Tractable Tbm

As the swiftly-fanning propeller slows to a stop outside the FBO I can see that the 900 looks quite different to the earlier machines. It features large (61cm) swept-up winglets and an unusual looking five-blade prop, which seems to be set closer to the air intake. The air intake is also a different shape, the exhausts appear altered and the small bump on the cowling that covered the prop governor is also missing. Photographer Jim and I meet Michel Adam de Villiers, VP of sales for Daher Airplane Business Unit, and Wayman Luy, Socata North America chief pilot, and after breakfast Wayman briefs me on the 900.

He really knows his stuff, and confirms that my initial impressions are accurate – this is a very different aircraft to earlier TBMs, even though the Pratt & Whitney CanadaPT6A under the curvaceous cowling is essentially the same as that fitted to the 700 and 850. Interestingly, the engine (a PT6A-66D) is actually capable of producing up to 1,825shp (1,360kW) at sea level. However, it is flat-rated to a maximum of 850shp (634kW).

The reasons for flat-rating an engine are two-fold. Firstly, any air-breathing engine produces the most power at sea level on a cold day, because the air it needs to ‘breathe’ is at its most dense. As the aircraft climbs the air density reduces and the power produced diminishes. However, if the engine is only producing around 50 per cent of its potential output at sea level, then it is possible to maintain the same power output all the way up to cruise altitude.

The other main advantage is that the engine is always running well below its maximum, which obviously greatly increases its life. And as the PT6A‑66D fitted to the TBM 900 never runs at even 50 per cent of its full potential, I’d be very surprised if one ever failed to make TBO.

I then ask Wayman about the various changes I’d spotted, and he explains that several years ago Socata decided to undertake a comprehensive examination of the aircraft’s aerodynamics. By creating a numerical model of the aircraft and then using a computational fluid dynamics program (CFD) it was possible to study localised airflow in

This is a very different aircraft to earlier TBMs.

tremendous detail, and this revealed that the prop, cowling, exhausts, air intake and plenum were all far from optimum.

Basically, the prop disc was too far forward of the air intake (which wasn’t the ideal shape and size) with the net result that not only was the turbulent airflow creating unnecessary drag, but the engine wasn’t ‘breathing’ satisfactorily due to the uneven airflow entering the induction plenum. Furthermore, the exhaust pipes generated turbulent flow in the exhaust stream as they were not the most advantageous shape. Of course, the previous models were far from wrong – it is just that the incredibly accurate data derived from the CFD analysis indicated that these areas could be improved.

All of these issues were addressed, and along with adding new inboard main undercarriage doors and installing a new five-blade prop these changes greatly enhanced the performance. In fact they have raised the max cruise from the 850’s 320kt to a hugely impressive 330kt, even though the power-to-weight ratio is the same. Finally, the new prop means that at only 76. 4dBa at takeoff the 900 is even quieter than the 850, which was quite quiet in the first place.

Access to the engine is good, as the new carbon fibre cowling has large ‘gull wing’ doors on either side which open wide and are held in place by sturdy support struts. The firewall is formed from a single sheet of titanium, while the governor has been replaced by an electrical system with mechanical stops and the starter/generator increased from a 200-amp unit to 300 amps. There is now no speed restriction on the use of the inertial separator.

The robust undercarriage features main wheels with a relatively wide track that retract inwards while thenosewheel retracts backwards. Twin doors cover the entire nosewheel assembly when retracted, but the doors on the main undercarriage only cover half of each wheel, which are fitted with huge hydraulic disc brakes. Taxi and landing lights consist of blocks of LEDs mounted in the wingtips.

The wings are interesting – they have a fair amount of dihedral, flush-riveted skins, now with big winglets, fences at approximately mid-span, huge Fowler flaps (which extend over about 70 per cent of the wing’s trailing edge) small Frise ailerons and upper-surface slotted spoilers (or spoilerons) which are interconnected to the ailerons.

The very large flaps were required to keep the stalling speed down, and the inevitable side effect is that the ailerons are somewhat on the short side, with a consequent degradation of control around the lateral axis. The spoilerons provide an elegant solution. There is a bulbous radar pod mounted on the port wing, but apart from that it’s astonishing just how smooth the wing and fuselage are.

As we walk towards the tail I notice several small yellow arrows along the fuselage, and Wayman explain that as TBMs are built to extremely high tolerances these are used in conjunction with lasers to ensure the fuselage is aligned correctly in the jigs during construction. The 900 has the same pair of ventral strakes directly beneath the sweptback fin as earlier TBMs, although it seems to me that the dorsal fillet immediately in front of it is larger. The rudder and elevators are both mass and aerodynamically balanced, with the elevators actuated by dual pushrods while the rudder is cable operated.

Anti-ice protection is provided by pneumatic boots on the leading edges of the wings, tailplane and fin, while the prop blades, pitot tubes, stall warner and windshieldsare heated electrically. The engine intake lip is heated by bleed air and features an inertial separator.

When viewed from the front the spinner is noticeably angled down and to the right.

As with all the TBMs I’ve tested, the build quality is exceptional, but as well as being well made it is also very thoughtfully designed. For example, the towbar is carried in its own specially moulded box which slides into a dedicated stowage area, there is a mirror built into the ELT bay and another (along with a light) in the nosewheel well to check the fuel filter.

The next big change that Wayman points out is the dedicated pilot door. Previously an option on the 700 and 850, it is standard on the 900 and confers several significant advantages. Possessing a – shall we say – ‘fuller figure’ I always find the transition from cabin to cockpit a bit of a squeeze (to be fair, on the 900 the seats are slightly narrowerand the centre console shorter) and so much prefer having my own door, and of course this arrangement allows the pilot to ensure that the big main door is secure. Finally, if being used as a small freighter it allows operators to fill the cabin to capacity without having to leave space for the aisle. (Most small freighters run out of space before they exceed their MAUW. ) Making the pilot’s door a standard item is a really good idea.

Talking of the cabin, the test aircraft’s was configured in a very luxurious club class, but it can be easily reconfigured.

While adjusting my seat and rudder pedals it seems to me that the field of view is slightly compromised by the tall glareshield, but Wayman assures me that this isn’t the case in flight, so with the sumptuous seat and rudder pedals set, I begin to acquaint myself with the layout of the controls and instruments. Although externally there are a number of changes, some subtle and some significant, from earlier TBMs that I’ve flown – the cockpit is very different.

Unsurprisingly, it’s completely glass. It has a massive 15in MFD in the centre and two large PFDs either side. Sensibly sited directly above the pilot’s PFD are an electronic standby AI that includes airspeed and altitude, plus orange ‘Master Caution’ and red ‘Master Warning’ annunciator lights. Above the MFD is the autopilot control panel, while the control panel for the ECS and an alpha-numeric keypad for the fully integrated Garmin G1000 are underneath.

The next big difference is in the centre console, which carries the elevator trim wheel and a rocker switch for aileron trim, a flap switch and fuel selector, the red ‘manual override’ control and the all-new single power lever. This controls the engine, propeller and fuel through a quadrant that resembles a lower case

It’s impossible to grab the wrong lever, when there’s only one lever to grab!

‘h’. To start the engine, simply click the ‘Start’ switch in the overhead panel to ‘On’ and at 13%Ng move the power lever forward to ‘Lo- Idle’. Once the engine has lit and the ITT is stable the lever can go further forward to ‘Hi-Idle’. Then raise the leather-covered ‘crown’ on top of the lever and slide it across to the left. This unfeathers the prop (automatically governed at 2,000rpm) and by moving the lever fore-and-aft you have forward thrust, ‘Beta’ (this flattens the prop pitch, which produces less thrust for taxi) and then reverse.

It’s a brilliant idea, brilliantly executed. It’s impossible to grab the wrong lever when there’s only one lever to grab! Running through the post-start checks on the electronic checklist I find myself wondering whether the MFD is actually too big! It really is huge, and almost draws the eye away from the PFD. Flap and trim positions are shown on the MFD, but the undercarriage uses lights co-located with the lever, which I prefer. The lever illuminates when the wheels are in transit.

As on nearly all turbine-powered aircraft, the switches for most of the electrical systems – such asthe lights, starter and generator – are in a neat overhead panel.

However, and unlike most turbinepowered aircraft, both the fuel flow and quantity are displayed in US gallons, whereas in most turbinepowered aircraft fuel is measured by weight and not volume. However, I think the reason Socata designed the system like this is that many potential TBM purchasers would be transitioning up from a complex piston-powered aircraft (which do indicate fuel quantity and flow by volume).

Another unusual feature is that among the seven switches fitted to the yoke, one trims the elevator and rudder. As the powerful engine turns a big five-bladed propeller and operates over a very wide (approx 260kt IAS) speed range, you don’t need a degree in aeronautics to appreciate that rudder trim is important, and the TBM series remain the only aircraft in my logbook fitted with a yoke-mounted rudder trim. Initially, I find this switch a bit of a stretch, as in my opinion a good ‘rule of thumb’ (see what I did there?) for the trim button is that it should be almost where your thumb rests naturally.

However, I soon adjust to it.

As soon as we are rolling I drew the power lever right back and ensure that it is on the idle stop.

Nevertheless, it still wants to taxi faster than I want to, so to avoid constantly riding the brakes I pull the power lever back into ‘Beta’.

Taxiing is very straightforward. The nosewheel steers through the rudder pedal and is nice and precise, while the hydraulic brakes are powerful and progressive.

Another neat feature is that the fuel tank selector automatically switches between the wingmounted tanks to prevent a lateral imbalance. Every five minutes when on the ground, and ten in flight, it changes tanks. Furthermore, should your fuel situation have deteriorated to the point that both tanks are showing ‘Low Fuel’ warnings on the MFD, the fuel selector automatically switches from tank to tank every 75 seconds to ensure every last drop of Jet A-1 is extracted. The two wing tanks have a combined total of 1,140 litres, and only 44 litres is unusable.

At the run-up point I set the trims and flaps and conclude the pre takeoff checks. As mentioned earlier, the yoke-mounted rudder trim is indicative of how important it is that the rudder is correctly trimmed, so I take care to make certain the rudder trim indicator is pointing to ‘T/O’. Unlike the 850 (which hadthe power artificially constrained to 700shp until the flaps were up) the various aerodynamic tweaks and a new torque limiter mean you have full power from the start.

Out on the runway I line up with the centreline, stand on the brakes and slowly increase the power to 40 per cent torque, then release the brakes and push the power right up, without exceeding 100 per cent. The big turboprop literally bounds forward and surges down the runway. The speed tape comes alive almost immediately and in less time than it takes to type this sentence we are racing past the Vr of 85kt and I ease the yoke back. Despite all the power there’s absolutely no trouble tracking the centreline, whichspeaks volumes for the efficient rudder trim. Everything happens so quickly that I honestly don’t know how much runway we used, but at our relatively light weight I doubt it is more than 500 metres. The extra power available for takeoff has made a great aircraft even better, while the winglets and strakes all combine to ensure plenty of controllability at high power and slow speeds.

However, the biggest disappointment (and just as it was with the Piper M500, see Australian Aviation April 2015) is that the engine doesn’t have FADEC.

This criticism is aimed at Pratt & Whitney, not DAHER, but in an aircraft this sophisticated you really shouldn’t have to manually set thepower accurately. There should just be detents in the power lever quadrant for takeoff and climb.

When taking off in a strong crosswind, for example, you shouldn’t have to monitor the torque, just concentrate on keeping straight. The same can be said when departing single-pilot into heavy IMC and a busy traffic environment.

In fact, having retracted the undercarriage and flaps and engaged the yaw damper I check the torque while adjusting the power and momentarily misinterpret the command bars on the PFD. However, that error could also be because I am a bit rusty with ‘glass’.

Anyway, as we rocket skyward at 125kt and over 2,000ft/min I get my scan going and hand-fly up to 20,000ft, before engaging the autopilot.

Once level at FL280 Wayman demonstrates just how flexible this machine is. Want to save time? Push the power up and the TAS is an incredible 330kt, while the fuel burn is still pretty reasonable at around 245lit/hr. Want to save fuel? Pull the power back and the fuel flow drops to 148lit/hr, while the TAS is still 252kt. Obviously the ‘range ring’ on the G1000 expands exponentially when you slow down, but possibly the most impressive aspect of the TBM 900 (to me, anyway) is just how many of the airports in range are available to us.

The pilot operating handbook claims that less than 750 metres is required for both takeoff and landing at MAUW, and that includes clearing a 50ft obstacle! There are very few public use airports in the States that are less than 1,000 metres, and it is this flexibility where the 900 really scores over the light jets. No light jet has anywhere near the range of the 900, nor can they use short runways.

The original plan was to fly down to the Keys, but even at FL280 we’re still firmly in the clag and

In less time than it takes to type this sentence we are racing past the Vr of 85kt and I ease the yoke back.

the forecast hasn’t improved, so we decide to head back to Sebring. As we’ve now got a decent tailwind we’re really covering the ground and I initiate a gentle descent. Our groundspeed is now nudging 360kt, or six miles a minute, and when you think we could be moving up to six people through the sky in club-class comfort at Mach 0. 5 while burning less than 250lit/hr it really is quite remarkable.

However, what I find even more remarkable is just how tractable the 900 is. Most turbine-powered aircraft are restricted by VMO, which is an indicated airspeed value that varies with altitude. However, the TBM is so strong that its VMO is fixed at 270kt, irrespective of altitude. Consequently, the red line on the speed tape can be viewed as being more like a VNE than a VMO, a big plus when you have to descend quickly. And should a rapid descent be required then pulling the power lever right back with the prop automatically governed at 2,000rpm makes the prop blades automatically go to ‘fine pitch’ to maintain turbine rpm. The prop disc then becomes a giant airbrake, allowing forimpressive rates of descent.

Need to really get down? (For example in the event of a pressurisation failure. ) Even more drag can be added by lowering the undercarriage and the first stage of flap, as the limiting speed for both is a usefully high 178kt.

Speaking of pressurisation, the ECS is integrated with the G1000 and can maintain the cabin altitude at approximately 9,000ft even when the aircraft is at its certified operating ceiling of 31,000ft.

As we descend through 12,000ft we pop out into clear air between two layers of cloud, so Wayman cancels our IFR flightplan, leaving me free to manoeuvre. I begin to experiment with the general handling, and am immediately impressed by how responsive the 900 is. The ailerons and their interconnected spoilers are smooth and effective, and although all the primary controls are purely mechanical (a combination of bell cranks, cables and pushrods) they are pleasantly light, with low breakout forces and very little ‘stiction’ in the control circuit.

The elevator is slightly on the heavy side, but we did have a fairly forward CG (and you don’t really want light pitch forces when you’re clipping along at 330kt).

One thing I note is that that I seem to have to use the rudder trim less than on earlier TBMs. As expected, any variation of either airspeed or power (and all that torque, precession and P-factor created by the powerful engine and big prop do produce considerable yawing moments) requires rudder trim to keep both the pedal forces neutral and the slip ball centred, but the 900 seems better damped in yaw.

This is probably down to the big winglets, redesigned fin and a more efficient yaw damper, and it is also interesting to note how little rudder is required in the turn, despite thefact that the wings have a relatively high aspect ratio. This is because the ailerons/spoilerons and rudder are interconnected.

All three primary controls are nicely balanced, well weighted, and – most importantly – agreeably harmonised.

Visibility throughout the turn – and indeed every phase of flight – is excellent. The pilots’ seats are situated just in front of the leading edge, and their location combined with the large windscreen confers a fine field of view and – as Wayman had predicted – you don’t notice the glareshield in flight. An examination of the stick-free stability reveals the longitudinal and directional stability to be positive and neutral laterally. The slow-speed handling is exemplary, as full lateral control is available post-stall because of the spoilerons.

Back at Sebring I turn downwind for runway 19 with the power at 55 per cent and trimmed for 120kt, then abeam the numbers set the flaps to ‘TO’, lower the undercarriage and turn base. On final it’s flaps to ‘LDG’, ease the power lever back to 25 per cent torque and trim for 90kt. Interestingly, the engine’s response to adjustments of the power lever seem much more linear than on some other PT6-powered machines that I have flown, while the extension of full flap pitches the nose down very nicely, for an excellent view of the runway.

Wayman recommends an initial approach speed of 90kt with a Vref of 85, and then on very short final to simultaneously ease the power back while trimming nose up. As he predicted, it practically lands itself, although obviously if you decide to go around you’d want to get some nose down trim in quickly. Get the nosewheel on the ground, pull the power into reverse and the deceleration is as impressive as the acceleration! Having made a mess of the initialclimb-out I taxi back for another go, and this time all goes well, and an accurate circuit is capped with an even better landing. Wayman is very complimentary, and even the lineman comments on how smooth he thought it looked as he chocks the wheels. I’m very pleased, but most of the credit should go to Wayman, who is an excellent instructor.

The 900 is an amazing aircraft – quite possibly one of the most impressive that I’ve ever flown. After all, how many aircraft do you know that can clear a 50ft obstacle using only 750m, fly over 1,700nm in less than seven hours, land over a 50ft obstacle and stop on a 750m runway, with 45 minutes of fuel still in the tank! And it’s the outstanding tractability that is most impressive. When you’re flying a jet, an abundance of airspeed or altitude can quickly become an embarrassment, but with the TBM you just pull the power back – that big prop disc is a very effective airbrake.

However, the reason why it impressed me so much isn’t because of the spectacular performance or opulent cabin. For me, the most remarkable thing about it is that it really is within the capability of many GA pilots. The takeoff and landing speeds are not excessively high and the systems are so beautifully designed that single-pilot IFR isn’t as challenging as it can be.

All this does of course come at a price, a price that contains a lot of zeroes! But if you can afford it, then the TBM 900 might just be the ultimate private aeroplane.

DAHER TBM 900

Technical
Specifications

Engine
Pratt & Whitney Canada PT6A-66D turboprop, flat-rated at 850shp (634kW)

Propeller
Hartzell composite five-blade, constant-speed, reversible, fully feathering
Performance
VMO 270kt
Cruise (TAS) 330kts
Stall 65kt
Climb 2,050ft/min
Takeoff to 15m 726m
Land over 15m 741m
Weights
Empty 2,099kg
MAX AUW 3,370kg
Useful load 1,271kg
Fuel capacity 1,140lit
Dimensions
Wing span 12.83m
Length 10.73m
Height 4.35m
Wing area 18.3m2
Price
With standard equipment: US$3,599,024
With ‘Elite’ package: US$3,798,414