Conducted 06/27/2012 –
The name of the game for Flight 4 was “find out why the oil temps are high”. We did a few thing to assist us in that goal. First, in a potshot attempt to solve the problem we added silicone seals between the wing root baffles and the center spar, just in case they were shifting and allowing air to escape. Next we added a second pitot tube at the NACA scoop cowling inlet along with a couple valves to allow switching between the nose pitot tube and the cowl tube for comparison. We also added an OAT sensor to the engine monitor in order to start gathering that data and allow for more useful comparisons of oil temps from one flight to the next. The last order of business was to fix the #1 EGT, which turned out to be a loose connection at the engine monitor.
It had been pretty warm for almost a week, but that would be a good time to work on oil temps, being if it works at 100F it will work at 30F. Winds had also been high which was still a little concerning, but Wednesday evening was looking like a good shot at calm winds, and it was. We rounded up our friend Curt to act as spotter/photographer and went out to the airport. John’s flight report follows:
I made sure to have everything ready with the laptop (good battery and all), and confirmed good connection to both the engine monitor and the GPS. She fired up nicely again and I wasted no time getting out to the runway, in an effort to minimize the amount of ground heating period. Unfortunately it was busy and I had to wait for a couple planes to land before being able to depart. Oil temps were about 209F by the time I took the runway and throttled up.
I made certain not to get too fast in the climb out this time, despite my concern for watching oil temps. As I leveled off at 5k oil temps had reach 232F, way higher than wanted, and right on the edge of the max continuous allowable. I decided to spend a couple minutes conducting my testing of the cowling inlet air pressure while I tried to wait out the oil temp stabilization/reduction. I found that airspeed readings at the inlet of the cowling were about 20-30Kts lower than readings at the nose mounted pitot tube. They were a little bouncy, which seemed to indicate the air was a little turbulent, so it was tough to be precise. Oil temps had not really dropped and instead had continued creeping up (albeit a little slower). I throttled back and brought the prop back further to 2250, but I started loosing altitude before much of stabilization or reduction in oil temp could be noted, which was now 236F.
I played more with throttle and prop controls, but suddenly found that I could not reduce RPM to below about 2400 with prop control full back. Further reduction in RPM could come only from reducing throttle. I climbed back up to 5K, which increased oil temps up to 244F in climb, which at that point made me decide it was not useful to continue to press the situation further. I now had high oil temps, and something not quite right with my prop control. That was enough going wrong for me to warrant calling it a day.
I notified my ground crew and the tower of my situation and that I was coming back down. I reduced throttle further for the descent, and used my rudders to add drag to steepen the descent without adding too much airspeed. I was able to drop 2000′ in less than 1 circuit at 120Kts airspeed. I joined a downwind leg for 31, and was cleared to land. At this point oil temps had dropped to 219F.
As I taxied back to the hangar the temps again rose to about 233F, but this is normal with no real cooling airflow. I shut down the plane and we put her away. Obviously more testing and work is needed on the oil temps. I’m also very concerned about the inability to bring the prop back enough. That issue must be identified and remedied before next flight.