Is it possible for an aircraft to be more than it appears? Yes, quite easily, it turns out — and the new Sling TSi by The Airplane Factory provides an excellent example.
Changes to Sling TSi appear to center around the use of the most powerful Rotax engine yet offered by the Austrian producer that dominates the world market for light aircraft powerplants.
Yet, notable as the new Rotax 915iS Turbo may be, that is only the tip of the proverbial iceberg. Below the surface, Sling TSi offers many further refinements and the new design is worthy of a deeper look.
Sling TSi and Rotax 915iS
A year ago, I had the good fortune to fly the Rotax 915 in Wels, Austria, at a Rotax journalist event following the Aero Friedrichshafen airshow. Given the engine manufacturer has its base near the Alps, this made for a beautiful time aloft as well as an educational one.
In two quickly linked flights, they let me compare the 135-horsepower 915 to the 100 horsepower 912iS. Other than power output, the two engines share many common features. Both are significantly lighter than legacy aircraft engines and both use higher technology, plus liquid cooling.
Flying both in a short time was most helpful but I was not familiar with either airframe well, so it was challenging to compare performance to my experiences in other aircraft.
With a fresh experience in the Sling TSi — after previously flying its predecessor, Sling 4 — I have a better understanding to pass along.
At the Copperstate Fly-In a couple years ago I flew Sling 4 with Rotax’s 914 Turbo. That powerplant offers 115 turbo-boosted horses for a few minutes of launch and initial climb and then 100 horsepower to altitude, with negligible power loss as you climb, thanks to the turbocharger.
That Sling 4 impressed me more than I expected. Earlier still I had flown Sling LSA, the company’s two seat entry to that new FAA category. Sling 4 was the South African company’s first four-seat entry.
Usually I prefer two seat LSA over four seaters because the lighter aircraft feel more agile, cost less to buy and operate, and have modern sophistication to match the best of any Type Certified aircraft.
As a died-in-the-wool LSA guy, dare I admit I actually liked the Sling 4’s flight qualities better than the company’s LSA? Certainly Sling 4 was a worthy achievement by the South African builder. That it could carry four occupants and perform well with 100 horsepower is a testament to overall efficiency of the design.
New Sling TSi
I had a good clue changes were coming to Sling 4, although I did not know what they would entail. When Rotax debuted its 915iS Turbo to the press at AirVenture 2016, The Airplane Factory boss, Mike Blyth, was present in the audience. As the press conference ended, Mike was out of his seat like a bullet to examine the display engine Rotax had brought. It was crystal clear to me Mike intended to employ this new powerplant. Sure enough, Sling TSi is the result.
As with Sling 4, Sling TSi is not a Light-Sport Aircraft. It cannot be flown with the Sport Pilot certificate. Several reasons explain why, even though the new model closely resembles the Sling LSA.
First, it’s a four seater. Secondly, it has much higher power. That’s allowed on LSA, but the Rotax 915 engine currently requires a constant speed prop not permitted under LSA regulations (though that could change in a couple years when a refreshed regulation is released). Thirdly, Sling TSi is too fast and too heavy to be a Light-Sport Aircraft.
Because Sling 4 and Sling TSi cannot qualify as Light-Sport Aircraft, they are kit-built aircraft. While this means an owner has to invest time in the construction of the aircraft — at least until used ones begin appearing on the market — a major benefit is much reduced cost. In addition, a kit builder gains an intimate knowledge of his airplane that a ready-to-fly buyer is unlikely to possess.
A Sling TSi airframe kit is approximately $55,000, although you can start with subassemblies and pay as you go. Adding the new 915 engine and a panel of digital instruments will add about $82,000, company officials estimate, producing a final price of about $135,000.
Given this airplane can haul as much as comparable Type Certified aircraft, it delivers good capabilities for about one-third the cost (though many details must be considered when doing such price comparisons).
Sling TSi with the new engine also operates for much lower cost as it burns only eight gallons an hour and can use premium auto gas — in fact, it runs cleaner on this fuel source.
Options for building include detailed kit components and good instructions that will take an estimated 1,200 hours to assemble, a quick-build kit option that will save 400 hours, or a professional builder assist program that can prepare the aircraft even more quickly and with greater assurance to uncertain builders. Professional build centers are presently offered in Michigan and Oregon.
The Airplane Factory developers and engineers made many upgrades from Sling 4. While it appears so similar that most casual observers could not tell the difference without closer inspection, the Sling TSi is a nearly brand-new aircraft from nose to tail, literally.
The distinctive Sling nose cowl has changed subtly, better accommodating the 915 and its new hardware.
Aft of the engine compartment, Sling TSi uses dimpled flush rivets on the front portion of the fuselage and on the leading edge of the wings. This clearly works to pick up the speed of Sling TSi without raising its stall speed.
The wing itself is a fresh new airfoil and wingspan is about 16 inches shorter on each side compared to Sling 4.
The tailplane now has counterbalanced control surfaces to reduce chances of flutter given Sling TSi’s speedier ways.
Numerous other smaller changes were made as the developers altered the Sling 4 to become Sling TSi.
Flying Sling TSi with the Rotax 915
The turbocharged, intercooled 915iS energized the Sling 4 airframe much more than the 914. The difference was clear.
Acceleration was fast. We rolled less than 500′ and climbed quickly from the start and kept going. Jean d’Assonville and I flew perhaps 300 pounds under gross, but others have reported Sling TSi performed vigorously even when loaded to full gross weight limits.
Aloft we saw 128 knots at modest cruise power and at 3,500′ MSL. Coming out to the 2019 Copperstate Fly-In at higher altitudes, Jean reported seeing better than 160 knots TAS and 180 knots GPS groundspeed, thanks to a tailwind. Although eight gallons an hour is the quoted fuel burn, he reported their flight averaged a bit over six gallons an hour.
Climb out of Buckeye Municipal Airport (KBXK) in Arizona — 1,000′ field elevation on a cool day — averaged 1,000 fpm and we saw 1,500-1,800 fpm on successive climbs from a touch and go.
Stalls in all configurations were very mild, even with full stick aft and no quick effort of recovery. At full power, Sling TSi would not stall and only wobbled the nose to signal the pilot. That wobble and a clearly audible stall warning, plus a very steep deck angle, gave plenty of notice to lower the nose, but Sling TSi hardly objected to the forced nose high attitude.
Handling was very responsive, but steady with a light touch even in steeply banked 720 turns. My efforts at dutch rolling quickly produced acceptable results when flying fast or slow.
Landing was straightforward. Sling TSi preserves energy very well — an LSA-like feel, it had — making roundout and touchdown very pilot friendly. Visibility is excellent, a very good thing at the busy Buckeye Municipal Airport when numerous airplanes entered the pattern to pay a visit to the fly-in.
In all, Sling TSi is a commendable achievement, a further refinement of the original Sling LSA introduced in 2009 and the Sling 4 from a couple years later. In a decade of existence, Sling has delivered more than 500 aircraft, Jean indicated.
Well done, Mike Blyth and team, well done indeed!
Sling TSi Factory Specifications
- Wing Span: 31.3′
- Cockpit Width: 44″
- Cruise Speed: 155 knots TAS
- Fuel Consumption: 8 gph
- Rate of Climb: 1,000 fpm
- Maximum Range: 800 nm
- Fuel Capacity: 45 gallons (optional tanks available)
- Maximum Gross Weigh: 2,095 pounds
- Empty Weight: 1,080 pounds
- Useful Load: 1,015 pounds
- Payload at Full Fuel: 745 pounds
- Powerplant: Rotax 915iS Turbocharged, Intercooled, FADEC
- Maximum Power Output: 141 horsepower