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-   -   Today's Engine Puzzler (https://vansairforce.net/community/showthread.php?t=182917)

N941WR 05-29-2020 12:26 AM

This is why you need to provide separate power and grounds to your P-mags!

This can't be stressed enough!

Also, the LED's on your P-mags should be either Red, Green, or off. If they are Orange, there is an internal fault and they need to go back to Emag for repairs.

Again, please rewire your P-mags!

RV10inOz 05-29-2020 12:43 AM

David,

My standard switches for Master, Mags and anything important are now the Honeywell Locking Toggle Switches. No if's but's or maybe's.

Please use them.

Adam 05-29-2020 06:30 AM

Well Im glad we finally got an answer, the benefit here is hopefully this may help someone with a similar problem. We all need to support each other, this is why this site exists. When you are dealing with a car a bad day is that your stuck on the side of the road, in aviation you end up in the desert on a river bed with your nose wheel in the sand,, if your LUCKY!

John Tierney 05-29-2020 06:46 AM

I'm with Bill R., the wiring doesn't sound right. There should be no "shared wire" for both PMAGs. Each PMAG should connect to the bus independently. The wiring diagram on pg 28 shows a wire from the bus to a breaker to a switch to the PMAG. I chose to use a switch-breaker combination.

Rick Meyer 05-29-2020 06:51 AM

A very nice apology
 
Dear David,
After receiving criticism for your style of post and your moral character as well, you simply responded with an explanation and a sincere apology. Not only that, after realizing that ?perhaps? this was not the most popular way to approach problem solving on this forum, that you would change your ways in the future. These things indeed take a great deal of moral character! So, I tip my hat to you, good job, and have a nice day.
Sincerely,
Rick Meyer

lr172 05-29-2020 07:04 AM

Quote:

Originally Posted by Rick Meyer (Post 1434408)
Dear David,
After receiving criticism for your style of post and your moral character as well, you simply responded with an explanation and a sincere apology. Not only that, after realizing that ?perhaps? this was not the most popular way to approach problem solving on this forum, that you would change your ways in the future. These things indeed take a great deal of moral character! So, I tip my hat to you, good job, and have a nice day.
Sincerely,
Rick Meyer

+1

more char's

Captain Avgas 05-29-2020 08:05 AM

Quote:

Originally Posted by N941WR (Post 1434343)
This issue was resolved a number of years ago and no longer applies.

Are you implying that in an engine-out situation with dual PMags that an ignition check is not warranted and that you do not recommend one as part of an emergency check list.

PhatRV 05-29-2020 08:06 AM

Quote:

Originally Posted by DavidHarris (Post 1434365)
First, my sincere apologies to folks annoyed with the puzzler. I used to enjoy listening to the puzzlers on CarTalk and thought this could be fun (glad you liked it Ray), but I'm sorry for those who didn't like the format and will avoid puzzlers in the future.

The issue proved to be an intermittent open connection in the common power wire to the PMAGS.

My son (age 14) and I had looked at the LEDs on the PMAGS while we were retiming them, and he knew they should be yellow or green when power they were properly powered and the key is in the OFF position. When I was unable to start the engine, he noticed that both PMAG LEDs were off.

We followed up with a voltmeter and found the PMAG power inputs were both 1.2 instead of 13 V. Then they went back up to 13 and then back down to 1.2 as we poked around. The only wires in series with both PMAG power inputs are the main power system between the battery and bus, and the short shared wire between the bus and the split to the two PMAG test switches. The rest of the aircraft was operating normally, so it wasn't the main power system, leaving only the short shared wire. We also looked at the ground connection, but it is short, sturdy, and showed continuity on the meter.

This shared wire had spade connectors on it. I spent a good deal of time shaking it the next day and briefly made the PMAG power drop out, but it was surprisingly hard to reproduce. We cut the wire out and replaced it with a wire with heat shrink solder sleeve instead of spade connectors. We then dissected the spade connectors and found a poor crimp that could be pulled apart with a good tug after all the heat shrink had been removed.

The aircraft has been starting reliably since that change, and now idles fine down to 750 RPM and the engine hasn't quit at any point.

In hindsight, this makes perfect sense. The crimp was good enough that it rarely acted up, and I'd been unable to detect the bad connection by shaking the wires back in March or earlier. When the PMAGS had a good connection, they would operate reliably down to lower RPM. When the connection was poorer, they lacked main power and would only operate off their internal generators, which I have now measured need 850 RPM on the left and 780 on the right PMAG, so they would drop out at low RPM as I was trying to set the idle or as the prop stopped windmilling after landing. The weak connection also explains my intermittent starting difficulties. I'm guessing that vibrations during starting and operation may have caused the connection to get better or worse at different moments.

The engine failed when I was at the top of a stall with partial flaps. The PMAG power wire must have not been good at the time, so the PMAGs were operating off internal power. Once the RPM became very slow at the top fo the stall, the PMAG generators stopped producing power, so the PMAGs both stopped making spark and their tach readings both dropped to 0. Although I pitched the nose down to increase windmilling, I was too close to the ground to do this for long, and must never have achieved high enough RPM and appropriate mixture settings to restart before having to commit to the landing.

I agree with Bob's comment about the PMAG switch ergonomics. My switches came with my Advanced QuickPanel. Brad at PMAG says he now recommends a "non-latching momentary pushbutton" but doesn't yet have a specific switch in mind. I'm not sure I love that because I'd also like the PMAG switch to have a locking OFF position so I can completely shut off power while working on the engine. Stein sells Milspec PMAG switches that can be used ON, locked OFF, or momentary OFF (for test). Unfortunately, the holes in my panel are about 1/16" too close together to accommodate these switches. Still thinking about what to do here...

I also like the notion of one standard magneto so that the ignition has independent failure modes.

David

Thank you for your very detailed explanation and all the steps to troubleshoot the intermittent problems. I am planning to install something similar to my RV8 and this thread has the importance that I need to save as I complete my build.

Bavafa 05-29-2020 08:40 AM

David,
Thank you for providing the cause. This was my first guess for the issue since each time it happened during low RPM.

Just to share or suggestion, I have a LED connected to the PMAG power switch on the panel which goes on when the power to the PMAG is cut off . This serves two purpose for me, one that I know my source of power to each PMAG is good (no blown fuse) and the second purpose is if I accidently flip the toggle switch or had forgotten to flip it back to ON during the run up test, the LED light will remind me of that.

N941WR 05-29-2020 09:58 AM

Quote:

Originally Posted by Captain Avgas (Post 1434429)
Quote:

Originally Posted by N941WR (Post 1434343)
This issue was resolved a number of years ago and no longer applies.

Are you implying that in an engine-out situation with dual PMags that an ignition check is not warranted and that you do not recommend one as part of an emergency check list.

Not at all. My response was to your comment regarding that P-mags are known to loose their timing. The last of these known issues was resolved with P-mag firmware version 40. Also included in that firmware release was delaying the firing event when in startup mode to four degrees after TDC to prevent kickbacks.

Like all ignitions, a pre-flight check should be performed, including dropping ship's power to each igntion, one at a time, to make sure their internal generators are functioning properly.

The OP's issue had nothing to do with the P-mags and everything to do with his installation.

1. He connected the power feed for both P-mags to one connector, which failed.
2. He connected the ground wires to the firewall, not the engine as recommended by Emag.
3. When he performed his stall, the engine RPM dropped below the point where it would self power the P-mags and because of the faulty installation the ignitions stopped producing sparks. Then during the OP's emergency actions, he inadvertently grounded the P-mags while in flight. Had he not done this, there is a very good chance the P-mags would have started firing once he lowered the nose and the engine RPM picked up.

As I said, this situation had nothing to do with the P-mags and everything to do with the installation and pilot actions.

In essence he took two independent ignition systems and introduced a couple of single points of failures.

Thank goodness the outcome was as good as it was.

The following was told to me by someone who supplies products to the E-AB market, "You don't have a proven product until you have 500 units installed in 500 homebuilts by 500 amateurs."


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