The concern that TCM has in that service bulletin has to do with de-tuning the crankshaft counterweights. Not all engines have counterweighted crankshafts. For example, the O-360 Lycomings generally don't, although there is a variant that does.

Some engine/prop combinations have vibration issues at certain rpm ranges (such is common on O-360 Lycomings, for example).

READ the manufacturer's recommended operating practices, AND give them a call for more information. The tech reps for both Lycoming and Continental are VERY helpful in my experience.

Of course, you'd best call TCM quick, cause in a few weeks Tech Services will be speaking Mandarin....

MTV

Z
My biggest concern(possably because I don't know enough to be concerned about other issues) is the idea of lugging, and as you say, I relate to it in terms of what I know about cars.
Thinking that if I'm using a lower power setting and relatatively high resistance caused by the pitch of the prop, am I setting myself up for problems in the future.
I am not usually in a hurry when I am flying, so slow cruise and burning less fuel is a good thing, unless I will pay a penalty for it in the future.
I use the vague term harm, because there is probably other considerations that I am not aware of.
Gary

It's pretty hard to "lug" the engine if you limit MP to 5 inches or less oversquare. I don't own a TCM, but suspect their concern re cruising less than 2300 rpm is related to dynamic counterweights. It's a good thing to have them weights slung out there and not swinging around due to engine power pulses at low rpm. Engines like the parallel valve Lyc O-360 in my Husky don't have dynamic counterweights, so no worrys there. What is a concern is doing a long descent with minimal power allowing the prop to drive the engine. Enough power should be carried to keep combustion pressure up enough to prevent piston ring slap (rings moving up and down in their grooves) as this wears the grooves.

what I am talking about is running under square

Bumper
What do you consider enough power to keep combustion pressure up?
Thanks gary

The term "squared" always causes me to squint one eye, because that fact that manifold pressure measured in inches Hg happens to correspond to propeller RPM divided by 100 is pure coincidence, right? By luck, the range of RPM and power have similar numeric representations on their respective scales, but it is merely a rule of thumb, correct?

So, if we're 19 *squared*, that's relatively low power, low rpm. Is it still a meaningful or appropriate relationship of power to rpm?

shortfielder wrote:what I am talking about is running under square

That doesn't fit my definition of "lugging". Assuming a constant speed prop, as you reduce power, manifold pressure drops, and the governer reduces prop pitch to try to keep prop speed as set. At some point the blades will reach their flat pitch stop and from this point rpm will drop as the throttle is further closed. You may be falling out of the sky due to to low a power, but you are not lugging the engine.

Okay, is operating at very low power for long periods of time bad? Well, yes, taken to the extreme I'd say so. That was the case when I was a cop and we'd sit for, ummm, sometimes our whole lunch hour with two cars side by side, engines idling to keep the heaters on. This tends to allow more blow by and sludge to form in the engine as oil temperature is not high enough to eliminate the water by product of combustion. But in our aircraft, if you are making enough power to stay in the air, I'm thinking the occassional climb at higher power will be enough to keep Mr. Motor happy.

I run my MP and RPM in the green. I have no manufacturer placards against certain MP RPM combos. If I wanted to operate outside the green arc, I would call the engine manufacturer. I like to run a lower MP when like you I'm not in a hurry. I keep the MP in the green. When my MP drops below the green, the RPM drop too. The prop control does nothing at that point.

Good day

shortfielder wrote:Bumper
What do you consider enough power to keep combustion pressure up?
Thanks gary

It's actually less power than one might suppose. The idea is to have enough throttle on that the prop isn't driving the engine to a great extent while the prop disk is creating drag. It doesn't take a lot of power to keep combustion pressures up enough to prevent ring slap.

Note that short periods of throttle off are not likely to do harm, e.g. short approach or pulling off the power for a semi-dead stick approach from abeam the numbers when flying a 7AC Champ. For long descents in the Mooney (dynamic counterweights), I go to course pitch for minimal drag, around 2100 rpm or so, and reduce MP to about 20 inches. On longer high speed descents, shock cooling can be an issue, so I reduce MP by an inch every minute instead of all at once. This is probably a "whatever", but it's what the Mooney POH prescribes.

I found this write up very informative.
http://www.avweb.com/news/pelican/182179-1.html
He goes on a bit about running squared.
It really goes into detail and a lot of it doesn't work well on a carbureted engine. Like leaning over peak with an uneven mixture getting sucked through a carbureted engine.
There are a lot of good points he makes though and well worth the read.
GJ

This a great if not often a controversial discussion, and I'll add a little controversy.

The following applies to injected and constant speed aircraft.

The most critical aspect of engine operation I think is mixture, not rpm versus manifold pressure.

And as a side note I am with Zane on the whole squared issue, especially when the instructor says it'll blow up if you run more MP than rpm. I don't see how the two relate. For instance, a power setting I may use is WOT, say I'm getting 26 inches out of that. 2000RPM and 50 percent power. How you say? LOP mixture. A leaner mixture burns slower, and there fore peak combustion pressure is further past top dead center, and is easier on the rotating assembly.

I am really curious about mtv's comment about the 550's not lasting like the 520's. MTV, do you know what CHT's these pilots were seeing when the longevity of the 550's suffered?

I think some of us have read the info by Mr Deakin on operating LOP, it's great reading. He operates a turbo normlized 550 wide open throttle on climb out from sea level (hurry run and hide now) and lean of peak, and he has quite a few hours running these 550s this way. I personally operate my io540 by the WOTLOPSOP.

If you look back at the Piper Malibu is it? The one with the TSIO-540. The one that was designed to run LOP. Well the pilots thougt they would be a little nicer to the engine and add a little fuel. What they didn't know/remember is that on the lean side of peak, richer is hotter and leaner is cooler, and they burned the engines up. LOP operation has been affected ever since.

CHT's are what we really need to be careful with. And the way we have the greatest affect over CHT's is mixture. This is also where we have the greatest affect on percentage of power.

When your POH gives you fuel flow for various power settings it's only accurate if the mixtures set properly. For instance, I usually operate my io-540 at wide open throttle max rpm and 55 percent power. I climb WOT and if my CHT's are getting war m I grab the mixture knob and give it a big yank, right after I say to my pilot passenger "watch this". once I'm safely LOP and my CHT's cool down in the process, a good discussion about LOP is bound to happen, old wives tales included.

As far as the old inch per minute power reduction thing, I think you can pull multiple inches in one pull, you just then have to control the temperature cool down with mixture. If your ROP and you pull five inches, and lean at the same time you can maintain temperature. Seems that inch per minute is more a rule for the masses so to speak. To be nice to our engines I like to warm them up and cool them down slowly and this can be better accomplished withth emixture knob than any combination of MP versus RPM.

Hopefully this isn't thread hijacking. It probaly is......

I just think that mixture should be discussed more. It probably would be if it wasn't the big elephant in the room.

Screw political correctness!

Good day

Paul

A good engine instrument is still the key to any of this discussion. Then have the courage to pull the mixture knob past ROP, Past Peak, to find what each cylinder is doing. If there is an induction leak, poor compression, partially blocked injector that affects 1 or more cyliders, only 1 egt and Cht probes, then it doesnt matter where you have the mixture knob.

I'm with Zane, squared numbers by themselves are a coincidence. Add a turbocharger and now instead of cruising at 23/23 you are cruising at 26/23 on what is essentially the same engine. Other than maybe pushing ridiculous numbers like 28" and 2200 RPM out of the typical TCM/Lyc engine I don't think you can lug an aircraft engine in the classic car sense of the term. But what do I know, I've forgotten how to start an O-200 much less a hot IO-520.

Below is a link to a Lycoming reprint. Go to the section on Low Power Low RPM Cruise at about PDF page 10 which is document page 44. There is a lot of great information in this document. It also talks about "Squared Operation" and that it applies to some Radial engines according to Lycoming but is not applicable to opposed engines.

http://www.lycoming.textron.com/support/tips-advice/key-reprints/pdfs/Key%20Operations.pdf

That's not openin up for me Is thre another way to get to this?
Thanks Gary

Try:

http://www.lycoming.textron.com/support/tips-advice/key-reprints/index.html

And open the Operations PDF near the bottom of the web page. It is a 4+ MB file so it may take awhile to open.

Zane wrote:

shortfielder wrote: possability of causing harm to my engine(pponk O-470-50).

I want to know what this "harm" is? We always speak of "harm" in sort of a mysterious, unspecified, vague bad consequences sort of way. I am not disagreeing that "harm" may occur, I just would like to know what the actual consequences are.

Low rpm + high load resistance? High torque required to spin the prop but the power isn't being generated. How are the forces on the crankshaft, camshaft, piston wrist pins, rods, etc increased? I would like to know where the stress is increasing and why. Where can strain finally occur?

I try to make the analogy of lugging a car with a manual transmission. We know for certain that can be damaging, but why are the forces actually increased on engine internals? Momentum and inertia carrying the crank into the next stroke?

There has to be a graph somewhere.

We never ran our tractors wide open and we used to catch hell from Dad if we run a tractor under load heavy enough that the engine could not accellerate with it. I guess that was like being behind the power curve. You could ruin the engine by taking it down to its knees where it couldn't come back up. Lots of fuel, lots of carbon on the rings and piston hammering would just pound out the bearings.

A tractor under load is a completely different beast than an aircraft engine spinning a propeller.

And, in any case, ever been around one of the old John Deere two cylinder diesel tractors?? Talk about lugging! And, they loved it.

MTV

mtv wrote:And, in any case, ever been around one of the old John Deere two cylinder diesel tractors?? Talk about lugging! And, they loved it.

MTV

That's because they are geared to put out 14HP and 9,000 Lbs. of torque!

mtv wrote:A tractor under load is a completely different beast than an aircraft engine spinning a propeller.

And, in any case, ever been around one of the old John Deere two cylinder diesel tractors?? Talk about lugging! And, they loved it.

MTV

Zane wrote:

shortfielder wrote: possability of causing harm to my engine(pponk O-470-50).

I try to make the analogy of lugging a car with a manual transmission. We know for certain that can be damaging, but why are the forces actually increased on engine internals? Momentum and inertia carrying the crank into the next stroke?

There has to be a graph somewhere.

"Dirtstrip wrote
We never ran our tractors wide open and we used to catch hell from Dad if we run a tractor under load heavy enough that the engine could not accellerate with it. I guess that was like being behind the power curve. You could ruin the engine by taking it down to its knees where it couldn't come back up. Lots of fuel, lots of carbon on the rings and piston hammering would just pound out the bearings."

Sorry, I need to be more surgical in my response. I was trying to answer just that portion of the engine lugging question. I'm not sure if a propped engine can be lugged.
4010/4020 are the first Deere's we ran, they were sixes along with the rest of the diesels we had, didn't lug like the old twins. Our gassers were fours. Dad never had a twin cylinder JD because they chugged so bad that the silage cutter blew chunks.