May 1, 2013
By Dave Hirschman
Photography by Chris Rose
Terry Humphrey has given many “on-wing” checkouts to pilots about to fly single-seat airplanes, and the General Electric H80 engine in the Thrush 510G agricultural aircraft makes his job especially easy.
“This engine is closer to being pilot-proof than any turboprop I’ve ever seen,” said Humphrey, a veteran crop duster and the laid-back chief instructor pilot at Thrush Aircraft, an agricultural aircraft manufacturer in rural Albany, Georgia, near the southwestern corner of the state. “You’d have to be brain dead to mess up the start. And even if you do mess it up, the engine won’t let you hurt it.”
On an overcast and cool afternoon, Humphrey stands on the left wing of the hulking Thrush and guides me through the engine start.
Battery on (and voltage checked); Start/Abort switch on; condition lever to idle (there’s no flight and ground idle); main fuel pump on; press the start switch on for five seconds—and let the automation do the rest. Fuel is introduced through a slinger ring instead of individual nozzles, and the igniters fire automatically. If engine sensors detect an unusually rapid rise in ITT, or other temperatures or pressures exceed preset limits, fuel is diverted from the combustion chamber to prevent a hot start and the costly damage that could result.
The automated start sequence lasts 20 seconds and, in this case, goes exactly as planned. Humphrey hops down and signals for me to move the prop out of feather, and the four-blade Hartzell growls as it moves into fine pitch.
GE developed the 800-horsepower H80 engine to compete against the venerable Pratt & Whitney PT6A across a wide spectrum of general aviation aircraft. There’s an STC to install H80s in Beech King Air C90s, and many other high-flying, pressurized aircraft are likely to follow with STCs of their own.
But the heavy-hauling, low-flying, hard-working Thrush is the first U.S. airframe certified with the H80, and Thrush officials say that if the new engine and GE support network can prove themselves in the uniquely punishing world of agricultural flying, the H80 can excel in other aviation markets, too.
“There’s no more demanding environment for an engine than this,” said Eric Rojek, vice president at Thrush. “Our customers work in remote locations all over the world. They carry heavy loads in hot weather and high elevations, and they depend on the very highest reliability and service levels. These are large, time-critical businesses, and lives and livelihoods depend on results.”
Tough Bird Five. There’s a 12-knot breeze out of west as I taxi from the Thrush factory to the adjoining Runway 34 at the Southwest Georgia Regional Airport, and several unusual aspects present themselves during the short ride to the runway threshold. First, unlocking the Thrush tailwheel requires holding the stick full forward—so between my short arms, an extremely spacious cockpit, and the stick’s long travel, I need to lean far forward in the seat to make the airplane turn. A tower controller kindly offers an intersection departure, which is standard practice for hurried factory test pilots who have logged many thousands of flight hours in these specialized aircraft. But I cautiously elect for the full length, even though this powerful, lightly loaded airplane will be off the ground in less than 20 percent of the available distance. Finally, the airplane’s call sign, “Tough Bird Five,” is impossible for me to say without grinning, or chuckling, or both.
With the short pretakeoff checklist complete, I line up with the centerline, advance the power lever, and hold the brakes. An Electronics International MVP-50T engine monitor shows prop rpm, ITT, and torque both digitally and graphically, with color-coded electronic round-dial representations. The prop is turning its maximum 2,080 rpm as I release the brakes and the airplane smoothly advances.
Small power-lever adjustments have a dramatic effect on torque, and getting the power setting just right is tricky. The H80 is rated for full power at outside air temperatures well above 100 degrees Fahrenheit. On this day, the OAT is barely 50 degrees F, and at Albany’s low elevation of 200 feet msl it is easy to over-torque the engine. (In the event of an over-torque, master caution and warning lights on the panel illuminate right away.)
Holding the elevator neutral, the Thrush tailwheel comes off the ground at about 40 mph, and I maintain a tail-low attitude. The airplane lifts off at about 65 miles an hour and accelerates steadily. I raise the electric flaps (set at 10 degrees for takeoff) at 85 mph. This Thrush has an empty weight of 4,700 pounds; it’s carrying about 170 gallons of jet fuel and absolutely nothing in the vacuous hopper. Its total weight is about 6,000 pounds, a shadow of its “working weight” of 10,500 pounds.
Like other modern ag airplanes, the Thrush is capable of carrying more payload than its empty weight. This lightly loaded 510G is climbing about 1,500 fpm at around 100 mph as I reduce engine power, pull the prop back to 1,900 rpm, and take in the view from pattern altitude.
Forward visibility is helicopter-like because of the low instrument panel and the sharply downward slope of the preposterously long, thin cowl. The propeller is about 20 feet in front of the cockpit, and it looks as though it could be in another time zone.
The strange perspective of the downsloping nose tricks me into climbing when the airplane appears to be in level flight. When the cowl is level with the horizon, the airplane is in a 10-degree climb.
Czech engine. Development of the H80 engine began soon after GE bought Walter Motors in 2008. Walter had been making engines for 60 years in the Czech Republic, and one of the most popular was a PT6 clone known as the M601 that was used throughout the Eastern Bloc.
Walter turboprops were flown from Siberia to Africa on many Transport-category and military aircraft, and the engines earned a reputation for ruggedness and operational simplicity during more than 17 million flight hours. The H80 is based on the M601 and has the same external dimensions. But better materials and design improvements allow the H80 to put out 800 horsepower while the M601 is rated at 650.
Length: 66 inches
Diameter: 22 inches
Weight: 382 lbs.
TBO: 3,600 hours (6,600 cycles)
Power: 800 shaft horsepower
All specifications are based on manufacturer’s calculations. All performance figures are based on standard day, standard atmosphere conditions.
A GE factory near Prague manufactures the engines and sends them in individual containers (which look remarkably like GE refrigerator boxes) to Thrush Aircraft for installation. The H80 weighs 382 pounds and is lighter than a PT6A-34AG, so the Thrush 510G had its Pinocchio-like nose extended another 14 inches to accommodate the new engine. The change also allowed Thrush to remove ballast from the Pratt & Whitney-powered aircraft, so a GE Thrush is more than 200 pounds lighter.
Wiring for all H80 electronic engine controls and sensors are routed through two cannon plugs. When an H80 engine is replaced in the field, technicians need only reconnect the two plugs to get all the electronic components hooked up again. The change is intended to radically reduce the amount of downtime required for engine changes.
Thrush officials say the H80 typically burns about 50 gallons of fuel per hour, roughly the same amount as a similar-sized PT6A-34AG at the low altitudes where ag aircraft normally work. For high-flying airplanes, GE officials say the H80 offers a quicker climb to altitude because of its high horsepower, and potentially faster cruise speeds.
Staying low. I’m tempted to climb to learn more about the engine’s climb performance and fuel consumption, but a slate gray overcast at 4,000 feet makes that impossible in this VFR-only aircraft. (A few Thrush aircraft, including those made for special missions, are equipped for IFR flight.) Instead, I maneuver at about 3,000 feet, an altitude ag airplanes like this one are likely to see only on ferry flights.
Unlike other Thrush models (and many other ag airplanes) that have spring linkages connecting rudder and ailerons, the 510G controls move independently, and control harmony and responsiveness are delightful. The roll rate is well in excess of 60 degrees per second, and the elevator is smooth and surprisingly light. Coordination exercises such as Dutch rolls and lazy 8s are comfortable and accurate right away in the 510G, and control feedback is direct and authentic—a big improvement over the artificial feel that comes with spring linkages.
Power-off stalls at 1 G are preceded by pronounced buffeting at about 60 mph, and the nose drops straight ahead at about 55 mph IAS as long as the inclinometer ball is centered. (And the inclinometer is prominently displayed front and center in the instrument panel.)
This particular 510G is fitted with spray bars and nozzles, and at a typical working power setting, indicated airspeed is about 155 mph in level flight. Turbine ag airplanes typically spray at 130 to 150 mph. The 510G has a VNE of 188 mph—a number that’s not out of reach in steep powered descents, even with draggy spray equipment hanging from the wings.
I’d like to keep flying the 510G all day. It’s rare to get the keys to a factory-new airplane of any sort, let alone one with the pure power, strength, and rowdy nature of this one. Its roomy cockpit; tremendous visibility; and smooth, quiet ride and comfort (why don’t other GA aircraft use airy mesh seats like this?) put the Thrush in a league of its own. But a line of rain squalls is closing in, and it’s time to get back to the airport. The wind is still out of the west and gusting to 18 knots.
Downwind for Runway 22 at 120 mph, flaps to half (or 7.5 degrees), and 90 mph on final makes for a stable and predictable approach despite the lumpy crosswind. I carry some power as the main landing gear touch down in a tail-low wheel landing. The propeller flattens out as I pull the power lever all the way back to the stop, and the Thrush clears the runway after a ground roll of 1,000 feet with light braking.
The airplane can stop in as little as 350 feet with reverse thrust and aggressive braking. But reverse prop pitch blanks the rudder and can make ground handling difficult, even with the locking Thrush tailwheel.
That engine. About a dozen 510Gs (with retail prices starting at $900,000) are currently working in the harsh and unforgiving low-altitude environment ag aircraft are built to endure. About 15 of the 60 ag airplanes Thrush manufactures this year will be powered by GE engines, and company officials expect sales of GE-powered Thrushes to double in 2014.
The price of a GE-powered Thrush is identical to the same airframe with a Pratt & Whitney PT6A-34AG. (GE sells H80s only through OEMs and doesn’t publish a retail price for the new engines.)
Ag operators—just like other GA business managers—are focused on issues such as engine reliability, technical support, maintenance, and parts availability. Thrush’s Rojek said he expects GE to win over ag operators, and serious competition in the turboprop engine marketplace will mean lower prices and better service for airframe manufacturers like Thrush, as well as individual aircraft owners.
“Pratt & Whitney makes a rock star engine and their service network has never been better,” he said. “GE knows the bar has been set very high, and they’re going to have to go to great lengths to succeed in a very competitive marketplace.”
Humphrey, Thrush’s chief instructor pilot, is planning many more on-wing checkouts for ag pilots and operators considering Thrush aircraft with the GE engine. The H80 has been certified in Europe, Russia, Brazil, and Argentina, an important consideration because just over half of the new aircraft Thrush sells this year are slated for export.
“If the H80 engine does well in agricultural aviation, other markets will be a snap,” he said. “There’s no more brutal operating environment than this one.”
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