Caravan torque-up

In last month’s Turbine Edition we looked at Nextant Aerospace’s new G90XT, a King Air C90A fitted with GE’s new H75-100 turboprop engines, complete with FADEC-like single-lever power controls (“A New King,” January 2017 AOPA Pilot). This month we continue in this vein with a review of Blackhawk Modifications Inc.’s latest engine upgrade program for the model 208 and 208B Cessna Caravans. Waco, Texas-based Blackhawk has been in the business of re-engining older turboprops since 1999. That’s when president and CEO Jim Allmon convinced Pratt & Whitney to provide the infant company with its first batch of 24 PT6A-135 engines for retrofit in Cessna’s Conquest I models—which came from the factory with 450-shaft-horsepower PT6A-112 engines. The flat rating and higher thermodynamic potential of the -135 engines bumped the Conquest I’s maximum cruise speed from 254 to 290 KTAS.

Today, Blackhawk is Pratt & Whitney’s second-biggest customer, after Textron Aviation. With 650 engine conversions, Blackhawk has become the big dog in the turboprop retrofit arena, and that certainly includes the 1,000-odd pool of pre-2008, pre-Garmin-G1000-equipped Cessna Caravan model 208 and 208B airplanes.

Caravans are working airplanes, used for cargo hauling, hunting and fishing trips, short-haul operations out of short and unimproved strips, parachute jumping, and other big-load utility roles. Often, the territory they work involves high terrain and high density altitudes. That’s where there’s no substitute for more power. And that’s where Blackhawk’s latest conversion comes in.

Caravans are working airplanes. Often, the territory they work involves high terrain and high density altitudes. That’s where there’s no substitute for more power.The mod replaces the standard original Caravan’s 600-shp PT6A-114, or the 208B’s 675-shp PT6A-114A, with a new 867-shp PT6A-140. This is the same engine used in Cessna’s latest Grand Caravan EX models.

As engine upgrades go, Blackhawk’s -140 is straightforward. The engine bolts onto the stock mount and reuses the single exhaust system, and no cowling modifications are required. The engine comes with a large-capacity oil cooler with extra cooling tubes—a response to Blackhawk’s African customers, who often face oil temperatures near redline. A more powerful, 325-ampere starter-generator is another plus that helps shorten spool-up times and keep engine starts cool; the stock starter-generator operates at 200 amperes. A new Hartzell three-blade, 106-inch diameter propeller also comes with the package, and so do new Howell engine instruments with analog and digital indications, and new fuel-quantity gauges. And for floatplane operators, there are optional start locks to keep the propeller blades in the zero-thrust position.

To see what those extra 182 horses could do, I visited Blackhawk and flew with Chris Dunkin, Blackhawk’s flight operations manager and central U.S. sales manager. We strapped into N807EV—an airplane bound for an Australian customer running a shuttle service—and fired up the -140 in seconds, thanks to the fast-turning starter. With full fuel and just two of us aboard, we weighed 8,000 pounds—well below the airplane’s 8,750-pound maximum takeoff weight. But despite its truck-like mass and clunky, angular looks, the Caravan feels and acts very much like a Cessna 182 or 206. Off we went, occasionally growling in beta thrust to spare the brakes, and trundling toward lonely Waco’s Runway 19, cleared for immediate takeoff.

For the maximum-performance takeoff and climb we set 20 degrees of flaps, and both of us stood on the brakes while I ran the power up to just below torque redline. The whole ship was shaking. “We won’t be able to keep it from moving,” Dunkin said, and he was right. No matter how hard we pushed, the airplane was starting its takeoff run—with or without our help. I wanted to rotate at the “normal” 70 knots, but by then the airplane was already off the runway. Then it was time for the VY climbout at 106 knots. I looked down and saw a 3,000-fpm climb. It stayed like that until 2,000 feet or so, then settled into a range between 1,500 and 1,700 fpm. By the time we hit our target of 10,000 feet a mere five minutes, 50 seconds had passed. In a standard-engine airplane it would have taken eight minutes, 25 seconds, according to the flight manual. Those three minutes may not mean much to the average pilot, but for a skydiving outfit it can mean two or more loads per hour, and as much as $20,000 more revenue per month. And to someone flying out of an airport ringed by trees or terrain, that initial climb rate carries a real safety factor.

For the landing, you might forget you’re in a Caravan for a moment and think you’re driving a Skylane. Next came a test of cruise speeds at 10,000 feet. I know, I know, you won’t see a Caravan on the air race circuit, but there are times when a little extra speed could come in handy. With interstage turbine temperature set just below redline, we saw 190 KTAS while burning 417 pph/62 gph. A normal cruise power setting produced 181 KTAS on 380 pph/57 gph. The standard -114A engine, on the other hand, would yield a 170 KTAS maximum cruise speed on 340 pph/51 gph. There’s an important caveat here: N807EV had no cargo pod. With the cargo pod, there would be approximately a 10-knot reduction in speed, but only a 200- to 300-fpm reduction in climb rate. However, the standard -114A engine would have given a cargo-pod-equipped climb rate around 950 fpm according to interpolations of the flight manual’s tables.

For the landing, you might forget you’re in a Caravan for a moment and think you’re driving a Skylane. The first notch of flaps can come down anywhere below the top of the green airspeed arc, the second at 125 knots, and Dunkin advised crossing the numbers at 75 knots with full flaps. Apart from needing to carry some power on the approach—so the prop doesn’t go into flat pitch and cause an airspeed-robbing surge in drag—landing the Caravan is pretty easy. Even if it does take you a while to figure out when to make a stylish flare, owing to your lofty seat height above the runway.

The -140 upgrade is the second Blackhawk re-engining program for the 208 and 208B Caravans. In the June 2014 issue of Turbine Pilot (“Blackhawk Boost”) we reported on the 850-shp PT6A-42A program. It’s still offered, and still provides healthy performance increases. But its installation requires a redesigned cowl and other modifications. The -140 conversion gives customers more power, and lower installed cost ($629,000 versus the -42A’s $677,000).

Blackhawk exemplifies the innovative activity in today’s turboprop retrofit and refurbishment market arena. There are several reasons why this company, and others like it, stand to thrive. One has to do with preserving value while increasing performance. Without a Blackhawk conversion, for example, resale values drop $700,000 or more. Then there are the economics of engine overhauls. If you’re going to overhaul your engines, why wait until TBO when you can overhaul early and get credit (Blackhawk offers $50 per hour for the -114A engine) for the remaining unused hours? The price of new aircraft is another factor. Why pay millions more for a new turboprop when an engine conversion, interior, and paint job can be done for less—and provide a performance increase in the bargain?

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