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Light flier

Peter Gray/SINGAPORE

With so many other light helicopters on the market, it was going to be interesting to evaluate the five-seat EC120B Colibri, the new multipurpose machine from Eurocopter and its Chinese and Singaporean partners.

The aim of my evaluation, which follows Flight International's technical description, was to see if the aircraft met the manufacturer's claims of high power availability, low noise, safety, comfort, ease of maintenance and multirole capability.

Low vibration levels, coupled with low fuel consumption and low direct operating costs are also at the heart of the requirements for a modern helicopter.

The EC120 was developed in answer to a perceived need for a new light helicopter that market studies indicated should to be available by 1997. Talks with China's CATIC/HAMC and Singapore Technologies began in April 1992, with full programme launch the following January. The maiden flight took place in April 1995, with European certification awarded at the end of 1997.

CATIC/HAMC has 24% of the programme, and is responsible for the design and production of the entire cabin structure and fuel system, while Singapore Technologies, with 15%, produces the access doors, tail boom and the composite material for the Fenestron tail rotor. Eurocopter is the technical leader of the programme, in charge of overall design, ground tests and production of the dynamic assemblies, installation of avionics, hydraulics and electrical system, and final assembly.

Weather conditions for the flight evaluation at Singapore's Changi Airport were good - wind 10-15kt (18-28km/h), air temperature 33°C, giving us a density altitude at ground level of 2,100ft (640m). Unfortunately, we were severely restricted in height by the air traffic control requirement for a journey from Changi to Seletar at 200ft, and a 600ft limit in the Seletar circuit. We were allowed occasionally to 1,000ft, however.

 

 

 

 

 

 

 

 

 

 

 

 

FLIGHT PREPARATIONS

Our prototype was fitted with all the telemetry equipment, which, with full fuel and Mark Wagner, Flight International's photographer, sitting in the back, brought the all-up weight before engine start to a convenient 1,700kg, 18kg over the maximum allowable. Our pilot was Didier Delsalle, a Eurocopter test pilot.

Delsalle's walkaround pre-flight inspection was straightforward. Access to the modern main rotor head was possible using footholds up the side of the cabin. We checked the main rotor blades. Access to all the oil levels was good - there was no need for torches and squinting. The effort to reduce drag was obvious throughout, even the door handles and sliding door mechanism have been designed to be flush with the cabin. The main rotor blades are well out of reach of tall passengers, even those standing on tip-toe and reaching up.

Moreover, they are fairly rigid, so are unlikely to flap down to a dangerous degree. This also allows the rotor to be started safely in 55kt winds, a comforting thought. From another safety point of view, it would be hard for the enclosed Fenestron tail rotor to harm anyone or hit anything.

Delsalle showed me the voluminous baggage compartment. I judged that there would be no problem carrying five large suitcases here - a great improvement on many other similarly sized aircraft. With this capability in mind, I did the following calculation to see how much weight the aircraft can carry:

Aircraft empty 895kg

Five people on board 410kg

Full fuel 325kg

Total 1630kg

This leaves just over 50kg for those five suitcases. So at last we have a light helicopter where you can fill all the seats, take full fuel and still have a useful amount left over for baggage.

This led me on to my next calculation: at this maximum weight, at what height and temperature will the aircraft do a 5ft hover? A quick look at the prototype flight manual showed that at sea level (zero pressure altitude) the EC120 will hover at a maximum air temperature of 49°C. Or, at 33°C, our actual temperature in Singapore, it will hover up to a height of 3,500ft. For those operators requiring an outside of ground effect (OGE) hover, this aircraft will do so at 42°C at sea level and go on to 2,000ft at 33°C.

An extra 90kg can be lifted for external operations. At this higher maximum take-off weight, the aircraft will hover OGE at sea level up to 36°C and up to nearly 1,000ft at 33°C. The underslung load hook is stressed for 700kg. The EC120 will lift this load with just over an hour's fuel (no reserves).

These are all impressive figures and are the result of an efficient main rotor and the small, light 375kW (505shp) Turboméca Arrius 2F engine combined with a low basic aircraft weight through careful design and the use of composites in many areas. The engine is slightly derated so it holds its performance up to altitude. For example, on an international standard day, an in ground effect hover (IGE) at maximum weight is possible up to 10,000ft, and an OGE hover up to 8,500ft.

 

 

 

 

 

 

 

 

GETTING STARTED

I installed our 1.85m-tall photographer in the back. The aircraft is on high skids, making the cabin floor quite high, but there is a convenient step running along the length of the skids. He tried all three seats and had ample head and legroom in all. With no centre pedestal, as there is in most other helicopters, his visibility was excellent. All seats come with a shoulder harness.

I installed myself in the comfortable right hand captain's seat and found a position to my liking by moving it, and the adjustable pedals, fore and aft. The four-point harness is an added safety feature. I looked around and liked what I saw - a very uncluttered instrument panel - mostly because so much information is neatly displayed or available on the quaintly named "vehicle and engine multi-function display" (VEMD). This unique piece of equipment computes and displays the main aircraft and engine parameters, such as which limit comes first of the T4, Ng or torque. It also displays fuel contents, ambient air temperature and some other parameters such as engine oil temperature and pressure, generator output, battery temperature and, most usefully IGE and OGE performance. This is most helpful when operating in hot, high and heavy conditions where so many accidents occur because the pilot exceeds the limits.

The remaining instruments are small but easily readable. Visibility is good, particularly forward and down, as I was to explore further when doing steep and vertical approaches and take-offs. For external load, vertical-reference enthusiasts, the view out down to the load on the long-line and around is satisfactory. Bearing in mind that the aircraft, too, is multi-functional, there is plenty of room for manuals, other documents and the rest of the paraphernalia that all pilots carry.

 

 

 

 

 

 

 

 

 

 

 

Similarly, there is plenty of room to install optional extra equipment, for example a radar altimeter, transponder, GPS, VOR, fuel flowmeter, DME, enhanced stability augmentation system or standby attitude indicator.

The collective pitch lever and cyclic pitch stick are equipped with the necessary switches and other controls to operate all the important systems, so avoiding the need to remove one's hands from the controls. These included a scroll button for the VEMD, windscreen wiper control and radio frequency change switch.

I closed the large door, held open by a gas strut, and prepared for start-up. Upon switching on the battery, the VEMD self tests and soon shows us that everything is serviceable and that we have full fuel. The system will not allow starter engagement if the rotor brake is on.

The smart VEMD displays the parameters we need for the semi-automatic engine start. The engine accelerates quite quickly, with a moderate turbine temperature peak. At 60% compressor speed, the VEMD changes to flight mode, presenting the first limitation indicator.

HOVER MANOEUVRES

The pull up to my first hover was straightforward, requiring few control inputs to achieve an accurate hover once established. While we were at maximum weight, I checked how much power we were using - 86% torque with plenty of power in hand. The turbine temperature and Ng were also well below full power limits. I liked the presentation of these parameters on the VEMD - they are easy to interpret. Visibility was excellent.

Sideways flight to the left and right up to the maximum of 30kt gave no problems, with plenty of pedal remaining available. Once up to speed, the aircraft required very little further control inputs from the pilot. The same was true of backwards flight at 30kt. Manufacturers of modern helicopters have eliminated the often sudden and severe flap forward of the main rotor disc, even at moderate speeds, that earlier helicopters produce, leaving you with the nose hard down and a lot of rearwards cyclic - usually when close to the ground.

An identical situation can occur when taxiing at slow speed in a strong downwind, so it is comforting that this will not occur in the EC120 and surprise the pilot.

ROTATION SPEEDS

Only your need for comfort limits the speed of rotation of turns on the spot. After my sedate efforts in both directions, during which I experienced no unusual phenomena, I handed over control to Delsalle. He put in a huge bootful of pedal and we hurtled round, the outside world becoming almost a blur. I could feel the sideways g force on my harness - and again, when we spun in the other direction. This demonstrates the power available from the Fenestron - unlike some earlier versions which have limited power in this manoeuvre.

While we had 10-15kt of wind, I held the aircraft in the hover with the wind from the right, then downwind, then from the left. The EC120 was well behaved and pilot workload low.

We climbed out of Changi and set course for Seletar at 200ft. While the aircraft was still heavy, I pulled maximum continuous power, which gave us 123kt (230km/h) indicated airspeed, just as advertised in the brochure. This is probably better than specification performance since we were at a density altitude of 2,300ft giving us a true airspeed of 127kt. I maintained balanced flight by referring to the high technology string on the outside of the windscreen, keeping it in a vertical position - simple, but effective.

I asked Delsalle to switch off the generator - the subsequent visual warning on the VEMD was good. All the electrical systems are DC, thus saving the weight and complexity of dual AC and DC systems.

The sun was shining brightly so we turned until it was on the instrument panel. Readability of the flat-panel VEMD and all the other instruments was still good. There is no need to memorise temperature, pressure and other limitations - all of those are clearly defined in the presentations and warning given for any exceedance.

We joined the busy circuit at Seletar. Pre-landing checks consist of merely checking the VEMD. This takes a few seconds. A normal approach on to the "H" was straightforward, the visibility again being excellent. My next manoeuvre was a very steep approach. Because of the good visibility, especially forward and down, I was able to finish up in the hover exactly over the "H" marking the landing spot. There was plenty of power in hand, although we were still heavy.

The next approach was to a hover 100ft over the "H". Again, I experienced no difficulties and used less than maximum continuous power for the OGE hover. At this point, I elected to carry out a vertical descent, bearing in mind that this is when vortex ring/settling with power can strike. This is an aerodynamic condition that can occur when in a powered descent in excess of 300-400ft/min (1.5-2m/s) with little or no airspeed. A fully developed vortex ring can lead to loss of control and is similar to stalling a fixed wing aircraft on final approach. Delsalle assured me, however, that the EC120 is not very prone to the condition even when in, full cyclic control is retained. So down we came, but slowly, and landed on the H.

We got clearance to climb to 1,000ft, from where we were to accelerate to the never-exceed speed (Vne) of 147kt - the maximum at lower altitudes is 150kt. Achieving Vne required a lot of power and a steep dive. Once there, the vibration levels were benign and handling was good. Steepish turns produced no significant handling, noise or vibration differences.

While ATC was still willing to allow us to 1,000ft, and after a demonstration by Delsalle, I carried out an autorotation. Unfortunately, for various reasons in this prototype, we were not allowed to do them to the ground, so we restored power at the end of the flare and came to the hover.

As expected, because of our high weight and density altitude, the rotor RPM wanted to exceed the maximum limit once established in autorotation, so one had to be vigilant and ready to anticipate this by raising the lever accordingly. I was too slow and we had a slight exceedance. The system warned us accordingly with an intermittent aural warning and the rpm indication changing to red. The aural warning sounds continuously for low rotor rpm, for example, and is heard intermittently for other events, such as exceeding maximum continuous or take-off power limits. The relevant instrument indication will change to yellow or flashing red. Fortunately, we were still within the generous rotor overspeed limits, which only test pilots are allowed to explore. The minimum rate of descent speed of 65kt gave us 1,500ft/min - very modest for our weight and density altitude. The flare at the bottom had bite and had the effect of increasing our rotor rpm, with enough time and extra lift to stay in the flare to reduce the touchdown speed to whatever is required and give us plenty of collective pitch to cushion a landing. The powered recovery to the hover is straightforward - the Arrius was very responsive with rapid acceleration. As expected after our vigorous spot turns earlier, there was plenty of tail rotor power and control available.

 

 

 

 

 

 

 

 

PITCH CONTROL PROCEDURE

Pitch control of the Fenestron rotor is done with a long flexible link - there are no hydraulics. Therefore, the hydraulics failure which I then explored requires no extra pedal effort. Delsalle switched off the hydraulics just after take-off. The gong sounded and the VEMD warning system showed us the problem. The collective lever stayed more or less where I put it, requiring just a little extra effort to move it.

The cyclic stick, however, wanted to ride back with some force so I jammed my forearm against my waist to prevent it doing so. The subsequent approach, hover and landing, were straightforward, but I would not like to have to fly the aircraft for any length of time in this condition. Delsalle is used to it and does not complain about it.

On our return to Changi, I did some steep turns. Visibility through the overhead panels is good and there were no complaints from the aircraft in the form of increased vibration. I handed over control to Delsalle to show me his steep turns (at 200ft). He rolled swiftly over to 90° of bank and did a 360¼ turn in both directions, then pulled the nose up high and kicked the aircraft round on a wing-over. While there are no published g limits in the flight manual, Delsalle quoted +2.5.

To check the effectiveness of the governor, I moved the lever fairly brusquely up and down and observed rotor and power turbine rpm, plus any pitching up/down of the nose. The rpm fluctuated within 2% with no change of attitude, a most satisfactory result.

I removed my headset and noted the level of noise, which is quite acceptable. I used the intercom to chat with our intrepid photographer and he with us. He was enjoying the flight and felt comfortable, despite the gyrations.

There was no slope available to land on, but Delsalle assured me that the EC120 will land easily on sideslopes of 12°, which is greater than most helicopters, and on up/down slopes of 10°, which is also above the average.

I observed the EC120 coming and going throughout the Asian Aerospace exhibition, where the aircraft was on show, and noted its quietness. This is good news for operators which would use it near congested areas. Eurocopter has deliberately kept the main rotor and the Fenestron rotor speeds to a minimum to limit noise.

Delsalle carried out a power assurance check using the VEMD. The results came up on one of the screens, showing us that the engine was in good health. The results are loaded into its memory for future reference.

In forward flight, the vertical fin offloads the power required by the Fenestron, reducing it to almost zero. Therefore failure of the pitch change mechanism should not present a major problem, provided there is a suitable surface available for a running landing. Failure of the drive shaft is always a much more difficult situation. Provided the pilot can keep up his forward speed to prevent the aircraft spinning, he should be able to fly to a suitable area to carry out a running engine-off landing.

We landed back at Changi and shut down. Delsalle interrogated the VEMD and found the record of our rotor rpm exceedance. It and any others will stay indelibly recorded in its memory for a further 31 flights. Other details of our flight were also there - the number of cycles, flight time, failures and previous failures. All this is good design and good management and should go far to prevent abuses and dissuade those dishonest "cowboys" whose exceedances go unreported.

EXCESSIVE FORCE

The EC120 is indeed a modern machine and meets all of the boasts in the brochure. The only disappointing feature is the hydraulics-off situation, where an excessive forward force is required from the pilot to contain the rearwards movement of the cyclic. I had no problem completing a circuit of the airfield, but anything longer, for example over hostile terrain where there are no suitable landing areas, will, I suspect, quickly tire the pilot.

I liked the good interface with all the equipment in the cockpit and the pilot. He should never be overwhelmed by what he sees and needs to do.

The first inspection is at 100h - I am told the pilot can do it. This is unusual and helps to fulfil Eurocopter's aim of ease of maintenance.

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