I was in Seattle all week in meetings with the FAA, and got home yesterday afternoon. I spent most of today at the hangar, intending to work on a list of things that I need to do on the aircraft someday. I got partway through that list when I discovered two new cracks in the plenum chamber cover. I had already discovered and fixed two cracks in the cover in the last few months. Today I found and repaired two more. I almost certainly need to make a more robust plenum chamber cover, but that will be a big job which I would rather tackle this winter. I'll keep repairing cracks for the time being.

Note: The plenum chamber cover is a mod that I designed myself - it is not part of Van's design. The basic concept is working well, but I have learned that I need to make it from thicker material. I also need to make some changes in shape and size to move it a bit further from the cowling, as there are marks where it hits the cowling when the engine shakes like a wet dog during startup and shutdown.

While at the airport, I ran into a young couple from Glasgow, Scotland who had stopped for fuel in a C172. They had flown into Toronto by airlines, took a bus to Lindsay, then rented the C172. They have a big trip planned to Quebec City, Mont Laurier, and eventually will return the plane to Lindsay and then head back to Scotland. Sounds like quite the adventure.

I got a bit of free time to head to the hangar Wednesday last week, and attacked the CHT indication problem. I reseated the connectors between the CHT #1 probe and the extension wire that goes to the Engine Indication System. Then I rechecked CHT #1 and #3 in boiling water. Now both were showing the same temperature - about 10 deg F too low. Now that CHT #1 seems to have the same errors as the others again, it will be interesting to see how it compares to the other cylinders next time I get flying.

While I was at the hangar, I made a cardboard template of the area at the rear of the canopy frame. Terry will use the template to make a removable cloth screen that will be part of a scheme to hopefully stop the air drafts coming from under the canopy skirt. Hopefully we can try it out this coming weekend.

I pulled the passenger seat cushions out and brought them home, so I could install a heated seat kit. But, I learned that the leather seat covers are glued to the foam cushion. So, it will not be possible to install the heated seat kit. Terry has a 12v electric blanket that a friend gave her - we will try that next time we go flying.

I was on the road from Thursday until late this afternoon, so nothing got done on the aircraft. I did take the time for an editorial cleanup on the POH.

I've done some thinking about this, and I wonder if the low CHT #1 indication could possibly be due to excessive resistance somewhere between the CHT probe and the engine monitor. Each CHT probe is connected to about 18" of metal shielded cable, then each of the two wires per probe has spade connectors that connect them to extension wires that go to the engine monitor. The CHT probes are thermocouples, and if there is a high resistance at one of those spade connections, it could lead to the engine monitor sensing a lower voltage than the CHT probe is actually creating.

Next time I have the cowlings off, I will inspect and reseat the spade connectors for the #1 cylinder, then I'll check it in boiling water again. If that doesn't do it, I'll disconnect the #1 and #3 CHT probes at their spade connectors and trade them, and check with boiling water again. It'll be useful to see if the problem follows the probe, or if it stays on the #1 cylinder.

If the problem stays with the probe, I probably need to replace it. If the problem stays on the #1 cylinder, I'll pull the connector at the EIS and check for pins that aren't fully inserted. Pulling and reseating the connector should clean off any corrosion too. Next, I'll swap #1 CHT with another cylinder by moving the pins in the connector, to take all the wiring out of the picture. if the problem stays on the #1 cylinder after all that, I'll contact Grand Rapids, as I almost certainly have a failed engine monitor.

I went out to the hangar this afternoon, pulled the cowling, then rigged up a metal can hanging from a step ladder to boil some water. Three of the four CHTs went to 202±1°F when the water was boiling furiously. CHT 1, the one that reads 50 - 60°F lower than the others in flight, went to 178°F. I looked at the wiring, and did find that one of the connectors at the back of the EIS 4000 was a bit loose. I tightened it and repeated the CHT checks, but there was no real change.

So, it looks like one third to one half of the low CHT indication is caused by some sort of instrumentation error. I need to sort that out before I make any more baffling changes. I removed the one change I had made, as I no longer trust the CHT indication on #1 cylinder, and don’t want to do anything that could cause it to go too high.

I had checked the CHT calibration using boiling water back in July 2006. At that time they all indicated about 3°F too low. Today the ambient temperature was just above freezing, and three of the four CHTs read about 10°F too low. The CHT indications use a reference junction inside the EIS 4000, and there is perhaps some sort of temperature sensitivity to it. In flight, I would have had the cockpit heat ON, and the cockpit temperature would hopefully have warmed up, so I suspect the error in the CHT would have been less. The atmospheric pressure was high today, so the pressure altitude was about 100 ft. Thus the boiling point of the water would have been 212°F.

I’m not sure what could be causing the low CHT #1 indication. I’ll contact Grand Rapids Technologies to get advice on what to do next.

This post documents a “gotcha” - hopefully some other folks will find this and avoid having to spend as much time troubleshooting as I did.

When installing my new Aero Technologies PCU-5000X propeller governor, I found that the governor control arm travel was large enough such that the prop control in the cockpit tended to hit one of its stops before the governor control arm hit its stop at the governor. I finally managed to get things adjusted so the governor arm would hit both the high and low rpm stops just before the prop control in the cockpit hit its stops. But there wasn’t much margin between the cockpit control and its stops.

When I got the aircraft flying, I noted that as the engine warmed up, the maximum selectable rpm would drop by more than 100 rpm. I pulled the cowlings, and confirmed that the governor control arm was hitting its max rpm stop before the cockpit control hit its stop. I discussed the problem with Aero Technologies, and they suggested that perhaps there was an internal oil leak between the governor and the prop. As the oil warmed up, the viscosity would decrease, and more oil would leak, which could impair the ability of the governor to control the prop. I’ve got an aerobatic prop, which defaults to coarse pitch (low rpm), and the governor sends oil pressure to the prop to force it to low pitch (high rpm). Thus an oil leak in the prop control path could cause the rpm to be lower than selected.

I used the procedure in Lycoming Service Instruction 1462A to confirm the oil leakage at the front of the engine was acceptable, but I couldn’t check the oil leakage at the back of the engine without pulling the prop governor. The access to the governor is poor, as it is on the back of the engine, surrounded by hoses, wire bundles, etc. So I put that task off while I did more thinking.

One day, in flight, I did some more experimenting. I recorded the max selectable rpm and the oil temperatures as the engine warmed up. Then, later in the flight, I fully opened the oil cooler door, and cooled the oil down, then checked the max rpm again. I found that the max rpm was lower than it had been earlier in the flight at the same oil temperature. There had to be another variable. Hmm.

I then hypothesized that perhaps the problem was due to differences between the coefficient of thermal expansion of the prop control cable and that of its sheaf. If the external sheaf expands more than the steel control cable, that would tend to reduce the travel of the cable end, and the cockpit control could then hit its stop before the control arm hit the stop at the governor. As a test, I adjusted the cable at the governor bracket to give more margin to the stop at the cockpit control when the governor control was at the max rpm stop. This meant that the low rpm stop could no longer be reached, as the cockpit control would hit its stop first. But, the low rpm stop is much less important than the high rpm stop.

On the next flight, I found that now the rpm only decreased 40 to 50 rpm as the engine warmed up. This is in the range reported by another local pilot who has three Pitts Specials with MT aerobatic props, so I think I have solved my problem.

Lesson Learned - Be sure to leave adequate clearance between the cockpit controls and the full throttle and max rpm stops. Otherwise you might be sacrificing some throttle or prop control travel after things warm up.

I also noted when I had the cowlings off that both exhaust hangar Adel clamps had broken at the engine mount. I had one clamp break a few flights ago, and now there were two more. The problem is that the exhaust moves with the engine, but the engine mount is fixed. My exhaust system is an early RV-8 system, with very short rubber pieces that attempt to allow some movement between the exhaust pipes and the engine mount. There is only about 3 inches between the bolt on the Adel clamp and the bolt at the exhaust system. The metal tubes that the rubber hoese pieces are clamped too take up about two of those three inches, so there is only about one inche of rubber tube that can flex. Not enough.

Apparently this design has had a high failure rate, and the currently shipping exhaust systems have long supports that attach to the bolts at the back of the oil sump. I studied that as a possible mod, but I’ve got a heat muff that is in the way.

I looked at one of the Mooney’s in the same hangar. The back end of its exhaust system is supported from the firewall area, hanging from springs.

I went to a local hardware store that had a large selection of springs, and picked up a couple to experiment with. I stretched the springs to make some space between the coils, and I squeezed the loops at the end to reduce the diameter, and twisted the springs to get 90 degrees between the loops on each end. The spring as I bought it is on the left, and the modified one on the right.

We’ll see how this experiment works out.

I zipped out to the airport today early, arriving around 7:30 AM, wanting to get a quick flight off before a cold front arrived. There was already about five knots of crosswind, which was a nice step up from yesterday’s essentially calm winds. I did a bit of cruise performance testing, then an aperiodic banging sound started. The sound didn’t change when I selected each ignition system OFF - ON, nor did the engine instruments show any anomaly. But, banging sounds are not what you want to hear, so I slowed down and headed back to the airport. 30 minutes airborne.

After I got back to the hangar, I took a close look over the whole aircraft, and found that the rubber wing root fairing seal had come loose above the left wing root.

I’ve been watching an anomaly with the prop governor. In the handful of flights I did after the prop change, but before the car accident, I noted that the max rpm would decrease about 100 rpm as the engine got up to temperature. The rpm would be close to 2700 rpm for the first take-off, but it would slowly decrease about 100 rpm over the first 10 minutes of the flight. I contacted Aero Technologies tech support, and they suggested I check for internal leaks in the prop governor oil system as described in Lycoming Service Instruction 1462A. SI 1462A calls for the prop governor to be removed, and a special cover plate to be installed in its place. The cover plate has fittings allowing the oil passages and external oil line going to the prop to be pressurized with an air compressor, using a differential compression tester. The input pressure is set to 40 psi, and the pressure downstream of the orifice in the differential compression tester must reed between 6 and 35 psi (this pressure is a measure of the amount of leakage in the system - lower pressure means more air flowing through the orifice, which implies greater leakage downstream).

I didn’t want to remove the prop governor yet, as it is a big job. So, I disconnected the oil line at the prop governor, and did the test from there. That allowed me to check for leakage downstream of the oil line - i.e. up at the nose of the crankshaft. With the warm, I got a reading of 12 to 15 psi, which is in the acceptable range. That is excellent news, because a problem in that area would require the engine to go back to the overhaul shop.

I discussed my prop governor issues with Andrew, a local Pitts Special pilot today. His three aircraft have MT aerobatic props too, but his prop governors are not the same as mine. He sees about a 50 rpm decrease in max rpm as the engines comes up to temperature. He suggested that perhaps I should defer digging too deep until I had switched over to my normal oil - at the moment I’m running Phillips Type M 20W-50 mineral oil. Andrew thought that perhaps the symptoms might change when I changed oil types.

I noted during this flight that the max rpm was not directly related to oil temperature as I had originally thought. I can vary the oil temperatue by opening and closing a door in front of my oil cooler. I noted max rpm vs oil temperature as the engine came up to temperature in the early part of the flight, then later on I varied the oil temperature and compared max rpm to the earlier values. I noted that even at the same oil temperature, the max rpm was lower later in the flight. This suggests that my earlier theory of excessive internal oil leakage that allowed greater leakage as the oil thins out might not be the winner.

I checked the travel of my prop control, and noted that the prop control in the cockpit was very close to its stop at the throttle quadrant when the control arm on the engine hit the max rpm stop. I wondered if somehow differential expansion of the prop control cable and its sheaf as things warmed up ahead of the firewall might possibly cause the prop control to hit the stop the cockpit before it hits the stop at the prop governor. I adjusted the cable at the prop governor to give a bit more margin to the stop in the cockpit. We’ll see on the next flight if that makes any difference.

I pulled the cowlings this morning, and did a detailed visual inspection - no issues found, other than a small oil leak at a hose fitting. I inspected the spark plugs, and they all looked normal. A bit oily, but that is normal early in the break-in. I removed the fuel injection nozzles, and held each one up to the sky to look through. Three of them looked fine, but the one for #1 cylinder was obviously quite clogged. The orifice in the restrictor fitting was approximately 75% blocked with some sort of debris. I put some acetone in an ultrasonic cleaner and put all the nozzles in there for 45 minutes. Then I blew them out with compressed air and did another visual inspection - they all looked clean.

After lunch, I reassembled everything, changed into my flight suit, and fired it up. The engine ran fine at my normal runup rpm of 1800 rpm, and at 2300 rpm, so I put the engine monitor on the EGT page and taxied onto the runway. The EGTs all looked normal after I advanced to full power, so I continued the take-off. The engine ran completely normally, so I did a one hour break-in flight. Tomorrow afternoon I’ll pull the cowlings for another inspection, and then do another break-in flight.

It felt really, really good to get the aircraft airborne again.

I got back out to the hangar on Saturday, and finished off 99.99% of the engine reinstallation. I had Dale, a very experienced builder, aircraft maintenance engineer, and retired official amateur-built aircraft inspector inspect things for me. There was no regulatory requirement for this inspection, but it was the smart thing to do, as I have had pretty much everything ahead of the firewall off and then back on. He found a short list of things, none of which would likely have caused an accident, but several of which would have eventually caused me some maintenance problems. Some of the problems had been there since day one, and had been missed by a whole bunch of people.

I took today off work, and spent the day at the hangar. First, I juggled the order of aircraft in the hangar to move the RV-8 from the back corner to a spot next to the door. I had planned to do this next weekend, but the weather forecast was for a lot of freezing rain this afternoon, which would leave a big sheet of ice on the ramp, and make it hard to push the two Mooneys outside so I could get the RV-8 in front. So I did the job this morning. In the end, the weather guys were completely wrong, and there was only about 60 seconds of freezing rain after lunch, rather than the 2 to 4 mm of ice they had predicted.

I fixed the last of the snags that Dale had found, then attacked the prop mounting. The MT prop has the same style of nuts attached to studs by roll pins as the Hartzell, and it was just as fiddly to mount. I had it mounted, torqued and safetied by noon.

After lunch, I installed the spinner, and then put the cowling on to see how the spinner matched the cowling. I didn’t bother putting the upper cowl pins in, as I would be taking if off immediately. I found that the spinner was exactly the correct length and diameter - MT had custom made it to my specs. The gap between the spinner and cowling is about 1/32” more than it was before, which is what I wanted.

I adjusted the alternator belt tension, checked the ignition timing, and installed the spark plugs. Next time I go to the hangar, I will do a quick engine run, then drain the fuel and do another weight and balance. I’ll need to track down someone to stand fire guard and look for leaks during the engine run.

The aircraft looks quite different with the three bladed prop. I’m looking forward to seeing how it performs with this prop.

It was pretty cold for the early part of last week, and we had a major snow storm on Wednesday, so I didn’t get much work done on the aircraft. I had hoped to get out to the hangar all day on Thursday, but I wasn’t sure how much snow was on the taxiways. I eventually found out that they had only received about five inches of snow, quite a bit less than we got at home. At lunch time I headed to the airport, and managed to get down to the hangar. I also spent most of Sunday there, and today. Progress has been slow, but steady. I am almost through all the details of the engine installation, and then will work on the new prop and spinner.