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.

[Ernie Martin]

OK, I'm buying the argument that from an engineering viewpoint an engine monitor appears more useful at ROP than LOP, and the further argument that it may not have been included in legacy aircraft because they didn't exist. However, I think you would agree that proponents of LOP consistently indicate the need for an engine monitor and that many engine overhaulers blame the lack of monitors for damage caused by LOP (although, I won't argue with your earlier view that some of these overhaulers are clueless on operation and such damage may be due to improper operation by the pilot rather than not having an engie monitor).

Ernie

[ipasgas1]

Great discussion...I have never been instructed on the lean of peak method so I will need to learn them for my next aircraft. My friend has a Cirrus SR22 and now my wife wants one of them instead of a 337 which is a discussion I got into a couple years ago and ended up with a 337. Hopefully, I will get out of my partnership and into my own so need to make a decision on which way to go...again.

[Walter Atkinson]

Originally Posted by Ernie Martin

However, I think you would agree that proponents of LOP consistently indicate the need for an engine monitor and that many engine overhaulers blame the lack of monitors for damage caused by LOP

LOL! Ya got that right. But, why are you right?

From my experience teaching these topics for over a decade to thousands of pilots, I would offer the observation that those who have come to understand mixture management and routinely operate LOP are the same pilots who have gone to the trouble to become educated about the relationships between the EGT, CHT, ICP, HP and BSFC curves as well as the value of engine monitors and how to interpret the data they display.

I would also agree with your premise about builders placing blame. These are usually the same builders who've never operated an engine LOP or even looked at the 5 Landmarks to Engine Management, much less understand their relationships. If one cannot draw the EGT, CHT, ICP, HP and BSFC curves they have little chance of understanding the issues we are discussing so openly.

[n86121]

20 years ago, when I bought my turbo 337, I had not really seen the need for turbos, but this one was STOL, etc, so I bought it.

I transitioned in a non-turbo, and remembered an anemic rate of climb once above 8,000 or so, with three on board plus luggage.

20 years later, I can testify the best part of the turbo's is they allow you to maintain a high climb rate all the way, to as high as you want (the best thing should you find yourself in icing by the way). In the 10k++ ft haze around Washington DC summers, it's nice to climb FAST to get above it all.

Trubo's also give you the OPTION of going fast at altitude IF YOU WANT. As a helicopter pilot first, often going down the beach, I often like low and slow. Throttle back, and you've got the efficiency of a C182, with a LOT more payload, and total redundancy.

The 337 turbos have automatic wastegates, which means
a) You can almost set and forget them to a desired MP pressure (almost), and
b) If you want to loaf along at low power and fuel flow, then just throttle back, bring the turbos almost idle, and you have a regularly aspirated engine.

You can have your cake and eat it too.

Yes, IF you take advantage of their boost in power at altitude, they will use more fuel.
If you operate the like a non-turbo, I speculate the engines work just like a non-turbo. MP is MP.

In 20 years I've overhauled both turbos to new, at about $3.5k each.
In the overall scheme of things not a big deal.

D

[Walter Atkinson]

David:

You hit the nail pretty squarely on the head with minor exceptions.

Originally Posted by n86121

b) If you want to loaf along at low power and fuel flow, then just throttle back, bring the turbos almost idle, and you have a regularly aspirated engine.

....

If you operate the like a non-turbo, I speculate the engines work just like a non-turbo. MP is MP.

Well, the turbos don't really go to idle, but they do slow down, BUT you do not have a "regularly" aspirated engine. The low compression pistons are not nearly as efficient as the normally aspirated model's higher compression pistons. To make matters worse, the increased exhaust back pressure from throttling back reduces the volumetric efficiency of the cylinders so MP is not really MP where the number of air molecules are concerned (increased IAT, too). Turbocharged engines are more efficient at higher MPs than lower MPs.

However, your points are well taken and I agree with your basic premise that turbos are hard to beat for flexibility and capability.

[hharney]

When operating LOP are the exhaust valves in jeopardy because of the decreased amount of cooling and lubrication from using less fuel? It seems that I have heard that cylinders are changed out more often on Cont. 360's when operated at LOP. Is this a management issue? It is not true?

[Walter Atkinson]

Originally Posted by hharney

When operating LOP are the exhaust valves in jeopardy because of the decreased amount of cooling and lubrication from using less fuel? It seems that I have heard that cylinders are changed out more often on Cont. 360's when operated at LOP. Is this a management issue? It is not true?

Herb:

Exhaust valve temperature is most affected by CHT. The lower the CHT, the lower the exhaust valve temperature. EGT has no effect on exhaust valve temperature. As a matter of fact, if you are at 40dF ROP and lean the mixture to peak, the EGT will be going up but the exhaust valve temperature will be going down. 40-50dF ROP is the mixture where the exhaust valve runs the hottest.

There is no difference in valve lubrication across the mixture sweep. Valve guides are lubricated by oil. The notion that fuel acts as a lubricant is misplaced. Fuel is a solvent, not a lubricant. Some claim that the lead in the fuel acts as a lubricant, but this is also misplaced. Lead exists in during the combustion event as a salt of bromide--lead-oxy-bromide. Salts are abrasive. Abrasives make crummy lubricants!

So, if running the exhaust valves cooler is desirable (it is) and running the combustion chamber cleaner to keep the exhaust valve cleaner and a better valve-seat interface is desirable (it is), then LOP mixture management is less stressful or damaging for the exhaust valves than ROP mixtures.

There is no hard data to support the claim that more cylinders are changed when operated LOP. There is hard data to support that the converse is true. There are over 400 million flight hours of data supporting the reality that LOP is easier on cylinders than ROP operation. There is data to support the contention that not running the mixture rich enough when ROP does put increased stress in the form of heat and pressure on the exhaust valve. That's probably where the notion came from that if you run too lean (not rich enough on the rich side) you'll burn up the exhaust valves.

Does that help?