Ahh, there is always another test to do. I live for it. I get so many requests for information and opinions so here goes (repost from my build log). Just my experience. Warning, there are P-mag comments herein.
I have long been battling a "prop surging" issue. I have concluded that there were a number of variables contributing to the symptoms which are now resolved. The first thing was that I had an MT prop governor that was known to have a tendency to surge. I sent it back to MT for update and still had the problem. I quickly abandoned the newly updated prop governor for a new PCU5000X which is known to be of very high quality.
Through testing the new prop governor, I found that I had some pretty severe prop surging (-+ 120rpm) on takeoff, only with high, 195+ deg oil temperatures. The surging would only happen on initial climbout with high oil temps and the symptoms would begin with a significant rpm drop of 100rpm or so. Then the prop would recover to the set point or slightly over shoot it. This would occur a time or two then settle down. I was convinced that the prop governor or the prop wasn't quite doing its job when the oil got hotter and thinner. I've been using Exxon Elite 20w50 oil. I had the PCU governor back at American Propeller twice. They declared it was fine. The second time, I also sent along the MT governor for reference at their request. They ran the revised MT governor and found that it still had a surging problem on the test bench. It currently sits on my shelf.
A lot of this testing occurred in hot summer OAT. It was suggested that maybe I was experiencing a hot fuel problem. Ok, maybe. I have a blast tube on my fuel pump and all of my fuel lines are in fire sleeve FWF. Enter much cooler ambient temps. I did some temp instrumentation of and around the fuel pump, lines, and gascolator. No way this was a fuel problem. Now with the lower ambient temps, I was having no prop surging problems "because" oil temps were way down. I was just enjoying flying for a while.
I'm not one to let a problem go unresolved so I used the opportunity with lower OAT to isolate the oil temps. I started slowly blocking off the oil cooler as one would do in cooler weather. No prop surging. Over the course of a few flights I added tape to get the oil temps up to the 195-200 deg range. The prop surging returns. Tanya and I were doing laps in the pattern one day as the oil temp got into that range.
This is when we had our last P-mag failure! We had been running for about 15min with oil temp at about 198 when we noticed the ignition had failed on a full stop, taxi back, and runup. I've written the story of the rest of this flight previously. The short version is that we restarted the ignition and did one more lap with the ignition failing on initial climb with the obvious demonstration that the ignition failing felt exactly like the beginning of our prop surging issue, except with only one cycle. Note, oil temp at about 198 and everything else very cool due to low OAT and lots of blast tubes.
So back to the most recent test. Ever since then I had been itching to do the same test with the new ignitions. OAT was still very cool and I brought the oil temp up. Lap after lap in the pattern with the oil temp 200-210 degrees and no prop surging. Nothing but perfectly smooth power. We "almost" always had "prop surging", now recognized as power (yikes!), problems on initial climb when the oil temp was this high.
My clear conclusion is that early on I did have a real prop surging problem with the MT prop governor. After that was resolved with a new governor, similar symptoms continued due not to the prop governor but because of intermittent ignition causing variable power in the condition of high power and high oil temperatures on the nose of the P-mags. Critical to these conclusions are the opportunities afforded by the change of season with cooler temperatures in order to prove the condition with artificially increased oil temp only. In the end, I think I was able to fail the P-mags almost at will with oil temp and power setting hence my comments that those cooling fins on the newer 114 model P-mags are probably more important than many people realize.
I am very pleased to finally have resolution to a number of problems all at once with replacing the P-mags with a normal Slick magneto and Lightspeed Plasma II+. There is no need to shoot holes in my method or madness as I'm a very happy camper
.
I have long been battling a "prop surging" issue. I have concluded that there were a number of variables contributing to the symptoms which are now resolved. The first thing was that I had an MT prop governor that was known to have a tendency to surge. I sent it back to MT for update and still had the problem. I quickly abandoned the newly updated prop governor for a new PCU5000X which is known to be of very high quality.
Through testing the new prop governor, I found that I had some pretty severe prop surging (-+ 120rpm) on takeoff, only with high, 195+ deg oil temperatures. The surging would only happen on initial climbout with high oil temps and the symptoms would begin with a significant rpm drop of 100rpm or so. Then the prop would recover to the set point or slightly over shoot it. This would occur a time or two then settle down. I was convinced that the prop governor or the prop wasn't quite doing its job when the oil got hotter and thinner. I've been using Exxon Elite 20w50 oil. I had the PCU governor back at American Propeller twice. They declared it was fine. The second time, I also sent along the MT governor for reference at their request. They ran the revised MT governor and found that it still had a surging problem on the test bench. It currently sits on my shelf.
A lot of this testing occurred in hot summer OAT. It was suggested that maybe I was experiencing a hot fuel problem. Ok, maybe. I have a blast tube on my fuel pump and all of my fuel lines are in fire sleeve FWF. Enter much cooler ambient temps. I did some temp instrumentation of and around the fuel pump, lines, and gascolator. No way this was a fuel problem. Now with the lower ambient temps, I was having no prop surging problems "because" oil temps were way down. I was just enjoying flying for a while.
I'm not one to let a problem go unresolved so I used the opportunity with lower OAT to isolate the oil temps. I started slowly blocking off the oil cooler as one would do in cooler weather. No prop surging. Over the course of a few flights I added tape to get the oil temps up to the 195-200 deg range. The prop surging returns. Tanya and I were doing laps in the pattern one day as the oil temp got into that range.
This is when we had our last P-mag failure! We had been running for about 15min with oil temp at about 198 when we noticed the ignition had failed on a full stop, taxi back, and runup. I've written the story of the rest of this flight previously. The short version is that we restarted the ignition and did one more lap with the ignition failing on initial climb with the obvious demonstration that the ignition failing felt exactly like the beginning of our prop surging issue, except with only one cycle. Note, oil temp at about 198 and everything else very cool due to low OAT and lots of blast tubes.
So back to the most recent test. Ever since then I had been itching to do the same test with the new ignitions. OAT was still very cool and I brought the oil temp up. Lap after lap in the pattern with the oil temp 200-210 degrees and no prop surging. Nothing but perfectly smooth power. We "almost" always had "prop surging", now recognized as power (yikes!), problems on initial climb when the oil temp was this high.
My clear conclusion is that early on I did have a real prop surging problem with the MT prop governor. After that was resolved with a new governor, similar symptoms continued due not to the prop governor but because of intermittent ignition causing variable power in the condition of high power and high oil temperatures on the nose of the P-mags. Critical to these conclusions are the opportunities afforded by the change of season with cooler temperatures in order to prove the condition with artificially increased oil temp only. In the end, I think I was able to fail the P-mags almost at will with oil temp and power setting hence my comments that those cooling fins on the newer 114 model P-mags are probably more important than many people realize.
I am very pleased to finally have resolution to a number of problems all at once with replacing the P-mags with a normal Slick magneto and Lightspeed Plasma II+. There is no need to shoot holes in my method or madness as I'm a very happy camper
.
