|Flights 25 - 27|
|Flight 25 11/21/04 1731 Lbs 101.9" 0.7 hrs
Since the last flight I performed a Condition Inspection including a PSRU treardown. I changed the oil to Castrol Synthetic and added Marvel Mystery Oil. The only sqawks from the inspection were a loss of torque on some of the engine mount bolts to the firewall and some chaffing on the duct from the NACA to the air filter. The PSRU showed no signs of wear. I removed the IRIS (intake manifold spliter) and wired the induction solenoid back to the resistor. I reinstalled the thermostat. I installed the wheel pants. I did a high speed taxi run to check the pants. There is still one spot that needs a little more trimming. There were clouds at about 4500 msl so I climbed to 3500'. The water temp rose quickly to 230 deg in the climb but leveled off on power reduction. The temps were inconsistent. Then they seemed to stabilize so I tried a higher power setting. The temps were now good so I did a speed run to French Valley. I did the full throttle point first. I got 171 kias at 5040 eng. RPM (2724 prop). This is 15-20kts faster than before the wheel pants. The water temp was down to 200 deg. so I continued. I did a point at 150 and 140 kias both showed 215 -225 deg water temp. Then when I slowed to 130 kias the temps rose to 240- 250. It didn't seem right since the water pressure was only 8 psi and the oil was less than 200 deg. I decided to head back home. I kept the speed down but the water temp stayed high varying between 220 and 250 with a few spikes to 270. The whole time the oil temp stayed around 200. It took 12 min to get back but I got a base entry and direct clearance to land. After shutdown there was a small amount of coolant on the cowl and the overflow tank was full. I suspect I had an airlock. If it had been the thermostat I don't think it would have been high and then low and then high again. Hmmm, the water pressure was low but the temp was high and I did get boil over. I wonder if the cap was tight? The trouble is that I don't trust the water pressure indication. It has typically shown pressures above the cap rating during flight even when the water temp is 180 deg. I've recalibrated it several times and its right on the ground, cold. Either I have a resistance to ground that throws it off when other electrical loads are on, or the higher temps are affecting it. The thing is, it has always read high, never low. I think it's trying to tell me that the pressure really was low. After the flight the cap was definately in place and at least past the first detent but I couldn't swear it was tight. I'll refill it and run a few times to be sure its full then do some pattern flight until I'm sure the cooling is back where it was.
I plotted the data from all the full throttle flights so far. It's in the spread sheet attached. The plot is indicated A/S vs HP. HP is calulated as RPM*MAP/702.5. This is an empirical formula. The 702.5 is a factor that provides the rated HP value at 5400 RPM and 29.92" MAP. This may not be real, but it will be a consitent HP measure for this engine. The plot shows a 19 kt gain for this flight compared to the average of all the other flights. The data is at varying altitudes however and this flight was the lowest. I'm not sure how that scews the data so I'll repeat the data at the same altitudes as the earlier flights. The 19kt gain is way more than expected!
Flt 26 11/26/04 1713 Lbs 101.8" 1.4 hrs
I thought after reviewing the indication of low coolant pressure but high temps that perhaps the pressure cap was loose on the last flight. So I did several ground runs checking the coolant level after each to be sure the system was full and I also made sure the cap was tight. Then I took off on this flight. Again the temps rose rapidly on climb out but cooled to normal in the pattern. I added power in the pattern up to full throttle with very little rise. It appeared that the thermostat was working keeping the coolant temp between 190 and 210 deg. I climbed to 5500' to get comparable data to my earlier tests without wheel pants. I started off at 130 kias and took data at 140, 150, and 160 (which was not WOT). Then I slowed to 120 and 110. When I slowed to 100 the temps shot up to 240 within a couple of minutes. Very strange. I was very near French Valley airport so I landed there to check it out. within 5 minutes of shut down the pressure indicated atmospheric, so I opened the coolant tank. It had a tiny amount of pressure which burpped and did not overflow. I went for lunch to let it cool some more and brought back a quart of water. It only took 2 cups. I decided to fly it home. The takeoff and climb was as the first one of the day and temps stayed low all the way back until I reduced power for descent. They came up then again but stayed below 240. This time I did see presures over the rated cap pressure of 22 psi. after landing the tank was still full. That coolant pressure gage is completely unreliable. OK the thermostat is coming out! After some discussion on the Cozy list and input from Phil Johnson I think I understand it. I don't know why the stat opens right after climb out but it seems that after high power tests when power is reduced the Tstat closes due to the low heat load from the engine and the good flow thru the radiator. Once it closes the engine begins heating up. The hot coolant can't get to the Tstat to re-open it because I have the bypass tube blocked and the cabin heater is the only path. The cabin heater line is only a 1/2" tube (1/9th the area of the main hoses). The theory is that this small flow thru the cabin heater is being cooled before it returns to the Tstat, so it stays closed. The choices are 1) unblock the by pass tube, 2) drill a hole in the Tstat as another bypass, 3) take out the stat. Number 1 is a little difficult because The tube was damaged when I plugged it. I can't drill a hole in the Tstat big enough to do any good. Number 3 seems the best for now. I really don't see why I need a Tstat anyway. When the engine is at high power I want all the cooling I can get. At low power, in cold weather it may cool to 160 or maybe even 140. I don't care at that point about emmisions or efficiency and I don't think there will be any harm to the engine at 140 and low power. On the ground having the stat open all the time will help keep the engine from heating up so fast. The Tstat is outta there!
The test data from this flight is much more believable than the last pants on flight. Duh, in that flight I compared IAS at high altitude to IAS at low altitude. So, about half the gain in IAS that I saw with the pants on at 2500' vs the pants off flight at 5500' was due to the power available difference from that 3" of MAP. taking this data at 5500' and comparing it to earlier data at the same altitude shows about a 10 kias gain from the pants.
Flt 27 12/01/04 1779 Lbs 101.9" 1.1 hrs
Ok, I pulled the Tstat out and refilled the system. I double checked for fullness. The flight card included speed/power points at 5500', airspeed cal, glide distance, and suddend power reduction to test cooling. Without the Tstat the cooling was back to the way it was before I put the Tstat in, perfect! Even in the climb the temp was less than 200. On sudden power reduction, the temps dropped as you would expect not jump up as they did with the Tstat. The data is definative, the lack of a bypass tube causes the Tstat to lock closed after power reduction. The OAT was about 52 deg at 5500' and at that temp during descent the coolant gets down to 150 deg. I think that's getting too low and I will probably operate in colder weather. So, I think I will put the bypass in and the Tstat back in and try that in a while. The glide data confirmed that my previous data point at 80kias was erronious, which was obvious looking at the data. Of course this data was with pants on, which unboubtably improved the glide somewhat. It now appears that the best glide speed is at 80 or below and is about 2.4 N Mi per 1000 ft. I'm still not happy with the airspeed cal technique. The low speed end is showing a 5-6 knot error that I do not believe. This will be repeated on a day with no wind. The flight was a complete sucess with no squawks, at least till I got back to the hangar. Then I saw some coolant drips from the cowl. So off it came and for the third time I found a tiny crack in the surge tank. I had lost about 1 quart of coolant and despite that I never saw a temp above 185. So the crack had nothing to do with the earlier cooling problems with the Tstat. Those tests had overflow to the tank this one did not.