Sling 4 Turbo

You know a designer has confidence in a new experimental aircraft when his first journey following the required home field fly-off is a circumnavigation of the earth. Then, again, the fact that the designer and the airplane are both products of aviation-besotted South Africa may provide a more apt explanation for such a mad adventure. Nonetheless, I told myself, I had no cause for concern that the example of said airplane I was about to fly at Sun ‘n Fun (SnF) this past spring had been constructed in just four days time.

The Sling 4 Turbo kit aircraft from The Airplane Factory (TAF) of Johannesburg, South Africa, is the four-place follow-on to the Sling 2, which debuted to much acclaim at AirVenture Oshkosh 2009 during an around-the-world journey, with designer Mike Blyth and TAF co-owner James Pittman aboard. Several months of flight tests preceded that westbound circling. Not so two years later, as the Sling 4, incorporating design lessons learned with the Sling 2, came to life, and the TAF team plotted another globe-girdling trip through OSH.

“It was literally a race against time—building the airplane, trying to get it ready and fly off the official test flight hours,” recalls Matt Liknaitzky, president of The Airplane Factory USA, as we performed a walkaround on N981RW, a Sling 4 factory demo, at Paradise City, SnF’s light aircraft HQ. A South African himself, Liknaitzky is a longtime colleague of Blyth’s and was closely involved in the Sling 4’s development.

With a bigger high-lift, high-drag wing and a turbocharged 115 hp Rotax 914 UL vs. the 2’s 100 hp 912 Rotax, the Sling 4’s useful load (992 lbs.) almost equals its empty weight (1,036 lbs.), and it cruises at 125 kts on a very economical 6 gph.

That first Sling 4 wasn’t finished in time for OSH ’09, but Blyth and his son Patrick launched on their circumnavigation anyway soon after. “They departed South Africa when the airplane had, like, 20 hours of flight time,” Liknaitzky says.

Two years later, in 2013, the Sling 4 made its belated OSH debut, via a relatively simple back-and-forth route. (“Round trip” might be confusing in this context.) Fast-forward three years: With TAF USA’s distribution operation in Torrance, California, established and excitement about the model growing, the company was eager to showcase the Sling 4 Turbo to SnF attendees.

Ground Effect

White with gold and red trim, N981RW is a noteworthy aircraft in its own right: the legend on its empennage, “Sling 4-4-40,” signifies this Sling 4’s construction in four days by 40 builders in a well-coordinated effort last year—performed to illustrate its ease of construction.

The primary differences between the Sling 2 and the 4 Turbo are the 4’s larger wings, its upgraded engine and the addition of the center fuselage section for the rear seats. The 4 also has a pair of gull-wing doors in place of the 2’s sliding canopy and windows for the rear seat.

Both Slings have a shark-like, predatory appearance, with a maw of an air scoop on the bottom of the cowl and eyelike air inlets on either side of the prop hub. Overall, the airframe has the high level of finish befitting a totally CAD-designed aircraft. “Everything fits perfectly the first time,” says Liknaitzky. The CAD-based manufacturing also allows TAF “to keep improving the kit and construction very easily,” he says.

TAF prefers to demo the aircraft with at least three people onboard to demonstrate its true four-place capability, but the rear seats had been removed from 1RW back in California to transport SnF display materials, so just Matt and I would be aboard. A six-footer, Matt has spent many hours in the back, and described the rear seating as “extremely spacious.”

The wide, lightly tinted gull-wing doors, anchored to pneumatic struts, make for easy ingress and egress. With front seats pushed forward, there’s plenty of rear-seat entry room—no contorting required. If you’re sitting in front, just step on the seat and climb in. Besides moving fore and aft, the backs of the forward seats are adjustable, as are the rudder pedals. While there’s no vertical seat adjustment, the pilot sits relatively high, and visibility is excellent. Taking stock of the interior, the cabin feels spacious, the layout logical and the appointments comfortable.

“The design started with the cockpit, ergonomically, around the human form,” says Liknaitzky, pointing to the positioning of the throttle, stick and other controls “exactly where the hands come to rest.”

Cockpit Features

The standard panel features a pair of 10” MGL Avionics iEFIS Challenger Multi-Function Displays (MFDs) facing the pilot and co-pilot positions. (An all-Garmin suite with a G3X Touch is available as an option.) A controller for the electrically operated propeller is at the top of the center panel, flanked by a steam gauge airspeed indicator and altimeter. Below, circuit breakers are set mid-panel over a double row of toggle switches controlling the aircraft’s other electrically driven systems, with flap switch, and choke and cabin heat controls to the left and right, respectively. The red handle of the ballistic recovery chute system (standard in both models) is at the bottom of the center panel. Throttle and parking brake are set on the console between the forward seats, joined to the panel by the intervening pedestal housing the fuel selector.

The propeller control operates the three-bladed composite and constant-speed prop, and works hands-off. It’s typically operated in Auto mode, offering three settings: takeoff, climb and cruise. Takeoff (5800 rpm) is maximum engine rpm; climb (5500 rpm) represents maximum continuous power; and cruise (5000) is the optimum performance/economy setting. Merely select the desired setting, and the electric prop controller does the rest. The rpm can also be set manually; a prop control toggle switch by the flap switch adjusts the rpm up or down, and will stay where set when the prop “hold” is engaged.

The prop can also be feathered, useful either in the event of an engine failure or for feathering on the ground because “people like to see the prop like this,” Liknaitzky says. He engaged the feathering controller, and we watched the propeller blades twist, taking about 14 seconds to cycle from coarse to fine pitch. A green light on the controller illuminates when fully feathered. “It looks like a turboprop,” Liknaitzky says approvingly of the feathered blades, now just thin black lines from the cockpit.

Shut the gull-wing doors before startup. They pull down easily on their struts into locking position. Turn on the EFIS, powered by a secondary battery; it contains the checklists and tests the other systems as they come online. Engage the toggles for the master, main and aux fuel pumps, electric prop controller and other electrical systems. This being the first flight of the day, Liknaitzky advised using the choke to enrich the mixture. Any concern that that signified an engine that needs coddling evaporated as the Rotax fired up as if it had paused in mid-thought.

Flying The Sling

The flight line at Paradise City is a constant blur of motion, reminiscent of World War I airfield scenes with ground crews pushing and pulling aircraft around and performing last-minute inspections before engines are started and aircraft join a line of aircraft waiting to climb into the endless parade of light aircraft doing circuits in the pattern or heading out for demo flights. We joined the procession, following the visual commands of wand-waving ground crewmembers.

With nosewheel steering and differential braking, ground handling is firm and highly maneuverable; we paused on the way to the run-up area and Liknaitzky performed a donut 360-degree turn.

During the run-up, the prop is switched from Auto to Manual, the pitch changed from coarse to fine and back, and Auto is re-engaged. A green prop control light indicates proper configuration for flight. All other run-up items are GA standard (with the exception of the 4000 rpm engine speed). Set one notch of flaps for takeoff.

Our plan was to fly out to the open expanse south of LAL’s airspace for some airwork, then to Lakeland South, the nearby turf strip airpark, before returning to Paradise City.

The Rotax 914’s full 115 hp is available for a maximum of five minutes continuous use, and always used for takeoff. To engage the extra boost, advance the throttle full forward, make sure the engine lights are all green, then pull up on the trigger within reach on the forward portion of the throttle, and advance it past the 100 hp detent to its stop. The extra 15 horsepower makes a big difference in performance, especially in high/hot conditions. Keep in mind, too, this is a turbocharged engine, and full power is available into the teens; it produces max continuous 100 hp up to 15,000 feet.

Rotation speed is 60 kts, and takeoff roll is about 700 feet (on asphalt) at max weight. With two onboard, using soft/short-field technique for Paradise City’s turf, we were airborne quickly. Liknaitzky recommends climbing out at 75 to 80 kts for optimum forward visibility and a comfortable climb angle, yielding an 800 to 900 fpm climb. We scooted out from under LAL’s controlled airspace at 400 feet before putting the propeller back in climb mode and ascending to 3,000 feet.

In straight and level flight, with the propeller set to cruise and full power, we exceeded 120 kts indicated. If you want to get somewhere faster, “just leave the prop in climb [5500 rpm] the whole time,” Liknaitzky advises. Though the airplane is noisier at that setting, it’s not a sound level a pair of decent noise-cancelling headsets can’t handle. With an autopilot standard, and the option to equip for IFR, the Sling 4 makes a great touring platform.

But the Sling 4 distinguishes itself most in hand-flying, where it feels like a fun four-seat fighter jet as the well-balanced stick is yanked around. Gamboling through steep turns and nudging the bottom of the envelope in slow flight, it exhibits excellent control harmony and ease of command. Yet, as responsive as it is, the fat wing ensures the airplane remains docile and forgiving. The low stall speeds (47 kts clean; 42 kts in the landing configuration with full flaps) provide another layer of safety. We attempted both power-on and power-off stalls, but as Liknaitzky predicted, with no passengers in back, the Sling simply mushed downward straight ahead when reaching the stall; with rear-seat passengers, it will enter a series of oscillation stalls until recovery, rather than pulling off to one side, he says.

Pattern operations are completely conventional. Full flaps are used for landing, dialed in on the flap selector as desired on the way down. Recommended approach is 75 kts, but with its low stall speed, 60 to 65 kts is perfectly acceptable for squeezing into tight landing spots—landing distance is 500 feet, and the gear are designed to handle the types of dodgy strips you’d expect to encounter when flying around the world. The Sling 4 isn’t a floater, and the wheels plant authoritatively. For touch-and-goes, push the throttle full forward, check the engine lights, then pull the trigger, goose the power up, and away you go. The destination is entirely up to you. With the Sling 4, the whole planet is yours.

Senior Editor James Wynbrandt is a multi-engine, instrument-rated pilot and an award-winning author of books and articles. He flies a Mooney M20K 252.

Sling 4 Turbo Specifications