Page 19 - Index

over 100 hours per year. What’s the dif- ference? At the end of the analysis, the difference is 14 knots of cruise speed (262 KTAS vs. 248 KTAS), two minutes of climb to FL230, five-minutes on a 400 nm flight, 10 gallons/hour in fuel burn and no change in payload. But, any -6 powered King Air B100 will cost hundreds of thousands less than the -10 variants.
Consider the JetPROP. The most pop- ular engine on a JetPROP is a PT6-35 engine, but a PT6-21 version is also avail- able. The -35 version probably outsells the -21 version by a 10-to-1 ratio but the differences are relatively minor: 17 KTAS (260 KTAS vs. 243 KTAS) of cruise speed, 3 gallons/hour (32 gph vs. 29 gph) in fuel burn and the time to climb to FL270 is only about a three-minute difference. But, the -21 JetPROP can be purchased for $90,000 less (on average). Personally, I think the -21 JetPROP is one of the best values in the PA46 world, mainly because it can be purchased at a lower price point and it still flat-out performs.
And, what exactly is the difference be- tween a Continental 520 and a Continen- tal 550 engine? The difference is in the stroke of the piston. A 550 engine has a 4.25-inch stroke and the 520 has a 4-inch stroke. However, both engines produce the same amount of horsepower as the 520 engine has a higher manifold pres- sure limit. So, the 550 engine breathes a bit better at high altitude, but the 520 is still a remarkable engine that serves many owners on many airplanes well. Still, the 550 version of any airframe will sell better than the 520.
My point in all of this is to consider the value that is found in an airplane that has the smaller engine. Most buy- ers in a particular category will dismiss the small engine airplanes purely based on “numerical prejudice,” meaning they simply feel that the bigger number must mean that it is “better.” The bigger num- ber does not mean it is better, it just means it is different. If you are a buyer of a twin or turbine airplane, I recom- mend taking a serious look at the smaller engines because a deal can oftentimes be found.
For instance, if you want a King Air 90, you’ll find lots of examples on the market, but the best deals are found on
an earlier King Air 90 with the PT6-21. Yes, the versions with the bigger engines will go a little faster and climb a little quicker, but the small engine versions can be bought for a song and they “sip” fuel compared to the bigger engines. The fuselage size, panel real-estate and cabin differential pressure are all the same. The wise owner of the smaller-engine version can smile all the way to the bank.
Most popular flight planning software (FltPlan.com, Foref light, etc.) even have profiles set up for the various engines on the various airframes. Whenever I
help a customer purchase an airplane, I always create a spreadsheet with the most common f lights and contrast the block-to-block times and the fuel burn expectations. The difference is usually negligible.
One other interesting thing about the smaller turbine engines: they usually develop similar torque at low-density altitudes. This translates into the nearly identical ground rolls on takeoff, and the initial climb rate is also almost identical too. Since both the larger and smaller engines have similar max torque
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October 2018
TWIN & TURBINE • 17