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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If you weren’t in as much of a hurry, you could plan to cruise at FL260 at more like 270 knots on about 62 gph. Cabin altitude at this height with the standard 4.6 psi pressurization system fully pumped up is 11,000 feet. With a full 267 gallons aboard, such a trip would allow an easy three hours plus reserve for 1,000 nm range, roughly the same as the stock airplane, but considerably quicker.

On the way downhill from our cruise checks, Conrad suggested I stop momentarily at 21,000 feet and shut down the right engine. Level and trimmed with the right mill feathered, right wing five degrees up, ball half out of center and the left thrust lever against the stop, airspeed finally stabilized at 240 knots true. This suggests single-engine service ceiling (SESC) is well above that height. (Conrad lists SESC as 27,000 feet, but even that may be conservative.) Normal multi-engine service ceiling, incidentally, remains the Duke’s original 30,000 feet.

In addition to strong climb and 300-knot cruise, another important payoff on the Royal Turbine is a significant improvement in payload. Conrad reports the prototype airplane started with an empty weight of 5,012 pounds against a gross weight of 7,000 pounds (with the VGs installed). Subtract 1,392 pounds of fuel, and the unconverted Duke was left with only 596 pounds of payload, barely enough for three folks plus baggage.

After Conrad’s turbine conversion, empty weight is now 4,480 pounds. Add the weight of 267 gallons of jet fuel (at 6.7 pounds per gallon), and the Royal Turbine winds up with a payload of 731 pounds, an easy four folks plus baggage.

Conrad plans to offer two engine options on the Royal Turbine. Both PT6As are flat-rated for 550 shp, but the -35 will maintain that power to 21,000 feet while the -21s begin to lose thrust at 16,000 feet. The difference with the -35s installed will be better climb at high altitude and about 25 knots more cruise in the middle flight levels.

Conrad has been through the STC certification wars many times, and he’s as familiar as anyone can be with the FAA’s requirements. He has already worked his way through many of the flight and engineering tests, and expects to have the Royal’s STC in hand by mid-summer 2005.

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