What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Today's Engine Puzzler

DavidHarris

Well Known Member
I had an engine puzzler that kept me occupied for two months. I'll post the story and clues (and red herrings) today, and then follow up with my solution and reflections in a few days.

In March I received the airworthiness certificate for N47HM, an RV7-A with a Superior XP-IO360 engine, dual PMAGs, and a Precision Airflow fuel servo.

About 8 hours into Phase 1 testing, my engine quit during stall testing (at the top of a stall at 48 KIAS, with partial flaps). Much to my surprise, it would not restart in the air despite playing with the boost pump, mixture settings, throttle, and starter, and pitching the plane down to increase the windmilling. I shut everything off and made a forced landing on the sandy bed of the dry Mojave River. Fortunately I landed into a good headwind, the sand was firmer than usual because of recent rains, and I held the stick full back, so the nosewheel didn't touch until I had come to an almost complete stop. The aircraft was undamaged. On the ground, I observed the right PMAG switch was off. I likely bumped it while entering a transponder setting during turbulence, although it is not impossible that I failed to turn it back on after turning it off during my runup test.

I had been on flight following and had reported the engine out to ATC. On the ground, I called the Victorville tower, and they sent the fire department out to meet me. I jogged about 3/4 mile to the nearest named road, met the fire department and sheriff, and then talked with the FAA. All was well, and they referred me to Jack Vanderman at Southwest Aircraft Recovery.

My family came up to meet me. The area was dubious, with burnt-out houses and ranches resembling junkyards. I found a sandy service road on the riverbank that reached within 150' of the airplane, and spent the night there in my truck to guard against looters. In the morning, I met Mr. Depue at Depue Airpark, a private dirt strip near Barstow, and got his permission to tow the plane over there. Jack Vanderman arrived with his flatbed trailer and aircraft crane, and we spent about 6 hours winching the airplane out of the riverbed, up the embankment, and onto the flatbed, then winching the trailer along the sandy road until it was firm enough to drive. He carefully drove 10 miles on Old Highway 66 to Depue, and the police car that passed us in the other direction kindly didn't bother our odd caravan. Jack's elderly father and my 14-year-old son both helped with the recovery and it was quite an adventure for four generations of aviators.

In hindsight, I would have done stall tests at 7000 AGL over Dagget airport rather than 3000 AGL over the desert. I would have looked for a dirt road rather than a riverbed. I would have aggressively tracked down engine issues on the ground before flying. I was thankful to have taken glider training last summer and to have memorized the emergency checklists and thought about them deeply. I was grateful for the help from the FAA, the Victorville Fire Department, Mr. Depue, and Jack Vanderman.

Two days later I went back to Depue, removed the cowling, did a lengthy inspection, found nothing unusual, put it back together, did a runup, and then departed the short dirt strip and flew back to my home base at Cable Airport. Flight was normal.

I had observed some issues during Phase 1 testing before the incident, and didn't troubleshoot them on the ground as much as I would have wished because I feared long ground runs while breaking in the new engine.

* The engine would sometimes quit during the rollout after landing when I was at low RPM. I attributed this (not quite correctly) to the idle being too low. Adjusting the fuel servo idle to 900 RPM prevented the problem, but caused a long landing, so I had set it back lower for further testing.

* The engine was also sometimes very difficult to start, even though I felt I was following the Superior and Precision instructions. Sometimes I would have to prime and crank up to 6 times, following the cool down instructions for the Skytek starter.

After recovering the airplane, I contacted Superior. Bill Ross, VP of Product Support, took decisive steps to help, at no cost to me, and gave instructions for testing before further flight. I wiggled the wires while monitoring the LEDs on the PMAGs to verify connectivity. The grounds both go separately and directly to the aircraft central ground stud on the firewall. The power lines go through test switches on the panel to a short shared wire going to the main power bus. The kill lines go through the key switch to ground. The PMAG LEDs turn on when the power line is at 12 volts and the kill and ground lines are properly grounded, showing connectivity. Aggressively wiggling either end of the wires on either PMAG wouldn't turn the LEDs off. I then removed the PMAGs and sent them back for bench testing. I removed the fuel servo, spider, and injectors and sent them back to Precision Airflow for bench testing. Everything came back looking normal. I reviewed the excellent Dynon engine logs and observed 0 RPM from both PMAGs after the engine failure, even though the prop was windmilling, which is an indication that the PMAGs were not powered up during the descent, despite have internal alternators that should provide backup power. I spoke with Brad at EMAG and Alan at Precision and both were very knowledgable and patient and helpful, but none of us could find a theory that explained all the facts. I was impressed by how all the vendors stood behind their products and took the time to walk me through everything even though I'm not a mechanic.

I reassembled the engine, changed the oil, replaced all the spark plugs, and started the engine again. Starting remained difficult at times. Superior confirmed from the engine logs that the engine break-in was satisfactory and that it was ok to do longer ground tests. I tuned the idle throttle and mixture settings using a screw and thumbwheel on the mixture servo, in consultation with Alan at Precision. I had a difficult time getting the idle right; if I turned it much below 800 RPM, the engine would quit at idle, while the manual called for 700-750 RPM idle. After a bunch of testing one hot afternoon, I finally found a setting at about 840 RPM where the engine would never quit on the ground at idle. Out of an abundance of caution, I waited until the cool morning to fly the aircraft. My son stood by as an observer with a fire extinguisher, and I started the engine again, but found the engine quitting when the throttle was pulled back to idle. I spoke with Alan again and he was puzzled and said there was no known temperature sensitivity for the idle RPM. My son adjusted the idle higher. Then I found the engine wouldn't start at all despited repeated priming and cranking.

Then my son told me he saw something. His statement was the clue that resolved the whole mystery. He and I made a small fix, and the aircraft has been starting, idling, and flying well for two weeks since then.

Happy puzzling,

David
 
Puzzler Photos

Mojave River Landing
IMG_3049-1-mojaveriverlanding.jpeg


Landing Site
IMG_3060-2-landingsite.jpeg


Lifting the nose wheel
IMG_3068-3-liftingnosewheel.jpeg


Winching the aircraft
IMG_3078-4-winching.jpeg


More winching
IMG_3081-5-morewinching.jpeg


Aircraft Crane
IMG_3083-6-crane.jpeg


Lifting
IMG_3101-7-lifting.jpeg


Flatbed Truck
IMG_3121-8-flatbed.jpeg


At Depue
IMG_3122-10-atdepue.jpeg


Departing Depue
IMG_8947-11-departingdepue.jpeg
 
Your son saw it instead of hearing it so it had to be the prop, cowling or something coming out of the exhaust. My guess is cowling distortion because everything else I can think of would have shown up during ground runs. Unless the cowling was off, then nevermind.

PS Good job on the landing, that looks REALLY soft.
 
Wow, you are one excellent A driver, the pictures and the story is just amazing. Congrats on a great handling and landing.
 
Maybe a good lesson here on a new build is to go with one std mag until basic system installation/operation has been proven.

Congrats on a safe outcome!
 
My guess is that you had a fuel line too close to a heat source (Exhaust). Pulling throttle back to idle allowed less airflow and hot fuel to boil in the line and aggravate the engine idle. Else possibly a leaking gasket in the intake manifold?
 
Mixture stop.
Servo nuts not tight
Hole in bottom of the sump (no sniffle valve)
plastic plug in spider leaking (need steel or brass)

If one does not have a definitive diagnosis of the problem, then there is no assurance that the problem is eliminated.
 
Last edited:
soooo

I dont want to wait till next week's episode, i want to return to the garage and keep building.

So what was the problem?
 
I have to say your approach here is somewhat annoying. This is a forum designed to help one another learn from our experiences and mistakes. Stating your symptoms and telling everyone that you'll come back in a week with the fix that you already know simply doesn't meet the spirit of what most contribute on this forum.

It is reminiscent of old and inappropriate television advertising. cliff hangers are fine for fiction and television dramas, but I just don't see it as appropriate for this type of community. I admit that I enjoy Vlad's mystery air strip posts, but don't believe this is the same.

Just imagine if you posted requesting help with diagnosing a problem and my reply was that I know what it is but won't give you the answer for a week in order to drive amusement for others on the forum.

JUst one man's opinion I suppose.
 
Last edited:
?
I wiggled the wires while monitoring the LEDs on the PMAGs to verify connectivity. The grounds both go separately and directly to the aircraft central ground stud on the firewall. The power lines go through test switches on the panel to a short shared wire going to the main power bus. ?

David
Please move the P-mag power grounds to separate engine case bolts. You are trying to keep your engine running, not your firewall.

We have seen this cause problems before, but never an engine failure.

However, in your case, I suspect either you had a loose fuel fitting or a fuel line without heat shielding. I had four engine outs during my 40 hours, all during slow flights, stalls, and once during a LONG final following a Cessna on a cross country pattern. Once I figured it out and insulated the hard line from my gascolator to my fuel flow transducer which is hard mounted on the firewall, the problem went away.
 
:eek:

Shows how a line doesn't have to sit next to an exhaust pipe to cause problems. Hard to imagine it got that hot at the location noted. Will pay special attention to that.

Brad, my issue only occurred during high power slow flight operations; power on stalls, slow flight, and dragging it in behind the aforementioned Cessna. Lucky for me, it restarted immediately once I pressed the starter as the electric fuel pump was already on. That's why I think his issue was a fuel leak.
 
Now back to the puzzler...

Backing up just a bit from the previous replies, the OP states:

"Then my son told me he saw something. His statement was the clue that resolved the whole mystery. He and I made a small fix..."

In the interest of the game here, you should be able to deduce a few things.

First, that the issue was something observed, "he saw something..."

Second, that the issue was a single source problem, "His statement was THE clue that resolve the whole mystery."

And, "He made the small fix...". In the photo, the son looked to be 16 or 18 years old or so, and was likely not an A&P (my apologies to the son if I'm way off here). This implies to me that it was something a semi skilled non mechanic and the Dad could handle easily (loose wire, loose hose clamp, pinched hose, etc.)

So my guess, for $100 and a weekend in Cali, Columbia, would be something like a collapsed fuel hose while cranking, or a big ignition spark leaking from a wire too close to some ground, or a connector rattling around during the cranking attempt, loose B nut ... that sort of thing.

This does not seem likely to be something like Fuel Vaporization or improper placement of engine baffles... or.. or... whatever the builders pet peeve of the day is today.

Stay tuned, there's more to come!

Cheers
 
I have to say your approach here is somewhat annoying. This is a forum designed to help one another learn from our experiences and mistakes. Stating your symptoms and telling everyone that you'll come back in a week with the fix that you already know simply doesn't meet the spirit of what most contribute on this forum.

It is reminiscent of old and inappropriate television advertising. cliff hangers are fine for fiction and television dramas, but I just don't see it as appropriate for this type of community. I admit that I enjoy Vlad's mystery air strip posts, but don't believe this is the same.

Just imagine if you posted requesting help with diagnosing a problem and my reply was that I know what it is but won't give you the answer for a week in order to drive amusement for others on the forum.

JUst one man's opinion I suppose.
I couldn't agree more. Someone in need of attention here. :rolleyes:
 
I'm a problem solver and love this type of puzzle. I have two ideas of what the problem was and suspect Bill R is spot-on.
 
Then my son told me he saw something. His statement was the clue that resolved the whole mystery. He and I made a small fix, and the aircraft has been starting, idling, and flying well for two weeks since then.

Happy puzzling,

David
Could it be that the fuel vent line getting partially blocked or fuel pump drain leaking indicating fuel pump issue? I first was going to suggest issue with power to the PMAG since the engine quits at a very low RPM (roll out and stall) and PMAG requires external power at low RPM or start but all that has been tested and verified unless the nice son saw something on that part that was not discovered during testing.

On other notes, you probably want to ground your PMAG to the engine block as oppose to the FW. Lots of discussion on that.
 
OK, I'll play along....

Fuel leak would be easy for an observer to spot.

Loose connection?
 
OK, I figured it out

Lack of primer.

That or because it is a tipup-slider taildragger with a nosewheel.
 
Backing up just a bit from the previous replies, the OP states:

"Then my son told me he saw something. His statement was the clue that resolved the whole mystery. He and I made a small fix..."

In the interest of the game here, you should be able to deduce a few things.

First, that the issue was something observed, "he saw something..."

Second, that the issue was a single source problem, "His statement was THE clue that resolve the whole mystery."

And, "He made the small fix...". In the photo, the son looked to be 16 or 18 years old or so, and was likely not an A&P (my apologies to the son if I'm way off here). This implies to me that it was something a semi skilled non mechanic and the Dad could handle easily (loose wire, loose hose clamp, pinched hose, etc.)

So my guess, for $100 and a weekend in Cali, Columbia, would be something like a collapsed fuel hose while cranking, or a big ignition spark leaking from a wire too close to some ground, or a connector rattling around during the cranking attempt, loose B nut ... that sort of thing.

This does not seem likely to be something like Fuel Vaporization or improper placement of engine baffles... or.. or... whatever the builders pet peeve of the day is today.

Stay tuned, there's more to come!

Cheers

A few more things to deduce. Maybe not fuel or spark related as OP says fuel parts removed, checked and replaced so loose fitting not likely. Also spark items removed, checked and reassembled. Still has issues.
I am guessing air induction. Tube loose and when son observed the engine cranking torque open a gap fix was easy as tightening the bolts.
 
So what is the answer. I don't have time to peruse threads that arnt active from the day before. I realized the OP wants to do this like IMC club but I don't have the wealth of knowledge spanning decades like you guys. So saying what was wrong up front is helpful for me. Like the AD about the double adel clamp or the open plug on the spider valve a while ago.
 
Loose battery connection?

My guess - loose battery connection. Whatever it was I always start off suspecting the easy and/or cheep things!
 
Doomaflachi

The doomaflachi disconnected from the wachama thingy.


Wayne
RV-9a purchased flying and still grinning
 
So what is the answer. I don't have time to peruse threads that arnt active from the day before. I realized the OP wants to do this like IMC club but I don't have the wealth of knowledge spanning decades like you guys. So saying what was wrong up front is helpful for me. Like the AD about the double adel clamp or the open plug on the spider valve a while ago.


Exactly

...where is the "Like" button.
 
Im not sure I like this puzzle and I'm not sure this is the way to handle this issue! I use and support this site because of information that i can use so I can prevent future issues, I have that similar engine, should I not fly it till I get the answer?, I'm not that paranoid but others maybe, not a big fan of your puzzle.
 
About 8 hours into Phase 1 testing, my engine quit during stall testing (at the top of a stall at 48 KIAS, with partial flaps). Much to my surprise, it would not restart in the air despite playing with the boost pump, mixture settings, throttle, and starter, and pitching the plane down to increase the windmilling. I shut everything off and made a forced landing on the sandy bed of the dry Mojave River...... On the ground, I observed the right PMAG switch was off. I likely bumped it while entering a transponder setting during turbulence.
David

OK, I have a few observations here, neither of which addresses your teaser question but which may be valuable to other pilots.

Firstly, if you were able to do something as dangerous as knocking off a PMag switch while "entering a transponder setting" then I would suggest your panel ergonomics leave a lot to be desired. Honestly, as a TC I see builders constantly putting very important switches unprotected in vulnerable locations.

Secondly, your emergency check list for engine failure did not include switching the left and right PMags off and on to check them independently. This is a "must do" for Pmags. These devices can totally lose their timing (many recorded cases) and if the timing becomes significantly advanced on one PMag it will cause the engine to quit...and in such a case there is no redundancy in the second PMag. The only way to get the benefit out of the second PMag in such circumstances is to determine which one has failed and switch it off...thus the required PMag check.

Finally, I suspect a number of people are getting a bit annoyed by the teaser question. And fair enough. Having people guess what went wrong with your engine is not achieving anything in these particular circumstances.
 
Last edited:
Add me to the list of people who don’t understand why someone would prefer to play games instead of helping people. Gosh if someone got injured or worse as a result of a similar issue that may have been alerted by reading this thread with an actual solution to an engine-out problem...
 
...

Secondly, your emergency check list for engine failure did not include switching the left and right PMags off and on to check them independently. This is a "must do" for Pmags. These devices can totally lose their timing (many recorded cases) and if the timing becomes significantly advanced on one PMag it will cause the engine to quit...and in such a case there is no redundancy in the second PMag. The only way to get the benefit out of the second PMag in such circumstances is to determine which one has failed and switch it off...thus the required PMag check.
...
This issue was resolved a number of years ago and no longer applies.

However, your comment regarding ergonomics is spot on.
 
Making Yourself Smarter Than You Actually Are

You've not provided enough information. I assume you've done this to make yourself feel better when some 75 year mechanic with 4 or 5 Charles Taylor awards under his belt working for NASA can't simply state the problem. You've created one of those "infomercials" that says ever 45 seconds "you'll be amazed at what I'm about to tell you". As previously stated you're technique is annoying at best and likely matches your personality of "oh look a shinny ball"

Good luck with your suckering people to make yourself feel smart.
 
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
 
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!
 
Last edited:
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.
 
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!
 
Last edited:
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.
 
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
 
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
 
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.
 
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.
 
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.
 
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."
 
Last edited:
Back
Top