A casual observer might think that the EC155B is just a stretched development of the AS365 Dauphin. Not so, says Eurocopter, although the manufacturer did incorporate some features from its experimental AS365X High Speed Dauphin, such as five high-inertia main rotor blades and a quieter, more efficient fenestron-type tailrotor.
The EC155 is faster than the latest Dauphin, has a much bigger cabin, an exceptionally large baggage bay (ideal for offshore operations) and new-technology main rotor head, cockpit and digital engine controls. The medium twin-turbine helicopter is primarily aimed at the corporate, offshore and police and emergency medical service markets. Emphasis is on passenger comfort in terms of space available, low vibration levels (especially at high speed), low noise and long range. Eurocopter's other aim was to reduce pilot workload, with a simple cockpit layout and operating procedures. The 12/14-passenger EC155 competes against the Bell 412 and Sikorsky S-76.
Flight International evaluated the aircraft at Eurocopter's Marignane plant in southern France. I spent the previous evening reading the flight manual and getting to grips with a new vocabulary filled with terms such as central panel display system (CPDS), vehicle and engine management display (VEMD), caution and advisory display (CAD), attitude and heading reference system (AHRS), flight control display system (FCDS) and primary flight display (PFD).
Our aircraft had test equipment on board (there are still flight trials to be done), but did have some passenger seats which I tried for comfort, headroom and visibility. The helicopter was equipped for single-pilot instrument flight rules (IFR) operations. The EC155 is presently certified by the French DGAC civil aviation authority and US Federal Aviation Administration. European Joint Aviation Authorities approval will take longer, says Eurocopter. Public transport Category A clearance will be achieved when required by a customer, the manufacturer says.
Limits indicated
A feature of the instrument panel is the first limitation indicator (FLI). This monitors torque, turbine outlet temperature (TOT) and engine compressor speed (N1) and compares them with maximum values relative to the aircraft's altitude and outside air temperature. A single needle against a single scale shows the pilot, at a glance, exactly how much power is being used and how much is in hand - a simple, but valuable presentation. The scale changes colour as the various ranges/limits are reached and a gong will sound when approaching any maxima. In the event of an engine failure, the presentation will automatically revert to the single engine display. There is also a digital presentation of torque, TOT and N1 for each engine on the same display. When one of the limits is reached, the corresponding digital readout is underlined.
The FLI is located on the Sextant-developed CPDS with displays of the fuel system, temperatures and pressures, in the form of colour-coded pointers with some digital presentations. Above is the caution and advisory panel. Some warnings, such as undercarriage up, low/high rotor RPM and engine failure, are accompanied by an aural warning. An engine fire will illuminate red lights in the fire panel on the affected engine side and on the appropriate fuel shut-off lever, so there is little chance of shutting down the wrong engine. A red master caution light also alerts the crew to the more serious malfunctions. Ten hard keys down the side of the liquid-crystal display (LCD) CPDS allow the pilot to select an enormous amount of additional information.
Two LCD screens directly in front of each pilot present all the flight and navigation parameters that the pilot needs, so his instrument scan is limited to just these two panels when performing, say, an instrument approach. The two screens are uncluttered and user friendly. There are the usual mechanical get-home instruments of airspeed indicator, altimeter and standby compass should the electronic displays fail.
The weather for our flight was good, with a light wind and 11°C outside air temperature. Eurocopter test pilot Didier Guerin showed me a typical pilot's pre-flight inspection. Access to all important components and fluid levels is good.
The EC155 has a low-maintenance, low-drag, low-noise main rotor with five distinctively shaped glassfibre and carbonfibre reinforced plastic blades. On the ground, the rotor tip at its lowest point is well out of harm's way. You would have to be exceedingly careless to stumble inadvertently into the shrouded tail rotor. Eurocopter's latest fenestron design features 10 offset blades, which make it quieter than its predecessors.
The baggage compartment, accessible from both sides, holds an impressive 2.5m³ (88ft³) compared with the S-76's 1.1m³ and the 412's 0.8m³. A wide sliding door and steps on both sides give good access to the big cabin, which has a usable volume of 6.7m³ compared with the 412's 6.2m³ and the S-76's 5.8m³. As in the S-76, the occupants of the EC155's four front seats use the wide pilots' doors, but there is a good gap between the passenger and pilots' seats for easy access and disembarkation. My 1.8m (6ft 1in)-plus pilot sat in one of the rear seats, where there is less headroom due to the rising floor, but he had plenty of space between his head and the roof. His legs were only just clear of the seat in front, however. Taller passengers would be better off in one of the front seats.
Noise levels will depend on the interior fit, but can be at low as 75dB. With the utility interior, the EC155 is one of the few helicopters that can take a full load of 13 passengers and full fuel. Because of the aircraft's high cruise speed of 143kt (264km/h) - which is even higher at altitude (155-160kt at 8,000ft (2,440m)) - efficient Turboméca Arriel 2C1 engines give the EC155 a range of 830km (450nm) with no reserves. The S-76 and EC155, both Arriel-powered, use about 1kg (2.2lb) of fuel for every 1km travelled at their best cruise speed. The Pratt & Whitney Canada PT6-powered 412 uses about 1.4kg/km.
On a standard day at its maximum weight of 4,800kg, the EC155's single-engined rate of climb is only about 150ft/min (0.76m/s), which is right on the minimum for Cat A certification, so Eurocopter is considering reducing the maximum operating weight for Cat A. Given the extra weight of a corporate or North Sea-equipped aircraft, this will erode the useful payload considerably.
Everything in reach
Getting into the right-hand pilot's seat was easy, thanks to the step and wide door. After attaching the four-point harness and adjusting seat and pedals, I looked around and liked what I saw - a neat, ergonomically pleasing cockpit with everything within easy reach. There was a large pilot input to the design of the cockpit and Eurocopter has reduced the complexities of the helicopter to simple but effective presentations, operating mechanisms and techniques. There is no need to use a checklist for start-up, pre-take-off or any of the other checks. A simple flow pattern around the overhead panel, centre console and instrument panel will suffice. The warning system will alert the pilot if anything is awry.
Engine and rotor start are controlled by the full-authority digital engine control (FADEC), so are fuss-free, well controlled and automatic. We had planned to start 20kg over the EC155's 4,800kg maximum take-off weight, but a third occupant had to drop out so we began the flight at 4,780kg.
Eurocopter had put up a second helicopter for air-to-air photography, so we proceeded to a photogenic area by a white aqueduct. We came to a hover, using only maximum continuous power. I saw from the FLI that we were torque-limited. The aircraft was trimmed (we were hovering with 10í of bank) and the controls released to allow the autopilot to do its stuff - which it did perfectly well. This autopilot is more accurate and effective than its predecessors. The production version will have four axes, which will give autohover, coupled instrument approach and go-around capability.
With 2.5 axes, our autopilot was capable of a hands-off autohover in a steady or no wind situation and could certainly hold the attitude and heading constant even when following an imaginary car doing 10kt along the runway. The autopilot knows the aircraft attitude and control positions at any given time and will warn the pilot if he attempts to fly through any set datum, such as an altitude hold or the never-exceed speed (VNE) for that weight and altitude. The beeper on the cyclic stick can be used to reset the datum in pitch and roll. There is a back-up stability augmentation system.
While still in a heavy hover, some pedal turns were introduced. Right pedal caused the power required to increase into the take-off band. I heard a single gong announcing this.
Healthy airspeed
After the photographic session we went to Eurocopter's satellite airfield for hover, circuit and other evaluations. On the way, I selected maximum continuous power and, at 4,300ft (1,300m), recorded a healthy 145kt indicated airspeed (IAS), which equates to 154kt true airspeed (TAS). Lower down, at 1,000ft, we achieved 149kt IAS, 150kt TAS. We were 200kg below maximum weight. While still heavy, we went to the VNE, now reduced by 5kt to 170kt because of our altitude (the EC155 will maintain a 175kt VNE up to nearly 3,000ft). Guerin deliberately exceeded 170kt by 5kt to demonstrate the warning system: the top arc of the airspeed indicator reverted to red. Vibration levels at this speed were benign; I could detect very little increase even when Guerin banked left and right.
On the way down, a lower altitude hold was selected on the autopilot and the controls released. The aircraft slowed down and levelled off, the altitude hold indicator going from amber to green.
The main rotor is not a rigid system, which can cause pilot induced oscillations, but fully articulated - so, as I expected, my first take-off to the hover was rock steady. I could easily and quickly see how much power we were using and how much we had in hand. I did not have to memorise any numbers for this, but merely glance at the FLI. Out-of-wind hovering, landing and take-off were all benign, requiring little skill from the pilot. Guerin allowed me to take the aircraft to 35-40kt in sideways and backwards flight. I could detect no unpleasant characteristics. After my own spot turns at modest speeds, I handed over to Guerin. We went round very quickly, our rate of turn limited only, at this high aircraft weight, by engine power. There are no nasty wind segments to avoid or be aware of. Guerin showed me a quick lift-off to the hover, hauling quickly up on the collective lever. We momentarily lost a little rotor speed (NR), but RPM stayed well within limits.
While in high-speed cruise, Guerin simulated an engine failure using the FADEC's training mode. This puts the helicopter on one engine, but holds the other engine idling just below the governed range, ready to come in. Due to the rotor's high inertia, NR reduced slowly. I heard the audio warning and lowered the lever gently until it stopped. There was no need to look at the NR gauge. The 30s single-engine power rating was automatically selected and a small clock-like presentation on the VEMD panel started to count down and the FLI display showed HI.
Altitude and heading mode were selected on the autopilot to allow it to fly the aircraft while I sorted out the problem. After 30s, I pressed one of two buttons under the head of the collective lever and engine power reduced to the 2min rating. Again I heard the NR warning, and again I lowered the lever a fraction until it stopped. Another countdown began and the FLI display showed LO. After 2min, I selected maximum continuous - using a different button designed to avoid pilot confusion. The result was another audio warning and another slight lowering of the lever. A true single-engined cruise speed at our weight of 4,630kg was a healthy 110kt.
While still fairly heavy, I did a slow, gentle single-engined run-on landing. Again, no extra pilot skills were required to land on my selected target or perform the landing. At Cat A weights, Guerin says, single-engined go-arounds are more difficult because of the rotor design and high inertia. Control of an exact climbing airspeed is not so critical, however, because of the flat shape of the power-required curve between 60kt and 80kt.
Because of the high reliability of the FADECs (a failure rate of one in a billion) there are no manual engine throttles, making single-pilot IFR even easier.
Steep turns were smooth and accurate - there is no need to use one's feet during turns. The door pillar is slightly intrusive; I had to move my head to see around it during the turn. The autopilot held us in a sustained 45° turn. We went to a sustained 60°. If non-sustained, there is no limit to the angle of bank.
Guerin did his best, at my request, to enter the condition of vortex ring or settling with power, where sections of the main rotor approach or enter a stall. This condition can catch out even experienced pilots, so some sort of warning is desirable. Guerin reduced our airspeed to nearly zero and allowed the aircraft to descend with quite a lot of applied lever - the exact conditions for vortex ring.
The EC155 waffled and vibrated slightly and we saw the rate of descent increase. In some helicopters, raising the collective lever at this point in a bid to contain the increasing rate of descent will cause the whole rotor to stall and the pilot to lose control while the rate of descent will increase alarmingly. It says much for the EC155's rotor system that, when Guerin raised the lever, the rate of descent stopped immediately and the helicopter recovered from the vortex ring condition. This is a commendable safety feature.
Brutal treatment
To check the quality of engine governing, I asked Guerin to raise and lower the collective lever as quickly as he dared. He went from autorotation to maximum continuous power and back, brutally. I felt the negative g as he lowered the lever. Rotor speed decreased and increased slightly, but stayed well within RPM limits - nothing to bring on the audio warning.
We explored single and double generator failures. A single failure brought on the appropriate warnings, but no services were lost. Non-essential services are dropped automatically after a double failure, but the pilot can override this if required and reselect or deselect systems at will. Double generator failures can be a nightmare in some helicopters, when a single pilot is flying in bad weather, but not in the EC155.
Raw flying
I flew the aircraft raw (no stability augmentation or autopilot), a condition which should never happen, says Guerin. I had no difficulty, thanks again to the fully articulated rotor system and other good aerodynamic qualities. There was no point in turning off the hydraulics to simulate a failure since there is so much redundancy that there is no difference in handling qualities with the loss of one system.
A failure of the tailrotor drive is more benign than in some other helicopters since the large, offset, vertical fin provides considerable anti-torque reaction at forward speed. The technique is to find the combination of forward speed and power that will keep the aircraft pointing straight ahead for the touchdown, which Guerin did at modest speed. I would, however, like to see a more comprehensive description in the flight manual of the various possible tailrotor failures.
Our rate of descent in an 80kt autorotation was 2,700ft/min, increasing to 4,800ft/min at zero airspeed. The flare at the bottom to the hover was uneventful, with the FADECs bringing in the engines rapidly.
Eurocopter assures me that hovering hot, high and on the weight limit still leaves pilots with plenty of tailrotor power available and that they are limited only by engine power available.
As we positioned for our approach and landing at Marseilles' international airport, Guerin did several 90°-banked turns to meet air traffic controllers' requirements, then showed me a sustained constant speed, constant rate of descent approach, the regime producing the worst vibration levels. But they were benign and hardly noticeable, unlike in some other helicopters which can make your teeth chatter.
After shutdown, Guerin interrogated the CPDS and obtained our flight time, number of cycles, engine power check results, details of any equipment failures and the cumulative time of any overlimit parameters.
The flight proved to me the EC155's design features of passenger comfort and pilot friendliness. Neighbours will appreciate its low noise signature. A pilot unused to a glass cockpit will require about 5-6h to be fully competent using the Sextant-developed system. Operators and customers will also appreciate the helicopter's built-in safety features, high speed and useful range - although at Category A weights with an offshore or corporate configuration, useful payload may be reduced significantly.
Lower costs
Eurocopter says the EC155's operating costs will be lower than those of its competitors, the helicopter probably requiring not more than 1h of maintenance per hour of flight time. So far, the manufacturer says, over 20 aircraft have been sold to police forces and corporations.
Source: Flight International