Ed_Wischmeyer

Ed_Wischmeyer

Well Known Member
To finish up the thread, "Declared an Emergency Today"...

Got the p-mags back from the shop, installed, and the plane ran up fine yesterday. Ferried it back home today, and *everything* worked as expected: prop gave the same minor surge on takeoff, speeds were back up, everything.

Quick summary of the original problem: With 8 hours on the 15W50 oil that replaced the 100 weight; and having just fueled the airplane; on a day that was perfect for carburetor ice; had a prop surge, declared an emergency, had a few power burbles on the way back to the airport I'd just taken off from, and I lost more than 20 knots of groundspeed with the MP and tach unchanged. After landing, the runup was fine.

But the next day, on runup, one p-mag was completely dead. Somebody else had had the same experience with a p-mag failure, also leading to an inflight power loss. My problem was a dying p-mag, and if I'd been more knowledgeable / more aware, I could have checked the mags in flight, restored full power (probably), and flown home.

By the way, the p-mags are a cinch to time. They have a manifold pressure sensor, and the way you time the mags is to turn the prop to top dead center (not 25 degrees before) and cinch 'em down tight. Turn on the master switch with the mags off and observe one color LED on the back of the mags; blow once and observe the LED color change to something else; blow again and observe the LEDs change to another color. You've just timed the mags.

Thanks to one and all for the thoughts, comments, and suggestions.

Ed
 
Seems to me there are a lot more Pmag failures per capita than magneto failures (by ratio) than many people are prepared to admit to.

This is speculation on my part, but when you know someone who has had a dual Pmag failure recently in a RV7 with about 50-100 hours on it, and I read and remember a few on VAF, it makes me wonder.

I know some will read this and be saying I am EI bashing, because I have declared a definite preference in the past, but I am not. I am however running a flag up the pole.

Food for thought. :cool:
 
The problem with your observation, Dave, is that very few people come on and post "I had a perfectly normal flight today" - they only post about problems. And the truth is, P-Mags had more failures in their early models than the later ones. Many of the failures you are hearing about are with early models that just don't get flown very often and also haven't been upgraded.

I've had more Slick problems in the last eight years than I have had P-Mag failures. Does that statistically mean anything? Nope - statistically insignificant and anecdotal.
 
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Ed_Wischmeyer said:
To finish up the thread, "Declared an Emergency Today"...

Got the p-mags back from the shop, installed, and the plane ran up fine yesterday. Ferried it back home today, and *everything* worked as expected: prop gave the same minor surge on takeoff, speeds were back up, everything.

Quick summary of the original problem: With 8 hours on the 15W50 oil that replaced the 100 weight; and having just fueled the airplane; on a day that was perfect for carburetor ice; had a prop surge, declared an emergency, had a few power burbles on the way back to the airport I'd just taken off from, and I lost more than 20 knots of groundspeed with the MP and tach unchanged. After landing, the runup was fine.

But the next day, on runup, one p-mag was completely dead. Somebody else had had the same experience with a p-mag failure, also leading to an inflight power loss. My problem was a dying p-mag, and if I'd been more knowledgeable / more aware, I could have checked the mags in flight, restored full power (probably), and flown home.

By the way, the p-mags are a cinch to time. They have a manifold pressure sensor, and the way you time the mags is to turn the prop to top dead center (not 25 degrees before) and cinch 'em down tight. Turn on the master switch with the mags off and observe one color LED on the back of the mags; blow once and observe the LED color change to something else; blow again and observe the LEDs change to another color. You've just timed the mags.

Thanks to one and all for the thoughts, comments, and suggestions.

Ed
Click to expand...

Just to state the obvious, the in flight prop surge is quite indicative of an ignition failure. Reduction in power output, rpm comes down, governor spools the prop back up to the requested rpm. Been there, done that many times, got the t-shirt and shorts stains.
 
Ignition failure

Usually an ignition failure results in a trivial power loss. This one resulted in a significant power loss and 20+ knots of speed. That's what was the fooler.
 
Ed_Wischmeyer said:
Usually an ignition failure results in a trivial power loss. This one resulted in a significant power loss and 20+ knots of speed. That's what was the fooler.
Click to expand...

Thanks for sharing this Ed. When a slick mag fails it exhibits different characteristics that a P-mag - it certainly did not seem obvious at the time, I have certainly learned something about this components failure mode.

So this begs the question a bit, was your P-Mag (s) an early model(s) and not have the updates? (Sorry, maybe I missed it)

Paul, I think you meant "very few people report . . " :) It's ok, we get it.

Electronics components fail high or low, short or open. FMEA provides the opportunity to ensure failure modes are somewhat controlled. Do the later P-mags fail off, or safe, so that the timing does not wander (potentially) wildly and cause potential damage? How is the reader supposed to know what vintage, serial number etc the failed unit is unless it is reported along with the number of hours to failure. All we know is IT failed and draw conclusions on that basis.
 
Paul, As usual I cant disagree with what you are saying, and in this case I agree, nobody reports a perfectly normal flight, however, I really do not see the relevance of perfectly normal flights.

The problem with my observation is that there does appear to be a large number of EI failures relative to the number in use compared to the old dinosaurs-magneto. And I am not just referring to the PMAG, so I am not singling out one brand.

As for the older units Vs Newer units, there may be some truth to that and it is pretty normal to expect that. However, where you are mistaken is the DUAL FAILURE that resulted in a dead stick landing recently was a set supplied on a new engine in 2013, and I am guessing but say early 2013, so they are in the 12-18moths ago range.

Anecdotal is hard to measure, and easy to scoff at, but that does not mean there is not a higher incidence. In my experience mags that have been serviced as per instructions, rarely give trouble. Sure old and under-maintained ones give grief, but you should not be surprised.

Food for thought.... ;)
 
4,900+ hours of experimental flying with 1 mag and 1 EI. Box score:
• 1 mag failure on the ground during run-up
• 3 EI failures in flight

I would never fly a homebuilt with dual EI's; my 14 will have one Bendix and one LSE.
 
deek said:
4,900+ hours of experimental flying with 1 mag and 1 EI. Box score:
? 1 mag failure on the ground during run-up
? 3 EI failures in flight

I would never fly a homebuilt with dual EI's; my 14 will have one Bendix and one LSE.
Click to expand...

2500 hrs, mags, three EI systems. Never had a failure of any that affected a flight.
 
No news as to failure cause

Problem in flight, checked out fine in the run up immediately after the event, hard failure the next day, and no specifics from the shop on the failure mode. Oh, well...
 
Ed, for clarification, please confirm that only one failed, but since you had to send it in you went ahead and sent both in to be looked at. They did not both fail right?
 
Only one failed

But given that the airplane was going to be grounded and that I'd be shipping one mag in for repair, it was an extra $90 or so to get em both checked. An inexpensive precaution, methinks.
 
Ed, after landing from the problem flight, the mag check was performed before shutdown, or did you shut down and later re-start for the mag check?

The mag check seemed normal (any doubts?) but it was done at low manifold pressure, not 25/2500?

On a subsequent day, did you look for a flashing yellow LED when the mag was discovered to be dead?

Did you happen to do an axial/lateral bearing check before sending the mag for service?
 
Post flight run up

Did a normal mag check, 1800 RPM, without shutting down after he incident flight. The next day I did a run up as a "why not" before we took the cowl off, so I did not check the LEDs.
 
Thanks Ed. It would appear the bad mag was supplying very advanced spark timing, thus the significant power loss without loss of MP. The smoking gun would be an EFIS record showing a shift to high CHT and low EGT, but if I understand correctly, this is a steam gauge bird. You may wish to take a peek through a spark plug hole. Patches of carbon deposit blasted off the aluminum would be another smoking gun.

The post-flight check was at low MP, a condition where significant advance is beneficial. However, that may not be the whole explanation for a reasonable run-up performance. Bearing failures, as reported here by another user, may result in different timing under different torsional conditions: http://www.vansairforce.com/community/showpost.php?p=850464&postcount=38

It was most likely dead the next time you tried to run because it failed its self-test routine, i.e. the sensor magnet range check. It's why I asked about a flashing yellow LED.
 
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