Tuesday, December 25, 2012
Transition To A Turboprop
MidWay between Piston Singles and Jets
I mentioned that most V-speeds depend on weight and temperature, but the never-exceed speed was an exception. In climbing, this becomes apparent—especially in older airplanes with round gauge panels. The airspeed indicators we're used to from piston singles/twins have a single indicator hand. But in turboprops there are two, a solid-color hand that behaves as we've come to expect, and a second hand with alternating stripes called a "barber pole." Glass panels offer an equivalent presentation.
Barber pole is really a variable red line. As you climb, and the air thins out, the speed of sound changes. At some point, it gets low enough to be an issue. Barber pole reflects this—as you climb, it comes down. Exceeding barber pole is just like flying beyond the never-exceed speed in a piston airplane—don't do it!
Descending from the flight levels takes time—even at 2,000 fpm, descending from 20,000 feet to sea level takes 10 minutes, and at four miles per minute, covers a lot of ground. Most turboprops these days have at least a GPS navigator (if not a full flight management system) with a vertical navigation feature, which can be set to show the descent rate required to reach pattern altitude a reasonable distance from your destination. This is where one of the nicest features of a turbine engine comes into play. Forget everything you ever heard about shock cooling. It's a non-issue for this class of airplane. And most of the time, you won't need to worry about ear pain for passengers (or yourself). Cabin altitude is determined by the maximum cabin pressurization differential, which varies by airplane. Many single-engine turboprops have a maximum cabin altitude of 8,000 feet or slightly higher: 9,000 for the TBM 850 at maximum certified altitude and 10,000 feet for the PC-12.
If you've impressed the pilot to this point, you may be offered the controls for the final approach and landing. Stick forces will probably be heavier than you're used to, but shouldn't be overwhelming. Some of these airplanes have special features, including angle-of-attack (AOA) indication and trailing link landing gear, that make it almost impossible to botch a landing. After all the wheels are on the ground and the flaps are retracted, keep your feet off the brakes and pull the PCL back to reverse the prop, and you'll hear that way-cool sound again—and probably get slowed down enough to make the first turnoff. Do it well, and there's a good chance you'll be invited back for another flight!
There's a lot more that I haven't space to cover here—including ground handling, which involves a lot more than just a towbar and muscle, external power, converting pounds to gallons for your fuel order (which depends on temperature), caution and warning systems (think annunciator panel on steroids) and advanced weather avoidance gear, among much else.
One last point: This may all sound quite challenging—and it is—but it's also a ton of fun! As with any kind of flight training, it's always a good idea to go with professional instruction or mentoring when transitioning to a turboprop.
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