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Loss of timing
If we are talking about the incident where arcing at the alternator apparently caused this failure, my recollection was that V40 was designed to prevent this type of issue.
However that is why we have dual ignition systems, if one malfunctions you go to the other and land ASAP. When my LSE ignition started to play up I knew straight away and wen to the mag. No damage to the engine at all. Actually I may well fit a a different type of ignition in my next lycoming, with fuel injection, but am a happy PMag customer especially with Bills EIC as you can monitor the mags and see what is going on with them. |
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P-mag wants you to remove the units and do an inspection. The act of removal and replacement is not horrible, but opening up the back of the engine every hundred hours is not fun and definitely increases the risk of dropping hardware into that gaping hole. But the inspection itself is compelling. You are looking to see that all that stuff is still in place. Shaft endplay, magnet alignment? All that stuff is important and let?s face it, fragile. Plenty of warnings to handle this with kid gloves in the P-mag manual. In contrast, the CPI sensor is bolted to the side of the case with a mount stout enough to lift the engine with. If you have an end play or magnet misalignment problem, the crankshaft is broken. So yes, to answer your question ? zero maintenance for CPI. Further, the CPI sensor is potted so it is essentially chemical proof. If you want to wash the engine down with solvent or degreaser, you?re not going to hurt the sensor. Contrast this with P-mag, where the case is open vented. You have to cover the Pmags with plastic or remove them to wash down the engine because the boards will get soaked. And yes, it happens. I had a board replaced because solvent entered the case and ate the board. But the maintenance free aspect is not the primary advantage of CPI. That belongs to the fact that the P-mag curve ? even the most conservative one ? is too aggressive. We have known for years that P-mag equipped engines run warmer and some even exhibit ?CHT issues?. And thanks to the fairly recent flight test efforts an dissection of their curve by several members here, the cause is now clear: Too much advance at high power. In fact, the issue is so well known that even the maker of the third party programmer recommends his product should be used to adjust the problem away. That, or you can mechanically retard the timing (as I?ve done on my -8). But this doesn?t really solve the fundamental issue, it just masks it. True, people are not melting down engines and the issue is manageable by ?spoofing? the standard program, but why not get an ignition that works right out of the box? And on the subject of ignition curves, P-mag doesn?t even offer the LOP switch function of CPI. This is a very useful feature and a compelling discriminator for those that do cross country work. So CPI delivers a safe, cool advance curve for takeoff and climb, as well as a fuel stretching LOP setting and everything in between. The components are robust, proven with decades of use, and maintenance free. |
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Considering that I am somewhat familiar with the maintenance recommendation of PMAG “ the opening up the back of the engine and all that you listed” I will leave that portion out of the discussion since the complexity and risk of it seems to be a matter of opinion. What I like to know, what advance curve is provided by CPI and how much of customization is expected for the end users/customer? Not all of us are either interested or knowledgeable in finding the best curve thru hours and hours of flight testing. With CPI, right out of the box, do I get a default timing that is an improvement over other EIS and what is involved in the switch for LOP (both in terms of installation and usage) Is it just a toggle switch? I appreciate the info. |
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So with CPI, every sale is for an individual engine and client, not a one solution fits all. We ask engine type, CR fuel octane and will enter a custom base map for you if desired, slightly conservative to be safe. No need for you to do any programming if you don't want to. To think that an A or B curve suits every engine and mission out there is simply nonsense. No way it's optimal for all engines, where we commonly have CRs from 7.5 to 10 and even higher in some cases. Data plate timing for IO-390s is a lot less than most other Lycomings, many people run mostly on mogas, some fly low or high, some fly ROP, some LOP. Interesting how many seem to discount the science of flight testing results by Nigel, Dan and Michael here on VAF. In short, we can enter a safe curve for YOUR engine and mission, no need for you to do much if you don't want to. Likewise you have the ability to fine tune (in logical 1 degree increments) if you wish, plus change the amount of LOP advance which is selected on/off with a small toggle switch. So, there is no "standard" advance curve with our products unless you don't give us any details, in which case, we'll generally enter 24 degrees of rpm timing for O-235, 290, 320, 360, 540 engines and 20 degrees on IO-390 engines with zero MAP advance or retard- pretty much standard mag timing. But, this would not be a good idea on a 10 to 1 engine running mogas. |
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Is there some data that compares a fined tuned curve of your system vs. the stock curve, lets say curve A of a PMAG in terms of fuel saving/additional power, etc? I am hoping to see a measureable difference (perhaps fuel burn would be a good measureable indicator). |
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The LOP function is activated by applying system voltage to a discrete pin in the CPI connector. The physical interface for the LOP function is a toggle switch in my case. The LOP function is programmed by scrolling through the CPI windows until you get to a discrete LOP window. You simply toggle up or down to get the additional advance you want (3 degrees in my case). Once set, activation of the LOP switch simply tacks on an additional 3 degrees advance to the existing map. If you’re idling at 20 degrees, then activating the switch will give you 23 (20 + 3). If you’re at the top of climb and the normal RPM and MAP values have you at, say, 32 degrees, then the LOP switch give you 35 (32+3). It’s also noteworthy that this function is deactivated at high MP levels. So if you forget to turn off the switch and do a go around, no problem. I'm glad Ross answered the “as delivered” program because I never used it. I went straight to building my own. A casual glance in the manual shows it to be very conservative at high power though, and testing confirms that’s exactly what is needed. In fact, my testing shows that even Lycoming’s data plate timing value is more than required for takeoff. My program pulls up to 5 degrees off the data plate value in some circumstances. And for the record, I'm stock (8.5) compression. |
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Too much or too little may cause power loss or CHT issues and too much can reduce detonation margins, especially on mogas with high CHTs and IATs. Too little is generally safer than too much. I think Nigel's data is the most complete and Michael's showed us the extremes of WOT/SL vs. LOP/ low MAP up high. I think the OP was really asking if the original software, hardware problems experienced by Pmags were now licked and only interested in actual reliability in delivering sparks in the Pmag offerings of today. You'll get different answers from different people depending on their experiences. This thread has taken a new direction discussing other factors outside reliability. I'm not sure that serves the purpose of the OP's question. There have already been other threads comparing the various EIs available today. |
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This issue is the breadth of the curve. P-mags deliver very good LOP efficiency because they advance far enough to do some good up in that rarified air. Unfortunately, they start advancing so early that down low and rich they make plenty of heat and cylinder pressure, but don't do more work. Plenty of credible flight test results on this site to review for confirmation. In short, a good hot spark can be delivered by any EI, and the engine architecture does the rest when LOP. Rich mixtures are easy to light and there's really no difference what lights it off. But timing is everything. The compelling issue is if the EI can advance far enough to light the LOP mixture, pull it back enough for the best power mixture, and retard enough to protect the engine at the SL, 100% power mixture. Most any EI can deliver on some of these conditions, but CPI does all of them and that's where the "performance advantage" is found. And I do agree that the OP's question has been answered long ago. Maybe the mods can split the "comparison" posts out into a more appropriate thread. My apologies for my role in the OT. |
I thought this was a thread about P-Mags.
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Dual P-Mags, 6 years, 650+ hours
A few data points and opinions. I was an early adopter of dual P-mags and have been running them for 6 years and over 600 hours. I had a few teething issues in 2011 during my phase 1 testing that were promptly addressed by P-mag.
At about the 150 hour mark I swapped out my aircraft spark plugs for auto plugs and haven't looked back. The P-mags are dirt simple to time, easy to install and operate as advertised. Company service and support is way above the norm. I get easy starts, smooth low RPM idle and can easily run my O-360 LOP. I'm not interested in experimenting with timing curves. I'm not saying there isn't a better system out there. It depends upon your mission. If I were to build again, I would make the same selection. |
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Of all the Pmag related threads I've read here, I can't remember a single post where someone from Pmag has participated in the discussion. Maybe I've missed a few? The question of reliability remains a mystery save for a small population of users who chose to share their experiences. I will be replacing my Slicks soon and have gone through a simular information seeking exercise. Enjoy your RV-8. |
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To get back engine power the pilot has to know what to do... turn off the offending P-mag. Now... who among us wants to have to troubleshoot ignitions in flight under an engine out situation? Thats why we have 2 igintions... right? So one can keep us flying until we are ready to land. With all other ignitions... if one quits or messes up or whatever, the other keeps you going to an airport. The pilot doesn't need to troubleshoot anything till on the ground. That is HUGE! If your ignition isn't automatically redundant like this, you can change it to be. No other ignition gets off timing like that. |
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If an engine quits in flight an ignition check is way down the list of things to do. If it occurs at take-off or landing it is highly unlikely that the pilot will even have the opportunity to do an ignition check. |
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From a CAsA bulletin on the subject: Quote:
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Timing makes a big impact on performance and even though many here don't want to hear it, it is variable based on many factors, the most profound being mixture. I can't imagine having an EI that cannot be adjusted based upon my mixture setting (ROP vs LOP). It would be like not having a mixture control and just feeding full rich through the flight regime. I do agree with Bill that if you favor simplicity over performance, the Pmag is a good upgrade option over the mag. However, I would still buy the CPI for cost and reliability. Just to give one example of the benefits of flexibility, I solved my FI hot idle problem by bumping my idle timing to 35. Larry |
Cockpit switches
Ross, with your upcoming CPI2, besides the actual unit you are now designing, what sort of cockpit switches do you recommend for a dual cpi setup? I?m guessing two independent on-off switches for each cpi.
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While it is true that auto manufacturers spend a lot of time developing timing and fueling maps, they do not tune them to extract maximum performance out of your vehicle. They are looking for emissions, reliability, and performance, not necessarily in that order. When I was doing the auto racing thing, I replaced the ECU and was able to pickup around 5% more torque and HP by tuning the car on a dyno. Of course it was tuned within a breath of its life, something auto makers are loathe to do for obvious reasons. Another way to look at it is, why are there so many different aftermarket automotive ignitions available, if the auto manufacturer's ignitions are so good? My biggest issue with multi component systems is the number of connectors that can fail. That is not to mention the additional complexity required by adding extra batteries and alternators to protect against electrical system issues. Then you still have the problem one LS user had a few years back. He was on short final when his alternator belt broke, ripping out the wires for the crank angle sensor. Instant glider. In the end, you as the builder have to weigh the risks, both set up and operational, and pick the system that you feel is best for you. |
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The auto ignitions are orders of magnitude more sophisticated and precise than a Pmag, CPI, LS or anything else in aviation short of Lycoming's IE2 or perhaps the Rockwell system on the Rotax 912iS, which they easily match or exceed. Any advance in timing will almost certainly affect knock margins and/or emissions. The aftermarket does not need to meet any emissions spec and most say "for off road use only". I don't see many aftermarket ignitions out there for the cars of today outside of Link, Haltech and Motec which are intended mainly for performance / race use at higher boost levels where factory ECUs are not mapped-that longevity/ warranty card again. No auto OEMs use integrated ignition controllers these days because they found out long ago that long term reliability is compromised by heat and vibration when attached to the engine. The Pmag integrated design was a marketing decision to make installation easier IMO (which it undeniably is), not something based on best engineering practice. No auto OEMs today use gear driven timing components because it's less precise and more prone to failure. These are reasons why Pmag mandates 100 hour inspections- to make sure the bearings, gears are ok and the electronics have not been overtemped or got wet. Pmag requires blast tubes for cooling as a result of their design decision and they use non-water proof screw type connectors externally. Really, in 2017? You don't see this stuff on modern auto ignitions. Poor belt maintenance and questionable installation likely caused the LS incident in Australia. Anyway, we can all learn from that and protect crank sensor cables with armor as we recommend. No way a thrown belt will take out our sensor or cables. The internal generator in the Pmag has caused issues as outlined in their own documentation. http://www.emagair.com/service-notes/ http://www.emagair.com/downloads/ More reliable than a backup battery? Doubtfully. More spinning, vibrating stuff inside to go wrong and cause damage to other critical parts. |
Edit, Ross beat me to it.
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I'll grant P-mag the benefit of the doubt that their issues are largely resolved (with frequent, repetitive inspections), but we all know that that has been a long, uphill battle - a battle LARGELY the result of the marketing decision to package it all together - But there is no way you can pound the drum that a "distributed" system is inherently less reliable. No way. To do so flies in the face of logic and absolutely overwhelming evidence to the contrary. It's time to put that bogey man to rest. |
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From CAsA's Flight Safety magazine, 01August14-22Sep14: Quote:
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These SDR's are a relatively new concept from CAsA, and only capture those that are reported, and only then in Australia, which has a relatively small GA fleet compared to the US, so it is certainly within the realm of possibility an American pilot would expect to experience such a phenomenon and be expected to react accordingly. Commentary here suggests this may not be the case, and if this is indeed true, I would encourage a mag-check to be incorporated as part of your IA's following engine roughness or failure and be practiced as such, at the earliest opportunity. As I said earlier, it was part of the spam-can checklists I was trained under and that is going back close to 20 years, and it is there for a reason. |
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The last post here shows a photo of the mount and armor mounting holes: http://www.vansairforce.com/communit...d.php?t=143608 Go to Page 5, post #44 last page. I should mention that the early LS crank sensor setup has been superseded by a new design which has the cabling mostly inside the baffle sheet metal. |
And another few examples using "Distributor" as the faulty part:
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https://www.aopa.org/asf//ntsb/narra...20050815X01247 This is also thought as part of the emergency checklist at least by my flight instructor and AOPA points it out too: https://www.aopa.org/news-and-media/...-magneto-check So not just a problem on the other side of the world.... . Oliver |
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Yes, the P-mags had some teething problems, most, if not all, of which are behind us. With thousands in use around the world, they are a proven ignition. Quote:
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I asked the gentleman if it would be possible to certify a traditional magneto today. His response was that there is no way to certify a magneto to today's reliability standards. |
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What we're talking about with PMAGs is something completely different. We're talking about a condition where the timing can advance suddenly and without any warning to such an extreme degree that it causes the engine to quit (or suffer damage). We need to see this issue in perspective. I'm guessing that there might be at least 400,000 conventional magnetos in service today in GA just in the United States. And yet engine failure caused by a properly maintained magneto suddenly (and without any warning) becoming wildly advanced is virtually unheard of. Now compare that to the PMAG of which there may be no more than a few thousand in service and yet with a well known history of incidents related directly to extreme timing loss. Maybe the PMAG is now beyond its loss-of-timing issues. I certainly hope so. I see that many PMAG owners claim that V40 has solved the problem. But I've heard that claim before many times over the last 10 years. It also puzzles me as to why, if V40 is the ultimate solution to the timing problem, it is not a mandatory revision. I'm not sure what that says. |
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You're a smart guy. You have developed and brought to market your own product. Though we understand your product owes its very existence to the shortcomings of the P-mag ignition, I'm not about to believe that you actually think the engineering required to accurately and reliably time a spark event is difficult. Hall effect sensors have been around a very long time. They are proven to be stone axe reliable - and hanging them on the crank and block/case has been used reliably for millions and millions of hours in rain, dirt, chemicals, heat and vibration without fail. So why then did P-mag have such issues with their own application when the rest of the motorsports world does not? It's because they took the "hard way" to force a non optimal engineering solution in exchange for favor in the market as an "easy to install" option. To their credit, many have bought in to this concept (including me) and their outstanding (in my experience) customer service has kept them around long enough to gain market share. Good for them, but that's of little consequence to those who have not realized the dream of trouble free ignition performance. Quote:
Both are meaningless statements. The real answer is a connector either meets requirements of the operating environment, or it does not. And it is abundantly clear that the weatherproof, locking, strain relieved connectors common in the current automotive world are more than up to the the task. Billions of hours of use illustrate this in spades. You can not invent a problem that has already been solved. Try again. ...Besides, do you really want to bring up connectors in light of the cheeseball stuff P-mag uses? |
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Had Ross's CPI not had such an ugly green control box I likely would have gone with CPI as my ignition of choice, but there was no way I was going to have a green monster in my cockpit! :p When it comes time for our impulse-coupled Slick to be replaced, Ross's CPI-2 might well get the nod. I've got a spot where I can mount the controller on a mechanism which would allow it to be stowed most of the time and swung out into view only those times when its needed. And I've got an essential bus with its own battery so who knows when a CPI might make its way into our airplane. |
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