Monday afternoon it was quiet at work, and I needed to clear the recent snow from in front of the hangar, so I took some comp time. Much to my surprise and delight, I found that Ron, the hangar owner, had just finished clearing the snow when I arrived. He had the day off, and must have felt like getting out of the house.

I hooked up the remote preheat control, and did some tests. I put it right next to a window, and the cell phone has an excellent signal. The control worked perfectly, so I left it running and came home.

Sunday morning, it was clear and cold. I made the two phone calls to trigger the preheat timer at 6:45, and drove out to the hangar just before lunch time, hoping to find that the engine was nicely warmed up. Instead, I found it stone cold, with the preheater not running. Drat. I could find no obvious reason why it had not come on. I did several more tests, and it worked every time. I’m not sure if I have an intermittent hardware problem, a software bug, or whether there was a momentary power outage. The current software always starts up with the preheat OFF. I plan to update it to periodically write the timer status to the EEPROM that stores the program, and to check the status when it starts up. If it finds that the timer was running on shutdown, it will turn it back ON at startup. I only recently found a forum thread that describes how to write to the EEPROM without erasing the program that the Parallax Propeller micro-controller loads from the EEPROM on startup, or I would have written the software to do this from the start of this project.

I know that Ron had to reset the breaker for the hangar door - perhaps the power to the remote control got interrupted somehow. I’ll need to do a bunch of testing before I can trust the code to write the status to the EEPROM, and I’ll need another Prop to do the testing on. My only Prop is at the hangar now, but I’ve ordered some more that should arrive in a couple of weeks. I’ll update the software the next time I’m at the hangar to have the preheat default to ON following a power failure. It will then go OFF after six hours. After plugging the system in, I’ll use the manual control to put the preheat OFF.

I am still agonizing over whether I should just leave the preheater plugged in continuously, or whether I should continue to only have it run prior to going flying. I have heard stories that claimed that a preheat system that runs continuously may lead to internal engine corrosion. The oil in the engine collects moisture when the engine is running, as the combustion gasses that blow by the piston rings have water in them - a byproduct of the combustion process. The air in the crankcase is also quite moist, for the same reason. It is quite likely that some of this moisture will condense inside the crankcase if the engine cools down to a cold enough temperature. If the whole engine was kept warm enough, there should be no internal condensation. This theory is supported by a study done by Aviation Consumer. But, this study was only on one engine, and it only lasted seven days. There is another theory, that if the engine oil is warmed by a preheat system, that this could cause some of the moisture may be pushed into the air in the crankcase, and this may increase the amount of condensation that forms if the top of the crankcase remains cold. The jury is still out in my opinion, and I’m not yet comfortable taking the risk.

I got a short flight off on Sunday, but it was delayed as I had to wait while the preheater did its magic. The runway was in much better shape - only 20% ice covered vice 70% the last time I flew. I did a few aerobatics, and some touch and goes. It was a nice flight.