Let’s Go Flying
We strapped into the left seat of MSN 273, a PC-12/45 model with a 9,921 lb. MTOW, accompanied by contract pilot Randy Schneider, president of Randolph Aviation, at Boulder City Airport at Boulder, Calif. With 2,704 lb. of fuel plus Finnoff as a passenger and various spares aboard, the aircraft's ramp weight was 9,880 lb.
Finnoff explained that the engine conversion adds about 40 lb. to aircraft empty weight. The -67P, because of its more robust components, weighs 21 lb. more than the -67B. The -67P also is fitted with a second 300A generator on the accessory gear box in place of the belt-driven, 115A standby generator, thereby adding another 19 lb.
The -67P requires more current for starting than the -67B.' optional dual battery system is recommended for frequent short cycle operations or for battery starting the aircraft at high density altitude airports. Use of a GPU is recommended for aircraft fitted with single batteries.
Finnoff is developing an STC for a simplified, dual lead acid battery retrofit package to upgrade aircraft that were originally delivered with single battery systems. The firm also is developing a 300A buss tie conversion kit to replace the original 150A buss tie that was fitted to aircraft delivered with -67B engines. This will enable the electrical system to take full advantage of the 300A secondary generator.
While not part of the original Finnoff -67P conversion, MSN 273 also is equipped with a five-blade composite MT propeller that is approved for installation on all PC-12 models. Finnoff Aviation is the exclusive North American after-market distributor for MT Propellers. The $58,500 MT prop for the PC-12 is 2.7 in. smaller in diameter than the original equipment Hartzell four-blade prop. The five-blade design results in lower thrust loading per square inch and the composite structure allows more optimum airfoil shaping for better root to tip lift distribution. The changes result in slower tip speeds and lower blade tip loading than with the Hartzell propeller.
Martin Albrecht, engineer and test pilot at MT Propeller Entwicklung GmbH in Atting, Germany, says the MT prop produces 10% more static thrust than the Hartzell, thereby reducing takeoff roll by 15%. He also says that climb performance is improved and that cruise speeds are up to 5 kt. higher. However, there are noor -approved AFM supplement documents to support such claims.
Still, the MT prop does weigh about 20 lb. less than the Hartzell, has better vibration damping characteristics and FAR Part 36 noise levels are 4 db lower. The composite blades are built from ultra-thin beech and spruce laminates, covered with a carbon fiber skin and protected by nickel cobalt leading edge abrasion strips. There is no life limit on the blades and the prop is reparable in the field. Albrecht also claims that interior sound levels are 6 to 7 dB quieter, but, again, there are no FAA or EASA documents to support such claims.
Finnoff Aviation also fitted MSN 273 with left and right side, twin flat-panel displays from Innovative Solutions & Support, a $225,000 option. Each pair of 10.4-in., portrait configuration displays replaces the original 5-in.Bendix/King EFS 50 EADI and EHSI CRTs on the left and right sides of the panel. The IS&S displays are much easier to read because of their size, they have excellent visibility in direct sunlight and they support many more functions, such as electronic charts.
At present, the IS&S PFD does not have a synthetic vision function, but an upgrade is in the works. On the down side, the PFD's indicated airspeed and altitude displays do not tie into the aircraft's Honeywell KFC 325 flight guidance system. The aircraft's original KAS 297C altitude/vertical speed preselect controller is retained and it isn't linked to the IS&S PFDs, so there is no adjustable altitude target displayed on the altitude tape. In addition, inputs to the KMC 321 flight guidance mode controller don't drive a speed target symbol on the PFD's air speed tape. This is an older federated, rather than newer integrated, avionics system.
Pre-start and start procedures remain unchanged from the original PC-12. The MT prop, having no adverse resonance characteristics, eliminates the AFM prohibition against operating continuously between 350 and 950 rpm to prevent prop damage.
Based on a 9,800 lb. computed takeoff weight and flaps 15 deg., rotation speed was 78 KIAS and target airspeed for 50 ft. was 98 KIAS. Computed takeoff distance was 3,400 ft. based upon Boulder City Airport's 5,299 ft. field elevation, ISA-10C OAT and 29.92 altimeter setting.
We departed on Runway 8. Estimated ground roll was about 1,800 ft. Our initial target altitude was 7,500 ft., giving us time to contact ATC to request an IFR climb to FL 300. Schneider suggested using a best-rate climb speed schedule based on angle-of-attack (AOA). Flying the aircraft one diamond fast on the PFD's AOA indicator caused the aircraft to climb at 123 KIAS to 118 KIAS, very close to the recommended best climb speed schedule for a -67B aircraft, but about 10 KIAS slower than the recommended climb speed for a PC-12NG powered by the -67P.
When we retracted the wing flaps, we noticed a rolling moment that had to be corrected with aileron input. Finnoff noted that the aircraft's control surfaces hadn't been precisely rigged after they were removed and replaced when the aircraft was repainted in 2013.
The rigging anomaly soon would prove problematic because of extra drag. While the aircraft climbed quickly to FL 300 at an average rate of 1,200 fpm at ISA-1C to ISA-9C temperatures on the north side of the jet stream in early January, it fell short of Finnoff's speed predictions by 5 kt. And that was in spite of its being equipped with the MT propeller. We lost another 5 kt. due to a torque meter calibration error. However, we believe its top cruise speed still would be very close to that of the NG after correcting for the torque meter error.
Finnoff was quite candid about the speed shortcomings of MSN 273. He said that previous flight tests showed the aircraft suffered a 5-kt. performance loss after repainting. Recalibrating the torque meter will increase engine output by at least 20 shp or 2.7% at altitude.
We later checked our results with Pat Reilly, a pilot who flies MSN 878, a PC-12/47 model that has both the Finnoff -67P and MT propeller upgrades. He said he routinely cruises at 270+ KTAS, topping the Finnoff AFM supplement predictions by 3-5 kt. Reilly said his aircraft's control surfaces are carefully rigged and that the aircraft has no rolling moments associated with configuration changes. He also crosschecks indicated torque output with ITT readings to assure the engine is developing full cruise horsepower.
Conclusions? While the aircraft we flew fell 5 kt. short of performance expectations, we believe that a properly rigged aircraft would meet or exceed Finnoff's predictions because of the flight test results originally obtained by Art Barth at FTA and because of feedback from Reilly. Subjectively, the MT prop also appears to reduce interior sound levels substantially and it most certainly lowers vibration levels.