Pilatus PC-12 Engine
Courtesy Finnoff

Turbine Engine Upgrades

How to unlock more performance and efficiency from a turboprop or jet.

Paraphrasing the 19th century British politician John Dalberg-Acton’s well-known take on the corrupting influence of power, “Power tends to spoil pilots, and additional power spoils them even more.” No matter how fast an airplane flies, there’s always someone wondering why it can’t cruise just a little faster, or climb a little quicker or carry just a bit more.

Satisfying those performance- minded cravings is why companies such as Blackhawk, Raisbeck Engineering, Nextant Aerospace, Soloy Aviation Solutions, Finnoff Aviation and other propulsion-modification creators exist and thrive today. Each company has managed to create a special spot in the heart of aviators by tweaking airplanes people already loved to make them fly higher, faster and farther. The trick is choosing the right airframe to transform.

The motivation to look at modifying an existing airplane rather than purchasing new is pretty simple for owner-pilots who want to move out of their Cirrus, Bonanza or Baron. The twin-engine piston market is virtually non-existent for starters, while a new Pilatus PC-12NG lists for about $5 million. A King Air C90 GT runs about $3.75 million and the smallest single-pilot twin-engine jet, an Embraer Phenom 100, lists for about $4.5 million. Cirrus, naturally, hopes many will choose the $2.75 million single-engine Vision Jet. Price, of course, is just one element in choosing the right airplane.

Successful mod shops have an innate ability to pluck just the right airframes, often from near obscurity, and update them with new power plants that can give factory-new airplanes a performance run for their money. Companies Flying spoke with said the market for modifications to turboprop and light jet aircraft has been good the past decade, provided everyone ignored the Great Recession of 2007-2009.

Raisbeck president Lynn Thomas said his company’s relationships with aircraft manufacturers have improved considerably — especially because companies such as Beechcraft offer some Raisbeck and other mods in their own catalogs.

Blackhawk president and CEO Jim Allmon said one market indicator is the cost of used airplanes to modify. “A few years ago, I could buy a runout King Air B200 for $1.4 to $1.5 million all day long. Now that airframe costs $500,000 more.”

Remember the Beechjet 400 originally designed by Mitsubishi Heavy Industries back in the late 1970s? It offered a comfortable cabin with a flat floor, but used a pair of ancient Pratt & Whitney Canada JT15s, making the airplane an underpowered gas guzzler.

Nextant Aerospace saw potential and invested in a redesign using technology, such as advanced fluid dynamics, that didn’t exist 40 years ago. The company swapped the JT15s for factory-new, fuel-efficient Williams FJ44-3As and remanufactured the airplane to become the Nextant 400XTi. With a quieter, more comfortable cabin, the 400XTi will fly nearly 2,000 nm, up from the original 1,300 nm.

Finnoff Engine Replacement in Pilatus PC-12
Finnoff Aviation replaces the PC-12's P&W Canada PT6-67B with a more powerful PT6-67P engine.Courtesy Finnoff

Broomfield, Colorado-based Finnoff Aviation turns pre-NG model Pilatus PC-12s into better-performing machines using an updated Pratt & Whitney Canada PT-6 power plant. CEO Chris Finnoff and his partner Greg Klinger replaced the original Dash 67B with a Dash 67P capable of 1,200 continuous shp along with a five-blade MT-composite propeller to give the airplane nearly a 15-knot cruise speed boost.

The new combination also increases climb performance dramatically while greatly reducing runway distance requirements.

Blackhawk is known primarily as a King Air mod shop, although it also upgrades the Cessna Caravan and Conquest 1, as well as Piper Cheyenne airframes.

Blackhawk has upgraded some 829 King Airs since the company first opened 20 years ago and is well-known for its XP-135A-modified King Air 90s and the XP52 upgrade to the King Air 200 series. Those mods created a 31 percent increase in available horsepower for both airframes, translating into a 35-knot increase in cruise speed for the 90 and 27 knots for the 200.

Blackhawk's most recent upgrade program for the King Air 350 — the XP67A — will shave half an hour from a 1,000-nm flight compared to a factory-new airplane.

Known primarily for aerodynamic designs, Raisbeck Engineering found a successful niche with its swept-blade turbofan props for the King Air 200 and 250.

Created through three years of joint efforts by Raisbeck and Hartzell Propellers, the sweep creates a larger-diameter propeller — delivering more thrust while also reducing cabin noise. Raisbeck, in fact, created an entire King Air upgrade package called Epic Performance that, when installed with the swept-blade propellers, produces a 30 percent decrease in the King Air’s runway distance needed to clear a 50-foot obstacle on takeoff, a 33 percent shorter overall takeoff distance at sea-level and a 20 percent reduction in the time needed to climb to FL 330.

On landing, the distance needed to clear a 50-foot obstacle declines by 20 percent while approach speeds drop by 10 percent. Raisbeck’s ram air recovery system for the King Air also increases available horsepower by 8 percent, while reducing fuel expenses between 8 and 11 percent.

Companies such as Soloy that entered the modification market early on, before aircraft manufacturers began rolling new single-engine turboprops off the assembly line, found favor with STCs for single-engine Cessnas such as the 206, 207 and Caravan, as well as a number of helicopters. However, early in the company’s history there was a power-plant conversion to the Beech A36 Bonanza in which the original Continental motor was replaced by a Rolls-Royce turboprop (see sidebar). The upgraded Bonanza cruises 35 knots faster at 12,500 feet than the piston edition.

Soloy Bonanza

Before single-engine turboprops such as the Pilatus PC-12, Piper M600 and TBM became the rage for owner-operators, turbine-powered airplanes often evolved from converted piston-powered machines. Soloy Aviation Solutions’ conversion of the Beech A36 Bonanza replaces the original 300 hp Continental IO-550 with a Rolls-Royce M250-B17F/2 producing 450 shp flat rated (380 shp actual) for takeoff. The new power plant and its reversible-pitch prop considerably shorten the takeoff ground run and deliver a spectacular, nearly 2,000 fpm rate of climb. The Rolls-Royce engine will carry takeoff power to about 14,500 feet.

Soloy A36 Bonanza
N847DD's owner replaced the original Hartzell three-blade metal propeller with a five-blade MT-Composite propeller.Courtesy Soloy

The converted A36 is easy to spot on the ramp because the power plant switch demanded mounting the much lighter turbine power plant farther forward to balance the airplane. The original Continental weighs 430 pounds versus 195 pounds for the Rolls Royce. Inside the elongated nose is an additional baggage compartment good for 120 pounds. This aircraft — N847DD — is also equipped with a TKS anti-ice system and air conditioning.

The switch to a turbine engine means a few changes in the cockpit too. For instance, the airspeed indicator no longer carries a yellow arc. In its place is a barber pole limiting the redline airspeed to 167 kias and replacing the original redline of 205 kias. That translates into either a pretty steep climb angle after takeoff, or pulling the power back to keep the speed within limits. The Soloy Bonanza also sports a single-lever power control, eliminating the propeller lever. This A36 also will maintain jet speeds to the outer marker if needed, without fear of shock cooling when decelerating to final approach speed.

Soloy A36 Bonanza Cockpit
The propeller control of the Soloy Bonanza is replaced by a single power lever, making engine operation more jet like.Courtesy Soloy

The Soloy A36 is a speed demon. The day I flew it, we climbed VFR to 12,500 feet in about eight minutes. With the power lever pulled back to maintain 167 kias the true airspeed climbed to just over 200 knots while burning about 27 gallons of jet-A per hour at altitude. The A36’s only drawback is that unless the original airplane was equipped with oxygen, the pilot might need to bring along a portable unit. On the descent, with power at flight idle, the airplane drops like a rock while remaining stable and balanced. Without pressurization though, that change could prove too much for many passengers’ ears, which might call for a more shallow rate of descent.

Duncan Aviation’s Dave Coleman, my ace copilot for the flight, said two wingtip tanks add 40 usable gallons to the Bonanza’s original 74 usable, giving the aircraft at least three hours and 15 minutes of flying time with reserves. He estimates the hourly cost at between $350-$400. Coleman thinks there are about 100 Soloy Bonanzas flying around the globe.

Raisbeck aircraft propeller upgrade
Raisbeck's larger-diameter swept-blade propeller develops more thrust without increasing noise of vibration.Courtesy Raisbeck

Decisions, Decisions

Most pilots would prefer a new airplane — except when it comes to paying for it, of course. Luckily, the successful formula of the modification business focuses on value, not simply on purchase price.

Blackhawk’s Allmon spoke about the selling points of the company’s new XP-67A upgrade for the King Air 350: “It turns that airplane into a jet-performance kind of aircraft. We’ve seen a huge interest from people who were [originally] thinking about an entry-level jet, like a Cessna Mustang or a CJ3, and found them a little too small. They want to haul six people 1,000 miles and those little jets don’t do that very well.” With brand-new engines, a Blackhawk XP-67A delivers a 40-knot increase in cruise added together with the King Air’s big cabin.

Finnoff Aviation’s upgraded PC-12 adds a five-blade MT propeller to a new PT6 that Chris Finnoff said, “gives the airplane as much as a 15-knot cruise boost and increases climb performance dramatically. The original PC-12’s max speed was about 250 knots. With the bigger engine, day in and day out, it’s now about 270 knots.”

He said the cabin noise is much reduced from the original airplane’s thanks to the aerodynamics of that MT propeller that decreased the overall prop diameter: “That reduces the Mach tip speed and helps make up for the drag added by the fifth blade. In the cabin, our customers tell us they’ve measured a 6 to 7 dB decrease in cockpit and cabin noise when compared to the original four-blade prop.”

Nextant Beechjet King Air Engine Replacement
Nextant's 400XP remanufacturing process replaces the original Beechjet P&W Canada JT15 with brand-new Williams FJ44-3AP engines.Courtesy Nextant

Raisbeck said another important element of its composite propellers is their long life. “You never toss out the blades like you do with a metal propeller,” said Bob Richardson, director of dealer support. Each overhaul returns the propeller to like-new condition, something not possible with a metal prop that dies a little bit each time a mechanic dresses a blade with a file.

Nextant’s project also is transforming C90 King Airs into the Nextant G90XT by replacing the original Pratt & Whitney PT6 with a GE H75A power plant that carries full power all the way to 22,000 feet. Nextant said the original engine would begin temping out around 16,000 feet. The Nextant G90XT speeds along some 20 to 30 knots faster than the original aircraft. The upgrade also eliminates the King Air’s propeller controls in favor of a single, jet-like power lever of interest to pilots searching for their first cabin-class twin.

Beechcraft King Air 350 Blackhawk engine upgrade
The King Air 350 upgrade from Blackhawk matches the new, more powerful P&W Canada PT6A-67B engines with 5-blade MT-Composite propellers.Courtesy Blackhawk Modifications

The Bottom Line

Most of these modification outfits design and sell the Supplemental Type Certificates they developed, leaving the actual installation work to other qualified shops.

Of course, installation isn’t free. Modifying an airplane also demands down time, possibly creating the need for a travel alternative. Some modification customers bring their airplanes to the shop, while others approach the STC owners directly and ask them to find a good candidate airplane.

Nextant Aerospace vice president Mark O’Donnell said the mod for one of his company’s remanufactured 400XTis runs about $3.4M plus another $600,000 for a good candidate airplane. “With options, most people should expect to spend closer to $5 to $5.2 million for a finished airplane that includes Rockwell Collins Pro Line 21 avionics in the cockpit.”

He said when comparing a new Phenom 300 or a CJ4 selling for about $9 million, the performance and creature-comfort differences are similar for about half the price.

Blackhawk’s Allmon said customers can expect to spend about $1.78 million for the King Air modification package and another $30,000 for installation. The upgrade work takes the airplane out of service for about a month.