IO-390 leaning?

[Derrickearly]

I have a IO-390 in my 1976 M20F, and I just found the engine's manual at https://www.lycoming.com/sites/default/files/IO-390-A Op %26 Install Manual 60297-34.pdf.  When leaning, I have always used rich of peak by -14C.  The engine manual recommends leaning to peak for economy when below 75% power.  "Best Economy Cruise (approximately 75% power and below) – Operate at peak EGT".  Anyone else run their IO-390 at peak?

Edited January 20, 2022 by Derrickearly
wrong manual

[carusoam]

13 hours ago, Derrickearly said:

I have a IO-390 in my 1976 M20F, and I just found the engine's manual at https://www.lycoming.com/sites/default/files/IO-390-A Op %26 Install Manual 60297-34.pdf.  When leaning, I have always used rich of peak by -14C.  The engine manual recommends leaning to peak for economy when below 75% power.  "Best Economy Cruise (approximately 75% power and below) – Operate at peak EGT".  Anyone else run their IO-390 at peak?

All the time…. When below 65%bhp…. Using the red box theory… or red fin… depending on who you are reading about it from….

With a NA engine we bump into this 65% limit around 8k feet or so…. Above this altitude… MP has dropped off.

When below 8k’ you have to adjust the throttle… to stay below 65%….

Lycoming will give higher numbers because it is safe… but costs YOU more….

The purpose of running at peak is to burn the most amount of fuel available with the amount of air going through the engine….

Of course one of the cylinders peaks first and another leaks last… so use the one that leaks last… (for LOP) and be a couple of degrees leaner… this technically allows all of the fuel to be converted to power.. none of it gets used for cooling…

 

You can read about this stuff at Savvy (?) the chief tech guy is Mike… the mechanic’s Mechanic…

Did I answer what you asked? 
 

Then consider the safety of running 14°C ROP….  
Why are you using Celsius? And being 50°F isn’t the nicest thing to do to your engine…

Ancient POHs all use 50°F ROP…. Most pilots around here have moved on from that… either more rich or LOP…

During your reading… look out for CHT control recommendations… see if it mentions 380°F….

Best regards,

-a-

[Bunti]

This is the original text from your Lycoming pdf:

(a) Leaning to Exhaust Gas Temperature. (Normally aspirated engines with fuel injectors or carburetors) (1) Maximum Power Cruise (approximately 75% power) - Never lean beyond 150°F. on rich side of peak EGT unless aircraft operator’s manual shows otherwise.

Monitor cylinder head temperatures.

(2) Best Economy Cruise (approximately 75% power and below) - Operate at peak EGT.

This says that you should never lean beyond 150F at 75 % power and in addition that you can fly at peak EGT below 75 %.  There is no margin. That could mean: 150F rich of peak at 75 % is right and at 74.9 % peak would be ok. That makes no sense to me.

My understanding of the engine experts and the red box  theory is more like that you can lean to peak or so if you are below 65 %.  Even leaning to peak minus 14 c (about 50F) ROP is not a good idea at 75 %.

I have the IO360, but the recommendations from Lycoming are the same:

If I fly with 75 % rich of peak, I usually lean to about  peak  minus 150F. Lean of peak, I prefer to fly somewhere between peak minus 20 to 50 F. The EDM930 shows a fuel flow of about 9 GPH and % power between 64 and 70.

[Derrickearly]

14 C change is equal to 14*1.8 = 25 F change.  Unfortunately, 25F is what I have been using for rich of peak based on my old M20F manual.  Here is a notional temp plot from the general IO-390 manual.  Looking at the plot, I've likely been peaking my cylinder head temperatures. :-(  Hopefully, cruising above 8k has kept me out of trouble.

[PT20J]

I am personally aware of a flight school with a fleet of C-172s that it has had for many years. They are really well maintained, frequently upgraded and probably the best older C-172s in the country. They regularly get TBO and beyond on the Lycoming O-320 engines. The airplanes did not come equipped with cowl flaps or CHT gauges. Recently two were upgraded to G3X Touch systems with EIS and now they have CHT and EGT for each cylinder. They found out that during climb, the engines run with CHTs will over 400 F. Now some of the CFIs are a little concerned about it.  But in the past, when no one knew about it, the engines didn't seem to care.

I'm not suggesting that we shouldn't take care of our engines. But, I do think they are sturdier than we may think.

Lycoming cannot make specific recommendations for a particular airplane because the induction system, exhaust system and cooling system all affect engine performance and these systems are designed by the airframe manufacturer, not the engine manufacturer. Thus, any general recommendation from Lycoming (except for limitations contained in the TCDS) are generally going to be very conservative.

Skip

[A64Pilot]

You can do anything you want to with the red knob at less than 75% and not hurt anything, and depending on RPM that 75% number can occur well below 8000 ft, but 8,000 is conservative, so safe to use it.

Personally I like to use 65% as my max to add additional cushion, plus I’m after economy and range. I run usually between 25C to 50C LOP, I use C as that’s what the gauge is calibrated in.

Using the rule of thumb of when LOP one GPH equals 14 HP, I know as long as I’m LOP that 9 GPH or less is 65% or less power.

65% power is 130 HP and 9x14= 126. (200 HP 360)

As long as 9 GPH is correct LOP, that makes ensuring your safe easy, cause it takes out the calculating MP vs RPM, charts etc. Just stay LOP and less than 9 GPH (200 HP 360) of course, I assume but do not know that a 390’s BSFC ought to be real close to a 360’s?

[PT20J]

Here's an old Lycoming paper on determining power from fuel flow that someone at Kitplanes dug up and a spreadsheet implementing the calculations.

Power_from_fuel_flow.pdf

Lycoming_power_from_fuel_flow.xls

[carusoam]

Thanks Derick!
 

Having Alexa do my math for me, didn’t work out very well… 
 

Below 65% bhp you are free to cruise at peak…. Which occurs at 8k’ and above most days…

 

Leaning during the climb has been better outlined than the old POHs… too…

 

What do you have for guidance there?

 

My IO550 uses a calibrated EGT… where the EGT is set to stay in a range (blue box method) 200-300°F ROP…. (?)

During the climb the EGT needle falls out the bottom of the box, a simple adjustment puts it back at the top of the box to continue climbing….

Best regards,

-a-

[Derrickearly]

14 hours ago, carusoam said:

Leaning during the climb has been better outlined than the old POHs… too…

What do you have for guidance there?

Here is what the Lycoming IO-390-A manual says about leaning during climb. 

"On engines with manual mixture control, maintain mixture control in “Full Rich” position for rated take-off, climb and maximum cruise powers (above approximately 75%). However, during take-off from high elevation airport or during climb, roughness or loss of power may result from over-richness. In such a case adjust mixture control only enough to obtain smooth operation - not for economy. Observe instruments for temperature rise. Rough operation due to over-rich fuel/air mixture is most likely to be encountered at altitudes above 5,000 feet.

Always return the mixture to full rich before increasing power settings."

[Bartman]

3 weeks ago we returned to KY after watching our UK Wildcats defeat the Iowa Hawkeyes in the Orlando Citrus Bowl. It was severe clear and cold, but strong winds from the North kept us low. Despite cruise at 4,000 to avoid headwinds we cruised LOP with varied RPM with FF just less than 10gph and around 70% horsepower to avoid a fuel stop. If ROP it would have required a stop for fuel. 
 

My newly rebuilt engine thanked me when we got home for running her hard. 

[Ragsf15e]

6 hours ago, Derrickearly said:

Here is what the Lycoming IO-390-A manual says about leaning during climb. 

"On engines with manual mixture control, maintain mixture control in “Full Rich” position for rated take-off, climb and maximum cruise powers (above approximately 75%). However, during take-off from high elevation airport or during climb, roughness or loss of power may result from over-richness. In such a case adjust mixture control only enough to obtain smooth operation - not for economy. Observe instruments for temperature rise. Rough operation due to over-rich fuel/air mixture is most likely to be encountered at altitudes above 5,000 feet.

Always return the mixture to full rich before increasing power settings."

Thats the same guidance as they give for the Io360A1A in my ‘68.  It appears they didn’t update much when they certified the -390.

While the guidance is what it is and probably won’t hurt anything, there’s a good “Pelican’s Perch” article by Deacon about the target egt method in climb.  It works well and maintains good cooling and power as you climb.  You need good engine instrumentation but it’s easy to execute.  Note sea level takeoff egt, lean as you climb to maintain that egt. That’s it.  If you leave full rich, you’ll notice your egt decline as you climb because you’re getting more rich.

[afward]

32 minutes ago, Ragsf15e said:

Thats the same guidance as they give for the Io360A1A in my ‘68.  It appears they didn’t update much when they certified the -390.

To some degree, changing the guidance with newer (but derived!) engine designs would be admitting the old guidance was wrong.  Considering attorneys nearly always advise against admitting fault, no one should be surprised...

LOP, done correctly, won't hurt the engine.  Even at relatively high power settings (>75%).  The trade-off is that you cannot get rated power that way (must run too lean to maintain detonation margins).  The benefit is lower CHTs, lower oil temps, cleaner oil, and lower fuel burn.  There is some concern for turbo health on such engines (hot oxygen may not be good for them), but I don't know that anyone has actually studied it yet.

Now, whether you choose to run LOP, peak, best power, or fully ROP is up to you...  All will get you there, just with different trade-offs.

I personally like to run LOP in most cases.  That gets me at least 17 MPG in cruise (TAS/FF), which is better than my truck so I'm happy.

[PT20J]

Lycoming hasn't changed its guidance for probably 50 years, and its engine designs haven't changed much either. The chart published in the engine manuals and reproduced above clearly shows that the the economy range BEGINS at peak EGT and extends to about 80 F LOP. The admonition about leaning only below 75% is really just a description of the red box concept: Below 75% power there is no red box. The suggestion that peak EGT is a "best economy" setting simply reflects the fact that it is a reasonable tradeoff between fuel consumption and power output. Power output drops off rapidly at weaker mixtures. When these engines were designed gas was cheap and people didn't buy airplanes to travel slowly. Note that Lycoming also says that CHTs should be below 400 F during economy cruise. So interestingly, all the modern concepts are contained within Lycoming's Operator's Manuals.

Skip

[Derrickearly]

10 hours ago, Ragsf15e said:

Thats the same guidance as they give for the Io360A1A in my ‘68.  It appears they didn’t update much when they certified the -390.

While the guidance is what it is and probably won’t hurt anything, there’s a good “Pelican’s Perch” article by Deacon about the target egt method in climb.  It works well and maintains good cooling and power as you climb.  You need good engine instrumentation but it’s easy to execute.  Note sea level takeoff egt, lean as you climb to maintain that egt. That’s it.  If you leave full rich, you’ll notice your egt decline as you climb because you’re getting more rich.

I really like your target egt temp approach!  Makes sense.

[A64Pilot]

9 hours ago, PT20J said:

So interestingly, all the modern concepts are contained within Lycoming's Operator's Manuals.

Skip

Not many realize that, there is honestly nothing “new” about the new way of operating these engines

Even if you go way back to the way we were taught to lean engines, that is slowly lean it until it begins to get rough or loses power and then enrichen just enough to make it smooth again or regain power, that puts you LOP in engines that can run LOP, (not all will), and for those that won’t probably right at peak.

Then finally while modern digital engine monitors are nice to have, they aren’t required, these engines were operated for decades safely and efficiently without them.

I’m not against them at all, just you don’t “have” to have one to safely operate LOP. I normally have one, just haven’t yet in my Mooney but plan to.

Back in the mid 70’s my Father would climb his 210 to 10,000 or so and lean it as far as it would run smoothly, he was no genius, almost anyone who was after economy  did so. those that were after speed ran it at best power.

Fuel has changed, we went from 100 to 100LL, but other then that I don’t know of anything else that has changed in the last 45 years or so?

I’m sure Lycoming recommends nothing less than peak because as you go LOP, the power goes away and Lycoming doesn’t want the reputation of a weak engine, which any spark ignition engine operating LOP is.

[Ragsf15e]

2 hours ago, Derrickearly said:

I really like your target egt temp approach!  Makes sense.

Not mine, but it does work well and it’s simple.

Its down a ways on this page in case you want to read from the source…

https://www.avweb.com/features/avweb-classics/pelicans-perch/pelicans-perch-64where-should-i-run-my-enginepart-2-the-climb/

[PT20J]

There’s also a target EGT slide presentation on the APS website

https://www.advancedpilot.com/tech.html

 

[Derrickearly]

The manual says for peak power "never lean beyond 150 F".  What does that mean? If I'm going for peak power, I would be tempted to use 100 F instead of 150 F ROP.

[Will.iam]

1 hour ago, Derrickearly said:

The manual says for peak power "never lean beyond 150 F".  What does that mean? If I'm going for peak power, I would be tempted to use 100 F instead of 150 F ROP.

Read the above link. 150F ROP keeps you out of the red area that is harmful to your engine by cooling the cylinders with extra fuel at high (75% and more) power settings. LOP is more fuel efficient but you cannot make high power running LOP on a NA engine unless you are at very low altitude, a turbo engines can go a little higher power but even turbo engines run into limits. We do not have a gauge for internal cylinder pressure but a close proxy is cylinder temperature and the test data shows keeping your cylinder temperature below 400 F for lycomings and 380 F for continentals will keep the internal cylinder pressures to acceptable levels. You have to have an all cylinders engine monitor if you are going to be running close to the limit to account for variances between cylinders to make sure one cylinder is not over the limit which reduces the life of that cylinder faster than  below the limit. If you were to lean your mixture to 100 F ROP you would see your cylinders start climbing in temperature until some temp passed 400 F. This a assuming your cooling baffles are in good condition as well or you might be above 400 even at 150 F!  I have a continental so my limit is 380 on my engine monitor to start doing something to keep the cylinder temp from rising past that point. My preferred range is 340-360 F cool enough for cylinder long life but hot enough to heat up the oil to boil off the water that collects in the oil and minimize the lead in the gas to not stick on the valves.

[Derrickearly]

15 minutes ago, Will.iam said:

Read the above link. 

Which link please?

[Will.iam]

30 minutes ago, Derrickearly said:

Which link please?

All of them but this one in particular and then read all of the other pelican briefs he has a ton of great pilot info. 

Its down a ways on this page in case you want to read from the source…

https://www.avweb.com/features/avweb-classics/pelicans-perch/pelicans-perch-64where-should-i-run-my-enginepart-2-the-climb/

[A64Pilot]

Your not going to foul a plug full rich at high power.

The  difference in fuel burned at 100 ROP and 150 ROP for the time your going to be at high power is negligible. I mean from takeoff roll to 8,000 is what maybe 12 min if your heavy?

Everything I’ve owned full rich takeoff EGT is well rich of 150 ROP anyway, so target EGT is safe on them.

Besides I believe at 150 ROP it’s making its max power, at 100 ROP power will be slightly less?

A little rich isn’t going to hurt anything at all, a little lean possibly could.
The good thing about climbing is if you get busy doing other things and forget about leaning for a few minutes, the engine gets richer and if anything is more protected.

If your a ROP guy and descend at high power, then you need to pay close attention as of course it’s getting leaner as you descend, if you descend LOP, then it just gets even leaner and won’t hurt itself, of course your not at high power LOP anyway.

Remember below 75% power you can’t do anything with the red knob that can hurt the engine, above 75% power you can, and do so relatively quickly too.

Personally I use 65% power for an additional cushion, besides I’m after economy over speed and that means lower power settings LOP.

[Derrickearly]

On 1/24/2022 at 12:07 PM, Derrickearly said:

The manual says for peak power "never lean beyond 150 F".  What does that mean? If I'm going for peak power, I would be tempted to use 100 F instead of 150 F ROP.

I received clarification from Lycoming on the above question.  "This means that you must be at least 150 degrees on the rich side of peak EGT.  For example, you would not want to be at only 125 degrees on the rich side of peak, or you would be excessively lean under the spelled out conditions."

I also asked what did they mean by peak EGT for economy.  "The first cylinder to reach peak egt would be the correct one. If you were to lean the last one to peak egt then the others would be lean of peak which is not recommended by Lycoming."

This goes against the lean of peak folks.

[afward]

1 hour ago, Derrickearly said:

I received clarification from Lycoming on the above question.  "This means that you must be at least 150 degrees on the rich side of peak EGT.  For example, you would not want to be at only 125 degrees on the rich side of peak, or you would be excessively lean under the spelled out conditions."

I also asked what did they mean by peak EGT for economy.  "The first cylinder to reach peak egt would be the correct one. If you were to lean the last one to peak egt then the others would be lean of peak which is not recommended by Lycoming."

This goes against the lean of peak folks.

"not recommended" is not the same as "prohibited".  Something to keep in mind: The manufacturers can only make recommendations that are supported by hard data generated as part of the certification process.  It would cost extra to certify LOP operations (plus add liability concerns due to past guidance), so they don't... And probably won't.

Thing is, they know LOP is a valid and useful operational mode...  They just won't directly say as much (though if you look at all the charts they publish, LOP is absolutely in the valid operational ranges...  as is under square operation).

I do think it's interesting that their idea of "Peak" means your richest cylinder could very well be running at a much higher CHT than if you ran 150F ROP, even though it's making less power and burning a lot less fuel...

Like I said before, how you choose to run your plane's engine is up to you...  As long as you aren't abusing the engine (like full power 50F ROP!) it'll get you where you're going.  Heck, the M20F POH actually _calls for_ 50F-100F ROP fuel flows for certain settings, and they aren't exactly known for falling out of the sky...

[carusoam]

8 hours ago, Derrickearly said:

I received clarification from Lycoming on the above question.  "This means that you must be at least 150 degrees on the rich side of peak EGT.  For example, you would not want to be at only 125 degrees on the rich side of peak, or you would be excessively lean under the spelled out conditions."

I also asked what did they mean by peak EGT for economy.  "The first cylinder to reach peak egt would be the correct one. If you were to lean the last one to peak egt then the others would be lean of peak which is not recommended by Lycoming."

This goes against the lean of peak folks.

Derrick,

at first…. I thought  you may have missed their intent…

Reading your response a third time… I realize there is a slight miss…

 

They are describing the method of leaning in detail…

When leaning LOP… it is done using the last cylinder to peak.

When leaning ROP… it is using the first cylinder to peak.

Leaning to Peak… the intent is to have all of the fuel get burned…  so use the LOP procedure…

 

This is just a simple way of keeping all the cylinders on the same side of peak as expected….

 

It is only really important if you have a large Gami spread… where first and last to peak are far apart….

 

Now I’m just confused… why Lycoming would make a statement that is easy to misinterpret… then hand it to you…

 

Best I can tell…

1) use this procedure for LOP and peak

2) Lean that procedure for ROP

Don’t mix them up, because you don’t want to leave some on the other side of the fence….  
 

Would it really matter, if you left a cylinder slightly more rich or less rich?  (Not a lot…)

But if you follow their procedure… the errant cylinders will be errant toward the safe side…

 

Don’t go so far to assume flying at peak is a good idea, and LOP isn’t….
 

How old was that recommendation?

Why didn’t they clear that up for you?

 

There are two concerns for Peak and LOP…

1) the temperatures achieved at peak, and the transition through Peak on the way to LOP….  Both have been discussed endlessly as the Red Fin or Red Box…

2) The amount of excess O2 that gets sent through the system is an oxidation concern in the exhaust system…  experience says the exhaust system is oxidation resistant enough, the extra O2 doesn’t have an extra effect…

Pp thoughts only,

-a-