Lean of Peak Now? Soon?

[Ernie Martin]

The increasing cost of Avfuel and a recent demonstration of lean of peak (LOP) operation has led me to ponder again this method of operation.

The demonstration was a lengthy trip I recently made with Nick Bailey in his 337G. We ferried his aircraft 1000 nautical miles over Caribbean waters from St. Thomas Virgin Islands (STT) to Miami's Opa Locka airport (OPF). For testing purposes, and because I felt that reliability would be thus enhanced, we operated one engine at LOP and the other one at ROP.

As expected, both engines operated flawlessly and the LOP engine saved about 2 gallons per hour. At the prevailing fuel prices (we refueled once in The Bahamas) trip savings would have been about $140 if both engines had operated LOP.

With fuel prices on the rise, and the possibility that the new FAA funding structure will increase the tax on fuel, those of you still operating ROP per the POH might want to consider again LOP operation and do the tradeoff analysis needed to determine if it's sensible for you, or the fuel price at which it becomes sensible. My position on the subject -- that under certain circumstances it's beneficial -- has not changed; it may be found in the third message (dated 09-06-04) of this message thread:

http://www.337skymaster.org/messages...&threadid=1208

For those of you new to the subject, this thread also contains other messages from experts on both sides of the fence, including links to published papers on the matter; please note that the link to the Lycoming paper has changed to http://www.lycoming.com/support/trou...es/SSP700A.pdf

Ernie

[Nick Bailey]

Thanks Ernie for the plug. Ernie's assistance was invaluable in assisting me through the Bahamas, but better, I got to divert to his incredible house in Great harbor due to solid thunderstorm line across our flight path. I learned a tremendous amount from Ernie and was glad he suggested the LOP/ROP setup. 2 gals. per hour per engine is correct, as noted on JPI 760 engine monitor with fuel flow. The fillup at end of flight confirmed those numbers from the fuel totalizer. But as Ernie has always maintained, this method is best utilized with engine monitor system, and by pilots who have been educated about the process of running LOP safely. In addition, many engines will not run LOP because of widely varying F/A mixtures in each cylinder. The GAMI jectors take care of that problem.

The obvious savings for me, a 200 HR/yr pilot, are about 800gals. a year. It is the not so noticeable long range savings that I think may be more signifigant.

Ask yuorself, Where does that extra 2 gals per hour go? Some out the exhaust but also a lot of it ends up just as deposits and gum on the engines moving parts and surfaces. After a recent compression check and borescope of both engines, my mechanic remarked that the engine was unusually clean and that he had rarely encountered such uniform compressions. I thinkit is because the GAMIjectors deliver close to identical F/A mixtures to all cylinders, and run LOP, the combustion event is close to identical in each cylinder, clean with little residue. Is it unusual in 3 years of operation that I have never had a fouled plug? When I hear of engines having cylinder problems and valve problems less than half way to TBO, I always wonder about a cylinder that runs continuously dirty, over rich. In summary, the long term savings of a cleaner, evenly balanced engine, run safely LOP, may be an even greater savings than just the fuel savings.

Down off the soap box, it's just a personal opinion..

[Jerry De Santis]

Is it 800 gallons a year saved or 400 gallons. Also. Most Skymasters the rear engine generally uses more fuel for cooling than the front engine. What engine did you operate LOP? Was it the front engine?

Jerry

[Jerry De Santis]

Okay, correction to my questions...It is 400 gallons per year per engine thus, the 800 gallons is correct.

Jerry

[Nick Bailey]

Jerry,

We operated front engine ROP, rear, LOP. By our calculations on the trip, Rear ran 2 GPH less than front. Hence if we ran front LOP, it would have saved an additional 2 GPH, or a toal of 4 GPH over ROP operation.

You are right about the fuel flow setup on the engines, at least on my setup. At WOT on takeoff and climb, my front engine indicates about 19-20 gals per hour. rear indicates about 22 GPH. ( I have the JPI 760 engine monitor) I have carefully checked my fuel useage over the past 3 years and the fuel flows are very accurate as far as I can tell. However some other data of interest. Front engine , (in the tropical heat I operate in down here in the islands, ) indicates fairly evem EGTs in 127-1300 range, with corresponding CHTs always betweem 350-380. Rear EGTs are 1200-1250, CHT's 320-350. , IE, rear does run cooler at WOTand climb. Indeed, because I subscribe to the target EGT climb tecnique, (1300 EGT) I can typically start leaning the rear before the front on climb. I make sue my CHT's never exceed 380 on climb.

The enginemonitor is an amazing tool and I've learned a tremendous amaont about engine function.

[Skymaster337B]

My engine seems to run rougher lean of peak. So I tend to be alittle bit rich. So far so good, even if I spend 2 gals per/hr more, I think it is worth it for longevity of the engine. Any thoughts?

[Ernie Martin]

Two thoughts.

First, running "a little bit rich" of lean of peak is bad. An engine with matched injectors (like GAMI) can be run at the recommended LOP setting, which I think is 50 - 100 degrees on the lean side of peak. If you can't achieve this, perhaps because of roughness, then you should follow the POH, which says to run 50 - 100 degrees on the rich side of peak. Running at near peak is not recommended. This is part of this LOP mantra: do it only with matched injectors (for smooth running), do it only with an engine analyzer, do it only if you've read and can follow closely the LOP procedures, which includes being 50 - 100 degrees away from peak. (Another condition I normally add is that your engine not be under warranty, since running LOP might give the manufacturer/overhauler grounds for voiding the warranty.)

Second, on the issue of engine longevity, there are two camps. The theory and the empirical data shows convincingly that if you run LOP properly, the engine will last longer; the combustion is cleaner and the engine (especially the exhaust valves) run cooler. I subscribe to that -- with emphasis on doing it properly. Another camp, led by an ex-member who has considerable experience with Skymasters, is that LOP harms the engine, and he has seen examples of that. I believe such instances are the result of improper LOP operation, but that's only my opinion.

All of this has been rehashed in considerably more detail in the thread that I reference in the first message above, and in the technical papers referenced in that thread. I strongly urge anyone considering LOP to read all of that material.

Ernie