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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."

Bavafa 05-29-2020 10:28 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

Plus 1

with extra characters

bifft 05-29-2020 10:46 AM

Great job keeping an A model upright in that soft sand. Shows that you landed it right.

It looks like you have the Anti-splat nosegear mod. Does it have witness marks that look like it may have hit the gear on this landing?

BillL 05-29-2020 10:48 AM

It is good to finally to hear the solution to the problem, and it was a bit frustrating, but lets be fair here guys, Paul Dye has posted a puzzler like this in the past. Perhaps a different implementation as he stayed with the posts, but the same basic idea.

WWonka 05-29-2020 12:41 PM

Quote:

Originally Posted by N941WR (Post 1434275)
Lack of primer.

That or because it is a tipup-slider taildragger with a nosewheel.

Gee Bill, Is it the tail dragger nose dragger thing again? I guess I have time to decide on which side of the coin I will fall. Nose dragging or tail dragging :D

I do admit that with posts like this, my list of what to watch out for is growing.

N941WR 05-29-2020 01:07 PM

Quote:

Originally Posted by WWonka (Post 1434509)
Gee Bill, Is it the tail dragger nose dragger thing again? I guess I have time to decide on which side of the coin I will fall. Nose dragging or tail dragging :D

I do admit that with posts like this, my list of what to watch out for is growing.

If you make the wrong choice John, I'm not sure we can be friends anymore.

hgerhardt 05-29-2020 01:10 PM

"You don't have a proven product until you have 500 units installed in 500 homebuilts by 500 amateurs."

So true, that.

WWonka 05-29-2020 01:45 PM

Quote:

Originally Posted by N941WR (Post 1434513)
If you make the wrong choice John, I'm not sure we can be friends anymore.

Well...... I suppose we will have to see.

It is good to know that there is a wealth of information available on the site and many who are ready to reach out to offer assistance. I feel, that I have a ways to go just starting out, but will continue browsing through the posts, especially on those items that impact my stage of construction. That and photos of flying aerospace vehicles. :D

wjb 05-29-2020 06:45 PM

Thanks for the reveal! Nice to know what happened. Just save the puzzlers for the 3rd half of the show ....

NYTOM 05-30-2020 06:43 AM

Whew !
 
I?m also about 8 hours into phase 1 with my 6A with duel Pmags.
I don?t think I?ve ever read a thread so fast in my life.
A very nice outcome that could have ended so much worse.:)

Walt 05-30-2020 07:00 AM

Quote:

Originally Posted by N941WR (Post 1434367)
This is why you need to provide separate power and grounds to your P-mags!

This can't be stressed enough!

Again, please rewire your P-mags!

All aircraft without a dual buss/dual battery system have a single point of failure. I'm pretty sure the documentation does not require or suggest dual electrical busses if installing 2 Pmags, as most other EI systems recommend.

I might add that this is not the first time I've heard of lost power to Pmags causing the eng to quit after landing or on final.

BJohnson 05-30-2020 07:32 AM

Imprints
 
Quote:

Originally Posted by DavidHarris (Post 1433977)
Mojave River Landing

From the imprints in the sand it looks like the back wheels came off the ground and landed off to the side of the main track. The spinner, prop blades and air scoop all left an imprint in the sand.

Great job landing the airplane in the soft field! It is encouraging to see an upright off field landing of an -A model. How short was the landing rollout?

rv8ch 05-30-2020 08:20 AM

Observant dude!
 
Quote:

Originally Posted by BJohnson (Post 1434695)
From the imprints in the sand it looks like the back wheels came off the ground and landed off to the side of the main track. The spinner, prop blades and air scoop all left an imprint in the sand. ...

Brice, very observant. I had not noticed that. I'm guessing that this must have been quite a ride. David is either very good or very lucky or both!

PilotjohnS 05-30-2020 08:23 AM

Engine tear down
 
Is it time for an engine tear down and inspection since prop hit the sand?

ronschreck 05-30-2020 12:00 PM

In summation.....
 
I'll give you a D- in wiring skills, a B+ in problem solving, an F in forum decorum and an A+ in soft field landing techniques. A good learning experience all around. :D

N941WR 05-30-2020 12:12 PM

Quote:

Originally Posted by Walt (Post 1434684)
All aircraft without a dual buss/dual battery system have a single point of failure. I'm pretty sure the documentation does not require or suggest dual electrical busses if installing 2 Pmags, as most other EI systems recommend.

I might add that this is not the first time I've heard of lost power to Pmags causing the eng to quit after landing or on final.

Walt,

No, the P-mags do not need a dual buss because they will operate independently in the event of an electrical failure.

The problem here is the OP turned off the P-mags and didn't realize it until he was on the ground. Had he not touched the P-lead, or turned it back on, the engine would have started up after he lowered the nose and his RPM's came back up.

That is the beauty of the P-mags, if installed correctly, as described in the manual, there wouldn't have been an issue.

This isn't the first time I have heard of people wiring them incorrectly. This is always a surprise to me as this is a critical system and yet builders continue to go against the advice listed in the installation manual.

rv6n6r 05-30-2020 11:01 PM

Haha I loved the puzzler. And what an amazing story about a forced landing with a very good ending. It was amazing to see that nosewheel plowed into the sand without a noseover.

Sure, I was a little frustrated like others to think I'd be waiting a week for the answer, but jeez not mad about it or anything. Hey we're a community here, and anyway who didn't love Click and Clack and their weekly puzzler?

I am inspired by this as I have had some puzzlers over the 20 + years flying my RV-6; I'll maybe post them in upcoming days. Nothing so dramatic as an engine-out landing in the desert, but still. And I'll be sure to have the answers right at hand - David learnt that lesson for me :eek:

Hitt7A 05-30-2020 11:15 PM

I can see both sides of the lesson here. But at the end of the day it?s all about learning, and in my book the op gets an a+ for both the landing and the learning. Are we not all intrigued by the cause ? And we will all remember the lesson by being intrigued. Thank you for both

Captain Avgas 05-31-2020 12:47 AM

Quote:

Originally Posted by DavidHarris (Post 1433972)

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.

David

David, your very interesting story has prompted much worthwhile discussion and debate about the merits (or not) of the PMag. Beyond that, what seems to be fascinating posters is how you managed to land a nosegear RV in such soft sand without buckling the nose gear and tipping over. I, like everyone else, am absolutely amazed how deep that nosegear is in the sand. I am imagining that if you had your nose gear fairing on the added resistance in that sand might have produced a different outcome.

Can you please provide more detailed information on your landing, particularly the last seconds. Did the tail rise up and threaten to go over. Did the main wheels come off the ground. Did the prop strike the ground. And finally, as asked by some-one else, were there witness marks on the nose gear indicating that the AntiSplat brace had come into play.

JordanGrant 05-31-2020 06:37 AM

Good post
 
David,
Good post, thanks for sharing, and I liked the puzzler.

As to forum practices and decorum, to be honest I'm kind of disappointed in the tone of some of the responses here. The worst thing this community can do is fuss at someone for both being creative and posting their choices/mistakes for all to read. It is always a risk to the ego to share things like this, and I think many of the respondents should have been more polite to David. Being aggressive is not going to inspire more compliance to your version of how the forum should go - it's just going to keep people from bothering to take the time to write at all and then we'll all miss the chance to learn. Please be careful about that, and be thankful to David for choosing to share his experience.

N402RH 05-31-2020 09:39 AM

Quote:

Originally Posted by N941WR (Post 1434765)
Walt,

No, the P-mags do not need a dual buss because they will operate independently in the event of an electrical failure.

The problem here is the OP turned off the P-mags and didn't realize it until he was on the ground. Had he not touched the P-lead, or turned it back on, the engine would have started up after he lowered the nose and his RPM's came back up.

That is the beauty of the P-mags, if installed correctly, as described in the manual, there wouldn't have been an issue.

This isn't the first time I have heard of people wiring them incorrectly. This is always a surprise to me as this is a critical system and yet builders continue to go against the advice listed in the installation manual.

I do not believe this is correct. The P-Lead (kill switch) was wired to a standard aircraft key switch, as long as the key switch was in the both position the P-Mags should have worked with enough RPM. You are always going to have multiple single points of failure when they are wired like the P-Mag manual. If any of the following components fail you would have the same result: Master Relay, Master Relay control wire, any of the ring terminals in the control wire wiring, Master Switch, Master switch ground wires.

Rob Hickman
N402RH RV-10

MCA 05-31-2020 10:10 AM

I was an early adopter of PMags and had my share of issues. Fortunately, they have addressed the issues since then.

It hasn't been mentioned explicitly so I'll say it here. PMags only generate their own power above a certain RPM, I believe it is around 1200-1500 RPM.

Therefore, PMags require ship's power to start an engine or operate at low engine RPM.

It is also important that pilots realize in the event of an electrical failure (as Rob mentioned above) you must keep the engine RPMs up at least 2000 RPM or higher, even on approach.

As mentioned in the Puzzler, pulling back power to a lower engine RPM during stall practice would cause both PMAGS to fail. Makes sense.

flyvans.com 05-31-2020 02:58 PM

Quote:

Originally Posted by MCA (Post 1434967)
...
It hasn't been mentioned explicitly so I'll say it here. PMags only generate their own power above a certain RPM, I believe it is around 1200-1500 RPM.
...

Marc, that must have been a really early model then...

I can assure from tests that the latest 114 models quit somewhere around the 800 rpm range. At the same time, flying/gliding at reasonable speeds you will never see below 1000 rpm (provided there is no mechanical or other similar malfunction/blockage).
So that limit is really mostly relevant during rollout, taxi and of course startup, which is impossible without external power.

MCA 05-31-2020 08:55 PM

Hi Bernie, it has been a while. Your numbers are certainly better than mine. :)

DavidHarris 06-01-2020 04:34 AM

Regarding the question about roll-out, I paced off the distance from when the tracks first appeared on the sand until I came to a stop, and it was 200-250 feet. I had the good fortunate of a strong headwind (more than 20 kts at altitude, uncertain of what it was on the ground but it was definitely blowing as the desert often does in the spring) and sand that was firmer after a recent rain. I don't recall the back wheel coming off the ground during rollout. Off roaders had left tracks in the river bed as well, which might be misleading. The aircraft had come to very nearly a complete stop by the time the nose wheel touched the ground and promptly dug in. I was in a five-point harness, but recall very little force coming to a stop, and no tail rise. There is a small black mark between the bottom of the anti-Splat and the nose leg, indicating possible contact of the two, but no scratches, chipped powder coat, or visible bends.

I discussed the possibility of a teardown with two mechanics and concluded it was not necessary. I do not want to debate this decision in a public forum and would kindly ask for others to PM me if you wish to critique my choice.

D Weisgerber 06-01-2020 06:49 AM

My P Mag will self power to just below 800 RPMs.

DavidHarris 06-01-2020 09:49 AM

I agree with almost everything Bill said but disagree with one point of his analysis.

Quote:

Originally Posted by N941WR (Post 1434765)
Walt,
The problem here is the OP turned off the P-mags and didn't realize it until he was on the ground. Had he not touched the P-lead, or turned it back on, the engine would have started up after he lowered the nose and his RPM's came back up.

I had turned off one of the two PMAG switches, most likely in turbulence before the event, though possibly while troubleshooting or as pilot error at the end of testing it during run-up. The other PMAG switch was in the ON position, and the key was in the BOTH position.

I am convinced the root cause was the bad crimp in the power wire between the main bus and the PMAG switches causing intermittent loss of main power to both PMAGs.

I believe that if I had lowered the nose sufficiently, the engine would have started up again based on the PMAG internal alternators. During a subsequent ground test, I found my left PMAG alternator runs down to 850 RPM and the left down to 780 RPM, which is consistent with expectations. By the time I attempted lowering the nose, I was too close to the ground to do it very aggressively or for long enough to manipulate the power and mixture settings while doing so.

It is also possible that the engine would have restarted better with the mixture briefly at cutoff, as in the normal starting procedure.

swaircraft 06-07-2020 10:53 AM

Thank You
 
David: Thank you for the kind word's!

Glade to hear ever thing is going forward, FLY SAFE

Jack Vandeman

Mike S 06-07-2020 11:23 AM

Welcome to VAF
 
Jack, welcome aboard the good ship VAF:D


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