When Errol van Rensburg contacted me about flying the new Sling TSi, I jumped at the opportunity after my experiences with the Sling 2.
The latest iteration of the Sling design is the Sling 2’s big brother, the Sling TSi model.
Based on the four-seat Sling 4, the Sling TSi features the upgraded power of the Rotax 915iS power plant instead of the 110-hp Rotax 914 Turbo.
This engine is based on the proven 912/914 series but offers increased horsepower with the inclusion of an intercooler along with the turbo. The resulting additions raise the power output to 141 hp, which can be held from sea level up to 16,000 feet.
The increased horsepower is transmitted through an electrically adjustable Airmaster three-bladed composite constant speed propeller. This increase in power, also allows a new service ceiling of 18,000 feet in an ISA atmosphere.
This is not just a cobbled together turbo added to the existing 1352cc 912iS, but a completely integrated design incorporating a dual-channel Full Authority Digital Electronic Controlled (FADEC)-style electronic Engine Management System (EMS) with redundant electronic fuel injection and ignition.
With this additional power-to-weight ratio and decreased weight overall, the Sling TSi is more than capable of carrying four people in comfort, performance and economy.
Performance? This was ably demonstrated on the day, which was not your best day for flying such a light aircraft. The day was partly overcast with a blustery 15-25 knot south-easterly wind on the Gold Coast bringing a strong on shore airflow, passing rain showers and big surf on the nearby beaches.
Fortunately the strong wind that made the windsock look as though it was starched was predominantly straight down the strip, but it did cause a bit of washing- machine-like turbulence on short final.
Before we took to the windy skies, I did a quick walk-around of the Sling TSi.
The Airplane Factory, with a redesign of the clamshell canopy doors, has improved the basic design. Otherwise, it is essentially the same except for the addition of more power under the cowling.
This re-design now incorporates a wider hinge bracket on each canopy to add strength to the doors and a little less transparent area compared to the Sling 4 to give improved shade over the front seat.
The maximum take-off weight has also been increased from 920 kg to 950 kg, adding 10 kg to the useful load, bringing it to 460 kg.
The side windows give exceptional visibility both forward and all the way around to the tips of the tail plane and with the forward seating position being located just behind the wing leading edge, there was also excellent visibility forward and downward. I did find, however, when airborne with the lower winter sun angles, that the inclusion of some sort of a retractable blind or visor over the front seater’s heads would be great as I found the sun kept coming in the top of my glasses whilst flying. A minor poinr.
The Sling TSi still retains the original design's all-metal construction, made from CNC-machined parts and skins with composite engine cowls and canopy frame and doors.
The undercarriage wasn’t left out from the improvements with more streamlined wheel covers reducing profile drag.
The interior wasn’t forgotten either, with four comfortably upholstered seats, the cabin easily fits four adults with more than adequate legroom for the back seat passengers.
This is not a 2+2 children design as van Rensburg (180 cm) ably demonstrated when he sat in behind me (187cm) and he still had more than adequate room without his knees even touching the seat back. I must admit I could have moved my seat another 20-30 cm or so forward and I still would have been able to fly in comfort, even on long flights. The cabin is also not confined like in some of these types of design with it being 115 cm wide at the elbow. The sides of the fuselage do have a marked flare outwards from the floor level to accommodate this extra elbowroom.
Both forward seats fold forward to allow easy access to the back. The back seat also folds forward to reveal the luggage area. There is even an extended section behind the left back seat that is wide and long enough to accommodate a surfboard if that left seat is left folded down. Access to the aft luggage area is through a lockable door on the aft left side of the fuselage.
All seats are equipped with three-point seat harnesses.
Fuel tanks are contained in the leading edge of the wing. The main tanks hold 180 litres (90 per side) and the auxiliary tanks that are located outboard of the mains, hold another 70 litres (35 per side).
On the panel
This particular Sling TSi is equipped with the latest Garmin 3X single-screen EFIS system. A second screen is optional and would be located on the right-hand side of the panel, replacing glove box.
The G3X EFIS system uses a 10.5” touch screen and can display a combination of Primary Flight Display (PFD), moving-map with either topographical terrain style or aviation charts like a VNC and like an iPad, the display can be slewed around or resized. The system can also be equipped with a synthetic terrain display, which the attitude, speed and altimeter information is overlaid upon.
The engine instruments are also displayed on this screen and touching any indication then displays more information about that sensor or they can be condensed down in detail.
This is also where the planned flight turn points can be entered for GPS navigation, which the autopilot can be engaged to follow.
The Garmin 3X was supplemented by a Garmin G5 back-up electronic flight instrument incorporating an attitude indicator, airspeed tape, altimeter tape and compass which is mounted in the centre of the whole panel. It even has an electronic skid ball on the 3.5” LCD colour display like that on the G3X. This unit can be optioned with a built in back-up battery with four hours endurance.
A Garmin GMC307 autopilot integrates wonderfully with the Garmin 3X allowing the pilot to select various flight modes that are then displayed on the G3X’s EFIS/PFD.
One great safety feature of the GMC307 autopilot is the inclusion of the lvl mode. When pressed, this will automatically level the wings and recover the aircraft from any unusual attitude back to straight and level. Obviously the pilot will still need to control the speed with the throttle.
Along the bottom of the panel are the various electrical system switches.
As the ROTAX 915iS is equipped with EMS, there are no magneto switches, but instead there are two lane switches, 1 and 2 located to the upper left side of the panel beside the ignition key and master switch. Along with the red LED along side each switch, a test is carried out as part of the pre-flight run-up to test each system.
On the forward centre console is located the rotary fuel tank selector. The auxiliary tank switches are red guarded switches mounted away from this rotary selector to avoid confusion. As the main tanks drain down, the auxiliary tanks are selected on to allow the fuel to transfer under gravity.
Located side by side a little further back on the centre console, are the throttle and the brake handle. Like the Sling 2, the wheel brakes are applied symmetrically by pulling the brake lever backwards while steering is achieved through a direct linkage from the rudder pedals.
To park the brakes, you first pull the brake handle back until movement is stopped and then rotate the small red park brake switch located behind the levers into the park position. This locks the brake pressure. I found the park brake switch to be a little small and wonder how long it might last if used in regular operation.
The electric propeller control is located to the left of the Garmin backup G5 within easy reach and allows the pilot to select the appropriate mode of the constant speed unit for the phase of flight. The modes are to, climb, cruise, hold and a manually-adjusted feather.
The unit also contains a switch for selecting either automatic or manual control of the propeller speed. When selected to man, a separate rocker switch is used to control the RPM while the throttle sets the manifold pressure.
The automatic system is so reliable and accurate, that the manual system is really only there as a back-up just in case. During our test flight, only auto mode was used an in the unlikely event of complete electrical power failure, the system drives the propeller blades to full fine.
Each straight control column stick is topped with a separate TRIM U/D flush push button along with a radio PTT and A/P disconnect.
Riding the whirlwind
Climbing aboard the Sling TSi is accomplished using a step protruding behind the training edge, stepping onto the non-skid walkway on the inner wing and simply stepping in. Rear seat passengers enter the same way with the front seats folded down.
The rudder pedals aren’t adjustable, but the seat can be adjusted fore and aft.
With our headsets connected to outlets inside the centre glove compartment and our three-point harness secure, we were ready to go flying.
Starting the Rotax is a straightforward turn of the key and it instantly fires into life. After the relevant temperatures were in the green, we were ready to taxy out for take-off. As the Rotax is liquid cooled, it takes maybe a little longer to reach these temperatures.
After a check of the two lane channels, and the relevant pre-take-off checks, we lined up and smoothly applied take-off power. There appeared to be no turbo lag with the smooth RPM increase. Acceleration was instant and with the 15-20 knot headwind, we quickly reached our initial rotate and lift-off speed of 55 knots with just one notch of electric slotted flap.
With a couple of beeps from the angle-of-attack (AoA) warning that’s built into the G3X, I must admit I was somewhat reluctant to raise the nose all the way up to achieve the best climb speed of 75 KIAS.
With the slight gustiness, I settled on around 80 KIAS, and with the flaps up, the prop control in climb, this gave us just over an average of 1500 fpm ROC at a pitch angle of 15o nose up, impressive for a four-seater with only 141 hp, two adults and 100 l of fuel onboard.
Settling down to an 80% cruise power setting at 3000 feet, prop in cruise, we accelerated to 135 KIAS cruise using only 27.5 lph. This equated to a speed of 141 KTAS as we cruised under the cloud base to an area to assess the handling of the aircraft.
The harmonization of the controls is how I remembered the Sling 2 was: positive, but not too light or any tendency to over-control in any axis. Gripping the stick a little lower than the handgrip allowed me to feel the aircraft better. I did find, however, that the rudder is very powerful and only slight pressure is required to keep the turns balanced and the skid ball centred.
After some clearing turns to both assess the roll rate, 3-4 seconds, 45o to 45o reversals, it was time to look at a clean stall.
As the speed started to bleed, the AoA warning beeping started to sound around 70 knots with slight buffet being felt closer to 60 as the speed decreased with a constant warning at 54 KIAS and with the stick near full back, only a mushing sensation was felt with no real appreciable nose drop evident. It just started descending and had to be held in the stall, but the ailerons were still quite effective.
After some more maneuvering around the area, it was time to return down through the bumps and strong winds back to the field.
The downwind leg was over and done with quickly with the 20-30 knots of tailwind at 1000 feet. Turning base and selecting one stage of flap below 92 KIAS brought the speed back to 85 and with one more stage back to 75-80.
Considering the gustiness of the conditions I declared to van Rensburg that I would carry an extra 5 knots over the normal 75-knot approach to allow for the gust factors. This worked well with the Sling displaying excellent handling in both pitch and roll considering the turbulent conditions and a tendency for a wing to drop was easily picked up.
After a couple of very slight balloons near the ground a smooth touch-down eventuated with directional control being easily maintained with the powerful rudder and direct nose wheel steering. I needed only a small gradual application of the brake handle to slow the aircraft towards the runway exit.
Shutting down with the usual ROATX shudder, Errol and I discussed the attributes of the Sling TSi. This is one heck of a small four-seater with performance that could easily take two people from the Gold Coast to Melbourne and almost back again on a single tank of fuel. Speaking of fuel, the TSi’s engine will run on premium unleaded.
Since Australian Flying's flight, van Resnburg tells me that he recently had three adults and a child in the aircraft and it still climbed at 1250 fpm and cruised at 115 KIAS at 50% power, which would have required 80% power in the lower-powered Sling 4 with the Rotax 914 turbo ... a great improvement.
The Sling TSi has all the excellent handling qualities of the smaller two- and four-seat variants, but now with the added capability of carrying four in comfort at faster cruising speeds and very economical rates.
The aircraft can be purchased as a complete factory-built item like the aircraft tested for around $320-350K, but you could save yourself around $100K in self-assembly and finishing.
This aircraft could become a serious contender to aircraft like the Cirrus SR20, Cessna 172/182, Diamond DA-40XL or Piper Warrior,s but at a significantly lower buy price and significantly lower operating costs while still maintaining the same state-of-the-art avionics.
There is ample panel space to mount two Garmin G3X screens, maybe an extra VHF, along with an intercom and audio selector unit and a transponder. With the use of integrated Garmin avionics, this would be a simple matter as all the units are designed to interface with one another.
Thanks to Errol van Rensburg of Global Aviation Products for inviting Australian Flying to be the first to fly such a great little aircraft.
Wingspan: 9.54 m
Length: 7.17 m
Height: 2.45 m
Standard Empty Weigh:t 490 kg
Maximum Useful Load: 460 kg
Maximum Take-off Weight: 950 kg
VNE: 155 KIAS
Cruise Speed @ 9500 AMSL: 148 KTAS
Max Crosswind: 15 Knots
Take-off Ground Roll (hard surface): 180 m
Landing Distance – Braked: 150 m
Maximum Operating Altitude: 18,000 feet
Endurance (main tanks only): 7 hours
Range @ 75% Power (45 min RES): 756 nm