October 13, 2005
Corvair College #9 was held in William Wynne's hangar at Massey Air Ranch (X50) near New Smyrna Beach, FL. This was my longest cross-country trip yet, at 530 statute miles, and required a fuel top somewhere in Georgia. I covered 1100 miles (I detoured around Atlanta and two restricted areas) on 35.6 gallons of fuel in about 7 hours total (round trip). That's about 5.1 gallons per hour average (including two climbs to 10,000', and two descents). I did the whole trip at wide open throttle, managing 165 mph ground speed on the way down, and 160 on the way back. I was doing about 3200-3250 rpm, with the engine leaned out for best economy. Not only did I make that trip three times faster than I could have driven it (and I drive pretty fast), I got 30 mpg, which is better than my GTI gets. When you factor in the straight line distance comparison to the drive, that's 37.5 mpg! The flight was pure joy, compared to the drive, which would have been painful, and would have taken an extra day. I had to leave early because north Alabama was going to be socked in on Sunday. On the way back, my Terra TX-760D crapped out, so I made the rest of the trip with no "distractions". It's now being repaired, and I've bought an ICOM A6 handheld for the next time that happens. On the descent into M38, I left the throttle in and got it up to 230 mph at 3500 rpm. That's a first!
I've been flying at around 10,000-11,000 feet, which gives maximum gliding distance, smooth air, and clear skies. Since I have a mixture gauge (LED bar graph using a Bosch O2 sensor for input), I lean it during the climb, because I can easily see when it's too rich, and continually adjust it to keep it reasonable. Then when I level out at altitude, I really lean it out 'til the engine looses a little power and then add a little back. At this point the bar graph on the mixture gauge shows only one red LED on the very bottom of the gauge. Anything below that and the engine runs just a tad rough, so I've learned that one LED is perfect, and I leave it there, but check it by re-leaning every half hour or so. That setting corresponds to something like 4.3 gallons per hour.
Here's the plot of the EIS information for the M38 (home airport of Hazel Green, Alabama) to Douglas Georgia leg of the flight. This shows fuel burns around 5.1 gph, but it was actually less than that. I'm still calibrating the flowmeter, but right now it looks about 17% high. On the return trip I had it leaned to the point of showing 4.3 gph, but I don't have that plot. My laptop battery was dead on the way back, because I left it turned on overnight and didn't figure it out until I left, so I didn't gather any data for that leg. The RPM is not really as flaky as the plot indicates, as my EIS tach function is still wandering around. Actual engine rpm is steady. I have a toothcounter coming that will solve this problem by counting teeth on the ring gear and providing that input into the EIS.
This is a snapshot of about a minute at 9500' altitude (the whole file is 7 meg). You'll notice several things from these numbers, one of which is that cylinder #6 needs a deflector in front of it to keep it from getting so cold, and cylinders #3 and #5 need a baffle to direct more air over them. The gph number is 5.1, but I leaned it down into the lower 4's on the way back, and had no problems. My laptop battery was dead on the way back, because I left it turned on overnight and didn't figure it out until I left, so I didn't gather any data for that leg.
Return to Mark Langford's KR2S project.