Dual P-MAG Reliability in 2017

[Toobuilder]

Originally Posted by SHIPCHIEF

...I would be comforted to know that an electronic flight control would have a progressive failure mode.

Edit - Ross beat me to the punch again...

Anyway, I'll just add that as long as the failure mode is benign to the ship (no fire, explosion, leaking, etc), then the demonstrated SDS product reliability well exceeds accepted range for aircraft use. Also keep in mind that electronics usually fail on power up, not in use. If I do a runup some day and find a coil has "suddenly" died since the last flight - might be inconvenient, but it's safe. One notable exception to this is P-mag, of all things. The history of "lost timing events" often happened in flight.

Besides, I think that's better than having dying magneto right on the edge and tempting me to make "one more flight"

[Chkaharyer99]

Originally Posted by skylor

Charlie,

Did you get the chance to meet the aforementioned CEO at Reno?

Skylor

I tried but the SDS CEO was in high demand and the line was long. Didn't want to be pushy. Besides, he was multi tasking what with all that floor sweeping and such.

I did speak with other SDS users and many who are considering SDS. Got many questions answered.

It was great watching you race at Reno. You had quite the cheering section and it was good meeting your very dedicated support team.

Are you considering EI? I think I remember you're running mags. Is that correct?

[DanH]

Returning to P-mag reliability....

Originally Posted by N941WR

I can't answer with certainty because I didn't design the P-mag but I believe you are correct that it is a backup ground. It is really needed for communication through the serial port.

(discussing Pin 1 ground) So what doesn't work if it is not connected...or connected somewhere other than a case bolt? You've been very specific in the past:

http://www.vansairforce.com/communit...6&postcount=10

http://www.vansairforce.com/communit...37&postcount=8

http://www.vansairforce.com/communit...38&postcount=3

http://www.vansairforce.com/communit...45&postcount=4

Since 2 and 3 are a serial port, I don't believe it would impact anything in flight. We have shorted them when developing the EICommander with no impact to out test P-mags.

Jumper in = ignore B
Jumper out = use B info.
EIC connected to jumper terminals = use signals from EIC to modify B info, in flight or on the ground.

Recall the mystery below? Since both the EIC and the P-mags were found to be A-OK, the conclusion was it had to be something about Nigel's serial wiring...

Originally Posted by nigelspeedy
Approximately 1 in 20 times I have experienced a fault after sending a new ignition setting. I cant say where the root cause of the problem lies but the symptoms are as follows. After you press the send button the engine begins to run very roughly and lose power. Like a very LOP mag check. Unlike the brief firing suspension that is normal this roughness does not go away. On the EICommander one of the PMags will constantly display the correct new timing value you have just sent (this is normal). The other PMag display will vary between the new value and 19.6 deg about every 5 seconds (this is not normal). The CHT will rise at a rate of about 20F per minute and the engine oil temperature will do the same. I have found two ways of fixing this fault. First, you can reload a new ignition setting, (just repeating the one you just sent has worked for me) but this takes a few button pushes and about 30 seconds all the while you will be distracted by your engine which feels like it is under great duress. Second, you can take the P Lead for the misbehaving ignition and turn it off then back on. This is quicker but be very careful to properly identify the correct ignition. I normally associate top with 1 or left and bottom with 2 or right. On the EICommander display the upper timing advance number is associated with the right ignition. It is labeled as such but the display is quite small and you could easily make a mistake in haste. Although the faulty ignition 'display' is alternating between the correct value and 19.6 deg I don't think this is when the ignition is actually firing as the level of roughness and CHT rise are counter to this. After seeing this fault I checked the PMag timing and they were both at TDC so I don't think timing was lost, as the odds of it being subsequently found perfectly are pretty low. I also sent the PMags back for an overhaul and they were both within spec. They have always run the latest firmware version. I have seen the error on both the left and right ignition, not simultaneously though. My EICommander was also returned and it had one of the comm boards replaced but I have seen this fault a couple of times since. I have never experienced this fault except immediately after sending a change. I never had this fault with just the PMags before I installed the EICommander. I have never used the PMag proprietary software to make changes to the settings.

An internal sort to ground would probably kill the generator; however, it would continue to fire, if ship's power is available.

(discussing a short to ground on the Pin 5 wire) Ship's power would not be available; it's a grounded power lead. Right after it grounded, the breaker opened. So, the system is on internal generator power, with the external power lead shorted to ground. Does it provide a path to ground for the internal generator?

Bill, I know these are hard questions, but one can't claim superiority based on immunity to external wire faults without clearly defining exactly what happens given wire faults in the competing system.

[rv8ch]

Originally Posted by DanH

Returning to P-mag reliability....

...

Bill, I know these are hard questions, but one can't claim superiority based on immunity to external wire faults without clearly defining exactly what happens given wire faults in the competing system.

Seems like some bench testing would not take too much time and effort. I'd do it on one of mine but I'm in "get 'er done" mode, and I don't want to fry one of my p-mags. Anyone have any pull with the emagair guys?

[ALagonia]

I am new to Experimentals. Have many hours flying behind regular magnetos. I have read this complete thread and others and still cannot find an explanation of what P-Mags are, how they work and what the advantages/disadvantages are. Or at least I cannot decipher this information. Can someone please explain in layman terms how P-mags differ from a regular Bendix mag, how they work and what the advantages/disadvantages are? I would just like to have an understanding of P-Mags. I am talking to a gentleman that has an airplane I have an interest in with dual P-Mags on an IO360 Superior Engine with Cold Air Induction.
Thank you

[Brantel]

Originally Posted by ALagonia

I am new to Experimentals. Have many hours flying behind regular magnetos. I have read this complete thread and others and still cannot find an explanation of what P-Mags are, how they work and what the advantages/disadvantages are. Or at least I cannot decipher this information. Can someone please explain in layman terms how P-mags differ from a regular Bendix mag, how they work and what the advantages/disadvantages are? I would just like to have an understanding of P-Mags. I am talking to a gentleman that has an airplane I have an interest in with dual P-Mags on an IO360 Superior Engine with Cold Air Induction.
Thank you

http://www.emagair.com/

[krw5927]

Originally Posted by DanH

Returning to P-mag reliability....

(discussing Pin 1 ground) So what doesn't work if it is not connected...or connected somewhere other than a case bolt? You've been very specific in the past:

http://www.vansairforce.com/communit...6&postcount=10

http://www.vansairforce.com/communit...37&postcount=8

http://www.vansairforce.com/communit...38&postcount=3

http://www.vansairforce.com/communit...45&postcount=4

The current Pmag manual (v LC114.28) has this to say regarding the pin 1 ground wire:

"Note: You cannot rely on the ignition’s mechanical attachment to the engine to provide ground. Aluminum anodizing acts as an electrical insulator, so the clamp connection to the anodized flange will not be a reliable ground."

Additionally, the Troubleshooting Tips version 04 on the website indicates "not having a proper ground connection" to be one of the most frequent installation errors.

This language seems to indicate the ground wire is pretty darned important.

[N941WR]

Originally Posted by DanH

Returning to P-mag reliability....





(discussing Pin 1 ground) So what doesn't work if it is not connected...or connected somewhere other than a case bolt? You've been very specific in the past:

http://www.vansairforce.com/communit...6&postcount=10

http://www.vansairforce.com/communit...37&postcount=8

http://www.vansairforce.com/communit...38&postcount=3

http://www.vansairforce.com/communit...45&postcount=4



Jumper in = ignore B
Jumper out = use B info.
EIC connected to jumper terminals = use signals from EIC to modify B info, in flight or on the ground.

Recall the mystery below? Since both the EIC and the P-mags were found to be A-OK, the conclusion was it had to be something about Nigel's serial wiring...

Originally Posted by nigelspeedy
Approximately 1 in 20 times I have experienced a fault after sending a new ignition setting. I cant say where the root cause of the problem lies but the symptoms are as follows. After you press the send button the engine begins to run very roughly and lose power. Like a very LOP mag check. Unlike the brief firing suspension that is normal this roughness does not go away. On the EICommander one of the PMags will constantly display the correct new timing value you have just sent (this is normal). The other PMag display will vary between the new value and 19.6 deg about every 5 seconds (this is not normal). The CHT will rise at a rate of about 20F per minute and the engine oil temperature will do the same. I have found two ways of fixing this fault. First, you can reload a new ignition setting, (just repeating the one you just sent has worked for me) but this takes a few button pushes and about 30 seconds all the while you will be distracted by your engine which feels like it is under great duress. Second, you can take the P Lead for the misbehaving ignition and turn it off then back on. This is quicker but be very careful to properly identify the correct ignition. I normally associate top with 1 or left and bottom with 2 or right. On the EICommander display the upper timing advance number is associated with the right ignition. It is labeled as such but the display is quite small and you could easily make a mistake in haste. Although the faulty ignition 'display' is alternating between the correct value and 19.6 deg I don't think this is when the ignition is actually firing as the level of roughness and CHT rise are counter to this. After seeing this fault I checked the PMag timing and they were both at TDC so I don't think timing was lost, as the odds of it being subsequently found perfectly are pretty low. I also sent the PMags back for an overhaul and they were both within spec. They have always run the latest firmware version. I have seen the error on both the left and right ignition, not simultaneously though. My EICommander was also returned and it had one of the comm boards replaced but I have seen this fault a couple of times since. I have never experienced this fault except immediately after sending a change. I never had this fault with just the PMags before I installed the EICommander. I have never used the PMag proprietary software to make changes to the settings.

We spoke with Nigel after he experienced this and struggled to reproduce it in our lab. In fact, we couldn't reproduce it at all. This was the first time we had been informed of such an issue.

Not many people ever change their timing in flight, for good reason. While the p-mag did not lose its TDC mark, it appears the shift angle (where it should fire in relation to TDC) was not accepted by the P-mag.

Based on what he experienced, we do not recommend changing the timing in flight. If someone insists on doing it, there are two different ways. One is the On the Fly option, which issues the timing command to the P-mags and is less disruptive to the firing sequence, or do it on the ground when the engine is not running.

We were not aware what Nigel was testing or we would have suggested he use the On the Fly option. This option does change the timing but does not try to write to permeant memory. The idea being that once a pilot finds a setting they like, they can land, and save it permanently.

This really doesn't have anything to do with the P-mag but does have everything to do with how the EIC communicates with them.

The display Nigel mentions is just that, a display. It displays whatever firing angle the P-mag reports to it.

(One other thing, the reason there are so many button presses to send a new timing configuration to the P-mags is so that someone doesn't send them a configuration by accident. That was by design, not a bad programming choice.)

Originally Posted by DanH

(discussing a short to ground on the Pin 5 wire) Ship's power would not be available; it's a grounded power lead. Right after it grounded, the breaker opened. So, the system is on internal generator power, with the external power lead shorted to ground. Does it provide a path to ground for the internal generator?

Bill, I know these are hard questions, but one can't claim superiority based on immunity to external wire faults without clearly defining exactly what happens given wire faults in the competing system.

Next time you are at SnF or OSH, stop by the Emag display. Their 114 P-mag is wired to four sparkplugs and no ground wire connects the plugs to the P-mag.

When I asked Brad about this, he said they use the second plug as the primary return path. Remember they fire two plugs at the same time (wasted spark), that was a convenient way to always have an adequate electrical return path. So, they have three return paths; the P-mag body, the ground wire, and the other sparkplug.

One other design feature of the P-mag is that once they are spinning and producing power, there is no way to shut them down. All the P-lead does is stop the plugs from firing but the internal electronics are still alive.

Remember, I am not the manufacture of the P-mag ignitions, nor are our companies connected. Everything I have written on this thread and others is based on what we have learned while working with the ignitions over the past 10 years. For answers as to why they are designed and function the way they do, you really need to go to Emag.

[skylor]

Originally Posted by Chkaharyer99

I tried but the SDS CEO was in high demand and the line was long. Didn't want to be pushy. Besides, he was multi tasking what with all that floor sweeping and such.

I did speak with other SDS users and many who are considering SDS. Got many questions answered.

It was great watching you race at Reno. You had quite the cheering section and it was good meeting your very dedicated support team.

Are you considering EI? I think I remember you're running mags. Is that correct?

I think the cheering section belonged to the guy with the Lancair 320 (Mark)! My team of two consisted of my Dad and my significant other...and they are very dedicated to supporting my Reno hobby!

I don?t currently have plans to swap out the mags, but if that time comes, SDS will definitely be at the top of my list. I really appreciate Ross?s openness and honesty here when it comes to discussing his products!

Skylor

[DanH]

Originally Posted by N941WR

We spoke with Nigel after he experienced this and struggled to reproduce it in our lab. In fact, we couldn't reproduce it at all. This was the first time we had been informed of such an issue.

Ok, discard Nigel's report, and consider timing loss with a known cause, the arcing alternator B-lead.

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

At first, it was claimed that V40 would have prevented the issue, but that was obvious nonsense, as noted by this gentleman...

http://www.vansairforce.com/communit...0&postcount=31

...and recognized by the manufacturer:

http://www.vansairforce.com/communit...5&postcount=49

So why is it relevant to this particular exercise? The P-mag is unique, in that it's the only ignition which allows the user to insert the body and mesh the drive gear at random, then write a TDC position reference electronically. It's a wonderful feature as it relates to installation and inspection, as it makes timing a P-mag dirt simple. However, all design is the art of compromise. The same feature is an Achilles heel; the easy-to-set TDC position can also be reset. V-40 (and I suspect other patches too) is a example of an attempt to prevent unintended reset given a specific condition. The case of the arcing B-lead is an example of timing reset caused by a less predictable input, so it's not likely to be fixed with a software patch.

All other ignitions physically reference crankshaft TDC to the ignition. As such, installation requires physical alignment of trigger and crankshaft position. Losing that reference requires outright mechanical failure. It is slightly more difficult to install, but more reliable in service.

I've attempted to run though some basic "what if" analysis, which as Mike pointed out, would be followed by an estimate of probability. It does not appear we're going to be able to complete that examination due to lack of information. Frankly, it makes no personal difference to me. I'm just trying to lead the conversation back toward a logical estimation of reliability.

I will say this, based on reported field experience. The major P-mag risk is random timing reset. The major risk with other systems is simply no spark. Random timing can take out an engine. No spark merely means soldiering on with the other ignition.

The architecture which allows random timing reset due to outside factors has nothing to do with the P-mag's significant benefit, its internal power supply. A system with a hard TDC reference and internal power generation would be a heck of an ignition...but that's not what we have here.

Next time you are at SnF or OSH, stop by the Emag display. Their 114 P-mag is wired to four sparkplugs and no ground wire connects the plugs to the P-mag.

When I asked Brad about this, he said they use the second plug as the primary return path. Remember they fire two plugs at the same time (wasted spark), that was a convenient way to always have an adequate electrical return path. So, they have three return paths; the P-mag body, the ground wire, and the other sparkplug.

One other design feature of the P-mag is that once they are spinning and producing power, there is no way to shut them down. All the P-lead does is stop the plugs from firing but the internal electronics are still alive.

Two things, and I'm outta here. One, it is easy to make sparks. The issue is the timing of those sparks. Two, all waste spark systems use the other plug in the paired coil as the return path for the secondary; that's why there is a wasted spark. It is very unlikely that the high voltage secondary is part of the ground path for control electronics.