Leaning

Allen, following your ez.org Hanger Talk note “Temps for the O-320 160hp”

You mentioned leaning in your thread. For the last couple of years I have flown what could be called extreme LOP. My VariEze can be flown with the throttle full open and the RPM reduced with mixture, down to around 2000 RPM. With the previous stock oil sump induction the lowest comfortable RPM with wide open throttle was about 2350, about normal I hear. I am not at all suggesting anyone needs to cruise at 2000 RPM, but rather per your comment, am offering some elemental thoughts on leaning during this experience. You proabably have more info than you can use. The simple intent is to mention some personal experience and sources. Satisfying curiosity and resolving the unknowns and concerns, they can be shelved and we can go fly.

Like you, my early guidance on leaning was to reduce the mixture until the engine roughens, then richen it up a little. A local engineer brought me a stack of material that turned out to be Lycoming’s leaning document. Reading it resulted in basically pulling the mixture back until the engine roughened, then richen it up a little. Unquote.
Beyond that, opinions were mostly conflicting. You could hear snips about running lean of peak, but consistent guidance was scarce, or so I though. The conflicting opinions and old wives tales prevented me from getting too far away from the basics. I had bigger fish to fry and should point out that the plane flew fine during those years of normal leaning.

You have heard about leaning before takeoff from a mountain airport. Not doing so usually results in running off the end of the runway or trimming a few TV antennas and chimneys. At times we have to do that here at 700 feet agl. On a 106 degree day the density altitude can be around 4000 feet. Taking off with the mixture full rich is like having the lawn mower choke on, with the engine staggering. Point is, basic leaning to peak for best power is appropriate at any point. Proper leaning during taxi should also be part of our education. And then use the checklist on before takeoff....

As you can see in the below referenced article, there was more than adequate leaning documentation available in the WWII pre jet era. Running LOP was specifically prescribed for better fuel efficiency, cleaner operation, cooler cylinder temps and longer engine life. Early airline competition was fierce and those guys had to know and do the best procedures. You have probably also heard of Lindberg spending time with P-38 pilots, and that his instruction on proper leaning enabled them to extend engine life and dramatically improve their range and operational capabilities.

This link, http://www.taturbo.com/future.html builds on comprehensive data from the peak of the piston aircraft engine era. It defines terms. It is particularly interesting and enjoyable to me because it mentions the mystical intermediate or follow-through step that I had previously discovered in my plane. After leaning and initially loosing some RPM, you can get back the power you thought you lost. Similarly, when digging for the good stuff in prop data, I was told to go to German engineering data from the late 1930s.

This article and others like it are the good stuff from the pros, where a guy can get basics or dig as deep as wanted. Using best practices on his engine, a guy may match the better designs. As I mentioned before, hopefully you will get to fly with or at least be around operators that practice and teach using the age old proven procedures rather than just running though all the urban legends. Responses to your note prove a wealth of experience is readily at hand.

Talking about leaning with other Eze pilots is interesting. We have a vast breadth of operational extremes. Commenting on my 1400 mile nonstop flight, a number of pilots have mentioned that they don’t routinely lean at all, and had never tried to fly more than 300 miles without refueling. I think their chosen operational level is fine and envy them because with a basic Eze they can live their lives and see and do everything they want right in their back yard.
That 1400 mile flight was flown “normally”. RPM was reduced with throttle and then mixture leaned to roughness and pushed up a little. Probably the main element in completing that trip was crudely determining when reducing the RPM where the largest airspeed loss occurred and cruising right above that speed. The trip was made at 2400 RPM. I still incorrectly believed that the valves could burn up if the engine was leaned too aggressively. My experience has shown different. Reducing the mixture above 8000 feet, the RPM and temps just reduce until finally there isn’t enough fuel for combustion.
Now, being a lot more experienced and having heard more about maintaining a specific angle of attack for best distance efficiency, I have a lot more to screw up.

Along the way I started to learn about a more aggressive LOP condition that made sense. Leave the throttle full open for better air flow through this Lycoming ‘air pump’. Then reduce the RPM with mixture. More potential for efficiency. However, because of significant differences in fuel delivery to the cylinders on some engines, -lots of fuel to one cylinder and not much to another - before the mixture could be reduced enough for much efficiency to be gained, the engine would be running too rough for most folk’s comfort level.

As I heard it, the limiting element causing poor induction with the Lycoming was that the oil pan has a short three or four inch vertical run from the carb before it split into four tubes in the spider. Besides the short mixture run, the carb jet shoots to one side. Thus there is very uneven mixture distribution. At peak and above, the engines run smoothly. But overall fuel burn is high. As the mixture is reduced, fuel levels and power from each cylinder becomes noticeably uneven, temps are different and the engine roughens. Looking back it’s easy to see why some spam can pilots could so readily move on from this effort to lean aggressively.

So. What is a guy to do with the imperfect design? The WWII and airline training on leaning used engineering data to determine the optimal operation for a particular engine. So by just doing a little of that pilot stuff, we have the option to do the same and get better performance without designing our own engine.

So how about getting balanced mixture? That’s another subject, that I have been flying through for the last two years. My intent here was to offer up some basic thoughts and experiences on normal leaning with an intake like yours. Some have successfully extended their intake run and improved mixture distribution. Am sure you are familiar with Gary Hertzler’s setup which uses a tube through the oil sump for a longer mixture run before splitting at the spider. At Oshkosh he was on the third leg of a trip still using the original fuel load. Joe Person mentioned Gary staying over with him and watching him flight plan at 2.5 gallons an hour.

We are in a time period where there is enough proof in some of the puddings to make things interesting. We hear a lot about fuel injection. Because his throttle body is so efficient, I asked Hertzler if the TB is better, or FI. He said that FI would ideally be the best.
For balance, I feel obligated to throw in my opinion of the best thing to have on the plane – Bug Guts! Very few things produce benefit that is worth grounding a flying plane. I recently came across something from the ‘80s in the ez.org CP link I think, on leaning, about RAF considering making a 24 hour flight in their new stock LongEZ.

There is potential for problems. The main caution we hear is “Do LOP leaning only above 8000 feet density altitude because there you can only produce 75% power and can’t hurt the engine”. OK, that doesn’t cramp my style too much. However, in the simple interest of accuracy, after re-reading the references quoted herein, and others, I am beginning to understand how useful using EGT can be at any altitude.

A friend has a powerful twin that he has pampered since new, sparing no effort or expense in maintaining it to the highest level. He went to the Advanced Pilot Seminars in Ada, OK and described his concern and mental conversion the first time they took off and immediately started leaning. Very scary for him, but now he has been there and done that and is confident with better procedures. I haven’t been there myself but have benefited from studying this presentation on their site. Advanced Pilot Seminars, Ada, OK http://www.advancedpilot.com/downloads/targetegt.pps#304,3,Slide 1

For a guy totally focused on getting his engine to TBO, his stress level would probably benefit from having watched the Cessna 150s at a local country airport here over the last 30 years that consistently made TBO. They monitored one cylinder CHT and were flown/abused mostly by very creative novices.

So with my previous 0-235, it was lean to roughness then richened a little. I could have certainly pursued further education, for sure using the “30F to 50F degrees below peak” mentioned in the referenced Back to the Future article. Bottom line, our engines are great. Even if the induction design is imperfect, if a guy gets up to speed on leaning with his setup, he is sure to get much more out of the plane. Hope this summary helps in your operational efficiency hunt. Mainly to get to simple useful practices from the references.

My plane now has a significantly different induction system, another subject. The sunset runs over the last couple of years have included fairly extreme LOP operations evaluating efficiency potential. Curiosity has me looking forward to making the Reno trip nonstop again with the 0-290. Hopefully Tim LoDolce is saving room for my cot in his kitchen.
Coming back from Oshkosh this year, for something totally different, the plane was flown with everything pretty much at peak. -First trip doing this.
Looking at the big picture, since the first Jackpot RACE in ’97 the plane has gained over 30 mph at a lower fuel flow with lower and more balanced temps. While certainly not required for the great Eze life, I would guess more balanced mixtures are a good thing.

Good flying
Bill James, Fort Worth VariEze