PMAGS or SDS

[Bavafa]

The SDS system by design allows for fine tuning. Compare this to “spoofing” PMAGS reported by others.

I believe you already mentioned that you don't know about PMAG, in fact none of us know since the map has not been shared publicly as far as I know. So, we don't know if the PMAG map is just as optimized or not. This is also in consideration of which engine is it getting installed on since we know some can take advantage of this great flexibility and some like my IO390 would not benefit much.
But many of us also know the installation of both have a different degree of complexity, this is especially true if you are already flying. The installation of one is more like a project as the other is rather more like a task.
So again, I believe there is NO definite better choice but many trade offs.

 

[DanH]

I believe you already mentioned that you don't know about PMAG, in fact none of us know since the map has not been shared publicly as far as I know.

Mehrdad, read this: https://www.danhorton.net/Misc/Nigel Speedy - Ignition Advance .pdf

Distributed with author's permission, also available at the Kitplanes website.

Applies to parallel valve.

 

[Bavafa]

Mehrdad, read this: https://www.danhorton.net/Misc/Nigel Speedy - Ignition Advance .pdf

Distributed with author's permission, also available at the Kitplanes website.

Applies to parallel valve.

Thank you Dan, much appreciate the info and the link.
I had read this before and re-read it again. I believe it was around the same time that I had decided to settle with something simpler for my safe flying. I remember one time that I was testing and had started to get dark and I made one advance change that made my engine run extremely rough. I was near a long runway so I doubt it would have been catastrophic but it made me realize that I don't know enough to experiment so much. So, based on your findings and another gentleman here that I can't remember his name and my own experiment I have settled on two timing advances, one that increases the advance to 24 BTDC for normal hamburger flying when I am ROP and nother to 29 BTDC when I am traveling which I am LOP.

One thing that I try to keep in mind, bad things to the engine may not happen in one big bang but as an accumulation of stress over time. This is the reason that I stop experimenting beyond my firm knowledge and understanding of the engine operation.

 

[akschu]

The P-MAG, not to be understated is self powered. No other EI does this. Contrarian's counter OH YEAH...my EI has double batteries, back up alternator and switches on the panel for main, avionics, backup, emergency buses. Great, but it comes at cost of weight and complexity. I never said having an electrically dependent ignition is bad, but it is something that must be addressed seriously. Even Ross at SDS had an off field landing in his Subaru powered RV6 due to ignition. We butt heads on automotive engines as well, however I would trust his CPi-2 product any day. Bottom line let's recognize that P-Mag makes a good and unique well supported product in the choices we have. Not for everyone. Fine. But don't spread fake news it does not perform well. That is categorically false.

There are two EI products that are self powered, SDS CPI-2 and p-mag.

The p-mag accomplishes this with an onboard generator that is built in that starts working at 1000rpm and the CPI-2 does this with a dedicated battery directly attached to the system.

You can't make the case that one is self powered and the other is not simply because the battery/generator is or is not inside the same housing as long as it's dedicated and part of the system. However, you could argue that the p-mag is much more compact and self contained and because of that it's easier to install.

Looking at this objectively, you basically have two solutions: one is mechanical with bearings, gears, generator, and the other is electrical with sensors and a battery backup.

In my risk analysis I look at it like this:

The p-mag has mechanical points of failure like bearings, but the CPI-2 does not.
The p-mag electronics/wires are subject to heat and vibration, but the only part of the CPI-2 subject to heat and vibration are the pickups and possibly coils.
The p-mag has some ability to give custom timing, the CPI-2 gives you tons of control. It can be as simple as a 20* mag or a 25* mag or as complex as what was posted above with button presses.

The only thing I don't like about the CPI2 is the install is more involved and it takes up panel space.

 

[akschu]

Largely true. Spark is spark, despite all the silly advertising claims.

Hey Dan, I was under the impression that something that could jump a larger gap with more power behind it could ignite leaner or richer mixtures than a mag, thus allowing you to go further LOP and making flooded hot restarts slightly easier.

Do you have any data on that? I'm happy to avoid mechanical devices and use electronics, but I was under the impression that it would work better on the far edges of the air:fuel ratios.

 

[Toobuilder]

"Toolbuilder": I find many of your comments to be a bit rude and sarcastic, and I really don't need your attitude.
I have had and installed every type of EI out there, so I really don't need a lecture from you!

Considering this thread is comparing 2 types of EI and their respective features, your off topic post about magnetos is also a "...bit rude and sarcastic..." and we certainly have plenty of threads debating the merits of magnetos vs. EI so we "...don't really need a lecture from you..." either. That said, this is the internet and I understand that short, seemingly curt responses are usually the result of convenience, not malice.

And yes, some of us "need" the flexibility that EI, and specifically SDS offers. My engine was built specifically around auto fuel and really hot weather flying. If I had magnetos (or fixed timing EI), the operating envelope and therefore utility of my rocket would be diminished. In my case the flexibility of the spark curve is an enabler to my mission.

 

[DanH]

So, based on your findings and another gentleman here that I can't remember his name and my own experiment I have settled on two timing advances, one that increases the advance to 24 BTDC for normal hamburger flying when I am ROP and another to 29 BTDC when I am traveling which I am LOP.

That would be Marvin. He does good work.

24 BTDC when rich is probably fine, although close to 20 would be better at high power. Don't know what it would take to do it with a p-mag

One thing that I try to keep in mind, bad things to the engine may not happen in one big bang but as an accumulation of stress over time.

Well said sir. It's a very real factor with too much advance. The issue is very high peak pressure. It's the fundamental behind why folks like George Braly have long promoted running LOP...the slow burn rate delays in-cylinder pressure rise, moving it further beyond TDC, where the piston has moved further down the bore. The result is far less stress on the studs, case, and aluminum heads. Adding advance moves peak pressure back toward TDC and higher.

To the best of my knowledge, the GAMI crew has never encouraged ignition systems with advance.

Here's a fundamental illustration from their seminars :

 

[DanH]

Hey Dan, I was under the impression that something that could jump a larger gap with more power behind it could ignite leaner or richer mixtures than a mag, thus allowing you to go further LOP and making flooded hot restarts slightly easier.

That's largely true, although the details are more complicated than the statement suggests. If forced to condense regarding power, long duration is more valuable than high amperage in extending the misfire limit. Moving toward the middle of the mixture range, more amperage speeds initial inflammation, effectively a small timing advance, but that's about all. Quoting a favorite reference (see below)...

...away from the lean or dilute* stable operating limit increasing the discharge current or duration has no significant effect on engine operating characteristics.

*("dilute" means diluted with exhaust gas via an EGR system)

Yes, generally more gap is better, but plug configuration makes surprisingly little difference. Practical gap is mostly a function of (1) available voltage, (2) voltage rise rate, and (3) the resistance of short circuit paths.

Although we get bombarded with advertising copy talking about high available voltage ("The Master Blaster offers up to 60,000 volts!"), reality says actual running voltage will be no higher than that necessary to form an arc across the plug electrodes. A system capable of 30kV and a system capable of 60kV will fire the plug much the same if it only takes 20 kV to jump the gap. Both systems will rise to 20, then begin to drop. It's known as the breakdown voltage.

Rise rate describes how rapidly secondary voltage leaps from zero to breakdown. Rapid rise is the best defense against plug fouling. A slow rise rate means there is more time for electrons to leak away via conducive deposits. It's why CDI systems are popular on 2-stroke engines. CDI's generally have a much faster rise rate compared to inductive ignitions.

Short circuit paths are simply any route with less resistance than the open plug gap. Although we tend to think of things like damaged plug wire insulation, the significant magneto problem is the distributor rotor. Open the plug gap too much, and you're likely to get misfire, but it's not because the secondary voltage isn't high enough to jump the plug gap. It's because jumping to a ground inside the distributor is now easier than jumping the gap. And it gets worse as altitude increases.

The best magnetos have large distributors to combat the above. Our EI's have none, so we run 0.035" gaps because we can.

Do you have any data on that? I'm happy to avoid mechanical devices and use electronics, but I was under the impression that it would work better on the far edges of the air:fuel ratios.

I recommend the most recent edition of Haywood's Internal Combustion Engine Fundamentals. The Bosch Electrical/Electronic Systems handbook is an old favorite.

 

[RV10inOz]

That would be Marvin. He does good work.

24 BTDC when rich is probably fine, although close to 20 would be better at high power. Don't know what it would take to do it with a p-mag


Well said sir. It's a very real factor with too much advance. The issue is very high peak pressure. It's the fundamental behind why folks like George Braly have long promoted running LOP...the slow burn rate delays in-cylinder pressure rise, moving it further beyond TDC, where the piston has moved further down the bore. The result is far less stress on the studs, case, and aluminum heads. Adding advance moves peak pressure back toward TDC and higher.

To the best of my knowledge, the GAMI crew has never encouraged ignition systems with advance.

Here's a fundamental illustration from their seminars :

View attachment 54731

Dan, I assume you may have done the APS class at some point, but to reaffirm your post, the reason much advance is of no value is that we run fixed speed engines. We show the effects of timing in Dyno runs and we have a similar graph to this showing standard, retarded and normal timing.

The only marginal gain is when at low MAP and very lean mixtures, a couple of degrees help.

All the best.

 

[bakercdb]

Well said sir. It's a very real factor with too much advance. The issue is very high peak pressure. It's the fundamental behind why folks like George Braly have long promoted running LOP...the slow burn rate delays in-cylinder pressure rise, moving it further beyond TDC, where the piston has moved further down the bore. The result is far less stress on the studs, case, and aluminum heads. Adding advance moves peak pressure back toward TDC and higher.

Dan
I have read some old P&W airline operating manuals and (IIRC) remember them advancing timing LOP as normal operations They were obviously shooting for both high efficiency and maximum engine life. Although those giant complex radials aren't our little flat engines.

Thanks for all the great input on the forum

(Some good info in those old publications. Seems like GA is rediscovering concepts known and used 60 years ago..)

 

[Carl Froehlich]

I note with interest no data on before and after engine efficiency (as in miles per gallon) with SDS. Who will want to offer this up?

I did post in 2020 about before and after engine performace when installing a single six cylinder pMag on my old RV-10 (still flying, pushing 800 hours on the pMag).

Six cylinder pMag - flying

All, I installed the final production verson of the six cylinder pMag on my old RV-10. I had installed a beta version, it is now replaced with this standard version that is being shipped out to customers. Installation was very simple. On install you set the timing to whatever you want. For...

vansairforce.net

Many of the posts on this thread based on opinion (mine included). I did however post a before and after efficiency gain when going from two mags to a single six-cylinder pMag and one mag on an IO-540 RV-10, flying with the same load and close to the same conditions. I'd be interested to see similar before and after data for SDS or just some other EI as compared to two mags.

As I have stated, I would assume such cruise efficiently gains are provided by any EI that has a reasonable timing advance like the pMag. But this is just my assumption.

Carl

 

[DanH]

...the reason much advance is of no value is that we run fixed speed engines.

Advance has value, but as you say, not because of RPM. For us, the value is found in compensation for faster or slower combustion rates. It's a Goldilocks thing....too little, too much, or just right.

Let's introduce readers to a concept with which I know you're familiar. As an empirical rule, most engines produce maximum torque when peak pressure is reached between 13 and 15 degrees after TDC. Our goal is to light the fire at the perfect point before TDC so maximum pressure is reached at the desired point after TDC. The thick books call perfect ignition point MBT timing, the spark advance which results in Maximum Brake Torque.

If combustion rate was the same under all conditions, then indeed, we could set one perfect fixed timing. However, burn rate is variable due to several factors. Mixture is a significant variable, very rich being slow, slightly rich of stoichiometric being fastest, and very lean being very slow. That's exactly what you're seeing in the APS illustration above. Here's the same shot, edited to add the desired point of peak pressure at 14 ATDC (magenta line).



In this illustration ignition timing is 20 BTDC for all three mixtures. The 50 ROP peak pressure (black) arrives too early; it's a fast burn mixture. The 50 LOP peak pressure (green) is quite late, because lean mixtures burn slow. The full rich peak (blue) is just faintly late. Slight leaning from full rich would nail the desired point of peak pressure. APS teaches the late peak for lean mixtures is a good thing, because it offers lower peak pressure, i.e. less engine stress. To compensate for the reduced torque, they add manifold pressure. It's a good way to run an engine, in particular if economy and longevity are the top priorities.

Enter the gearheads. They want the the last bit of performance, no matter how you define it. The peak pressure point for a lean mixture is late, and besides, with a non-turbo Lycoming we can't just bump up the manifold pressure. So what to do?

Note the position of the LOP peak pressure, at about 24 degrees after TDC. If we replace the fixed timing ignition with one offering variable timing, we could lean to 50 LOP, then ask our ignition to advance to 30 degrees. Lighting the lean mix 10 degrees earlier would shift peak pressure to 14 degrees after TDC...perfect! For that lean mixture, 30 BTDC would be MBT timing.

Ahhh, but there's a catch. Current EI's adjust timing based on manifold pressure and RPM. They currently cannot incorporate mixture state into their advance programming. Consider the black 50 ROP peak. It's already too early. Adding 10 more degrees of advance would place peak pressure almost on TDC. Pressure, cylinder stress, and temperature would all go way up the scale. Not cool.

That's why a single ignition advance schedule can't deliver correct timing for both lean mixture and best power mixture. It takes two switchable maps, or an advance yes/no choice. Owners flying EI's with a single advance schedule need to be aware, and set up the system conservatively so it's not like Goldie's porridge too hot.

 

[kearney]

Note the position of the LOP peak pressure, at about 24 degrees after TDC. If we replace the fixed timing ignition with one offering variable timing, we could lean to 50 LOP, then ask our ignition to advance to 30 degrees. Lighting the lean mix 10 degrees earlier would shift peak pressure to 14 degrees after TDC...perfect! For that lean mixture, 30 BTDC would be MBT timing.

Ahhh, but there's a catch. Current EI's adjust timing based on manifold pressure and RPM. They currently cannot incorporate mixture state into their advance programming. Consider the black 50 ROP peak. It's already too early. Adding 10 more degrees of advance would place peak pressure almost on TDC. Pressure, cylinder stress, and temperature would all go way up the scale. Not cool.

That's why a single ignition advance schedule can't deliver correct timing for both lean mixture and best power mixture. It takes two switchable maps, or an advance yes/no choice. Owners flying EI's with a single advance schedule need to be aware, and set up the system conservatively so it's not like Goldie's porridge too hot.

For those who are unaware, the SDS system allows spark advance and mixture adjustment with the flip of switch / push of a button.

In my case, I lean 8% and advance 5 degrees (20 total) BTDC when I go LOP. This happens instantly. The advance squeezes a little more power out and offsets *somewhat* the power loss due to fuel reduction. Both the advance and the mixture adjustment can be set and/or adjusted in flight. My 350+ hours flying this way have been unremarkable.

 

[M McGraw]

Many of the posts on this thread based on opinion (mine included). I did however post a before and after efficiency gain when going from two mags to a single six-cylinder pMag and one mag on an IO-540 RV-10, flying with the same load and close to the same conditions. I'd be interested to see similar before and after data for SDS or just some other EI as compared to two mags.

As I have stated, I would assume such cruise efficiently gains are provided by any EI that has a reasonable timing advance like the pMag. But this is just my assumption.

Carl

I think spark is spark so long as it is enough spark to light the mixture. With that said, two different systems at the same advance should yield exceedingly similar results. I suspect you could just have mechanically advanced your magnetos to the tested cruise position and gotten the same result. The issue then becomes can you safely climb to that cruise altitude with that same magneto and are your CHT’s acceptable to you. The advantage of variable EI is far more nuanced than a singular test condition. The advantage of EAB is we each have the right to find that compromise.

 

[U2drvr]

Ahhh, but there's a catch. Current EI's adjust timing based on manifold pressure and RPM. They currently cannot incorporate mixture state into their advance programming. Consider the black 50 ROP peak. It's already too early. Adding 10 more degrees of advance would place peak pressure almost on TDC. Pressure, cylinder stress, and temperature would all go way up the scale. Not cool.

That's why a single ignition advance schedule can't deliver correct timing for both lean mixture and best power mixture. It takes two switchable maps, or an advance yes/no choice. Owners flying EI's with a single advance schedule need to be aware, and set up the system conservatively so it's not like Goldie's porridge too hot.

The latest version of SDS (EM6) can add an O2 sensor and use that data in addition to MAP and RPM (like all modern cars do) to adjust both mixture and timing. This is not recommended for 100LL because the lead quickly fouls the O2 sensor, but the days of 100LL will soon come to an end (hopefully.)

 

[gmcjetpilot]

There are two EI products that are self powered, SDS CPI-2 and p-mag.

No the SDS has back up battery with limited life.

The p-mag accomplishes this with an onboard generator that is built in that starts working at 1000rpm and the CPI-2 does this with a dedicated battery directly attached to the system.

Correct, been following EI since Jeff rose. (late 80's)

You can't make the case that one is self powered and the other is not simply because the battery/generator is or is not inside the same housing as long as it's dedicated and part of the system. However, you could argue that the p-mag is much more compact and self contained and because of that it's easier to install.

Yes I can and don't care. One NEEDS a battery one does not. You are confused or conflating self powered electrically independent to back up power. I am just saying there is a difference, and one is more independent. P-Mag (and the Slick or Bendix Magnetos) are truly electrically independent, traditional Magneto to even greater extent. For those who don't know the P-Mag uses ships power when it is available. . No need to beat the horse, it is dead.

Looking at this objectively, you basically have two solutions: one is mechanical with bearings, gears, generator, and the other is electrical with sensors and a battery backup.

In my risk analysis I look at it like this:

The p-mag has mechanical points of failure like bearings, but the CPI-2 does not.
The p-mag electronics/wires are subject to heat and vibration, but the only part of the CPI-2 subject to heat and vibration are the pickups and possibly coils.
The p-mag has some ability to give custom timing, the CPI-2 gives you tons of control. It can be as simple as a 20* mag or a 25* mag or as complex as what was posted above with button presses.

The only thing I don't like about the CPI2 is the install is more involved and it takes up panel space.

All great points. Tons of controls, bells, whistles, or wires to through firewall and panel... Great. If that turns you on, go for it. I don't need tons of control. It is an aircraft engine droning on at 65% power for hours punctuated with short periods of steady full takeoff, steady climb and descent power.

I never poo-poo any electronic ignition of which there are far far more than what has been mentioned. Great kit plane article

Electronic Ignitions

Electronic ignitions can offer benefits over the standard magnetos, including lower maintenance and better fuel economy.

www.kitplanes.com

The most comprehensive EI (ElectroAir/ jeff rose) vs a Bendix 1200 (high energy magneto) test.

https://www.electroair.net/pdfs/ignition_dynamicsl.pdf

https://www.electroair.net/pdfs/ignition_dynamicsll.pdf

https://www.electroair.net/pdfs/ignition_dynamicslll.pdf

Here is my analysis.

• P-Mag bearings is a NON issue, inspection out of an abundance of caution and is not hard to do. The completion or detractors will make hay with it. True DRILLING holes to put magnets in your ring gear fitting and mounting pickups and wiring near the alternator belt does not have a "bearing" so to speak. I have had a belt become "undone" and whip around the cowl and do some minor damage. If it takes out the sensor or wiring you may lose both ignitions. I could be paranode but hey "it is not paranoia if they really are out to get you". Ha ha. The chance of bearing issues on P-Mag causing grief is less than a wayward alternator belt in my opinion. Both rare and preventable with basic maintenance. End of that.
• You can adjust the P-Mag with two canned advance curves or customize it with a computer or EI Commander (but you are not smarter than the existing curves). Yes other brands of EI have way more flexibility. Do you need it? I NEEED a Ferrari but I drive a VW. Also PRO ENGINE builders fear amateurs' monkeying with timing curves. You can damage an air-cooled Aircraft engine very quickly, so conservative curves (not optimal race timing of a street rod) is wise. If you have a hot rod aircraft engine FIXED timing may be best, which a magneto does, or a P-Mag does if selected. CONSERVATIVE = Safety. Aircraft engines have a NARROW range of operations. It is not rocket surgery, or brain engineering. Ha ha. Curve adjustment is way more useful in cars. Also if your car engine blows up you pull over.
• People understand electrical architecture better now and how to keep the spark going on EDI (Electrically Dependent Ignition).
• SDS CPI was clever to integrate battery backup as an optional purchase to the basic unit. Nice.
• Add to ANY EI, something like a TCW IBBS BACKUP BATTERY SYSTEM, 12 volt, 6 amp-hour, Li-Fi-PO4 $410.00 , weight 2lbs 2oz.+ wires, switches
• Add your own essential isolated DC back up battery bus, 15 ways to Sunday. I have seen schemes that shames the B777. (all of these backups adds weight)

None of this is in dispute. However as an example, the fancy Dimond diesel twin DA62 and predecessor DA42 has had at least (may be more) two loss of power accidents I know of due to ignition failure. It uses automotive based diesel engines and is 100% electrically deponent, both ignition and fuel injection. if a $1.49 million dollar plane with two engines can have this happen, total loss of power due to power failure and loss of ignition (and fuel injection) your RV can to. I suggest we don't be too cavalier. Even SDS CPi Ross had loss of ignition long ago (pre CPi). A lesson he learned. I think now everyone knows.l how yo guard. I fly GA planes as a CFI. I have had total loss of electrical power. The Battery kept radio and transponder going. Engine needs no electricity for spark or fuel.. The engine gauges were vacuum except Turn coordinator. Actually it had two G5 gamin's with back up batteries for about 30 min. It was VFR so I and student land. It was a belt issue. On C182 they can shake off belts. Again protect your timing pickup from the belt if running magnets on the ring gear bracket.

. The P-MAG does have some advantage, self powered, electrical independence from a battery. If you choose to play mental gymnastics with a side of cognitive dissonance that this is trivial or not important, OK. There is NO DEBATE in my mind, the P-Mag is a cool design and the only one on market like it. If it was easy others would do it. It is not easy. The other designs could be cobbled together with off the shelf stuff.

16 years P-Mags have been out, (before my time as customer). There were some early teething pains. Those were resolved, and it has become a reliable trust worthy high energy (HE) Electronic Ignition (EI) distributor less, inductive ignition. Many OPINIONS of P-Mag come from rumors, myth and some early design issues long ago addressed.

The design has been refined long ago from the 113 to the 114, and has also been stable for a long time (CLICK ON LINK IF YOU WANT TO SEE)

114 Series – E-MAG Electronic Ignition

emagair.com

Series 114 Refinements:​

• New sensor magnet mount – New design and manufacturing process for position sensor magnet mount.
• Firmware – The routine for setting, storing, and loading timing information has been completely rewritten to assist recovery functions following gray power and system reset events. [This feature was first introduced in firmware version 27 for installation in series 113 ignitions.]
• Sensor Alignment (self-monitoring) – If the processor detects a position sensor misalignment at power-up, it will block further operation until proper alignment is restored. The block also activates an LED alert signal.
• Internal Power Transition – P models will transition to internal power as soon as engine speed permits, at which point the internal alternator becomes the “primary” power sources and the aircraft buss becomes the “back-up”. Typically,800 rpm is needed to self-support. By 1400 rpm the ignition is fully transitioned off the aircraft bus.
• Finned Nose – Fins have been added to the nose section that (in conjunction with blast tubes) further improves cooling, and allows us to eliminate some (but not all) of the openings in the electronics case.
• Spark Plug Alerts – Circuit board hardware is added to report (via EICAD v4 to be released soon) the ignition coil discharge rate.
  • A rapid discharge rate indicates a spark plug or plug lead is fouled (shorted).
  • A slow discharge rate indicates a spark plug or plug lead is open (broken).

The difference is two P-mags gives you redundant power / ignition apart of any battery. Electrically Dependent Ignitions (EDI) regardless of number of alternators/batteries is still subject to failure modes. Often these back up systems are modest and not for sustained flight. The P-Mag has many safety and alert features that don't get hype as it is designed to not have a fancy panel display. I like fancy but I also like simple and get the job done. I will not lie I am jellious of the fancy panel. I got over it for what I paid for my P-Mags (got a new used pair).

 

[gmcjetpilot]

The POINT I WAS MAKING (not re-hash the P-Mag debate) is HOT SPARK WARS.... You know you only need about 0.20 to 2mJ to ignite gasoline engine. 1 Joule is equal to 1 Newton over 1 meter. One Joule is equal to 1 joule per second or 1 kg⋅m2⋅s−3. One watt equal to one joule (J) per second: W = J/s. When we say mJ it is milli-Joule, milli or 1/1000th of a joule. Watts are also expressed in volts x amps. So the energy is very low but VOLTS very high to jump the gap. All ignition produce high voltage to make a spark jump the gap of the plug under high combustion pressures.... It is not that hard to get high voltage with a coil which has primary and secondary windings. Coils are transformers and not magic or special secret sauce. All EI's are using coils made for automotive industry, Ford, Chevy, Bosh, NGK, DENSO, MSD... They come in many forms, including Integral Ignition Coils that go directly on the spark plug. Cool. Most we see now are coil packs to drive 1, 2, 4, 6 or 8 spark plugs. P-Mag use two coil packs in one 4 plug tower, with the lost spark principle, very common and simplifies the system, timing, lower weight etc... Works well. Most EI's use lost spark. To have one dedicated coil per plug is "better" but overkill for a low RPM 4 stroke engine. It would add weight.

PMAG quote:

"High Energy Spark – When is enough… enough?​

​

Ignition shoppers are sometimes encouraged (by our competitors) to compare the spark energy output of different electronic systems. The implication and challenge being, the greater the energy – the better the ignition. E-MAG has a distinctly different perspective that runs counter to some, if not most, in the industry. To explain, we’ll start with our own design objectives: Spark energy should be increased ONLY to the extent necessary to achieve the intended result – AND NO MORE.​

​

This approach stems from a simple truth. The benefits of high energy spark are non-linear. Meaning, after an initial boost there is little or no benefit derived from more (and more) energy. There is, however, an increased burden in the form of additional heat, stress, wear, and weight associated with the creation and constraint of excess spark energy. These can be managed, but if the additional energy doesn’t produce a benefit – why do it in the first place?​

​

E-MAG uses a closed-loop control to manage and regulate spark energy at predetermined (elevated) levels. Our energy output is a function of deliberate design choice – not a limitation of capacity. Again, the goal is to deploy the minimum energy required – not the maximum amount possible.​

​

This energy strategy has other benefits. E-MAGs are smaller, lighter, and operate cooler than competitors. This allows us to mount directly on the engine . . . . where ignitions were designed to go. Even more important, direct mount provides the drive for E-MAGs built-in electrical power back-up . . . which is the “elephant in the room” when it comes to comparing and contrasting the merits of flight-critical electronic systems. ​

So the P-Mag is making way more spark energy than "needed" by a factor 8 to 20 times. There is a point of diminishing returns. The FORD EIS 4 cylinder tower coil can make 40,000 volts. Who cares if its' Ford or Chevy. P-Mag sizes the spark properly. You can vary the VOLTS and DURATION of the spark by adjusting the gap. Small gap lower volts (spark size) but gives longer duration, larger gap requires more voltage and shortens duration. The P-Mag sets NGK plug gaps to 0.035 and fires them easily, even in super lean conditions. More spark energy will have limited benefit, some but limited benefit. However for bragging rights people point to their big coil. Ha ha. I have SEEN one brand of EI and their "test" results which I find suspect? I am just saying. If I take it at face value, even if they claim over twice the spark energy, I go back to "so what"? Is that needed? May be in some Reno air race engine run well over red line it can benefit?

I would love another CAFE Foundation type test with many EI brands side by side in a controlled manner (aircraft flight test) and see how much difference their is. As I said Magnetos are not bad. Most of the benefit in EI's they all have: "hot spark" (more than enough), less or no moving wear parts, no points, no rotor, no distributor cap and the advanced timing gets you 90% of what is possible. Car test of multi strike top end MSD CD (Capacitive Discharge) ignitions adds 5 HP in 350 HP car engines peak power. That is a bit over 1% in extreme conditions (higher RPMs than an aircraft engine). Other factors such as induction, exhaust. Also as I said autopilot is like finding a few miles per hour block speed on a trip. Most pilots heading and altitude wonders when hand flying. Going stright and level is more efficient.

To get full benefit or pay back on investment on your EI you have to fly more than less at +8000 feet (10,000 feet better) and lean as much as possible (as allowed by engine manual). LOP with smooth engine is holy grail. Say you save $5 and hour on fuel. You spent $5000 on the EI. So pay back is 1000 hrs of optimal high flying low power LOP flying, Lets say half of your time is doing low power LOP optimal flying. That is 2000 hours total. You fly 100 hrs a year. That is 20 years pay back? .Regardless is less maintenance of an EI has value.

As was pointed out P-Mag recommends 100 hour bearing check as some defect or weakness. You pull it out and check for play. Put it in and time it easily, another P-Mag benefit, ease of timing. As I said the aftermarket EI Commander can monitor timing "jitter" which, according to EI Commander, indicates play in bearing. This is not P-Mag saying this but EI Commander, but they claim you never have to remove the P-Mag if you have this cockpit monitor. Personally having a look is good. It can be done in a few hours (assuming you already have the cowl off and doing other work). Plus P-Mag users with way more time on them report no wear after many 1000's of hours. The bearings are not expensive. Also I do believe the early bearings have long been up graded. I am pretty sure they do this to maintain price sensor gaps. It is not like a catastrophic failure just precise tolerance. It is a clear CON of the P-Mag it has direct accessory case drive which means you have to check it. It also is the PRO due to ease of installation and compact integrated design. No free lunch.

What if another ignition has 2 or 3 or 10 times the spark energy of another EI which functions fine? Great. That flame thrower ignition will uses more power, the electronic components including the coil (which can burn out) get HOT HOT HOT. Coil burnout is fatal and happens, but it is rare if you are not over saturating the coil with higher power input with huge spark plug gaps. Will an ignition hotter than the sun give better performance? Yes. How much. No one really has proved it by careful reputable experiments, observation, data, math, science, physics, and documented flight test. Not withstanding the bench test by one EI brand who does not disclose all the test parameters, all ignitions EVEN THE MAGNETO make plenty enough spark to make an engine go BANG, BLOW, SUCK, SQUEEZE and BANG again over and over. We (engine makers) have been doing this well over 100 yrs. Delco 1912 (Charles F. Kettering) first on a Cadillac. The HE EI's came out widely in mid 1970's and distributor less coil on plug EI's by the 1990's. It is old tried and true technology. BTW the old points coil ignitions worked. Hot spark but limited timing advance, all mechanical. EI was a big gain over that.

If you DESIRE the HOTTEST spark known to mankind... well P-Mag may not be it. If the hour or two once a year/100 hrs (recommend) is too much for you than not for you. If you want easy installation and 99% of the benefit an EI with timing advance can give , with TRUE ELECTRICAL independence, ease of installation, than P-Mag is worth the look. The non technical side is Customer Service. E-Mag air has excellent support from near Dallas (central USA) and the staff is well suited to keep this company going for many decades more, even after Brad retires. Is it for everyone? No. It is right for me... Yes, I did THUNK about it, secure in my decision.

I am not going to point out short falls of other brands. Per the Kit Plane magazine article on ignitions I link to in previous post, there are many EI's. Some are certified some not. NOTE certified ones do have advance timing but do NOT allow user modification. No shock. I will say Magnetos are NOT garbage (but do require 500 hr service and really do wear, plastic gears, points, rotor, cap). The difference, true real world difference for the average RV builder with a stock Lycoming using a magneto vs EI flying a 100 hrs a year is going to be small. The difference between different EI brands in performance will also be small, but clearly some have more flash panel displays. Nice. All will give better overall performance over a magneto, easier starting, smoother running, ability to lean deeper and maintain smooth operations (if indication and exhaust are tuned properly).

I get the passion, favoritism and loyalty of one brand of EI over another. I have no dog in fight, I think they all have something to offer. They are all pretty cool. The P-Mag just happens to be THE ONLY ONE that does not need a battery of any kind to run in flight, plus bonus is easy to install.

 

[RV6_flyer]

The most comprehensive EI (ElectroAir/ jeff rose) vs a Bendix 1200 (high energy pressurized magneto) test.

https://www.electroair.net/pdfs/ignition_dynamicslI.pdf

https://www.electroair.net/pdfs/ignition_dynamicslII.pdf

The above two links did NOT work.

Going back to the Domain URL, I was able to get to the correct URL location and documents.

https://www.electroair.net/pdfs/ignition_dynamicsll.pdf

https://www.electroair.net/pdfs/ignition_dynamicslll.pdf

 

[Bavafa]

No the SDS has back up battery with limited life.

I am interested to learn if anyone has tested this either in flight or on the ground. Run the engine and flip your master or whatever that kills all electrical system to OFF.
BTW, I am not implying that it will not work only if it has been tested to confirm.
Currently I am troubleshooting a RV10 that has Light Speed ignition with two alternator and two backup battery. He had an engine out in the run up that was as a result of loose battery cable.

 

[DanH]

The P-Mag just happens to be THE ONLY ONE that does not need a battery of any kind to run in flight...

McQueen, do you throttle to your typical run up RPM, switch battery power to OFF for both, then check one ignition at a time?

Currently I am troubleshooting a RV10 that has Light Speed ignition with two alternator and two backup battery. He had an engine out in the run up that was as a result of loose battery cable.

In other words, one ignition was inop when checked on the runup pad?

 

[Chkaharyer99]

I am interested to learn if anyone has tested this either in flight or on the ground. Run the engine and flip your master or whatever that kills all electrical system to OFF.
BTW, I am not implying that it will not work only if it has been tested to confirm.
Currently I am troubleshooting a RV10 that has Light Speed ignition with two alternator and two backup battery. He had an engine out in the run up that was as a result of loose battery cable.

Mehrdad,

Yes. Definitely.

I bought and installed the SDS CPI2 in my RV-8. I’m pretty sure I got one of the first units SDS built. I also have the SDS battery backup system installed. It uses a 12 volt 2.9 AH AGM battery. During run up, before each flight, using the SDS CPI controller/display, I push a few buttons to check the voltage and operation of my backup battery. The controller switches off power from the primary source, in my case I have it wired directly to the ships main battery. I also do a mag check to see what my RPM drop is. In addition to the aforementioned procedures, I purposely toggle off the main power to one SDS channel at a time then both channels off to be sure the system automatically shows a fault (Red LED on the display) but also switches over to the backup battery. The switch over occurs instantaneously and seamlessly, there is no noticeable change. In flight I have switched off one channel then both and have ran it that way to verify it is operational.

Currently I run only one Plane Power alternator. I have had two plane power failures. One in flight. I plan to switch out the Plane Power for a B&C Alternator. I recently bought the Monkworkz - Ultra Lightweight generator and will install that soon As well. After taking a flight in your beautiful RV-14 equipped with PMags, I got panel envy. Thank you BTW. The quality of your build is outstanding.

My RV-8 is a parallel valve IO-360 with CS prop. Mechanical fuel injection via Bendix. considering SDS EFI.

 

[Toobuilder]

...APS teaches the late peak for lean mixtures is a good thing, because it offers lower peak pressure, i.e. less engine stress. To compensate for the reduced torque, they add manifold pressure. It's a good way to run an engine, in particular if economy and longevity are the top priorities...

Some clarity on this point that you have foot stomped at least twice in this thread....
Let's assume for the moment that the rich mixture, TO power ignition timing stamped on the data plate results in the PCP arriving at the optimum crankshaft angle for best torque. And lets assume the ignition timing matches that engine operating condition. Lets then assume that we go LOP and instead of allowing the fixed timing and the slow burn result in a late arrival of PCP (and lower stress), we advance the timing such that the PCP shifts back to that same "optimal" crankshaft angle for best torque...

In a NA Lycoming, does the "increased stress" of the advanced ignition timing exceed the stress the same engine saw at a sea level takeoff 10 minutes before?

 

[DanH]

In a NA Lycoming, does the "increased stress" of the advanced ignition timing exceed the stress the same engine saw at a sea level takeoff 10 minutes before?

Of course not. However, it does last longer.

 

[Bavafa]

Mehrdad,

Yes. Definitely.

I bought and installed the SDS CPI2 in my RV-8. I’m pretty sure I got one of the first units SDS built. I also have the SDS battery backup system installed. It uses a 12 volt 2.9 AH AGM battery. During run up, before each flight, using the SDS CPI controller/display, I push a few buttons to check the voltage and operation of my backup battery. The controller switches off power from the primary source, in my case I have it wired directly to the ships main battery. I also do a mag check to see what my RPM drop is. In addition to the aforementioned procedures, I purposely toggle off the main power to one SDS channel at a time then both channels off to be sure the system automatically shows a fault (Red LED on the display) but also switches over to the backup battery. The switch over occurs instantaneously and seamlessly, there is no noticeable change. In flight I have switched off one channel then both and have ran it that way to verify it is operational.

Mehrdad,

Yes. Definitely.

I bought and installed the SDS CPI2 in my RV-8. I’m pretty sure I got one of the first units SDS built. I also have the SDS battery backup system installed. It uses a 12 volt 2.9 AH AGM battery. During run up, before each flight, using the SDS CPI controller/display, I push a few buttons to check the voltage and operation of my backup battery. The controller switches off power from the primary source, in my case I have it wired directly to the ships main battery. I also do a mag check to see what my RPM drop is. In addition to the aforementioned procedures, I purposely toggle off the main power to one SDS channel at a time then both channels off to be sure the system automatically shows a fault (Red LED on the display) but also switches over to the backup battery. The switch over occurs instantaneously and seamlessly, there is no noticeable change. In flight I have switched off one channel then both and have ran it that way to verify it is operational.

Currently I run only one Plane Power alternator. I have had two plane power failures. One in flight. I plan to switch out the Plane Power for a B&C Alternator. I recently bought the Monkworkz - Ultra Lightweight generator and will install that soon As well. After taking a flight in your beautiful RV-14 equipped with PMags, I got panel envy. Thank you BTW. The quality of your build is outstanding.

My RV-8 is a parallel valve IO-360 with CS prop. Mechanical fuel injection via Bendix. considering SDS EFI.

Charlie,
That is great and thanks for sharing. Your test is somewhat like my test when I kill the ship's power to the PMAG which I do at every run up. On your next pre flight or after the flight, switch off your main battery/electrical system to make sure that is still running. As mentioned, my friend's RV10 with LS survives the typical test run but somehow removing the battery cable and main alternator as active, the engine will not run.

 

[Bavafa]

McQueen, do you throttle to your typical run up RPM, switch battery power to OFF for both, then check one ignition at a time?



In other words, one ignition was inop when checked on the runup pad?

No, while I don't know the exact circumstance of the engine failure during the runup area and right before takeoff, we have replicated the engine failure and it is repeatable if the main alternator is active and the battery cable is removed. This might have to do with the way VPX works as the VPX will trip the field CB due to an overvoltage that it sees when the battery cable is remove. This is a new to him RV that he has bought and we don't have all the info on the wiring so it is a troubleshooting in progress situation.

 

[Toobuilder]

Of course not. However, it does last longer.

So considering that a NA Lycoming typically has no limitations on TO power and will run happily at that power for a long time (with adequate cooling, etc), then even "optimized" timing at LOP is still some lower level of stress than the engine architecture is designed to accommodate.

 

[Chkaharyer99]

Charlie,
That is great and thanks for sharing. Your test is somewhat like my test when I kill the ship's power to the PMAG which I do at every run up. On your next pre flight or after the flight, switch off your main battery/electrical system to make sure that is still running. As mentioned, my friend's RV10 with LS survives the typical test run but somehow removing the battery cable and main alternator as active, the engine will not run.

Good suggestion. I will. Thanks for the tip.

 

[DanH]

So considering that a NA Lycoming typically has no limitations on TO power and will run happily at that level for a long time (with adequate cooling, etc), then even "optimized" timing at LOP is still some level lower than the engine architecture is designed to accommodate.

Of course. Note the Disciples of Ada also boost power when LOP. You advance timing, they advance manifold pressure. Neither is wrong. Which church to attend depends on what you're flying. Remember, the vast majority of the certified fleet runs on fixed timing.

 

[Bill Boyd]

Considering this thread is comparing 2 types of EI and their respective features, your off topic post about magnetos is also a "...bit rude and sarcastic..." and we certainly have plenty of threads debating the merits of magnetos vs. EI so we "...don't really need a lecture from you..." either. That said, this is the internet and I understand that short, seemingly curt responses are usually the result of convenience, not malice.

And yes, some of us "need" the flexibility that EI, and specifically SDS offers. My engine was built specifically around auto fuel and really hot weather flying. If I had magnetos (or fixed timing EI), the operating envelope and therefore utility of my rocket would be diminished. In my case the flexibility of the spark curve is an enabler to my mission.

Michael, you have set an example by your tone here. I'm not sure how the trophy system works on the new site, but if there's a Proverbs 15:1 award, you just bagged it.

I appreciate you handling this better than I would have, and we can all learn from it, to the benefit of the whole neighborhood. Well done and thank you.

 

[Bill Boyd]

McQueen, do you throttle to your typical run up RPM, switch battery power to OFF for both, then check one ignition at a time?



In other words, one ignition was inop when checked on the runup pad?

Another consideration for the P-mag operator: do you know the RPM threshold at which your specific P-mag specimens are no longer capable of self-powering? It's above idle. Brad has you test this, last time I looked. Commit this number to memory in your emergency checklist. Best not to cut throttle on final in a loss-of-ship's-power scenario, or you could (depending on windmilling effects) be facing an additional "helmet fire" just when you need it least.

Hundreds of hours on P-mags in the RV-6A. 100+ on the CPi2 in the RV-10. Popcorn at the ready

 

[Toobuilder]

Of course. Note the Disciples of Ada also boost power when LOP. You advance timing, they advance manifold pressure. Neither is wrong. Which church to attend depends on what you're flying. Remember, the vast majority of the certified fleet runs on fixed timing.

Since we almost exclusively fly NA engines and that is our target audience, I believe we need to be extremely clear that “optimum” ignition timing at ANY possible operating regime does NOT create harmful stress in the engine. I continue to see references on this forum concerning attempts to optimize ignition timing as something “hot rodders” or “racers” do. Not always - some of us have the tools to accomplish a level of engine management that has only recently been available, and we use those tools to keep the PCP/crank angle relationship as close to optimum as possible across the operating envelope. Yes, the vast majority of the certified fleet runs fixed timing - but that is certainly NOT a testament to efficiency or reliability, it’s mostly due to certification red tape.

So to foot stomp the “Goldilocks“ theme once again - timing can be too cold (late), too hot (early), or “just right” (optimum) - and optimum does not diminish engine life.

 

[akschu]

<sigh> I guess batteries don‘t count for self powering. Guess I need a generator for my phone…..

 

[Toobuilder]

<sigh> I guess batteries don‘t count for self powering. Guess I need a generator for my phone…..

Yeah, I don’t see the practical distinction either. If the chemical energy supply in the SDS backup battery outlasts the chemical energy supply in the fuel tanks, what difference does it make where that energy comes from? How is this different than the backup batteries attached to the EFIS displays? Is anyone going to land, refuel and then launch back into IMC running only on the backup power to their EFIS or ignition?

In the context of our airplanes, a “backup” gets you on the ground safely; a “good backup” gets to your next fuel stop.

 

[akschu]

Yeah, I don’t see the practical distinction either. If the chemical energy supply in the SDS backup battery outlasts the chemical energy supply in the fuel tanks, what difference does it make where that energy comes from? How is this different than the backup batteries attached to the EFIS displays? Is anyone going to land, refuel and then launch back into IMC running only on the backup power to their EFIS or ignition?

In the context of our airplanes, a “backup” gets you on the ground safely; a “good backup” gets to your next fuel stop.

Exactly, both the generator and battery are internal to the system in that they are both dedicated and managed by the system. Thus, I boils down to modes of failure and mx.

Lead acid batteries are super reliable but if you do no mx and only fly twice a year, then probably replace it yearly.

i do agree with Walt that ignition failure in Dillingham is probably easier to address if you have mags, but then again, nothing is preventing me from installing a mag in that case….

 

[Retooferab]

The reason I started this post was to learn more about the two systems. I had read about both on their websites and was wondering what most people’s thoughts were on the two different system. I don’t think that there’s a right or wrong system as they all work to achieve the same end result. I think some may do I a little better than others but it doesn’t seem that there’s a big difference in performance with either of these systems.
I’ve read this thread a couple of times now and there are a lot of knowledgeable people on here.
I’m thankful for all the information I have gained.

My plane currently has one magneto and a Light Speed ignition system. At a little above idle rpm it occasionally has a miss in the engine that is noticeable. I thought it may be ignition related. I’ve pulled the cowling and checked everything and it all looks good but I have yet to find the source of the miss.

 

[lr172]

Since we almost exclusively fly NA engines and that is our target audience, I believe we need to be extremely clear that “optimum” ignition timing at ANY possible operating regime does NOT create harmful stress in the engine. I continue to see references on this forum concerning attempts to optimize ignition timing as something “hot rodders” or “racers” do. Not always - some of us have the tools to accomplish a level of engine management that has only recently been available, and we use those tools to keep the PCP/crank angle relationship as close to optimum as possible across the operating envelope. Yes, the vast majority of the certified fleet runs fixed timing - but that is certainly NOT a testament to efficiency or reliability, it’s mostly due to certification red tape.

So to foot stomp the “Goldilocks“ theme once again - timing can be too cold (late), too hot (early), or “just right” (optimum) - and optimum does not diminish engine life.

I fully agree. I can't see how optimizing peak pressure occurrence is harming longevity of the engine. Pretty much EVERY modern automotive engine does this. They even go so far as to install knock sensors so that the ECU can continually push the timing advance right up to the edge and then back off just a hair. Many of these engines go to 250000 miles or 8000 hours. Most of the stress is coming from the absolute pressure level and not the relative position at which that pressure occurs, assuming it is sufficiently ATDC. so, running LOP even with optimized peak pressure still lower absolute pressures than running at PEAK. Operations at LOP produces cylinder pressures well below that of higher power regimes. Sure we can keep the retarding the timing until the engine only produces half it's power and that should REALLY extend the life of the engine. This is a balancing act and the only ones who really know the outcome are the ones that run these on dynos for months, then tear them down.

 

[DanH]

Since we almost exclusively fly NA engines and that is our target audience, I believe we need to be extremely clear that “optimum” ignition timing at ANY possible operating regime does NOT create harmful stress in the engine.

Come on Mike, that's a straw man. No one, including me, has said MBT timing is bad.

My interest is education. You're kicking me for explaining what a respected school teaches its students, a fleet segment who for the most part do not have the variable timing option, and thus cannot adjust to MBT when going lean. Is it wrong to explain what they do, and more valuable, why they do it?

I also explained the fundamentals (complete with illustrations) underlying the need for two timing schedules if MBT is to be achieved with both best power mixture and very lean mixture. Your preferred approach, yes?

Personally I use a third approach, but it's only suitable for the angle valve.

Different churches. I was raised Catholic, but it's interesting to know what the Methodists think.

 

[Walt]

i do agree with Walt that ignition failure in Dillingham is probably easier to address if you have mags, but then again, nothing is preventing me from installing a mag in that case….

Don't forget the mag gear, ignition harness, plugs and P lead you'll have to source/install if doing a field conversion.
(If it's on a 6 cylinder, you'll also need the mag gear/bearing assembly that you likely removed.)

 

[JGT]

SDS for a new built, P-Mags for an upgrade, easy choice

Don't forget the mag gear, ignition harness, plugs and P lead you'll have to source/install if doing a field conversion.
(If it's on a 6 cylinder, you'll also need the mag gear/bearing assembly that you likely removed.)

For my basic budget RV-8 0-360/FP build for ~100 hrs/ yr normal flying, would mags and auto plugs be the least expensive to install and maintain ?

 

[Carl Froehlich]

For my basic budget RV-8 0-360/FP build for ~100 hrs/ yr normal flying, would mags and auto plugs be the least expensive to install and maintain ?

If you stay with standard mags, you will also need to stay with aviation plugs.

Carl

 

[Toobuilder]

...APS teaches the late peak for lean mixtures is a good thing, because it offers lower peak pressure, i.e. less engine stress....

Not "kicking" you Dan, just suggesting a potential blind spot you may have BECAUSE you are so familiar with the subject. The above quote could easily be taken out of context for the less familiar.

 

[DanH]

For my basic budget RV-8 0-360/FP build for ~100 hrs/ yr normal flying, would mags and auto plugs be the least expensive to install and maintain ?

In the context of least expensive, look at a dual Light Speed Plasma III. It comes complete with plug wires, plug adapters, and auto plugs, plus it doesn't require mag drive gears. Although base prices are kinda similar, the extras can run up the tab.

Plan B? A listing here might net nearly new mags plus harness, from folks changing to EI's.

 

[Toobuilder]

i do agree with Walt that ignition failure in Dillingham is probably easier to address if you have mags, but then again, nothing is preventing me from installing a mag in that case….

That's debatable too. Depends on the failure mode. If I had to find a coil for my Bendix 1200 magneto or a coil for my SDS CPI because I was AOG in some Podunk town I'll bet I could source and install the SDS unit faster most of the time.

 

[Toobuilder]

In the context of least expensive, look at a dual Light Speed Plasma III. It comes complete with plug wires, plug adapters, and auto plugs, plus it doesn't require mag drive gears. Although base prices are kinda similar, the extras can run up the tab.

Plan B? A listing here might net nearly new mags plus harness, from folks changing to EI's.

I'd offer that if one looks at the basic CPI system and sources only those unique bits from Ross - and the rest of the commodity items locally, you can go pretty "cheap". The "and on" costs of mags are fairly compelling too, especially compared with CPI.

 

[DanH]

Not "kicking" you Dan, just suggesting a potential blind spot you may have BECAUSE you are so familiar with the subject. The above quote could easily be taken out of context for the less familiar.

The quote begins with "APS teaches..."

 

[gasman]

Yeah, I don’t see the practical distinction either. If the chemical energy supply in the SDS backup battery outlasts the chemical energy supply in the fuel tanks, what difference does it make where that energy comes from? How is this different than the backup batteries attached to the EFIS displays? Is anyone going to land, refuel and then launch back into IMC running only on the backup power to their EFIS or ignition?

In the context of our airplanes, a “backup” gets you on the ground safely; a “good backup” gets to your next fuel stop.

You could do that with a back-up battery. You can't do that with a P-mag. You would also be able to taxi off of the runway and to a safe location with a back-up battery.

 

[Carl Froehlich]

You could do that with a back-up battery. You can't do that with a P-mag. You would also be able to taxi off of the runway and to a safe location with a back-up battery.

Not a true statement. The pMag runs just fine with no electrical power input down to ~900 RPM or so (as I have tested). Trivial to manage.

As I have found in the field, backup batteries can become just dead weight if not maintained. The other problem with backup batteries is having more than one way to get the power from the battery to where you need it (for keeping the engine running or the panel up for IFR flight). I know of one RV with a wheelbarrow of backup batteries that has landed twice with a dark panel.

Understand how your electrical system works and what happens when something goes wrong.

Carl

 

[Walt]

In the context of least expensive, look at a dual Light Speed Plasma III. It comes complete with plug wires, plug adapters, and auto plugs, plus it doesn't require mag drive gears. Although base prices are kinda similar, the extras can run up the tab.

Plan B? A listing here might net nearly new mags plus harness, from folks changing to EI's.

Lightspeed is worst choice IMO, I've seen more problems with LSE than all the others combined, especially the Plasma III.

 

[RV6_flyer]

If you stay with standard mags, you will also need to stay with aviation plugs.

Carl

Slick and Bendix mags can use auto plugs but in addition to auto plugs / spark plug adapters, you will need to purchase and or fabricate an auto spark plug harness. There is at least one outfit that sells a kit.

 

[RV6_flyer]

Lightspeed is worst choice IMO, I've seen more problems with LSE than all the others combined, especially the Plasma III.

Ditto.