Question:
How can we test if our aircraft engine is conforming?
Come on, who has the answer first?
Approach peak from the lean side and confirm all cylinders temps rise as you do so. If they do then they were all on the lean side of peak. Worst is to have one cylinder in that 'red zone'
Approach peak from the lean side and confirm all cylinders temps rise as you do so. If they do then they were all on the lean side of peak. Worst is to have one cylinder in that 'red zone'
This is not a competition on who can get in their one-liner reply first 
Especially as "Approach peak from the lean side" is incorrect because most engines will be running far too rouch then - if running at all.
The instructions are here.
In essence, you start with the engine well rich of peak. Set up your normal cruise settings - typically 65% for best engine life. Set up the plane flying straight and level, on autopilot if you have one, in clear VMC with minimal turbulence.
You then slowly lean, reducing the engine fuel flow 0.2 USG/hr at a time or so, noting down the EGTs of every cylinder each time.
If they all peak within about 0.5 USG/hr then the engine is well enough balanced to operate peak EGT or even LOP. If not, then you order a set of GAMI injectors.
My results are here: before after
The second peak in the 2nd one above, which occurs well in the LOP region, is fairly normal and is ignored.
Especially as "Approach peak from the lean side" is incorrect because most engines will be running far too rouch then - if running at all.
I think that is an opinion rather than a fact. GAMI suggest as I wrote at least in their engine course.
That's most curious since gami.com (the link I gave) is George Braly's own company and AFAIK he is the person who runs the APS course!
Sure you could do it both ways, but the "average" engine is not going to be running at all smoothly LOP which is where you propose to start the GAMI test procedure.
For the procedure to work and yield data which is consistent and useful for GAMI to work out the injector flow rates, and hopefully get it right first time, the flight has to be smooth, with nothing going on to upset the data collection. This is going to be difficult if you start way LOP at which many/most engines will be coughing and spluttering, not to mention not delivering much power so you have aircraft trim / engine cooling airflow issues, whereas all engines will run just fine ROP. Once one is past peak EGT, on all cylinders, the test can be terminated because the required data has been collected, so there is no need to go far into the LOP region.
I think you are both right!
Clearly the question should have been put better!!
As far as I see it is advisable to confirm if the engine is conforming for ROP and LOP operation. Fuel savings can be very worthwile ROP if the engine conforms. LOP is not possible unless the engine is conforming.
What is a conforming engine, though?
That would be an engine with a tested fuel flow on all cylinders whilst leaning during cruise and not just dripping fuel from all injectors into a meassuring cup on a stand!
First thing needed is a multi cylinder engine monitor. No engine monitor, no test.
As Peter wrote and also quoted the link from the superb GAMI website, their test would confirm what they call a GAMI spread. Their method is very well explained on their website.
Following the Gami test the spread should be 0.5 gal/ hour or less. This is not to be seen as a single test and everything will work forever. Far from it; it should be repeated at least once or twice per year.
Even if the engine has been made conforming by fitting for example Gami injectors, any subsequent engine work, a small induction leak, a poor ignition component not up to scratch and the Gami spread will be outside that target again. One example is Peter's post here regarding high resistance spark plugs.
Therefore, it is in the pilot's and passenger's interest to be sure that all of these components are conforming when going out on a cross country flight, right?
Only if the engine is conforming can LOP operation be successful.
Once that has been established one can best lean as JasonC wrote, by carrying out the big pull to a safe place deep LOP and then setting mixture to a known fuel flow and CHT only; or by leaning from the lean side to ROP and setting to an EGT value like 50 degrees LOP.
The confusing thing is that this method is a LOP leaning operation with ROP leaning parameters. But it works great!
Opinions differ which method is better, I personally use both since I believe both have their benefits.
Peter, Now that I have an EDM-730 (and GAMIs), I also plan to run peak EGT at 75% power most of times (below 7000). What has been your experience with these power settings in terms of engine longevity, over the years?
Regards!
(I have a vague feeling that I’ve asked this before, but when I search through my old postings I can’t find it. Apologies if I repeat myself, but if I did ask before I’ve in any case forgotten the answer…)
How do you set power for peak EGT operations?
The POHs I’ve looked at basically only provide power setting information for some “recommended” mixture setting such as 100° ROP for the PA28-181 or 50° ROP for the Cessna 172S. There is information about the fuel flow and TAS at peak EGT, but no power setting information.
Clearly (at a given altitude and temperature) a particular rpm (for fixed pitch prop. aircraft) or rpm/MP combination (for VP aircraft) will give a particular TAS.
Since the POH states that the TAS is lower for peak EGT operation than “recommended” mixture, the rpm (and/or MP) must also be less than with “recommended” mixture but there is no information about these lower figures.
So — how do I properly set power when this rpm (and/or MP) figure is not in the POH?
The only way I can figure is to set the rpm/MP according to the power setting table, lean to peak, enrich to recommended EGT, readjust power to table values (as the rpm/MP will have increased during leaning), then once again lean to peak letting the rpm/MP drop to whatever the value will be. But this procedure with leaning to peak twice seems a bit roundabout.
A few percent don’t matter. Just set a reasonable MP/RPM combo and then lean to peak EGT. As long as you’re below 75% BHP, you can’t do much harm provided you’re within CHT and TIT limits.
If you want peak EGT then the only way to control power is with the MP i.e. the throttle (prop RPM gives you a second order effect but normally you set the RPM to where the engine “feels happy”).
Lyco say you should be at 75% (or less) of max rated power for peak EGT.
A lot of people say you should be at 65% of max rated power for best engine life.
So, at top of climb, set the MP with the throttle (about 23" for 65%), set the RPM to say 2300, and lean the mixture for peak EGT. Job done.
Above about 8000ft, the throttle will be fully forward to get 23"… and the power % will gradually fall as the air gets thinner still.
If you have an accurate flowmeter, you will learn the settings so at low level, say 3000ft, I set 23" 2400rpm and 11.5 USG/hr and that’s it. The IAS should be 138kt and it always is.
This assumes you have an EDM700 or similar. If not, the procedure for peak EGT is that you lean until there is a sudden falloff in the airspeed, and then enrich just a little to get back. This is worth a quick read.
