BMP, engine mismanagement or not?

[N427EF]

The expressed concern is a rapid increase of piston diameter without time for a matching increase in cylinder diameter, with cylinder/piston scuffing as a result.

Precisely my concern after reading the ECI report.
Just to be sure, no one is advocating a slow BMP. It's either a BMP or traditional gradual leaning staying on the rich side for climb and once level in cruise at around 65% power again gradually leaning over to LOP.
I was doing my BMP at 1500 feet with 85% power and CHTs in the 320 and dropping after the BMP but as I pointed out EGTs rise instantly and this is consistent with the concern expressed in the ECI report.
No one says EGTs of 1400 degrees is a bad thing but going from 1180 to 1400
in less than 2 seconds is maybe what worries me a bit.

[stu517]

The kings of LOP are the APS folks in Ada, OK. The only issues in the old world about running LOP was that the fuel injectors might have been mismatched and the pilot thinking he was lean was actually slightly ROP.

I have always run my engines LOP and not only does it generally extend the life between overhauls. As in this thread the naysayers say "i heard from a friend" etc but never show any scientific proof to back what they are saying.

Net net if you have the time hit up George Braly or Walter Atkinson in person or take one of their online courses. Please do not propagate the anti-LOP nonsense

[sailvi767]

I don't think this is a anti LOP thread. The discussion is about the BMP as a method to get there.

George

[N427EF]

I don't think this is a anti LOP thread. The discussion is about the BMP as a method to get there.

It is most definitely not a LOP thread, been doing that for years.

It is specifically about a BMP at take off power, 85% or so.

[zav6a]

The theory of heat flash causing near siezure as suggested by the ECI paper is interesting but it would seem to me that we would have far more broken engines as evidence if it were that simple.

I can come up with circustances that are far more aggravating and common than BMP when it comes to abruptly increasing heat flux to the piston with a relatively cold cylinder. Advancing the throttle on take off, advancing the throttle after a long throttle off descent in cold air, and for that matter, the normal Lycoming-recommended leaning procedure.

It would seem that the APS folks woould have seen something amiss in the thousands of pulls they have done ona highly instrumented and inspected engine.

[N427EF]

http://www.sportaviationonline.org/s...n/201210/#pg30

I should have posted it sooner. it's what this thread is all about.

[sailvi767]

I have read the APS pages and think its great info. I have not however noted any information on non boosted 360's. I think there could be significant differences between boosted and non boosted engines as well as items on individual engines such as piston squirters when looking at heat transfer. I would love to see some data on a stock io360 trying these techniques on a test stand. For the moment the ECI experience is all I have found.

George

[DanH]

Originally Posted by N427EF

It is specifically about a BMP at take off power, 85% or so.

Let's note that the 25"/2200 data dump in the first post is 65~70% for an IO540, not 85%. For an IO-360 angle valve it would be about 65%. There is nothing about that chart to suggest all is well at 85%.

I bring up the IO-360 because it is the only engine for which we seem to have some actual detonation data. The one scenario which might swell a piston very rapidly is detonation; heat transfer to the combustion chamber surfaces spikes upward instantly when the boundary layer gets blown away.

The ECI bulletin says they were doing a mixture pull for a detonation test at a "rich cruise power setting", but they don't tell us the actual MP and RPM. They also say they didn't record evidence of detonation. As such, I will not claim detonation was the root of their problem....but I will point out it could become your problem.

This is an IO-360 chart for 2200 RPM and a whopping 28.8" MP. The power line says 140, about 70%. In mixture sweep from bog rich to very lean, there is only the slightest hint of detonation:



However, a BMP at 2400 RPM and 28.8 could be risky. Look close at the detonation zone, then look close at the EGT values. Pulling to 50 LOP at this power setting would leave you parked within the detonation zone (about the 56 lbs/hr point at the bottom of the chart). This is about 87% power:



To be realistic, not many of us will set 5 notches oversquare at sea level WOT and do a Big Mixture Pull. However, you might be inclined to do one at a manifold pressure typical for having climbed clear of the pattern, 27" and 2700.....and you would be fine, at about 92% power:



Here's the point(s).....

Percent power is a lousy way to express do and don't ops.

That said, you can probably do a BMP at any setting below 65%, and 70% doesn't look unreasonable based on the data available. When in doubt, higher power settings should probably be undersquare for a BMP. Yeah, I know what they say about running the big Continentals, which brings us to....

The above charts are for a specific engine. I can't prove it, but I am perfectly wiling to assume that nothing specific transfers to another engine model or brand.

The manufacturers are entirely capable of supplying the raw data we need to make educated decisions, but they won't do it. Neither does APS, who only gives us the red box.

The 2400/28.8 chart nicely illustrates that you may not be able to pull lean enough to avoid a problem at some power settings. At the same time it illustrates why you want to pull through the near-peak and peak zone as quickly as you can if you've selected a pro-detonation MP/RPM combination. Dawdling in that detonation zone at some higher percentage power setting may be bad for your pistons.

And one last thing.....if you have plenty of cooling, why bother reducing RPM, doing a BMP, and climbing LOP? You're way back on HP, so the climb takes a lot longer. Sure, fuel flow is less, but total fuel used isn't very different. The full power, mixture for best power climb gets you pushed over in cruise sooner and further on toward the destination in less time. Want to save fuel? The data above says if you must do a BMP it is better to keep RPM up. Look at the 27/2700 chart. A BMP to 50 LOP reduces fuel flow to 61 lbs/hr from nearly 85 lbs/hr at 150 ROP with a loss of only 12 horsepower. You save fuel and keep most of the climb rate.

[N427EF]

I think I have the answer I was looking for based on your charts and
elaborate details in the previous post.

I should have been more precise about what part of my chart I wanted opinions on but just to be sure it was the take off part with 83% power,2400 RPM and 28.00 MAP is where I did a BMP. Unfortunately the chart looses interactive properties by posting a snap shot and I failed to position the vertical yellow line in the right place.
Here it is ther same chart one more time, cropped to show the important part as well as the precise numbers at the time of the BMP.
Probably best to save the BMP for cruise settings.

[RV10inOz]

Doing the Big Mixture Pull is all about getting from the full rich zone, over to a LOP setting of some sort, without spending large amounts of time in a detonation possible zone. This is not as much a problem on a NA engine as it is a TC or TN engine.

LOP climbs do work in both NA and TC/TN engines however, they really are only of significant benefit in a turbocharged engine. The problem is those who do not have a good understanding of what they are doing can make a mess of LOP climbs on turbocharged engines and for that reason alone, George, Walter and John do not actively promote them outside their APS live course....simply because if you do them wrong, you will shorten the life of your engine.

For all the NA engines, mostly the sort in RV's there is little value in doing LOP climbs, the time and distance flown Vs fuel use is negligible and not worth it. So in short, while you can do them, don't bother.

The best practice for all NA climbs is to ensure correct fuel flow at sea level ISA (HP rating / 10) in USGPH, take note of EGT going through 700-1000 AMSL, and every couple of thousand lean back to that target EGT. If climbing beyond 10,000 you may want to chase the extra few ponies and less fuel flow and climb around 75f ROP and this will give you the best climb performance and clean up those cylinders a bit.

I did a bunch of climb tests a little while back for George's interest, and took video and with the full data set, it was absolute proof that the best method of any, and I did them all, was the Target EGT method. Time to climb, distance to climb, CHT's everything was in your favour. Doing full rich to 5000, or 25/2500 or LOP did nothing good.

Ernst, I noticed you were worried about high EGT's...... mate that is not a worry at all, no such problem, except for TIT, but you knew that all along

The ECi article

That article is brimming with pony pooh! Rapid leaning.....cylinder rapidly heating..... no data as to what they did, or what they found, just the creation of some more urban myths and old wives tales. If that were real, automotive engines would be failing all over the place.

Rapid leaning as per a BMP could not heat the piston like that anyway, and in fact on a turbo engine the very reason for doing a BMP is to avoid the Peak Pressure climbing high and close to TDC.....that is the whole point.

If any of you have been to the Carl Goulet Memorial Engine Test Facility, and seen these things done on several engine types, Lycoming and TCM, you would quickly understand that this ECi article is someones poor explanation for a failure they did not understand, or wanted to cover up. In which case why would they print it?

It is interesting to note that the OWT's and rubbish from TCM and Lycoming seemed to start appearing at a great rate of knots after the departure of folk like Carl Goulet. I am sure this is not a coincidence.

By the way, those of you who have ever considered taking the APS course, I see that for this week only (up to Friday 23rd) John Deakin will give you a $100 credit if you do the fun test and then choose to take the online course. This new fun test is aimed at getting people to recognise they do not know what they don't know, and is a great way to have a :toe dipped in the water".

Can I suggest that when you create a user name to do the fun test, use your name followed by VAF, to show that your VAF community as in different to all the others. Mr Deakin is always interested to know where folk come from and the info is not of any other use.

I might start a whole new thread for this....... It is a great offer!