Flight test: Cessna TTx
- Credit: Archant
Descended from Lancair’s Columbia, and previously known as the Cessna 400, there’s no confusion about the handling and range capabilities of this speedy machine. Words Dave Unwin, Photos Cessna
As the gleaming Cessna TTx turned onto the taxiway I glanced at my watch and noted it was 1102. “Sorry I’m late,” said Peter Herr, as we shook hands outside Gamston’s operations building. “Hey, what’s a couple of minutes between friends,” I grinned, then paused. “Hang on, have you just flown direct from Germany?”
The TTx represents a significant departure from the norm for the Cessna Aircraft Company. Although it has built more than 190,000 single-engined aeroplanes, most had two things in common. Irrespective of whether the engine was a piston or a turbine?or if the third wheel was at the front or back?they were made of metal and had a high-wing configuration.
However, not only is the TTx of composite construction and with a low-wing layout, it is also the first Cessna that was not designed and certified in house, as it is derived from the Columbia 300, 350 and 400 series designed by the Lancair Company of Bend, Oregon. Having flown all the Columbia series (albeit many years ago) I was very much looking forward to seeing just how much Cessna had done to what was always a very impressive machine.
Despite having a fixed undercarriage, the TTx is the fastest single piston-engined four-seat tourer in the world and, as you’d expect, the wing features some advanced aerodynamics to allow it to function efficiently and safely at the extremes of the operating envelope. These include large drooped ‘cuffs’ on the leading edge, located at approximately the same chord line as the inboard end of the ailerons, and little plates attached to the outboard ends of the ailerons.
These plates project down into the high-pressure air and constrain the span-wise airflow, increasing the efficiency of the ailerons and ensuring they remain effective, even at high alpha. There is no washout (built-in twist to reduce the angle of attack of the outer portion of the wing): instead two stall strips on each leading edge ensure that the wing stalls at the root well before the tip, and Peter assured me that the combination of cuffs, plates and large Fowler flaps all combine to grant the TTx excellent low-speed characteristics, despite its impressive top speed.
The high speed corner of the envelope was the bit I was looking forward to examining. It’s not hard to make a 310hp turbocharged aircraft go fast, nor is it particularly difficult to design a four-seat aircraft to fly slowly. The real achievement is to make it do both.
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Cessna may not have had a lot of experience of constructing with composites but it clearly learned quickly, for close inspection of the two-spar wing reveals it to be extremely well made and extraordinarily smooth. Although the aircraft is made primarily from GRP, the main spars, doors, cowlings, flaps and all the flying controls are made from carbon fibre composite, as are the tailplane ribs and spars. Metal is used only for the undercarriage legs and for the mounting tubes for the tailplane.
Another change from most single-engine Cessnas is that pushrods are used to operate the ailerons and elevators. The flaps and speedbrakes?another deviation from the Cessna norm?are electrically actuated; the flaps have three settings: up, 12° for takeoff, and 40° for landing.
As the TTx is certified for IFR, lightning protection is provided by the incorporation of a metal mesh (copper or aluminium) into every exterior surface of the aircraft. Composite aircraft can be badly affected by lightning strikes, as the materials used in their construction are non-conductive, and because the TTx is very much an ‘electric aeroplane’ it is vitally important that the energy from a lightning strike?or even an accumulation of static electricity?is dissipated safely and effectively.
Consequently, a considerable number of static wicks protrude from the trailing edge of the wings and elevator to allow any build-up of static to be discharged safely without adversely affecting any of the electrical systems. The FIKI (flight into known icing) package uses TKS fluid via a ‘weeping wing’ system for the leading edges of the wings, fin and tailplane, and a slinger ring for the prop.
The tricycle undercarriage is a fixed tubular steel arrangement fitted with toe-actuated hydraulic Cleveland brakes and a castoring nosewheel. At 2.2m the wheel track is relatively wide, while the wheelbase is only slightly smaller at just over 2m. All three wheels are quite closely spatted (as you’d expect of an aircraft that has been designed to fly fast with a fixed undercarriage), the mainwheels using 6.00-6 tyres and the nosewheel a 5.00-5.
However, the downside is that as the tyres are not very big, if operated at the 1,633kg MAUW on a soft surface the TTx would soon sink down to the spats. Unlike most Cessna singles, it is not a good aeroplane for soft or unprepared runways (to be fair, neither is its closest competitor, the SR22). While this is a trivial point in the USA, which has plenty of hard-surfaced runways, in Europe even some quite large fields are all-grass.
Interestingly, the mainwheel spats are fitted with small NACA ducts to allow the heat to dissipate should the brakes be used over-enthusiastically. And if you’re wondering why the undercarriage is fixed, the reasons are simple: cost, complexity, weight, and cheaper insurance where there is no danger of landing wheels-up!
The aircraft I flew was fitted with the increasingly familiar Hartzell ‘Scimitar’ three-blade propeller (although McCauley props are now standard) set behind a highly-polished spinner. It is turned by a 310hp Continental TSIO-550-C fitted with dual turbochargers and intercoolers which can put out up to 85% power at 25,000ft, and all 310hp at altitudes as high as 18,000ft. There’s an intriguing plunger in the cowl’s port air intake which allows the oil cooler’s inlet to be adjusted prior to flight to suit ambient air temperature. Somewhat surprisingly, cowl flaps are not fitted.
The elevator is a two-piece unit, while the rudder appears noticeably larger than on the Columbia (both in chord and span), and a substantial, raked ventral strake has been added towards the rear of the empennage. This increases keel area to aid in spin recovery, for whereas the 300 and 350 progenitors were certified with the FAA as being ‘spin resistant’ (incapable of departing controlled flight into a spin), the 400 and TTx are ‘spin recoverable’.
Access to the cockpit is very good. The generously-sized gull wing doors open wide and are held up by gas struts?and sensibly-sited handles and steps make it easy to step up onto the wing. Instead of a large non-slip walkway, there are merely slender strips of non-skid material on the wing. Clearly, every effort has been made to reduce drag.
My initial impression of the interior is that it is more like an expensive car than a GA aircraft, as the seats and sidewalls are covered with hand-stitched leather. Another feature that enhances the automotive analogy (but diminishes the aircraft in my eyes) is that the restraint system is an inertia-reel three-point harness. Although very comfortable, I didn’t much care for it, as the only restraint system better than a four-point harness is a five-point harness!
On the plus side, the energy-absorbing seats exceed current FAA certification requirements, the cockpit incorporates a roll-cage capable of supporting three times the aircraft’s weight, and in the event of the aircraft coming to rest inverted it is possible to jettison the doors.
Behind the rear seats, which are held in by pip-pins, is the capacious baggage bay which can not only carry a good weight but?more importantly?a considerable volume. It is accessed via a large, lockable door on the port side, and an excellent feature is that you cannot remove the key from the lock unless it is secured.
I like the location of the stepped circuit-breaker panel, which is on the port sidewall by the pilot’s left knee; it is both easy to see and, more importantly, reach. Any pilot who has ever fumbled with a recalcitrant circuit-breaker will readily agree. Another non-Cessna feature is the sidestick. Note that this is a true, fully articulated sidestick and not the forward and aft sliding ‘side-yoke’ fitted to Cirrus aircraft.
I also approve of the electronic climate control system, which incorporates a full air conditioning package?a vast improvement over the heating and ventilation systems fitted to most light aircraft. I’m not so keen on the location of the park brake?it’s also on the port sidewall under the panel and a bit of a stretch. Neither Peter nor I are as thin as we once were, and he allowed that it would be better if it were a bit more accessible.
Dual electrical systems
To meet and exceed the requirements of this ‘electric aeroplane’, two 28-volt/15-amp hour batteries are fed from a pair of powerful alternators, and distribute the power via separate busses. Not only are these dual systems entirely independent, but either one has the capacity to power all the essential systems?including standby EFIS, fuel pump and flaps?via its own Essential Bus Circuit.
The primary flight display (PFD) will always have power, as it is connected to both busses?the level of redundancy provided is quite outstanding. One further refinement is that, should one alternator fail, all the pilot needs to do is press the ‘cross-tie’ switch to ensure that both batteries are charging and allow even the non-essential systems to continue to be powered.
The avionics package is Garmin’s amazing G2000, and the instrument panel is filled with the two twelve-inch PFDs, and an L3 Communication ‘Trilogy’ standby EFIS (electronic flight instrument system) to the left of the pilot’s PFD. The G2000 is the ‘piston’ version of the G3000?or is it the other way round?that I discussed in my flight test of the Piper M600 turboprop (Pilot August 2017).
So rather than repeating everything about how intuitive are the digital touchscreen and shallow menu structure, how much I like the Synthetic Vision and 60/40 screen split, or how it retains the same ‘ESP’ and ‘USP’ protections provided by the GFC 700 autopilot’s enhanced automatic flight control system, (which can even fly coupled go-arounds)… well, let’s just say that it truly is brilliant. In fact, until you fly with a G2000, it is difficult to appreciate just how powerful it is.
Despite the amazing avionics suite, the TTx panel is noticeably less cluttered than that of the Columbia 350 that I flew in 2004, as some of the switches (big, chunky rockers) have been moved to a neat overhead panel. It was interesting to note that despite everything being electronic, manifold pressure and rpm are shown on analogue presentations as well as digital.
There was also something I’d never seen before: the ‘Pulse Oximeter’ below the standby EFIS. This allows the pilot to monitor their pulse and oxygen levels regularly by inserting their index finger?a worthwhile check when cruising at FL250 in an unpressurised aeroplane (and one that perhaps gives new meaning to the exhortation to ‘Get your finger out’?Ed).
All three primary engine controls are of the Vernier type and are mounted in a neat line at the base of the panel, along with the flap selector and buttons for ‘Go Around’ and ‘Rudder Hold’ (a feature that is especially useful in the climb, as we shall see). The speedbrake switch is located between the throttle and prop plungers, perfectly placed for your right index finger.
However, I’m not entirely convinced about its ergonomics. Although lifting it up does raise or extend the speedbrakes, this is not as logical as you may at first think, as deploying them makes the aircraft either slow down or descend. If I’d designed this system, I’d have made the switch function the same way as the undercarriage and flap selectors do on most aircraft i.e. up to fly and down to land?and then relabelled the switch in and out instead of ‘up’ and ‘down’.
Trimming in both pitch and roll is all electric and is done via a neat little ‘coolie-hat’ switch on the sidestick’s top which also has buttons for ‘Control Wheel Steering’, autopilot disconnect and of course a PTT. Trim and flap position are shown on the G2000. The flap switch is exactly how all flap switches should look: large, aerofoil-shaped and with the limiting speeds marked next to the relevant setting.
The engine starts readily and, having inflated the door seals, simply taxying out towards the active runway gives an indication of the TTx’s character. It really feels solid. The undercarriage provides a firm, comfortable ride, with an excellent turning circle (courtesy of the castoring nosewheel) and powerful, progressive toe-operated hydraulic disc brakes. The field of view is good.
Out on the runway I bring the power in slowly. All engines should be treated with respect, and this is doubly true if they’re turbocharged. Furthermore, a swing is more likely with a castoring nosewheel at slow speed if full power is applied too quickly?and we have 310hp turning a large, three-blade prop.
Acceleration is excellent: any tendency to swing is easily controlled once the powerful rudder has some air flowing over it and we quickly reach the Vr (rotation speed) of 70 knots. Smooth application of aft sidestick and we rocket skyward. Although the speed for best climb, Vy is 110kt, forward visibility is somewhat constrained at this speed due to the steep deck angle, so I lower the nose and climb at 125. This still produces over 1,000ft/min, although climbing at Vy would increase the climb rate to 1,400.
During the walkaround I’d noted the absence of pilot operated rudder trim (the small trim tab is only ground adjustable) and had expected to have to apply quite a bit of right rudder during the climb. However, with the rudder hold system all you do is centre the slip indicator on the PFD, then press the Rudder Hold button. It’s great?in fact if climbing at full power at the best angle speed, Vx of only 82kt, the pedal loads would probably become quite onerous without it.
To explore the general handling we climb rapidly to 6,000ft for a look at the stall characteristics and stick-free stability. As you would expect, the twin turbos ensure there’s absolutely no drop-off in engine performance as we climb, and the manifold pressure remains rock-steady at 35 inches.
For such a fast aeroplane the slow speed side of the envelope is very benign. Irrespective of whether the flaps are up or down, and with various power settings, stalls are very gentle. Clear testimony to the efficiency of the wings’ drooped cuffs, stall strips and those plates on the aileron’s outboard ends is the fact that full roll control is retained even when the wing is completely stalled. At our relatively light weight, this occurred at an IAS of 55kt.
An examination of the stick-free stability revealed it to be positive directionally, and longitudinally, and neutral laterally. The TTx would be quite an easy aircraft to hand-fly on instruments, although with such a powerful autopilot I’m sure most people wouldn’t want, or bother to do so in IMC. That said, in VMC the TTx begs to be flown by hand.
Although quite clearly designed as a serious travelling machine, it really does possess extremely fine handling. Breakout forces are very low, there’s practically no stiction and all three primary controls are agreeably harmonised, well balanced and nicely weighted, providing crisp and precise handling, while the rudder hold?effectively a zero-slip rudder trimmer?definitely spoils you! The field of view in the turn (and indeed every phase of flight) is good, while as the wing loading is quite high, it provides a nice stable ride in turbulence.
Time for a look at the cruise. The TTx really hits its stride at FL250 but, while cruising at 25,000ft puts you above most of the weather, I doubt many people are keen to fly an unpressurised aircraft like this as high as that. As it is we do not have enough time in hand to climb to altitude and really make the best use of those twin turbos and intercoolers, but the numbers I see at more representative altitudes are still hugely impressive and?perhaps more importantly, exactly what the POH says they’d be. In the USA it is possible to fly VFR below FL180, and I think that most pilots would plan to cruise at around 14-16,000ft.
At those altitudes a power setting of 80% (32in MP and 2,500rpm) produces a TAS of an incredible 220kt, for a fuel flow of around 80 lit/hr. And remember, the undercarriage is ‘down and welded’. Pick up a decent tailwind (and it can get windy up there) and groundspeeds in excess of 300kt are perfectly achievable.
The numbers for range and endurance are also very good.
The two fuel tanks have a total capacity of 400 litres (380 useable), which means that even with IFR reserves you can safely plan your refuelling stops to be at least 850nm apart. And of course, if you want economy the ‘speed squared’ law means that only a slight power reduction improves both range and endurance appreciably.
Now for some circuits.
The G2000 makes navigation simple, but I still manage to arrive both faster and higher than intended, so extend the speedbrakes. They work well, which is useful as at only 117kt the Vfe is not as high as I would like. Flying the TTx in the circuit is easy, with a fair field of view, effective flaps and of course those speedbrakes. Pitch trim changes with flap selection are easy to trim out and the trimmer is perfectly geared.
On final, the aircraft is very speed-stable, and I have no difficulty holding the briefed speed of eighty knots. However, even with the speedbrakes out, the TTx really is very slippery, and having turned base a bit early I have to cheat and throw in a steep sideslip to sort things out. The aircraft slips well.
For the first landing I retract the speedbrakes on short final, and we float further than I intended. The touchdown is fine?just a little deep, while the ‘go’ part of the touch and go is… well, let’s say emphatic. On the second approach, I extend the downwind leg, leave the speedbrakes out all the way down and give the throttle Vernier an extra half twist in the flare to ensure the engine is at idle.
Result? After a delightfully smooth touchdown I could have made the first turnoff with only minimal braking?a ground roll of 300m. Not bad for something that can cruise at 235kt!
If it was good before…
This is a hugely impressive machine. I liked it when it was a Columbia, and all the changes that Cessna has implemented have made an excellent aircraft even better.
And, of course, now that it’s a Cessna product, the after-sales support is superior too, because Textron Aviation has service centres all over the world.
Bearing in mind that a reader recently expressed his displeasure at my acidic appraisal of Beagle’s products, by now you’re probably thinking ‘has Dave lost his edge, or has Cessna bought him a good lunch?’ Well the answer is neither?the TTx really is that good.
The parking brake could be better sited, and putting the headset holders in the roof wouldn’t be a bad idea, and there’s a large blank space on the starboard side of the panel that could easily take a big glove box. And it’s not a grass strip machine?but you already knew that.
If you’re flying an aircraft that can cruise at 235kt and 25,000ft it’s unlikely that a grass strip will be your destination?more that you’ll need somewhere with Customs facilities!
I think it is the sheer size of the speed envelope that impressed me the most. As I said earlier, it’s not difficult to make an aeroplane go fast, or go slow. The trick is to make it do both, and the Cessna TTx does just that.