Embraer designed the EMB-314 Super Tucano to meet unique Brazilian requirements, but hopes to find a wider market for the powerful turboprop as an advanced trainer/light attack aircraft
Due to its location and size Brazil has some unique and demanding defence requirements. The largest country in South America, it shares 11,000km (6,800 miles) of borders with seven countries. While Brazil's south is modern and industrialised, the same cannot be said of its north. The Amazon river basin to the north comprises over 60% of Brazil's territory, its rain forest and scrublands a haven for illegal activities.
In 1990 a joint civil/military co-ordination agency, the Amazon Protection System (SIPAM), was formed to tame this region. Critical to SIPAM's success is the implementation of the Amazon Surveillance System (SIVAM), which has both air and ground components. Raytheon is SIVAM prime contractor, with Brazilian manufacturer Embraer supplying the aerial component, which uses three aircraft to fulfil its mission. The EMB-145RS and EMB-145SA AEW&C, based on the Embraer's ERJ-145 regional jet, will handle ground and air surveillance duties, respectively. The teeth of SIVAM will be the company's EMB-314 Super Tucano, designated the AL-X, or A/AT-29, by the Brazilian air force.
While similar in appearance to the EMB-312 Tucano turboprop trainer from which it has been developed, the Super Tucano is a markedly different aircraft. The aircraft's fuselage is 1.3m (4.25ft) longer: 0.3m ahead of the new wing and 1m aft . The extra length is needed to handle the increased power and torque of its Pratt & Whitney Canada PT6A-68/3 turboprop. As installed in the Super Tucano, the engine is rated at 1,200kW (1,600hp), more than twice that of the Tucano's PT6. The airframe structure has also been strengthened to allow load factors of up to 7g and -3.5g in a clean configuration
Internally, the Super Tucano bears scant resemblance to its predecessor. No longer a mere trainer, it is now a capable light attack aircraft. Central to this new capability is an avionics system developed by Israel's Elbit. Two mission and display processors and a 1553B multiplex databus form the backbone of the system. A head-up display (HUD) with 24° field-of-view is the primary flight display, while two 150 x 200mm (8 x 10in) colour liquid-crystal multifunction displays provide a clean, flexible workspace for the pilot. Standby flight instruments are centrally located below the HUD's upfront control panel. The throttle and stick are host to a number of switches, providing a true hands-on control capability.
As part of SIVAM, the Super Tucano is designed to operate in the extremely rugged Amazon river basin. Most of the structure is conventional aluminium, with only the rudder and several access panels made of composites. Flight controls are manually operated, improving maintainability in austere conditions. Crew comfort is enhanced by an effective air-conditioning system based on an air-cycle machine. Avionics are housed in a bay aft of the rear cockpit. Although cooled by fans and outflow from the pressurised cockpit, the avionics are designed to operate without cooling for several hours in tropical conditions. Either mission data processor can operate the entire avionics system, the other acting as a back-up. Two batteries are installed and allow operations without an external power cart. Finally, the on-board oxygen generating system eliminates the requirement for bottled oxygen supplies at remote locations.
The Super Tucano will not venture into harm's way unarmed. Two 0.5in machine guns are mounted mid-wing. Each has a 250-round magazine, and a rate of fire of 1,100 rounds/min. Five weapons stations, one on the fuselage centreline and four underwing, can carry a total of 1,500kg (3,300lb) of stores. Each pylon features NATO-standard lugs and a stores interface unit, which communicates with the stores management system and allows the aircraft to carry a wide range of stores.
Primary air-to-air armament is the Brazilian MAA-1 Piranha short-range infrared-guided missile, but other Sidewinder-class weapons can be carried. Air-to-ground ordnance consists of 112kg Mk81 and 227kg Mk82 unguided bombs, as well as other free-fall weapons in these weight classes. Unguided 70mm rockets can be carried in pods containing 19 each, while Raytheon AGM-65 Maverick air-to-surface missiles can also be carried. Rounding out the Super Tucano's armament capability is the ability to carry a 20mm gun pod.
Flight International was able to evaluate how the Super Tucano may perform in the advanced trainer and light attack roles during two flights from Embraer's production facility at San Jose dos Campos. The first flight concentrated on the trainer role, and was flown with Embraer test pilot Antonio Bragança Silva in the prototype two-seat AL-X (aircraft 802).
During the walk-around inspection, Silva pointed out the 2.39m-diameter, five-blade Hartzell constant-speed propeller - a clear sign of the turboprop's high power output. All inspection panels were accessible from ground level. Overall, I found the inspection straightforward, and not unlike that for a complex single-engined civil aircraft. Cockpit entry was from atop the left wing, a built-in step eliminating the need for an external ladder.
Once settled into the zero/zero Martin-Baker Mk10LCX ejection seat, I found the field of view from the front cockpit to be good. I was easily able to see the six o'clock position over my left and right shoulders, a valuable attribute in a combat aircraft. Flight management system initialisation was easy to accomplish. Aircraft position is determined by a combined embedded global-positioning/inertial reference system and radar altimeter. The inertial platform took only 4min to align. A separate standalone global positioning system (GPS) receiver provided an additional level of redundancy for position information.
Pre-start actions were few, limited to turning on external lights and fuel boost pumps. Once the start switch was engaged, the throttle was put into the START position at 14% gas generator RPM (NG). Light-off was immediate and T5 temperature peaked at 730°C (1,350°F), well below the limit of 1,000°C. The throttle was moved to the IDLE position when the propeller began to unfeather. After 40s the engine reached an idle RPM of 66% NG and T5 stabilised at 670°C. Pressurisation and air-conditioning systems were turned on in preparation for taxi. Once the parking brake was released, idle power was sufficient to start the aircraft rolling. During the taxi I found the manual nosewheel steering direct and responsive. Toe brakes, which used 207bar (3,000lb/in2) aircraft hydraulic pressure, easily controlled speed on the downhill portions of our taxi.
As there were no external stores on the aircraft, the two-position electrically operated flaps were left retracted for take-off. The Super Tucano has a single thrust lever that controls the engine and propeller. Once lined up on runway 15, I held the brakes and rapidly advanced the throttle to the maximum power position. The PT6's power management unit, similar to a full-authority digital engine control, prevented the turboprop exceeding temperature or torque limits.
Once engine parameters had stabilised, I released the brakes and applied right rudder to counteract the yawing motion induced by the propeller wash. The engine was producing 86% of maximum allowable torque as the aircraft accelerated down the runway, with the outside temperature at 22°C. At around 50kt (90km/h), the automatic rudder trim (ART) system became active and applied some right rudder, reducing the amount I needed to apply. Pitch forces were light as I rotated the aircraft to 8° nose up. The 4,155kg aircraft (including 455kg internal fuel and 300kg of test equipment) lifted off the runway 30s after brake release at 95kt and after a ground run of 800m (2,500ft). Gear retraction caused no change in pitch forces as the aircraft accelerated to a climb speed of 140kt.
The yawing tendency which occurs when thrust or airspeed is changed in a singe propeller aircraft is due primarily to two additive factors. The first is the effect of propeller slipstream on the vertical stabiliser. The second and far more significant one is a function of angle of attack (AoA). While the propeller's plane of rotation is fixed relative to the aircraft, the airflow each individual blade experiences is a function of the aircraft's AoA. The Super Tucano's propeller, when viewed from the cockpit, rotates in a clockwise direction. At positive AoAs the down-going blade, the right side in this case, experiences a greater AoA than the up-going, left side, blade. Because of its bigger "bite", the down-going blade produces more lift (thrust) than the up-going blade and this yaws the aircraft to the left. As aircraft AoA is reduced this yawing moment is reduced, and may in fact reverse direction at negative aircraft AoAs.
Manufacturers try to minimise rudder trim required for co-ordinated flight by either canting the vertical stabiliser, or offsetting the thrust line of the engine. The Super Tucano's engine is canted 3° left of centreline. The ART seeks to further reduce required pilot rudder inputs in response to changes in airspeed and power levels. While the system did a reasonable job of compensating for propeller-induced yaw forces, I still needed to use my feet to maintain co-ordinated flight.
After turning towards the working area, I started a climb at 140kt. The climb to 18,000ft above mean sea level, from a field elevation of 2,085ft, used 30kg of fuel and resulted in an average rate of climb of 1,500ft/min (7.62m/s). During the climb the aircraft was difficult to trim in the roll axis, either wing dropping slightly at random intervals. Once level at 18,000ft, I accelerated the aircraft and noted a fuel flow of 165kg/h when stable at a tactical holding airspeed of 150kt. Although we were only 30km from the airfield, we could have maintained this orbit for about 2h and landed with 30min of reserve fuel. Optional 320 litre (84USgal)/260kg fuel tanks, one on the centreline and two under the wing, will greatly increase on-station times over the clean aircraft. The single-seat AL-X variant carries an additional 300 litres/425kg of fuel in place of the rear ejection seat.
Tactical holding complete, I retarded the power to idle and slowed the 4,065kg aircraft at 1kt/s in preparation for a clean- configuration stall, gear and flaps retracted. Moderate airframe buffet at 100kt preceded the full aft-stick stall, which occurred at 94kt. Control in all three axes was good during the stall, with a slight wing rock (±10°) about a predominantly wings-level attitude. Releasing back stick pressure allowed the aircraft to recover and fly out of the stall.
Aircraft response during a landing-configuration stall, gear and flaps down, was similar to the clean stall. Unmistakable airframe buffet was felt at 90kt, 6kt before the full aft-stick stall. The aircraft again settled into a stable nose-high attitude and 2,000ft/min rate of descent. As was the case with the clean stall, releasing back stick pressure allowed the aircraft to regain flying airspeed.
Satisfied with the Super Tucano's benign stall characteristics, I next looked at what would happen if a pilot ignored stall warnings and applied full pro-spin control inputs at stall onset. In a clean configuration and with the power set to idle at 15,000ft, I abruptly applied full aft stick and full right rudder at 95kt, 1kt above the stall speed. In less than 2s the aircraft rapidly rolled to the right and tucked under before settling into a 50° nose-low right-hand-turn spin. I held full pro-spin controls for an additional two slightly oscillatory turns, each taking about 2.5s. After the third turn I neutralised the stick while applying full left rudder. The stall was broken and yaw rate stopped in about one turn. A 2-3g pull-out returned the aircraft to climbing 180kt flight at 12,000ft.
A second spin, accomplished by putting in full left rudder at stall onset as well as full aft stick, was much like the right spin, but this time I just released the stick and rudder when it was time to recover the aircraft. After the controls were released the rate of rotation initially increased and the nose dropped. After two turns the rotation stopped and the aircraft recovered to controlled flight in a 70° dive. Wings-level climbing flight was attained only 3,500ft below the initial spin entry altitude.
Acceleration to 310kt, 10kt below maximum operating speed (Vmo), showed the Super Tucano to be stable near its maximum operating speed. Aircraft response to sharp control inputs in each axis was well damped. The roll axis seemed to become more stable as airspeed increased, with the aircraft not displaying any tendency to roll off as it had in the initial climb. The acceleration to Vmo allowed further evaluation of the automatic rudder trim. While the system markedly reduced the magnitude of rudder input required to counter propeller-induced yawing, pilot inputs were still required. I found the throttle-mounted rudder trim rocker switch convenient for maintaining co-ordinated flight. But the ART will need further refinement before the Super Tucano can provide a feet-on-the-floor, jet-like experience.
Before leaving the work area, a loop, barrel roll and pitch-back manoeuvre were accomplished with the power set to maximum. Additionally, a full-deflection aileron roll at 200kt showed the Super Tucano's rapid roll capability, taking less than 3s to complete. Aircraft response during all manoeuvres was predictable and precise. Control forces in the pitch and roll axes were light, and well harmonised. Overall I found the Super Tucano to be a delightful aerobatic machine.
Return to San Jose dos Campos was via a simulated flame-out landing pattern. Over the field at 2,000ft above ground level, at 120kt, Silva retarded the throttle to idle to simulate an engine failure. I started a 20°-bank left turn to establish a downwind "low key" position at 1,500ft abeam the desired touchdown point. Visually superimposing the left wingtip on the runway was a good guide for finding the correct lateral displacement on this no-wind day.
The gear was extended before starting the final turn and I slowed the aircraft to 110kt. Half way through the final turn we hit the "base key" position at 800ft. On final I extended the flaps and crossed the threshold at 100kt. A smooth flare allowed the aircraft to touch down 1,500ft from the approach end.
Once on the runway the flaps were retracted and power advanced to perform a touch and go. The gear was retracted before starting a left climbing turn to a 1,000ft downwind leg. Gear and flaps were lowered in the base turn and I flew the final approach at 110kt. Touchdown was 1,000ft from the threshold and the toe brakes allowed me to slow the 3,915kg aircraft smoothly to taxi speed. During the 1h flight I appreciated the Super Tucano's performance and flying qualities, finding the aircraft easy to manoeuvre and land - good characteristics for the training role.
For my second flight Embraer test pilot Marcos de Oliveira Lima, who replaced Silva in the back seat, prepared a data transfer cartridge (DTC) with our mission plan and simulated weapons load. DTC information was transferred to the flight management system (FMS) after engine start. Take-off again was from runway 15, and I turned to follow the HUD-displayed guidance to the first turn point in Brazil's Paraiba Valley. Initially, I held 200kt at 1,000ft above ground level, where fuel flow was 230kg/h. Pushing the throttle to just short of maximum accelerated the aircraft to 240kt and increased fuel flow to 315kg/h.
Overflying the first turn point caused the FMS to sequence automatically to the next waypoint, while providing updated steering cues. A caret in the HUD showed the airspeed to be flown to arrive at each turn point at the desired time. The Super Tucano felt stable at low altitude, while the turboprop engine allowed me to maintain the desired airspeed easily along the entire route.
A small rural airstrip 50km north east of San Jose dos Campos was the simulated target for the mission. Before rolling in on the first pass, I selected the air-to-ground master mode via a stick-mounted thumb switch. HUD symbology now included a continuously computed impact point (CCIP) pipper (aiming mark) that showed where the simulated Mk82 bombs would hit the ground.
Unlike an aircraft with a radar or laser range finder, the Super Tucano cannot directly determine its height above the target, a key factor in determining where the bombs will hit. Instead, the weapon system approximates by using measured radar altitude as the aircraft height above target, an acceptable assumption over level terrain. Over steep or rolling terrain the pilot can manually insert known target elevation into the FMS, the system then using aircraft GPS or barometric aircraft altitude to solve the height above target equation. In two bombing runs, I found the HUD symbology and required switch actions to resemble those I learned as a Lockheed Martin F-16 pilot in squadron service.
After the second bombing run, a 3-4g idle-power break turn avoided a simulated surface-to-air missile (SAM). The nose tracked smoothly across the horizon as I manoeuvred the aircraft's tail away from the threat. Light airframe buffet at 150kt was an excellent cue to either ease off the g or push up the power to maintain flying airspeed. Wiring is provided for fuselage-mounted chaff and flare dispensers. When installed, a hands-on-throttle-and-stick switch will facilitate their employment in combat conditions.
Having defeated the SAM, I selected the 0.5in machine guns for my last attack run on the airstrip. During the strafe pass, an "in range" cue over the CCIP pipper alerted me to open fire. Except for the aircraft's slower speed, strafing in the Super Tucano seemed much like strafing in the F-16.
During our return to San Jose dos Campos, Oliveira explained the two weapon-system master modes designed for operations against airborne targets. The "Intercept" mode ties the Super Tucano into the SIVAM surveillance system. Intercept guidance is sent to the aircraft over a UHF datalink. Once the target is identified, the pilot can select the "dogfight" master mode with the stick-mounted thumb switch. In a dogfight the pilot can engage the target with either infrared-guided missiles or the machine guns. While I did not perform any air-to-air engagements, the Super Tucano's manoeuvrability and weapons suggest it will make it an excellent killer of slow-moving aircraft and helicopters.
After sampling the Super Tucano's combat capabilities, flying an instrument landing-system approach to a full-stop landing seemed somewhat anti-climatic. During my flights I was able to evaluate the Super Tucano's handling qualities in several flight regimes. Responsive roll characteristics and predictable behaviour at high angles of attack should allow pilots to employ the aircraft effectively on both combat and training missions. The powerful PT6A-68/3 was highly responsive and allowed carefree throttle movement throughout the flight envelope. The avionics and weapon system are representative of those found in the current generation of frontline fighter/attack aircraft, enabling the Super Tucano to perform the light-attack role or train pilots for fast-jet operations. Overall the aircraft is a capable lightweight, low-cost combatant that is ready to tame the Amazon.
Source: Flight International