Peter Gray/SINGAPORE
Eurocopter has brought two completely new turbine helicopters to the market in the past two years: the light single-engined EC120 and the light twin-engined EC135.
Before putting pen to drawing board to design a new light twin, Eurocopter asked operators what they wanted. Later, during development, the company also involved operators, making changes as required. The result, Eurocopter says, is "a quiet, fast, high performance, multi-role aircraft with excellent safety, comfort and manoeuvrability suitable for corporate transport, emergency medical service [EMS], search and rescue, aerial and police work". Operating costs are designed to be low.
Flight International test flew the EC135 at Asian Aerospace at Singapore earlier this year. My pilot for the evaluation flight was Dominique Cappelaere, chief pilot of Samaero, a Eurocopter company in Singapore.
WEIGHTY MATTERS
The day was fine for an evaluation flight with 10kt (20km) of wind and an air temperature of 33°C, giving us a density altitude of 2,700ft (800m). We were at an air show and not at the manufacturer's factory, so we were unable to ballast the aircraft up to maximum weight. With full fuel and Flight International photographer Mark Wagner in the back, we were 230kg (510lb) short of the Category A ground-level and rooftop helipad weight of 2,660kg, and 285kg short of the clear heliport and maximum permissible weight of 2,720kg. The aircraft was fully equipped for instrument flight and had several other optional extras. It weighed in 245kg above the normal basic empty weight.
Category A performance guarantees that, in the event of an engine failure, the aircraft can either land back safely or continue the take-off, climb out and cruise on the remaining engine, all with guaranteed minimum rates of climb.
The basic aircraft empty weight ex-factory, without any extras, is 1,465kg. A full fuel tank, which gives a range of about 665km (360nm), weighs 570kg. This allows seven people with bags, at a combined 98kg each, to be carried within the maximum permissible weight of 2,720kg. According to the flight manual, the EC135 will provide Cat A performance from a raised ground-level or rooftop helipad at sea level at about 16kg below this weight. The weight then starts to reduce with any increase in eight or temperature, but only by 45kg/1,000ft or about 23kg/°C.
In Singapore, on the day I flew, the maximum allowable weight was reduced to 2,670kg - still enough to carry seven people at 93kg each. These are impressive operating weights: rooftop or raised helipad weights are usually a lot less than the maximum permissible.
The allowable operating weights out of a clear heliport are equally impressive. The EC135 will provide Cat A performance at 2,720kg up to 50°C at sea level or up to 9,600ft on a standard day.
The aircraft's maximum permissible weight with an underslung load increases to 2,900kg. The load hook is stressed for 1,360kg, but, in reality, the aircraft will pick up 1,085kg up to 46°C at sea level or up to 9,000ft at international standard atmosphere conditions.
We had another limitation for our flight - altitude. Air traffic control would allow us only 200ft on our transit from Changi to Seletar and 600ft in the Seletar circuit, although it occasionally allowed us to go to 1,000ft.
WIDE INSIDE
Cappelaere showed me round the aircraft. I noted the two wide, sliding passenger doors, which close totally flush. Litters can be loaded easily through these or the two rear clamshell doors. Because of the size of the aircraft, there is plenty of space between the rear doors and the fenestron tailrotor, which allows loading of litters, freight and baggage while the rotors are turning, without endangering the loaders.
Like the EC120, the EC135 has a level floor from the rear compartment to the cockpit. The seats can be removed quickly and easily, and the panel dividing the cabin from the rear bay removed in seconds to provide a voluminous storage area - the cabin offers 3.3m² (35.5ft²) of floor space and 3.8m3 (134ft3) of volume, while the baggage compartment has 1.2m² and 1.1m³, respectively. The large cabin allows up to six passengers to sit in comfort and the interior to be comprehensively outfitted for EMS work.
Having opened the rear clamshell doors to show the large baggage area, Cappelaere lowered the large hinged avionics tray from above - a neat use of space, giving excellent accessibility to equipment which is often difficult to reach.
To overcome the noise and less desirable characteristics of earlier fenestron tail rotors, Eurocopter has slowed the fan down, redistributed its 10 blades and added stators. The fan is enclosed in the vertical fin, protecting people who might get too close and preventing damage should the pilot hit an obstruction. The noise level of the main rotor has also been addressed.
There are built-in steps and handgrips to allow access to the main rotor head. The bearingless rigid main rotor system requires little maintenance, has few moving parts and provides long life and low drag. Because of its rigidity, the rotor can be started and stopped in high winds with no blade sailing - a phenomenon when blades can flex so low as to hit the fuselage.
The rotor blades are composite. Indeed, much of the fuselage is composite and crashworthy. Cappelaere pointed out the fuel system, which is also designed to withstand an impact, while the tanks are divided into two sections to allow the level floor.
We installed the 1.86m-tall Wagner in the back. The floor is quite high because of the tall skid gear, but there is a boarding step which runs the length of the skids, making access easy. The passenger seats are crash resistant and have shoulder harnesses with an automatic locking system. The seats have headrests to protect the neck from whiplash injuries.
Cappelaere offered me the right-hand captain's seat. Stepping up and getting in was fairly easy, although a grab handle would be useful. Despite there being only fore and aft adjustment on the seat and pedals and no up and down movement of the seat, I was able to find a comfortable flying position - this proved to be important when I tried my first hover. I could reach everything easily. The seat has a headrest, four-point harness with an automatic locking system and is crash resistant.
In front of me was the T-shaped instrument panel. There is a choice of electromechanical flight instruments or an all-glass cockpit. In the middle of the panel, visible to both pilots, is the cockpit display system (CDS), digitally presenting torque, engine parameters, electrics, air temperature, fuel quantity, engine cycles and the advisory and caution system and engine failure troubleshooting information.
I was slightly disappointed to see that the CDS gives contents in each fuel tank, but not the total - you have to add this up yourself. There is a switch on the panel for scrolling through the display pages and another on the stick to reset the display.
The advisory, caution and warning system is smart - in the case of more than one event, it prioritises the most important and stores in memory those items it has no room to present immediately. Audio and visual warnings are used to attract the pilot's attention to the most significant potential problems, such as low rotor RPM, entry into transient power conditions and engine fire (a fire bell rings).
There are two engines available - the Pratt & Whitney Canada PW206B and Turboméca Arrius 2B1 - each providing almost the same amount of power, but with slightly different characteristics. For example, while the maximum contingency 2min 30s single-engine power of the Arrius is 560kW (750shp), that of the PW206B is 546kW. The Arrius will give a slightly higher recommended cruising speed of 126kt, compared to 122kt for the P&WC-powered helicopter, but the EC135 will hover at slightly higher altitudes with the PW206B and has a higher single-engine ceiling and longer endurance, albeit at lower Cat A weights.
IMPRESSIVE HOVERS
The twin-engine and single-engine hover heights, both in and out of ground effect, are impressive. This is due to the use of lightweight, but powerful yet efficient engines and high performance rotor blades. The engines are capable of providing much more power than the aircraft needs and more than the limits of the main gearbox. This gives the pilot the luxury of operating an aircraft that maintains good performance when hot, high and heavy, and has power in hand for any contingency (there are generous transient limits - all recorded and indicated to the pilot at the time). All this is achieved using a modest 170kg/h of fuel.
I am told that the gearbox power limits will be increased eventually, allowing even better performance. The maximum permissible weight is also likely to increase by 100kg, to 2,820kg.
There is a wide choice of instrumentation from just the basics to a single-pilot instrument set-up, including additional radios, twin VOR/ILS, ADF, transponder, DME, standby horizon, second altimeter, duplex autopilot, moving map display and weather radar. There is plenty of room for these extras. It is refreshing to see that there is room in the cockpit to store manuals, instrument plates and other equipment which pilots like to carry - but there is no space for a clipboard to hold an instrument approach chart.
Even though our aircraft was loaded with equipment for single-pilot instrument flying, the presentations were uncluttered and easy to interpret. There are no space-consuming temperature and pressure gauges - the CDS monitors these and advises of any approaching exceedance. There are switches on the overhead panel, which I did not find so easy to read, but this is inevitable in an aircraft of this size. The outside visibility, both around and down looked good. I was to explore this further when I did some steep approaches and hovering at 100ft.
READY TO START
After cockpit familiarisation from Cappelaere, I was ready for my first engine start. There are several methods, depending on how quickly or slowly you want to go - both engines to idle or to flight or individually to idle or flight. The full-authority digital engine controls (FADECs), after running through a self-test programme, will allow any of these. I elected to start one engine to ground idle and the other to flight. I selected ground idle on the front panel switch and sat back to watch the slow, cool start. I then selected flight on the same switch and selected flight on the other engine while my hand was there.
The CDS automatically converted its presentation to flight mode and showed us that everything was in order. There was nothing else to do; even the automatic flight control/stabilisation system was already on and tested.
Cappelaere kindly warned me that, because of the rigidity of the main rotor head, the cyclic stick is more sensitive than on the average helicopter. He was right and I came to a wobbly hover, although I held my position over the same spot. It took me several minutes to learn to relax on the cyclic and not move it - and the helicopter - about so much. I could see easily from the instrumentation how much power we were using and how much we had available. At our modest weight, we had plenty in hand.
Hover taxiing to the exhibition's take-off point was straightforward, with much less tendency for my self-induced wobble once forward speed was achieved.
We departed for Seletar and levelled out at 200ft. While we were still fairly heavy, I selected maximum continuous power (the 69% torque was easy to interpret) and sat back watching the speed build up. The choppy air at this low level in the heat of the afternoon made a steady speed impossible, but we achieved about 140kt indicated airspeed, which at the density altitude gave us a true airspeed of nearly 145kt. So the aircraft is as fast as advertised.
The sunlight was bright, so I turned downsun, putting it directly on to the instrument panel. All the presentations were still easy to see.
Pre-landing checks involved merely checking the CDS. My first approach to the hover square at Seletar was easy, the excellent visibility, particularly down, making it even easier.
Fast sideways and backwards flight was benign, requiring little input from me once the groundspeed had stabilised. Even at an estimated 30kt there was an adequate amount of pedal remaining and no tendency for the rotor to flap forward in fast backwards flight. Spot turns proved that there is plenty of tailrotor power available. Unlike other helicopters, which have headings where hovering becomes even more difficult because of wind direction, this aircraft is vice free up to 7,000ft and 30kt of wind, I am told.
During the transition to the climb, Cappelaere selected idle on one engine at 40kt. There was no rotor droop. I continued our acceleration to the best rate of climb speed of 65kt, which we achieved easily, and adjusted the power, climbing all the way. We had a healthy single engine rate of climb. We came round to finals and, after a flat approach, keeping some speed in hand, we achieved a single engine hover 4ft over the H.
We next tried another transition and, at a much lower speed, Cappelaere "failed" an engine, I flared to adjust my touchdown speed and we did a slow running landing on to the grass, Cappelaere calling out the torque - we used nowhere near the maximum.
Our Vne was 150kt (this holds good up to 2,000ft at maximum gross weight), so we climbed to 1,000ft, selected maximum continuous engine power, then, as the speed built up to 140kt, lowered the nose. This is always a testing manoeuvre for any helicopter. Any tendency to vibrate excessively or suddenly increase noise will be revealed at Vne, as will any tendency to be affected by retreating blade stall or compressibility effects on the advancing blade tips. The EC135 was quite docile in all respects at this high speed, with some turns thrown in. The low level of vibration is due to Eurocopter's Anti-Resonance Isolation System. The EC135 was quite benign in 85-90í banked turns through 360í. Visibility into the turn was excellent through the overhead panel.
To test the effectiveness of the FADEC in the cruise, I raised and lowered the collective lever rapidly through large power ranges. The FADEC stayed with me - rotor RPM varied by no more than 2%, there was no pitch up or down of the aircraft's attitude and the engine acceleration as I quickly raised the lever was almost like that of a piston powerplant.
I removed my headset to check the noise level. Both cockpit door windows were open (Cappelaere had experienced trouble keeping the air conditioning system on line) so the noise level was quite high. Closing them reduced it to comfortable levels.
WARNING SIGNS
The well written flight manual lucidly describes the 90 advisory, caution and warning signals and the immediate actions that some warnings require (140 over the whole range of malfunctions) so it is best to carry it at all times. Good initial training and subsequent recurrency testing will be required.
We tried just a few malfunctions. Cappelaere switched off a generator. The CDS immediately informed us and we studied the electrical system to confirm what had happened. The remaining generator and battery were quite capable of providing all the required electrical power. This is part of Eurocopter's design philosophy of providing redundancy of all the important systems, thus ensuring a safe aircraft - important if you are single pilot flying in instrument conditions. Similarly, there are two hydraulic systems and a redundant main gearbox lubrication system.
I reset the generator and it came back on line. An engine fire will produce a continuous gong and a red light illuminates the overhead fire button. You lift the protective cage and press it. This cuts the fuel to the engine and fires the extinguisher bottle. There can be no confusion and the wrong engine shut down in this aircraft as has happened, tragically, in other twins.
Cappelaere then removed all the stabilisation and I flew the aircraft raw. There was hardly any difference in feel and, for once, I did not go into a self-induced oscillation. It was necessary, of course, to fly the aircraft with more concentration to prevent it wandering off on its own, but this small extra workload would not cause a problem if a single pilot had to fly it like this over long distance. A hydraulic failure causes no difference in handling quality, I am told. The fenestron tail rotor has a cable operated pitch-change mechanism.
Seletar ATC allowed us to go to 1,000ft again, for an autorotation. We came down at the minimum rate of descent speed of 75kt, which gave us a modest 1,700ft/min (8.6m/s). I kept a wary eye on the rotor RPM, which tended to be skittish, but its control with small movements of the lever was good. I did a powered recovery at the bottom. I could feel the flare bite, slowing our rate of descent, building up the rotor RPM momentarily and giving me time to level ready for the landing. I raised the lever, bringing back the power, and the engines quickly accelerated and held us in the hover. There was plenty of pedal in hand throughout.
I flew a steep approach and, as expected, downward visibility was excellent - I had no trouble arriving exactly over the H. Similarly, an approach to 100ft and subsequent hover at this height was trouble free because of all the visual cues available. I was able to descend accurately over the H from 100ft and land - my first landing. I went vertically back up to 100ft, my position over the H staying constant.
The change-over to manual throttle on one of the engines was easy, bearing in mind that the aircraft is approved for single pilot instrument conditions. I reached up and selected manual on the engine management panel. As instructed, I selected 25% torque and left it there throughout the circuit, approach and landing. The other engine did most of the work and all the RPM governing. To prevent a possible overspeed when lowering the lever fully to land, the engine is cut at this point.
There was no slope to land on, but Cappelaere assured me that the aircraft will cope with an impressive 14° sideways on and 12° upslope.
I used the intercom system to talk to our photographer in the back. He had tried all the seats and found enough head and leg room. Noise levels were acceptable and visibility good. He found, like me, that, after 1h 40min, the seat cushions are excessively hard - a great shame with an otherwise excellent helicopter.
Easy to operate
Eurocopter has designed the EC135 to be easy and cost effective to operate. The 50h inspection is composed of three simple checks which can be done by the pilot. The next inspection (100h) incorporates two additional items which, too, can be done by the pilot. These inspections continue to the 400h check, which is done by a technician and takes two days.
The consortium has ensured that the usual sources of excessive noise in helicopters, the main and tail rotors, have been addressed. An independent survey puts the flyover noise level at 6-8dB below the US Federal Aviation Administration's maximum allowable limits.
Several factors have contributed to the production of a safe aircraft: redundancy of the important systems, crashworthiness of all the seats, the fuel system and fuselage; the ease of operation and interpretation of the systems and displays, particularly for a single pilot instrument flying operation; the enclosed fenestron and rigid, high-set main rotor.
Last year, Eurocopter signed orders for 58 EC135s and its backlog includes more than 100 machines bought by customers in 17 nations. The production rate is to increase to 50 aircraft a year, up from the 20 initially planned.
Source: Flight International
