October 2012 Issue
Turboprop Conversions: Pricey, Capable
The current crop of turboprops have impressive performance and with additional tankage, short range isnt the problem it used to be.
Power and speedtwo of aviations touchstoneshave been pursued as long as there have been airplanes and people willing to throw money at them. Aftermarket designers have hung ever-larger piston engines on factory airframes, with varying levels of success, for decades. By the 1980s mod shops were bolting on turboprops in place of reciprocating engines and achieving impressive speeds, despite the challenges of assuring the airframe could handle the horsepower and juggling the fuel/payload equation on the small airframes. The small size and high power density of turbine engines makes them attractive, as does the increasing difficulty of obtaining avgas outside the U.S. However, theres no free lunch; jet fuel weighs .7 of a pound per gallon more than avgas. That adds up because turbine engines have higher fuel specifics than piston pounders. For each horsepower output, the turbine uses more fuel than does a piston engine. The result is that the light weight of turbines is offset by the need to carry more, heavier fuel to achieve reasonable range. This becomes particularly acute in the relatively small, piston-powered airframes, and their correspondingly small wings and fuel tanks, designed for piston fuel consumption specifics.
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