Tuesday, October 25, 2011
Piper Meridian: Everyman’s Turbine
Piper’s Meridian is the least expensive, production, single-engine turboprop in the world, still the leader of the Piper tribe
A truly slick Bonanza could sometimes manage 200 mph, and there were a few Mooneys that could match the magic 200, but the majority of piston speedmeisters in those days were twins.
Today, speed is measured in knots, and the bar has been raised accordingly. Two-hundred knots (230 mph) is the new, not-so-impossible dream, but again, there are few single-engine, piston airplanes that will achieve that goal. Flying 250 knots (287 mph) is a VERY difficult task, and no current, certified piston single achieves that speed (though the Mooney Acclaim S comes close).
The New Goal
That may be a contributing factor in the emergence of single-engine turboprops. Piper's Meridian is the most recent entry into the certified uniturbine market, a good idea that was finally born in 2001.
The Meridian reintroduced Piper to the high-altitude regime. While it's true the turbocharged Mirage, Matrix and Seneca V are all capable of flight at 25,000 feet, few pilots choose to cruise that high with piston engines.
Turbines are made for the high road, and the Meridian will spend virtually all its time in the flight levels where traffic is usually light, weather and turbulence are most often well below and terrain isn't a factor unless you're flying in Alaska, the Andes or the Himalayas.
Turboprops in general employ massive simplicity masquerading as complexity, and that's only appropriate, as the Meridian is among the simplest of turboprops. The myth among piston pilots is that turboprops and jet engines are almost too complex for mere humans, and that's exactly backward.
Piston powerplants are, by far, the more complex, especially those on such heavy general aviation iron as the 421, Duke and Commander 680. True, things happen faster in a turboprop or jet, but the engines themselves are almost ridiculously simple, especially in contrast to piston mills that may have 250-300 moving parts.
Turbines dispense with turbocharging, operating as normally aspirated, flat-rated engines. Their potential power at sea level is far in excess of full-rated power. The pilot restricts power to a given torque limit at sea level, then adds power as he climbs higher. On the Meridian, max thermodynamic rating is 1,029 shp, but the flat rating is limited to 500 shp. This is somewhat analogous to the old manual turbochargers on Aerostar 601s that demanded adding power as you climbed higher.
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