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Saturday, January 1, 2011

A first look at the all-new Cabri G2

A compact trainer with a roomy interior that has forgiving autorotation characteristics. Too much to hope for? Maybe not. First-time contributor Thomas Skamljic gives a thorough look at the Cabri G2.

By Thomas Skamljic

Since you are reading this, chances are high that you are also one of the poor souls who suffer from a disease called helicoptering. Therefore, I trust that you know that the Cabri G2 is built by Guimbal Hélicoptères in France and you know that Cabri is a little goat (also called a kid) in French. What you might not know is, Cabri also stands for Comfort in Autorotation Belongs to Rotor Inertia and that basically sums up one of the main intentions of Bruno Guimbal when he set out to develop a new helicopter—to design a little helo with great autorotation characteristics.The Robinson R22 and R44 come to mind and I am very thankful to Frank Robinson for developing the R22. I really like it a lot. I like the way the R22 handles; I could even handle an autorotation in earnest. Needless to say that “If you can fly the R22, you can fly all the other helicopters...” from my flight instructor was a huge ego boost when I was let free for the first time in the R22. In short, the R22 was certainly my machine.

Later, when I did my first autorotation in an R44, I thought that perhaps my love affair with the R22 should be reconsidered. From that moment on I knew that a good trainer should be the size of the R22 (with a bit more elbow room) and should have the forgiving autorotation characteristics of the R44.

Here you can see the small storage compartment for another 5 kg (11 lbs) under the instrument console. In this compartment there is a cigarette lighter-style socket for any appliance with a maximum of 13.7-volt DC. Thomas Skamljic
Fortunately Bruno Guimbal, designer of the Cabri and founder of Guimbal Helicopters, had the same idea and a tip of my chapeau to him as he has taken “my” idea and turned it into reality in the form of the Cabri G2. I got a chance to fly the Cabri with Alex Neumann, chief pilot at Heli Aviation.

The helicopter available for this flight was s/n 1009 and it had a grand total of 25 hours of flight time. With the two of us on board and about 100 liters of fuel (approx. 26.4 gallons), we were about 30 kg (approx. 66 lbs) short of MTOW of 700 kg (1,543 lbs). After a short pre-flight briefing we started the walk around. Neumann explained the finer details of the Cabri. Checking all the fluid levels is super easy as absolutely everything is in direct view. Open two cowlings and there is complete access to the engine (your maintenance department will love that). The cowlings and the doors are held in place via gas springs.

The airframe and tail boom are all-composite, strong and corrosion resistant. The main rotor is a fully articulated (soft in plane), high inertia three blade rotor system. When you check the rotor system of the Eurocopter EC120 and the Cabri you will find certain similarities. This is not surprising when you know that Guimbal was the deputy chief engineer for dynamics and transmission of the EC120 during his time with Eurocopter. The main advantage of this system is it is free of mast bumping but it does need a bit more hangar floor.

The rotor tips fly a little bit low so a careful eye on interested onlookers is advisable. The wind speed limit for rotor start up and shut down is a generous 40 knots. Access to the main rotor is facilitated via a step on the cross tube on the right side. You can get on that step and easily perform a thorough inspection of the main rotor, mast, dampers, screws—you name it. Nominal rotor speed is 530 rpm. Rotor blades are carbon and fiberglass reinforced composite, with a large steel tip weight and a lead balance weight to increase rotor inertia. The leading edge is stainless steel.

The Cabri is equipped with a Lycoming O-360-J2A engine (as is the R22). But the engine output in the Cabri is 145 hp MCP against 131 hp TOP in the R22. A notable difference is the ignition system. The Lycoming on the Cabri features one “ordinary” magneto plus a custom modified and certified (STC EASA E.S.01001) Light Speed Engineering Plasma II+ ignition system. The reasons for going electronic are the gains in efficiency, performance, reliability and safety. Thus Bruno increased performance and safety without the cost, weight and complexity of an injection system.

The electronic pilot monitor (EPM) LCD screen is large and easy to read. Thomas Skamljic
Any engine equipped with a carburetor can experience carburetor icing. The consequences of carburetor icing can be very serious so the Cabri is equipped with an automatic carburetor heat system to reduce the risk of carburetor icing and pilot workload. If in doubt, the pilot can override the auto system and manually put the carburetor heat switch into hot or cold mode.

A massive belt makes sure that the power from the engine is transferred to the main rotor gearbox and the Fenestron.

The fuel tank holds 170 liters (1.5 are unusable) of fuel and should make a flight range of 700 km (15 min reserve) possible. The fuel itself is housed in an untearable fuel bladder and all the structural elements to hold the fuel bladder are reinforced. During the certification tests the soundness of that system was demonstrated with a 15-meter free fall drop test. No leakage occurred.

The cooling system is a direct drive squirrel cage blower with the cooling air entering the engine compartment via the air intake on top of the cabin roof in front of the main rotor gearbox. The air is then being ducted/forced through the engine compartment. During my flight the CHT and oil temperatures remained firmly in the green and actually more to the cold.

The Cabri has a dedicated luggage compartment opposite of the fuel tank, which can cope with 200 liters or 40 kg of luggage. There is another small luggage compartment for another 5 kg (or 12 liters) under the main instrument console. In this compartment there is a cigarette lighter socket for any appliance with a maximum of 13.7-volt DC. Soft stuff can be put under the seats and should all of that still not be enough, the left seat pan can be removed to provide for additional luggage space if flying solo.

The Fenestron has seven blades and is very powerful according to Neumann. Translated into the POH lingo: A wind speed of 35 knots at all headings was demonstrated at sea level. The Fenestron rotor speed is 5.148 rpm. Apart from being a safety bonus, the Fenestron has some noise advantages as well.

All compartments are easily accessible. Oil check is quick and easy (see orange cap above).  Thomas Skamljic
In order to reduce the noise signature of the Cabri G2, Guimbal decided that the exhaust gases have to go straight up into the rotor flow. The fly over sound exposure level of the Cabri is 75.7 dB at max power. Contrary to what I expected to see, the tail boom was perfectly clean.

It is a traditional skid-type landing gear with the tubular structure attached to the airframe with soft rubber pads. These pads are very soft and you will feel that softness. Of course these pads are tuned to guard against ground resonance so there is no additional damper. On the Cabri, the oil check is super easy as the dip stick is so readily accessible.

Removing the doors does not lower any speed limits and the doors can held be partially open for improved ventilation. The locking mechanism is simple and effective.

With a cockpit width of 1.24 meters, the Cabri offers more elbow space than the R22 (1.12), and has the same cockpit width as the R44.

Getting into the Cabri is easy and the seat is comfortable. The seats are certified to the new Part 27 standards, which means: a vertical 30g impact in the end is a 3g impact thus reducing the risk of spinal injury.

A four-point harness holds you in place and cyclic and collective fall readily to hand. Each cyclic has a four-way hat switch on top with which you can reduce the stick forces to zero. The cyclic is a real stick and flight instructors will be pleased to learn that they can keep their hand on the cyclic all the times without trouble. You can remove the second stick in a matter of seconds without tools.

All compartments are easily accessible. Oil check is quick and easy (see orange cap above).  Thomas Skamljic
The view from the cockpit is excellent. There is no central bow in the middle of your field of view and the instruments and the glass instrument are easily readable. Under all conditions of my flights with the Cabri, no matter where the sun came from, all the information displayed on the monitor was clearly visible.

With 16.5 cm diagonal the electronic pilot monitor (EPM) LCD screen is quite large. All the standard engine and rotor monitoring instruments are available on screen. From my perspective the best part of the EPM is the MLI or multiple limit indicator. The MLI clearly displays the available power margin. The red line on the MLI is always the maximum available power, which is calculated by the EPM dependant on density altitude. So no need to check placards where the numbers have faded into obscurity. Power is not displayed in some strange unit called MAP but in percent like larger helicopters.

The EPM has an intro page that will give you the take off and landing times. That clock is started the moment rrpm is higher than 400 and vice versa. Another nice feature is the fuel page. Every flight on this page is listed with TO and LDG times and the average fuel consumption. The lowest figure I saw was 39 liters/hour and the highest was 43 liters/hour. There are different fuel flow modes available (average fuel flow, instantaneous fuel flow and flight time remaining) and all the info can be displayed in SI and in English/U.S. units. The EPM is complemented by traditional steam gauges. All the usual warning lights are above the EPM and there is an additional vertical row of three lights to give a visual warning for high and low rrpm and a green light when everything is perfectly fine. These lights serve as a backup should the EPM fail. There is an aural warning as well.

The mixture handle sits next to the rotor brake on the cabin roof and should always be full rich. The switches for the magnetos are placed there as well. The throttle is as twist grip on the collective and needs to be twisted quite a lot. It is not possible to roll on power from idle to max power in one move. An electrical governor helps in keeping the rotor speed in the green. The governor engages at 400 rrpm and disengages if rrpm falls below that number.

Start up needs a little bit more information. First, there is no key. There is a remote central lock anti-theft device to lock and unlock the doors. The key ring transmitter sends a code to the Cabri and the electronic brain of the Cabri checks whether the holder of the transmitter is a good guy. If you are confirmed a good guy, the doors unlock and the engine starter is enabled. If not, the doors remain locked. Should a thief decide to enter a bit more forcefully, he can press the start button but to no avail (that’s the anti-theft part of the keyless entry system).

But you are a good guy and end up in the middle of nowhere and the battery in the “key” is flat, what to do? Of course Bruno took care of that as well. You open the right hand cowling, turn a backup key to the right and the door to the luggage compartment springs open. Since the luggage compartment is accessible from the cockpit you can reach the door opening mechanism through the luggage compartment and open the door. Now the door is open and you can enter but you still can’t start the engine. What you need to do is to remove the “code” sticker because this sticker hides a few micro switches. Adjust the micro switches and off you go. Of course you need to know the code …. And should you park your Cabri among many other Cabris and forget where you parked your Cabri you can “call” your own Cabri and the helo will respond with a flashing strobe light. Very clever stuff indeed.

Before you engage the start button you have to wait for the EPM to complete the self-test. The allowed rpm drop on the plasma is 100 rpm and 300 rpm on the magneto. Neumann engaged the start button and immediately the engine sprang to life and also immediately the Cabri started to wobble. These soft elastomeric mounts really are very soft but then a good protection against ground resonance is a very useful feature.

Since Heli Aviation is operating at the moment from a parking lot behind some buildings, Neumann flew the take off and departure. I monitored his actions very closely but could not find anything extraordinary. With power to spare we lifted off, did a hover check and flew the prescribed departure route. Clear of the buildings and on the way to the nearby airfield Neumann handed me the Cabri and right after my first stick inputs I immediately felt at ease. What I noticed though was that I somehow underestimated the necessary amount of pedal for a collective change. I must admit that the resulting flight was a little bit unsmooth (although Neumann did not complain). Another interesting observation was that the collective was a little bit sticky meaning there was always a break out force to overcome. I did check whether this had to do with the friction or just because this Cabri was so particularly new. As it turned out it was not the friction. The advantage of course was that the collective stayed put and did not move on its own.

With the cyclic the breakout force was not an issue but I had to adjust my flying to the higher stick forces and the longer stick travel. The stick forces are a lot higher than in the R22. Now this does not mean that this is good or bad, flying the Cabri is just different to flying the R22. To put that into perspective: a fly by oil helicopter (i.e., a helicopter with hydraulically powered controls) will spoil you a little bit in this regard as there are no stick forces and the stick travel is minimal and my Jet Ranger time certainly did spoil me. However Neumann was kind enough to point out that up until now, every pilot with a hydraulic background was in for a surprise when flying the Cabri. He also told me that students find it easier to cope with the Cabri due to the larger control movement and higher stick forces making over controlling is less of an issue for a helicopter novice.

In the meantime we arrived at the airfield and I set us up for the approach with 50 KIAS and a RoD of 500 FPM. The Cabri held the speed very well. My only problem was the pedal work, which as mentioned before required more input than I anticipated. I came to a neat hover a bit short of the intended spot but for the first time it was OK. Landing was soft. All the instruments were firmly in the green. Considering our weight and OAT of 19 degrees I found that performance quite astonishing. Keeping the hover position and altitude was not really an issue in the Cabri. Spot turns were a breeze. Sideways flight or rearward flight (I had no GPS on board but the speed was quite high) was no problem either. When the MLI turned read and showed 104 percent we still had some pedal left (wind was from 2 o’clock and a bit gusty). Two more circuits convinced me that the Cabri really is easy on the pilot. These benign handling characteristics of the Cabri will certainly reassure every flight instructor who is sending off a student on his first solo flight.

Hover Auto: Roll off the throttle, wait a little bit and then pull the collective. With a little bouncing we landed quite smoothly. What was immediately clear to me was that the rotor really has a lot of energy stored in it. So I was really looking forward to the real autorotation. Off we headed to the practice area. During the short straight and level flight to the practice area I pulled 100 percent power and got 100 KIAS flying at 2,500 feet at an OAT of 17 degrees C. Fuel flow was 48 l/hr. The vibration level was markedly higher than at 80 or 90 KIAS. Neumann attributed this to the blades, which will undergo tracking in 3.5 hours, a normal procedure after the initial “break-in” period. So we flew a few minutes straight and level and after having trimmed up the Cabri it was possible to take the hand off the cyclic and the Cabri kept heading and attitude remarkably well. I wanted to know whether the Cabri would be so stable in a turn. So stick to the left (or right, I did not detect any significant difference) a little bit of collective and some minor adjustments with the cyclic and the Cabri circled nicely without further inputs from me If you are in the business of observing things on the ground you will certainly like that trait.

Still at altitude I tried some more enthusiastic maneuvers i.e. banking left and right up to 60 degrees of bank and the like. It was just pure fun! The Cabri reacts immediately, without protest or showing signs of stress.

In the meantime we arrived at the practice area and having completed two steep approaches to our landing spot and we started with the autorotations.

Neumann initiated the auto by rolling off the throttle. I flew the helo and tried to keep the rotor speed in the green. Of course I waited a little bit before dumping the collective, however due to the stickiness of the collective I unintentionally checked the low rotor speed warning. Pushing the collective down brought the rotor speed up and almost to the upper end of the green. From then on I had no troubles adjusting the rotor speed appropriately. The RoD was between 1,400 and 1,600 FPM and the speed was 50 KIAS. On the way down he told me that he will start the power recovery a little bit higher than what I was probably used to. The reason for that procedure is simple. The governor really has bite and the ensuing yaw requires quite a lot of quick pedal to keep the nose heading the right way. And so it was.

It was time to head home and we climbed to 3,000 feet. On the way back Neumann suggested to try a low-g maneuver. My rather timid try on this maneuver neither impressed the 4-point seatbelts nor Neumann, so he took over. He pushed the cyclic massively forward and fortunately the seatbelts worked perfectly fine. The nose down attitude was almost 90 degrees. Apart from a protesting engine (which resulted in some pedal work), the Cabri showed no sign of strain. Pullout was effected with a guesstimated 2g and immediately upon starting the pullout the engine ran smoothly again.

Converting speed into altitude (OK, a little bit of altitude), Neumann pulled the stick back and raised the nose to about 80 degrees. A boot full of left pedal turned the nose earthwards and neither the Cabri nor the engine protested. The Fenestron did not have any problems stopping the rotation at the desired heading. Fixed-wing guys would call that kind of maneuver a stall turn or hammerhead. Of course I had to try it myself and it is serious fun! Having done that I immediately started thinking about a Cabri beefed up for aerobatics so that one could have all the fun of the BO105 but at a more affordable price (not every helicopter pilot is sponsored by Red Bull). For obvious reasons Guimbal Hélicoptères does not encourage aerobatic flight in the Cabri, however the very reassuring behavior during these maneuvers should prove that the small Cabri really has great safety margins. We were almost back home. Shut down is standard. The rrpm (150) at which you can engage the rotor brake is clearly displayed on the EPM. After completing the post landing checks and with the rotor stopped I contemplated my flight with the Cabri. There is a lot of good stuff the Cabri offers but I did find some room for improvement.

First, adjustable pedals to insure a really comfortable seating position on longer flights and second, the location of some instruments should be reconsidered. I had trouble checking the VSI as the VSI was hidden behind my right knee and Neumann had troubles checking the ASI as this instrument was hidden behind his left knee. With adjustable pedals this problem should be solved however. (Guimbal told me that nice adjustable pedals are in final development, and will be standard next summer).

Speaking of instruments, with the clever EPM already in place perhaps there is a way to teach the EPM to generate a “settling” warning. Perhaps a future full glass cockpit. Since helicopters are often used for photo flights the doors should get a reasonably sized “photo window” to make photographers happy.

Of course you can always remove the door, but that’s rather impractical and really only an option for warmer climate regions. Another small item in this regard, in order to make full use of the fact that the luggage compartment can be accessed from the cockpit the pilots seat should be reconsidered. At the moment minimum crew is one pilot on the right seat. Personally I am not sure whether I would be very happy to have a photographer on the left seat trying to get the lenses out of the luggage compartment behind my neck.

The Cabri is a very capable helicopter, very agile and a lot of fun to fly. However, for the new kid on the block to be successful, the whole package has to be right, that is the helicopter has to perform well (which it does), training, service and maintenance have to be in place and what can be called customer care has to be up-to-date. So, building the helicopter is the easy part—the tough job is to sort out all the other details and this takes time.

The Cabri G2 was built with the training market in mind. The very forgiving high inertia rotor system and the fact that there is no danger of mast bumping is a huge safety benefit for helicopter students and helicopter addicts who do not have a chance to fly on a daily basis.

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