Page 6 - Volume 12 Number 8

The 5-bladed, composite MT propellers perform as good as they look. They offer a number of advantages over the stock, 4-blade metal props, not the least of which is offsetting the weight penalty of the heavier -67A engines.
For our quick evaluation flight, Blackhawk’s Regional Sales Manager Chris Dunkin and I departed tiny Gwinner, North Dakota, (GWR) on a hot and blustery day in the northern Plains. The Outside Air Temperature (OAT) was ISA +19 on the surface. Using a climb schedule of 160 KIAS to 10,000 feet, then 140 KIAS to level off, we were able to climb directly from GWR’s 1,260-foot elevation to 28,000 feet (FL280) in only nine minutes and 25 seconds! That’s an average rate-of-climb of 2,838 Feet Per Minute (FPM), compared to the book figures of approximately 17 minutes or 1,600 FPM for a standard King Air 350 (at comparable weight and atmospheric conditions). During this climb, a maximum ITT of 820° F was flown. While 840° F is the published ITT cruise climb limit (versus 785° F for the -60A engine), 820° F is a suggested maximum in-flight ITT for prolonging engine life. Upon level off, where OAT was ISA +11, cruise speed quickly settled in at 335-340 KTAS (and Mach 0.55-0.56). Book figures for a -60A equipped 350 in those same conditions would be 280-290 KTAS. That’s a 13-18 percent boost in cruise performance! Of course, there is a fuel penalty associated, but most of it is offset by the quicker climb to the most fuel-efficient altitudes combined with the shorter flight times achieved through an average 15.5 percent increase in cruise speed.
Although the fastest flat out TAS for the XP67A will be achieved in the FL250-FL280 range, where maximum torque/power is available, few operators will likely linger at those altitudes. Assuming the aircraft has current Reduced Vertical Separation Minimums (RVSM) certification, FL320-330 will likely be the XP67A pilot’s
4 • KING AIR MAGAZINE
sweet spot. At those altitudes, typical cruise speeds of 325-330 KTAS can be achieved at 725 Pounds Per Hour (PPH) fuel flows, at/below the suggested 820° F ITT limitation, all with a comfortable cabin altitude of around 8,500 feet. Pilots who choose to operate at the maximum certified altitude of FL350 (which the XP67A can reach without even breathing hard), will experience even better fuel efficiency, but will also have to contend with less comfortable cabin altitudes in the 10,000-foot range.
Other minor changes in operating limitations exist between a standard 350 and Blackhawk’s XP67A. To be fair, some are not positive, such as slightly lower maximum ISA operating limits (3-6° F lower than the ISA +37 limit for the -60A engine, depending on altitude). Yet, those are extreme limits that certainly encompass only a tiny percentage of operating hours. Another is that POH/AFM takeoff speeds and field lengths are increased by one percent and landing distances are increased by two percent with the XP67A modifications. All fairly small sacrifices for the overall dramatic increase in performance. Also, Blackhawk will likely, in time, undertake a more extensive flight test program to revise such limitations via additional data, as these increased limits are simply buffers that were mutually acceptable by the FAA and Blackhawk in order to simplify the initial certification process.
Mission Flexibility
Regardless of the aircraft type in question, a primary goal for owners or pilots is always mission flexibility. Of course, one of the hallmarks of the entire King Air family has been just that since the first King Air 90s rolled off the line over a half-century ago. Each successive
A closer look at the new fixed flap and modified oil cooler air exit port, which helps improve oil cooling, allowing higher ITT limits.
AUGUST 2018