Ethan Posted Sunday at 02:08 AM Report Posted Sunday at 02:08 AM I heard told the only reason the 252 was certified to 28,000 feet was so Mooney could claim the max speed of 252 mph TAS. I fly my 231 mostly below 18,000 feet and agree that the sweet spot is 11-17,000. I do, however frequently get up to FL190-210 to top weather. I find that engine cooling becomes more and more of an issue the higher I climb because the air is so thin, though it's cold the density is so low it offers little cooling.
Fly Boomer Posted Sunday at 11:11 AM Report Posted Sunday at 11:11 AM 9 hours ago, Ethan said: I heard told the only reason the 252 was certified to 28,000 feet was so Mooney could claim the max speed of 252 mph TAS. I fly my 231 mostly below 18,000 feet and agree that the sweet spot is 11-17,000. I do, however frequently get up to FL190-210 to top weather. I find that engine cooling becomes more and more of an issue the higher I climb because the air is so thin, though it's cold the density is so low it offers little cooling. When the 252 made its debut in 1986, everyone was astounded at what a difference there was in both engine management because of the absolute pressure controller, and because of the hugely improved cooling (different cowling, infinitely adjustable cowl flaps, etc.). The 231, of course, got the TSIO-360LB after a bit, and that was an improvement over the original GB, but the TSIO-360MB in the 252 was a night-and-day kind of improvement. Most 231s have benefitted from aftermarket mitigations, and the differences now are not as dramatic as they once were, but the 252 will still probably be happier going higher than the 231. If everything is working as designed, the 252 is pretty happy in the low to mid 20s, but many pilots, including Bob Kromer, are wary of going higher because of the potential for oxygen delivery or absorption issues. All that said, heat will always be a problem for any turbocharged airplane. I once asked John Deakin at an APA seminar in Ada Oklahoma why turbocharged airplanes were more problematic at higher altitudes. At the time, I didn't understand his one-word answer: "heat", but eventually I understood that there just aren't enough air molecules up there to carry away the heat. Here is an old article by Bob Kromer who was the test pilot for the 252 development: Bob Kromer - Flying The 252.pdf 2
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