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  #21  
Old 05-01-2019, 04:50 PM
Bavafa Bavafa is offline
 
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Quote:
Originally Posted by bkervaski View Post
So my takeaway is that if I want to run LOP with dual pmags I need to have something like the EIC32 to dynamically advance the timing in flight?
I know Carl and Brantel already responded and correctly noted.
Only to add that if you want to have the ability to change timing in flight, i.e. some thing similar to LOP switch, then you will need one of the EIC model.

Speaking from my own experience, I gained very little by switching timing dynamically with my IO360 driven plane.
With my new IO390 driven plane, I have installed the EIC but my main use of it is for safety/monitoring the health of PMAG rather change timing on a fly.
If you have room on your panel to install one, I do recommend it.
My feed back for PMAG, I have had a very positive experience and recommend it.
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  #22  
Old 05-01-2019, 04:54 PM
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M McGraw M McGraw is offline
 
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Quote:
Originally Posted by Bavafa View Post
Dan,
I am curious about the 28 BTDC at LOP (Advancing only by 8 degrees) and would this imply that if ROP, we can advance more and still safe but with LOP it will not be safe?
I know you are a very fact and data driven person, just curious about the data on this and possible cause of more advance at LOP (up high and below 60% power)


P.S. Curve A, providing the PMAG is set correctly will give about 9 degree advance.
Post #46 in the following thread will explain how I got to the advance numbers below:
http://www.vansairforce.com/communit...=N829MS&page=5

I have a bit of data on the IO390 both ROP and LOP. I basically started at 20BTDC @100ROP and worked slowly in one degree increments watching the CHT and KTAS. There becomes a point at which the speed no longer increases yet the CHT continues to increase meaning I’m not getting useful work out of the advance merely decreasing my detonation margin. The angle valve engine appears to be a bit more linear than the parallel valve engines meaning there is less advantage to high advance when LOP. I see some people post parallel advance numbers in the 30s and higher. That will not help you with a 390.

My ROP curve starts at 20BTDC for takeoff and advances to 23BTDC as the MP decreases. My LOP curve is at 28BTDC. In the data below I did a comparison of 100ROP and Peak at 23BTDC (that is what STD means). The rest of the data is +5 (28BTDC) for 25 to 175LOP. The engine had a slight miss at 200LOP so that data was eliminated. The range number is merely 50 gallons times NM/gal it is meant as a trend, if you use those numbers you will flameout eventually. What I did find, and is not represented in this data, was that at 150 and 175LOP I could increase the advance to 31BTDC without much increase in CHT, but not above 28BTDC between peak and 125LOP.

So, if I were using dual P-Mags the compromise of 20BTDC ROP and 28BTDC LOP would be my goal, unless there is a way to use 20, 23, and 28.

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Last edited by M McGraw : 05-01-2019 at 05:32 PM.
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  #23  
Old 05-01-2019, 05:58 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by M McGraw View Post
...
So, if I were using dual P-Mags the compromise of 20BTDC ROP and 28BTDC LOP would be my goal, unless there is a way to use 20, 23, and 28.

...
That is the beauty of the P-mags, they will advance from 20 to 28 (or more) automatically, depending on their configuration. No user input is required.
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RV-9 (Yes, it's a dragon tail)
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Last edited by N941WR : 05-01-2019 at 06:00 PM.
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  #24  
Old 05-01-2019, 05:58 PM
Bavafa Bavafa is offline
 
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Quote:
Originally Posted by M McGraw View Post
Post #46 in the following thread will explain how I got to the advance numbers below:
http://www.vansairforce.com/communit...=N829MS&page=5

I have a bit of data on the IO390 both ROP and LOP. I basically started at 20BTDC @100ROP and worked slowly in one degree increments watching the CHT and KTAS. There becomes a point at which the speed no longer increases yet the CHT continues to increase meaning Iím not getting useful work out of the advance merely decreasing my detonation margin. The angle valve engine appears to be a bit more linear than the parallel valve engines meaning there is less advantage to high advance when LOP. I see some people post parallel advance numbers in the 30s and higher. That will not help you with a 390.

My ROP curve starts at 20BTDC for takeoff and advances to 23BTDC as the MP decreases. My LOP curve is at 28BTDC. In the data below I did a comparison of 100ROP and Peak at 23BTDC (that is what STD means). The rest of the data is +5 (28BTDC) for 25 to 175LOP. The engine had a slight miss at 200LOP so that data was eliminated. The range number is merely 50 gallons times NM/gal it is meant as a trend, if you use those numbers you will flameout eventually. What I did find, and is not represented in this data, was that at 150 and 175LOP I could increase the advance to 31BTDC without much increase in CHT, but not above 28BTDC between peak and 125LOP.

So, if I were using dual P-Mags the compromise of 20BTDC ROP and 28BTDC LOP would be my goal, unless there is a way to use 20, 23, and 28.

Thank you Marvin for the info and the link. I went back and read all six pages, great info.

My own and very limited data jibes down with what you have indicated here for LOP. My average for the LOP is 170k at about 8.3G and this is what the standard A curve (max of 28BTDC)
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  #25  
Old 05-01-2019, 06:09 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by N941WR View Post
Dan, in the case of an angle valve, like the 390, you can set to start at 20* for takeoff and high power settings and when running LOP, low power, you can cap the advance at 28. That is standard P-mag operation. There is no need for a "LOP switch". The engine will run just fine at those settings.
Bill, I don't give a rat's butt about ignition brand, or how maps are switched. I only care about physical fact. Using the same timing for both LOP and ROP is a compromise.

The chart below is from Taylor's Internal Combustion...; I've added some notes and marked mixtures in familiar terms referenced to peak EGT. The specific values are from a standard research engine. They will not transfer to a Lycoming in absolute terms, but all the trends will be exactly the same. Physical fact, like gravity.

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  #26  
Old 05-01-2019, 06:43 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by M McGraw View Post
]
My ROP curve starts at 20BTDC for takeoff and advances to 23BTDC as the MP decreases. My LOP curve is at 28BTDC.
Marvin is flying a dual map system. So am I, but not the same brand.

Quote:
In the data below I did a comparison of 100ROP and Peak at 23BTDC (that is what STD means). The rest of the data is +5 (28BTDC) for 25 to 175LOP.
100 ROP vs Peak at 23 BTDC exactly matches what I'm seeing...about three knots in trade for a lot of fuel. Further LOP makes speed fall off rapidly without a lot of additional fuel savings, just like your data above.

Quote:
So, if I were using dual P-Mags the compromise of 20BTDC ROP and 28BTDC LOP would be my goal, unless there is a way to use 20, 23, and 28.
Which is what I was trying to add to the OP's list. He must decide on and understand a method of setting a max of 28...Emag software, jumper, EIC, clocking, whatever.
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Last edited by DanH : 05-01-2019 at 06:54 PM.
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  #27  
Old 05-01-2019, 07:03 PM
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rv6ejguy rv6ejguy is offline
 
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I'll second Dan's comment and thank him for the chart from Taylor.

Yes, you do need to tell the ignition whether you are ROP or LOP to optimize where PCP occurs. Can't be just MAP based since flame speed varies nearly 40% at the extreme ends of ignitable mixtures.

BTW, Marvin isn't running PMags in case some folks are not clear on that.

Thanks Marvin for posting your test results here after extensive repetitions. Most interesting.
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  #28  
Old 05-02-2019, 06:34 AM
BillL BillL is offline
 
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Quote:
Originally Posted by DanH View Post
Bill, I don't give a rat's butt about ignition brand, or how maps are switched. I only care about physical fact. Using the same timing for both LOP and ROP is a compromise.

The chart below is from Taylor's Internal Combustion...; I've added some notes and marked mixtures in familiar terms referenced to peak EGT. The specific values are from a standard research engine. They will not transfer to a Lycoming in absolute terms, but all the trends will be exactly the same. Physical fact, like gravity.
Dan, thanks for the time investment to show the fundamentals here. The angle valve will likely be more sensitive per degree. It is a fast burn combustion chamber (likely some swirl) that provides faster combustion (heat release) and, therefore, better SFC and power.

Dan/Marvin, are you finding that after at cruise and LOP, and under 8000 ft, that the timing can tolerate some advance? And a little speed increase? [yes, I am challenging the rule "timing advance under 8000ft provides no benefit"]
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  #29  
Old 05-02-2019, 07:44 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by N941WR View Post
That is the beauty of the P-mags, they will advance from 20 to 28 (or more) automatically, depending on their configuration. No user input is required.
Any EI with a manifold pressure sensor can advance automatically. That would be every EI currently available, unless we count the Briggs and Stratton Magnatron

A key goal in engine design is to require very little ignition advance, i.e faster combustion. For a given RPM, an engine which requires less advance to arrive at peak cylinder pressure in the 14 degrees ATDC ballpark is generating less pressure prior to TDC. Excessive pressure rise prior to TDC is a loss. In the case of the 390 (and probably the angle valve 360), that is exactly what is happening when 28 degree timing is combined with a fast burn ROP mixture selection.

Most folks in the airplane world have failed to note a great divergence. On one hand we have the LOP operating mantra promoted by GAMI/APS. It assumes fixed timing, typically magneto based. Going LOP with fixed timing pushes the point of peak pressure further after TDC. The result is lower CHT and a slight power loss. With a turbo, add another inch of MP to regain the power. With an NA engine, adding 100 RPM pretty much does the same.

On the other hand we have the mantra of LOP with ignition advance. The advance compensates for the slower combustion rate of the lean mixture (see the Taylor chart, previous post), returning peak pressure to a point closer to TDC. Early adopters tended to be the performance-at-any-cost type; Klaus would be a fair example with his hotrod EZs. As we've seen (refer to Nigel Speedy's recent data, for example), at altitude, the parallel valve engines respond to more and more advance with more and more speed, and no one seems to have found an absolute performance limit (the practical limit is CHT rise). The practical result was a trend toward more advance being incorporated into electronic ignitions.

Among consumers, the resulting CHT increases during ROP climb have become synonymous with EI, when in fact it is not EI, but the advance schedule dialed into that EI. It is entirely possible to run an EI with fixed timing, just like the GAMI/APS case. Or, one may select an EI with dual maps, and select less advance for ROP climb. Note the engine control computer in your automobile shifts the advance map in lockstep with fuel mixture; it's invisible to the operator.

Both LOP mantras run cleaner, i.e fewer engine deposits and lower fuel burn. The GAMI approach (delayed peak pressure) results in lower cylinder pressures, i.e. less mechanical stress and lower CHT. The more advance method is equally clean and generally results in higher power at upper altitudes, at the expense of higher CHT.
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  #30  
Old 05-02-2019, 07:45 AM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by DanH View Post
Bill, I don't give a rat's butt about ignition brand, or how maps are switched. I only care about physical fact. Using the same timing for both LOP and ROP is a compromise.

The chart below is from Taylor's Internal Combustion...; I've added some notes and marked mixtures in familiar terms referenced to peak EGT. The specific values are from a standard research engine. They will not transfer to a Lycoming in absolute terms, but all the trends will be exactly the same. Physical fact, like gravity.

Dan,

That is good information but my point is, the P-mags work just fine for LOP operation without an added switch or timing point.

For what I suspect is the majority of pilots, the existing timing method (adjusted for different engines, as previously discussed in other threads) works very well.
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