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11-13-2012, 11:19 AM
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Join Date: May 2010
Location: Denver
Posts: 564
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Duane,
I will need to do an oil change in about 5 more hours, which may be delayed by my wife's knee replacement next week. Should have a new dental scope by then, so the screen resolution will be improved. I have the 9:1 pistons and roller cam in my XIO-540. See you soon.
Jim Berry
RV-10
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11-13-2012, 01:32 PM
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Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,167
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Quote:
Originally Posted by Ironflight
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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I wish I had the data you mention however I don't have access to the actual conditions. Here is a link to the ECI service bulletin. It is certainly not definitive however it was enough to keep me from trying the technique.
http://www.eci.aero/pdf/93-6-7.pdf
George
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11-13-2012, 02:51 PM
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Join Date: Dec 2009
Location: Boulder, CO
Posts: 4,435
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Quote:
Originally Posted by N15JB
....Now I make the Big Pull in 2-3 seconds till I see 10.9 GPH fuel flow and leave it there.
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This is entirely consistent with my experience with a carbureted Continental O-470 in my Cessna 180, flying out of Longmont. Except that for this slightly smaller engine, the fuel flow is slightly lower, pretty much in proportion to the displacement.
The only thing worth adding is that if I fly much richer than that the valves start to stick on start-up. The engine is happier relatively lean than relatively rich, especially at low power.
Dave
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11-13-2012, 04:14 PM
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Join Date: Oct 2005
Posts: 1,516
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ECI report
The ECI report is quite sobering, especially in light of the fact they were not able to detect a detonation event on their sophisticated engine monitoring equipment.
There is no doubt, EGT's rise rapidly during a BMP and may cause damage.
I also know of other anecdotal reports coming from engine overhaul shops
who claim to know what kind of engine monitoring equipment is installed just by looking at the cylinders and pistons. That being evidence of rapid heating and cooling events due to using fuel flow information to lean engines.
I was under the impression that I was able see what is going on inside the cylinders by closely monitoring temperatures but the ECI report shoots that idea full of holes.
__________________
Ernst Freitag
RV-8 finished (sold)
RV-10 Flyer 600 plus hours
Running on E10 mogas
Don't believe everything you know.
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11-13-2012, 04:36 PM
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Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,167
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I have read everything I can find on how to lean and run a piston engine since prior to buying my RV6 I had limited as in no experience with piston aircraft engines. There is a lot of conflicting information out there. One of the things that may contribute to those conflicts is lumping turbo or supercharged engines in with regular engines. Much of the data is geared toward the turbo 540's. It may well be that there is a significant difference in how the cylinders and pistons cool and heat up in a boosted verses a non boosted engine. Perhaps someone with more experience can comment on that. That could mean that a BMP is fine on a boosted engine but not so fine on a non boosted engine.
George
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11-13-2012, 05:35 PM
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Join Date: Aug 2006
Location: santa barbara, CA
Posts: 1,682
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The ECI document is a Service Instruction from 1993. Engine monitors have come a long way since then and LOP operations, including the big mixture pull, are pretty much mainstream operational procedures, especially in our experimental world. This all seems like a bunch of hooey. BMP has worked fine for me.
erich
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11-13-2012, 06:35 PM
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Join Date: Nov 2005
Location: San Francisco, CA
Posts: 525
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Nice catch on the 1993. There is little hard data in the ECI report, so it is hard to take it too seriously. However, I can see the potential risk of shock cooling by mixture alone. Normally, i think of shock cooling by rapid throttle movement, but the mixture control could do the same effective thing.
In an extreme case, you could go from a high power setting to mixture cut-off and that would certainly be a bad thing to do.
I will probalby tweak my takeoff to climb procedure a bit given the above to minimize any risk of cooling the engine too rapidly.
__________________
#40533 RV-10 Builder and CFI
1/2006 Started build
10/19/2011 First flight
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11-13-2012, 06:36 PM
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Join Date: Nov 2005
Posts: 121
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LOP lowers CHT
Quote:
Originally Posted by N427EF
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.
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Having flown over 1000 hours in the Lean Of Peak (LOP) world, CHT's of 380 while rich of peak (ROP) would actually come down quite nicely LOP. I would be more worried about detonation with CHT's 380 ROP than CHT's 380 and LOP... but at 65% I usually saw highest CHT's around 360-350 LOP.
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11-13-2012, 09:52 PM
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Join Date: Aug 2006
Location: santa barbara, CA
Posts: 1,682
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I went to the trouble of emailing Mike Busch and asking his opinion on the the ECI rapid leaning service instruction cited in a previous post. For those who value his opinion, here was his reply:
"Personally, I think the ECi SI is misguided. Whoever wrote it equated rapid leaning with rapid CHT change. Rapid CHT change is not a good thing, but a properly executed "big mixture pull" going from quite ROP to quite LOP will not result in a rapid CHT change and will not hurt anything. (Doing the BMP slowly will definitely hurt things.) If doing a rapid BMP was harmful, explain to me why my engines are both at 200%+ of TBO and 9 of my 12 cylinders are at 4700 hours total time in service."
Makes sense to me. I certainly don't see rapid drops in CHTs when doing the big pull.
Erich
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11-14-2012, 03:40 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by erich weaver
"Personally, I think the ECi SI is misguided. Whoever wrote it equated rapid leaning with rapid CHT change. Rapid CHT change is not a good thing, but a properly executed "big mixture pull" going from quite ROP to quite LOP will not result in a rapid CHT change and will not hurt anything. (Doing the BMP slowly will definitely hurt things.)"
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I too think the SI is misguided on several fronts. However, in fairness, nowhere does the SI equate rapid leaning with rapid CHT change. 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.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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