2000 rpm, 25" MP, 155 MPH 7.5 GPH, Anything wrong with this picture?

[jetdriven]

Byron, I "liked" your post already, as I agree with it with one exception. Do you disapprove of LOP ops without an engine monitor if power is always limited to no more than 65 percent? I actually use 60 percent as my limit most of the time, and I believe my percentage of power to actually be less than indicated due to a slightly high reading JPI FS-450, but you get the idea. As you know, my cruise efficiency numbers are right in line with yours.

I figure if my airframe made it to almost 10,000 hours with four engines, each lasting well past TBO, with just the OEM gauges that were installed when I purchased her in 2006, that I am likely to be able to do the same using this method after having added fuel flow and digital EGT equipment. Time will tell, but I think that it is important for people to know that they can safely operate LOP without an engine monitor if they otherwise follow your guidance and are just willing to forego the last 10 percent of power that is very inefficient aerodynamically anyway.

Jim

|I think if someone (like you) knows what is going on under the hood, they can do 65% LOP with a factory EGT. I just did that yesterday between Tulsa and McAllen, TX in a 1963 Cessna 210 (IO-470). Climbed to 6500', and leaned to 20 LOP for a 5 KIAS speed loss. Single point EGT. I got that plane burning 11 GPH, which is pretty good for a 210 flying 150 KTAS. I went to 75 LOP first thing to check smoothness, so I knew it had balanced injectors. We all know that there is no mixture setting that can harm your engine below 60-65% power. Just as a general rule, I would be extremely careful and not recomment LOP without an engine monitor.

We also ran our new engine at 83% power LOP for quite a few hours and it liked it, but you gotta stay on top of it.

[garytex]

Dav8or "Every mechanic I've asked has glazed over in that "Oh God, please don't make me do that" look then tell me everything is fine,It's not a big deal."

The biggest problem is getting to the intake in front of the RSA. Schedule the work for a time that the lower cowl will be off for other work. Then just hook up a shop vac on the pressure side and spray the usual suspects with soapy water. Aditionally the super lazyman's quick and dirty check is to remove the cheek plates and at idle, spray the runner connections with carb cleaner and look for an increase in idle rpm. Don't back your cheeks into the prop.

As an aside, the best common sense AC mechanics I have run into have been in small shops, older guys with lots of experience who still enjoy the "figguring it all out" part of the process. I must have been very lucky, as I have run into a series of good, smart fair ones. And every time i have paid too much for something, there have been four or more guys in the shop.

[jetdriven]

The GAMI high-low test will reveal an intake leak. Climb to 10,000 where the MP is 19 inches, and do a GAMI lean test. Write it all down. Then descend to 1500 feet, and set the throttle to 19" of manifold pressure. Repeat the GAMI lean test. The difference between the two tests is WOT at 10,000 feet there is only ambient air presure in the intake tract, no vacuum. At 1500 feet, you have 9 inches of manifold vacuum. Any intake leak will draw in air pretty good, because of the vacuum. If the cylinders peak in the same order, everything is fine. If a cylinder or two peaks way sooner, those are the leaking cylinders. Investigate the intake tube gaskets at the head and the O-rings at the intake plenum. Do this once per year.

For an inflight LOP mag check, climb to 3000' and set the mixture to 50 LOP or just shy of the onset of roughness. First I will give you the brief, then the procedure. The risk of a bad mag or plugs is a severe misfire which will run rough (or complete shutdown) and fill the exhaust system with unburned fuel. When switching the mags back to "both", you run the risk of damaging your exhaust with an overpressure, because of the unburned fuel lighting off in the exhaust and muffler. The secondary risk is a prop overspeed when the engine surges and the prop cannot compensate fast enough.

Brief: you are going to switch the magneto to "L" for 60 seconds, then back to both, then to "R" for 60 seconds, then back to both. (Just like a runup on the ground, but longer).

IF the engine runs very rough OR if the engine shuts down:

pull the mixture to ICO, wait 5 seconds,

put the ignition switch back to "BOTH",

pull the throttle back halfway or more,

then go rich until the engine lights off (it will instantly),

then smoothly add throttle back to cruise.

This prevents exhaust damage or prop overspeed. Do not instinctually go back to "BOTH" immediately. Follow the procedure.

Ingition switch to "L" and wait 60 seconds. The airplane will slow down 5 knots. The engine tone will change. The EGT's will rise 50-100 degrees uniformly across all cylinders. It may tremble slightly. If you have a roughness that is tolerable, note which EGT is not in line with the others. That's your offending plug or lead. Go back to "BOTH" and let is stabilize. Then repeat the test on the "R" position. If the engine shuts down you have a bad mag.

The left magneto runs the top plugs on the left bank and the bottom plugs on the right bank. The right magneto is opposite. The ignition switch on the "L" position grounds (and kills) the right magneto. The inflight LOP mag test stresses the ignition system as much as possible. Any deficiencies will show themselves, and you can rectify them for smoother LOP operation.

[garytex]

I thought of a valid reason not to run 20 - 25. Crankshaft torsion. The crank winds up and unwinds with power pulses from the piston power downstroke. Crankshaft dampners help ameliorate this I think. We have none on the A1A motor. And running like that may do nasty things to the crank. I want to talk to an engine designer about that. Is it "lugging" the engine?

[DaV8or]

I thought of a valid reason not to run 20 - 25.

I wonder why you would want this power setting? I don't think it would buy you either speed, or economy. I seriously doubt it would result in a broken crank. It would however, depending on mixture setting, put you closer to detonation.

[garytex]

DaV8or:

It was quiet, and turned in around18 -19 mpg. And yes I think it squeezes detonation margins, as my first concern. Crank torsion is a second. Both together are enough for me to feel that the quiet side of it is inadequate benefit to use it as a regular practice. Too bad, as it was really quiet.

[garytex]

Additionally, according to a little half assed research I did, if the pulses hit a natural harmonic frequency, evidently it sure enough could break the crank.

[DaV8or]

Additionally, according to a little half assed research I did, if the pulses hit a natural harmonic frequency, evidently it sure enough could break the crank.

Well, I have to assume that during the certification process of both the motor and the airplane, that this harmonic frequency would be detected if it existed and either a engineering correction made, or an operational limitation placed on that power configuration.

[garytex]

I am assuming that's why 20-20 is all that is in the POH

[jetdriven]

Didnt those older Mooney's have a red arc between 2000-2500 RPM? I would assume its for that reason.

[garytex]

They vary some depending on prop, mine is 2100-2300 RPM for an A1A (no counterweights) in a 67 F. Mine also shakes harder below 2550, so thats where I usually run it. Some, I think the Cs also have "not under a certain MP". It is a torsional vibration issue, although the usual thing that breaks is prop tips. The A1A has a high or the highest rate of loosing 3-4" of prop tip of any ac engine I read somewhere. I can't remember the source, but it wasn't a bad source. I think your J has a counterweighted crank. Do you have a red arc?

[jetdriven]

I agree the A1A is hard on props, although I havent heard or many failures. The J has (depending slightly on model) a yellow arc on the tach to avoid continuous operations below 15" manifold pressure between 1500-1950 RPM. You transit through that on landing, and the airframe buzzes slightly. Th airplane won't maintain flight below 15" and 1950 RPM, so I suppose you shouldn't do an idle descent from 10,000 feet.

[frankw]

Recently transitioned to my (new to me) '76 M20F with 30hr engine three blade prop - and this site has been great resource, thanks to all.

 

Having trawled various websites I fly LOP and over square, typically 22-23 mp and 1950 rpm at 2000ft returns me 110k/135mph at 6-6.5 gals/hr. I have an EDM700 (and still struggle to understand the "find LP function"), so I lean to roughness and enrich to just smooth and monitor EGT (1350 or below), CHT (350 or below) & oil temps (188 or below). Gami injectors will be my next upgrade. My M20F has Monroe aux tanks (2 x 17) = 34 + mains 64 = 98 gals total. So at the above cruise setting I have a max "theoretical" range (if my maths/assumptions are right with no head wind) of say: (98gals/6.5gals/hr) = 15hrs endurance /130mph = 1960 straight line miles... this affords me a degree of comfort :-)

[rbridges]

Recently transitioned to my (new to me) '76 M20F with 30hr engine three blade prop - and this site has been great resource, thanks to all.

 

Having trawled various websites I fly LOP and over square, typically 22-23 mp and 1950 rpm at 2000ft returns me 110k/135mph at 6-6.5 gals/hr. I have an EDM700 (and still struggle to understand the "find LP function"), so I lean to roughness and enrich to just smooth and monitor EGT (1350 or below), CHT (350 or below) & oil temps (188 or below). Gami injectors will be my next upgrade. My M20F has Monroe aux tanks (2 x 17) = 34 + mains 64 = 98 gals total. So at the above cruise setting I have a max "theoretical" range (if my maths/assumptions are right with no head wind) of say: (98gals/6.5gals/hr) = 15hrs endurance /130mph = 1960 straight line miles... this affords me a degree of comfort :-)

 

good luck telling that to your bladder.  

[carusoam]

Welcome aboard Frank.

Best regards,

-a-

[frankw]

My max comfort time is approx 5 hrs in my Grob 109B - but then glider pilots have to cultivate a strong bladder... no nambi panzis' at cloud base :-) 

 

ps

thanks carusoam - shall we meet half way across the pond?

[flyingvee201]

Bladder and not to mention your COLON!  LOL

[frankw]

Nay worries... I'm half Scottish... the secret of life and a rock solid constitution is... porridge, I sheet you not :-)

[EDNR-Cruiser]

I checked the manual of my '66 M20F again and other than the info I see every day, like performance charts or the red arc of my Mooney between 2100 and 2350 RPM, I also found a small chart for maximum HG with min RPM.
 

Limit manifold pressure for continous operation:

> 2400 RPM - no limit

2300 RPM - max. 28,0" HG

2200 RPM - max. 27,4" HG

2100 RPM - max. 26,8" HG

2000 RPM - max. 26,1" HG

1900 RPM - max. 25,6" HG

The above data is also in line with that found in a Lycoming performance and operations chart of the IO-360 A1A engine. My M20F has the usual IO-360 A1A and a Hartzell HC-C2YK-1BF/7666A2 prop.

The funny thing is that the Mooney performance charts don't list RPMs below 2350 RPM except for max. endurance at 1950 RPM and 17" HG with a fuel flow of 5.6 gal/hr and a max. endurance of 11 hours and 26 minutes at 2500ft... - and that is definitely more than even my well trained (and certified) iron butt is willing to endure!

But to come back to the initial question: based on my M20F manual there seems nothing wrong with flying at 2000 RPM and 25" HG and I will definitely give it a try, too, even though noise level is no longer a concern since Santa Clause was so kind to bring me a Lightspeed Zulu 2 last XMas. 

 

[phecksel]

nice necro thread

 

Climb out, pull those props back a bit.  Full RPM's make a lot of unnecessary noise.

 

MP OWT, pinch hitter instructor that flew with my wife insisted, no demanded she never let the engine get over square, or it would blow up... keep in mind she couldn't swing the j-bar and was going to land gear up anyway!

[Hank]

On departure, I use WOT and Full RPM from then end of the runway to cruise altitude. Pulling either back only reduces airspeed, increases time to climb, reduces cooling airflow through the cowl and increases engine temps.

Even my lowly C can be settled into cruise configuration at 8000' (7500 agl here) in less than 15 minutes from engine start. Climb speed is controlled mostly by oil temp in warm weather; slowing down only increases engine temps and prolongs exposure time. We all agree on the over square myth, just stay out of the red band on the tach.

[garytex]

EDNR

Thats exactly what I was looking for.  High MP and low RPM is a nice addition to the bag of tricks.  My dogs' headsets are not so good, and that yields a much quieter cruise.   The other day my ANR headset ran out of battery about 15 min from home, and I leaned further, and reduced RPM to 2300, and it became somewhat quieter, but my ears still rang for a couple of days.  I should have gone to 2000 rpm.

Thanks, Gary

Maybe Kevin will chime in on any prop blade issues.

[jetdriven]

nice necro thread

 

Climb out, pull those props back a bit.  Full RPM's make a lot of unnecessary noise.

 

MP OWT, pinch hitter instructor that flew with my wife insisted, no demanded she never let the engine get over square, or it would blow up... keep in mind she couldn't swing the j-bar and was going to land gear up anyway!

A Mooney is a rather quiet aircraft, not really any louder than a 172 from listening to them come and go so much all day.  Here's another thing, altitude is a very effective noise suppressant as well. Instead of climbing at 2500 RPM, climb 200-300 FPM faster at rated power and you will be higher over the neighbors when you pass over.

[scottfromiowa]

EDNR

Thats exactly what I was looking for.  High MP and low RPM is a nice addition to the bag of tricks.  My dogs' headsets are not so good, and that yields a much quieter cruise.   The other day my ANR headset ran out of battery about 15 min from home, and I leaned further, and reduced RPM to 2300, and it became somewhat quieter, but my ears still rang for a couple of days.  I should have gone to 2000 rpm.

Thanks, Gary

Maybe Kevin will chime in on any prop blade issues.

That is weird...ringing for three days...We have the same engine. The noise levels in my cockpit are not over 90dba without headsets. Not as loud as a lawn mower...Shouldn't have ears ringing for that length of time...really at all. HHHHmmmmmm, curious.

[bonal]

I'm still learning the best way to operate my 64 C. Reading all the posts on this subject line seems a diverse number of opinions. What I do is climb WOT full rich unless very hot day at 120MPH for around 800 to 900fpm leaning slowly as I climb. At cruise and all cleaned up I run WOT adjust mix for what seems smoothest running and rpm around 2500 gives me my best IAS with MP between 21" to 24" depending on DA. For me the hardest thing is I only have the standard gauges and I doubt they are very accurate but I keep my temps in the green and as far below what the gauge shows to be 400cht as possible. So far it seems good but there is not much you can do with crappy gauges I sure do like all the comments on the subject makes me want to learn as much as I can.