A P-Mag Perspective and Challenge
For awhile, I?ve hesitated posting this opinion piece / report / review, but for the sake of RV safety, discussion, and a P-Mag status check, I have decided to go ahead and post the following. I will say up front that I am not a P-Mag fan, and I question its basic design, performance, initial quality, and long-term reliability. On the other hand, I know that there are many RVers on this forum who are quite happy with their P-Mags and have flown them successfully for many hours. So I hereby challenge the many P-Mag fans to jump in and tell me where I?m wrong; if I?m wrong, or tell me if I might be right; partially anyway. So here goes:
Last summer at Chino, two new P-Mags didn?t do very well attached to a new Lycoming engine during its initial flight test phase: a coil failure in one; timing offset and a factory rewire for the other. The timing offset was detected by an EI Commander and then confirmed by a rotation check and the EICAD software. My personal opinion is that anyone running a P-Mag should have an EI Commander in the cockpit.
http://www.eicommander.com
http://www.emagair.com/eicad/
The good news is that E-Mag as a company was very supportive and responsive in diagnosing and fixing these problems. The bad news is that they happened in the first place; involving both P-Mags on one engine. I think everyone has been assuming that the P-Mag is over its initial quality and long-term reliability hurdles, but that appears to me to be a questionable assumption. I realize that my sample size is very small, but it is disturbing and unexpected. Also, P-Mag problems continue to be reported here and elsewhere. As I said before, I understand that many RVers are happy with their P-Mags, but there still seems to be a good case for caution.
Note: After being factory-fixed, the two mentioned P-Mags have now flown for over 120 hours without problems except for a very small, one-to-two degree, timing variation known to be common to P-Mags. Reportedly, this variation is mainly due to Lycoming gear lash at the magneto mounting location and secondarily due to P-Mag sensing and computing resolution. In my opinion, this small variation is not a big deal, though; regardless of the causes.
My Design Perspective: Bolting the ignition electronics directly to a hot, vibrating engine and then bathing the electronics with EMI from an immediately adjacent coil doesn?t seem like a good idea. Installing an alternator in the same small box is obviously a challenge. In other words, the P-Mag?s compact, single-box design comes with several design and environmental trade-offs in exchange for its simple, swap-out installation. When it?s working, the P-Mag does provide good starting, easy timing, and increased fuel efficiency due to the advance curve.
On the other hand, it is my personal opinion that any of the other electronic ignitions (Electroair, Lightspeed, EFII, etc.) are better in terms of design, performance, and reliability than the P-mag. These other ignitions deliver the same (usually better) starting, timing, and fuel efficiency advantages along with much higher spark energy for more complete combustion and improved performance. Due to their distributed installations whereby the individual components are located in environments that they are designed to easily tolerate, these ignitions are not as environmentally-challenged as the P-Mag. Granted, they require more work to install than a P-Mag, but it is relatively easy work. Also, I would think that anyone switching from a P-Mag to one of the other ignitions would see a noticeable performance improvement; particularly if it is a two-to-two swap-out or upgrading to a ?FADEC? system.
The more familiar I become with the P-Mag (or E-Mag as it is now called), the less I understand its popularity other than it ?seems? like a logical evolution of the standard mechanical magneto and is certainly an easy one-package swap-out. In my mind, if you are going to go with electronic ignition, do it right with the ignitions specifically designed to provide a new, higher level of performance and reliability; not a compacted, low-energy, and environmentally-challenged electronic ignition trying to mimic a standard magneto.
In Summary, My View (Only!) of P-Mag?s PROS & CONS:
PROS:
Everything is in one box. (Easiest installation of any electronic ignition. Essentially, a magneto swap-out.)
Self-Powered above approximately 1200 ? 1500 rpm.
Comfortable for magneto traditionalists. (Great marketing idea.)
Super-easy to time.
Good starting. (Initiates a quick, 5-pulse output to overcome its single-pulse low spark energy.)
Improves fuel efficiency.
Certification goal.
CONS:
Everything is in one box. (Operating environment concern about the long-term detrimental effects on the ignition electronics and other ignition components caused by engine temperature, vibration, and coil EMI/RFI.)
190 deg F temperature limitation. (Temperature strip attached to the box. Blast tube is mandatory.)
Dependent on aircraft power below approximately 900 rpm. Partially dependent on aircraft power up to approximately 1200 ? 1500 rpm. (Be observant when reducing power.)
Weak spark energy. (About half that of a standard magneto. Personally, I do not buy E-Mag?s enough-is-enough; less-is-more marketing. I believe the coil output has been limited in an attempt to mitigate the EMI/RFI issue.)
Questionable initial quality and long-term reliability. (Of course, I?m biased by what I saw, but I?m also aware that others have honestly reported their continuing P-Mag problems and concerns.)
Timing is not exact. (Varies slightly; not a big issue in my opinion, though.)
E-Mag seems to have dropped their original certification goal? (Apparently, certified engine/aircraft manufacturers are not buying the P-Mag concept?)
Thanks for listening. I hope this VAF thread helps improve our collective understanding of the P-Mag electronic ignition system. Fly Safe!
I know they had a past problem with an internal magnet working loose and causing problems, I assume from vibration and/or poor original design but their fix seems to have addressed that.
