How do you set your cruise?

[bcg]

I've been chatting with the guy I'm buying my C from and he mentioned that he sets his cruise by leaving the throttle at full and reducing the RPM to 2350 - 2400.  He says this gives him about 140knots at 9GPH at 7500 - 8500 feet.

I've normally read it the other way, that RPM is left close to full (2500 or so) and the manifold pressure is lowered to set cruise.  Maybe that's just for turbo though.

Now I'm curious to know what the norm is for the NA motors in the vintage Mooneys.  Do you reduce RPM and leave throttle/manifold pressure at full or leave RPM at 2500+ and lower the throttle/manifold pressure?

[Oscar Avalle]

I own a M20C. What I do at least is reduce RPM to 2350 and keep full throttle.


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[Fly Boomer]

13 minutes ago, bcg said:

curious to know what the norm is

The GAMI Guys (Advanced Pilot Seminars) say WOTLOPSOP:  Wide Open Throttle/Lean Of Peak/Standard Operating Procedure.  Even if you don't want to do LOP, stick with WOT.

[bcg]

5 minutes ago, Fly Boomer said:

The GAMI Guys (Advanced Pilot Seminars) say WOTLOPSOP:  Wide Open Throttle/Lean Of Peak/Standard Operating Procedure.  Even if you don't want to do LOP, stick with WOT.

Sounds like I have been misinforming myself.

So that brings up another question for me.  How do you go LOP with a carbed motor, especially without an engine monitor?  On the Cherokee I'm flying right now, we lean until the engine stumbles and then go rich until it runs smoothly plus a hair more.  I'm guessing this is a little ROP but, without a monitor, I can't say for sure since we don't really know when we've peaked.

[Fly Boomer]

1 minute ago, bcg said:

So that brings up another question for me.  How do you go LOP with a carbed motor, especially without an engine monitor?

You probably don't.  Carburetor engines usually won't do LOP.  But the monitor would tell you if your leaning technique is causing elevated temperatures.  Mike Busch says 380 max for Continentals, and a little higher for Lycoming. 

[Ragsf15e]

As long as you’re high enough to cruise below about 75% power, you can just leave wide open throttle and reduce rpm to desired (I use 2500).  Somewhere around 6500’ or so, check your poh.  If you live somewhere low and want to cruise at 2500’, you’ll want to reduce mp and rpm to avoid running the engine really high power for a long time.  Lycoming recommends 75% power or less during cruise for maximum longevity.  You’ll likely want to be ROP in a C but LOP may be possible with a monitor.  

[Fly Boomer]

3 minutes ago, Ragsf15e said:

As long as you’re high enough to cruise below about 75% power, you can just leave wide open throttle and reduce rpm to desired (I use 2500).  Somewhere around 6500’ or so, check your poh.  If you live somewhere low and want to cruise at 2500’, you’ll want to reduce mp and rpm to avoid running the engine really high power for a long time.  Lycoming recommends 75% power or less during cruise for maximum longevity.  You’ll likely want to be ROP in a C but LOP may be possible with a monitor.

This is good.  The WOT recommended by Braley and others assumes yo will limit percent power by going lean of peak.

[MikeOH]

Another WOT, pull rpm to cruise pilot, here.  I also lean in climb (oh, the horror!) to maintain SL take-off EGTs.

[Bryan G]

17 minutes ago, MikeOH said:

Another WOT, pull rpm to cruise pilot, here.  I also lean in climb (oh, the horror!) to maintain SL take-off EGTs.

Same, I can’t remember where I read it but I usually wait until 3k to start leaning…and for my M20F 1250 EGT is about right.

Edited August 8, 2022 by Bryan G

[PT20J]

Some carbureted Lycomings will run LOP because the intake tubes are all the same length and they run through the sump which warms the mixture for better atomization. A LOP operating procedure was in the PA28-161 POH way back in the 1970's.

[1964-M20E]

WOT, 2550RPM, LOP but I do have fuel injection so lean as much as you can.

[KLRDMD]

45 minutes ago, Bryan G said:

Same, I can’t remember where I read it but I usually wait until 3k to start leaning…and for my M20F 1250 EGT is about right.

That would be on the runway at my airpark. Add in factors that account for dentisty altitude and I'm often over 5,000 ft.

Edited August 9, 2022 by KLRDMD

[McMooney]

22 to 23 in / 2300 rpm.

or if higher than about 7500 ft, wot and 2300 rpm.

rop or lop depending on mood.

actually been playing with over square lately so like 22/23 inches and 2100 rpm

[Shadrach]

12 hours ago, bcg said:

Sounds like I have been misinforming myself.

So that brings up another question for me.  How do you go LOP with a carbed motor, especially without an engine monitor?  On the Cherokee I'm flying right now, we lean until the engine stumbles and then go rich until it runs smoothly plus a hair more.  I'm guessing this is a little ROP but, without a monitor, I can't say for sure since we don't really know when we've peaked.

Peak is close enough to best economy (best BSFC, as in most power per unit of fuel). As others have stated, leaning to stumble and enrichening to smooth will get you as close as you can get on all cylinders with a carbureted engine.

[Shadrach]

Wide open throttle

ram air open 

2500rpm

mixture is dependent on goal and CHTs.

[M20F]

I bring the RPM back to 2600 at minimum, helps a lot on the noise. 

[Bryan G]

I read the power setting articles from Bob Kromer, that’s where I got the above 3k leaning method from. Here are screen shots of different pages from different articles, one for climbing and one for cruise.

[Hank]

@bcg, Ignore all the responses from.people flying E, F and J models, their fuel injected engines are considerably different than our carbureted ones. But they mean well . . .

I set power using the Performance Tables in my Owners Manual. I used to aim for 65-70% and leaned 50° ROP (which drives the fuel injected crowd crazy!), but now I follow MAPA's advice and use Key Number of 46 (MP + RPM).

I'm pretty much down to three power settings now in my C:

• Low Altitude ~<3500, 23"/2300
• Mid Altitudes 3500-7500, 22" /2400
• High Altitude, WOT-/2500

High Altitude is wherever I can't make 22" anymore; and "WOT-" means to pull the throttle back until the MP needle wiggles, with the goal of cooking the throttle plate enough to make turbulent flow through the carburetor for finer fuel atomization and more uniform mixing before going to the intakes. Fuel Injection, which you and I don't have, works best at WOT.

On a recent trip to the NC coast, I leveled off at 7000 msl and set 21" / 2500 out of habit. After 15-20 minutes, I changed to 22" / 2400 and releaned, then watched both the ASI and groundspeed increase from ~136 to 142 (mph on ASI, knots on groundspeed); being IFR, I couldn't do a 3-way TAS test, and I don't have fuel flow. But faster is nice!

[hammdo]

I'm similar to Hank

but 7000 ft to 10000 ft I'm WOT, 2400 RPM, lean out (I have a G2 which makes it easy). Sometime 2500 up to 10000 ft

she will true out between 145 and 148 knots (I have speed mods galore but in no hurry to use more fuel ;o).

-Don

[Shadrach]

7 hours ago, Bryan G said:

I read the power setting articles from Bob Kromer, that’s where I got the above 3k leaning method from. Here are screen shots of different pages from different articles, one for climbing and one for cruise.

Yeah, I respect Bob but his climb recommendations are abusive in my opinion. He makes no real case for using his recommendations other than maximum available power in climb. He recommends the following:

Wide open throttle

Max Rpm

leaning to 100° ROP in climb at 3000’DA

At 2500’ and 5000’ DA, at full rich, my POH power table shows 98% and 90% power, respectively.
 
Leaning to 100° ROP, in climb, at those power settings, is a bad idea (to put it mildly out of deference to Bob). Perhaps when he wrote the recommendation back in 2005, he didn’t know what he didn’t know.

[midlifeflyer]

12 hours ago, bcg said:

Sounds like I have been misinforming myself.

So that brings up another question for me.  How do you go LOP with a carbed motor, especially without an engine monitor?  On the Cherokee I'm flying right now, we lean until the engine stumbles and then go rich until it runs smoothly plus a hair more.  I'm guessing this is a little ROP but, without a monitor, I can't say for sure since we don't really know when we've peaked.

Agree with @Shadrach's comment.

LOP contemplates being able to determine which cylinder is the last to peak. Carburetor aside that's going to be difficult without an engine monitor. But all is not lost. I recall Mike Busch saying at a seminar that the method most of us were taught as student pilots - lean until engine roughness, enrich until smooth - results in the best economy setting with cool temperatures almost  as well as assisted LOP methods. 

Edited August 9, 2022 by midlifeflyer

[211º]

9 hours ago, Hank said:

 

I'm pretty much down to three power settings now in my C:

• Low Altitude ~<3500, 23"/2300
• Mid Altitudes 3500-7500, 22" /2400
• High Altitude, WOT-/2500

I bet that @Hank has this as a shortcut on his computer - when I saw this topic come up, I wondered how far down I'd see this list. I like it - simple and easy to remember. 46 for the win with 2400 being the mid-level number; lower, lower than 2400; higher, higher than 2400.

[Hank]

6 minutes ago, 211º said:

I bet that @Hank has this as a shortcut on his computer - when I saw this topic come up, I wondered how far down I'd see this list. I like it - simple and easy to remember. 46 for the win with 2400 being the mid-level number; lower, lower than 2400; higher, higher than 2400.

Don't forget the WOT-! Our fuel injected friends want maximum airflow, but our carbs want internal turbulence to atomize and mix the fuel. 

[Rjfanjet]

Mike Busch says 420 max CHT for lycomings. I'm in SLC, so WOT everywhere I go. I reduce to 2500RPM for climb out of 400' and cruise at 2400RPM. I'm also in no hurry to get anywhere. 142 kts pretty much all the time, no speed mods.

[201Steve]

Get an engine monitor