FLIGHT TEST: Robinson R66 - swansong sweetheart

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robinson r66, john croft/flightglobal
 © John Croft/Flightglobal
The R66 offers five seats and high-performance efficiency with a turbine engine

Since introducing the two-seat R22 in 1979, Robinson Helicopter has strived to expand and develop its product line, certificating an array of mission-oriented options for the type and introducing the four-seat R44 in 1992.

Many options were developed for the R44, including dedicated TV news and police versions and, most recently, the increased-performance R44 II. Throughout these developments, questions about a turbine-powered machine arose persistently. Knowing that the piston-to-turbine jump was a big one - mostly in terms of economics - Robinson held off. Until now.

The latest addition to the Robinson stable, the R66, offers a simple, efficient, high-performance five-seat machine with a turbine engine, at prices below those of its competitors.

As a package, the R66 in many ways is company founder Frank Robinson's swansong: the culmination of his more than five decades of experience in the industry. Robinson retired in August, after the R66 received its Federal Aviation Administration certification, and was succeeded by his son, Kurt.

IN-HOUSE CONSTRUCTION

Although outsourcing has become popular with many manufacturers, Robinson constructs as much of the R66 as possible in-house. Keeping everything from detail parts to assembly close to home helps assure quality and allow direct control of production rates.

The production floor is modern, with many automatic, computer-controlled machines. The lighter engine, advanced production techniques, and Robinson's emphasis on simplicity have resulted in an impressively low empty weight for the R66. While a typical R44 weighs 680kg (1,500lb), the R66 that I flew was 587kg.

The R66's larger fuel load can eat into the weight available for passengers and cargo, but even so the R66 gives you quite a bit more load capacity than the R44, as well as more power and better performance.

Although the aircraft look similar externally, it is clear that the R66 is truly a new model - not just an R44 with a turbine engine.

Introducing me to the R66 was chief test pilot Doug Tompkins, who made the first flight in the first prototype R66 and conducted the majority of the development and certification test flights.

Robinson's founder, Frank Robinson, is also an experimental test pilot who performed many of the initial flights on the R22 and R44. For the R66 programme, he left the demanding early experimental flights to Tompkins.

For our flight, the outside air temperature was 15°C (59°F) at sea level with a light wind, a perfect standard day. John Croft, Flight International's Americas editor, joined us as an observer and photographer. Tompkins carried out a standard pre-flight pilot's check. He pointed out some of the basic differences from the R44 (which I had flown earlier).

From the front, obvious external differences are the slightly wider fuselage profile and the lowered window line, which improves forward and downward visibility. I was to explore the visibility aspect when I did a steep approach and a vertical descent from a high hover.

The 1.87m (6ft 3in)-tall Croft took one of the outboard rear seats. Head and leg room were adequate. Tompkins, 1.75m, sat next to him in the centre seat. Because this seat is slightly further forward and higher, their shoulders did not touch. The cabin, slightly longer cabin than the R44's, gives a bit more legroom.

However, when Croft occupied the centre seat, he had to bend his head slightly forward against the roof and cock his legs sideways into his neighbour's leg room space. Prudent loading would put smaller individuals in the centre rear seat, particularly for long flights.

robinson r66 production, john croft/flightglobal
 © John Croft/Flightglobal
Robinson constructs as much of the R66 as possible in-house in California

Although all the seats are crash-attenuating - they crush in the event of a hard landing, thus absorbing some of the impact - there is still some room beneath them for bags. Under-seat storage is restricted by a placard showing allowable load height and is not as voluminous as the R44. Robinson's integrated crash-attenuating seat design is unique for helicopters and required considerable engineering effort.

The need for under-seat storage is mostly negated by the large aft baggage compartment, a major improvement from the R44, which has none. The lighter Rolls-Royce 300 engine, officially model 250-C300/A1, was located further aft than the R44's Lycoming, making room for the compartment.

ROOM FOR GOLF CLUBS

Tompkins says that at least one design criterion - quite important to some customers - was the ability to accommodate golf clubs. There is no smoke/fire warning system for the baggage compartment, but there is a cockpit light to warn if the baggage door is not closed.

As we continued to walk around, Tompkins pointed out a small horizontal end plate at the bottom of the lower vertical stabiliser. This was found during early flight tests to increase autorotation stability and is also used on float-equipped R44s.

Tompkins continued his inspection, checking the external lights - including the bright, LED anti-collision light - and accessing the engine and gearbox compartments through generous cowl doors. Access to all components during the pre-flight inspection was easy. Inspection of the main rotor is accomplished via hand holds and foot rests cleverly designed into the fuselage.

To an airport refueller, the R66 looks much like the avgas-consuming R44, so pilots will have to be vigilant to ensure the correct fuel is used. There is a prominent placard listing approved fuel types near the fuel cap, which is sleekly covered by a small cowl door on the upper, left side of the fuselage.

I settled into the right-hand pilot's seat, looked around, and liked what I saw: a pilot-friendly cockpit, well designed with easy-to-read presentations. The outside visibility, for both pilot and passengers, is superb. There is no seat adjustment, but the tail rotor pedals are adjustable, and Robinson provides an extra back cushion for short pilots.

In small cockpits, I have often found little or even no space for stowing items such as checklists and the pilot's operating handbook. Such is Robinson's impressive attention to detail that several spaces have been provided in the R66.

Tompkins used some of his chief pilot influence during the design stage to have the pedals moved slightly farther apart than in the R44, making the pilot's leg position more comfortable. The instrument panel has all the well-presented instruments the pilot needs.

Our aircraft had space for nine instruments in the main panel, and two were unused, available for optional equipment. As on the R44, a rotor brake is standard equipment. The five-place intercom system can be voice activated or keyed and allows for various levels of pilot/crew isolation.

Engine and rotor start was easy. After going through the checklist with Tompkins, I pressed the starter button on the end of the collective pitch lever and waited until we had 15% compressor RPM (N1), at which point I turned on the fuel. We had a fast engine light up and acceleration, but it stayed well within temperature limits. An auxiliary power plug (for ground power carts; we used one for our start) is provided on the fuselage right side. By leaning out of my door, I was easily able to verify that the plug was disconnected.

The T-bar cyclic stick design is unique to Robinson aircraft and the same as on the R22 and R44. After lift-off, I pulled the cyclic my way, settled my hand on my thigh, and took over the hover from Tompkins.

Some pilots, including me, have initially had trouble adequately controlling the hover with this system. However, in the R66 I was able to hover accurately, land and take off with no over-controlling. I had a bit of directional control difficulty when attempting to fly sideways to the right, downwind, but Tompkins invited me to try into the wind and the difficulty disappeared.

When Tompkins demonstrated the manoeuvre downwind, I noted that he used tiny, frequent pedal movements instead of my larger, infrequent ones. Practice, no doubt, would overcome my difficulty.

I completed the usual test pilot sideways and rearward flight controllability checks over the taxiway at 17kt (31km/h) the demonstrated speed per the pilot's operating handbook), then I handed over control to Tompkins.

He went much faster without running out of cyclic authority or tail rotor control. In many other helicopters, when flying fast backwards or, more realistically, hovering in a fierce tailwind, the main rotor disc flaps forward. The pilot corrects this with aft cyclic stick and, sometimes, can run out of authority with the nose hard down and the cyclic hard back - most alarming.

r66 ga
r66 ga

The R66 does not have such a problem. Tompkins flew the R66 backwards at high speed. I did not detect any control authority problems. He also spun from rearward to forward flight during a fast taxi run, thus demonstrating the power of the new tail rotor.

The R-R engine also responded well, keeping up with the rapid change in power demand and controlling torque fluctuations within allowable limits. Out-of-wind landings were benign. Unlike some competitive helicopters, the R66 has no difficult wind conditions in the hover.

Engine control is very simple - just a throttle on the end of the collective pitch lever (the collective) which is either fully open or closed. A hydro-mechanical governor maintains RPM as power demand changes. A beeper switch on the end of the collective can be used to fine-tune the RPM setting if required. I did not need to do so.

The 300shp (245kW) engine, the overall light weight, and the increased area of the main and tail rotor blades combine for impressive performance. A major R44 customer feedback item was the need for increased performance, particularly at hotter temperatures and higher altitudes. This issue was partially addressed with the R44 II, and the R66 offers further improvements. On a hot day at sea level, a fully laden R66 will hover at about 80% torque with 20% still available.

In the most demanding case, the R66 can hover at maximum gross weight, out of ground effect at 3,250ft with an outside air temperature of 44°C.

The rate of climb is also impressive, for example 1,250ft/min (6.35m/s) at sea level, at maximum gross take-off weight and 15°C. On my flight at lower weight with 100% torque, we got over 2,000ft/min. The vertical speed indicator stops at 2,000ft/min. In cruise at maximum continuous power, we achieved 118kt.

Vibration levels are lower than with the R44. Perhaps the continuous purr of the gas turbine engine instead of the irregular thump of the R44 piston engine contributes to this. As with the R44's Lycoming engine, Robinson worked closely with R-R to get an engine optimised for the airframe. R-R designed the new model RR300 with several features to suit the R66, and Robinson placed a large upfront order. The deal was done.

The 300 engine is simpler and requires less maintenance than the Model 250 it was derived from, says Kurt Robinson, the new chief executive. Emphasis was also placed on efficiency, but the turbine is still thirstier than its piston counterparts. Although Robinson had a hand in the specifications and was the first customer, the engine is available to other manufacturers.

VIBRATION LEVELS

At the VNE of 140kt, achieved in a descent, there was a slight increase in the vibration level, but 30° turns in both directions did not increase this. Certification requires the aircraft to be flown at VNE plus 10% to allow a buffer for the inattentive pilot, without aerodynamic or other problems. Tompkins says that the R66 meets this requirement without any obtuse handling difficulties. Croft recorded our dive speed of 142kt.

Level and descending steep turns left and right revealed the good visibility afforded by the low-cut window and windshield lines. On some aircraft, door struts can impede visibility in turns, but they were not obtrusive in the R66.

Due to their small size and other features, all Robinson helicopters have low-inertia main rotors. This means that in the event of a sudden engine failure, the pilot has to lower the collective quickly to prevent the rotor speed falling below the stall level - about 80% rotor RPM in most cases.

There is no recovery procedure for a stalled rotor. Fortunately, engine failures are a rare event in the Robinson world since the engines are reliable and de-rated from the engine manufacturers' limits when used in Robinsons.

 robinson r66 cockpit, john croft/flightglobal
 © John Croft/Flightglobal

Nevertheless, lowering the lever soon after a sudden engine failure is a very critical emergency procedure in both the R22 and R44, and failing to react quickly enough has been a factor in several accidents, particularly for novice pilots. The R66 is a bit more benign.

I invited Tompkins to chop the throttle while straight and level at 100kt and do nothing until he had to lower the collective. (Do not try this unless you too are a chief test pilot.) He floored it after about 1.5s. The rotor RPM stayed within limits. He could probably have waited a bit longer.

Torque decay during a simulated engine failure with a turbine engine is slower than during a real failure, but I think the demonstration showed that the rotor system is a little bit more forgiving in terms of RPM decay than the R22 or R44.

At a safe height, I invited Tompkins to enter a vortex ring state (settling with power). In this situation, the helicopter descends at a moderate rate at low airspeed with power on. The airflow around the main rotor blades swirls, re-circulating through the rotor disk and greatly reducing lift.

The aircraft rapidly picks up an excessive descent rate. Some pilots, not recognising what is happening, will pull more collective to try to reduce the rate of descent. This aggravates the situation and the helicopter continues to accelerate down.

The R66 properly exhibited the warning signs pilots are taught to look for: heading direction waffling from side to side, increased rate of descent, and sloppy control feel.

I saw 2,000ft/min, the maximum, on the vertical speed indicator. Tompkins employed the standard recovery procedures - lower the nose, get forward speed and recover to level flight - resulting in a quick and benign recovery.

I next invited Tompkins to lower and raise the collective as fast as he dare. The engine was responsive thanks to the latest R-R compressor and fuel control design. Torque and rotor RPM parameters stayed well within limits, despite the wild power changes. There was hardly any change in the pitch attitude.

I carried out a steep approach to the numbers on the runway. In some helicopters, the nose has to be cocked sideways to keep the intended landing site in view. Not in the R66, thanks to that large windscreen. A vertical descent from 100ft was also easily achieved.

In the airport traffic pattern, we tried various autorotations. The first ones terminated in a powered recovery to a hover, to test the response of the turbine engine.

Most turbines are slower to accelerate than their piston counterparts. This, I thought, might be a problem for experienced Robinson piston pilots practising such a manoeuvre. Not so. The throttle has to be opened slightly earlier in anticipation of the recovery, but the engine's acceleration is more than adequate and should not cause prudent pilots any difficulty.

 R66 BONUSES

In addition to the engine, which is lighter, more powerful, and able to burn a wider variety of fuels, several notable differences from the R44 are:

  • A slightly wider fuselage to accommodate a centre rear seat
  • A 300lb (136kg), 0.51m3 (18ft3) rear baggage compartment
  • Crash-attenuating seats
  • A wider-chord main rotor blade
  • A longer-span and wider-chord tail rotor blade
  • A slightly longer cabin for increased rear-seat legroom
  • A wider undercarriage
  • A higher main rotor hub
  • A Rolls-Royce-supplied engine monitoring unit that flags exceedances, sensor faults and start cycles
Power-off touchdowns also presented no difficulty. At 60kt, we had a rate of descent of 1,300ft/min, a gentle experience. Some of the helicopters I have flown come down in autorotation like a piano. But even a zero airspeed autorotation gave a modest rate of descent.

A maximum range autorotation - at 100kt and with rotor RPM reduced to 90% - gave a flat approach, a modest rate of descent, and plenty of inertia to flare off the speed at the bottom.

Handling qualities in the flare - slowing down the aircraft to the required touchdown speed, speeding up the rotor momentarily, and giving the pilot time to get the touchdown just right - are better than with the R44. I noted that little right pedal was required to keep the aircraft straight during touchdown. This represents a remarkable difference from most other helicopters.

Tompkins chopped the throttle from a 5ft hover. The aircraft settled fairly quickly, as expected, but there was sufficient time to raise the collective and apply a little pedal. He then went to about 10ft. Just a slight pause before raising the collective produced the same result, a gentle touchdown.

He then carried out a manoeuvre which I have never experienced: he chopped the throttle from a 5ft hover and did nothing. The aircraft turned through 90° and landed only slightly hard - very impressive.

With the hydraulics off - the switch is readily accessible on the pilot's cyclic - the controls are slightly heavier, with more interaction between the cyclic and collective than on the R44. However, the aircraft is readily controllable, and a flat continuously decelerating approach with a gentle run on landing is easily achieved.

At the end of the flight, Tompkins demonstrated sloped ground landings. All four directions - cross-slope (x 2), down-slope and up-slope - were limited to about 5° before running out of cyclic authority.

Shutdown, accompanied by a mandatory engine deceleration check, was straightforward.

I read the pilot's operating handbook and the notes to newcomers. An experienced R22/R44 pilot with some previous gas turbine experience requires only about 1h's flight instruction/practice plus three ground school lessons and an exam to make the R66 transition, says Tompkins. Less experienced pilots may require about 7-8h flight time.

The handbook is uncomplicated and comprehensive with much common sense, not least in its final section, "Safety tips and notices". This describes incidents and accidents, their causes, and how to prevent recurrence.

I am amazed that other manufacturers, both of rotary and of fixed-wing aircraft, do not provide similar information. The handbook also has a list of preventative maintenance tasks that a trained pilot can carry out.

OVERHAUL

The engine and main gearbox, plus some other components, have a time between overhaul of 2,000h. The main rotor blades have to be replaced at 2,000h. Those components that do not have a specific TBO are replaced on condition only.

There are 279 litres (73.6USgal) of usable fuel. Going for range at 100kt burns about 76 litres an hour while cruising at 115kt burns about 83-87 litres an hour.

Early indications are that the R66 will replicate its predecessors' successes. Some demonstration helicopters have already been sent to distributors. There are more than 100 on order: 40% to US buyers, 60% elsewhere, about the same ratio as R44 sales. Robinson has not yet indicated any intention to develop a model beyond the R66, but will certainly be busy providing mission-specific options similar to those for the R22 and R44.

With FAA certification complete, European approval is clearly a priority, especially given the order numbers above. The FAA, Robinson, and European authorities are working together to make the process as quick as possible.

Priced at $800,000, with rivals' five-seat turbines in the $1.4-$1.6 million range, and with its simplicity, good performance, efficiency, and projected multi-role versatility, the R66 carries forward the Robinson tradition.