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-   -   Dual P-MAG Reliability in 2017 (https://vansairforce.net/community/showthread.php?t=154003)

RhinoDrvr 10-08-2017 12:05 PM

Quote:

Originally Posted by Nova RV (Post 1209436)
Since I did not start this thread, I apologize to Evan for stirring up some people's feathers. I made the assumption that since the title of the thread is "Dual P-MAG Reliability in 2017" that he wanted info specifically about P-Mags since the comparison thread entitled " SDS CDI vs Pmag" would have seen to cover that topic specifically but I stand corrected. As far as being called out by name by one individual questioning my motives, so be it.

I am looking for P-MAG experiences and reliability data as that was the only thing holding me back. I looked at SDS-CPI, Lightspeed, etc...I like multiple layers of redundant systems and I think P-MAG does that. Also it seems like the new shaft retainers, and v40 firmware have turned P-MAG into a very durable system. I think I?m sold.

Bicyclops 10-08-2017 12:40 PM

Not redundant enough?
 
For my own level of comfort, self powered ignitions are not required. Making sure that they receive the necessary electrons to keep running can be handled by good system design and by resource management.

I think the OP already has a backup battery. I don't know how big it is, but it is a form of redundancy. I have 2 PC 680s for my 2 Plasma IIIs. I've done the calcs and can run out my gas without sweat after an alternator failure. I'd have to shut down my second EFIS to be able to run out completely full tanks, but the point is I would have lots of time, hours of it, to find a good place to land and troubleshoot. I considered adding the 8amp alternator and decided that I don't need it and the extra weight for the level of redundancy that I require. I could go with an EarthX to replace one of my 680s and save enough weight for the 2nd alternator, but I still don't think I need it.

I'm not bashing P-mags. I just don't think that they necessarily add redundancy that you can't design for with a different ignition system. If I were choosing today, I'd go with CPI and a wiring design similar to what I have.

Ed Holyoke


Quote:

Originally Posted by SHIPCHIEF (Post 1209399)
For CPI to fit the OP's bill, you would have to add a redundant power source, and I don't mean a back up battery.
A B&C vacuum pad alternator would 'almost' fit the bill, but it is a single power source, so it's still a little short of the 'self powered' spec for dual ignitions.
CPI single unit ($1170) dual unit ($2275?)
B&C SD-8 with PMR1C-14 and 504-1 (14v) ($545.00)
Total: Single: $1715 dual: $2850
Still in the ball park price-wise, The Dual CPI option is a better price, but if it's a 'one casing device' might lack the redundancy the OP desires.
I run a Pmag and a Bendix mag on my RV-8 and my T-18, a noticeable improvement over 2 mags.
I'm also slowly accumulating parts for a Ford EDIS (possibly with MegaJolt) system. I would probably add the B&C SD8, because I also use dual automotive electric fuel pumps to AFP mechanical fuel injection. I probably have added risk with a single battery system.
An interesting discussion.


rv6ejguy 10-08-2017 01:57 PM

Quote:

Originally Posted by RhinoDrvr (Post 1209473)
This post captures my desires for an ignition the best. Highest amount of redundancy, and I’m willing to sacrifice extreme top end performance for reliability and redundancy. Still leaning towards dual P-MAG’s. The SDS-CPI, besides the box asthetics, would require a second alternator, which P-MAG’s do not. The P-MAG installation has 5 backups. Alternator, Left PMG, Right PMG, Battery 1 and Battery 2 before the engine stops turning does CPI offer that?

Since it seems some people on this thread are still evaluating choices, I'll respond to this post.

You're still flying a single engined aircraft with several single points of failure. Most commercial airliners don't have even quadruple backups, let alone quintuple redundancy.

On a typical CPI setup you'd have a main battery, single or dual alternators and a backup battery, possibly for other electronics. With the new CPI2, we'll have an option for a additional dedicated backup battery with monitoring system. That's quadruple or quintuple redundant power sources. Enough for a single engined aircraft? Most people would probably think so.

Remember one CPI only draws about 1 amp on a 4 banger at 2400 rpm. An 18 AH backup battery would run one CPI for around 16 hours, 2 CPIs for 8 hours- far more time than you have fuel for. If you want a battery backup, you can do that for about $40 as I've done in my -6A. You don't need a massive battery for backup power with such low current draws.

As Mike said, no inspections outside of annual spark plug checks. P Mag recommends 100 hour inspection intervals requiring removal. I suspect few people actually do these however. CPI requires no blast tubes, there are no moisture concerns and the crank flange mounted sensor system is more reliable than a series of gears and bearings which several people have noted failures on.

The CPI2 will address concerns with appearance, panel space and backup power as well as introduce some new features.

Nothing can beat a P Mag for ease of installation but as always, I invite people considering EIs to look at each potential system available and weigh the pros and cons. No one system is the best for every customer.

Last week, I sent a client who phoned us for a CPI over to P Mag as he had too many things to change to install a CPI in my view. Surprisingly, he'd never even heard of P Mag. In the end, I think he'd be better served with their product given his wants and circumstances.

Bevan 10-08-2017 04:04 PM

Quote:

Originally Posted by Bicyclops (Post 1209481)
For my own level of comfort, self powered ignitions are not required. Making sure that they receive the necessary electrons to keep running can be handled by good system design and by resource management.

I think the OP already has a backup battery. I don't know how big it is, but it is a form of redundancy. I have 2 PC 680s for my 2 Plasma IIIs. I've done the calcs and can run out my gas without sweat after an alternator failure. I'd have to shut down my second EFIS to be able to run out completely full tanks, but the point is I would have lots of time, hours of it, to find a good place to land and troubleshoot. I considered adding the 8amp alternator and decided that I don't need it and the extra weight for the level of redundancy that I require. I could go with an EarthX to replace one of my 680s and save enough weight for the 2nd alternator, but I still don't think I need it.

I'm not bashing P-mags. I just don't think that they necessarily add redundancy that you can't design for with a different ignition system. If I were choosing today, I'd go with CPI and a wiring design similar to what I have.

Ed Holyoke

In my opinion, self-powered EI are going to be best method for the masses because they are the closest thing to what they are replacing, the self-contained magneto. For those who want EI and don't want to fiddle with maps, curves, backup batteries, remote boxes and significant wiring changes, and want the engine to keep running if the master switch gets turned off, Pmag is he clear choice.

I don't recall any threads about wanting to adjust timing curves with magnetos.

The Pmag concept is correct. At first there was some concern that the design was not going to be as reliable as a standard mag (all it needs to be in my book) but I think we're at the point now that one can say the Pmags are reliable enough, understood, still installed in redundant pairs as usual, and well supported by the factory. They just work.

Bevan.

Toobuilder 10-08-2017 07:37 PM

Quote:

Originally Posted by Bevan (Post 1209541)
In my opinion, self-powered EI are going to be best method for the masses because they are the closest thing to what they are replacing, the self-contained magneto. For those who want EI and don't want to fiddle with maps, curves, backup batteries, remote boxes and significant wiring changes, and want the engine to keep running if the master switch gets turned off, Pmag is he clear choice.

I don't recall any threads about wanting to adjust timing curves with magnetos.

The Pmag concept is correct. At first there was some concern that the design was not going to be as reliable as a standard mag (all it needs to be in my book) but I think we're at the point now that one can say the Pmags are reliable enough, understood, still installed in redundant pairs as usual, and well supported by the factory. They just work.

Bevan.


The above is fine given the context that the idea to emulate a magneto is a "marketing decision". Unitized construction is a means to differentiate their product, and no doubt it has appeal with some. But the decision to go down that path was certainly challenging, as the reliability reports from the past will clearly attest. But unitized construction is far from the "correct" choice from an engineering standpoint, as evidenced by the near complete abandonment of that concept decades ago by virtually every other vehicle manufacturer. Billions of miles of operation show that the distributed system like CPI also "...just work..." to paraphrase the above. Plenty of ways to skin a cat.

Now, the OP's requirement has become clear that he wants a very, very high level of redundancy and complete isolation from ships power. Thats his right and clearly if he sticks with that requirement, all battery ignitions are off the table. Pretty much limits the options available. And if the discussion turns to probability of failure of ships power, that is a WHOLE different can of worms.

Sounds like the OP is pointed in the direction that makes him comfortable. Thats a good thing. Its also a good thing that we can share information in a civilized manner, even if the information is not what we want to hear. We need to remember this is largely a data driven excercise, not politics or religion.

Captain Avgas 10-08-2017 09:10 PM

Quote:

Originally Posted by Bevan (Post 1209541)

The Pmag concept is correct. At first there was some concern that the design was not going to be as reliable as a standard mag (all it needs to be in my book) but I think we're at the point now that one can say the Pmags are reliable enough, understood, still installed in redundant pairs as usual, and well supported by the factory. They just work.

Bevan.

The misconception about PMAGs is that if you have two of them you automatically have redundancy. But that has not always proven to be the case. Their specific weakness is that they have been susceptible to losing their timing. And if one of the PMAGs loses its timing to a very advanced position it can cause the engine to quit, regardless of the type of ignition system on the other side. In other words one faulty PMAG can take out a second PMAG, or it can take out a Lightspeed EI, or it can take out a conventional magneto.

This type of failure, whereby the failure of one ignition renders the second ignition useless, is a characteristic of PMAGs. I have never heard of a single case, ever, of such a thing happening with dual magnetos.

It may well be that bolting all of the solid state components for the PMAG system directly to the engine in such a hot, vibrating environment will always be problematic. I'm not sure about that.

A number of aircraft with dual PMAGs have had complete engine failures after the timing was lost on just one PMAG. There are other incidences of serious engine damage being caused by the same problem. At this very moment there is another thread on VansAirforce dealing with exactly that scenario whereby the owner had to have his whole top end overhauled because he lost timing on his single PMAG which rendered his second conventional magneto useless. See here:

http://www.vansairforce.com/communit...d.php?t=144336

It seems to me that the PMAG is always one revision, one recall, one software update from being the genuine article.

My personal opinion is that ALL of the EI systems for Lycomings have their own serious limitations. I have a conventional magneto on one side and a Lightspeed EI on the other. The limitations of the Lightspeed system is that it is dependent on external electrons and it has a lot of exposed wiring and connectors that can fail or be damaged. But it seems to be relatively immune to loss of timing. Would I use two Lightspeed ignitions....no way Jose....too much downside and virtually no additional gain.

I find that having EI on one side greatly improves engine performance and I am prepared to put up with the increased risks of the system for that advantage. But I am not kidding myself that my system is as safe and reliable as two conventional magnetos. And neither should you.

Bavafa 10-08-2017 09:11 PM

Quote:

Originally Posted by rv6ejguy (Post 1209513)
Since it seems some people on this thread are still evaluating choices, I'll respond to this post.

You're still flying a single engined aircraft with several single points of failure. Most commercial airliners don't have even quadruple backups, let alone quintuple redundancy.

On a typical CPI setup you'd have a main battery, single or dual alternators and a backup battery, possibly for other electronics. With the new CPI2, we'll have an option for a additional dedicated backup battery with monitoring system. That's quadruple or quintuple redundant power sources. Enough for a single engined aircraft? Most people would probably think so.

Remember one CPI only draws about 1 amp on a 4 banger at 2400 rpm. An 18 AH backup battery would run one CPI for around 16 hours, 2 CPIs for 8 hours- far more time than you have fuel for. If you want a battery backup, you can do that for about $40 as I've done in my -6A. You don't need a massive battery for backup power with such low current draws.

As Mike said, no inspections outside of annual spark plug checks. P Mag recommends 100 hour inspection intervals requiring removal. I suspect few people actually do these however. CPI requires no blast tubes, there are no moisture concerns and the crank flange mounted sensor system is more reliable than a series of gears and bearings which several people have noted failures on.

The CPI2 will address concerns with appearance, panel space and backup power as well as introduce some new features.

Nothing can beat a P Mag for ease of installation but as always, I invite people considering EIs to look at each potential system available and weigh the pros and cons. No one system is the best for every customer.

Last week, I sent a client who phoned us for a CPI over to P Mag as he had too many things to change to install a CPI in my view. Surprisingly, he'd never even heard of P Mag. In the end, I think he'd be better served with their product given his wants and circumstances.

Is this really the only advantage of CPI over PMAG, 100 hour inspection vs. no inspection? BTW, my understanding has been that PMAG asks to inspect at each annual which is relatively a minor inspection.

With CPI, do we ever need to inspect the crank sensor position/mount or is that not required at all?

Canadian_JOY 10-08-2017 09:44 PM

Quote:

Originally Posted by Captain Avgas (Post 1209605)
The misconception about PMAGs is that if you have two of them you automatically have redundancy. But that has not always proven to be the case. Their specific weakness is that they have been susceptible to losing their timing. And if one of the PMAGs loses its timing to a very advanced position it can cause the engine to quit, regardless of the type of ignition system on the other side. In other words one faulty PMAG can take out a second PMAG, or it can take out a Lightspeed EI, or it can take out a conventional magneto.

This type of failure, whereby the failure of one ignition renders the second ignition useless, is a characteristic of PMAGs. I have never heard of a single case, ever, of such a thing happening with dual magnetos.

This comment carries some weight with me, however I believe in fairness to the folks at EMagAir the comment should be qualified. I watch ignition discussions reasonably closely on this forum and don't believe I've seen any significant complaints of a PMag losing it's timing if running Version 40 firmware.

If one has their PMag updated to V40 it would appear the loss of timing events may well be a thing of the past. As a V40 user I certainly hope that's the case.

WAM120RV 10-09-2017 04:29 AM

Problem solved!
 
Quote:

Originally Posted by Canadian_JOY (Post 1209618)
This comment carries some weight with me, however I believe in fairness to the folks at EMagAir the comment should be qualified. I watch ignition discussions reasonably closely on this forum and don't believe I've seen any significant complaints of a PMag losing it's timing if running Version 40 firmware.

If one has their PMag updated to V40 it would appear the loss of timing events may well be a thing of the past. As a V40 user I certainly hope that's the case.

This is the problem with this kind of thread. The OP was asking about V40 P mags against mags and one other ignition system. V40 solved the loss of timing issue but someone brings it into the debate, why?

Captain Avgas 10-09-2017 05:27 AM

Quote:

Originally Posted by WAM120RV (Post 1209641)
V40 solved the loss of timing issue but someone brings it into the debate, why?

I refer again to the concurrent thread 'PMAG Problem' on VansAirforce. The OP of that thread, Loal Wood, required a top end job done on his Lycoming after his sole PMAG lost timing. This is what Loal Wood had to say on his thread following a discussion with Brad at Emag about the incident:

I talked to Brad at Emagair about the evaluation of my Pmag. This is what I learned.

The inspection of my Pmag did not reveal any damage or discrepancies.

My Pmag did not have the V40 update installed.

As stated on the Emag website V40 is not a mandatory update.

He said there is no reason to believe that the V40 update would have prevented my loss of timing issue anymore than the V37 that was installed at the time of the event.

Brad said they do not have enough definitive information at this point to know why this inflight timing event happened.


Now, if I'm reading this right EMAG have stated that they do not know why Loal's PMAG (V37) lost its timing and they have no reason to believe that V40 would have prevented the timing loss.


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