Royal Turbine Transformations

September 27, 2007
Written by Blair Watson
301-beechHere’s a riddle: What’s new and old (but still in good shape), covers 150 metres per second, has eight blades, and climbs very quickly? The answer is in Spokane, Washington at the Felts Field home of Rocket Engineering, a company that has done some remarkable aircraft modification work since 1990. Its latest project, and the answer to the riddle, is the Royal Turbine, a Beechcraft Duke turboprop.

Rocket Engineering’s first modifications involved installing a more powerful piston engine in the Mooney 201 and 231 (206 aircraft were modified). President and CEO Darwin Conrad then turned his attention to the Piper Malibu/Mirage (PA-46), a pressurized, single pistonengine airplane. He knew that replacing its original engine with a Pratt & Whitney Canada PT-6A would result in significantly better performance and engine reliability.

Two variants of the PA-46 turbine conversion are offered: the JetProp DL and DLX. The DL includes a new, 550-hp PT- 6A-21 engine and costs US$459,900. The DLX’s price is US$50,000 more because of the 560-hp PT- 6A-35 (de-rated from 750 hp). Both conversions include a new four-blade Hartzell reversing propeller, two batteries, a custom-made cowling, and more. The engines have a TBO of 3,600 hours and a five-year warranty. An optional Shadin engine trend monitoring (ETM) system eliminates the need for a hot section inspection and costs US$19,900 installed. The ETM system has extended the TBO on some PT-6As to 6,500 hours. To date, 180 PA-46s have been converted, including two from Canada.

The JetProp climbs at 3,000 fpm and cruises at 248 knots (DL) and 260 knots (DLX) at normal power. Both aircraft have a ceiling of 27,000 feet. At FL250, the DL burns 31 gph and the DLX, 34 gph. With full fuel and a payload of 356 pounds, the JetProp DLX’s range at normal power is 1,000 nm and the DL’s is 100 nm more. The JetProp needs only 1,200 feet to take off (MTOW, sea level, ISA) and 1,000 feet to land. With Jet A currently costing $1.15 per litre, the aircraft’s direct hourly operating cost is about C$295.

After the JetProp program was established, Rocket Engineering designed a PT- 6A-21 conversion for the Beechcraft Bonanza (B36TC). The cost is US$409,900. The Turbine Air initially climbs at 3,000 fpm, has a maximum altitude of 25,000 feet, and consumes 29 gph while cruising at 225 KTAS at FL180. The conversion includes a header tank to feed the engine, a second elevator trim tab actuator, and an increase in useable fuel from 120 to 136 gallons. Since the B36TC is an unpressurized aircraft, a fan is installed to direct jet fuel odors overboard and Rocket Engineering designed a lightweight stalk that attaches to the pilot’s headset as part of the oxygen delivery system. To date, ten B36TCs have been converted.

A reliable, fast, and efficient twin, the Beechcraft Duke features a rugged airframe, quality construction, and a striking appearance. Duke production began in 1968, with the A60 coming out in 1970 and the improved B60 being built from 1974 to 1982. Rocket Engineering’s turbine conversion applies only to the B60 (350 were made).

For the Royal Turbine conversion, a B60 owner chooses either PT-6A-21 or -35 engines. Being new, the 3,600-hour TBO and five-year warranty apply. The conversion cost is US$807,000 and US$907,000 respectively, and includes new four-blade, Hartzell reversing propellers and two 24-amp sealed leadacid batteries, which are installed in the forward nose compartment. The Duke’s Janitrol heater is modified to burn jet fuel, and annunciators, engine switches and instruments are added to the new cockpit panel. The engine instruments are analog with digital readouts, which eliminates the need for a propeller synchrophaser. New cowlings, low-drag exhaust stacks, inertial ice separators and other components are included in the conversion price.

At FL270, a Royal Turbine with -35 engines cruises at 292 KTAS and consumes 67 gph. Reports say that the aircraft reached 301 KTAS at FL230 while burning 75 gph. The published performance numbers are: Ceiling and maximum single-engine altitude – 30,000 and 27,000 feet; twin- and single-engine rate of climb – 4,000+ fpm and 1600+ fpm; MTOW and useful load – 7,000 and 2,550 pounds; and Vmc and Vso – 95 and 73 kt. Like the JetProp, the Royal Turbine needs 1,200 feet to take off and 1,000 feet to land. With 220 gallons of fuel, a pilot and four passengers (175 pounds each) and 110 pounds of baggage, the aircraft can fly 625 nm IFR (zero wind, 100 nm alternate). Maximum range with full fuel (279 gal) is 1,000 nm. Based on the current fuel price, the direct hourly operating cost is approximately C$430.

The average price of a B60 Duke is US$280,000, with an average TTAF of 3,300 hours. The cost of a Royal Turbine conversion (-35 engines) and all the options listed is approximately US$1.11 million. Factor in the average aircraft purchase price and the total is US$1.39 million.

In October, I visited Rocket Engineering’s facility and had a demo flight in the Royal Turbine. The company is an FAA-approved parts manufacturer and makes components for its conversions such as cowlings, nacelle tanks, engine mounts and connectors.

The aircraft’s cabin has a surprising amount of headroom, as Tim Moore, a company sales rep. showed me before the demo flight (Tim is 1.92 metres tall). To enter the cockpit, I had to squeeze between the seats, but once in place, there was adequate space between Conrad and myself. He mentioned various features of the Royal Turbine, including the semi-transparent knob on each propeller lever that illuminates in the event that torque, propeller rpm, and ITT decrease significantly. The pilot retards the lever with the illuminated blue knob to feather the failed engine’s propeller.

Starting the PT-6A-35s was straightforward. After confirming that switches were in their correct positions and circuit breakers were in, Conrad turned on the battery, confirmed adequate voltage, activated the fuel pump and auto ignition, checked the annunciator panel, and engaged the left engine’s starter. Once N1 reached 15%, fuel was introduced and the ITT rose to 630°F, well below the maximum of 850°F. The ITT peak during the right engine start was similar. N626N’s avionics included an altitude pre-select, which Conrad recommends because of the high climb and descent rates possible in the Royal Turbine. Like the JetProp and Turbine Air, most converted B60s will probably be flown single-pilot.

Manoeuvring the Royal Turbine on the ground is not difficult due to the B60’s nosewheel steering and differential power when required. Braking to control taxi speed is needed infrequently thanks to the propellers’ beta range. After completing the aircraft checks and receiving clearance to take off, Conrad taxied N626N onto the runway, momentarily stopped the aircraft, then advanced the throttles. Once torque had increased to takeoff power, which took only a few seconds, N626N accelerated quickly enough that I was pressed firmly into the back of my seat. Within ten seconds and 1,000 feet from our starting position, we were airborne. The aircraft had 90 gallons of fuel onboard and weighed approximately 5,450 pounds.

Once the gear was retracted, Conrad raised the nose to 20° and climbed at 120 KIAS, pegging the VSI at 4,000 fpm. Climb rates in a lightlyloaded Royal Turbine have been as high as 5,800 fpm! Through 8,000 feet and at 140 kt, the VSI was 3,700 fpm. Through 14,000 feet, Conrad lowered the nose somewhat and the aircraft accelerated to 175 KIAS, while climbing at 2,000 fpm. After leveling off at 17,500 feet to remain in uncontrolled airspace, the Royal Turbine accelerated to 272 KTAS, burning 86 gph at normal cruise power.

After a few minutes, he demonstrated how the Royal Turbine handles with one propeller feathered. The aircraft will not be difficult for pilots to control in the unlikely event of an engine failure thanks to Beechcraft’s stable design and Rocket Engineering’s engine alignment work. At FL230, the Royal Turbine will cruise at 240 KTAS on one engine.

Heading west toward Felts Field, Conrad put N626N in a steep descent, which was not a problem for us thanks to the B60’s pressurization system. Leveling off, he slowed the aircraft, joined the circuit, and extended the landing gear. On final approach, Conrad reduced the airspeed to 120 kt and extended flaps to full, decreasing to 90 kt over the threshold. After touching down, he applied reverse thrust, then normal braking. Our weight was about 5,200 pounds and N626N used about 900 feet to land.

During the past 15 years, Rocket Engineering has developed niches that have appealed to many pilotowners and operators. The Royal Turbine is the latest example and Conrad estimates that the company’s latest endeavour will result in 200 Royal Turbine conversions.

Canadians wanting their B60, B36TC, or PA-46 piston aircraft converted to turbine by Rocket Engineering will require Transport Canada approval of the relevant Supplemental Type Certificate and a Private Operator Certificate, obtained through the Canadian Business Aviation Association.

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