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  #1  
Old 11-12-2012, 06:41 PM
N427EF N427EF is offline
 
Join Date: Oct 2005
Posts: 1,564
Default BMP, engine mismanagement or not?

With so much talk about the Big Mixture Pull,"BMP" and experts like Mike Bush,
as well as the good folks from APS advocating this kind of engine operating procedure, I decided to try out this old and now newly discovered engine management technique.
The gragh shows a one hour flight where I did everything I was tought not to do.
Based on what Mike Bush explains in the latest SA article I tried the following:
Full throttle, reduce RPM only "oversquare", BMP on climb out "1500 feet"
Climb out well lean of peak with Cylinder Head temperatures well below 380.
Mine dropped to less than 300 F but EGTs where much higher than on the rich side of peak. Fuel flow was about 5 GPH less than on the rich side of peak. The GAMI spread as calculated by the EG view software shows 0.00GPH
on this flight. All was done on mogasE10 which I have been using for almost a year now and avgas in the left tank only for take off and landing.
Looking at the numbers, I can't see anything wrong with my new technique.
High MP and low RPMs contribute to a much more quiet cockpit environment
and less friction loss apparently. The fuel savings are obvious and although my engine does not suffer from high temperatures of any kind, lower CHTs are even better.
Flame suit on,what do you think?

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Ernst Freitag
RV-8 finished (sold)
RV-10 IO-540 8.5:1
Running on 91 Octane E10 mogas since 2011
Don't believe everything you know.
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  #2  
Old 11-12-2012, 07:25 PM
airguy's Avatar
airguy airguy is offline
 
Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,590
Default

I haven't brought myself to do the BMP early and climb WOTLOP yet, but that's usually because I'm in a hurry (always, it seems) and want full power for climb and keep it rich enough to keep it cool, then pull it as soon as I level out.

Logically I know it would only cost me a couple minutes of additional flight time and save a fair bit of fuel by climbing LOP, I just don't do it. In an RV where climb airspeed is 100+ it makes more sense because you can keep the engine cool easily - but in my 172 (until I get my 9A flying!) that's not an option and I'm just scared of cooking a cylinder - so I continue to throw fuel at the problem.
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Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #3  
Old 11-12-2012, 09:57 PM
N15JB N15JB is offline
 
Join Date: May 2010
Location: Denver
Posts: 566
Default

Ernst, welcome to the LOP club. I have been doing this for 2+ years, with the blessing of Allan Barrett once I passed the 25 hour mark. I pull the plugs and borescope every cylinder with each oil change @ 25 hr interval. Did I mention that I am compulsive? Plugs, valves and pistons all look great. My home field elevation is 5800' so I am below 75% power almost as soon as I get off the ground, but I follow the same procedure when operating out of sea level fields. All of this was preceeded by 2 rounds of balancing my AFP injectors. and I routinely cruise at 10.9 GPH and WOT. When I first started running LOP I would do a slow pull, and it scared me to see CHT's climbing. Now I make the Big Pull in 2-3 seconds till I see 10.9 GPH fuel flow and leave it there.

Jim Berry
RV-10
Barrett XIO-540
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  #4  
Old 11-12-2012, 10:46 PM
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DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 10,345
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Looks like 25" and 2250 RPM, LOP. Have your Lycoming O-540 power chart handy? I think you'll find this MP and RPM setting is on the safe side of the "Limiting Manifold Pressure For Continuous Operation" line. Factory approved, so to speak.

The chart assumes best power mixture, so LOP isn't a detonation concern on 100LL. The mogas is a wildcard. For sure lower octane means less detonation margin, but your CHT lines suggest you have enough.
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Last edited by DanH : 11-16-2012 at 05:47 AM.
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  #5  
Old 11-13-2012, 07:42 AM
Wayne Gillispie Wayne Gillispie is offline
 
Join Date: Apr 2009
Location: USA
Posts: 1,499
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I have tried LOP climbs at gross weight in the summer and preferred getting to 10,500-13,500 where we can get some air conditioning going sooner. I may try it again with winter flying and better engine/wing/prop performance.
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  #6  
Old 11-13-2012, 07:56 AM
sailvi767 sailvi767 is offline
 
Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,388
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I considered trying the BMP. I talked with the guys at ECI and they did a BMP with a engine in the test stand. On one attempt the engine experienced a immediate problem and had extensive damaged. They attributed it to the BMP and don't recommend it for ECI engines.

George
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  #7  
Old 11-13-2012, 08:34 AM
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Ironflight Ironflight is offline
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Join Date: Jan 2005
Location: Dayton, NV
Posts: 12,829
Default

Quote:
Originally Posted by sailvi767 View Post
I considered trying the BMP. I talked with the guys at ECI and they did a BMP with a engine in the test stand. On one attempt the engine experienced a immediate problem and had extensive damaged. They attributed it to the BMP and don't recommend it for ECI engines.

George
At what power setting were they operating? 100% ? 75% ? 65% ? Without that info, this is anecdotal and means absolutely nothing - no conclusions can be drawn from the presented statement.
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  #8  
Old 11-13-2012, 08:48 AM
N427EF N427EF is offline
 
Join Date: Oct 2005
Posts: 1,564
Default

Thank you for the feed back.
I wish you could tell us more about this test stand damage.
Unfortunately it is this kind of information that rests in the back of my mind
and casts doubt on the BMP.
With precise details available to the pilot through advanced engine monitors
I am certain I would be able to spot a detonation event. Certainly CHTs anywhere near 380F would keep me from doing a BMP.


Quote:
I considered trying the BMP. I talked with the guys at ECI and they did a BMP with a engine in the test stand. On one attempt the engine experienced a immediate problem and had extensive damaged. They attributed it to the BMP and don't recommend it for ECI engines.
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Ernst Freitag
RV-8 finished (sold)
RV-10 IO-540 8.5:1
Running on 91 Octane E10 mogas since 2011
Don't believe everything you know.
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  #9  
Old 11-13-2012, 08:58 AM
zav6a zav6a is offline
 
Join Date: Dec 2005
Location: Sedalia, Colorado (KAPA)
Posts: 320
Default Jim

Jim B

Also hanger at KAPA. I will peek in to see your borescope image the next time I see your cowl off.

I do the 4 cylinder version of the big pull consistantly at 7500 feet - about the time takeoff/airport environment workload is dropping off. In my case, I pull to 6.8 gph on my little 320 (with AFP) after slowing the prop to 2500, and can typically leave the mixture alone all the way up to 12,500. It inches closer to peak EGT with the climb but stays at least 15 LOP.

Works at lower altitude too. Get off the ground about 1000 feet ROP, set prop to 2500, throttle manifold to 75%, pull the fuel flow to 6.8 and like clockwork - 50 LOP. Makes mixture management easy. Really cold to really hot weather only seems to make a 0.2 gph difference either way. I think AFP compensates for altitude density to some degree.

As a proportion of rated horsepower, I should be pulling to 6.7 gph, (10.9*160/260) so we are really close.

I put in 9:1 pistons about 700 hours ago. No issures.
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  #10  
Old 11-13-2012, 09:00 AM
zav6a zav6a is offline
 
Join Date: Dec 2005
Location: Sedalia, Colorado (KAPA)
Posts: 320
Default Little BMP

Jim B

Also hanger at KAPA. I will peek in to see your borescope image the next time I see your cowl off.

I do the 4 cylinder version of the big pull consistantly at 7500 feet - about the time takeoff/airport environment workload is dropping off. In my case, I pull to 6.8 gph on my little 320 (with AFP) after slowing the prop to 2500, and can typically leave the mixture alone all the way up to 12,500. It inches closer to peak EGT with the climb but stays at least 15 LOP.

Works at lower altitude too. Get off the ground about 1000 feet ROP, set prop to 2500, throttle manifold to 75%, pull the fuel flow to 6.8 and like clockwork - 50 LOP. Makes mixture management easy. Really cold to really hot weather only seems to make a 0.2 gph difference either way. I think AFP compensates for altitude density to some degree.

As a proportion of rated horsepower, I should be pulling to 6.7 gph, (10.9*160/260) so we are really close.

I put in 9:1 pistons about 700 hours ago. No issures.
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