bad part

[steve]

part 3 of 3 from marc's list

 

Continued from Part 3: So what's happening here? As Mr. Cottner and Mr. Read have stated, the Pmag/Emag units lose timing information, firing at arbitrary and sometimes random times. Clearly, this screws up the workings of the engine, sometimes to the point of having no power whatsoever. Mr. Cottner had four failures and lost his airplane because of this failure mode - Mr. Read had to make a precautionary landing, and I had three failures and one precautionary landing. Emagair has issued a SB on both the 113 and 114 units. If you recall, I had timing issues with my 113 units as well. They have instituted a "fix" for the issue, notwithstanding that the 114 mechanical redesign was in part already a "fix" for the problems with the 113 versions. The Emagair units use a small magnet and a hall effect sensor to determine crankshaft position. It's an ingenious solution, because it uses a sensor that can determine crank position within 1 degree, not just when at TDC or within 10 - 30 degrees, as some other EI's do. However, the mounting of the sensor magnet has been flawed from version 113 onward. In version 113, the magnet was epoxied into a metal cup at the end of a shaft. The other end of the shaft had the magneto gear on it and was in intimate contact with the accessory case gears inside the engine, along with the engine oil. This guaranteed that the shaft would get just about as hot as the oil in the accessory case - about 200 F, if not more. Due to the very thin bond line of the epoxy holding the magnet in the cup and the differential CTE's (coefficients of thermal expansion) of the magnet and cup, the thermal stresses in the epoxy can be very large, cracking the epoxy. This would allow the magnet to rotate, thereby losing positional accuracy and timing. After having this failure mode pointed out to them (by me) a year and a half ago, and after having refused my offers to assist them in redesigning the mechanical portion of the units gratis (I am a mechanical engineer with 27 years of experience), Emagair, with an EE but no ME on staff, redesigned the magnet holding portion of the units for the version 114's. They soldered the magnet into a large brass holder, and then glued the holder onto the same shaft that the cup had previously been attached to. They then added two locktited set screws to the holder which applied force to the shaft. There was no flat on the shaft where the set screws touched it. This "fix" was far worse than the disease it was attempting to solve, and is the root cause of the horrible performance of the version 114's under heat and vibration loading. Now that the mass of the brass holder has been made much larger than the mass of the magnet alone, the stresses in the glued bond-line are far higher than previously, and under heat and vibration is guaranteed to fail eventually. The set screws do absolutely nothing, since the CTE of brass is much higher than the CTE of the steel shaft, so as the system gets hot, the set screws don't even touch the shaft. Failure of the glue bond line is sufficient to cause the holder to be able to rotate, with the same mis-timing issues as with a magnet disbond in the version 113 units. Although Emagair has issued an SB, describing a "fix", I do not have ANY confidence in this "fix"'s actually working in the long term. As with Mr. Cotner's warning, I don't believe that the keyway and roll-pin are anything resembling an adequate solution to the magnet mounting problem, which is obviously NOT specific to my engine and/or installation. As more hours are put on these units (I fly 120 hours/year - more than twice the homebuilt average), more will fail, and I have no confidence that this fix will substantially change this situation. Recommendations: My recommendations, based on my opinions and my examination of MANY Emagair unit disassemblies are these: 1) If you are flying with a version 113 or 114 product from Emagair, ground your plane immediately and remove the units. Do NOT fly with them, or with the "fix" described in the SB. It will work for a while, but for how long? 2) If you have a unit that you have purchased but haven't used yet, return it for a refund - do NOT put it on your aircraft and fly it. 3) If you were considering Emagair products for your engine, consider something else - do NOT purchase one and put in on your aircraft. When Emagair have hired a competent mechanical engineering firm to redesign their systems, have FULLY tested the units under O-360 type vibration loads for thousands of hours, and publicly published the results, THEN in may be appropriate to consider these units. Until then, it is not. If Mr. Cotner, Mr. Read, and my experiences with these units put Emagair out of business, and it costs some of you the opportunity to get a refund on your units, I'm sorry for that, but Mr. Cotner was lucky, and relying on luck to keep people alive is not acceptable. Everything that I have written here is either my personal experience, my opinion, or my recommendation based on my opinion. I know that many of you are saying (to yourselves or to others) "I told you so", and you're right - you told me so, but my desire for Emagair to succeed overrode what should have been enough evidence to the contrary. Feel free to write me with "I told you so" messages, if it makes you feel better. I'm happy to address any issues, comments, or questions that anyone may have. Since Emagair never responded to my entreaties to sign an non-disclosure agreement with them, I do not have any responsibility not to explain the inner workings of the units or the problems therein. PLEASE, PLEASE, PLEASE - distribute these messages (and Mr. Cotner's and Mr. Read's) to any and all aviation related mailing lists, fora, and printed newsletters. -- Marc J. Zeitlin mailto:marc_zeitlin@alum.mit.edu http://www.cozybuilders.org/Copyright © 2008 http://www.mdzeitlin.com/Marc/______________________________________________________________Cozy_Builders mailing listHome: http://mailman.qth.net/mailman/listinfo/cozy_buildersHelp: http://mailman.qth.net/mmfaq.htmlPost: mailto:Cozy_Builders@mailman.qth.net

[Jon Matcho]

Any easier to read version can be found at this web page.

[Marc Zeitlin]

Folks:

 

Since posting the first warning, I've had numerous email exchanges with other folks who've had failures of Emagair products and who have expressed an interest in understanding the SB "fix" and why I am not convinced as to its efficacy.

 

I've posted an addendum to the warning at:

 

http://www.cozybuilders.org/Emagair_Warning/

 

about 1/2 way down, with messages from Daniel Tracy, who's an ME at Boeing (41 years experience, flying an RV) who's had 5 Emagair EI failures in 160 hours. I've also posted excerpts of my responses to Bob Nuckolls, who wrote the "AeroElectric Connection", moderates the "AeroElectric Connection" mailing list, and whom I respect very highly.

 

Questions, comments, flames are welcome.

[Lynn Erickson]

Folks:

 

Since posting the first warning, I've had numerous email exchanges with other folks who've had failures of Emagair products and who have expressed an interest in understanding the SB "fix" and why I am not convinced as to its efficacy.

 

I've posted an addendum to the warning at:

 

http://www.cozybuilders.org/Emagair_Warning/

 

about 1/2 way down, with messages from Daniel Tracy, who's an ME at Boeing (41 years experience, flying an RV) who's had 5 Emagair EI failures in 160 hours. I've also posted excerpts of my responses to Bob Nuckolls, who wrote the "AeroElectric Connection", moderates the "AeroElectric Connection" mailing list, and whom I respect very highly.

 

Questions, comments, flames are welcome.

are there any pics of the internals?

[Marc Zeitlin]

are there any pics of the internals?

Nope. Not if they're not on the Emagair web pages.

[gmcjetpilot]

• Brand new forum member, 40 yrs in aviation both EAA, EAB and Commercial, CFI, ATP, EAA member since 1987 and built 2 kit planes. 
• Yes true a misfiring (traditional) magneto can cause loss of power and negate the 2nd mag, even if the 2nd Mag is functioning properly. THAT IS WHY when you learned to fly loss of power you checked the MAGS by turning one of the mags off and on, one at a time. Same with EMAG or PMAG.... Most of the problem post on EMAGS / PMAGS are from 2008 when they were new. They did have some past issues, which are history and sorted out. There is no ignition totally reliable.
• The advantage of the EMAG or any EI is then advanced timing verses fixed timing. Yes the spark is HOTTER for EI but traditional Magnetos are no slouch. The other advantage is using Automotive plugs (cheaper) that can be gapped to a larger size making for a "bigger" spark. That advantage only really helps when operating well under 75%, think high altitude.  All EI's hold a fixed timing say at that magic 25BTDC. Too much advance at higher power settings (above 75%) you can cause detonation and severe engine damage. Bottom line EI promises (and mostly delivers) easier starting and better efficiency from 2% to 4% may be more. 
• I just bought a set of used PMAGS for my current project so I researched it. I see some limitations still exist even with past issues sorted out. The big one is continuous maintenance. You have to remove the EMAG (this includes PMAG) every 100 hrs condition inspection. I think this is part of the magnet issue. Although fixed it is like any service bulliten on airplanes and engines, even if there is a limited problem and mostly addressed the SB stays for continuous airworthiness. 
• (Note EMAG does not make EMAGS anymore, they are all PMAGS (the ones that can be self powered). They do support EMAGS. I am not sure but they can likely upgrade an EMAG to a PMAG, but not sure.  
• The other limitation is the cooling. This is an induction coil ignition. Then coil is in the electronic ignition housing with the "distributor cap". Coils get hot spitting out 10's of thousands of volts 1000's of times a minute. So PMAGS require air blast cooling tubes. With canard pushers down draft cooling I think is better as long as you route cool are into accessory area, but in tractor engines that upper accessory case area where the mags are is kind of stagnant air wise, and heat rises and soaks the magneto area when you shut down on ramp. Not sure what max Temp PMAG allows, but they now have 200F / 93C tell-tale heat sensitive sticker on housing. Experimental, it is up to you to keep them cool and flight test iwith temp probes. 
• Note there is no distributor cap rotor in the PMAG like old car ignitions or aircraft magnetos. It is all electronic with a LOST SPARK. Meaning each cylinder gets 2 sparks per 4 cycles, one near top of compression stroke to make power, and one at top of exhaust stroke that does nothing, thus wasted spark. So it is "solid state" but there is moving parts. The reason for this is to save weight and complexity two cylinders are fired as pair together.

Other electronic ignitions require redundant electrical, ships power or no ignition. They also don't use the engines accessories case to drive a "MAGNETO" type accessory. Almost all other EI's use a fixed crank trigger off the engine case, and a magnet in the ring gear (technically not a flywheel but called flywheel by some). NO moving parts except the magnet in the ring gear. So except for the alternator belt breaking and taking out your wires or hall effect sensor it is very reliable. However there are wires all over and more external connections, plus the need for electrical power. 

Edited November 6, 2022 by gmcjetpilot