Anyhow, the most interesting part of the trip was not the show, it was the flight out there and back. Instead of flying Southwest, I decided to fly my RV-6... that you’re pretty well acquainted with by now. On Monday August 24th after work I flew to Davis (EDU) to see my girlfriend and mom. Then early on Tuesday I took off from EDU headed for Ely, Nevada (ELY). At Ely the engine ran a little rough during my taxi to the fuel pit after landing. When I went to kill the engine by leaning the mixture it didn’t die in the usual way but kept rumbling on for a bit. Finally it quit and I got out.
I bought gas, did an extremely thorough run-up and took off toward Denver. The flight went quite smoothly until on landing, the engine started mis-behaving again. Again, I couldn’t quite stop the engine using only the mixture knob so I grounded the mags to kill it. It died, less gracefully than usual but it did die. I hopped out of the airplane and scurried off to the conference.
I didn’t think much more about things until it was time to fly back. Again, I performed a very through run up and the engine ran great t all throttle settings except idle. I decided that idle was the least important of the power settings and took off. I flew from Denver (APA) to Four Corners (FMN) and then from FMN to Whiteman, CA (APA).
As I was flying over the Grand Canyon, I began trying to use the autopilot system that we had built for the RV. As you know it runs on an EEE-PC running some Matlab code we wrote. Unfortunately, every time I engaged the altitude hold, the autopilot would try to point the plane straight at the ground. Needless to say there we some bugs in the code. I started sifting through the bugs with the stick between my knees and in about 10 minutes I had the code working properly.
Between the Grand Canyon and Bullhead City, I was able to do some gain tuning, and with quite a bit of derivative gain, some proportional, and nearly zero integral I was able to stabilize the autopilot to some degree. It wasn’t perfect but it wasn’t so bad for a first step. All that was really missing was a low pass filter on the barometric pressure input. For some reason, spikes would appear on the barometric pressure input and these would cause the derivative error signal to spike. Needless to say this made the flight somewhat rough so I quickly coded up a running average filter and it smoothed things out quite a bit.
As I was passing the Grand Canyon and coding, I could already see cumulous clouds building on my route toward LA. I contacted ATC to see if they could inform me on where the weather was. Fortunately, the cumulous clouds were all on the San Gabriel’s just south of my route. I continued toward LA until the clouds were just off my left wing tip. Finally, as I was just south of Palmdale I noticed giant columns of precipitation and lightning. It was quite stunning. I kept trying to capture pictures of the lightning, but without a light activated shutter, or really long exposures, it’s nearly impossible to capture lightning.