Thinking about dual pmags ...

I was just thinking about installing dual pmags, not sure I'm going to do it, just a thought exercise. If I have to pull my slicks for one of the SBs I'll likely consider it. I wanted to install them during the build but it was one of those things I didn't know much about.

This is an RV-14A with an IO-390, dual slicks.

I have spare breakers already installed in my panel I can use.

Using the ACS-510 key switch.

Just to make sure I have my head around the project if I do it:

1. I'll need a 3-way splitter for my MAP sensor tube, one to the Vans MAP sensor, one to each pmag.

2. I'll need to remove the jumper from the ACS-510 switch.

3. I'll need to provide 12v to each pmag via a 5 amp breaker.

4. I'll need the drive gear and different length studs since my left slick has an impulse coupler.

Doesn't seem terribly painful. Am I missing anything? Any other suggestions/thoughts welcome.

A few years back, I went from dual slicks to 1 & 1...a slick and a pmag.

~400 flawless hours later, it was time to make a decision on the remaining slick which was starting to show some age...IRAN or upgrade to a 2nd pmag?

Based on the perfect service from the pmag, it was an easy decision to jump to the upgrade.

Your list looks pretty complete, you?ll be able to use the existing Mag L/R switches you have to control the respective Pmag.

You might consider swapping the breaker out for a switch/breaker instead...there needs to be a way of shutting off 12v power to each Pmag to check the internal alternator before flight, and I?ve been taught that circuit breakers should?t be used for switches.

Good upgrade, as the magneto while reliable...has it?s share of issues and problems to overcome.

Rob

Ps-I got a nice 3 way brass tee at the aviation division of the local hardware store...NOT a box store! Also, couldn?t find brass at auto parts places either-just plastic. Look for one in 1/8? sizing...

You?ll be able to use the existing Mag L/R switches you have to control the respective Pmag.

Click to expand...

You might consider swapping the breaker out for a switch/breaker instead...there needs to be a way of shutting off 12v power to each Pmag to check the internal alternator before flight, and I?ve been taught that circuit breakers should?t be used for switches.

Click to expand...

Thanks for the vote of confidence! So using the mag L/R switches won't turn off the pmags for the check?

bkervaski said:

Thanks for the vote of confidence! So using the mag L/R switches won't turn off the pmags for the check?

Click to expand...

Yes, they will.

But what you want to check is (with the MAG “ON”) is turning 12v power to the mag “OFF” to make sure it runs on its internal alternator.

So the MAG switches control the spark, the switch breaker controls the 12v power to the mag from airplane power...

Edited to add: Read page 22 of the Install manual under “P Model Alternator Check” and correct page number.

What you have with the CB’s will work...but I just don’t like the idea of pulling a CB each time then resetting it. CB’s weren’t designed to have as active a life as a switch and I used a couple of these in 3 amp in lieu of a pure CB:

https://www.aircraftspruce.com/catalog/elpages/pbcircuitbrkr2.php

Studs

You will likely need to replace the Mag studs with shorter studs on the accessory case.

So the MAG switches control the spark, the switch breaker controls the 12v power to the mag from airplane power...

Click to expand...

Ahh. Makes perfect sense now, glad I made the post. Thank you!

You have a 390 angle valve, so decide on some method of holding max timing to 28 BTDC when LOP. That would be too much when ROP, but P-mags don't have an option to switch timing maps. Bill might have a way to do it with an EIC.

DanH said:

You have a 390 angle valve, so decide on some method of holding max timing to 28 BTDC when LOP. That would be too much when ROP, but P-mags don't have an option to switch timing maps. Bill might have a way to do it with an EIC.

Click to expand...

The new VAF advertiser ?Engine Bridge? guys have an intriguing product out there as well, similar functions to the EIC...

DanH said:

You have a 390 angle valve, so decide on some method of holding max timing to 28 BTDC when LOP. That would be too much when ROP, but P-mags don't have an option to switch timing maps. Bill might have a way to do it with an EIC.

Click to expand...

Per Lycoming's recommendation, we set our dual P-mags to 5 degrees after top dead center to allow the p-mags to fire at the Lycoming recommended 20 degrees before top dead center. I think I said that right.

DanH said:

You have a 390 angle valve, so decide on some method of holding max timing to 28 BTDC when LOP. That would be too much when ROP, but P-mags don't have an option to switch timing maps. Bill might have a way to do it with an EIC.

Click to expand...

Given my dissimilar, almost simultaneous issues on both early build pMags (latest firmware though) and although they didn't quit working - having a monitoring system became a must have for me. I installed Bill R's EIC32 and so far, it gives me warm fuzzies being able to visually monitor the timing and other parameters of each pMag.

DanH said:

You have a 390 angle valve, so decide on some method of holding max timing to 28 BTDC when LOP. That would be too much when ROP, but P-mags don't have an option to switch timing maps. Bill might have a way to do it with an EIC.

Click to expand...

With the either the original EIC or our new EIC32 there is no need for a LOP switch, similar to what you find on other ignitions.

I manage this by capping the max advance at 28 and starting it at 20, to match the manufacture's recommendation. To do this, you must change the configuration of the P-mags, not just "clock" them. There are multiple ways to do this, of course our preferred method is to use the EICommander.

See THIS thread on timing your P-mags.

The new EIC32 is your best bet as it is our growth path and will include some new features in the future.

N941WR said:

With the either the original EIC or our new EIC32 there is no need for a LOP switch, similar to what you find on other ignitions.

Click to expand...

Time out.

With an EIC, how do you do an switch from a max 28 map (LOP) to some lesser max advance for ROP operations? Walk us through the buttonology please.

DanH said:

Time out.

With an EIC, how do you do an switch from a max 28 map (LOP) to some lesser max advance for ROP operations? Walk us through the buttonology please.

Click to expand...

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. In fact that is really close to what we recommend for a P-mag configuration.

Note: Different settings for a parallel valve engine or an engine with high compression pistons.

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?

bkervaski said:

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?

Click to expand...

No.

Follow the pMag install instructions. Set timing with the crank at 5 degrees ATDC for your IO-390 and install the pMag jumper. This will yield a max power timing of 20 degrees BTDC (just like your mags) and a low MP (high altitude) max timing of 30 degrees. This 10 degree advance is what I want for my operations. If you really want a max of 28 degrees of advance then you can use the EIC unit to cap it at 28. This is done on the ground.

My recommendation, just follow the pMag install instructions and fly on. I have 800+ hours running the standard 10 degrees of advance (25-35 degrees for my 180hp engines) and find it to be a good set up. The RV-14 I helped with also runs the standard 20-30 degrees of advance. I’ve flown it and tracked the engine parameters, full power to high LOP ops. The engine is very happy.

Carl

bkervaski said:

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?

Click to expand...

No.........

Read my post linked above on explaining how the P-mags work or give me a call, my number is in your PM's.

You can run LOP with almost any timing setting. Heck, certified aircraft do it with fixed timed magnetos.

In the case of the P-mags, I can run up to 100 degrees LOP with my carburetor and dual P-mags.

DanH said:

You have a 390 angle valve, so decide on some method of holding max timing to 28 BTDC when LOP. That would be too much when ROP, but P-mags don't have an option to switch timing maps. Bill might have a way to do it with an EIC.

Click to expand...

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.

Emags will work fine lean of peak all by themselves. With your IO-390, you?ll need to manage the curve (jumper out) with either the EICAD program, free from Emagair, the EICommander from Bill, or the Engine Bridge controller using your iPhone or iPad (enginebridge.com). I think Bills EIC, and Enginebridge allow you to adjust things on the fly, the EICAD program does not, at least that?s what I think...... I am running dual Pmags with the jumper in on my IO-360, and I?ve set timing at 1.6* AFTER top dead center for starting, which slides the whole curve 1.6*, so I get 25* at full power (vs 26.6*), and ~33.5* at full advance (<22? MAP). I can lean until it quits, and it doesn?t get rough - and the CHT?s stay cool. I don?t see any issues here. If you want to go faster, push the red knob forward, if not, pull it back a ways.

Jumper in (curve A) gives you 26.6* advance in high power settings - 25? or more MAP - and about 35* advance below 22? MAP (up high). The ?B? curve is much more aggressive, but the one you use if you want to manage it (jumper out). Unmanaged, it would probably only be appropriate for a very low compression A-65, or a lawn mower engine in your airplane, so if you are leaving the jumper out in your RV, you will probably want to use one of the 3 previously mentioned programming options. I think Brad at Emagair designed this ignition system to allow an improved variable ignition system that doesn?t require the operator to burden him/herself with ignition management inflight. Engine Bridge allows you to program up to 10 different timing curves that you can select via Bluetooth on you iPhone for the situation you find yourself in. For instance, lets say you are taking off from a hot, high altitude airport. Select the ignition profile you have set up for that situation. Then you are flying enroute at high altitude and want to run the most optimum LOP profile, so you select that curve that you have previously programmed - via your iPhone. Then you get to your destination in Mississippi and are expecting a possible low altitude go around because of weather and you select a profile you have programmed that optimizes that type of low altitude operation. Don?t ask me what differences in timing that these situations would require are, but someone probably has an idea about what would be better in certain situations.....

Me - personally, I was just looking for a better, more efficient ignition system than Slick mags to operate my stone age engine. As long as it runs smooth, burns gas as efficiently as possible (for such an archaic converter of energy), and doesn?t require as much maintenance - I?m in. And that?s why I have 2 Pmags.

Bavafa said:

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.

Click to expand...

Actually the red zone is mostly on the ROP side.

bkervaski said:

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?

Click to expand...

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.

Bavafa said:

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.

Click to expand...

Post #46 in the following thread will explain how I got to the advance numbers below:
http://www.vansairforce.com/community/showthread.php?t=150828&highlight=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.

M McGraw said:

...
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.

...

Click to expand...

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.

M McGraw said:

Post #46 in the following thread will explain how I got to the advance numbers below:
http://www.vansairforce.com/community/showthread.php?t=150828&highlight=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.

Click to expand...

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)

N941WR said:

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.

Click to expand...

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.

M McGraw said:

]
My ROP curve starts at 20BTDC for takeoff and advances to 23BTDC as the MP decreases. My LOP curve is at 28BTDC.

Click to expand...

Marvin is flying a dual map system. So am I, but not the same brand.

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.

Click to expand...

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.

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.

Click to expand...

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.

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.

DanH said:

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.

Click to expand...

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"]

N941WR said:

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.

Click to expand...

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.

DanH said:

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.

Click to expand...

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.

BillL said:

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"]

Click to expand...

Bill, it's a good question, and I don't know the answer (see below). In theory, I think overall advance response should be similar down low.

I've been mostly exploring response to mixture with fixed timing, as the lower CHT dovetails with my low cooling mass flow approach to drag. My advanced map results match Marvin's, except I can't get as way far LOP with constant flow injection; he has electronic injection. I generally don't run an advanced map in anything other than cruise, and I generally cruise above 8000, where it's all more efficient.

N941WR said:

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.

Click to expand...

Sure, it works fine for LOP. I just spent 20 minutes writing exactly that.

The issue is running hotter in climb at best power mixture. Personally, I see little logic in buying a 390, and then CHT-limiting climb performance.

DanH said:

SNIP

The issue is running hotter in climb at best power mixture. Personally, I see little logic in buying a 390, and then CHT-limiting climb performance.

Click to expand...

Dan,

As always your logic is spot on, but perhaps not an overriding factor for how many of us fly.

Flying an RV-14A, IO-390 with dual pMags set at 20 degrees BTDC with the jumper in (10 degrees of advance) I note CHTs max out at 380 degrees or so during a hard climb (coming down after 4K? or so depending on how you lean), and cruise CHTs in the 350 range. On a 100 degree day with a heat soaked engine climb CHTs will be higher, as it would be with Mags.

I also note my limited experimenting with running the pMags jumper out (adds another 5 degrees of advance) the engine was not as happy.

For me, getting the LOP efficiency is the priority. I agree with your hard ROP climb issue, but have never experienced any practical limiting CHT problem on an RV running dual pMags (as in limits typical to that of standard Mags).

The only time I had CHT issues was my experimenting with reduced cooling drag (RV-10, IO-540 and standard Mags). The cruise speed at LOP gained several knots for the same fuel flow, and CHT in cruise where in the 360 range. I did have to keep the nose down for climb to keep CHTs at 400 or so. Trade offs - and for me managing the climb to gain cruise efficiency was my option.

For those doing time to climb, racing and such, I defer to their best judgement.

Carl

N941WR said:

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.

Click to expand...

The point is, this CANNOT be optimized under both conditions without the EI knowing whether it's ROP or LOP. As Dan said, the result of too much advance ROP is high CHT and a loss of power. This has been documented by flight testing by several people now who've done extensive experimentation.

Here's the chart we publish to show graphically show why the LOP switch is necessary to optimize the point of PCP with changes in AFR:



In hot climates, during climb, CHTs can be the limiting factor with too much advance, just as Dan states.

Your statement is not supported by the flight test data.

Why not squeeze all the efficiency out of the package if you easily can? There is no tradeoff to doing it right and applying the science.

Since the original thread is about using PMAG, I ask, wouldn?t? using a version of EIC in conjunction with PMAG essential accomplish the same thing. One custom program that limits timing between 20-23 degree for ROP and then switch to the second program (in flight) to Curve A or even second custom curve for LOP.

My limited flying so far (about 50 hours or so) jibs down with Carl?s numbers. With a hot soaked engine and 86 degree weather I had no issues with CHT climbing from sea level to 12000 but my oil temp limited me to shallower climb (700-800 FPM)

Bavafa said:

Since the original thread is about using PMAG, I ask, wouldn’t’ using a version of EIC in conjunction with PMAG essential accomplish the same thing. One custom program that limits timing between 20-23 degree for ROP and then switch to the second program (in flight) to Curve A or even second custom curve for LOP.

Click to expand...

That would be nice but in practice it can't be done that way or at least not in a reasonable and safe way IMHO. The EIC has an "on the fly" ability to change timing parameters while the engine is running but it is not really intended to do what you describe. It also can only send changes to one ignition at a time when doing so.

The EIC can do "mass changes" where it can send one of the stored configs to the ignitions. To be honest I don't know if that works while the engine is running or not because I have never been brave enough to try it in flight.

Nigel reported some issues when trying to make on the fly changes to the Pmag config in flight. http://www.vansairforce.com/community/showthread.php?t=146427

The serial protocol on the Pmag stinks and is very limited and full of bugs/quirks/limitations. The EIC does a good job with what they have available to work with. I assume the newer EngineBridge has as well. Seems EmagAir is not ready to improve or change the serial protocol so we are stuck with the limitations.

The lack of error/CRC checking and proper handshaking can also lead to random reports of issues when trying to change the PMag config. Could explain Nigel's reports. Even the EIC documents speaks of cases where ignitions may not get updated properly.

Brantel said:

It also can only send changes to one ignition at a time when doing so.

Click to expand...

I am not sure if this is correct. I had done it with my old plane in flight and multiple times and did not have any issues. I have not tried it on the new plane. If I recall correctly, the advise is to do both at the same time instead of one at the time.
Perhaps Bill can comment on this.
I need to go an read Nigel's report one more time. I know he did a fair amount of testing and the part that I followed was mostly related to using different curves.

Bavafa said:

I am not sure if this is correct. I had done it with my old plane in flight and multiple times and did not have any issues. I have not tried it on the new plane. If I recall correctly, the advise is to do both at the same time instead of one at the time.
Perhaps Bill can comment on this.
I need to go an read Nigel's report one more time. I know he did a fair amount of testing and the part that I followed was mostly related to using different curves.

Click to expand...

Carl Froehlich said:

Dan,

As always your logic is spot on, but perhaps not an overriding factor for how many of us fly.

Flying an RV-14A, IO-390 with dual pMags set at 20 degrees BTDC with the jumper in (10 degrees of advance) I note CHTs max out at 380 degrees or so during a hard climb (coming down after 4K? or so depending on how you lean), and cruise CHTs in the 350 range. On a 100 degree day with a heat soaked engine climb CHTs will be higher, as it would be with Mags.

I also note my limited experimenting with running the pMags jumper out (adds another 5 degrees of advance) the engine was not as happy.

For me, getting the LOP efficiency is the priority. I agree with your hard ROP climb issue, but have never experienced any practical limiting CHT problem on an RV running dual pMags (as in limits typical to that of standard Mags).....
Carl

Click to expand...

I would suggest the CHT numbers above indicate excess timing advance for the 390. The chart below is CHT and oil temperatures at high power ROP cruise. The CHT temps are 30 degrees lower despite running as high as 182KTAS. These speeds are obviously running the -14 pretty hard and yet the CHTs are closer to 320 than 350. After engine break in, in a timed climb at 120KIAS to 11,000? I never saw CHT reach 350.

Can anyone with standard slick mags chime in with ROP cruise CHT numbers? That would help me understand if the difference in these numbers are cooling efficiency or timing differences.

One note about the chart below. The areas in the yellow circle are during engine break in. All other numbers are after break in.

Brantel said:

Click to expand...

This is what I was just reviewing again and if I understand it correctly and have never tried it, that refers to change timing on an existing and running program on the fly (I.e. increasing or decreasing Max advance) and not sending a new and saved timing curve/program to the PMAG.

What I was suggesting is to have a program, lets say C, and configure that for 20-23 degree and another program, lets say D, that has the curve of 25-28 degree. You start with the C and as you climb and get to your LOP setting, change the program to D by pushing that to both PMAGs.

Carl Froehlich said:

Dan,
As always your logic is spot on, but perhaps not an overriding factor for how many of us fly.

Click to expand...

Facts is facts. More advance = higher CHT, regardless of flight profile.

Ignore tribe. Subject is merely when the spark is delivered. Sometimes a study of the data suggests a change in how one flies.

For an example, take a close look at Marvin's data posted here and in the previous linked thread.

LOP at 9000 PA, best speed was 172 KTAS at 29 BTDC and 9.5 GPH:



OK, so climb a bit more. At 23 BTDC, CHT is lower, so it's easy to pick up the nose for a higher climb rate, thus the same time to pushover. Leaning to peak EGT at 23 BTDC, we have 175 KTAS at 9.1 GPH:

M McGraw said:

I would suggest the CHT numbers above indicate excess timing advance for the 390.

Click to expand...

Yep. I don't run CHT quite as high as Carl's example, using about half the cowl exit area.

It's funny how these threads have those who strive for perfection and those who say "good enough".

Not sure how many times this needs to be said, but there is a significant difference in optimal timing for a rich or lean mixture. An EI that uses RPM and MP has NO WAY to know which mixture setting is being used because mixture is a pilot discrete variable. Without the pilot making a discrete command to the ignition to tell it what the mixture is, the EI will be wrong for one of them. It's either going to be optimal for ROP and "good enough" for LOP, or the other way around. Without the discrete you will be too advanced and hotter than needed during high power ops or not advanced enough and slower during LOP cruise. There are no alternatives if you only have a single map. Period. Dot.

Bavafa said:

This is what I was just reviewing again and if I understand it correctly and have never tried it, that refers to change timing on an existing and running program on the fly (I.e. increasing or decreasing Max advance) and not sending a new and saved timing curve/program to the PMAG.

What I was suggesting is to have a program, lets say C, and configure that for 20-23 degree and another program, lets say D, that has the curve of 25-28 degree. You start with the C and as you climb and get to your LOP setting, change the program to D by pushing that to both PMAGs.

Click to expand...

That?s why I posted that there are two different download methods in my post.

Nigel seemed to indicate that there can be periods of no fire while downloading and occasional serious issues where one PMag loses its mind during online changes. Not something most people want to accept for normal use.

Same as before, revised for clarity and a minor math correction:



Now, a bit of data fun. In #33, Ross posted a flame speed chart from an entirely different source. At first glance, it may appear to quite a lot different compared to the above chart...



However, look close at the Y axis on each chart. They are reversed; a lot of crank degrees is the same as a slow speed in feet per second. So, flip the chart from SDS so the velocity scales match, and...well, facts are facts.

BillL said:

...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"]

Click to expand...

I waited until this thread appeared to be dying down so I would not cause too much thread drift.

To answer your question, yes I find advantages to using advance well below 8000’; however, I only like WOT and the -14 will jump up to yellow line fast. My procedure is to set WOT then immediately do “the big pull” flip the switch to LOP advance curve and find peak from the lean side. The lower my altitude the leaner I need to run to keep outside the red box and below yellow line. Rather than thinking of altitude as my limit I use percent power and MP.

Further to Bill's question, I went back to CF Taylor for another chart, this one flame speed vs intake pressure. As before, I've de-cluttered and added familiar terms, here translating psi to inches of mercury. The box defines the manifold pressure range of interest for non-turbo engines operating below 18,000 feet, standard day, 15 to 30 inches Hg. For the entire range, flame speed to 95% alight only slows by about 6 degrees at 18,000. Bill asked about 8000 or less. Pressure there would about 11 psi, thus a climb from sea level to 8000 would only slow flame speed by about 4 crank degrees.

In general, pressure change alone (i.e. altitude) has less effect on required advance than mixture change. However, when combined, the charts spell out why we use advance with low manifold pressure and lean mixture. At the same time (and in particular for the angle valve) they show why it makes little sense for a non-racer to use the same advance map when climbing at WOT and best power mixture. Best power mixture (150 ROP, for example) requires zero additional advance (go back and look at the flame speed vs mixture chart), and the pressure loss with altitude requires only a little.

As a rusty pilot (really rusty) that is close to having a flying 7A soon, I've been following this thread with interest. One question I have is why the angle valves like less advance, or should I say react more poorly to excess advance?

I have a 390 in my 7A with dual P-mags

Thanks- sorry if a dumb Q I should know

Dual p mag

I took the plunge last year when my mags came due for inspection. Since I'm local I picked them up at the factory. They gave me a full tour and took time out of their busy day to answer all my questions.
The install was straight forward, the mags work perfectly. Starts, hot or cold are no longer an issue. I highly recommend them!
RV-7
IO360 M1B
WW RV200 prop

dreed said:

One question I have is why the angle valves like less advance, or should I say react more poorly to excess advance?

Click to expand...

It's a good question. The short answer? As compared to the parallel valve head, the intake port, combustion chamber, and piston dome shapes all promote greater chamber turbulence. Within limits, more turbulence during combustion is a good thing, speeding burn rate. A higher burn rate requires less of a head start (more ignition advance) in order to arrive at peak pressure in the 15 to 20 ATDC ballpark.

The general configuration difference is the shape of the chamber and piston. The angle valve chamber is a moderate dome, while the parallel valve chamber is mostly flat-topped. The common piston configurations match the chamber shapes, domed and flat respectively. There are a number of interesting design aspects to the hemispherical chamber, but strictly limiting the conversation to chamber turbulence, the key factors are probably increased swirl and the addition of some squish.



To visualize swirl, imagine looking at a cylinder from the valve cover end. Note the location of the intake tube, offset from the valve. Using your x-ray vision, the port and inlet flow would thus look like this:



The goal of careful port shaping is to promote a spiral flow into the chamber. The flow doesn't run straight into anything, so it keeps a lot of velocity, going round and round as the piston travels down the bore and then up again on compression.

As the piston approaches the top of the bore, two sparks initiate combustion, one on each side of the chamber. Each forms a small kernel of flaming gas which grows, spreading across the chamber.

This is a typical piston for an angle valve. Note the valve reliefs in the center, and the raised areas at left and right. The spark plugs (and our two spreading balls of burning mixture) are above those raised areas. As the piston nears TDC, those raised portions approach the underside of the chamber dome. The effect is to squeeze those zones, forcing the hot gasses toward the center of the chamber. The combined swirl and squish accelerate the combustion process with forced turbulence...thus requiring less ignition advance.



There are other factors, but swirl and squish are typically the most important in the case of any fast burn 2-valve chamber.

Squish clearance (how close the piston gets to the head) is still quite wide in the Lycoming. How far can the principle be pushed? In high performance engines, it is sometimes set to be so close that details like rod stretch and crankshaft flex come into play. Here's one from my personal Wayback Machine, a piston for a pentroof 4 valve Honda. The flat squish areas cleared the underside of the chamber by only 0.035" when measured statically; the close clearance was created by welding filler material into the chambers, then milling it flush with the gasket surface. Very close squish like this serves a dual purpose. Obviously it increases chamber turbulence, but it also quenches gas temperature in the squished areas, killing any chance of detonation in the tiny amount of gas remaining there.

Excellent visuals Dan.

To add to Dans excellent and factual coverage, 4 valve engines typically use tumble rather than swirl to attain faster heat release. Also, there is a volumetric efficiency cost (reduction) due to the intake energy used to generate the swirl that will yield a lower ultimate BMEP by comparison. Squish doesn't affect Vol-eff and the benefit over the slightly increased pumping loss is worth the effort. Piston valve pockets are necessary with the piston-to-head reduction as valves open faster than the piston moves near TDC.

I was going to respond with a quick and dirty answer, but I just knew Dan would come along and save me the effort.

Part 2 however relates right back to the title of this thread. The total timing advance as well as the curve itself is significantly different between the angle valve and the parallel valve. Throw in a few more compelling variables like compression, displacement, rich/lean, etc, and the timing schedule becomes very distinct to each configuration. Yet, the Pmag only comes with one part number that fits anything from a whezzy low compression 235 to a fire breathing high compression AV 400. Does anyone really think a simple timing shift of a few degrees is going to result in optimized timing for the entire Lycoming engine line? No way, no how.