Mixture leaning and EGT gauge?

[Tiddles]

Can someone advise me on how to use the Exhaust Gas Temperature (EGT) gauge to assist in leaning the mixture. There is a 'red' indicator that can be manually rotated and set, but I cannot recall its purpose!

The current method that I use is to pull out the mixture control until there is a drop in engine RPM and then push it in a bit to recover the cruise RPM. I am sure that using the EGT is supposed to make it more efficient.

Also at what height do people typically lean the fuel mixture. I tend to use it above 3000'

Thanks

[Tinstaafl]

Using an EGT:

Lean the mixture until peak EGT is reached. Move the red adjustable needle so that it marks the temp. that is peak EGT.

Enrichen the mixture so that the EGT is now 'xxx' degrees cooler than the previously marked peak. 'xxx' relates to whatever the a/c manufacturer recommends.

The adjustable needle is only there so that you don't have to remember what the particular temperature happens to be - you need only ensure that the EGT is the appropriate number of divisions below the red needle.


The mixture may be leaned at ANY altitude.

[Flyin'Dutch']

Interesting reading for when the weather is cr@p:

http://www.lycoming.textron.com/main.jsp?bodyPage=support/publications/keyReprints/operation/exhaustGasTemperature.html

You will find plenty of interest on this site.

BTW just to elaborate in Tinstaafl's remark:

The mixture may be leaned at ANY altitude

Indeed as long as you do it at less than 75% power.

Have fun!

:eek:

FD

[Final 3 Greens]

The mixture may be leaned at ANY altitude .....Indeed as long as you do it at less than 75% power.

At the risk of being anally retentive, make sure that you're fully rich on final in case a go around is required.

[Davidt]

have alook at www.avweb.com
John Deakin has published a whole series of articles on engine management much of which centers around leaning technique. He argues that the technique described above ie running rich of peak is exactly the wrong thing and advocates running lean of peak particularly on 6 cyl injected engines.
I have no idea whos right but its all thought provoking stuff, very informative.
I did have shares in a Cherokee 180 which fouled the bottom plus if you didnt lean whilst taxiing.

[dirkdj]

Flying lean of peak is a very interesting option on fuel-injected engines with proper instrumentation (all-cylinder EGT/CHT gauges).

One additional benefit is that flying LOP generates little or no carbonmonoxide (CO). This is a significant safety benefit in single engined aircraft.

On engines with carburettor, I would lean until beginning of roughness, and then enrichen slightly, at any altitude at or below 75% power.

On the ground lean very agressively, so much that take-off power is impossible to obtain without enriching.

[AC-DC]

Indeed as long as you do it at less than 75% power.

As far as I know you can lean at any power setting, including above 75%, the difference is how much you lean. At 65% I fly at pick (11.5-12g/h) or 50 rich of pick (13g/h) while at 75% I fly at 100-150 rich of pick (14-15g/h).

[Jhieminga]

The school I'm currently flying with has a fleet of 3 BE36s and 3 BE58s, in the 'old days' they used to have 8 BE36s, and they ran them all at 20 degrees lean of peak to save fuel (amongst other logical reasons). However, at some point they realised that they had to replace exhaust valves on a very regular basis! (At least, that's the story as it was told to me) And ever since, we're all leaning to 20 degrees RICH of peak.

This may not be the case for many other engines but it did cause a change in procedures down here.

[dirkdj]

Jhieminga,

Running 20 LOP is FAR better than 20 ROP in the BE36 and 58.

The cause of the short valve and cylinder life is the sloppy QC at the TCM factory.

My two hangar mates had exactly the same problem. If the exhaust valve/guide is not correctly centered it will not last for more than a couple hundred hours.

On a TCM TSIO-360 with brand new 'Top Care' cylinders, all six exhaust valves guides were worn beyond repair after less than 200 hours.

As usual, read John Deakin's article 'Fried Valves' on www.avweb.com.


If the valves are not put in straight and centered, no amount of leaning technique is going to rectify the problem.

http://www.avweb.com/news/columns/182155-1.html

FlyingDutch,

Here is some reading for you, best to read after the Lycoming cr@p:

http://www.avweb.com/news/columns/182131-1.html

[englishal]

You can lean at any power setting and indeed you should lean for take off at high desity altitudes....Also if making an approach into a high DA airport it is probably best not to set full rich on final, else you won't get full power in a go-around....

Won't be much of a problem in the UK of course.

Rgds
EA:D

[Flyin'Dutch']

I have read John Deakin's articles before many a time and they make very good sense.

As you say the Lycoming folk completely slate any LOP practice in their articles but interestingly the POH for the Cirrus 22 (with TCM engine) actually states that LOP is fine 25-50 LOP EGT) for Best Economy.

Best Power is advertised at 75 degrees ROP.

Like the single throttle pitch lever in the Cirrus; certainly could get used to full FADEC which would take care of mixture as well.

FD

[dirkdj]

Hi Dutch,

I rather like having a mixture control, with associated control instruments. Sometimes I may want to use all the power I can get at 100 ROP, other times I want range and economy at 40 LOP, while keeping away from the 'danger zone' (red box).

From what I heard, it seems that the FADEC from TCM is fairly brain-dead.

We are very lucky to have such a pool of engine knowledge available OUTSIDE of the LYCON manufacturers.

Interesting to know about the Cirrus POH. This book is written by the airframe manufacturer and not by the engine manufacturer.

[Flyin'Dutch']

Hi Dirk

The one thing that I found most interesting when reading the series of articles that you referred to yesterday was that he thinks that above all the CHT is the one to go for.

Yet it seems sort of accepted practice that the first thing to add when improving engine monitoring is an EGT!

See your point re the Cirrus POH, but would have thought that they (Cirrus) would have had close discussions with TCM about this.

FD

[dirkdj]

Dutch,

there is one more very important parameter in the ROP/LOP discussion: peak power pulse.

Because of the nature of the mixture, a ROP mixture will burn more quickly while a LOP mixture is slower burning. Compare it to hitting the piston with an iron hammer versus a rubber hammer.

Also important : since ROP mixture is burning faster, more power is excerted earlier in the cycle, when the piston is still at the beginning of its travel, too close to top center.

When pulling back the mixture 'over the peak', the tone of the engine changes, mainly due to this effect.

I consider a proper EGT/CHT all-cylinder analyser money very well spent. Saturday, during runup in my friends A36, mag drop was noted. It turned out that both plugs on cylinder 4 were not firing. easy to spot and to fix with a JPI.

Also, the JPI has optional data memory, it collects all data every six seconds and stores it (about 50 hours worth of flying).

[FlyingForFun]

Dirk,Since ROP mixture is burning faster, more power is excerted earlier in the cycle, when the piston is still at the beginning of its travel, too close to top centerI'd expect the spark to be advanced or retarded an appropriate amount, such that, for whatever mixture the manufacturer recommends, the bulk of the power is delivered at the time when it's going to be most effective.

Note the important phrase there, though: for whatever mixture the manufacturer recommends.

FFF
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[dirkdj]

FFF,

Unfortunately, on the current (1940-1950ies technology) engines, the ignition advance is fixed (22 BTDC on my engine) and is a compromise optimised , I believe, for full power full rich, hardly the way we run engines most of the time.

All other things being equal, a LOP mixture burns slower and thus is more effective at a more useful time in the power cycle.

Most of our cars have electronic ignition now (unless it's a diesel of course), but GA engines haven't changed in eons.

The most promising development right now, in my eyes, looks like the PRISM system where an optical probe in the spark plug head looks at the combustion event, and advances or retards the ignition of that cylinder individually, according to the needs and conditions of the moment (power level, fuel type, temperatures, etc). This system will permit use of unleaded fuel even in high power turbocharged engines.

[FlyingForFun]

Ok dirk, I'll admit I've never actually looked inside a magneto. I'd always assumed they have some kind of mechanical advance/retard mechanism, similar to that used in the distributor of car engines pre electronic ignition.

FFF
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[Tinstaafl]

The only automatic timing adjustment in a standard magneto is the retard mechanism for starting.

[bluskis]

EGT v CHT the EGT reacts almost instantaneously to changes in mixture, whereas the CHT is comparatively very slow to react, unless you are in a throttle closed dive. So the reason for adding an EGT gage is to be able to adjust the mixture to the setting you want in a few seconds.