Shadrach Posted February 10, 2016 Report Posted February 10, 2016 46 minutes ago, StinkBug said: This just seems like a bad idea to me. If the P lead were to break in flight on a normal mag, you just keep on flying and the only problem is that you can't shut the mag off with the key. With this setup if the P lead breaks your mag quits, which could kinda spoil your day. Seems like it's kinda defeating the whole point of a magneto, which is that it provides spark no matter what. A P-lead is secured to the Mag with a knurled nut. It's not likely to fail...Not impossible, but highly unlikely. Quote
Jim F Posted February 10, 2016 Report Posted February 10, 2016 The Bendix 200 and the dual mags(not sure on the part number) are the mags with an internal shorting bar. The P lead has a threaded cap that screws into the mag and ungrounds the shorting bar. If the P lead wire breaks (opens) the mag stays hot. One of the checks you should do before shut down is quickly switch the mags to off to verify the engine drops off and then turn to both then idel cutoff for shutdown. This tells you both P leads are connected. Quote
StinkBug Posted February 10, 2016 Report Posted February 10, 2016 2 hours ago, Jim F said: The Bendix 200 and the dual mags(not sure on the part number) are the mags with an internal shorting bar. The P lead has a threaded cap that screws into the mag and ungrounds the shorting bar. If the P lead wire breaks (opens) the mag stays hot. One of the checks you should do before shut down is quickly switch the mags to off to verify the engine drops off and then turn to both then idel cutoff for shutdown. This tells you both P leads are connected. That makes more sense. I was thinking it was some kinda electrical connection to the shorting bar. I'm not terribly familiar with the physical workings of an aircraft magneto, only the general principles. I've only worked with motorcycle mags, which are definitely different. Quote
N201MKTurbo Posted February 10, 2016 Report Posted February 10, 2016 11 hours ago, StinkBug said: This just seems like a bad idea to me. If the P lead were to break in flight on a normal mag, you just keep on flying and the only problem is that you can't shut the mag off with the key. With this setup if the P lead breaks your mag quits, which could kinda spoil your day. Seems like it's kinda defeating the whole point of a magneto, which is that it provides spark no matter what. Having a live mag while working on a plane is a bad idea. 2 Quote
StinkBug Posted February 11, 2016 Report Posted February 11, 2016 13 hours ago, N201MKTurbo said: Having a live mag while working on a plane is a bad idea. I tend to think that having a dead one in flight is a worse idea, but we've already established that the way the mags in question work is different from how the description led me to believe. 1 Quote
gsxrpilot Posted February 11, 2016 Report Posted February 11, 2016 I've got Slick mags on my C. Just recently the P-lead did come off one of the mags. I noticed it during the run up. I would get a normal drop on one mag and no drop on the other. After pulling the cowl, we discovered the P-lead hanging lose and not connected to the mag. We also found the nut laying in the bottom of the cowl. By the way, the engine ran just fine as I flew the plane back to the shop to get the situation looked at. It can happen. Quote
Shadrach Posted February 11, 2016 Report Posted February 11, 2016 44 minutes ago, gsxrpilot said: I've got Slick mags on my C. Just recently the P-lead did come off one of the mags. I noticed it during the run up. I would get a normal drop on one mag and no drop on the other. After pulling the cowl, we discovered the P-lead hanging lose and not connected to the mag. We also found the nut laying in the bottom of the cowl. By the way, the engine ran just fine as I flew the plane back to the shop to get the situation looked at. It can happen. That was likely a maintenace induced failure. No doubt the plane ran fine as your mag was hot all the time. If you had been running Bendix Mags you'd known the moment it happened as you'd have seen it on your engine monitor in the form of elevated EGTs across the board. 1 Quote
thinwing Posted February 11, 2016 Report Posted February 11, 2016 On February 10, 2016 at 5:13 AM, N201MKTurbo said: Having a live mag while working on a plane is a bad idea. I learned something the 200 series mags did use that design ( hard to believe)cause you sure don't see that in slick/ Bendix 1200 S !Any way Looked up the s20 and 200 series mags and guess what most common mod is?Yep,disabling the grounding bar by installing a new coil terminal stud into the magneto contact points cover. K Quote
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