37 Hours – Oil Cooler

Here’s an update from about 37 hours since the first flight. I found a few hours ago that I was getting high oil temperatures. This turned out to be an indication of several minor factors that were working together. First, the ambient temperatures started rising with the arriving spring season. Second, I didn’t really come up with an optimal mount for the oil cooler. I had it right next to the cylinder, but it’s really better for there to be some space between the cylinder and cooler. Also, I had the cooler mounted in such a way that it could trap air. A better arrangement would have been to have the inlet down low and the outlet at the highest point, which would naturally purge any air from the cooler. Another factor is that the 7-row cooler that I started with is probably a little bit too small. Bob seems to think that it should be adequate, but I read about many other installations where the 7-row proves to be too small for the angle-valve 360s.

To help resolve the problem, I’ve made several changes to the oil cooler arrangement. Note from the future- I’ve subsequently moved the oil cooler to the firewall. See this post. First, I found a 9-row unit. It is the same width as the 7-row, just a little bit taller. I removed the back left baffle and fabricated a new mounting system. The new mount scoots the oil cooler back about an inch, and also rotates it closer to horizontal. One thing that I haven’t yet done, but plan to do, is to flip the cooler over so that the outlets are on the top. A better arrangement would be to have the oil cooler sitting with the long dimension running vertically, but I’d have to make more extensive changes to mount it that way.

I have completed almost all of my data gathering. A few days ago, I flew down to Shelby to get some fuel. When I had topped off the left tank, I tried to install the fuel cap but found that the threads had seized. I had not lubricated the threads with anything, but Bob suggests a regular application of fuel lube to keep the threads from galling. I borrowed a vice from the friendly folks at the maintenance shop, and was able to use my onboard crescent wrench to apply enough force to snap the center male threaded part in half at the o-ring gap. This allowed me to separate the parts of the fuel cap. I borrowed the airport courtesy car and drove a few miles to the hardware store, where I picked up a 3″ long 6-32 screw and nuts. My plan was to drill the center vent hole and cut threads in the lower portion, allowing me to hold the cap together with the 6-32 bolt. The hardware store didn’t carry thread cutting taps, so instead, I drilled the vent hole up to the major diameter of the number 6 threads, and just used a nut on the bottom.

This arrangement worked to seal the tank, but not to allow for any venting. While flying on one tank is not an optimal arrangement (indeed, it is even advised against by Bob because of concerns about unporting the feeding tank during uncoordinated flight), it was sufficient to get me home for a 10-minute flight. The right tank was completely full, so unporting the inboard side was highly improbable.

Once I got back home, i was able to salvage the bottom piece of the cap, and of course all of the o-rings. I chucked the bottom piece of the cap into the drill press vice so that the vent hole was in line with the drill chuck, then I started increasing the size of the vent hole. I used about four sizes to get up to the minor diameter of the 1/2″ threads, which left just a few small pieces of the old male threads in place. I was able to pick out most of those pieces with a scribe, at least enough of them to allow me to get a thread cutting tap started. I worked it back and forth slowly and the threads cleaned up just fine. I used a steel bolt from the hardware store with coarse 1/2-13 threads to make a temporary center post. I drilled a 1/8″ hole through the middle of the bolt, which will allow the cap to vent. Since the bolt has a hex head instead of the airfoil-shaped vertical blade, cap removal requires a wrench. This gets me back to a flying condition while I wait for a replacement cap to arrive. You can be sure that I have since added some lube to the threads on the other cap too! I’ll use the repaired old cap as a spare, which I’ll carry in my onboard tool kit.

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Hours Logged This Session:
Total Hours: 1883.75

Gross Weight Testing

Today I continued adding ballast to the Bearhawk to test how it performs at heavier weights.  My ballast is 80 pound bags of concrete, so I started with 160 pounds in the back seat.  The weight wasn’t really noticable during a few stalls and some phugoid tests.  Since I was flying with close to half tanks on that flight, this weight gain was not much above my solo full fuel weight.  On the next hop I added 160 pounds to the front right seat.  As with before, this weight didn’t seem to matter very much. 

For the next flight I added two more bags to the back seat.  By now, the pitch stability was still pretty good, though the phugoid definitely started to show a higher amplitude.  The takeoff roll was noticably longer (perhaps 700 feet or so) and the uphill back-taxi required much more engine power.  The latter indicator might have also been related to the somewhat soggy runway.  For the first time, I was able to land tailwheel-first.  The landing flare was much easier.

For my final configuration, I added 105 pounds to the baggage area and another 80 pounds to the front right seat.  To recap, that’s 240 pounds in the front right seat, 320 pounds of concrete (plus another 20 pounds of fly-away-kit), plus 105 in the baggage area.  I was at about 1/3 fuel, which would mean that when I flew up to HKY to top up the tanks, that would put me about 8 pounds short of the max gross 2500.  I should mention that with each additional weight increase, I also measured the main landing gear tread.  As the weight increases, the gear spreads out.  Bob advises that the center-to-center distance of the main landing gear tires must not exceed 72″ at max gross, an fortunately mine did not.  

That heavy configuration had my CG at 21.88 inches by my calculations.  Bob specifies a limit of 22.5 inches, but I didn’t really care for flying it at 21.88.  If I encountered a little updraft, I found myself working the elevator control back and forth to maintain level flight.  If I trimmed for level flight at around 80 knots, bumped the stick aft about 2″, then let go, the resulting pitch up was 1.6g all the way up to around 25 degrees.  While I thought all of this through over lunch at HKY, I decided not to test any further aft.  Instead I made a note that 21.5 will be my operational limit.  To get there for the next flight, I moved the 80 pound bag from the baggage area to the back seat, and left the 25 pounds of kitty litter in the back.  Then I topped off the tanks and took off.  As before, the most noticable difference was the longer takeoff roll and climb rate.  

I had intended to fly around the pattern a few times, but all of this extra weight made it apparent that my tailwheel tire was a little bit low on air.  On the second landing (which was not one to be especially proud of anyway), the tailwheel started to shimmy as I slowed through about 25 knots.  I attributed the shimmy to the low tire pressure and departed for home.  On the way I tried to validate my calculated high-altitude performance with a climb to 10,000 feet.  I had to level off several times along the way due to high CHT and/or oil temperature.  This tells me that I need to improve the effectiveness of my cooling, since the OAT was right around freezing.  I have made a few adjustments and am going to try again on another day.  

In summary, I would say that the fully-loaded Bearhawk, particularly at a fully-aft CG, is a whole different animal than an almost-empty one.  This is the case with every other airplane that I’ve flown in both conditions, so I’m not surprised.  The good news is that from the family-hauling standpoint, I won’t be that heavy or that far aft.  My concrete family is at least 300 pounds heavier than my regular family, at least as of now.

Flying Update

I have found that the engine is running a little less smooth than I think it should. This is a challenging problem, in part because it may be running just fine. I have a fair amount of experience in single-engine piston airplanes, but most of it is not in recent times. At idle, I hear an occasional miss, even with the mixture leaned. The other day, I took off with the intent to fly for a few hours, but at 2500 RPM and full throttle, it was running rough enough to make me turn back towards the airport. To be fair, I’m not sure if a non-pilot passenger would have noticed it. I leaned the mixture a little bit and the roughness went away, but this didn’t make sense, because it was exceptionally cold that day, and the density altitude was probably well below sea level. On another day I found 150 RPM drop during a ground mag check, when I turned off the left mag. I tried running the engine up a little bit and leaning aggressively, but had no change. I taxied back on the rough mag and hopped out to check the exhaust pipe temperatures. All except number 1 were around 350 degrees, while number 1 was more like 300. I swapped the bottom plug from that cylinder to the top, and tried another mag check. This time the drop was on the other mag, confirming that the plug was to blame. I replaced it with a spare that I had on hand and took off to conduct an inflight mag check, as described by Mike Busch.

His process involves using the EMS data logging, so I figured getting that started would be a good first step. I had noticed earlier that when I went to the data logging menu in the D180, instead of the usual choices of “on” and “off”, I had a message that said “Error 4.” With me not having the tools to address that problem right then, I took off anyway and conducted the check as Mike describes. I wrote down the EGT changes, but as he points out in his articles on the subject, that’s not really enough information. The good news is that during those checks, I didn’t get any significant roughness. The bad news is that I had some wacky EGT numbers. The cylinders were all fairly even when running ROP, but one was about 300 degrees lower when running LOP. I resolved to get the data logging working, then fly on another day to get more valuable numbers and see what’s going on. I never have installed the little blocking plates in front of the front two cylinders, since the Vans baffle kit instructions say to not install them unless you find that you need them. I have been reading reports from Husky owners that they get much better LOP operations with similar plates in place, because the cylinders run more similarly to each other. So that’s another avenue to explore.

To address the “Error 4” in the data logging menu, I did some Googling to find that it is a bug with the Dynon. Speculation is that the data log file becomes corrupted. The fix is for Dynon tech support to send a file, which I then send to the D180 as a “restore firmware backup.” The repair file is firmware version specific, and Mike at Tech support sent the version that corresponds with the latest firmware. I was due for an update anyway (though I didn’t realize it just then) so I downloaded the latest support program and went back out to the airport. I went through the usual ritual of powering off both the D180 and D100, then updating the HS34. Then I updated the D180, then the D100. After all of the firmware updates, the Error 4 message was still there, so I sent the repair file. The good news is that the new file fixed the problem, but the bad news is that there wasn’t any log file there. The D100 did have a good file though, and it has been extremely fascinating to study. Now I’m looking forward to getting to fly again and get some good data from the D180, which will be much more valuable, since it should have EMS data too.

In fact, with having so much information available in the logs, I think I’ll plan to redo the bootastrap glide tests, to try to provide better numbers for the data plate.

First Flight

Last week I drove down to Charlotte to pick up the airworthiness certificate. I got back into town with it just as a cold front did, and it took these 9 days to get a day with the right combination of me being in town and the weather being good. The weather was perfect all day today, and the flight went well. I flew for about half an hour, then came back to do a thorough inspection. I found a few more minor items to correct, such as the direction of the elevator trim. It worked backwards to how I thought it should work, so I just flipped the wheel around to reverse it. In that process, I noticed that the nut in that bolt had no cotter pin, which goes to show that even with several sets of eyes looking over an airplane, things can get overlooked! Everything looked good with the inspection, so I put it all back together and flew again. On the second flight I repeated much of the first, though I expanded the initial stall testing by adding flaps. At the end of the flight, instead of ending after one landing, I flew around the pattern for 5 more. The challenge with test flying a new airplane is that there are several goals to achieve. One is to validate the airframe and systems, but another is to train the pilot. The landings were more for the latter goal, though of course they also helped with the first. I feel very confident with the directional control on the ground, which was one of my main concerns about the flight testing. I find that I have a little bit of a heavy wing, and a few other minor things to fix, but that’s what the next 40 hours are for.