View Full Version : Leaning Techniques

17th May 2002, 10:18
Have heard of various leaning techniques beyond the traditionnal "enrich once at EGT peak"
Finally, I found on the web those advices from a senior pilot who affirm you won't kill your engines by leaning to get a 50 F drop on EGT

Here is the link


Have tried on the Seneca am flying every day, seems to save some fuel and numbers look fine (EGT, CHT, F.Flow )

So what are you views , wise techies ?

17th May 2002, 14:41
Yes indeed, can be done on the 6 cylinder engines that have very good mixture distribution (fuel injected), especially those that have GAMI injectors fitted. This technique was used on round piston engines for many years because they generally have superchargers which ensure good mixture distribution to each cylinder.

17th May 2002, 16:40

I have been flying LOP since about 1997 when the GAMIjectors came out, I believe I had the first set in Europe (sn 1023).

In combination with a JPI -cylinder engine analyser, and a good understanding of the combustion event, you will never fly ROP again unless needed for high altitude performance.

They just passed sn 10000 about a month ago.

They were Aviation Consumer's gear of the year about 97-98.

It is a pity so many pilots and mechanics believe the Old Wives Tales about flying too lean. Please read the rest of John Deakin's engine management columns as well, they are very well done and based on data, not rumours.

big pistons forever
19th May 2002, 02:25
You should have a look at the " aftermath " column in the last
" Flying " magazine. It discusses the fatal crash of a Australian
PA 31 after a double engine failure. Overly aggressive leaning
was implicated in the accident. Personnaly I run all turbocharged
flat engines at a maximum of 1400 - 1440 deg TIT depending on the particular engine. I know of one operator who tried to fly a
C421 with lean of peak mixture settings. He lunched 3 engines in 18 months.

19th May 2002, 03:00
Have to agree bigpistons, these turbo engines need to be kept cool for long engine life....or any life at all.

Chuck Ellsworth
19th May 2002, 05:04

Like I mentioned in another thread, there are three things that will ruin piston engines.

( 1 ) Heat

( 2 ) Friction, ie. high R.P.M.

( 3 ) Ham fisted throttle jockeys.

Cat Driver:

:D The hardest thing about flying is knowing when to say no.:D

19th May 2002, 06:06
I was unfortunate to have had an event leading to the failure of one piston and subsequent engine shut down on a PA-31. Data on our engine handling technique was used to compare to those used by Whyalla Airlines (who had an accident in 2000 which killed 8 people in a PA-31) to establish if engine leaning was a contributing factor. The report can be found at http://www.atsb.gov.au/aviation/occurs/occurs_detail.cfm?ID=317. It seems that Whyalla's double engine failure was initially a failure of the crankshaft of one engine, and the second engine, having had a company endorsed history of having been operated lean, holed a piston and led to that engines demise.
These high power engines are very sensitive to lean engine handling (all operators investigated were operating engines within engine manufacturer's recommendations). Unless comprehensive engine analysis instruments (ie: JPI 6 cylinder egt, etc) are used, using a single probe egt and leaning beyond peak egt is foolhardy, just to save a couple of litres of fuel per hour.

20th May 2002, 17:09

The Australian report is a very poor proof that leaning LOP is bad, on the contrary; in most POH's you will find that 'leaning to best economy' as mentioned in the report is 25F ROP.

Now I completely agree that 25F ROP is too rich or way too lean, go to 25F LOP or 100F ROP and then you're safe. During climb and cruise CHT and smoothness must be observed, I keep CHT below 380F at all times. On turbocharged engines TIT will also be a limit.

GAMI is providing the Australian CAA with updated engine data, a Navajo engine is running on their test stand following this accident.

On the other hand, it is wrong to blame all current TCM and Lycoming QC problems on pilot leaning techniques. One of my friends just had major problems after 200 hours since new cylinders with TCM valve wobble, on a turbocharged TSIO-360. immediately fingers were pointing to his LOP flying, forgetting that valve wobble is caused by improper centering of the valve guides during installation, no pilot action could have caused this.

Leaning beyond peak is safe and proper operation, if engine runs smoothly and temperatures are monitored. In fact LOP temperatures will mostly be lower than for a similar horsepower output ROP.

I pay for my own engines and fuel.

22nd May 2002, 08:27
I know I may present a simplistic point of view on this one, but it seems to me that whatever the method (LOP or ROP ) you end up with lower temperature than the EGT peak ....So I can't see a heat related factor playing in the scenario.
second point; if you are using LOP techniques, you have more air than fuel in your combustion chamber, and therefore a better "cushion effect" ?
I accept any comment about those techniques, but I would appreciate a scientific explanation of the reasons why we should avoid or recommend those methods.

big pistons forever
23rd May 2002, 03:24
Running LOP increases the likelyhood of lead oxybromide deposits on the cylinder heads. These deposits become superheated and will induce preignition. The preignition will probably not be perceptable and can lead to catastophic piston or cylinder failure in minutes. Also you are right when you say engine temps will be less LOP as well as ROP. The problem is if you are well ROP and your attention wanders the engine can go a fair bit leaner or richer and chances are nothing bad will happen.
If you are LOP a mixture change either way is bad. A bit more lean and the engine will start surging or even quit. A bit more rich and the engine temps go way up. Your a better man than me if can fly single pilot IFR in busy airspace and still have enough brain cells left to keep a continuos eye on engine temps. In the early days of the Piper Malibu, Piper recommended 50 deg LOP operations. In theory it should have worked but in practice too many folks were melting their engines so I believe they now recommend ROP ops. I have always operated turbocharged flat engines well ROP and have had good luck but I know there are others who swear by LOP ops so go figure:)

23rd May 2002, 07:49
As a matter of fact, I am using LOP only on long flights (2 to 4 hrs) and ROP on short ones.
As you said, single pilot IFR ops don't leave much time to keep the eyes on the engines clocks.
I am flying the Seneca of my boss since 300 hrs, among them, I will say, 150 are LOP.
What you mention about the Malibu is not totally surprising but I am not sure ROP totally solved the problems, since Malibu have always been known for engines problems ( I was told not a lot of owners bring their engines to the potential ....)
Anyway, I appreciate your contribution to this somewhat complex , but interesting subject.

Thank you all.

Dale Harris
23rd May 2002, 09:59
As far as Lycoming L/TIO 540's are concerned (PA 31) Lycoming do not recommend LOP operation. If you use the figures in the manufacturers handbook (engine) none of them are LOP. Everybody has ideas about engine operation, I, for one, believe that the engine manufacturer know his engine better that anyone. 150 to 300 hrs of operation is NOT a test likely to reveal accelerated wear and tear. Try 1500 to 2000 hrs for some accurate figures. At a replacement price of 65000 oz dollars, a couple of extra litres per hour is sweet F.A. in comparison.

Edited to add this If you can get hold of a publication from lycoming called "Lycoming Flyer Key Reprints" you should. A very interesting read, including leaning, maintenance, and performance tips for all lycoming engines. excellent read for pilots.

23rd May 2002, 12:53
It is interesting to note that manufacturers' engine operating handbooks suggest a more conservative leaning approach and airframe manufacturers somewhat closer to the maximums permitted.
One is selling engine longevity and reliability, the other, a more economical?/performance related argument to have their products look good on paper to a buyer. Why are airframe manufacturers' performance charts unfactored?

24th May 2002, 13:04

It is very easy to understand this duality: a knowledgeable engine man will tell you to run the engine at 100F ROP for best power, and at 25-40F LOP for best economy.
Because cruising at 100F ROP will give very bad range, the airframe manufacturer will recommend so-called 'best economy' at 25F ROP, which the engine man will say is the worst place to run the engine with the highest CHT.

Another very significant advantage of running LOP is that NO carbon monoxide is produced, so leaking a exhaust system will not kill the pilot.

My experience with LOP has been very positive, I only wish that the equipment (GAMI, JPI, information) would have available sooner.

The real research in piston engines is no longer in the TCM or LYC faxtories but happens in a small three letter town in Indian country. Pretty soon we'll be able to replace our magnetos with interactive reactive electronic ignition with variable timing in function of the combustion event, permitting the use of unleaded fuel, or autogas, even in high powered turbocharged engines.

Places to visit: www.avweb.com : columns: all of John Deakins articles on engine management, www.gami.com
If you want to talk to the real experts: www.avsig.com (maintenance and aircraft).

24th May 2002, 14:44
Oh dear !

each post leads me in another direction to make my mind !
It's worst than Eurocontrol re-routing !

Go ahead guys !

Dale Harris
25th May 2002, 04:49
Sorry dude, I have yet to meet a "knowledgable engine man" who recommends running a turbocharged lycoming engine anywhere LOP. Especially if he is paying the bills!!!!

25th May 2002, 08:23
Try reading this about Lycomings LOP:

When I was running my TIO-541's LOP was not yet 'reinvented', but today I wouldn't hesitate to try LOP and watch the temperatures and smoothness. The JPI was not yet available then. TIT at 900C or fuel flow (whichever was reached first) was the limiting factor for leaning , and the instrument needed calibration every year.

Porcorosso, since you are flying a twin, how about running one side LOP and the other ROP for a while, report what you find, including oil analysis.

Running LOP smoothly is also a very good indicator of the general health of your engine, induction leaks will show up quickly, marginal spark plugs, bad spark timing, etc. If an injector gets slightly clogged, that cylinder will run more lean (out of the danger zone) and the engine will run rough and let you know immediately. While ROP, a clogged injector can put the cylinder right in the danger zone without you ever knowing it.

If not yet equipped: this would be my priority: first get the JPI and learn to use it, then install GAMIjectors (if needed, maybe you have the perfect set of TCM injectors), then gather some data (JPI datalogging feature is perfect, download all temps to your PC and see the engine parameters for every 6 seconds of every flight from runup to shutdown).

Don't listen to OWT but make up your own mind, then you will have the option of running ROP or LOP when conditions require.