(FLIGHT TEST) – The Guimbal Cabri G2 has developed a large and loyal band of followers across Africa. Many of these were students who learned to fly this endearing and very competent helicopter with Starlite Flight Training in Mossel Bay.
HISTORY AND DEVELOPMENT
The French might make quirky cars, but they build great helicopters. The Guimbal Cabri G2 is a product of the talented Bruno Guimbal, a Eurocopter engineer.
While designing the Eurocopter EC120 during the 1980s, Bruno Guimbal decided to independently pursue the development of a two-seat piston engine helicopter. Looking at the experiences of Robinson, Guimbal decided that his chopper would feature many of the safety and technological advances found in larger turbine-powered helis. These features included a 3-blade Spheriflex main rotor, Eurocopter’s Fenestron shrouded tail rotor and a strong, impact absorbing, composite body shell.
Eurocopter was so impressed with the concept and design that they funded the development programme and provided technical assistance during testing. In April 1992, the first prototype Cabri G2-01 conducted its maiden flight, which lasted for a total of 45 minutes. In 2000, Bruno Guimbal left Eurocopter to launch Hélicoptères Guimbal, in Aix-en-Provence Aerodrome, France, in order to certify the Cabri and get it to commercial production.
ON THE GROUND
A first glance it is small, yet clearly not a Robbie 22. On the ground the smooth aerodynamic lines just look right. Like an Italian sports car it is low, and the main rotor is about 25cm lower than a R22. This means that you have to be extremely cautious of loading or unloading pax while the blades are turning.
On closer inspection, the Cabri is – dare I say it – better built, and with obviously better European technology. Fit and finish is excellent, and it’s clear that there has been much attention to detail. Competing aircraft are obviously the Robinson R22 and the whatchamacallit Sikorsky/Schweizer/Hughes 300. So the expectation was for a modernized cross between a 300 and a 22, perhaps priced at the top end of the two seat helicopter market. and indeed the Cabri G2 is more expensive than a Robbie 22, but you get a lot more for the money.
The bottom-line is that the Cabri G2 is like a proper little Eurocopter; built with the latest technology. So it’s not really comparable to either the R22 or the 300.
Confirming the Cabri’s functionality as a trainer, there’s nothing unusual or difficult about the pre-flight, though you need a torch to check the main rotor gearbox oil level.
The high rubber mounted skids are able to pivot like the EC120, which reduces the likelihood of ground resonance. Cabris can also be specified with a hook attachment for sling training.
A mast inspection of the Spheriflex rotor head shows how similar it is to the far larger EC120 and even the Oryx/Super Puma. But this is not surprising as Bruno Guimbal and Eurocopter own the patents. The fully articulated rotor eliminates the risk of mast bumping, one of the primary reasons Robinson pilots have to undergo special training. The Cabri’s pilot cannot induce mast bumping by doing a low-g manoeuvre or by inadvertently flying into high turbulence. Having said that, a low-g pushover still is not recommended, since the Lycoming engine is not rated for low-g manoeuvres . In addition the Cabri rotor has a higher inertia than the R22’s 2-blade system, so autorotations are far safer.
The three composite rotor blades are manufactured with Eurocopter processes including their patented bonding methods for the stainless steel leading edge caps. The blade attachment forks are integrated into the blades.
There are no life limits on the main rotor blades and the whole rotor system is exceptionally strong, as evidenced when Bruno Guimbal built a test blade with all possible defects built in. He then hammered it until there was a large hole at the root. They fatigue tested it for months before inspecting it and finding it was still more than strong enough.
To test the Spheriflex rotor head they failed the main hub and then demonstrated 200 hours of safe flight. The main rotor driveshaft is milled from a billet of stainless steel, eliminating quality control risks.
You inspect the engine by opening hinged clamshell cowls that are held up with gas struts. Inside is the bullet proof Lycoming 0-360. To give it an extra margin of safety it has been de-rated from 180 to 145hp. The old Lycoming carburetted clunker is in marked contrast to the modern technology employed everywhere else by Guimbal. But as a concession to efficiency, the ignition system has one magneto and an electronic ignition unit for the other side.
Access to the engine is easy with everything pretty much at eye-level. Key items like the oil filler and dip stick are not in awkward, hard to reach places. Showing the attention to detail, the cowl latches include a safety lock that will hold them closed, even if they have not been latched properly.
Noteworthy are the engine baffles which can be removed in half an hour for maintenance, which is in marked contrast to the Robbie 22. Also in contrast to the other two, the engine pivots to engage the clutch and the main gear box carries the belt tension. This has the benefit of not changing the drive train alignment.
‘a fuel bladder designed to Formula 1 safety standards’
The Cabri uses a fuel bladder designed to Formula 1 safety standards. It holds 170 litres, giving about a 5-hour endurance.
Even the exhaust is a thing of beauty. It uses a 4 into 1 free-flow exhaust made of inconel (commonly used in F1 exhaust systems) which exits through the top of the tailboom to help reduce the aircraft’s noise signature. And to show that they thought of everything the exhaust manifold has a u-bend so if it’s parked out in a rain storm the water cannot get down the exhaust to the valves.
Moving back to the tail, Guimbal holds the rights to use the Fenestron on aircraft below 1200kg. The Cabri’s Fenestron uses fail safe injected plastic blades with high tensile stainless steel spars, so maintenance is minimal. The profile of the Fenestron shroud has been designed to avoid tail rotor vortex issues.
The Fenestron also provides for significant bystander safety and greatly reduces the risk of tail rotor strikes in confined areas or during misjudged approaches and landings. And it’s a lot quieter than an open tail rotor. The shrouded tail rotor’s blade pitch range and alignment is easily checked according to markings on the tail shroud.
Getting in is easy and the doors are held open by pneumatic struts. Unlike the ‘garden gate’ door latch of the Robbie, the Cabri has elegant latches and are dual pinned to ensure flush closing and a good seal. You can even lock the doors with a remote key.
There is plenty of headroom for tall pilots – even wearing helmets. The cabin may look small, but it can comfortably accommodate big South African farmers. The cabin has plenty of shoulder room and is 15cm wider than an R22. Seats are comfortable and there are 4-point shoulder harnesses that are easily latched in one click. Of particular note are the seats which are designed to make a 2000fpm vertical impact survivable. Guimbal estimates that half of helicopter crash fatalities could be prevented by the crash protection features built into the Cabri and few examples crashed in the hands of students trying autorotations bear this out. Needless to say, it meets the very latest EASA safety standards.
Another improvement on the R22 and S-300 is the 200 litre baggage bay which is rated to hold a very useful 40kg. It is accessible from a hatch on the right side of the fuselage and also from inside the aircraft, meaning that a camera or flight bag can easily be stowed and accessed in flight. There is also a small compartment in front of the instrument binnacle to stow the removable dual controls.
The instrument binnacle features a normal set of instruments, except for the RPM and engine monitoring which display on the Electronic Pilot Monitor (EPM). This digital display also includes a Multiple Limit Indicator (MLI) which combines several critical performance indicators (engine speed and power setting, fuel flow, oil temperature and ambient air pressure) into one instrument for the pilot to monitor. So the dangers of South Africa’s high density altitude take-offs should be reduced.
The display shows how much power as a percentage is available at any time. A read out of % of throttle on start-up is given, helping to reduce the likelihood of an over-speed on start. The EPM also displays fuel and flight time remaining as well as carburettor temperature (which is monitored and controlled automatically). It is even a flight logger. Should the EPM fail, there is an independent backup for rotor rpm management which uses three lights to show low, normal and high rotor speeds.
The controls are all beautifully built and finished and fall to hand as you would expect. The cyclic has a conical trim hat. Mixture and mag switches are located in an overhead console – just like a big heli. The pilot’s pedals have an elegant two position adjustment available. There’s even a cup holder, an auxiliary music input and that essential – a 12V accessory jack.
FLYING THE CABRI
Start-up is straight forward carburetted Lycoming. With a warm engine you can have the clutch fully engaged and be off the ground in 15 seconds, which must be nice for car tracking and anti-crime operations. You run through the usual checks for mags, carb heat, clutch, and rotor horn, plus checking that the backup rotor rpm warning lights operate correctly. Then gauges green, caution lights off, power limit checks (displayed on the MLI), and you are ready for takeoff.
Having completed the start-up and checks, the first thing is to confirm which pedal will be needed as the Cabri rotor turns clockwise and it needs right pedal as power is added. The best technique in the Cabri seems to be to add in the amount of pedal you might expect, and then a good inch more.
Keeping it straight requires significant pedal offset, yet the heli still has full tail authority in 35kts for all directions at sea level. With half tanks and two up, a maximum performance vertical climb showed 2000fpm to 1000 feet.
The Cabri is light on the controls and nimble and thus a lot of fun to fly. You can flick it from one very steep bank to the other with no effort, climb and push over the top if you want to, and generally have a ball without feeling at all like you are approaching any limits of the aircraft. You can point this helicopter wherever you want it to go, and if you happen to be not all that coordinated about it, doesn’t matter – the Cabri feels very forgiving.
As a good trainer, the Cabri feels robust and friendly, and not remotely like it’s just waiting for an opportunity to bite you. The footwell windows are great so you can look out past your feet – and that’s something you can’t do in the R22 or S-300.
Something you can do in both of those American helis though, is open a vent to let air in. This is noticeably lacking in the Cabri, except for a small vent in the door that doesn’t work very well and it can get sweaty inside if you’re in the sun without much airspeed. The challenge of cabin ventilation has however been cleverly solved as the doors are held open by a gas strut to about 5cm, when hooked onto a looped string. As the airspeed increases above 40kts, ram air closes the doors automatically. And of course, as you decelerate below 40kts, the door strut pushes them open again. So constant fresh air is available in the cockpit. And air conditioning is an option.
‘It is a better, classier and more exclusive heli…’
Early Cabris were noted as having a vibration on the pilot’s side at around the 85 kt mark. However that vibration was eliminated by three vibration absorbing pendulums (VAPs) in the rotor head. These can also be retrofitted to earlier aircraft.
Out of wind slope landings are not the usual challenge as the Cabri pivots on the rubber mounted undercarriage so that the cabin doesn’t lean to the same degree as the skids.
For those used to learning to fly on Robinsons. Pat Malone, writing for Pilot magazine provides interesting insights into the Cabri and its Fenestron. He observes that deceleration and spot turns are where you need to understand the Fenestron. Turning left, you need to understand the non-linear Fenestron response. The Cabri is the only piston-engined helicopter with a Fenestron, and the instant availability of torque without turbine lag speeds the yaw. The cure is to get your right foot all the way to the floor and sit there until it stops − and don’t touch the collective.
Straight in and 180 degree autorotations to a power recovery are easy to execute without drama. You need to be quick with the yaw control on recovery though, as the Cabri governor tends to snap the throttle open – more than the R22 does.
Using claimed empty weight figures, the Robbie 22 offers a 519 lb usable load and the Cabri 597 lbs, meaning you can carry a good deal more fuel with you in the Cabri than the short hops that a 22 allows with two average people on board. The R22 however, wins the competition for IGE hover performance. The Cabri definitely prefers to be by the sea and not the highveld. With that 519 lb on board at ISA, the R22 offers 9400 feet IGE hover and the Cabri offers just 6000 feet. At 20 degrees C, the 22 is down to 8000 and the Cabri to 5000 feet.
With a light fuel load but the high inertia rotors and wide rotor rpm range (yellow extends from 450 to over 600rpm) there were no particular requirements for careful pitch adjustments to manage the rpm throughout the descent or flare.
Hover engine-off landings turned into a non-event requiring no more than correcting the yaw, letting it settle, and then adding collective to cushion the landing. Into a light wind there seemed to be no chance of running out of collective and it was easy to hold the Cabri off the ground before a gentle touchdown.
If you took all the desirable characteristics of the R22 and S-300, eliminated the niggles, and then added latest technology and safety measures as well as the look and feel of a Eurocopter, then the Cabri is the result. It sits somewhere between the two in terms of size and useful load, has the spacious cabin of the 300, and exceeds the cruise performance and Vne of the R22.
Where the Cabri wins massively in any comparison is in technology and safety features, though these do come at a cost. The Cabri is priced about US$100k higher than an R22 putting it in the same bracket as the R44 Raven, which of course has 4 seats and a faster cruise speed. However, Robinson helicopters require full overhauls at huge cost every 2200 hours – while the Cabri does not.
The Cabri has no fatigue life limited components, with all components including blades and flight controls being maintained on condition. The engine and two gearboxes have 2200hr TBO lives specified and the fuel bladder has a 15 year finite life limit.
Whilst that isn’t to suggest the Cabri could be maintenance free, it does also mean that there is no calendar full strip and inspection required as with Robinsons. A Cabri G2 owner said that he loved the Cabri because as a former R22 owner flying a small number of hours, he said he could ‘feel’ the calendar time ticking away on his R22 every day he didn’t fly it.
The absence of hugely expensive calendar overhauls and life-limited components also means that there should be negligible devaluation of the aircraft taking place as time passes, regardless of whether it is used much or not.
This has to be a huge advantage for private owners who aren’t likely to fly according to the Robinson formula of 2200 hours every 12 years, diligently saving U$100 an hour to fund the pending overhaul. The disadvantage though is that there will never be ‘cheap’ Cabris on the market such as there are for entry level R22 owners buying nearly timed out machines.
A big question is how often you need the two extra seats in the R44. In practice R44s are seldom flown more than two up. This makes the extra fuel burn and hourly cost of the R44 hard to justify.
It’s fair to say that the Cabri isn’t likely to be produced in Robinson volumes, but this is not Guimbal’s intention. It is a better, classier and more exclusive heli. For owners who are willing to spend more to get more, who place fair value on the technology and safety that the Cabri helicopter offers, and who want to avoid a traditional calendar maintenance cost regime, the Cabri G2 is likely to find a new market niche all of its own.
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