Bennett Posted November 21, 2012 Report Share Posted November 21, 2012 My M20J is up at LASAR for its annual. I have the two separate mag option, and since they were close (40 more hours) to 500 hours since the last inspection, Mike suggested that they be instructed to remove both mags and send them out for the 500 hours inspection. I agreed, as this sounds like good maintenance practice. Although I have been flying for many decades, and well over 15 years or so in Mooneys, I have never had an in-flight mag failure. Having two separate mags sounds like a good safety factor. At every run-up (every flight) I dutifully test both mags, and note that the RPM drop is less than 75 RPM. My question is: are there any special settings (RPM, MP, FF etc) in a one mag situation to use before landing at the nearest suitable airport? Thank you for your replies and comments. Quote Link to comment Share on other sites More sharing options...
thinwing Posted November 21, 2012 Report Share Posted November 21, 2012 Hi Bennett...as I understand your question,you are asking for engine settings in the case of a magneto failure.So the thing is,after all the drama of the typical mag failure...misfire/crossfire/sudden silence when switching between l/r mag etc...the engine will be running on the second mag but not at the same lean mixture...so I would get down to lower altitude and richen up....I have never seen specific single mag performance #s in the POH...its really a guess...the engine just has to prove it can run on a single mag during cert...not make the same rated power...the mag failure I had in a Baron...the effected engine made noticable reduced power..but I had another good engine so i proceeded to home airport...in a single..I would be landing soonest...k Quote Link to comment Share on other sites More sharing options...
N601RX Posted November 21, 2012 Report Share Posted November 21, 2012 It all depends on the failure mode. If one just quits it wouldn't be a big deal. If one started cross firing or somehow advanced itself, then it is very possible the engine would not produce enough power to maintain altitude. In that case you would want to figure out which one was bad and run off the other one. Quote Link to comment Share on other sites More sharing options...
jetdriven Posted November 21, 2012 Report Share Posted November 21, 2012 An engine running on one mag is effectively retards the timing, as the flame front originates on one side of the chamber and progresses in one direction only. Two plugs fire and the flame front meets in the middle. So, the peak cylinder pressure takes longer to build. I'd run it well ROP at 65% power or less, and land ASAP. You will notice your airplane slows down a couple or 5 knots whn doing an inflight mag check for that reason. Quote Link to comment Share on other sites More sharing options...
FloridaMan Posted November 21, 2012 Report Share Posted November 21, 2012 I've experienced a mag failure. The plane suffered a slight loss in performance and the EGTs read sky-high -- I'm guessing from fuel still burning as it entered the exhaust. Quote Link to comment Share on other sites More sharing options...
philipneeper Posted November 22, 2012 Report Share Posted November 22, 2012 i have experienced a mag faileeeee fligt a well... the left mag faied and the right kept on ticking. I was at 3500 feet and the engine started sputtering. I richened the mixture and it ran decently til i got to my home airport and landed. A lil scary but nothing you havent been trained to handle. Quote Link to comment Share on other sites More sharing options...
jetdriven Posted November 22, 2012 Report Share Posted November 22, 2012 I've experienced a mag failure. The plane suffered a slight loss in performance and the EGTs read sky-high -- I'm guessing from fuel still burning as it entered the exhaust. Retarded timing For those of you that have had magneto failure, were these Slicks, Bendix, or the Bendix Dual? Quote Link to comment Share on other sites More sharing options...
Skybrd Posted November 22, 2012 Report Share Posted November 22, 2012 Retarded timing For those of you that have had magneto failure, were these Slicks, Bendix, or the Bendix Dual? Byron, a few months ago, before I had my engine changed, one side of the dual bendix mag quit. On preflight it passed the runup test but some time in the flight it failed. I noticed something wrong when the LOP procedure attempt didn't work right. I ran it much richer to keep egt correct. After landing I checked the mags and noticed one was dead. It turned out to be an internal failure of the cam follower/points. When they put the cam follower together they accidently installed part of it on the wrong side causing the nylon part to be near the points. It partially melted the nylon part and caused the points to be closer together to the point they stayed closed. This dual mag only had about 100 hours since overhaul. Quote Link to comment Share on other sites More sharing options...
Bennett Posted November 22, 2012 Author Report Share Posted November 22, 2012 Thank you all for sharing your experiences, and advice. Obviously the POH is not helpful in that the emergency check lists do not address this circumstance. I usually run ( thanks to Knute) LOP, and I have wondered if I should go ROP if I were operating on one mag. With a less efficient fuel burn - incomplete fuel burn? I would think that adding more fuel (richer mixture) would not be helpful. I think I would reduce power as much as practical and land as poon as possible. I do like the idea of two separate mags, and reading the comments on the replies reinforces my decision to have the mag checks done at this time, even if we are shy of 500 hours. Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted November 23, 2012 Report Share Posted November 23, 2012 With both mags firing the fuel charge burns from two locations, with one mag firing it only burns from one location. This has the same effect as retarding your timing, it will lower cylinder pressures and reduce power. This will make the engine less prone to detonation and will reduce stress on the engine. Because the fuel charge is burning slower there will be less heat transferred to the cylinder thus reducing CHTs and more heat left in the fuel charge when the exhaust valve opens raising the EGTs. A rich mixture burns faster than a lean mixture, so some power can be recovered by going ROP. nothing you do will harm your engine. Quote Link to comment Share on other sites More sharing options...
carusoam Posted November 23, 2012 Report Share Posted November 23, 2012 My lost magneto experience comes from C152s... One magneto has lower power than two. Could not climb to 2,000' AGL. The only setting I was looking for was where to be setting the plane down safely. That was enough single magneto ops for me. The plane had just come out of maintenance. Run up was good but began failing in flight. I would not want to perform maintainance to both magnetos at the same time. If they got on different schedules on their own, that would be fine with me... Best regards, Quote Link to comment Share on other sites More sharing options...
FloridaMan Posted November 23, 2012 Report Share Posted November 23, 2012 Mine are slicks. We were wondering why the EGTs were acting weird intermittently. Then the plane was extremely difficult to start (left mag failed and the plane is equipped with a Slickstart system). We didn't know it at the time, but Parker managed to hot start the airplane refueling -- possibly on just the right mag. We discovered the dead mag on the mag check. Interestingly enough, if we tested the mags at idle, both worked, but at runup RPM, regardless of mixture setting, the left mag would be dead. We were fortunate to have a local A&P come out and repair the plane during the week. He disassembled the magneto and found that even though the coil tested as good, it looked burned, so he replaced it which fixed the problem. Quote Link to comment Share on other sites More sharing options...
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