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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! |
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!
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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.
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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 |
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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. |
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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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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? |
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.
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I do admit that with posts like this, my list of what to watch out for is growing. |
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"You don't have a proven product until you have 500 units installed in 500 homebuilts by 500 amateurs."
So true, that. |
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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 |
Thanks for the reveal! Nice to know what happened. Just save the puzzlers for the 3rd half of the show ....
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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.:) |
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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. |
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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? |
Observant dude!
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Engine tear down
Is it time for an engine tear down and inspection since prop hit the sand?
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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
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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. |
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: |
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
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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. |
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. |
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Rob Hickman N402RH RV-10 |
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. |
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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. |
Hi Bernie, it has been a while. Your numbers are certainly better than mine. :)
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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. |
My P Mag will self power to just below 800 RPMs.
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I agree with almost everything Bill said but disagree with one point of his analysis.
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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. |
Thank You
David: Thank you for the kind word's!
Glade to hear ever thing is going forward, FLY SAFE Jack Vandeman |
Welcome to VAF
Jack, welcome aboard the good ship VAF:D
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