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today are not substantially differ- ent than they were 80 years ago. We still use magnetos, still have lead in our fuel, and still have catastrophic engine failures. Yes, there’s been some advancements in techn- ology, some major ones. But, not many advancements in engines that develop more than 350 horsepower. So, if you dream of more performance and more reliability and you want to fly your own airplane and go far, you will have turbine dreams.
The horizontally opposed piston engines that dominate the owner- f lown cross country market have a gob of parts that move in different directions, they have four separate strokes happening in the same small space every second, and have complex systems that are required to keep the engine developing more horsepower than originally intended. It is a testa- ment to the fabulous engineering of these machines and the broad cadre of wonderful maintenance providers that keep these engines running that we don’t have more accidents than we
have today. It really is old technology. The turbine engine? They too are a wonderful technology, but it is much simpler. The turbine has fewer parts and those parts all move in a continu- ous direction. Things turn in a turbine engine, and things push and pull in a
piston engine.
The key to a turbine is that the four
stages of developing energy (intake, compression, power, and exhaust) hap- pen in separate areas of the engine. So, the intake does nothing but intake, the compression section does nothing but compress air – you get the point. And the area where combustion occurs, the “hot section,” is where the power is generated. Because heat translates into wear with any engine, the hot section of a turbine gets lots of attention at maintenance events. “Nozzle inspec- tions,” “borescopes of the hot section,” and “hot section inspections” are all new terms that replace “top overhaul,” “cylinder replacement,” “valve guide wear,” and “corrosion on the cam” that happen with a big piston engine. With the turbine conversion comes a whole
new vocabulary, a whole new language that must be learned.
Whereas a piston engine in a typical owner-f lown cross-country airplane is an engine designed for less horsepow- er, and then we ask more of that engine to increase the horsepower, most tur- bine engines in the owner-f lown world are engines designed to create far more horsepower than is actually used in the owner f lown application. Most turbine engines are “derated,” which means the torque is limited to a number that can be managed by the airframe. For example, the PT6-42A found in a Me- ridian is nearly identical to the engine found in a King Air 200, except that the Meridian is derated to 500HP and the King Air is derated to 750HP. The PT6- 42 could develop more than 1,000HP if an airplane were strong enough to “let the horses run free.”
So, the PT6-42A in a Meridian is nev- er really challenged at all. At most, it is developing only half the horsepower it could create. There’s a lot of margin built into a turbine. That makes me feel good about sitting behind a turbine.
12 • TWIN & TURBINE / April 2022
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