Along with costlier maintenance, foreshortened TBOs represent the true incremental cost of pressurization. Bottom line: Engines in P-model aircraft work hard and simply dont have as long a real-world TBO as similar non-turbo aircraft. Whats more, because this engine will be in climb mode longer, you will have to carry more fuel- and P-models often come with additional capacity-to altitude, further hurting climb performance. (This assumes the P-model doesnt pack significantly more horsepower, which is most often true.) Now you have a heavier airplane, struggling for longer climbs to higher altitudes where its asked to perk along sniffing very thin cooling air at reduced indicated airspeeds. As a rule, pressurized airplanes are heavier than their turbocharged counterparts and so have lesser climb performance. While the ride atop the weather is often sublime, it makes more work for the engine. And that means to justify those long climbs, you really need to have some distance to cover and fairly often. So as a generalization, pressurized airplanes are considerably more likely to be up in the flight levels on a regular basis. Still you have to consider stage length and winds, among other factors, as you determine optimum altitude. But in a pressurized airplane, theres little incentive from the comfort standpoint to diddle around down low. The typical non-pressurized, turbocharged airplane rarely goes above 10,000 feet unless theres a compelling reason to do so-weather, smooth air, a ripping tailwind-because of the inconvenience of donning an oxygen mask. Pressurized aircraft use turbo systems similar to (and in some cases the same as) their unpressurized brethren, so there shouldnt be much difference in the maintenance requirements or longevity, right? Not so fast. On top of that, theres the maintenance issue for many turbo applications just working on the engine is more difficult because of all the extra hardware. Turbocharged engines, as a rule, consume more fuel and live shorter, more costly lives than similarly powered non-turbo models. (Turbines, in case youre curious, do the same thing, only taking bleed air from one of the high-pressure sections of the engine.) There have been systems using engine-driven compressors-superchargers for the cabin-but all the modern models employ an air-bleed from the turbocharger system to provide cabin pressurization. (See the sidebar for an explanation.) For one thing, pressurization comes inexorably with turbocharging. Of course, theres more to pressurizing an airplane than sealing up the fuselage like a giant ZipLoc bag and pumping in a bunch of air. Well examine pressurized twins in a subsequent article for now, well focus on two pumped-up singles, the Piper Malibu/Mirage series and Cessnas P-210, with an honorable mention of two other models, Mooney M22 and the Lancair IV-P homebuilt. If you can afford a twin, the universe of pressurized choices is larger but the costs are significantly higher, even for modest airplanes such as the Cessna 340. The range of choices in pressurized airplanes is not large, mainly because of limited market demand and the high cost of building them. Inherently conservative, the manufacturers based most of the early designs on non-pressurized models, a tactic thats good-because the airframe and engine combination are already well known-and bad-because a pressure vessel is ideally circular in cross section, something you wouldnt want for space reasons on a non-pumped model. Several manufacturers have given pressurization a go in the piston market, pumping up the cabins of singles and twins. (Lets not think about the headwinds coming home, okay?) You want to make the most of your airplanes altitude performance in total comfort. You want to fly among the big iron where the air is smooth and the tailwinds tantalizingly strong.
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