[Walter Atkinson]

Ernie:

**On yourt last message, the one which is just above this reply, I for one welcome your participation.**

Thank you. That is very kind.

**I'm not buying the rest of your points in that message.**

That's fine. Shall we take them one at a time for the purpose of furthering our understanding?

**I won't dwell on all of your points, since the meeting in Key West is a better forum for that, but here is a brief outline.**

Unfortunately, I am not going to be able to be in Key West.

**On the claim of longer-lasting engines, readers understand that we're talking cruise operation, when the component stresses (e.g., temperatures) are so much lower than design limits that the differences are immaterial.**

You may wish to look at the data on this. If this were true, jump planes which go to altitude at very high powers and do the slam dunk, never spending any time in cruise would not go to TBO. Most do. A cursery look at the ICP data on a live-running engine is convincing that that assumption, while on the surface being logical, is in error. Cruise powers at 25dF ROP is not necessarily good unless the power setting is quite low.

**To say it differently, the exhaust valve at ROP runs much cooler at cruise than design limits, so running it even cooler at LOP doesn't add life.**

Again, you might want to look at the data on this. According to Lycoming's data and others which supports it identically, the temperature of the exhaust valve is frequently hotter in cruise at 25dF ROP than at full takeoff power. This is particularly true in a Skymaster's rear engine. (notice how skillfully I threw in the Skymaster reference! <gg>) A cursory look at the data on exhaust valve temperature as a function of mixture will confirm this. (ref: 1943 NACA study and 1966 Lycoming data.) There is no need to argue this reality as it has been measured. I have the studied charts if you would like to see them. An exhaust valve at 65% power with a CHT of 375 will be running a lot hotter than the same valve at takeoff power with a CHT in the low 300s. It's in the data.

**Saying that engine monitors are more important to have for ROP than LOP defies logic.**

It does seem to defy the common logic, but it's true. I can prove this to you very easily. Consider an engine which has very good F:A ratios and can be run ROP or LOP and still be smooth. Let's assume we are LOP and an injector becomes partially clogged. The engine will instantly run rough and you will know it--without an engine monitor. Now, assume the same engine is being run ROP--say at 100dF ROP. The same event occurs. The partially plugged injector will place that cylinder less rich; it will run a much hotter exhaust valve temperature. It will continue to run smoothly and unless you have an engine monitor, you will not know that you have a clogged injector. On the next takeoff, that cylinder will not be rich enough and may end up detonating. If you do not have an engine monitor and are a ROP guy, you will not know you have a problem until the engine has a failure of the cylinder. This has been a common problem for years and no one has known it until engine monitors came along. We have a rather large file of these very events. It's not uncommon.

**To your credit, you and other advocates of LOP admit that proper operation at LOP requires a monitor (or analyzer).**

Not those who UNDERSTAND the issue above. The need for an engine monitor has little to do with the mixture being LOP. As a matter of fact, if you do not have an engine monitor it is VERY wise and highly recommended that at least every few flights you set a LOP mixture to be sure everything is OK. (see above example)

**While the experience of millions of hours of ROP operation show that the basic guages installed originally is all that is needed for reliable ROP operation of these engines (more on the "robustness" of the engines below).**

We have a gowing number of cases in our files which show this to have been an erroneous concept on our parts in the past. I used to believe that, but no longer do--since I've SEEN the data coming in. In addition there are about 400 MILLION flight hours of data which contradict that notion.

Your reference to Lycoming is not germain. LOP has not been the norm as Lycoming claims since radial engines went out of service. None of these flat engines have ever been routinely run LOP until GAMIjectors came along (exception being the TSIO-520BE). That statement from Lycoming is disengenous. For other really silly statements from Lycoming I recommend reading the recent lawsuit transcripts. Look for the article in Aviation Consumer soon on this topic. At this time I cannot comment further.

**So, since their procedures must account for all pilots, they changed to ROP, the easier, more tolerant procedure.**

No, they want you to think they changed to ROP. That's not factual. They suggested ROP because their engines would not run smoothly LOP because they have poor F:A ratios. They simply didn't want the complaint department phones ringing off the hook. Lycoming's verbal position is not even in harmony with their own data. Their engineering data is correct and does not support Rick Moffett's current position.

We are unaware of ANY TCM warranty denial based on the LOP issue. If there has been one, we would love to have it cited. We cannot find one. Anyone know of one? We have POHs from almost every engine they have built and have numerous references to LOP being OK... including in Cessnas.

**And in the related thread George took issue with my statement to stick with what the manufacturer tells you -- ROP -- by citing other manufacturers like Lancair and Cirrus which approve LOP operation. But this is a Skymaster forum and the readers understand that I was discussing Skymasters.**

He included Cessna. There is absolutely nothing about the engine in a C-337 that makes it any different than the same engine in any other model aircraft. If you know of a germain difference, I would appreciate you letting me know. How does the engine know it's in a Skymaster?

The other points in your post are personal preference items and not factually debatable. I will repeat, the reason to have an engine monitor has little to do with leaning or saving gas. It has to do with saving your engine and your life. The files are growing weekly with examples of this.

Thanks again for your thoughtful comments. As an engineer (I think you are an engineer, right?) you would be quite amazed to SEE this data for yourself. It is compelling. I can assure you that six or seven years ago, I would have agreed with everything you've said. Looking at the data on real, running engines and operating them based on that experience has introduced me to the taste of crow.

Please understand, we teach that ROP and LOP mixtures both have their place. We recommend methods by which either can be accomplished with performance, safety, and longevity concerns addressed.