FLIGHT TEST: Robinson R-44: Raven reborn

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Frank Robinson built his first helicopter at home. Thirty years on, his company sells more helicopters than anyone. We flew the latest: the uprated R44 Raven II

r44Riding the wave of a civil market recovery, Robinson Helicopter is well on the way to breaking its record of 690 deliveries last year. Buoyed by the weak US dollar, the Torrance, California-based manufacturer shipped 385 light helicopters in the first half of the year – 76% of all North American civil rotorcraft production, and more piston singles than Cessna produced in the first six months.

Robinson’s philosophy of producing simple, reliable and affordable helicopters is paying dividends as the civil market makes a strong recovery after a long period of stagnation. With two-thirds of the company’s helicopters going abroad, the weak dollar certainly helps. US civil helicopter exports are well on their way to beating last year’s total, and a substantial portion are Robinson R22s and R44s.

Such success is a vindication for founder Frank Robinson, who designed the two-seat R22 at his house and flew it himself in August 1975 after he was unable to find an established manufacturer interested in his vision for a low-cost helicopter. The R22 BETA was certificated in March 1979 and the first production aircraft, with a price-tag of $40,000, was delivered later that year. The scaled-up four-seat R44 Raven followed, with certification in December 1992 and first deliveries in February 1993.

Today, twice as many R44s are sold as R22s, and most of those are Raven IIs, the latest model. Robinson delivered its 6,000th aircraft, an R44 Raven II, in April, by which time the company had opened a second manufacturing hangar enabling production to be ramped up to an unprecedented 20 helicopters a week. To keep up, engine supplier Textron Lycoming has a production line specifically for Robinson.

The Torrance factory has a large area devoted to safety courses conducted every month. The R22 is probably the lightest aircraft – rotary- or fixed-wing – most pilots have flown, and the course focuses on the potential hazards of flying small helicopters. A large percentage of accidents are caused by irrecoverable loss of rotor RPM, because a light helicopter has much more control power but a lot less rotor inertia than a heavier machine. The course emphasises safe flying techniques and highlights those to be avoided, such as low-g cyclic pushovers and abrupt, harsh manoeuvring. The flight manuals reinforce this by prohibiting certain manoeuvres and offering safety tips.

Since Flight International last flew the R22, in 1992, a number of improvements have been made. Starting at $185,000, the current Beta II model has the more-powerful Lycoming O-360-J2A engine, capable of 180hp (135kW) but limited by the manufacturer to a 5min take-off and climb rating of 131hp. Derating ensures maximum power when operating hot and high and increases reliability, provided the pilot observes the limits. Other enhancements in the Beta II include an auxiliary fuel tank that extends endurance by 65%, a 5.5% increase in maximum gross weight to 622kg (1,370lb), stainless-steel main rotor blades and an RPM governor.

When Flight International last tested the R44, in 1993, its simplicity and performance were impressive, but less desirable was the cyclic-stick lag, vibration and shake. Starting at $357,000, the latest Raven II model is equipped with hydraulic controls, as well as a Lycoming IO-540 engine capable of 300hp but derated to 245hp, an increase of 20hp over previous models. The engine is fuel-injected, doing away with the carburettor heat control – mismanagement of which has caused many an engine failure – but now requiring at least one operating fuel pump.

Safety derated

Derating the engine improves safety, provided the pilot observes the published maximum manifold pressures for the power settings, and US National Transportation Safety Board statistics for the period from 1998 to 2002 show an R44 engine failure rate of zero. The same statistics show R22 and R44 accidents with mechanical or maintenance causes to be the lowest among the six helicopter types surveyed – 4% and 6.5%, respectively, compared to between 11% and 21% for the others.

Maintenance inspections on both types are required every 100h, with nothing scheduled in between, apart from oil changes. Teflon-lined elastomeric and sealed bearings eliminate most lubrication requirements. The main and tail rotor drive systems have maintenance-free flexible couplings. Control runs use push-pull rods – no cables or pulleys. No component is lifed below 2,200h or 12 years.

One reason for the Raven II’s popularity is the new engine, which increases altitude performance, payload and speed. Maximum gross weight has increased from 1,090kg to 1,134kg, while empty weight has gone up from 635kg to 684kg. This still leaves plenty of payload available – with full standard fuel, the aircraft can carry four occupants with baggage and has a range with no fuel reserve of about 405km (220nm) cruising at 105-110kt (195-205km/h). With the additional standard auxiliary fuel tank, which reduces the payload by about 50kg, range increases to around 650km.

To test the world’s fastest-selling helicopter, Flight International paid another visit to Torrance to sample the current Raven II model. The weather was good, with an air temperature of 29°C (84°F) giving us a density altitude of 2,000ft (600m). The aircraft weight was 188kg (415kg) below maximum, at 946kg. My pilot was Robinson deputy chief pilot Dan Benton.

At just over 10m, the R44’s main rotor diameter is 31% longer than the R22’s. Size matters when it comes to rotors, with even a slight increase in diameter providing a much larger increase in inertia, making the rotor more stable and giving the pilot more time to react to a sudden power loss. Weights in the blade tips also help.

Introduced in 2002, the all-metal blades have thick stainless-steel leading edges and stainless-steel skins. An extended chord increases effective lifting area, reducing vibration, and new aerodynamic blade-tip caps help reduce noise. At 3.3m high, the rotor is well above head height. Droop stops prevent excessive blade flapping.

A large vertical fin helps reduce tail-rotor load and noise and, according to the flight manual, may provide limited controlled straight and level flight at low power settings and airspeeds above 70kt in the event of tail-rotor drive failure. But an autorotation and engine-off landing is then required. Four V belts transfer the engine drive to the main gearbox. The gearbox is simple in design – single stage and splash lubricated.

Our aircraft had the optional leather seats, each with a diagonal/lapstrap inertia-reel harness. There is ample headroom even for tall passengers, although leg space is just adequate. There is no post or bulkhead in the middle of the cabin limiting the outside view, so the all-round visibility from all seats is excellent. I was impressed by the low cabin noise level compared with other similarly sized helicopters.

Robinson’s unique “T-bar” cyclic stick allows easy access to the pilots’ seats. I pulled my half of the stick vertically down onto my thigh, where I rested my forearm. Although it seems different, the dual cyclic moves the same way as in other helicopters due to the free hinge at the centre pivot. I adjusted my pedals – the only adjustment – got comfortable, and pressed the starter button on the collective lever. The engine fired immediately. The starter will not operate if the rotor brake or clutch-engaged switch is on or the low-RPM warning circuit-breaker is out – good basic safety features. There is a duplicate starter button on the cyclic stick and, in the event of an in-flight restart attempt, the pilot can choose the most convenient. The new 28V system gives plenty of electrical power. All controls, switches, instruments, checklist and circuit breakers are within easy reach.

Smooth handling

Remembering my problems back in 1993 with overcontrolling due to the stiffness of the cyclic and the delayed response from the auto-trim system, I pulled up into my first hover. The hydraulic system eliminates those difficulties and gives smooth handling, allowing an accurate and easy hover. A quick glance at the easy-to-read manifold pressure gauge showed we had plenty of power in hand – to be expected at a weight well short of maximum. No throttle movement is required by the pilot – the RPM governor does it all. I could feel the throttle move as I pulled up the collective. The unique dual RPM gauge at the top of the panel showed constant revs throughout, controlled by the governor.

I flew at 40kt to the right, still with some left pedal in hand and no engine power problem, then 33kt to the left, again with no control problems, and 35kt backwards. Then Benton took control and did some high-speed turns on the spot, combining this with sideways and backwards flight and clearly demonstrating the helicopter’s good handling qualities. Out-of-wind hover, landing and take-off in all three directions produced no hidden handling difficulties.

After transitioning to forward flight using the take-off profile recommended in the flight manual, we levelled at 1,000ft, pulled maximum continuous power and watched the speed increase to a steady 117kt – a true airspeed (TAS) of 120kt. Benton says the aircraft will do 117kt TAS – the brochure figure – at maximum weight. A slight dive brought us to the never exceed speed (VNE) of 130kt. Above 910kg this reduces to 120kt. Handling was crisp and benign, even during turns both ways. I slowed to 100kt and applied 60º of bank, rolling from one direction to the other. Visibility into the turn is excellent, and vibration levels benign.

In level flight at maximum continuous power, Benton closed the throttle and did nothing for as long as possible while I checked rotor RPM (NR) droop. After one second, it was time to lower the lever and restore the power. He repeated the exercise, but came gently back on the cyclic as NR started to fade. We got an additional two seconds before the recovery was initiated. The flight manual highlights this technique in the event of power loss.

At a safe height, Benton went into a steady power-on descent with the airspeed indicator flickering. This was to induce vortex ring state, where the airflow over the main rotor gets disturbed and destroys a significant amount of lift. All the classic symptoms appeared – increased vibration, increased rate of descent (I could feel the aircraft accelerating down without looking at the vertical speed indicator), and the heading swinging from side to side. Benton eased the stick forward, the vibration returned to normal, the heading stopped waffling and he applied power. The R44 shows good symptoms and has satisfactory recovery characteristics.

Good governor

To demonstrate the RPM governor, Benton raised and lowered the lever quickly as I watched NR, which changed by ±2% – a satisfactory result. An unserviceable governor is a no-go item, but flight without it can be practised for training purposes. On my previous R44 flight I was able to return to the field, hover and land with no handling problems, governor off.

The hydraulic control system, meanwhile, provides smooth, vibration/feedback-free handling. The system runs at relatively low pressure, 31-34.5bar (450-500lb/in2), its pump driven off the main gearbox so that, in the event of an engine failure, the pilot still has hydraulic power. There is a switch on the cyclic to turn the system off, but this requires electrical power so that, in the event of a total electrical failure or if the circuit-breaker pops, the system stays pressurised. The Raven system does not power the tail rotor controls. I switched it off. Immediately, the collective wanted to go down, which is usual. While straight and level, apart from preventing the lever from riding down, no additional force was required. But I was surprised at how much force was needed to move the lever and stick. The flight manual gives no landing advice, just “land as soon as practical”, so I elected to carry out a flat approach using as few control inputs as possible and running on at slow speed. I would need some practice to be able to carry out a well-controlled hover and landing with no hydraulics.

With the hydraulics restored, circuits performed using a steep approach to a designated spot showed excellent downwards visibility and I had no problem in coming to a neat hover over the spot. A vertical climb to 100ft and back down again was also problem-free, with good visibility.

Unlike the narrow power-on NR limits of 101-102%, the power-off limits are generous at 90-108%. The main rotor will stall at about 80%, so the pilot would have to be careless to let this happen. The first autorotation was at 90kt and 100% NR. A gentle flare allowed plenty of time at the bottom to level off and restore the power. Next, a more aggressive flare reduced the ground speed to zero, again followed by a powered recovery to the hover. After a little practice with a good instructor, a solo student should be able to perform these with safety.

We then autorotated at the recommended speed of 70kt, flared off all the forward speed and had the skids on the ground by 80% NR. This should give confidence that a pilot can autorotate onto rough ground or other harsh terrain with zero speed, avoiding a nasty run-on landing. A minimum-rate-of-descent autorotation at 55kt and NR of 90% gave 1,250ft/min (6.35m/s). A best-range autorotation of 90kt and 90% NR gave 1,700ft/min, but the glide was noticeably flatter. A zero-speed autorotation (not mentioned in the flight manual) gave 2,000ft/min and took 300ft to recover to a normal autorotation. Control of NR during all of this was easy.

Next we took the aircraft to a hover at 400ft, the top of the avoid curve given in the flight manual. The aircraft was fairly light by this stage. The throttle was closed, the lever dropped, and the nose lowered. The aircraft established normal autorotation speed and NR fairly quickly, giving us adequate time to flare at the bottom, restore the power and come to the hover. An engine-off landing would have been uneventful. Then we put the aircraft down on the steepest ground slope available, -7º. There was still cyclic movement available.

Quality handling

The Raven II flies well, the hydraulic system providing a major improvement in handling qualities. Although two-bladed rotors have disadvantages, the biggest being higher vibration, I found both the R22 and R44 to be remarkably smooth, even at speed. And there are advantages: with the rotor aligned along the fuselage, the R22 is just 1.92m wide and the R44 2.1m, requiring little hangar space.

Although piston-powered, the R44 competes with more expensive light single-turbine helicopters such as the Bell 206 JetRanger. The Raven II’s fuel consumption is about half that of the JetRanger, at 55-60 litres/h (14-16USgal/h). Based on my experience with the type, the JetRanger has a range of about 540km with full fuel and cruises at around 110kt at maximum continuous power.

Despite its higher price, the higher-performing Raven II is the Robinson of choice for missions other than passenger transport. The Clipper II comes with fixed or pop-out floats; the IFR Trainer is equipped for instrument flight training, with expanded panel; the Police Helicopter comes with factory-installed FLIR and searchlight; and the Newscopter is equipped for electronic news gathering.