Pilot Journal
Friday, July 1, 2005

“301 Knots!”

Take the Beech Duke, add turbines, and you get that magical number

301 knotsIt’s a magic number and one not often seen in turboprop corporate aircraft. A bare handful of propjets can touch 300 knots in cruise—the Piper Cheyenne 400LS, Commander 1000, Mitsubishi Solitaire, Beech Starship and King Air 350, and the Socata TBM 700.
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In total, Beech delivered just under 600 Dukes, 350 of which were the later, improved B60s, built between 1974 and 1982. The B60 carried more fuel than the straight 60 and the A model. Today, most of those last 350 airplanes sell for $150,000 to $300,000.

301 knots
The Royal Turbine Duke’s upgrades include a Garmin avionics suite, an MX20 MFD and weather forecasting software.
If that seems a bargain, it is—except for one major problem. Beech fitted the Duke with a pair of TIO-541 engines, a model that was to prove one of the least reliable in the industry. Original TBO was only 1,200 hours, and reaching even that was questionable. In the early ’70s, new crankshafts, cylinders and other upgrades increased TBO to 1,600, but again, most Duke owners had little chance of reaching TBO. No matter how well the engines were treated and maintained, Dukes rarely got past 1,000 hours before needing significant tops or even major overhauls.

The engines were so unreliable that many Dukes spent much of their time on the ramp or in the shop. Like all sophisticated, medium twins, Dukes suffered other ills associated with pressurization, hydraulics and electrics as they aged, but the engines were, by far, the major problem.

Nevertheless, Duke owners almost unanimously adored their airplanes. The swept, stiletto shape was an immediately recognizable winner. When the airplanes were up and running, they manifested the same delightful handling as the Baron plus significantly better climb and cruise performance. (Beech even condescended to mount the throttles in the proper, far-left position rather than in the center console as on the Barons.)

Up high with everything trimmed out, the Duke was alleged to be capable of 233 knots, although 215 to 220 knots was probably more realistic, meanwhile pouring 45 gph through the engines. Pulled back to 63% (yes, 63%) with 232 gallons in the tanks, Dukes could still manage 195 to 200 knots, endure for 5.5 hours and range out more than 1,000 nm.

Conrad reasoned that things could only get better and more reliable (if more expensive) by replacing the troublesome TIO-541s with P&W turboprops. With his experience installing and flying the PT6A-21 and -35 in the Malibu Jetprop, he knew the P&W engine was about as bulletproof as they come, rated for 3,600 hours between overhauls and willing to run that long with very little service.

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