Air Test ESP

Intrigued, I draw the power lever back, trim forward and push the nose over into an ever-steepening dive. The waiting waters of the Atlantic Ocean loom large in the windscreen and the VSI is pegged at 6,000ft/min as the altitude tape tumbles through 12,000ft. With less than two minutes to live it’s clearly time to start recovering, but instead I simply release the controls, wait, watch – and hope that the M500’s systems are as good as they say they are! The day had begun rather differently from most flight test assignments. Upon arriving at Piper’s famous Vero Beach facility, photographer Jim and I were ushered into a meeting room by director of corporate communications Jackie Carlon and given a thick sheaf of documents sternly labelled ‘Proprietary and Confidential’. These pertained to the latest addition to Piper’s very successful M-Class, the new M500 – an aircraft so secret that when I revealed its existence to your editor (in confidence) later the same week he said “the M-what? Never heard of it!” As had no one else, because, in a major scoop, I was honoured to be the first journalist in the world to be given the opportunity to evaluate this intriguing new aeroplane. Over the course of a long and thorough briefing, Jackie and Piper demo pilot Dave Athay explained exactly why what I was about to fly was so special. The acronyms and initialisms flew thick and fast as the myriad features that make this machine so remarkable were revealed, and when ESP was mentioned I could scarcely believe it (in fact, ESP means electronic stability protection – of which more later).

Unsurprisingly, this aircraft offers all the latest refinements that you’d expect to find on an aircraft of this class, such as an Iridium transceiver, XM weather, a digital pressurisation system, electroluminescent cockpit placards and an extended squitter transponder and traffic advisory system that has ADS-B In and Out functionality.

However (and as impressive as all the above undoubtedly is), what really made me sit up in my seat was when Jackie began to describe the enhanced autopilot flight control system (AFCS). This system incorporates facets such as the ability to perform a coupled goaround, automatic underspeed and overspeed protection, an expanded autopilot engage envelope, a ‘Level Mode’ facility and electronic stability protection. By now my head was buzzing, but working on the premise that a single flight is worth ten briefings, it was clearly time to go flying.

Interestingly, when I walk out

The M-what? Never heard of it!

onto the ramp at Vero Beach later that morning the aircraft certainly doesn’t look that special, being simply painted in a single shade of off-white and with the N-numbers rather crudely stencilled on the side.

In fact, it looks more like a utility turboprop about to be ferried to some foreign air force. Piper has worked hard to keep the M500 ‘off the radar’ – and as this report is possibly the first time you’ve ever heard of it I’d say the company has done a pretty good job.

Of course, the M500 still shares the same PA-46 type certificate as the Matrix, Meridian and Mirage. It has essentially the same high aspectratio wing (it has slighter greater wing area, due to the large wingroot fillet) and is fitted with large singleslotted flaps and relatively wide, narrow chord ailerons.

One slight difference is the row of vortex generators on the wing, but the fuselage, fin and tailplane all look the same (although the M500 is actually fractionally longer). It also has the same undercarriage, which has a wide-track but relatively short base. There is a large LED taxi light on the nosewheel strut and powerful LED landing lights in the wing’s leading edge.

It has all the sort of equipment you’d expect to find on an allweather aeroplane, including weather radar (in a small pod under the starboard wing) pneumatic rubber boots on the leading edges of the wings, fin and tailplane, deice for the prop and a heated pilot’s windscreen.

In common with some other Piper retractables the main wheels (which retract inwards) are not covered by doors. The nosewheel retracts aft.

In fact, it is only when you’re studying the cowling that the real difference between the M500 and the Matrix and Mirage becomes apparent. Unlike the large air inlets that are abeam the spinneron the piston-powered versions of the PA-46, the M500 has the primary air intake below the spinner and a small scoop in front of the windscreen. And if you’re still wondering what sort of engine lurks beneath that smooth cowling, the two huge exhausts sprouting from both sides dispel any doubt – it’s a variant of the most successful turboprop ever made – the Pratt & Whitney Canada PT6.

This particular version of the famous free-turbine engine is the PT6A-42A, and although it is capable of producing 850shp (630kW) at sea level on an ISA (international standard atmosphere) day, on the M500 it’s flat-rated to 500shp (373kW). This confers two significant advantages. It leads a very under-stressed existence (and is consequently very reliable), and can continue to produce its full-rated power right up to around 25,000ft, unlike many other engines which experience a considerable dropoff in power at altitude. It turns a four-bladed Hartzell propeller and is fed from two wing tanks with a combined capacity of 644 litres.

Up the airstair, through the sumptuous cabin and into thecockpit and I immediately see that – as Jackie had implied – most of the differences between earlier PA-46s and the M500 are in the cockpit. The MFD has been reduced in size (from 15 inches to 12) and the panel is better for it. On the Matrix the MFD was so big that it almost distracted you from the ten-inch PFD. The panel just looks better balanced with the smaller MFD, and it has also allowed the autopilot controller to be moved up from underneath the MFD to just below the glareshield.

Whether this is what drove Piper’s engineers to scale down the MFD or is simply a useful by-product of that decision I don’t know, but it is a definite improvement. It isn’t that the Matrix’s autopilot controller is badly placed (it isn’t, being easy to both see and reach) it’s just that the AP controllers in turbine-powered aircraft are usually located towards the top of the panel.

Another change is that the standby analogue ASI, AI and altimeter immediately to the left of the pilot’s PFD have been replaced by an Aspen Avionics EFD-1000 Evolution standby instrument. I last saw one of these when I flew the Pilatus PC-21, and it really isa cracking piece of kit. An entirely self-contained unit (it even has an integral battery), it not only provides airspeed, altitude and attitude but also navigation information. Look closely at the accompanying cockpit picture and you’ll see that there isn’t even a ‘whiskey compass’ on the M500’s flightdeck! To ensure that the panel is as clutter-free as possible many of the switches are in a neat overhead panel.

Obviously the power control levers are very different, with just a fuel condition lever and power control to operate. This mostly controls the engine (the prop is automatically governed at 2,000rpm), although lifting it up and back over a gate allows you to select ‘Beta’ (this flattens the prop pitch, which produces less thrust) and then ‘reverse’.

Other little differences between the M500 and the Matrix I flew last year include the addition of rudder trim (a small rocker switch to the left of the flap selector) and deleting the three green position indicator lights next to the undercarriage lever (the undercarriage’s status is now shown on the MFD). The very neat alpha-numeric keypad at the bottom of the centre console remains thesame. This controls the same fully integrated Garmin G1000 avionics suite; although with the M500 the digital pressurisation system is also linked to the G1000. The cabin heater has also been greatly improved, with a rotary knob for climate control replacing the rather crude push/pull knobs.

With Piper’s manager of experimental flight test Craig Masters in the other seat and a Piper dealer called Rich in the cabin we prepare to start the engine. Thus far I’d been extremely impressed by the M500’s level of sophistication, so you may well imagine my surprise when Craig produces a large POH and begins reading the pre-start checklist. Having flown many aircraft fitted with electronic checklists I am frankly amazed that the M500 doesn’t have one, although I strongly suspect that this omission will soon be rectified.

Starting the turboprop engine is very straightforward, simply press ‘start’ and above 13 per centNg move the fuel condition lever to ‘run’. The PT6 lights with its characteristic muffled ‘whumpf’ and we get a nice cool start. Obviously we keep a close eye on the inter-turbine temperature (ITT) gauge during start-up (and mistakes can be expensive) but it never looks like getting close to its upper limit. Nevertheless I’m really am surprised that there’s no FADEC.

Taxiing out I notice that despite holding the power lever on the idle stop it consistently wants to accelerate, so to avoid constantly riding the brakes Craig suggests pulling the power lever back into Beta, which works well.

Out at the run-up point we conclude the pre-takeoff checks rapidly, and with the trims and flaps set I carefully point the big cowling down the centreline, stand on the brakes and slowly increase power to 40 per cent on the torque gauge, then release the brakes, push the power lever forward and then hurriedly pull it back a bit whenthe torque indicator slips into the red. I just can’t believe this engine doesn’t have FADEC! At 2,329kg the M500’s MTOW is around 350kg greater than the Matrix’s, but with about 160kg of fuel and three POB we’re well below that, while ambient conditions are pretty close to ISA, with a slight crosswind from the left. Now, the initial acceleration of a Matrix or Mirage is somewhat pedestrian, but the M500 positively surges down the runway and the rotation speed (Vr) of 85kt comes up very quickly.

Positive rate – gear up, flaps up and the M500 scorches skyward at 120kt and 1,200ft/min.

The best rate (Vy) speed is 100kt but the forward visibility is distinctly compromised as the deck angle is really quite steep, and as both Craig and I like to see where we’re going I take his advice and trim for 120kt. Even at this less-than optimum speed the climb rate is pretty impressive, and I soon discover why Piper has given the M500 electric rudder trim. That big prop does indeed produce considerable amounts of torque, precession and P-factor and I very quickly notice that whenever I adjust either airspeed or power I also need to adjust the rudder trim in order to keep both the slip ball centred and the pedal forces neutral. An ‘out of trim’ arrow on the MFD shows which way to press the rudder trim rocker.

One of the best-kept secrets in aviation is that the engines of turbine-powered aircraft are significantly easier to operate than piston-powered machines, so whereas in say a Bonanza, Cardinal or Comanche I’d have been constantly adjusting throttle, prop, mixture and cowl levers to optimise performance, with the M500 all I do is occasionally tweak the power lever (and if it had FADEC I wouldn’t even have to do that!).

Barely 10 minutes after brake release I level off at 12,500ft above the Atlantic. The centre of the M500’s operating altitude is the mid-20s (it is cleared to operate at up to FL300) and at these altitudes it will comfortably cruise at a TAS of about 255kt while burning around 105kg of jet fuel an hour. With a maximum fuel load of 515kg (although the size of the fuel tanks is measured by volume, fuel uplifted and consumed is calculated by mass) the M500 has a range of about 1,000nm plus a 45-minute reserve.

Of course, if you fill the tanks you can’t fill the seats, but most – if not all – aircraft in this class require some sort of compromise regarding utilisation of the useful load.

The beauty of operating a turboprop is that you’re ideally placed to make the best use of the upper winds, and this is where features such as XM weather and having all the systems (including the new digital pressurisation system) fully integrated really score. The G1000 can even manage your descent for you, which can be veryuseful when you’re clipping along at 30,000ft with a groundspeed of 300kt. Just give it the desired altitude to be achieved by a specific waypoint, and it will work out the vertical profile and even include a top of descent point.

This really is a serious travelling machine, specifically designed for people who have some serious travelling to do.

However, the purpose of today’s flight is not to confirm its cruise characteristics or VNAV capabilities but to explore the virtues of its enhanced autopilot flight control system – and I’m extremely eager to find out just what this powerful new AFCS can actually do. While we’ve been climbing up to our operating altitude Craig has given me a brief ‘refresher’ on the system, and as he has been instrumental in its development he knows it ‘inside-out’.

Usually I’d explore the slow flight and stall characteristics before digging any further into the envelope, but as the M500 has essentially the same wing (and similar wing loadings) as the Matrix and Mirage I am familiar with its behaviour, so with Craig’s approval (and with an attentive Rich paying close attention from the cabin) I start with a look at the electronic stability protection, or ESP. This uses the same actuators, processors and sensors as the GFC700 autopilot, but functions independently of the AP and actually only comes into play when the AP is disengaged and the pilot is hand-flying. It is automatically disabled below 200ft AGL.

Essentially it operates in three modes – roll, pitch and high airspeed – by introducing a correcting force while still providing the pilot with feel. For example, once I rolled the aircraft past 45 degrees of bank I became aware of a subtle but significant resistance through the yoke. At 60 degrees the sensationPositive rate – gear up, flaps up and the M500 scorches skyward at 120kt and 1,200ft/min. was no longer subtle but a quite substantial self-righting force, and although I could have either physically overpowered it or temporarily disabled the system by pressing the AP disconnect or CWS (control wheel steering) buttons, the sensible (and logical) course of action was to just let go and let it sort itself out, which it promptly did by returning to straight-and-level flight.

Intrigued, I try a few more excursions in roll and then move onto various pitch angles, and once again (this time at 15 degrees nose down and 17 degrees nose up) I sense the self-righting force through the yoke. Alternatively, should you be hand-flying and become incapacitated – possibly by illness or vertigo – and begin to feel you are losing control, all you or the person sitting next to you has to do is punch the blue ‘LVL’ on the panel. This automatically engages the AP and returns the aircraft to straight-andlevel flight.

This is all very impressive, as the important point to remember here is that should the ESP activate it is entirely automatic, while for the ‘LVL’ mode to be engaged only requires one clearly marked button to be pushed. Furthermore, if the ESP has been engaged for a significant length of time (it’s quite complicated, but essentially it’s any 10 seconds in a 20-second period) then the AP auto-engages in level mode. A further enhancement of the GFC-700’s capabilities is that the AP’s engagement envelope has been expanded significantly and it can engage up to +/-50 degrees in pitch and 75 degrees in roll.

Now, some of you may be thinking “this is all well and good, but if the pilot’s temporarily incapacitated and the non-pilot passenger has punched the ‘LVL’ button, what’s to stop it stalling?” Patience – I was coming to that.

Under Craig’s direction, I press theaforementioned ‘LVL’ button and then draw the power lever back to idle. The airspeed bleeds away as the AP initially maintains straightand- level flight, and then as the airspeed becomes dangerously low and the angle of attack increases the underspeed protection (USP) kicks in and smoothly lowers the nose to maintain the speed at around five knots above the value at which it would stall.

I was hugely impressed – and even more so when Craig explains that the enhanced AFCS also provides for coupled go-arounds. If you just hit the TOGA button on the power lever the AP levels the wings and pitches the nose up nine degrees, but if the published missed approach procedure is loaded and active the AP will fly it – all the pilot has to do is push the NAV button on the AP controller. And should you be sufficiently remiss to press TOGA but neglect to increase power, the USP system automatically pitches the aircraft to maintain an IAS just above stall warning activation.

Frankly, I found the whole thing rather incredible – as systems boasting this level of sophistication are typically only found in giant jetliners, not GA aircraft with six seats and only one engine! Descending rapidly back towards Vero Beach it suddenly occurred to me that I hadn’t even thought about the new digital pressurisation system. It functions so smoothly that I was completely oblivious of its presence! The cabin pressurisation runs at 5. 6psi, which equates to a cabin altitude of approximately 10,000ft when the aircraft is at its certified operating ceiling of 30,000.

A power setting of 55 per cent torque and a speed of 100kt seems about right on the downwind leg, and as we pass abeam the numbers I select the first stage of flap and lower the undercarriage before commencing the turn onto base andgoing to Flap 2. As we turn final the long cowling somewhat blocks my view of the runway, but full flap smoothly pitches the nose down, greatly improving the view. Easing the power lever back to 25 per cent torque drops the speed to 90, but I’m momentarily distracted by an Archer in front of us that the traffic advisory system has detected but neither Craig nor I can see.

Unfortunately I allow the M500 to dip slightly below the glideslope but quickly retrieve the situation with some power, take the power back off on short final and cross the fence bang on the Vref of 85. All I have to do now is land, but I make the same mistake as with the Mirage and Matrix and try for a fully held-off landing, with its associated prolonged float. Get that wing in ground effect and it just doesn’t want to stop flying! With all three wheels eventually on the runway I pull the power lever into ‘Reverse’ – the engine bellows hoarsely and within seconds we’ve lost 40kt and I move the power lever back into idle to avoid prop erosion.

Later that evening I make a few notes, think about what I’ve just seen and begin to realise just how important – and influential – the latest aircraft from Piper might be. And these technologies will continue to mature, to the extent that – one day – the ‘LVL’ button may be replaced by an ‘EMERG’ button that literally flies the M500 to the nearest suitable airfield and lands it. This isn’t the same as the (in my opinion flawed) concept of pilotless airliners, but simply an emergency feature. But can you imagine what a confidence booster this would be for nervous passengers? Remember that the M500 is a single-pilot machine.

Way back in 1939 Piper practically created practical general aviation with the immortal J-3 Cub. Now, some 76 years later, Piper has quite possibly taken aviation safety to (if you’ll pardon the pun) another level.

Piper PA-46
Meridian M500
Technical
Specifications

Engine
Pratt & Whitney Canada PT6A‑42A
turboprop, flat-rated at 500shp
(373kW)
Propeller
Hartzell composite four-blade
constant-speed
Performance
VMO 188kt
Cruise (TAS) 260kt
Stall 60kt
Climb 1,315ft/min
Takeoff to 15m 854m
Landing over 15m 640m
Weights
Empty 1,559kg
MAX AUW 2,329kg
Useful load 770kg
Fuel capacity 644lit
Dimensions
Wing span 13.10m
Length 9.0m
Height 3.40m
Wing area 17m2