Rich of Peak (ROP) vs Lean of Peak (LOP)/Engine operation

[kevin]

Not in a P like yours or T. With a turbocharged engine you should pull the throttle back to mfg recommended MP and RPM, just leave the mixture full rich. The WOT reference was for a normally aspirated airplane.

Kevin

[kevin]

Here is RAM Aircraft's position on ROP/LOP:

http://www.ramaircraft.com/Maintenan...Operations.htm

Kevin

[Kevin McDonnell]

Thanks for that RAM link. I wish someone from that company were available to explain some of their points:

1) "mis-management at LOP settings can cause both dynamic stresses and thermal stresses that hammer main and rod bearings, burn pistons, burn valves, and cause cumulative exhaust system damage."

How do you burn things when your temps are lower?

How do you hammer things when the pressures are lower?

What causes the cumulative exhaust system damage? If it's not from heat, are they trying to make a case that it's chemical damage?

If they've performed the detonation testing, are they saying that LOP is more prone to detonation? (How could that be????)

2) "RAM reminds it’s customers and friends in General Aviation that mixture management of a turbocharged Cessna 414A at FL230 is more complex than the mixture management required of a normally aspirated Cessna 210 at 9,500 feet. "

Sounds like a little doubletalk. They are switching 3 variables in this sentence: aircraft, altitude, and turbo-charged – not a sign of clear thinking (or at a minimum, clear communications). While all would agree that turbo vs. NA are different, the aircraft reference is nonsense. That leaves us with the altitude variable.

All things being equal, how does altitude make mixture management more complex? Naturally, NA have less MP as they climb, etc. But what about turbos? General cooling can be a bigger challenge in the thinner air. And sometimes there's power limitation to protect over-working the turbos. Other than perhaps higher CDT (pre-intercooler) and IAT (post intercooler), what's different in the mixture management? The ideal fuel/air ratio is a constant.

Inquiring minds want to know ...

[Walter Atkinson]

Kyle:

Yes, as you pay more attention to the engine, you will begin to want better data on its function. It goes with the territory of good engine management. Sorry. <g>

As for reducing rpms moving the thetaPP toward TDC, yes, that is correct. The effect of reducing rpms 100-200 is very small on thetaPP, however, and I tolerate that for noise abatement. If that's not an issue, I leave the rpms full forward. Throttle has more effect on thetaPP than rpms and mixture has the largest effect of all.

Those of us who are familiar with these effects will compromise on the noise abatement issue with slightly reduced rpms with the undertanding that it's not optimal, but an acceptable compromise.

[KyleTownsend]

Walter:

This discussion on "ThetaPP" led me to another thought concerning all of this test stand work that has been done.

Was anything done to either duplicate, or otherwise allow for, the free-air slipstream velicoty at cruise (aka a wind-tunnel-like arrangement)? Otherwise, wouldn't "ThetaPP" be over-stated for all of the cuise tests?

Or perhaps it doesn't matter with a constant speed prop?

I think I am running out of brain cells on this one.

Kyle

[Walter Atkinson]

Many of the things RAM says about engine operation are not in harmony with the known laws of physics. You have picked up on several of them. Now, there is that outside chance that Sir Isaac Newton and all other observers are wrong and the non-engineer owner of RAM is right. His own chief engineer does not agree with those company policy statements concerning engine management.

When asked for data supporting their position, they don't offer any.

[KyleTownsend]

Here is the key phrase in the RAM article:

>RAM supports the installation of balanced or matched fuel flow nozzles, >but does not, in fact cannot, condone or approve their use to operate an >engine at an unapproved mixture setting.

And the key word is "cannot."

Reading between the lines, I think their position is that the certification tests were conducted at the manufacturers recommended power setting (right or wrong), and that if either RAM or the engine manufacturers now try to recommend different operating procedures, they would open up a huge can of "liability worms."

From a business perspective, I don't know that I blame them.

In the end, the Pilot In Command is the FINAL AUTHORITY.....yak yak yak.

But, if something breaks, you can't blame it on RAM or Continental.

Oh well.

[Ernie Martin]

Kevin, on your last message above this one, the key word in item 1 is "mis-management". RAM, Lycoming and I are not saying that proper LOP operation -- be it via FADEC or a savvy and attentive pilot with an analyzer -- can damage the engine*. But mis-management can. And while Walter and George assert differently, there is general agreement by engine manufacturers and overhaulers that ROP operation on this type engine is easier to manage and far more tolerant of pilot mis-management.

Ernie




_________________
*I should note, however, that at least one person believes that LOP operation, even when properly done, is harmful to an IO-360.

[Walter Atkinson]

Kyle:

**Was anything done to either duplicate, or otherwise allow for, the free-air slipstream velicoty at cruise (aka a wind-tunnel-like arrangement)? Otherwise, wouldn't "ThetaPP" be over-stated for all of the cuise tests?**

I do not think that has any effect.

[Walter Atkinson]

Ernie:

**there is general agreement by engine manufacturers and overhaulers that ROP operation on this type engine is easier to manage and far more tolerant of pilot mis-management.**

That is a common statement which remains without any supporting data and one for which there is ample data to the contrary.

To quote Anatole France:
"If fifty million people say a stupid thing, it is still a stupid thing."

The number of overhaulers who still think ROP is better and LOP is more difficult to do is dwindling as they come to the APS class. As a matter of fact, one of the premier overhaulers in the US has decided to offer an extended warranty for their engines which are run as recommended by APS. We've now had six of the major engine overhaulers join us and many more of the smaller shops and we have extended that offer to RAM. They said that they didn't need to come see any data; their mind was made up. They actually said that to me!

Beech, TCM, Lancair, Cirrus and Flight Safety are among those companies which have sent some of their employees to the class. Lancair has incorporated our techniques in their training sessions for new owners.

I am no expert. The data is the expert. The data doesn't care who says what, it's always the same. Oh, and the combustion event doesn't know if there is an engine monitor measuring it or not.

[KyleTownsend]

The reason that I brought up the "theta PP" and slipstream velocity is because:

The engine running in "still air" (eg: doing a runup on the ramp) at a given RPM is analagous to a car driving up a steep hill.

The engine running at the same RPM in a 200 knot slipstream is more like driving "down hill."

Or, at least, that would be the case with a fixed pitch prop.

I am having trouble getting my brain around how that would work with a constant speed prop, especially at the governor stop-limits.

Kyle

[Walter Atkinson]

Kyle:

Oh, I see what you're asking now.

The thetaPP will be affected by the rpm, not the load on the crank of whether it's going "uphill" or "downhill." If the rpm does change with a fixed pitch installation (as it would be in your scenario), then the thetaPP would change. This would be a very small effect.

[big al 08]

do what you wish, it's your engine and money. fanitical opinions are on both sides
so!!!!!! do what is comfortable for you!!
gone to tbo with two mills and most likely could have exceed 2k, but more comfortable changing at tbo. it is really you who makes the checks out(what the
hell it's only $60-$70lk.right?) let all the preachers preach, because i dought they will pick up a frig'wn dime when s___ hits the fan. just like the faa says - the final authority is the "bozo in the left seat", not the sooth sayers

{political statement removed, even though I think it is a joke, sorry rick -webmaster}

ps: is a subject beath to death and never will be resolved, vote your wallet

[Walter Atkinson]

**fanitical opinions are on both sides**

That may well be true.

OTOH, the data has no opinon. It is what it is. It is measureable by any observer. A person is either six feet tall, or they are not. That can be measured. Why argue over it? Of course, one may choose to believe the data or not. For that matter, one may choose not to even take the time to look at the data.

The good news is that all of the engineering data from all sources on piston engine physics agrees. (The laws of physics are everywhere the same.)

Based on the data, I think OJ did it. Silly me. <g>

"A man without data is just another man with an unsupported opinon." Unknown.

[gwbraly]

>>And the key word is "cannot."

Reading between the lines, I think their position is that the certification tests were conducted at the manufacturers recommended power setting (right or wrong), and that if either RAM or the engine manufacturers now try to recommend different operating procedures, they would open up a huge can of "liability worms."<<

Kyle,

You might reconsider "who" is the "manufacturer".

With respect to the RAM engines, RAM holds the STC to convert the TSIO-520 from its 325Hp TCM version to its 335Hp RAM version, with RAM's data plate.

Regards, George