reason.

Isn't there a table for this in the Cessna POH??

 

[flyingcheesehead]

I don't know of a fuel injected certified airplane that will handle the leaning by itself. Actually I think the Diamond TwinStar might do this but I could be wrong Kent!?

Yes, the TwinStar leans itself. It has FADEC (Full Authority Digital Engine Controls) meaning there are a pair of power levers in the cockpit to select power output, and a computer (two per engine, actually) is actually controlling throttle, prop, and mixture.