To Lean or not? Above 75% HP

[Boilermonkey]

I recently bought into a Mooney partnership of a M20C. It has a single cylinder EGT/CHT gauge setup.

I'm coming from a G1000 equipped C182 where we had all sorts of bells and whistles, so I apologize if this question is basic.

The POH states to lean ROP by 100 degrees, however, do not lean above 75% HP.   The performance tables show nearly all the RPM/MP settings that I would use cross country below 10K feet being above 75% HP.  This is quite different than the C182 where the performance numbers were all 50 degrees ROP irregardless of power setting.

So, do people lean above 75% power?  If so, what's your rule of thumb (obviously keeping the CHTs below 400 is a good idea...)

If you don't lean, what type of temps and fuel economy do you see?

OR, an I missing something?

[Mooneymite]

I definitely lean, but below 75%.  Like you, I only have basic engine instruments, so I just use the POH charts and keep my RPM's low and my altitude high,.  If you want to run the high power settings, the chart fuel-flows jump way up because they assume no leaning.

Mine is a completely stock C (1974), no mods whatsoever.  I get book speeds almost right to the knot.

Perhaps those with more sophisticated engine instrumentation can operate a little more aggressively?

[carusoam]

Without four EGTs and four CHTs, the ability to know what is going on with your engine is pretty limited.

there is a daily discussion around here on how to run an O360 LOP.  If all you got to go on is lean til rough, then increase the mixture until smooth, then add 50°F... It is best to have some instrumentation to go with that.

Modern engine training technology uses 65% or less power as a safe place to lean the engine without fear.  Using altitude to limit the engine power, about 8k' and above is a great place to test your leaning experience for full throttle.

Using your POH you can set the MP for 65% power or less and then lean from there.

A G1000 is nice but clearly not required.  There are used engine monitors and some low cost ones that can fill the gap.

High EGTs can lead to High CHTs.  High CHTs can cause some damage or increased wear.  The owner's manuals and early POHs don't give very good guidance on how to run the engine in the modern world.

Hope that helps.

Best regards,

-a-

Edited May 5, 2017 by carusoam

[Hank]

What power settings / altitudes do you use? I find it impossible to get > 75% power at 9000 msl.

Climb to 21" MP or less, pull the throttle back until the MP needle wiggles (to close off the Full Throttle fuel enrichment circuit), and pull back to 2500, then leag. Confirm this with your Performance Tables. No, I never fly WOT for the reason I just mentioned.

Down low for short trips, I use 23"/2300 and lean.

For mid-length trips, I use mid-level cruise altitude and 22"/2400, and lean. 

For longer trips, WOT- and 2500 and lean.

[Boilermonkey]

Key number 46...where have I seen that before 

Thanks for the guidance!

[flyboy0681]

At and above 6,000 feet I can't get book value for MP. All I can eek out is a max of 22.3 inches. Would this be an indication of a problem with the gauge or induction system?

[Mooneymite]

MAP and barometric setting are, of course inter-related.  If you read 29" MAP at sea level with the engine shut down, when you ascend 6,000', 23" is about you'll read. 

Yes, there are variances in MAP readings.  Your MAP gauge may be off a bit.  Also, for pressure altitude, don't forget to set 29.92 (for performance reference, not ATC) when you're matching book MAP with altitude.

There's a great article (including a little quiz!) on MAP HERE

[Hector]

At and above 6,000 feet I can't get book value for MP. All I can eek out is a max of 22.3 inches. Would this be an indication of a problem with the gauge or induction system?

Typically my C will make 22 at 8500. 21.8 @ 9K, 21 @ 10k, 20.1 @ 11k, 19.5 @ 12k, 18.7 @ 13k, 18 @ 14k, 17.5 @ 15k, and 16.7 @ 16k.

22 @ 6k seems low. Could be a gauge issue, could be induction, and could be a tired engine. Probably not the latter if compressions are good.

[Cyril Gibb]

On 2017-05-04 at 9:52 PM, carusoam said:

there is a daily discussion around here on how to run an O360 LOP.  If all you got to go on is lean til rough, then increase the mixture until smooth, then add 50°F... It is best to have some instrumentation to go with that.

I've been biting my tongue for a few days because I don't want to start a new bun fight... however... the OP is a relative newbie and I believe the leaning instruction may be bad advice.

Lycoming operators manuals from the 70s until right now have discussed leaning without complete engine instrumentation.  They have consistently described the leaning technique to achieve Best Power and Best Economy.    note also that this applies to the 0-360 and is applicable under 75% power... other displacements vary somewhat in the leaning guidance (italics are mine)

Best Power:  Lean until a drop in power (rpm or airspeed depending on fixed pitch or constant speed props) then enrichen to get peak power back.  (that would put you at about 150 ROP)

Best Economy: Lean until engine roughness and then enrichen until smooth. (that would vary but should put all cylinders somewhere LOP)

If you lean until roughness, putting you somewhere LOP, then enrichen to smooth and then add 50°F, you may have driven some cylinders into slightly ROP.  ...potential red box.

Perhaps the confusion may be due to truly ancient instructions that said to never run anywhere LOP, where the guidance was lean to power reduction, enrichen to smooth and then give it a half turn richer.  Conflating the leaning instructions for the old "always run rich" to the latest "how to set best economy" I think is an error.

apologies in advance if I've stepped on any toes 

 

[Marauder]

I've been biting my tongue for a few days because I don't want to start a new bun fight... however... the OP is a relative newbie and I believe the leaning instruction may be bad advice.
Lycoming operators manuals from the 70s until right now have discussed leaning without complete engine instrumentation.  They have consistently described the leaning technique to achieve Best Power and Best Economy.    note also that this applies to the 0-360 and is applicable under 75% power... other displacements vary somewhat in the leaning guidance (italics are mine)
Best Power:  Lean until a drop in power (rpm or airspeed depending on fixed pitch or constant speed props) then enrichen to get peak power back.  (that would put you at about 150 ROP)
Best Economy: Lean until engine roughness and then enrichen until smooth. (that would vary but should put all cylinders somewhere LOP)
If you lean until roughness, putting you somewhere LOP, then enrichen to smooth and then add 50°F, you may have driven some cylinders into slightly ROP.  ...potential red box.
Perhaps the confusion may be due to truly ancient instructions that said to never run anywhere LOP, where the guidance was lean to power reduction, enrichen to smooth and then give it a half turn richer.  Conflating the leaning instructions for the old "always run rich" to the latest "how to set best economy" I think is an error.
apologies in advance if I've stepped on any toes 
 

Cyril - thanks for the post. When the POHs were written for the older Mooneys, the EGT gauge, on a single cylinder, was an option. So a lot of what was written was based on simple (if any) instrumentation. With the advanced engine monitoring capabilities, fine tuning of these parameters is now possible.

I have been conservative on leaning above 75% and don't lean when I am above 80%. Does anyone know of any available literature that does a good job of explaining the danger zones (red box, leaning at high engine power output, etc.)?


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[cnoe]

What's wrong with leaning continually to a "target EGT" as described by Braley, Deakin, etc. (as long as your fuel system is set up properly and in good working order)? For those unfamiliar with the technique you can find more about it here: https://www.avweb.com/news/maint/184596-1.html

 

I start leaning during climb-out as soon as my EGT starts to drop (with power settings well above 75%). I'm still considerably more than 200 degrees ROP with CHTs rarely above 365 F. I maintain a healthy margin from detonation while not unnecessarily pumping excessive 100LL out the exhaust pipe.

 

 

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[Cyril Gibb]

While I'm still here, and avoiding what I was supposed to be doing, working on the bathroom renovation , a note to simplify things for newbies if they want to play with LOP.  For ROP power calculations there's a myriad of variables that make my head hurt, although using the POH power tables are good enough for government work.

LOP is much simpler. Cruiser has an excellent LOP Power% calculator in the MooneySpace download area.  For LOP, power % is a simple calculation using fuel flow, (for anyone that has a fuel flow readout).  You only have to know one number: your 75% fuel flow rate.  If you're LOP that 75% fuel flow rate never changes...hot/cold/wet/dry/higher/lower/whatever.

I always cruise WOT/LOP/low RPM after my initial climb.  I know that for my plane when LOP, 75% power is approximately 10GPH.  I'm not a stickler for the 75% thing, so if I'm battling a nasty headwind I might go above 10GPH.  In tailwinds I might lean below 10GPH if that would avoid a fuel stop.  The point is that in cruise, the only engine control I use is the mixture.

One number to remember. Easy Peasy.

[Cyril Gibb]

2 minutes ago, cnoe said:

I start leaning during climb-out as soon as my EGT starts to drop (with power settings well above 75%). I'm still considerably more than 200 degrees ROP with CHTs rarely above 365 F. I maintain a healthy margin from detonation while not unnecessarily pumping excessive 100LL out the exhaust pipe.

Yup, I do the same thing until I get to cruise, but only at high rpm to keep cylinder pressures (hence temps) down.

 

[cnoe]

1 minute ago, Cyril Gibb said:

Yup, I do the same thing until I get to cruise, but only at high rpm to keep cylinder pressures (hence temps) down.

Agreed. I climb out at WOT and max RPM (2,700 in my case) unless prohibited due to noise restrictions. In the Mooney I never understood why some reduce power during the climb.

9 minutes ago, Cyril Gibb said:

For LOP, power % is a simple calculation using fuel flow, (for anyone that has a fuel flow readout).

A good approximation (for my NA IO360) seems to be ("14.9" x GPH) / 200 = %HP. So in Cyril's setting of 10 GPH this would be: 14.9 x 10 / 200 = 74.5% HP.

Lastly, my previous post had a link to the APS powerpoint about leaning techniques that appears to be a dead link. I have the .pps file saved and will gladly share it if I can successfully attach it here. Trying...

targetegt.pps

[carusoam]

The link above is working from here...

on the other point...

The 14.9 number is based on Compression ratio. I don't recall the equation.  But it isn't very complex.

Of course we would all have to have the same CR to be able to use 14.9

Most NA engines we fly the CRs are near 8+ (?)  TC'd and TN'd engines are a bit lower CR.

 

As for the last point of lean to the target EGT.  This is a well accepted principle for the IO550 engines.  The ship's EGT gauge includes a blue box that is an acceptable range for target EGT during the climb.  IIRC, the range is 200-300°F ROP.  For G1000 birds, they have a white box on the display...

Best regards,

-a-

Edited May 8, 2017 by carusoam

[gsxrpilot]

7 hours ago, carusoam said:

The link above is working from here...

But were you able to download the slide presentation?  The link to the article works but not the slide deck.

[Brian Scranton]

No matter what the power % is, if you're ROP, just stay out of the red box, right? So, for 75%, you just have to be 225 ROP, 250 if you want 80%

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

  

[pinerunner]

Without EGT and CHT on all cylinders I'd stay full rich until the manifold pressure is in the safe zone. I'd be conservative about where the safe zone is. I'll let others argue about where that is. I also wouldn't count a low power setting based on low rpm and high manifold pressure as safe for aggressive leaning (still assuming no EGT and CHT for three of your cyinders) since the energy per stroke would still be quite high and you'd be going slow over top dead center where heating of the cylinder head and top of the piston would be maxed. If you're sure you're LOP on all cylinders then the flame front is slower and you can monitor the CHT's to be sure you're not too hot then fine. But without monitoring all cylinders then the old rules of thumb are what keep you out of trouble. 

[carusoam]

36 minutes ago, gsxrpilot said:

But were you able to download the slide presentation?  The link to the article works but not the slide deck.

The link went to a 9 page .pps presentation.  It didn't proceed in full PowerPoint style (on my iPad).  It just had the full everything on the screen at one time finished Look.

Best regards,

-a-

Edited May 8, 2017 by carusoam