Power setting M20C

[carusoam]

11 minutes ago, Lukon said:

 

Are you guys saying I could do even better with a touch of carb heat? Does this let you lean a bit more, before it runs rough?

Yes...

That is what they are saying...

Not magic.... but, if you improve the distribution of fuel amongst the cylinders... you can approach the efficiency seen by fuel injected engines... by being able to lean more,  evenly...

Excess fuel going to any one cylinder, just gets wasted...

Too little fuel going to a cylinder, has it run rough...

Hank’s method...

first, cuts the extra fuel supplied by the secondary fuel nozzle...

second, the cocked throttle plate adds a touch more mixing of the air / fuel mixture...

Third, adding carb heat improves the evaporation of fuel droplets in to burnable fuel vapor...

This is great for cruising along LOP, or near LOP, or at peak... as long as the red box /65% BHP is observed for engine safety...

at 10k’ and above for an NA engine... all is good.  Well under 65%bhp available at that altitude...

M20Cs are magical planes... the more instrumented they are the more magical they can become...

Best regards,

-a-

[cliffy]

1 hour ago, carusoam said:

first, cuts the extra fuel supplied by the secondary fuel nozzle...

Sorry but pulling back the throttle does not "close " any extra nozzle or cut any extra fuel supply once you start pulling the mixture control out. 

I explained this in a previous post . Extra fuel is only supplied at WOT and full rich mixture for climb cooling. By pulling back the throttle with full rich mixture you OPEN an extra AIR BLEED going into the main metering nozzle supply thereby "leaning" the mixture to less than needed for climb. You do not "close" any "secondary nozzle". This is mostly useful in fixed pitch prop airplanes once cruise altitude is reached and the throttle is pulled back for cruise speed RPM at somewhat below 7500' where red knob leaning is usually not used. 

Once you pull the mixture knob out enough to go below the TOTAL FF provided by pulled back throttle air bleed and full rich mixture- the air bleed "leaning" is no longer effective. Its there, but the total fuel flow is lower than  that provided by the "enrichment circuit  AIR BLEED LEANING.

Once you start leaning with the big red knob only it controls the total FF

Angling the throttle plate will, however, even out the mixture distribution in carb'd engines thereby allowing more of the fuel sent to the cylinders to be actually burned and used for more MPG. 

[jetdriven]

I thought the M20C carburetors have no economizer circuit?

[Hank]

28 minutes ago, jetdriven said:

I thought the M20C carburetors have no economizer circuit?

No, we have the economizer. I.need to dig out my Marvel Schleber book again, but my memory of it doesn't jibe with cliffy's explanation above. Pulling the throttle back to create as much turbulence as possible without decreasing MP is effective. Adding partial carb heat varies from plane to plane; if it helps yiu, gi for it.

Nothing let my C run smoothly LOP until I rebuilt the air intake and carb heat bellows, now it will run 25°LOP if I don't mind going slow . . .

[carusoam]

Good news... my memory matches Hank’s... 

Not so good news... my memory isn’t very good...

I’ll see if the M+S book is in my iBooks somewhere...

Couldn’t find my copy of the carb drawings and things...

So I went online...

I got closer, but still no answer...

https://msacarbs.com/technical-data/service-bulletins/

Best regards,

-a-

[tigers2007]

Slight carb heat (enough where it doesn't start to raise the carb temp) levels out my EGT's all the time. Note, you'll probably need a decent engine monitor. I have a Insight G1 (get a G2 if you go with Insight).

[cliffy]

When at WOT, the throttle arm presses down on a plunger that closes the air bleed line with a pin. The pin is spring loaded to the open position so when the throttle arm moves up and away from the pin top it opens the bleed air line to the normal fuel discharge nozzle in the throat of the carb. Air flows through the tube into the fuel discharge  nozzle due to the lower pressure at the nozzle (being situated right at the middle of the carb venturi throat) being lower (due to air flow through the venturi) than the normal atmospheric pressure at the other end of the vent passage. The air mixes with the fuel  effectively leaning the mixture to get rid of the extra fuel required for cooling at WOT/full rich setting. There are several dash  number carbs and each has this air bleed very accurately calibrated for each particular dash number. That is part of the FF differences in each dash number carb also. 

[Bob_Belville]

I am reminded again that it’s usually not what I don’t know that gets me in trouble... it’s what I do know that ain’t so.


Sent from my iPad using Tapatalk

[Lukon]

On 10/10/2019 at 4:46 PM, carusoam said:

Yes...

That is what they are saying...

Not magic.... but, if you improve the distribution of fuel amongst the cylinders... you can approach the efficiency seen by fuel injected engines... by being able to lean more,  evenly...

Excess fuel going to any one cylinder, just gets wasted...

Too little fuel going to a cylinder, has it run rough...

Hank’s method...

first, cuts the extra fuel supplied by the secondary fuel nozzle...

second, the cocked throttle plate adds a touch more mixing of the air / fuel mixture...

Third, adding carb heat improves the evaporation of fuel droplets in to burnable fuel vapor...

This is great for cruising along LOP, or near LOP, or at peak... as long as the red box /65% BHP is observed for engine safety...

at 10k’ and above for an NA engine... all is good.  Well under 65%bhp available at that altitude...

M20Cs are magical planes... the more instrumented they are the more magical they can become...

Best regards,

-a-

Okay, so I played with the carb heat on the way back from Vegas last weekend at 10,500’

When I introduced a little carb heat, the EGT dropped significantly, along with power. I wasn’t able to lean much more, before it ran rough, and couldn’t get back to the original EGT.

[carusoam]

Lukon,

got a carb temp sensor?

was that without an engine monitor?

it is really hard to control things, with enough precision, without the nifty instruments...

Still, things should be able to return to initial settings after making a change...

it really helps to have engine controls with vernier attributes too...

if you have an engine monitor... want to post data from the flight?

Best regards,

-a-

[Lukon]

Sorry for the delay replying. I've got limited instrumentation. Basic EGTs and head temps; Cylinder #3 sensor is on the fritz. I can only view one cylinder at a time.  No carb temp. Only the Prop has Vernier type control.  I definitely cannot get lean of peak. I fly very slightly rich of peak, just rich enough to smooth out. Cylinder #1 at around 1365 deg I think.

[86Xray]

On 6/6/2019 at 8:36 PM, 1967 427 said:

I think most pilots will go to altitude if they are on a flight that will last more than 1.5 hours.  I normally go to  9.5 to 11.5k and at those altitudes I go to WOT, and back off (as others do) until I see the MP just start to drop.  Below you can see I am @ 10.5k ft., 2500rpm, 18.7MP, which calculates out to 60% power.  The engine loves it as indicated by the T&P, the last think I want to do is to hurt my engine, and I get to take advantage of the winds aloft.  If you look closely you can see that I'm showing 170kts across the ground.  Fun to see 170 in a 1966 C.

I

 

 

 

I happened to notice your N# is 3487X. I just bought 3486X as my first plane and I’m getting checked out in it right now

Edited December 18, 2019 by 86Xray

[gsxrpilot]

On 10/10/2019 at 5:23 PM, Lukon said:

Are you guys saying I could do even better with a touch of carb heat? Does this let you lean a bit more, before it runs rough

Sometimes yes that works, sometimes it doesn't. Sometimes add a touch of carb heat, get it lean and then remove the carb heat. Getting really lean with a carby engine is a bit of a crap shoot. But it's worth the effort.

BTW mine always liked altitude as well.

[DJE22]

@Hank, curious about your comment MP needle wiggle:

I generally run ~70% power in my C. After a while, I've pretty much settled on these: 

--3500 and below:   23"/2300

--3500-6500/7000:  22"/2400

7000/7500 & up:  WOT- /2500

For WOT-, I reduce throttle just enough to make the MP needle wiggle, set RPM and lean. Airspeed is generally 140-145 mph. Up high that good for ~147 KTAS.

I’ve read similar comments before and don’t recall what the basis for reducing until needle wiggle...please share, thank you!

[carusoam]

Hank will be around soon...

But, if you are familiar with the M+S carburetor...

There is a second fuel nozzle that is open for added cylinder cooling...

It is called something like the enrichment circuit... 

Turn that off after the climb to bring the excess fuel cost down.

The method of cutting out the enrichment circuit... bring the throttle back to witness the MP needle wiggle...

See if I got that right...

It helps if you have a fuel flow gauge...

Best regards,

-a-

[Hank]

12 hours ago, DJE22 said:

@Hank, curious about your comment MP needle wiggle:

I generally run ~70% power in my C. After a while, I've pretty much settled on these: 

--3500 and below:   23"/2300

--3500-6500/7000:  22"/2400

7000/7500 & up:  WOT- /2500

For WOT-, I reduce throttle just enough to make the MP needle wiggle, set RPM and lean. Airspeed is generally 140-145 mph. Up high that good for ~147 KTAS.

I’ve read similar comments before and don’t recall what the basis for reducing until needle wiggle...please share, thank you!

Anthony got it right, his memories of C ownership are correct. You can leave the throttle wide open but will need a different movement of the mixture due to higher fuel flow.

But slightly cocking the throttle body inside the carb will hopefully create / increase turbulence in the airflow inside it, resulting in increased atomization of the fuel (smaller droplets).and improved, more uniform mixing of the fuel droplets into the air. If each cylinder gets equal amounts of fuel, it will run smoother; if one cylinder receives more fuel than the others due to great variability in fuel droplet size, it will make more power and the engine will run rougher when you lean it.

Leaning just until the economizer circuit closes off leaves maximum fuel flow for maximum power and speed. But at lower altitudes, keeping this power requires RPMs to be reduced into the red arc on the tach in order to abide by the Key Number for our engine. But the Key Number is only 65% power and is a protective strategy to enhance engine life while still obtaining good performance, and is not mentioned in official Mooney or Lycoming publications . . . It's just another choice that you the aircraft owner get to make.

[brndiar]

Hi,

Tomorrow is my bird finally ready to fly Flight test #1 after a general motor overhaul with brand new 3 blade Hartzell Prop.

Please, how can I find 75% power setting for a given density altitude  in that "complex" Lycoming chart? To be honest, unable to locate A on full throttle altitude curve......

Of course, there are "Performance Tables" in M20C POH, for different altitudes, but for standard temperatures only - not the case nowadays here.

thanks,

milos

 

 

[carusoam]

What does your break in instructions recommend?

Most often an NA engine goes through break in at max MP, full rich, varying the RPM through a range.... making changes every 15 minutes or so...

 

Another method of setting %HP is Using MAPA key number protocol... MP + rpm/100

Using less than 100% hp looks like it may be an attempt to keep things from over heating?

Do you have a FF instrument?

 

For interesting reading on current O360 CHT control... find @ragedracer1977 he has done some fine writing on the subject over the last few days...

PP thoughts only, not a mechanic...

Best regards,

-a-

 

[cliffy]

I"ve dropped in the Lycoming SI for engine break in after overhaul if you don't have it

Follow this for your break in   Pay attention to the ground run in instructions at first also. 

Go to 7500' altitude (actually density altitude but 7500' is close enough) with full power and you are turning 75% power Any higher and you won't get 75% 

https://www.lycoming.com/sites/default/files/Lycoming Reciprocating engine Break-In and Oil Consumption.pdf

 

BTW, there was an A&P several years ago dinged by the FAA for doing an overhaul and doing his own run in procedure, seems the FAA asked him if he knew more than the engine manufacturer.

One more comment- you will notice that the SI speaks to having the engine gauges calibrated before the break in. In truth, it can't be called "an OVERHAUL" unless it follows the factory instructions including calibrated gauges. Without calibration its in reality a "repaired" engine. Small bit of trivia but if you don't believe me go ask the FAA.  I've had this discussion a couple of times with them. Nobody does it but its just a bit of trivia. 

Edited April 15, 2020 by cliffy

[Tcraft938]

On 6/6/2019 at 7:50 AM, Hank said:

As altitude increases, manifold pressure decreases. Raising RPM brings power back up. Look at your Performance Chart. 

Also the props are most efficient around 2500, or so my Hartzell book says

[carusoam]

A few things that are important to the plan...

 

• Internal cylinder pressure.  More ICP for better sealing...
• ring travel... higher rpm is actually different than lower rpm... 
• Safety... machinery and people.

PP thoughts only, not a mechanic...

Best regards,

-a-

[Tcraft938]

On 6/6/2019 at 5:30 AM, brndiar said:

Hi,

For 3 Months a bought a M20C. Usually Fly 2300 RPM, 20 MAP which gives me cca 105-110 knots GS at 5000 Ft /less than in POH/.

Folks, mit what RPM/MAP do you fly your Mooney?. What is up to you most economical settings? Any suggestions for Cruise setting?  Thanks,

milos

I am currently nearing the end of break-in of a new engine and hartzell prop.  Per the break-in instructions I am to keep the power up flying at safe altitudes that will give at least 75% power for flights of at least an hour (assuming no problems).  On a pretty standard day at 5000/5500 ft I am 23" MP at 2400 rpm.  This is giving me around 154 mph (134kts) indicated and 176 mph (152 kts) True Airspeed at 76% hp per the POH and run full rich.  If go higher I lean just until it is very smooth.  The airspeed is a little better than book, I think my MP might be reading an inch or so low.  However fuel flow is lower than book even at VERY rich.  CHT's even on warm day are never 322 cruise or 362 in climb.  Break in doing well.  Mineral Oil consumption stabilized at 6 hours use.  Has 29 hrs on it now, in annual and all 4 cylinders are 79/80.  I was told to not move the MP around much when flying and vary the RPM in 100 RPM increments about every 20 minutes or so, but try not to go below 75% power unless in the pattern or landing.  I'm no expert, just sharing my experience based on what the shop and A&P told me to do.  So far, so good.

[cliffy]

The point at which the oil consumption stabilized was where the engine was basically fully broken in.

Your speeds and temps are remarkable.  Have you double checked the speeds with a 3 or 4 way GPS run? 

I presume most of this flying was solo so I have to ask about your CG and where it is sitting. Can you mention say what 25 pound block you weight fits into  150-175    175 - 200     200-225 etc    Just trying to get a handle on CG position.

[brndiar]

#1Testflight after a Motor GO + New Prop. I was impressed. The airspeed was a little  better than book :-)

[carusoam]

Could be the TopProp efficiency?

Best regards,

-a-