The Sirius, from Czech manufacturer TL Ultralights, has been flying under the radar for quite a while but it’s now time to put it through its paces.
I’ve pointed out before that the Light Sport Aircraft (LSA) was really beginning to blur the line between ‘classic’ aircraft, such as the Piper Cadet or Cessna 152, and as soon as I saw the Sirius at a rally this year, we agreed that that line had been blurred still further. A flight test was arranged for the following week, and as it turned final my initial impressions were reinforced: it really does look like a C152, or possibly a scaled down 182. Owner Peter Ronfell was barely out of the cockpit before I began studying the aircraft with considerable interest. With in excess of 30,000 150/152s made, Cessna’s classic trainer remains one of the most successful GA aircraft of all time and, while I’ve flown literally dozens of types that were intended to replace it, I’ve still never flown one that was a real contender. Could the Sirius make the grade? I couldn’t wait to find out!
Closer inspection confirms my initial impression – it does indeed seem to be very much like a composite 152, but with better access and a bigger cockpit. Power is provided by – you guessed it – a 100hp Rotax 912S, fitted with both the ‘soft-start’ system and a slipper clutch. However, and unusually for a 600kg aircraft, the test aircraft had a three-blade electrically-actuated constant speed ‘Power Max’ propeller.
The engine installation is very neat and extremely accessible. The top and bottom halves of the cowling are easily removed by undoing Dzus fasteners and there’s lots of room to work around the engine. There is also a small hatch in the top of the cowling for checking the oil but you can’t see the coolant expansion tank. This may be deliberate as it’s a good thing to check the hoses occasionally too.
The battery intrigued me – it’s a tiny Odyssey PC310 and is actually worth a mention. Originally developed for military aircraft requiring very high power delivery for short durations, this is a pure lead (not lead alloy) maintenance-free dry cell battery which uses TPT (thin plate technology). It can be mounted upright or flat and the manufacturers claim it has exceptionally good anti-vibration properties with a fast recharge capability and recovers well from heavy discharge. However, the best bit is that it weighs only 2.7kg yet can put out in excess of 2,250 amps for five seconds, even at very low temperatures. I was impressed!
In common with the 21st Century theme there is no carb heat (it has the SkyDrive coolant-heated water jacket system) although the 912iS is also an option, and one I’d probably exercise if I were buying one. Carburettors are so last century. The undercarriage looks suitably robust. The main wheels are carried by a composite bow while the nosewheel strut consists of a sliding steel tube with an internal spring for shock absorption. Now, most LSA-type aircraft typically offer either a castoring nosewheel with steering via differential braking or a steerable nosewheel and non-differential braking, whereas most ‘classic’ GA types usually offer both. Interestingly, although the nosewheel steers through the rudder pedals, they also provide toe-operated differential braking.
For a ‘small’ aircraft the Sirius has many features usually found on larger ones. Impressive, as too was the fact that the main wheels feature split rims, making it easy to change a tyre. All three wheels feature snug-fitting spats and the mainwheels are fitted with hydraulic disc brakes. Inspecting the brakes requires part of the spat to be removed: a feature I wasn’t so keen on. Checking the brakes is part of the DI – and you shouldn’t have to remove screws to do so.
The thin, strut-braced wings use a laminar-flow aerofoil and have a 65-litre fuel tank in each (45-litre tanks are an option). They feature a slight taper and slightly down-turned wingtips. Two excellent features are the fuel caps which have integral calibrated dipsticks that even a 1.72m-tall journalist can refuel without a ladder. The large single-slotted flaps are electrically actuated and have three settings, 0, 15 and 45 degrees. As with the rest of the aircraft the wings are solidly constructed. In fact, bearing in mind the laminar-flow aerofoil section, I was surprised there were neither stall strips nor stall warning vanes and made a mental note to carefully check not only the actual stall but also the aircraft’s behaviour when approaching the stall.
I also noted that the pushrods and Rose joints for the flaps and ailerons are faired over, the big pitot on the port wing, the block of 12 LED taxi/landing lights built into the port wing’s leading edge and the strobe and position lights faired into the wing tip. The tail consists of a fixed tailplane and two-piece horn-balanced elevator, slightly sweptback fin and horn-balanced rudder.
All the primary controls are actuated by pushrods except the rudder, while the port elevator carries a cable-actuated trim tab. There are ground adjustable tabs on the right aileron and rudder.
Initially, I thought that the small door on the starboard side gave access to the baggage bay, but this is where the optional BRS is located. This is manufactured by Galaxy – unlike most BRS units that simply shoot the ‘chute out, the parachute is fired away from the aircraft in a container, and only deploys when nine metres from the aircraft. This greatly reduces the possibility of the canopy fouling on the aircraft or being damaged by debris. An additional nice touch is the sensibly sited tiedown rings. These can be critical for light aircraft and it’s shocking how many designers neglect to fit them.
Thus far (and despite doing my best) I’d found very little to complain about, and this pattern continued. Access to the cockpit is excellent, as the sills are low, the gull-wing doors open wide and are well braced by gas struts. Good cockpit access is important, as many potential customers are no longer in the first – or even second – flush of youth. The Sirius really scores here – unlike most of its contemporaries it has panel-mounted yokes. Now, the stick or yoke question is almost as universal as the high or low wing debate, but one thing is irrefutable: when getting in and out you can’t beat a yoke that sprouts from the panel (except maybe a sidestick, but let’s not even go there!).
The baggage bay can take 25kg and is accessible during flight. It’s also easy to load as the seatbacks are held in place by Velcro and can be quickly removed, while additional storage space is provided by the map pockets built into the doors and the glove box under the neat lift-up central arm rest. The comfortable seats feature four-point harnesses but do not adjust. The windscreen is adequate but not overly large, and although the rear windows ensure the cabin is well lit I couldn’t help but feel that the overall field of view would be enhanced by a skylight.
The cockpit is generously proportioned (an impressive 1.13m at the widest point) and seems even bigger. It’s clearly been designed to accommodate large people, and although the pedals adjust I could’ve used a cushion to both raise me up and push me forwards.
Continuing to acquaint myself with the layout of the controls and instruments I think once again that this is how a 21st Century 152 should look. Yokes, adjustable rudder pedals, toe brakes, nosewheel steering and, a pleasant surprise, an entirely analogue panel. Well used to most modern aircraft having either Dynon or Garmin glass, the unusual arrangement is refreshing – or is the Luddite that lurks somewhere within most aviators who learnt to fly in the last century emerging? (Of course, various Dynon options are available).
All the flight instruments are on the right with the engine gauges mostly on the left except the tachometer and manifold pressure gauge. A curious anomaly is that the AH and altimeter have been transposed, but that’s the way Peter likes it. The test aircraft had an iPad mount in the centre of the panel, although the DI was noticeable by its absence.
A sub-panel extends down from the centre of the instrument panel and this carries the flap selector and co-located position indicator lights, fuel valve, fuel pressure gauge and plungers for the choke and cabin heat, plus two toggle switches for the electric prop. These initially confused me, as there is a fairly typical prop control lever next to the throttle. The prop can be selected to either MANUAL or AUTO by use of the left side toggle switch. When in MANUAL the switch on the right of the panel is used to increase or reduce pitch as required, while if AUTO is selected then the right switch is redundant and the pitch control lever is used in the conventional fashion instead. Why have two systems? I don’t know! A small green light illuminates when the prop is on the fine pitch stop, whichever system is used.
The fuel selector is well placed but I’d also like a ‘Both’ setting. Another instrument anomaly is the fuel pressure gauge, which – considering the Sirius is a high wing design – is both rather large and prominently placed. I also thought that the green light for the auxiliary fuel pump was too bright. It’d be a real distraction when night flying. Finally the plungers that actuate the choke and cabin heat knobs are just a little too alike for my tastes and should really be different shapes. It might be a bit awkward if you pulled one and, instead of getting an agreeable flow of warm air into the cabin, the engine suffered a ‘rich cut’! The fuel quantity can be checked by either referring to the optional fuel computer or looking at the sight tubes in the wingroots. These show only the last 20 litres in each tank, which is still enough for well over two hours of flight.
The panel is almost completely free of switches, with only the key-type rotary magneto/starter switch in it and most of the other toggle switches set in a neat overhead panel. A centre console between the seats contains levers for the throttle, prop and pitch trim, with the parking brake knob behind your right leg and a handy power outlet behind your left. Each well-sealed door has a central spring-loaded latch and an over-centre lever that drives the two fore-and-aft locking pins. A nice touch is that this lever covers the latch when closed. Unfortunately, there are no DV panels, but as the doors can be opened in flight (or removed altogether) their omission isn’t a real issue.
Taxiing out reveals a bunch of promising characteristics; positive nosewheel steering and powerful, progressive hydraulic wheel brakes which are both operated through the rudder pedals. During the run-up checks I discover that you’re definitely aware when the flaps are in transit as the rather loud flap motor is directly overhead and it vibrates. Peter tells me that a fix is in hand as a second bracket will be fitted to stop the vibration.
As the grass runway is only 400m long and we’re taking off towards rising ground I’m especially focused upon the take off and climb performance, particularly as we have two fairly heavy pilots and around 100 litres of fuel onboard. It being the second week in September I’d anticipated that the ambient conditions would be close to ISA, but with an OAT of 23C it’s remarkably hot and there’s barely a breath of wind blowing down the runway. I wonder briefly if I might be in for a bit of a thrill, but have forgotten the advantages conferred by a C/S prop. Lined up to the left of the Chipmunk camera-ship, I give it a five-second head start and then open the throttle.
Acceleration is excellent and a smooth rotation at 40kt gets us off the ground and accelerating quickly towards the Vy of 70kt and an initial climb rate of around 1,000ft/min. As we climb away to the east I begin to experiment with the general handling but before I can really come to any definite conclusions the sudden appearance of Keith’s camera lens indicates it’s time to move into close formation for the air-to-air photos.
This is always an enjoyably challenging aspect of the job as it requires very accurate flying. On this occasion it was particularly hard work as it was a bumpy day (we spotted several gliders above us, testimony to the strength of the thermals) while I also really missed not having a skylight. Interestingly, the different requirements of a formation photo-shoot (i.e. extreme crossed-controls) occasionally highlighted unsatisfactory handling characteristics that might otherwise have remained unnoticed during normal flight.
The Sirius behaved well, with crisp controls, and a responsive engine, while the field of view is typical of a high-wing aircraft. With the photo session complete I continue my examination of the general handling characteristics. A sequence of turns and reversals using varying degrees of bank demonstrate that the roll rate is agreeably brisk without being skittish. Only small amounts of rudder were required to keep the slip-ball centred. Harmony of control was as it should be, with the ailerons being the lightest and the rudder the heaviest, while breakout forces were low with very little ‘stiction’, despite the fact that there was only 60 hours on the airframe.
The elevator trim has authority and the lever is logically placed. An examination of the stick-free stability confirmed that the directional stability – although positive – is not quite as strong as I’d expected. Laterally, it is just slightly on the positive side of neutral, while the longitudinal stability is strongly positive, as having trimmed for 90kt, pitching up until the speed drops to 80 and then releasing the stick, the Sirius returned immediately to the trimmed speed. I began to suspect that the CG was markedly forward – an exploration of the stall characteristics confirmed this.
High stick forces were required when slowing down to explore the slow side of the speed envelope (I never trim into a stall), whilst a positive is that the Vfe is higher than many similar machines. High stick forces aside, slow flight is benign although I must say that the pre-stall buffet is barely perceivable and wonder if perhaps either stall strips or an artificial stall warner might be a good idea.
The Sirius finally quit flying at 35kt IAS with 0 flap, and about 30kt with 45°, although at such slow speeds I’m never convinced off the accuracy of an ASI due to position error. It’s certainly super slow, and if the speed is reduced at one knot per second it never really stalls but just sort of mushes while the sink rate increases. By hauling the nose well above the horizon I finally got the nose to drop, but it really is exceptionally well-mannered.
Accelerating out of the final stall I asked Peter what power settings he typically cruised at and, acting on his advice, used 4,000rpm and about 22ins MP, trimmed slightly forward, and let her accelerate. At 3,000ft the IAS was 90kt, for a TAS of 96 while the fuel computer showed we were burning 15.8 lit/hr. Obviously she’ll go faster at the METO of 5,500rpm but burn (in percentage terms) a lot more fuel – about ten litres an hour more in fact! For those who doubt the irrefutable truth of the ‘speed-squared’ law consider this – a 10% increase in speed burns about 50% more fuel! The Sirius’s’ sweet spot’ is 90kt at 4,000rpm, which at 5,000ft in still air returns a creditable 6.3nm/lit or 32mpg: better than many cars. Furthermore with up to 130 litres available the still air range (no reserve) is an impressive 738nm.
Checking back on the ground I studied the windsock carefully for, although thus far the Sirius had proved to be more capable than its 20th Century counterparts, Cessna’s engineers definitely got the 152’s flaps right. Indeed, any pilot transitioning from a 152 into a modern LSA soon learns to monitor their airspeed carefully. If you’re in close to the runway and either hot or high you may easily end up with an embarrassment of speed or altitude!
All through the flight I’d constantly felt that the CG was quite well forward and this was confirmed in the circuit. Despite placing the trim lever straight onto the aft stop it seemed I was carrying several kilos of backpressure to maintain the promulgated Vref of 55kt. To be honest, in the prevailing conditions this actually felt a bit fast, and as it stalls at 30 I’d have liked to have shaved at least five and possibly even 10 knots off.
However, this particular airfield wasn’t the place to experiment (the undershoot area is non-existent) and holding 50 all the way down would’ve required so much backpressure that it would be distinctly uncomfortable.
I’d like to try a few landings with the CG further aft and a longer runway, so that I could aim to touch down at the start of the second third of the tarmac. Anyway, after a couple of touch-and-go’s for Keith’s camera I went for a ‘full stop’. Despite the forward CG, nil wind and hot weather we were still down and comfortably stopped in around 300 metres with only light braking, although the actual touchdown could’ve been softer. Taxiing back for another go, I rotated at 30 instead of 40 and got airborne a lot quicker, while my second landing was considerably smoother.
“You’re exactly right” he replied and went on to explain that the PowerMax prop is three kilos heavier than the original two-blade Kiev prop and has only recently been fitted! TL Ultralight recommends putting 1.5kg in the tail and I can confirm that it really needs it. (I understand that since I flew it the weights have been installed, and the CG is much more satisfactory).
Nevertheless it’s an impressive machine, and the grass runway, hot day and lack of wind had provided a taxing test, passed with consummate ease. Furthermore, with our combined weights and the 100 litres of fuel, we’d been nudging the 600kg MAUW. TL claim an empty weight of 297kg but this demo aircraft had ‘all the trimmings’ (Galaxy BRS, C/S prop, long-range tanks etc) and weighed in at 345kg.
To conclude, I feel that in many respects the Sirius is closer to a classic light GA type than most of the 40-plus LSAs I’ve tested since the class was introduced in the US a decade ago. With its control yokes, toe brakes and steerable nosewheel, comparisons with the classic Cessnas most of us learnt on are inevitable, because that is clearly what it is intended to be. It’s certainly much closer to a 21st Century 152 than the late, unlamented 162!
The Sirius is currently marketed in Australia by KG Aviation. I reckon that any pilot contemplating trading in their old 150 or 152 should seriously – or even Siriusly – consider the Sirius.