Turbo vs NA

[Walter Atkinson]

Ernie:

These conversations are very beneficial. Let's look at some of these issues with a little more depth.

Originally Posted by Ernie Martin

1. Balanced Injectors. Many (most?) engines -- even new ones -- don't have balanced injectors and don't operate smoothly at LOP without GAMI injectors. We are in agreement here, except that Walter seems to suggest that a conforming engine (new or overhauled) has to have balanced injectors and operate smoothly at LOP. In theory perhaps. In practice, forget it. You almost certainly will have to buy GAMIs.

By definition, a conforming engine is one that conforms to the design. They are designed to have balance F:A ratios. As you so correctly state, they usually don't. That makes them mostly NONconforming engines. If they were, they would run like they were designed to run--across the entire mixture spectrum. As you also correctly state, "forget it!"

Originally Posted by Ernie Martin

2. Engine Monitor. Walter views these monitors as a) mandatory, but not to operate LOP, and b) more necessary for ROP operation. I'm baffled by the latter point, in part because I've never heard it before and because it seems to run counter to what airplane manufacturers have historically done (i.e., they tell you to run ROP and they don't equip their aircraft with an engine monitor). But on point a) every article I have read in support of LOP clearly indicates a need for an engine monitor. As an example, take the one in the July 2009 issue of AOPA Pilot magazine at www.gami.com/articles/frugalflyer.php. Here is an excerpt: Electronic engine monitors that show cylinder head and exhaust gas temperatures for every cylinder are necessary for safe LOP operations. Here's another: GAMI showed that with precise fuel/air metering systems and graphical engine monitors high-compression and turbocharged piston aircraft engines could run safely and reliably LOP. In the article, engine overhaulers specifically point to LOP without engine monitors leading to engine damage. In the recent May 2011 issue of the same magazine, in the dogfight article on LOP vs. ROP, it's stated that those engine rebuilders who now accept LOP operation require both balanced injectors and engine monitors.

This is a major misunderstanding by quite a few folks.

Consider this ONE condition:
You do NOT have an engine monitor. You run ROP. You have a conforming engine that has balanced F:A ratios. One injector partially plugs and the fuel to that cylinder is reduced. That puts that cylinder not as rich as you assume it is by your leaning. That cylinder is running hotter and quite possibly in the most detonation-prone mixture possible and you do not know it. The HP curve is very flat ROP so the engine does not run rough to let you know you have a problem. Your next takeoff makes this worse as that cylinder is run near best power during takeoff and detonates.

Now, consider the same situation--no engine monitor, but you run LOP. As soon as the injector partially plugs, one cylinder becomes leaner just like before. BUT, this time the partially plugged injector results in that cylinder putting out less HP than the rest (due to the slope of the HP curve LOP). Due to this, the engine runs rough and you immediately know you have a problem that needs addressing BECAUSE, a conforming engine will run smoothly LOP. Because it has begun to run rough, you know something is not right.

So, if you run ROP as a matter of routine WITHOUT and engine monitor you should run LOP occasionally to be certain it will run smoothly and everything is still conforming. If your engine is not conforming, you will not know.

If you run LOP as a matter of routine, the absence of an engine monitor is not nearly as critical.

Remember, the engine manufacturers and OEMs wrote those POHs before engine monitors were invented. They should be re-written, but I wouldn't hold my breath.

Since the most detonation-prone mixture is 50dF ROP and that's where the OEM has recommended operating in many cases, you can't do ANYTHING worse, ROP or LOP than do what they recommended. That's a fact of science which is confirmed by all data from every source.

The concept that you need an engine monitor to operate LOP more than ROP is simply wrong. We routinely operated Twin Beeches, DC-6s, DC-7s, and many others LOP since the 1930s and had no engine monitors. We did that with a single CHT, no EGT at all.

All of that said, I will not make an IMC flight without a working engine monitor--no matter how the mixture is set. I've seen too many "saves" through the use of monitors.

Originally Posted by Ernie Martin

So, at the risk of being repetitive, LOP is a good choice if you have "balanced" injectors (read: GAMI injectors), engine monitoring with cylinder-by-cylinder EGT/CHT readings, the willingness and ability to understand and manage the leaning process, and preferably an engine no longer under warranty from an overhauler which prohibits LOP.

We don't disagree all that much. I would simply "refine" your position to include proper understanding of WHY engine monitors are important--and it's not for leaning. It's for saving you money, your engine, and maybe saving your butt. And, you need it MORE if you operate ROP.

The only issue is the last one. TCM and Lycoming both support LOP ops. TCM has since the early 80s. Lycoming came around last year.

They did realize that they were delivering nonconforming engines and to keep their tech support lines from ringing off the hook, they suggested running ROP so their engines would run smoothly.

I don't have a SkyMaster POH handy, but I'll bet the engineering charts are in them that do show the LOP side of the mixture chart. Cessna has been including those charts in most model's POHs for a long, long time.

Ernie, thank you for the good conversation.