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Piper’s M600 - the Evolution of the Species

In a first for this magazine, we have done a flight test of an early model and then the latest model of the same plane on consecutive months. The reason is because the upgrades Piper has wrought to its already successful M series have changed a really good aircraft into an all-round excellent one. It also shows what that rarity, technological progress in general aviation, can achieve.

 

 

 

The original Piper Meridian was an upgrade of the Malibu piston single, in that it replaced the Malibu’s 350 hp Lycoming with a 500 hp Pratt & Whitney PT-6. As we saw last month, while a fine aeroplane, it was always the baby of the turbine singles – and disparaged by Pilatus PC-12 and TBM owners. But, now, 17 years after the introduction of the Meridian, Piper has given it an upgrade and make-over to create a far more capable aircraft than the Meridian (now called the M500) we flight tested last month.

In July, the first M600 arrived in South Africa and it was the perfect opportunity to see what Piper had achieved with its radical make-over.

The key changes are more power – as the name suggests, up from 500 to 600 hp – a whole new wing, plus numerous cockpit and cabin upgrades. The Meridian/M500 is often considered a bit short on useful load and range, so the M600 addresses both these shortcomings handsomely, as was amply demonstrated by South African Piper agents NAC flying a brand new M600 around Africa for a demo tour. With more power and more wing, the M600 can fly a 200 lb pilot, two 200 lb passengers and 50 lb of baggage more than 1,480 nm at long-range cruise and land with 100-nm IFR reserves. The M500, by contrast, can fly the same payload about 800 nm.

I met NAC director, JP Fourie, and Piper Europe’s demo pilot, Thomas Nielson, at Stellenbosch Airfield (FASH) and got to check-out the latest and greatest Piper offering in the metal.

 

ON THE GROUND

On the grass at FASH, the M600 was parked next to ZS-DCG, the first Meridian to arrive in South Africa – and externally the differences are subtle. The most obvious is the M600’s new five-bladed composite Hartzell prop, required to maintain good ground clearance while absorbing the extra 100 hp. The other big difference is the wing, with the M600’s lacking the wide fillet at the fuselage intersection. While larger in chord, the new wing is only slightly longer (one inch on either side), with minimal hangar implications.

Interestingly, the increase in power has not done a whole lot for cruise speed, which is still typically around the 260 knots described last month by Colin Chapman for his Meridian. And if you really want to fly for range, work on a 184-knot long-range cruise speed. For the M600, this yields an eight-hour endurance – and there’s no on-board potty (although there’s an optional relief tube).

At a 260-kt typical cruise, the M600 can fly more than 1,200 nm in just over five hours. This is pretty much the same cruise speed for a Pilatus PC-12 and just 25 knots slower than a typical cruise for the hot-rod TBM 930 and Cirrus Vision SF50 pure jet.

Being a Piper, the price is always keen, and the M600 we sampled, N600EU, with all the bells and whistles and options in Piper’s ‘Expression’ package, carried a price tag of US$3.2 million. Not cheap by many standards, but a lot more affordable and sensible for the owner pilot than the TBM 930 at US$4.7 million and the much larger PC-12 NG at more than US$5 million. The M600 is, thus, by far the lowest priced pressurised single-engine turboprop with comparable range and performance.

Giving the M600 a new wing was the most cost-effective performance improvement, as the Meridian's wing was based on the original PA-46 Malibu piston. The M600’s wing not only has more fuel capacity than that of the M500, it’s also longer and stronger to handle the large increase in operating weight. Compared to the M500, the M600’s wing is thicker, but it has better lift-to-drag characteristics at cruise speed, as well as a tamer stall. Furthermore, the spars and ribs are taller and thinner, reducing weight.

But it’s not just the wing and engine that differentiate the M600 form the M500. The whole aircraft structure has been significantly beefed up, and this is most evident in the very impressive Vmo redline speed of 250 KCAS. This 62-kt increase means you can now just put the nose down and keep up with the big jets when descending into a busy airport. 

A surprising feature pointed out by demo pilot Thomas Nielsen was the weight of the elevator. It evidently has a large internal weight that holds the elevator in the down position.

For the observant, another change over the M500 is the larger radar dome, now faired into the leading edge of the right wing instead of in a pod hanging below. Thomas says the radar now costs just three knots in cruise speed. Interestingly, the vertical tail has not needed to be increased in area or height to accommodate the extra engine power and torque.

The fuselage is unchanged and you enter via the fold-down clamshell air stair door, making it a ‘cabin-class’ aircraft that impresses passengers. When closed, the bottom step folds down to provide two cup holders – nice touch.

The quality of the fittings and furnishings is very impressive – as good as any business jet I’ve seen. Thus, the worktable between the seats is a surprisingly sturdy carbon-fibre textured fold out table. 

There is a large internal baggage compartment, rated for 100 lbs, behind the rear seats. These seats flip forward for access to baggage and to make more space available. A feature I particularly liked was a button that reclined the rear seats. This further improved the already sufficient headroom for a six-footer, and made it supremely comfortable for passengers on long flights who want to snooze.

Each passenger seat has an eyeball air vent, an audio jack and yes, a cup holder. The interior is compact, but the seat backs of the co-pilot and mid-right passenger fold down to ease access to the cockpit.

This is a pressurised aircraft with all the considerations that entails. Behind the co-pilot’s seat is an emergency oxygen tank and a single quick-donning mask for the pilot. Two chemical oxygen generators and six passenger oxygen masks supply the other occupants in the event of a loss of cabin pressure. A full oxygen tank can supply the pilot for 25 minutes and the O2 generators last for 15 minutes. While that’s enough for an emergency descent, a slow loss of cabin pressure due to engine failure could be a problem if it’s necessary to stretch the glide to reach a distant field. Glide time from FL280 to a comfortably breathable 12,000 ft could take 20 minutes, depending on aircraft weight, resulting in hypoxia before reaching a safe cabin altitude.

A feature I really liked was the provision of not just USB plugs for each seat, but also mains power sockets in the cabin and the cockpit – great for running a laptop or games, or whatever gadget keeps the kids happy. In N600EU, they are 110 volt US fittings, but I am assured that you can have them in South African or European 220 volt as well.

For paperless cockpits, two USB charging ports in the cockpit make it possible to use two tablet computers for electronic charts.

The M600’s PT-6A-42 engine is essentially the same as the -42 fitted to the more than 1,200 Beech B200 King Airs flying. So, it’s thoroughly tested and spares and maintenance skills are commonplace worldwide.  

The remarkable thing about the PT-6A is how long Pratt & Whitney have held out against installing a FADEC system. The A designation means that the fuel control unit has a manual override which provides emergency engine control should the normal pneumatic servo functioning of the fuel control unit fail, or if the power control (throttle) lever linkage fails. It doesn’t, however, provide overspeed, over-torque or over-temp limiting, so it has to be treated with kid-gloves. Now that Cessna has selected the FADEC equipped GE Turboprop for its Denali PC-12 competitor, perhaps Pratt will finally update its venerable PT-6.

The power rating of the M600’s -42 is 1,050 shp, providing a large flat-rating margin for the Piper’s 600-shp limit. The benefits are a strong hot-and-high airport performance and a 1,500-fpm climb rate nearly all the way to FL280.

To keep the price down, Piper has made a number of trade-offs. Notably, it skipped RVSM certification, limiting the maximum operating altitude to FL280. But this is an optimum altitude for the M600’s PT-6A-42 and it is uncluttered airspace below the large airliners.

Another cost saving, and one that will perhaps be more keenly felt by African operators, is the lack of a full inertial separator to divert dirty air from the turbine and increase ram-air recovery during cruise. Instead, the M600’s plenum chamber has an integral inertial separator that allows small debris and ice particles to exit through outlets on the bottom of the cowl.

Another, at first glance, surprising absence is aileron trim, particularly given the long span wings with fuel tanks extending to near the tips. However, pilots don’t have to worry about keeping the tanks balanced as the engine draws fuel from both tanks simultaneously. Should an imbalance happen, the G3000 automatically turns on the boost pump in the heavier tank so that it feeds more fuel to the engine until balance is restored.

Each fuel tank has a heated fuel return line that automatically supplies surplus fuel warmed by the fuel/oil heat exchanger to prevent fuel gelling at altitude. Each tank also has an internal electric boost pump used for starting, for high-altitude vapour suppression and for back-up to the engine-driven low-pressure boost pump.

 

THE COCKPIT

In the cockpit, the next big improvement is evident – the state of the art Garmin G3000, which features three 12-inch displays and two touch screen control units in the centre console. Display colour conventions are intuitive and ergonomics are a strong suit, but it takes a while to learn all the touch screen sub-menus, even if you are familiar with the G1000.

I have been a bit sceptical of touch screens, as they can be hard to use accurately in turbulence. Piper has thought of this and each touch pad comes with a rail below it, on which you can place your thumb and thus stabilise your hand for accurate touching. The pilot seats also have fold down arm rests, which stabilise your arm.

In addition to the hugely capable G3000, there is a wonderful collection of avionics features that make this a truly modern aeroplane. These include a Sirius XM satellite radio that provides weather and entertainment, an Iridium Satcom phone, an engine fire detection system, DME, Stormscope and a hybrid TCAS 1/ADS-B traffic advisory system – and for Africa, even an ADF.

A feature specifically enjoyed by JP Fourie and Thomas Nielsen on the long ferry to South Africa was the satellite based text service that provides instant connectivity anywhere in the world. Coffee and sandwiches should be waiting for you when you arrive.

The landing gear is hydraulic, with pressure supplied by an electric pump. Like Piper’s piston singles, there is a simple emergency extension system that allows the wheels to free fall, and spring-loaded down-locks hold the gear fully extended.

This is a very electrical aircraft, so electrical redundancy is essential. The electrical system includes a 38-amp/hour 24-volt battery in the engine compartment, plus an engine-driven 200-amp, 28-volt DC starter/generator and an engine-driven 135-amp, 28-volt DC standby alternator. These three sources power a single busbar from which power is distributed through main, nonessential systems and nonessential avionics busses. A separate battery-powered emergency bus provides essential power to the pilot’s PFD, AHRS 1, ADC 1, com/nav radios.

For cabin climate control, the G3000 has an automatic thermostat that mixes warm and cool air to achieve the desired temperature. An engine-driven, vapour-cycle air-conditioner cools the cabin in hot weather. The G3000 also automatically controls cabin pressurisation by venting air through dual outflow valves, using air data and landing field elevation as references. The 5.5-psi pressurisation system provides a 9,600-ft cabin at FL280. An emergency bleed air system provides a redundant pressurisation source for the cabin. Bleed air is also used to inflate de-ice boots on the wings and tail leading edges.

The G3000 standard avionics package is feature rich, with synthetic vision PFDs, a 40-watt solid-state weather radar, digital autopilot, terrain and traffic awareness systems, dual SBAS GPS receivers, dual comm/nav radios, dual solid-state AHRS with GPS rate aiding, dual digital air data computers and an ADS-B OUT/IN-compliant Mode S transponder.

Other features include a prominent ‘blue button’ marked LVL, for the electronic stability function, which will right the aircraft from any unusual attitude, an automatic emergency descent mode, one-touch automatic level-off mode, hypoxia recognition system and under/overspeed protection, along with Garmin electronic flight charts, safe taxi system and the Aspen EFD1000 integrated ‘glass panel’ – relegated to a mere standby.

The 10-inch dish of the weather radar gives a nine-degree beam width that makes it challenging to identify weather hazards at long range. But the radar has a very respectable 218 dB performance index and a maximum range of 285 nm.

The autopilot has a coupled go-around feature, substantially reducing pilot workload during low-visibility instrument approaches. Just add power (carefully!), retract the gear and the flaps, and the system will automatically fly you to the missed approach fix. The flaps now have just three settings: Up, Takeoff and Landing.

 

FLYING THE M600

Starting the PT-6A-42 is straightforward for anyone who cut their teeth on a Cessna Caravan, or any one of the myriad aircraft that use this ubiquitous engine.

Demo pilot Thomas Nielsen and I had sat in the cockpit draining battery power while he ran me through the G3000s capabilities, and we had only switched the battery off when its voltage dropped to 24.5 volts. Nonetheless there was no danger of a hot start – especially on a cold Cape winter’s day.

Once the 600-shp engine is turning and burning, you run a main generator and back-up alternator check, switch on the avionics, pressurisation and air-conditioning, and programme the G3000 using the touch-screen.

Before takeoff vital actions include a prop overspeed governor check. There is no stand-alone prop control lever. Once the throttle is advanced for takeoff, prop rpm stabilises at a constant 2,000 rpm for the duration of the flight.

For the takeoff roll, the lack of FADEC means that you have to carefully set 1,575 ft-lb of torque. As with most PT-6A installations, throttle response in the M600 is not linear. As the gas generator rpm increases, throttle response becomes far more sensitive. It’s all too easy to overshoot maximum torque or temperature settings because of ham-fisted power lever movement. Fortunately, if you accidentally nudge torque or temp redlines, three warning bongs and red video alerts on the EICAS clearly remind you to pull back on the throttle.

Downhill on Stellenbosch’s 01, with about a 10-knot headwind component, two up and half tanks, the M600 was airborne just past halfway down the 760 m runway. Rotation is at 75 KIAS and lift-off at 81 KIAS. A nice characteristic, and one that differentiates it from the Saratoga and its smaller siblings, is that the moment you apply back pressure to rotate, it is keen to fly and seems to jump into the air with the long nose raising to a 12-degree nose-up pitch and comfortably settling there.

If you look for it, you can feel a small increase in pitch forces as weight comes off the wheels. That’s because the main wheels have been mounted further behind of the C of G than the M500’s, to reduce the propensity of the earlier models to fall on their tails with two large people in the rear of the cabin and none in the cockpit.

With gear retracted, accelerate to 100 KIAS and retract the flaps. A typical cruise climb is 145 KIAS, at which speed, and at typical weights, the VSI will maintain 1,500 fpm to FL200. The five-blade carbon-fibre Hartzell prop is credited with adding 250 fpm to the climb performance over the original four-blader.

Straight and level, the M600 accelerates to 260 KTAS while burning 250 lb/hour in ISA conditions. For the descent, a key advantage is the M600’s 250 KIAS Vmo redline (62 knots higher than that of the M500 Meridian) which allows you to get down smartly.

Other reviewers report that clean and dirty stall behaviour is a strong suit of this aircraft. At a weight of 5,500 lbs, the aircraft stalls clean at 71 KIAS and 60 KIAS with gear down and full flaps. There is only the slightest tendency to roll off when held in the stall, but it is easily countered with minor roll control inputs. As the aircraft has very strong speed stability, stall recovery was immediate as soon as back pressure on the yoke was released.

In the circuit, the non-linear throttle response makes precise speed control a challenge. Aim to cross the fence at 85-90 knots, depending on weight. An interesting change is that, compared to the M500, the M600 has higher pressure tires that make for firmer touchdowns.

Using moderate prop reverse and braking, it should be easy to stop the aircraft in 1,800 ft – under 550 metres.

 

PRICE

Piper has once again focussed on value for money. It has delivered more than 550 Meridians, not because of its unmatched performance, but because of its unmatched price. Piper claims a base price of just under US$3 million, which gives the M600 a unique place in the market. All its competitors start at well over US$4 million – and the Cessna Denali is expected to cost over US$5 million. This is an aircraft that targets owner pilots who want 1,200-nm range, single owner operating affordability and airliner avionics at a price 30% cheaper than the competition.

It really is the ideal personal plane, and it will be interesting to see whether the million Dollar cheaper pure jet Cirrus Vision SF50 makes inroads into the M600’s established market.

 

 

 

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