AOPA Article on LOP

David-aviator · #1 07-02-2009, 09:32 AM

I read the Dave Hirschman article on LOP. It is a good read. I can see why some are so taken in with this subject, even a Lycoming exec is coming around although cautiously recommending LOP only at 65% or less.

But what Mr. Hirschman and others are focused on are turbo charged high end 6 cylinder engines. Hardly any mention of a 4 cylinder stock Lycoming except don't do it with a carb or without very complete engine information, preferably in graphic form.

I can see why guys are doing it, there are benefits in economy but probably not as apparent at a basic level of a stock 180hp 0360. It is mentioned that Cirrus requires pilots use LOP, but no mention as to why or what's behind some of the 128 NTSB reports on Cirrus crack ups.

My max EGT spread is 39F at a peak low power setting (1400-1439), is that close enough to consider LOP ops? CHT runs between 338-352.

Seems like 39F may not be close enough to do it.

Radomir · #2 07-02-2009, 09:36 AM

David,

That spread is completely irrelevant for doing LOP properly. You want all your cylinders to peak at (or as close as possible to) same fuel flow.. individual numbers will be different and they are not at all important..

All engines benefit from LOP..

David-aviator · #3 07-02-2009, 03:54 PM

Quote:

Originally Posted by Radomir

David,

That spread is completely irrelevant for doing LOP properly. You want all your cylinders to peak at (or as close as possible to) same fuel flow.. individual numbers will be different and they are not at all important..

All engines benefit from LOP..

Radomir,

I do not understand your response.

The readings yesterday, just rich of the rumble, were
1419
1420
1439
1400
The cylinders can not peak at the same time because the EGT's are different. #3 will be there before #4. How can the spread not be relevant?

It would seem logical for LOP to work, all cylinders would have to be at peak at nearly the same time before going into LOP. If the cylinders are not LOP together, the procedure would not make sense, like operating with a carb or without a temp sensor in each exhaust.

frankh · #4 07-02-2009, 04:03 PM

The actual EGT numbers them selves are irrelavent.

I.e one may show a peak of 1400 and another may show 1430. All we are doing is finding out WHEN the peak number (whatever the actual number may be) occurs, i.e at what total fuel flow.

So say #1 has a peak value of 1400..and this occurs at 8.1 GPH. Cylinder 2 has a peak value of 1435 but this occurs at 8.0GPH.

Well we now say the flows for those two cylinders are such that they are 0.1 GPH apart.

its the actual EGT number that does not mean anything.

Frank

Jim P · #5 07-02-2009, 05:45 PM

And it's been mentioned on the forum previously, but Don at AFP will work with you to collect and analyze the injectors to get the EGT peaks as close as possible. They will send you info on taking data while you peak, enrichen, then re-peak and go LOP. Based on that data, they will recommend possible changes to you rinjector restrictors.

plehrke · #6 07-03-2009, 05:14 AM

Quote:

Originally Posted by frankh

The actual EGT numbers them selves are irrelavent.

I.e one may show a peak of 1400 and another may show 1430. All we are doing is finding out WHEN the peak number (whatever the actual number may be) occurs, i.e at what total fuel flow.

At what altitude are you getting the 1400F? How do the EGTs vary with altitude? My peak (based on an EDM-700 with probes 2" from flange) typically are 1500-1550F for 5000-6000 ft. I get 1500F for 8000 ft. I have found nothing that says if there is an exceptable range for EGT but I see all people that post numbers have them in the low 1400F. Should I be worried that they are that high?

yakdriver · #7 07-03-2009, 06:16 AM

Phil, Again the temp reading is irrevalent, it is when they peak. My probes are 4" from the flange and the highest reading I get is about 1460. I have AFP injection and Don helped me balance my injectors. All my cylinders peak within .1 gph But the individual egts have around a 50 or 60 degree spread. I can run 20" 2450rpm at 10,000 ft and get 175kts true @ 9gph rop or 168 kts true at 7.4 gph lop. Don

David-aviator · #8 07-03-2009, 06:58 AM

Quote:

Originally Posted by yakdriver

Phil, Again the temp reading is irrevalent, it is when they peak. My probes are 4" from the flange and the highest reading I get is about 1460. I have AFP injection and Don helped me balance my injectors. All my cylinders peak within .1 gph But the individual egts have around a 50 or 60 degree spread. I can run 20" 2450rpm at 10,000 ft and get 175kts true @ 9gph rop or 168 kts true at 7.4 gph lop. Don

I finally got it.

The peak EGT can vary from cylinder to cylinder - the key is when one peaks and begins to drop off as you go LOP, the other cylinders do likewise and do not continue to rise toward peak.

Every one of you said the same thing and for some obtuse reason I had a mental block and it made no sense....this morning it does.

I think in determining just how balanced the injectors are, I will lean to peak and into LOP very slowly and at very low power like 50-55%. I can not hurt the engine and the injector balance can be observed.

Thanks for the patience....

Geico266 · #9 07-03-2009, 08:11 AM

Quote:

Originally Posted by David-aviator

I finally got it.

Every one of you said the same thing and for some obtuse reason I had a mental block and it made no sense....this morning it does.

I think in determining just how balanced the injectors are, I will lean to peak and into LOP very slowly and at very low power like 50-55%. I can not hurt the engine and the injector balance can be observed.

Thanks for the patience....

Don't be too hard on yourself, it takes awhile to understand the prinicple, but you are on the right track. Take pride in the fact that you want to learn! This is why I love experimental aviation so much. There is always room for improvement and learning new things, this forum is the place to do it!

Here is a sample of the data I ran on my IO-540.

After squaring the engine RPM & manifold pressure you need to write down the temps on each cylinder (a helper is really a good idea) after you lean the fuel flow approximately .2 GPH each time and the engine EGT temps stabilizes. The reason for this form is this "draws a picture" to determine which cylinder needs what restrictor to get the cyinders to peak at the same time. Red is Peak EGTs. If you notice in my example this run was done with the new restictors replaced in the #2 cyinders. The number #6 cylinder the 1st to peak, and could possibly have used a richer reducer, but I thought we were close enough. The goal is to get all cylinders to peak within .5 GPH.

This is a good example of how the temps themselves are irrelevent, my indicated peak EGTS never hit 1400F. Also, fuel burn goes from 14 GPH to 11GPH in this power setting. Also, the oil temps run 20F cooler.

In my example I forgot to label each EGT, but you get the point.

Hope this helps.

pvans · #10 07-03-2009, 08:16 AM

Just make a table and record the EGT value for each cylinder at a bunch of mixture settings ( say every 0.3 gph) from near full rich until you get the "rumble".

Graph those curves, EGT vs. Temp.

If the peak of each curve comes close together, you can see if lean of peak on all cylinders can occur at the same time. If you have injectors, you can install slightly larger or smaller injectors in the cylinders that peak too soon or too late to better balance the engine.

FWIW, my Lycoming O-360 with an Ellison "carburetor" did not run very smoothly lean of peak until I installed a Lightspeed ignition system. By advancing the spark at lower power settings the engine is quite happy lean of peak. Saves about 20% on fuel consumption.