For more than a century of powered flight, engine technology has been the main key to improving aircraft performance. And so it is with Aircraft Industries’ latest version of the venerable L410. It is fitted with 800 shp Czech H80 powerplants and was just certified in April 2013. It has only 50 shp more per side than the previous version, but it offers much improved hot-and-high airport and climb performance, faster cruise speeds on warm days and at least five percent better fuel efficiency.
Operators of the-powered L410 also will benefit from a TBO increase from 3,000 to 3,600 hours, no fuel injector nozzle maintenance and no midlife hot section inspection. The water injection system also has been eliminated. The H80 shares its type certification with the 1990 Walter M601E, but dissassemble the engine and profound internal changes are apparent. The two-stage axial and single-stage centrifugal compressor take full advantage of GE aerodynamic expertise to raise the compression ratio, and improved metal alloys boost temperature margins.
GE bought Walter in 2008, moved the plant to a factory next door to Kbely Airfield and completely revamped the production process.
Friday before the Paris air show, we strapped into the left seat of a GE-powered L410UVP-E20 at Kunovice, Czech Republic, accompanied by factory test pilot Petr Jarocky, for a first hand, albeit brief, demonstration of its improved performance. UVP is the Russian equivalent of STOL (short takeoff and landing) in English. The UVP has increased wingspan and a taller tail that enable it to use the increased horsepower of the twin H80 engines to full advantage.
The -E20 designation indicates that it is certified toCS23 commuter category standards. Similarly, the L420 is an -E20 certified to FAR Part 23 commuter category standards. The GE powered version, equipped with five-blade Avia AV 725 props, was certified in April 2013.
Basic Operating Weight was 10,390 lb with the two of us in the cockpit and a full array of flight test equipment bolted into the main cabin. Two flight test engineers, plus all their kit, added 440 lb. Loaded with 1,763 lb of fuel, computed takeoff weight was 12,595 lb, about 87% of MTOW.
Airport elevation was 581 ft, OAT was 17C and QNH was 1023 Mb. At that field elevation, the full 800 hp takeoff rating was available to 33C and up to 40C for one engine inoperative conditions. Balanced field length is not published in the AFM, thus it’s necessary to compute accelerate-stop and accelerate-go performance, plus V-speeds, using more than a dozen charts. This airplane begs to have a software app for your iPad or laptop that would automatically compute airport performance.
With 6,600 ft of concrete available, runway length wasn’t a limitation, so we used simplified speed computations for flaps 18 degrees: 78 KIAS for V1 takeoff decision speed, 81 KIAS for rotation and 100 KIAS for the V2 OEI takeoff safety speed. OEI climb gradient was 4.9%.
L410’s cockpit is a blend of traditional and modern features, having left and right side Universal Avionics PFDs, an optionalKFC325 autopilot, TCAS and E EGPS, plus a plethora of analog gauges in the instrument panel, more than a dozen circuit breaker toggle switches in the overhead panel and some Czech and/or Russian design oddities. For example, there is an electrically controlled and hydraulically actuated ground spoiler system that’s activated by a guarded switch on the left hand control wheel, a nosewheel steering tiller lever on the control yoke stalk and a low-speed, roll control assist system that is activated in the event of an engine failure on takeoff.
Prior to start, Jarocky hand-pumped the hydraulic system to build pressure before he pulled the parking brake. After engine start, we rolled out of the chocks. Braking action was very smooth. Engine driven pumps supply the 2,100 psi hydraulic system that powers the anti-skid wheel brakes, along with the landing gear actuators, nosewheel steering, roll control assist system, flaps and ground spoilers.
Cleared for takeoff on Runway 21 Center, Jarocky fine-tuned the power setting. Amber lights in the central warning display illuminate if takeoff torque, 2,080 prop rpm, gas generator speed or temperature limits are exceeded. With the wide flat-rating of the GE engines, the only practical limit is the possibility of exceeding maximum torque.
Initial rotation forces were pleasantly light. We retracted the landing gear with a positive rate of climb. Retracting the flaps resulted in a pronounced nose-down pitching moment. Make a note. Use electric nose-up trim during the entire time the flaps are retracting and nose-down trim continuously when the flaps are extending.
Engine power changes also produce noticeable thrust induced lift over the wings, requiring elevator and trim inputs. Using 1,900 rpm and climb power, we settled into a 500 fpm climb and then leveled off at 4,000 ft. We reduced prop speed to 1,700 rpm for cruise. Interior sound levels dropped considerably. At cruise power, the aircraft trued out at 200 kt on 800 lb/hr fuel flow.
Rolling into a steep turn, we noted that aileron inputs require heavy feet on the rudder pedals to maintain balanced flight. Pitch force is heavy at 1.4g in a 45-degree banked turn. But, the aircraft is easy to control and very honest in its feedback to the pilot.
Stall behavior is a strong suit. In clean, flaps 18 (takeoff) and flaps 42 (landing) configurations, stall is preceded by aural and audio warnings, plus aerodynamic stall warning buffet. Hold the yoke all the way aft, there is very little wing roll off if the ball is in the center at full stall.
Returning to Kunovice for pattern work, Jarocky advised using 90 kt as an approach speed at flaps 42 degrees. At our 12,000 lb landing weight, though, Vref actually was 77 KIAS at our landing weight of 12,000 lb. The aircraft is very easy to fly in the pattern and throttle response is quite linear. With full flaps, drag is high, so steep approaches may be flown with comfortable airspeed control. When flying normal glidepaths it takes moderate power to maintain the desired approach speed. It’s easy to get slow, if you don’t hawk the airspeed indicator.
In the flare, we floated because of the excess airspeed. The aircraft has trailing-link landing gear all the way around, plus large, low pressure tires, so touchdowns are very smooth on paved runways.
Our next two landings were on one of the two grass strips that parallel the paved runway at Kunovice. Again, the trailing-link landing gear and big doughnut tires make for small touchdowns and roll outs.
For the final landing we used the ground spoilers, full braking action and maximum prop reverse. Landing distance was 2,850 ft.
Conclusions? The GE H80 engines are breathing new life into the fourth-generation L410, even though the design is half a century old. The 19-seat aircraft retains all of its rugged design heritage and off runway versatility. Yes, it has legacy Eastern Bloc design quirks dating back to Let’s original goal of creating an Antonov An-2 successor, but that’s part of its charm. Aircraft Industries already is cutting metal for the next generation L410, planning to add even more horsepower, flat-panel avionics and increased fuel capacity. It’s likely that GE power, among other improvements, will extend the L410’s production run for several years to come.