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Three Bears

posted Apr 17, 2011, 2:40 PM by George Finlay   [ updated Apr 17, 2011, 2:40 PM by Natalie Cauldwell ]

We are investigating which of the three single-engine turboprops would be best suited for the 600 nm trip my dad often made for Lily Tulip Paper Cup Co., from White Plains NY (KHPN) to Augusta GA (KAGS), with three coworkers, and two pilots, for a total payload of 1200 lbs, at a realistic average weight of 200 lbs for American men.

Goldilocks would break baby bear, the Meridian, with that test load, even at the higher 5134 lb maximum takeoff weight permitted on serial numbers higher than 157. With a typical empty weight of 3500 lbs, our load brings zero fuel weight so close to the maximum takeoff weight, that all the Meridian could do would be to fly around the departure airport for a short while. So baby bear is out of the competition.

The Pilatus 12, papa bear, has more than enough capacity. With a maximum takeoff weight of 10,450 lbs, and a typical empty weight of about 6200 lbs, the test load puts the Pilatus at 7400 lbs zero fuel weight. To be conservative, we will allot 250 lbs of jet A for taxi and climb to FL250, another 720 lbs for 2 hours of high speed cruise at about 260 KTAS, 170 lbs for descent and landing, and a generous 360 lbs for reserve, totaling 1500 lbs of fuel, for a take off weight of 8900 lbs.

Double the distance to 1200 nm and add a 60 knot headwind, and you are at the Pilatus’s limit, close to maximum takeoff weight because of the extra fuel required, and too slow to be practical for a that trip.

How about momma bear, the Socata TBM? If she is capable of making the test trip comfortably, the company could save on purchase price and operating expenses. With a maximum takeoff weight of 7400 lbs and a typical empty weight of 4800 lbs, our test load brings us to a zero fuel weight of 6000 lbs. The TBM850 needs about the same 200 lb allowance for taxi and climb to FL250, but once there, the ISA performance charts appear to show a significantly higher true airspeed of 310 vs the Pilatus’s 260 knots, but with a significantly higher fuel burn of 450 lbs per hour, vs the Pilatus’s 360 lbs per hour. Awarding the TBM about 30 minutes less time at cruise, my calculations show only slightly less fuel required for the test trip, 1400 vs 1500 lbs for the Pilatus. That fuel load will put the TBM inside the maximum weight allowed for take off, but just barely. So only if this crew and these passengers will not routinely need to fly further than the 600 nm test trip would this airplane work out.

That is unlikely, making the Pilatus the only truly practical choice, which is why there are more than 800 of them in service worldwide.