Peter Gray/CASCINA COSTA, ITALY
The prototype A119 Koala was produced at about the same time as Agusta's first A109 Power, but because sales of the latter exceeded expectations, effort was diverted to production of the twin-turbine Power at the expense of development of the single-turbine Koala.
The Koala is now in full production. As a derivative of the A109, the A119 has the same size fuselage, shares many common components and benefits from the proven helicopter's design features. For the operator who does not need two engines, and wants the same cabin, cockpit and baggage space, but at lower cost, the Koala appears ideal. The helicopter seats eight comfortably, whereas nearly all its competitors (Bell 206L-4 and 407, and Eurocopter AS350B3 and EC120) seat seven or fewer. Only MD Helicopters' MD 600N also seats eight.
The Koala, however, boasts more volume per passenger than any of its competitors. It is designed for multi-role passenger transport (utility and corporate); emergency medical service (EMS), with a single 2m (6.6ft) litter and four medical attendants or two 2m litters with two attendants, with two pilots; or aerial work. The interior is easily and quickly convertible from one role to another - the seats can be removed without special tools and stored on board to make way for litters, also stored on board. There is no need to remove the co-pilot's seat to make space for the litters
Another flexibility is the choice of fuel tanks - three standard; four or five optional. They all fit neatly behind the rear seat in the cabin extension. The five-tank configuration will give an endurance of nearly 6h. There is provision for installation of the special EMS equipment and other optional extras.
Unobstructed cabin
The big, unobstructed cabin allows plenty of freight to be carried. The lack of any obstruction between the cabin and cockpit is good for the training role where extra trainees can see from the cabin what is happening in the cockpit. Other Koala design criteria include low operating costs and high speeds, the combination of which produces a cost per seat kilometre which Agusta says is the lowest in its class.
My flight was with Agusta experimental test pilot Giuseppe Lo Coco. With an outside air temperature of 28°C (82°F), we were already at a density altitude of over 2,000ft (600m) - good conditions for a test flight taking the aircraft to the edges of its performance envelope: hot, high and heavy. Sometimes, when the test aircraft is fitted with telemetry equipment, there is insufficient space for extra ballast to load the aircraft to its maximum weight. For our evaluation, there was no such problem.
We were heavy, exactly on the maximum gross weight of 2,720kg (6,000lb). Advertised empty weight is 1,430kg, but our aircraft, completely equipped and with the standard three fuel tanks, came in at 1,600kg. Production aircraft will be between 1,550kg and 1,580kg. So, taking an average of 1,565kg, there is 1,155kg available for pilots, fuel and payload. With full fuel in the standard three-tank model, the aircraft will carry eight people, with a maximum weight of nearly 84kg per person.
Agusta has produced a helicopter which will carry full fuel and a full complement of passengers. As well as being useful to the operator, pilots and passengers, this also prevents overloading the aircraft, sadly not an uncommon occurrence. With an underslung load, maximum gross weight increases by 130kg; Agusta expects to grow this to 280kg. The aircraft will lift comfortably its maximum hook weight of 1,000kg, up to several thousand feet.
A standard pre-flight inspection is done quickly and efficiently, with all the vital components easily accessible. Access panels are flush to reduce aerodynamic drag. Lo Coco and I spent time going over the aircraft in some detail.
The airframe makes extensive use of aluminium honeycomb structural panels. These absorb noise and high frequency vibrations, and the Koala needs no additional vibration absorption system, Agusta says. Honeycomb structures also have multi-path shock absorbing characteristics and continue to carry loads after a failure has occurred.
We climbed on top and examined the four-bladed fully articulated rotor system. The blades are composite and designed to produce maximum lift with minimum noise. They have no finite life or overhaul time, but are "on condition only" and can be changed without re-balancing. The main rotor clearance from the ground is 2.54m - well out of harm's way. The tip caps help reduce noise. The main rotor head is slim for low drag and its elastomeric bearings eliminate the use of mechanical bearings, which also eliminates lubrication.
The A119's single Pratt & Whitney Canada PT6B-37A engine occupies the same space as the A109's two engines, so access is excellent. The turboshaft is capable of providing 750kW (1,000shp) but the main gearbox limit is 670kW (the same as the A109), which means the pilot can rely on full transmission power being available when operating hot, high and heavy. This is comforting to any pilot in such conditions. Agusta says the Koala will hover in and out of ground effect in all temperatures at altitudes similar or higher than any of its competitors.
It was comforting to see the two hydraulic pumps on the main gearbox, powering the flight controls. This is the same system as the A109's. Only one hydraulic supply powers the tail rotor pitch-change system, however, so I made a note to switch this off during my flight to see if I could make an approach to the hover at a selected spot, hover and land. This has not always proved easy in other helicopters. As now usual, the gearbox has a 30min dry run capability.
The nose section is slightly smaller than the A109's, but there is still plenty of room for additional avionics and other equipment, including another electronics compartment at the back. There are wide and high sliding doors on both sides of the cabin to allow easy access for litters, as well as passengers. Although the skids put the aircraft quite high off the ground, passenger access is easy. Head and leg room and seat pitch are ample.
The 0.95m³ (33.5ft³) baggage compartment at the left side of the rear fuselage has a weight limit of 150kg and will take a 1.9m-long load. A removable extension increases this to 2.3m. The door swings open through 170° to admit longer loads. Baggage can also be stored behind the rear seats.
Lo Coco pointed out the offset vertical fin at the end of the tailboom, which helps reduce the amount of tail rotor thrust required. The tail rotor has Teflon-lined pitch-change bearings, which require no lubrication, and, like the main rotorblades, are individually interchangeable.
Comfortable cockpit
Having installed myself in the four-point harness, and adjusted the comfortable seat and pedals to my satisfaction, I liked what I saw. To speed delivery, the first production Koalas, including the aircraft on test, have conventional flight instruments, but the next batch will have an electronic integrated display system (IDS) with liquid crystal displays (LCDs). The conventional instruments were clear and easy to read, however. The instrument panel is small, adding to the excellent all-round visibility. Agusta has provided large chin windows for downwards vision. Our aircraft was well equipped with avionics, but still had plenty of room for more, both in the cockpit and in the airframe.
The engine electronic control (EEC) senses the position and rate of movement of the collective lever to maintain 100% power turbine (NF) speed and so 100% rotor speed (NR). Acceleration rate is controlled, but the EEC allows the engine to go from idle to flight rpm in under a second, an impressive achievement for any engine, especially a gas turbine. If the EEC fails, a governor control ('MEC' mode) will take effect at the last engine setting. If a second failure of the fuel control unit should occur there is a manual backup - hence the twist grip throttle on the end of the collective lever.
Starting was easy - press the starter button, open the throttle at 12% compressor speed (N1) and watch. The pilot can monitor turbine temperature with the throttle if necessary. My first hover was accomplished easily and accurately with little effort. A glance at the instruments told me how much power I was using (72% torque) and how much I had available (100% at maximum continuous, 110% at the 5min take-off rating). We had plenty in hand, a comforting situation at this weight and density altitude.
All the usual hover manoeuvres were benign. I reached 41kt (76km/h) in sideways flight to the right before having to apply full left pedal, at which point the aircraft slowly yawed to the right. To the left was even more impressive - 44.7kt. This was a good demonstration of the amount of tail rotor power available. Backwards flight at 44.7kt produced a steady nose-up attitude with no tendency for the nose to dip.
While still almost at maximum weight, we made the transition into forward flight, levelled out pulling maximum continuous power and awaited results. We got a healthy 142kt indicated airspeed which equates to 149kt true airspeed. This is faster than I have achieved in competing helicopters and above the Agusta- advertised speed. While still heavy, I dived slightly to reach the never-exceed speed (VNE) of 152kt. Vibration levels were benign even with turns in both directions.
Rotor power
The main rotor, although slightly smaller than the A109's, has plenty of power. Rapid rolls to 60° of bank from one direction to the other showed crisp response. Although there is a flight manual limit to the angle of bank, in reality there is no aerodynamic limiting factor. We flew a sustained 60°-banked turn (2g) at 120kt; the g limits are 0.5 to 2.5. The Koala has the same dual-redundant stability augmentation (SAS) system as the A109 - this returns the aircraft to the pilot-selected attitude after any upset - and a three-axis duplex autopilot. The latter is a luxury indeed and helpful at high speed. I flew the aircraft using just the trimswitch on the cyclic to adjust the attitude, which was held accurately.
Vortex ring condition/settling with power is hard to achieve deliberately, Lo Coco said, but we tried. In a near-vertical descent with about 50% torque, the vibration level increased noticeably. But there was still plenty of cyclic, pedal and lever control and we flew out of the condition with no problem. So the warning is there, and it is up to the pilot to recognise it.
I asked Lo Coco to raise and lower the collective lever through a large power range as rapidly as he dare, to check engine response. He did so viciously. Thanks to the anticipator, sensing lever rate, there was little change in NR. The attitude remained constant.
I next asked him to chop the throttle while at high forward speed. The main rotor system is comparatively light, so NR dropped quickly to 88%, but speed is easily regained by lowering the lever (within one second) and, if you wish, flaring. Lo Coco said there is still good control at 80%. Pilots should be aware of the rapid droop, however, and be quick to lower the lever in the event of a sudden engine failure.
We disengaged the autopilot and both SASs so that I could fly the aircraft 'raw'. Unlike some helicopters I have flown, I had no handling difficulties and was able to come to a good controlled hover over the designated area, do spot turns and land without difficulty. Likewise without the number one hydraulic system, which drives tail rotor pitch control. Pedal response was less crisp, but entirely manageable. Failure of the number two system had no effect on aircraft handling or feel.
As with most other Koala systems, the electrics are simple, DC power being supplied by a 200Ah starter generator and battery. AC is an optional extra. We switched off the generator in flight, and the battery continued to supply full electrical power. The resultant warning was adequate.
Next I flew steep and vertical approaches to a spot on the runway. Chin windows and good all-round visibility allowed accurate arrivals.
Reversion to manual engine operation was easy using the well-designed throttle, and the PT6 was easy to control down to the hover and subsequent landing - so easy that I did not bother with a low-level go-around. Unlike in many other helicopters, the manual throttle is connected to the rpm governor so raising the lever automatically increases power and vice versa.
In autorotation, the minimum rate of descent speed of 80kt gave a modest 2,000ft/min (10m/s). Powered recoveries to the hover were easy and safe, given the rapid and comforting engine acceleration, though the flare had to be started early and prolonged to reduce the 80kt to zero ground speed.
The best range speed of 110kt gave us a flatter glide and we went further. The height/-velocity avoid area ("dead man's curve") goes quite high, to 850ft. I asked Lo Coco to hover at 850ft, chop the throttle, enter autorotation and land, engine off. On the way down, we got 80kt and 100% NR at 250ft. The rest of the manoeuvre was a straight-in, engine-off landing.
Pleasant response
The A119 Koala was pleasant and responsive to handle, and quick. Power available from the main and tail rotors and engine should satisfy all pilots. Provision of the LCD-based IDS will enhance the already likeable cockpit. Operators will appreciate the competitive costs, engineers the accessibility and maintainability. Agusta offers to maintain the aircraft, with a choice of three different programmes.
Direct hourly operating cost, including labour and fuel, is calculated by the manufacturer to be $262. Maintenance time is expected to be 1h or less for every flight hour. These figures are a result of a design criterion that as many parts as possible do not to have a retirement life or time between overhauls, but are changed based on their condition.
Passengers will enjoy the comfort, low noise and vibration levels and high speed. Over 20 aircraft have been sold so far to 18 customers worldwide. At $1.8-2 million, the Koala is nearly half the cost of the $3.5 million A109 Power. The choice is: one engine or two?
Source: Flight International
