PowerFlow Comin'

If you’re wondering why you haven’t heard from me for a while, it’s just because I’ve been very busy and because the Cheetah has been down for maintenance. After our last trip to Missouri, I became very unhappy with what appeared to be the Cheetah’s poor and deteriorating performance, which was accompanied by engine roughness at full rich mixtures at almost any altitude above sea level. I became convinced the airplane had a carburetor problem, and though it took a little while to convince my mechanic of that, we did indeed begin examining the carburetor to see if there was anything wrong with it. There was, and it took three trips to the shop to get the carb rebuilt and working as it was supposed to. It does now, as evidenced by a climb to 7500 feet, the highest altitude I’ve been at in the Cheetah since I’ve owned it, with 300 to 400 fpm rate of climb remaining. We at least now have the airplane climbing at close to “book” performance values. Cruise has improved as well. Though I’m not sure exactly how much yet, the airplane has turned in 124 knots ground speed at 3500 feet and 141 knots ground speed at 7500 feet, both times at close to 75% power. (I suspect that the 124 knot speed had little input from the wind while the 141 knot speed had a fair bit.)

Still, those numbers are with the airplane light-loaded and on a cool day. To try to maintain something close to that in the summer time, I have ordered a PowerFlow exhaust system to stick on the airplane. I debated with myself and discussed my options for improving performance with my mechanic and my wife and ultimately decided that adding a PowerFlow held less financial risk than performing a TOP and adding the High-Compression STC (160HP) which is something we’re now planning on doing next year (e.g., the August 2009 annual inspection). If the PowerFlow proves to add almost nothing, I have 60 days to pull it back off and send it back for a refund. Performing a TOP held no such option, and I believe I can get at least another 100 -150 hours out of my worst cylinder before pulling it for repair.

It will be interesting to see if the PowerFlow peforms as advertised. I will, of course, post my impressions and results here as soon as the system is on the airplane. That will be sometime in the next four to six weeks.

In the meantime, I’m writing up the story around the second test flight after the carburetor rebuild which happened with my wife aboard. Check back for that. It will be posted in .pdf format with a link to the file.