O-360 Performance & Leaning

[Hank]

I collected data on a trip South at the end of July; too bad I didn't think to record CHT & Oil Temp. Note that while I do have the "optional Carb Temp gauge" that I do not have fuel flow, either.

 

Here's what I did headed down:

9000 msl, 57ºF, 30.11 setting

21"/2500, 50ºF ROP

137 mph Indicated => 161.7 mph True

 

This was the trip back north:

10,000 msl, 53ºF, 30.11 setting

20"-/2500

at Peak EGT, 53ºF OAT:

130-133 mph Indicated => 156-159.6 mph True [call it 158]

 

at 50ºF ROP, 56ºF OAT:

135-140 mph Indicated => 162-168 mph True [call it 165]

 

In all cases, I reduce throttle from WOT enough to make the MP needle move slightly, hoping that I am inducing turbulence for improved fuel atomization and a more homogenous fuel/air mixture. I did experiment leaning all the way to rough with varying amounts of Carb Heat, watching the Carb Temp gauge; maximum carb temp rise was about 20ºC, with no noticable smoothing. I did this going both directions.

 

Both legs were loaded the same [me, wife, luggage, 50 gals], putting us ~200 lb. under gross.

 

Book numbers are:

 

7500 msl, 32ºF

21"/2500, 72.1%, 158 mph gross, 162 mph at 375 lb. under

 

10,000 msl, 23ºF

20.2"/2500, 53.7%, 161 mph gross, 164 at 375 lb. under

20"/2500, 53.0%, 160 mph gross, 163  at 375 lb. under

 

I ran 30 minutes at peak followed by 33 minutes Rich, but forgot to stick the tank when I landed . . .

 

What does all this mean, other than that my O-360 won't run LOP and I seem to be achieving book speed despite the 3-blade prop out front?

[Hector]

Your numbers are pretty darn close to mine. I recently posted my experience trying this out after I installed an EDM-730 in my 67C. I can get very close to running LOP, in fact 3 of the cylinders go LOP without roughness but by the time I get the last cylinder to go LOP I start to feel some roughness. Changes in throttle or carb heat seem to have no effect. The best I have been able to achieve is 3 cylinders running LOP with the last right at peak ( all CHTs in the 350-370 range). Still... doing 140 Kts while burning under 9GPH is alright with me.

[DanM20C]

Hank,

 

I suspect the speed hit you take with the 3 blade is offset by the other speed mods you have.  My numbers are nearly identical to yours, I might even have 1 or 2mph on you.  I don't have any speed mods other than the Scimitar 2 blade prop.  I plan to try the brake reversal and lower cowl enclosure but haven't got around to it.  I would love to hear if anyone on the forum has done a good before and after test of those mods. 

 

I think you are right on moving the throttle back for improved fuel atomization.  When I'm up at altitude (9-11K) I will leave WOT and lean until I just start to feel the first signs of roughness.  Then I pull the throttle back slightly and it usually smooths out before I even see the manifold pressure needle move. 

 

Dan 

[Hank]

Speed mods, speed mods . . .

 

I have two speed mods:  201 windshield, lower guppy mouth closure.

I have two non-speed mods:  201 wingtips, one-piece belly [NOT Bill Wheat's carbon fiber one!]

I have one unspeed mod:  3-bladed airbrake out front.

 

Fuel burn is very regular at 9 gph when traveling. The trip above was 2:50 outbound to a 40' msl grass strip, then 0:30 low-level beneath the layer [~1500-1700 msl] for fuel, and I took on less than 30 gallons. Now I need to look for that blasted receipt!

 

But I'm happy to achieve and sometimes beat book speed. From engine start to 7500', power set, leaned out and settled into cruise is still under 15 minutes; 9000' is right on 15 minutes if temps aren't too hot. The joys of non-towered fields and good airplanes!

 

DAN--

 

I wonder if it makes a difference:  throttle back then lean [me], or lean first then throttle back [you]? I've read about doing this in several places, but don't recall right now if any particular order was specified or not.

[DS1980]

Lean first and then play with the throttle and carb heat at the offset of roughness. The idea is to mess with setting because the engine is starting to run rough, not make it " more smooth" since there isn't such a thing. This also gives a hint about where your EGTs are at in case your gauge is inop or the airplane you are flying doesn't have one. Remember too, its all about CHT.

[Oscar Avalle]

Speed mods, speed mods . . .

 

I have two speed mods:  201 windshield, lower guppy mouth closure.

I have two non-speed mods:  201 wingtips, one-piece belly [NOT Bill Wheat's carbon fiber one!]

I have one unspeed mod:  3-bladed airbrake out front.

 

Fuel burn is very regular at 9 gph when traveling. The trip above was 2:50 outbound to a 40' msl grass strip, then 0:30 low-level beneath the layer [~1500-1700 msl] for fuel, and I took on less than 30 gallons. Now I need to look for that blasted receipt!

 

But I'm happy to achieve and sometimes beat book speed. From engine start to 7500', power set, leaned out and settled into cruise is still under 15 minutes; 9000' is right on 15 minutes if temps aren't too hot. The joys of non-towered fields and good airplanes!

 

DAN--

 

I wonder if it makes a difference:  throttle back then lean [me], or lean first then throttle back [you]? I've read about doing this in several places, but don't recall right now if any particular order was specified or not.

Absolutely... Speed Mods are the key. I am getting the same figues, but with full throttle and 2300 RPM at 8500 feet. Fuel flow is 9.3 GPH. CHTs 380- 400 (I have a LASAR ignition andit advances timing thus CHTs are high...).

 

I have the 201 windshield and several of the other speed mods that can be installed on a M20C.

[AmigOne]

FWIW: Mike Bush says that "50 deg ROP is the worst place to be", he recommends 100F. My 68 M20C on my recent trip across the USA (leg OSH-RAP), 10500 OAT 60F, 20.5/2300, fflow 8.5GPH, temps: cyl 1-4 1445/363 1278/377 1475/318 1295/377, oil 175F. TAS in that flight about 160MPH. I don't use the JPI to lean, my main concern is always CHT and by now I know what numbers I am looking for. MBush also says that CHT is more important than EGT because of the errors in the way EGT is calculated by the instrument (or something like that).

[teethdoc]

I'm VERY new to my m20J and still have a lot to learn.  My transition CFII has a fair amount of mooney time and is a big ROP guy.  I tried to play with it last week and felt like I could not get it LOP.  It seemed to start getting rough at peak before is would ever go back down.  I can get it down to about 11.5 (older flow guage so accuracy may be questionable) and then it starts getting rough.  I'm screaming across the ground at 11.5, but still curious why i can't get it LOP.

[Jeff_S]

I'm VERY new to my m20J and still have a lot to learn.  My transition CFII has a fair amount of mooney time and is a big ROP guy.  I tried to play with it last week and felt like I could not get it LOP.  It seemed to start getting rough at peak before is would ever go back down.  I can get it down to about 11.5 (older flow guage so accuracy may be questionable) and then it starts getting rough.  I'm screaming across the ground at 11.5, but still curious why i can't get it LOP.

 

A stock IO-360 A3B6D should do LOP operations without major modifications, as long as fuel flows are reasonably consistent and manifold pressure is as well. You can have your A/P check those things. You really shouldn't need the GAMI injectors because with only four mouths to feed the fuel flows with stock injectors are fine.  I assume you have the proper instrumentation to see the EGT/CHTs on each cylinder. If so, then you should try the GAMI lean-test  to see if you can identify your GAMI spread between cylinders...this may also point to where the problem lies and help you diagnose.

[DS1980]

My transition CFII has a fair amount of mooney time and is a big ROP guy. That's unfortunate. LOP has been around long enough that any idea that ROP is better than LOP is a function of stubbornness and/or ignorance. I was in the second category before someone sat down and showed me the physics. If you want to sail through TBO, change CFIs to somebody that knows how engines work. Sorry for the bluntness, but what's the excuse for somebody who's job it is to teach engine management, but doesn't know how an engine operates? Food for thought, and money in your wallet.

 

I tried to play with it last week and felt like I could not get it LOP.  It seemed to start getting rough at peak before is would ever go back down.  I can get it down to about 11.5 (older flow guage so accuracy may be questionable) and then it starts getting rough.  I'm screaming across the ground at 11.5, but still curious why i can't get it LOP. You can and will. You need 4 things to run LOP:

1.) A per-cylinder engine monitor that shows EGT, CHT and bonuses are a lean function and %HP.

2.) Balanced fuel injectors

3.) A pilot that understands not what to do, but what NOT to do and when.

4.) The ability to ignore the "experts" that tell you you're going to ruin your exhaust valves and jugs from running LOP. Remember, it is the experts (no quotes there, the REAL deal) that learned about LOP, teach LOP, and use LOP.

 

You really shouldn't need the GAMI injectors because with only four mouths to feed the fuel flows with stock injectors are fine. That's good if it's your experience, as it saves money. Stock injectors that have a 0.5 gallon fuel flow margin between all of them are an exception to the rule. GAMI sells a lot of their balanced injectors because of this.

 

[rc454]

I've been checking TAS with our M20C for years. It consistently trues out somewhere between 143-151 KTAS, usually around 147 KTAS. I don't specific numbers here in front of me but typically I am level somewhere between 8500-10500' and near max gross weight and run as lean as possible without roughness with the throttle wide open and no carb heat. Average segment length is 1.5-2.0 hours and fuel burns are usually around 9.2 GPH. This figure is as high as 10 on short segments or as low as 8.2 on the longest segments (3+ hours) but I rarely fly nonstop over 2 hours. (Who wants to sit that long with 4 people in the airplane.?)

 

Higher altitudes produce slower speeds.

 

We have the LASAR cowl closure mod installed. I was new to the airplane when we installed it and didn't have much data from before installation so I really can't give what I would deem valid comparison numbers. Also, at that time we had major CHT/OIL temp gauge indication problems and so often had to run with rich mixtures and cowl flaps open just to be conservative. We have reliable engine gauges now (a Mitchell Aircraft mini-gauge pack) and I'm finding I can run at peak EGT with cowl flaps closed even on the hottest days and still see CHT's of 350-370 and oil temp of 210-215.

 

By the way, the biggest thing we noticed with the installation of the cowl mod is that suddenly cowl flap position had an observable affect on oil temp. Prior to that we could never see any difference in oil temp with cowl flap position.

[carusoam]

It's good to see reliable engine instrumentation data and it's effects in a C model.

Best regards,

-a-

[rbridges]

 

edit--delete

[fantom]

For what it's worth, I've been running sub 65% power LOP for years now with just the factory single probe CHT instrument.

 

No wonder it takes you sooooo long to get anywhere

[jetdriven]

Sometimes flying slower and skipping a fuel stop is faster to destination. 

[garytex]

Jetdriven: Sometimes, nothing… Flying slower with no fuel stop is always faster I've played that game. Even a fast fuel stop Ads 45 minutes to an hour

[pinerunner]

Jetdriven: Sometimes, nothing… Flying slower with no fuel stop is always faster I've played that game. Even a fast fuel stop Ads 45 minutes to an hour

 

I'm glad to read this. I thought it was just me being slow taking an hour.

 

Dave