Can you help me understand what's going on?

[Chris B]

I have been playing around with my new MVP-50p on my newly overhauled 0-540.  I have been struggling to get the Lean Find - ROP process to give me reliable leaning guidance.

This morning I went up to play around again and captured something interesting (at least to me).  I can't understand what the data i showing me, hoping you guys can help.

If you look at the savvy report here, specifically between the times 00:23:30 and 00:32:00 you will see what I am talking about.  I was at 7500ft, 20/2300, around 65% HP.  Book called for cruise fuel flow of 11.5ish gph.  Following the old lean until rough, rich until smooth it start to become rough around 10gph and smooth out around 11.5gph.

The first 2 leaning attempts with the Lean Find feature (00:24:10 and 00:25:32) looked as expected, all EGTs peaked and fell off as I went pretty far LOP.   The 3rd and 4th attempts ( 00:29:08 and  00:31:00) look different.  As I went far LOP, pretty much the same fuel flow as attempts 1 and 2, the EGHTs didn't peak and fall off, they just remain kind of flat.  I wish I would have paid attention to how rough the engine was running during each attempt but I didn't.  I just know it was very rough as the fuel flow got low but not sure if there was a variation between the attempts.

What I can't wrap my head around is why the two different patterns? 

 

What do you guys think?
 

[carusoam]

1) You have an O540…

2) it has a carburetor…

3) it has six cylinders…

4) show a pic of its intake system… because I’m not familiar with what Cessna put on their engines…

5) Expect that lean til rough, then enrichen… probably brings you back into the ROP mode…

6) Air distribution in six cylinder engines is greatly improved using curvy, equal length, tubes….

7) Fuel distribution in six cylinder engines is greatly improved using balanced fuel injectors…

8) EI’s MVP engine monitor is really nice… a really fine instrument to be using on an engine constructed to use the lean til rough method….

9) nice work detailing exactly what you did… it would be impossible to follow without the notes…

10) If you have a vernier style red knob… you can slow the leaning process down as you near the rough not rough zone….

11) To better understand what your hardware can do…. You would have to detail more about what you have…

 

Our EI guy around here is @oregon87 he may have better input regarding your engine and it’s controls….

PP thoughts only, not a mechanic… or Cessna pilot… 

Best regards,

-a-

 

[Chris B]

Not the best picture but you should be able to get an idea of their plumbing.

I am not looking to run LOP, I will be sticking to ROP.

I am just confused why I would see a clear peak and fall off of the EGT during one lean find attempt but another attempt the EGTs would climb and just remain flat. 

[carusoam]

Guess it depends on which cylinder you are watching…

If you include the FF and EGTs on one graph…  makes it a bit easier to follow…

you can watch how one or two  EGT are staying ROP and the others are varying with FF…

 

To measure the quality of fuel distribution… people use what is called the Gami spread…

Note the FF value at each cylinder’s peak EGT…

Then subtract the highest from the lowest…

 

You may find… EGT 2&4 are both staying flat through one exercise… it is hard to find a peak for these two…

 

What is the data capture rate set to on your MVP?  One data point per second? 
 

The graph shows lots of data… but sliding the data line over the area doesn’t stop on every zig of the graph…

clicking off 0.1gph at a time, let data collect… twist the red knob again for another .1gph, wait, twist, wait, twist, wait….

 

A close Gami spread… all peaks occur within 0.5gph….

a wide Gami spread… 1gph may not be enough to cover them all…

If there is a close grouping of five… and one odd ball….  This is when you talk to your mechanic about looking for an air leak….

 

keep in mind… all leaning experiments should be kept under 65%bhp… at 11gph you are probably in a good zone…

PP thoughts only…

Best regards,

-a-

[ArtVandelay]

The first time you came from high fuel flow down to 8, the 2nd time from 11 to 9. Not really apples to apples.

[Chris B]

I am not sure of the data collection speed.  I never changed it from its default.  I will take note of that on my next flight.  I will also do the gami spread and while I'm at it, the induction leak test and see if that shows anything interesting.

Here is an example of the lean attempt that has me stumped.  Top is odd cylinders and the bottom is even.   I am pretty sure at the low FF point (8.6gph) the engine was running very rough and that is why I starting coming back in with the FF.  Again, this is all very new to me but I would expect with a very rough running engine, the EGTs would fall off but maybe I am wrong with that expectation.

[carusoam]

Each cylinder is its own engine…  six small engines flying in tight formation….

Things get rougher as one cylinder produces less power than the others….

Things get noticeably rougher when a cylinder stops firing….

In the above graph….

All EGTs keep rising with the FF decrease… 

No peaks are being encountered…

EGT#2 is showing behavior unlike the other five….

 

 

The speed of which you turn the red knob will affect the data you are trying to understand…

It looks likes in 30 seconds you have run from rich to lean…. A change of about 3gph….

 

Leaving no time for the process to catch up to what you are doing….

 

This is typical of Aviation 101 type training where the student is taught to do a run-up as fast as possible…

Everything is in transition constantly… nothing stabilizes…

it will be even more difficult to find peaks because you blow through them faster than the thermocouples can heat up…

 

Watch how things work during the run-up…

While checking each magneto…. How many data points does your MVP collect?

Do you wait about 15 seconds for the graphs to stabilize at the new EGTs..?

Or do you just note the rpm drop and click the switch again….?

 

You are going to find that the MVP is not part of aviation 101…  it is much better than that.

Cylinder EGT stabilizes a few seconds slower than engine rpm…

 

The older standard of data collection used to be 6 seconds… 

At the rate FF is changing, EGTs stabilizing, data being collected…. It’s amazing the graphs are giving something recognizable….  

 

Start with the run-up… see how long it takes for the EGTs to stop rising after you turn one of the mags off….

 

The sheath protecting the TC’s wires takes time to heat up and cool down….   More of a heat transfer 101 kind of lesson….  
 

Soooo….  While you are learning Combustion science…. And digital instrumentation science…. You get to learn a bit about heat transfer on a small scale as well…

If you enjoy this stuff….   Go Mooney!  
 

Best regards,

-a-

[Chris B]

Thanks for your suggestions.  Next flight I will lean at a much slower pace and see what it looks like.

You mentioned EGT#2, not sure if its related or not but #2 CHT also runs significantly cooler than the rest.  It is up front so that might be expected but it has the oil cooler mounted in front of it.  #1 has a baffle in front of so it is blocked a bit also.

I did end up running down to the plan to check on the data capture rate.  It is currently set at 0.3 seconds.  This sure does seem like a pretty fast capture speed.  Should I change this?  If so, what would be recommended value be?

[carusoam]

2 hours ago, Chris B said:

Thanks for your suggestions.  Next flight I will lean at a much slower pace and see what it looks like.

You mentioned EGT#2, not sure if its related or not but #2 CHT also runs significantly cooler than the rest.  It is up front so that might be expected but it has the oil cooler mounted in front of it.  #1 has a baffle in front of so it is blocked a bit also.

I did end up running down to the plan to check on the data capture rate.  It is currently set at 0.3 seconds.  This sure does seem like a pretty fast capture speed.  Should I change this?  If so, what would be recommended value be?

data capture rate and onboard memory are related…

Older monitors would run out of memory after a few years, and drop the oldest files to replace with new…

It will happen faster with more data points per second…

If you are getting three data points each second… that is really good…. Compared to the 6 seconds per data point… more is better unless you run out of memory… 

To keep from running out of memory….and losing data… download the data and save it to a disk every couple of years… or have Savvy save it for you…. 

+1 for verifying what yours is actually set at… there isn’t a single perfect setting for all pilots….

it takes a few seconds for temps to stabilize with each change….

you don’t want to find out your data rate was too slow and missed the peak that you saw on the display…

 

The next fun thing to chase after…

With one cylinder not behaving the same….

EGT is the supply of heat…

baffling and other air seals are the source for cool…

CHTs are the result of EGT battling baffling…. 

 

If all the EGTs are nearly the same… and one CHT is higher or lower… it is probably a baffling issue for that cylinder… 

If one EGT is standing alone… it is often a blocked fuel injector or a leaky air intake tube…

 

Since you don’t have many fuel injectors in your carb… expect air leaks to be the source of different EGTs… 

 

The nice thing about fuel injectors… they are set up for one on each cylinder…. Delivering the same amount of fuel to each cylinder…

Varbs depend on statistics to randomly distribute the same fuel amongst all of the cylinders…. And this can change with the various levels of MP….mostly designed around one operating condition… (cruise or max power)

 

The really cool part….

Now you have awesome data to work with…

What to do with it next…

Since you already mastered sending the data to Savvy….

You can pay them a little more to have them compare your data to other planes and engines similar to yours….

This will point out issues like an alternator getting in the way of one cylinder’s cooling airflow…. 
you will learn if this is unique to your plane or if your whole cohort is suffering from the same malady…

 

Savvy has a whole bunch of interesting services both free and paid for…

It becomes really worth it when you are hunting down a tough engine challenge…

Once you have collected enough info about your engine… you have a year’s worth of info to compare against…

 

PP thoughts only, we have a really good Savvy guy around here….

Best regards,

-a-

[skykrawler]

Cyl 4, next to 2 is also 'different'.  I have seen more than one engine monitor with channels connected to the wrong cylinder.

 

[Chris B]

i have checked all the wiring and everything looks fine. 

i am leaning towards i have an induction leak somewhere between #2 and #4.  here is the EGT deltas between ~25 inches and ~15 inches.  visually i am not seeing and signs of a leak.  i haven't had time to do a pressure test yet.