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KINGSingle-lever power controls, and more IS BUYING NEW ALWAYS BETTER? For those wanting to boost the value of their current turboprop, instead of writing a megamillion-dollar check for a factory-fresh model, there are alternatives. The most recent example is Nextant Aerospace’s G90XT, a project that takes Beechcraft’s popular King Air C90A series of airplanes and transforms them into modern- ized designs via a bundle of supplemental type certificates.

BY THOMAS A. HORNE PHOTOGRAPHY BY CHRIS ROSE When it bought Walter

The stock, 550-shaft-horsepower Pratt & Aircraft Engines, of 250 knots, or about 19 to 20 knots more Whitney PT6A-135 engines are yanked, GE was gunning for than the standard airplane. and replaced with GE’s H75 engine. The To comply with the C90A’s type certifi- panel gets a complete upgrade, featuring a Pratt & Whitney, whose cate, the H75-100, although certified at 751 three-screen Garmin G1000 avionics suite, PT6 line of turboprops has shp, is derated to the same 550 shp that the including Garmin’s GFC 700 autopilot and PT6A-135 produces. flight control system; single-lever power been the uncontested ruler controls eliminate the original prop levers; of the market for 60 years. SINGLE LEVERS AND ELECTRONIC the fuel and pressurization systems are CONTROLS simplified and digitized; and Raisbeck’s The combustor/hot section was beefed “We wanted to make an airplane that wing lockers and dual aft-body strakes are up with new alloys to prevent the crack- would be so safe and easy to fly that any- also part of the basic deal, which is priced ing and thermal stresses that plagued the one stepping up from a piston twin—or at $1.9 million. A revamped interior can M601. A computational fluid dynamics even a complex single—would feel com- also be ordered, which will bump the price examination led to a redesign of the com- fortable in the G90XT’s cockpit,” Heublein up to $2.4 million. pressor section, which involved changes said. Thus the decision to equip the air- to the compressor wheels’ airfoil cross plane with electronic engine controls GE’S DEBUT sections from tip to root that produced a (EECs) and electronic propeller gover- In 2008 General Electric bought Walter more efficient, constant flow of air across nors. Together, they permit single-lever Aircraft Engines, a Czech turboprop the length of each blade. Instead of fuel power control. engine manufacturer. Walter’s back- nozzles, the fuel system uses a centrifugal The EECs compare compressor speed ground was in making engines for the slinger ring to deliver fuel to the combus- and fuel scheduling, as selected using the Eastern European market during the tion chamber, obviating the need for fuel power levers, and then send this infor- Cold War era. More recently, its 750- nozzle maintenance and eliminating hot mation to rotary variable differential shp M601E engine was used in Lancair’s spots in the combustor, which in turn elim- transformers (RVDTs). The RVDTs, which Propjet, a sleek, 325-knot, pressurized kit- inates the need for hot section inspections. act much like potentiometers, send linear plane that was discontinued in 2012. But Recommended time between overhauls signals that electrically govern propeller GE didn’t have kitplanes in mind when it is set at 4,000 hours, although Nextant rpm and blade angle. The result is a linear bought Walter. It was gunning for Pratt & Executive Vice President of Global Sales delivery of power and propeller synchro- Whitney, whose PT6 line of turboprops and Marketing Jay Heublein said this may nization throughout the power band. has been the uncontested ruler of the mar- eventually be increased. From flight idle through maximum take- ket for 60 years. Because the combustor can withstand off power, the power lever throw is quite Nextant and GE partnered to come up higher temperatures and the compressor short—maybe four inches. with the G90XT’s vastly improved engine. section is so efficient, Nextant says the “With the standard configuration, Although the engine case may trace its H75-100 burns less fuel than the C90A’s you get maybe 80 percent of the engines’ roots to the M601, it’s about the only stock PT6A-135 engines at any given total power in the last 20 percent of the component that bears any resemblance. speed, has an 11- to 12-percent better spe- power levers’ travel,” said Nathan Marker, And while the G90XT’s new H75-100 is a cific fuel consumption (SFC, the mass Nextant’s vice president of flight opera- reverse-flow engine (air enters the engine of fuel needed per mile), and 10 percent tions and chief pilot. “There’s that sudden from the rear, and exhaust leaves via a pair lower direct operating costs. At FL240 and surge of power during the takeoff run, so of forward-mounted stacks) that’s about standard conditions, Nextant says the H75- you end up ‘walking’ the power levers up all it shares with the PT6 engine design. 100s also push the G90XT to cruise speeds to full power for a smooth acceleration,

THE H75-100 (left) is based on the Walter M601 design. Intake air enters the rear of the engine, at the screened area, and exhausts through forward- mounted stacks. A slinger ring sends an even mist of fuel to the hot section. The propeller is a four-blade Hartzell (opposite), but a composite MT propeller is being considered, as well as other prop designs. and to prevent a torque exceedance. With engine. These are mechanically connected the XT it’s a smooth acceleration.” By the to the engines. way, torque, interstage turbine tempera- In the event of a fuel control unit ture (ITT), and prop rpm exceedances are malfunction, an EEC failure, or a power automatically prevented by the limiting rollback, the condition levers are used functions of the EECs. You could, Marker like the manual override (MOR) levers said, slam the power levers all the way for- found in single-engine turboprops. ward during takeoff, and torque would not Moving a condition lever will allow the blow past redline. Not a good habit to cul- pilot to advance or retard power. There tivate, but it’s nice to have the protection. are no high or low idle detents like true At altitude, the EECs will also keep ITTs condition levers, but there are fuel cut- away from reaching redline. off positions. Although any single-lever power con- As for propeller feathering, this auto- trol system is apt to be labeled as full matic feature kicks in when the bleed air authority digital engine control (FADEC), output of the bad engine drops, creating the G90XT’s is not. True FADEC systems an imbalance that’s sensed by a shuttle have dual digital channels; the XT’s power valve. Autofeathering takes the offend- levers have what can be considered sin- ing engine’s propeller to feather, although gle channels. While there’s no mechanical guarded switchlights on the center pedes- connections between the power levers and tal can be used to feather manually. the engines, there are digital connections, All this may sound complicated, but chiefly the EECs. Redundancy comes in the engine systems operate in the back- the form of the red condition levers at the ground, and normally require little pilot right of the power quadrant, one for each management other than monitoring the

gauges. And moving the single-lever quantity gauges on the G1000’s MFD. And THE G90XT SUBPANEL retains the switches power controls. remember the three traditional pressur- of the original airplane, but has spiffed-up, backlit lettering (opposite, top). ization dials and gauges? They’re gone too, Autofeather is standard with the G90XT, WALL-TO-WALL GLASS replaced by a digital pressurization system but prop feathering is finalized by using Those gauges are located on the G1000’s that gets its information from the G1000’s guarded switchlights (opposite, middle). The XT’s panel features the G1000 and a multifunction display, along with other flight plan and other information. There’s a new fuel control panel located forward of system information. Gone are the analog new air conditioning system, too. One with the power quadrant (opposite, bottom). gauges traditionally found in King Airs. dual evaporators that Nextant says can Add one of Nextant’s custom interiors to the standard modification and you can Garmin’s GFC 700 autopilot and flight con- move three times the volume of air than have a club seating layout like the one trol system, mounted on the glareshield, the stock airplane, and is powerful enough above. Nextant is no stranger to radical provides all the usual autopilot functions— to draw down cabin temperatures from 125 airframe and engine mods. Its 400 XTi, a Williams-reengined Beechjet with 74 sales, along with the flight envelope protection degrees to 75 degrees in five minutes. undergoes a 9,000-man-hour remanufac- features that are becoming so popular on In other words, nearly everything about turing process. The G90XT goes through recent-model airplanes. Roll or pitch the the XT’s panel is new. Except for the sub- the same process, including compliance with all airworthiness directives and man- airplane past predetermined limits and the panel switches. They have the same old datory service bulletins, replacement of all autopilot servos automatically apply cor- King Air look and layout, but have a more life-limited components with new or zero- rective force. Fight the controls, and the modern look to their labelling. timed units, and a landing gear overhaul. servos fight back. The harder you fight, the harder the servos fight back. Keep this up INTERIOR MAKEOVER and the autopilot will automatically engage Want a new interior to go with all that new to right the airplane. There’s also under- hardware? Nextant offers an optional redo speed and overspeed protection to keep of the cabin that includes bigger, thicker

you away from a stall, or exceeding VNE. insulation for noise reduction. Because the Remember the King Air’s sidewall- insulation can be compressed, the cabin’s mounted fuel control panel, with its large composite shell has been expanded, giving gauges? In the G90XT that’s gone. Nextant the cabin three more inches in width and put the fuel controls on the center pedes- 1.5 more inches of headroom over stock tal, forward of the power levers, and the C90As. New seat designs are also available, and so are mechanically or electrically fuel (about 277 gallons) was 9,398 pounds. pilot workload and simplicity of engine operated, pleated sunshades. Maximum takeoff weight is 10,100 pounds. management. But the G90XT brings As you might expect, it acts just like a another message. GE has launched its A NO-SURPRISE FLIGHT King Air—solid, predictable, and stately. challenge to Pratt & Whitney. Nextant’s Nextant is closing in on the G90XT’s Yes, the ailerons are a tad heavy, but that’s first King Air reengining and modification certification—expected in the first quarter a complement to the airplane’s aura of package may not be its last. “The GE engines of 2017—so I took a brief flight in the substance, and can be a good thing in and other improvements are scalable to company’s flight test airplane. Beside instrument conditions. After levelling at other models in the post-1983 C90 King Air me was Marker who, in his eagerness to 10,500 feet and setting a modest, 71-percent fleet, like the C90B and C90GT,” Heublein show off the EECs at work, the smooth torque, we saw 208 knots true, burning said. “And our certification could expand to acceleration and the single-lever simplicity, 260 pph/39 gph per side. The envelope the earlier C90 models if we choose to, and was lobbying for me to just fling the power protection worked as advertised, and probably will.” levers to the stops for takeoff. So I did. Off soon it was time to return to base. Like Textron has also heard the GE call. Its we went, without that sudden delay, then most “baby” King Airs at our weight, upcoming Cessna Denali single-engine surge, of torque and noise you often get VREF worked out to be 100 knots, and the turboprop will feature GE’s 800-shp H80 when flooring a turboprop. A glance at the airplane needed a fair amount of nose-up engine. Here’s betting that Pratt & Whitney MFD showed everything in the green, and trim to get a decent flare. is already at work on a FADEC version of the PFD registered a 1,400-feet-per-minute Anyone with time in a conventional the PT6. AOPA climb on the ISA +11 day. Our takeoff weight King Air would have to agree that Nextant with two passengers and 1,848 pounds of has hit the mark when it comes to ease of EMAIL [email protected]