July 2012 Issue
RANS S-7S Courier
Randy Schlitter and the gang continue to push and prod, tweak and improve this utility airplane.
Media relations in the homebuilt-aircraft industry is a funny thing. Some companies would like you to know when they've changed from AT&T to Verizon or that their new distributor in East Nowhereistan can now take orders. And some—most, actually—just go about their business, churning out kits, steadily improving the product, making less stretch into more where development resources are concerned. It's hard to know when something is new.
Previous S-7S panels have this forward tilt at the top, but RANS has introduced a new vertical panel.
Like the time I walked under the wing of the RANS S-7S and almost pranged my forehead on the aileron spades. It was a pleasant surprise, then, to duck under the latest version of the S-7S (actually an LS, more on that later) at this year's Sebring LSA show and see the spades had been removed. Their exit indicates the biggest single change in the 2012-model S-7S: a heavily revised aileron-control system with new surfaces. Ball bearings support the ailerons, and the surfaces themselves now have a prominent bull nose that helps reduce stick forces. The concept is simple. As the trailing edge rises, the extended leading edge drops below the wing's lower surface and gains the benefit of an aerodynamic counterbalance. This force, ahead of the hinge line, helps drive the trailing edge further up—or at least reduces the effort required to hold it there. In flight, these new ailerons are transformative—the S-7S has never handled better—and, as good news for owners of already built 7s, the ailerons can be retrofitted for around $1200.
A Long Line of Revisions
Tweaking the ailerons is just another in a long line of development steps designer Randy Schlitter has provided in the S-7 Courier, an airplane originated so that it could be used as a trainer for RANS's single-seat models. Schlitter intentionally built the cockpit to emulate the solo machines. In time, the S-7 created a niche of its own as a pert, clean utility design that may share some of the venerable Cub's layout but tries to evoke none of its nostalgia.
Two comfy chairs, one in front of the other, provide a comfortable perch for sightseeing.
Over time, the S-7 evolved. There are short- and long-fuselage models in its history, with the switch-over taking place in the mid-1990s. The stretch is 21 inches aft of the cockpit, which helps with stability. "It added 11 pounds to the empty weight," says Schlitter of the stretch, "but I wanted to do it for our certification program. I knew the longer fuselage would improve stability." That certification program was to make the S-7 a Primary Category aircraft; the category, launched in the early 1990s, carried the hopes of a simplified certification process. That effort failed to gain traction, in part because the certification process was still cumbersome. By contrast, getting a design approved under the ASTM consensus standards is much easier, which explains all the new airframe manufacturers since 2004.
RANS also gradually phased in aerodynamically balanced tail controls, first the elevator and then the rudder. Finally, in this much-abbreviated model history, came the S models, which had a deeper, wider firewall, a new cowling, and a host of other structural and convenience updates. An LS, in today's terminology, is simply a S-7S built by the factory as an SLSA.
You might miss the details on the S-7S's constant-chord wing, but the absence of aileron spades tells you this is the latest version, a sweet-handling delight.
As Schlitter says, "I like to keep improving the designs. I have lots of ideas." So it is with the current S-7S kit. And in this case, we have the driving forces of Light Sport Aircraft rules pushing updates. One example: The S-7S can be built with a carbon-fiber cowling, wingtips, spinner and boot cowl (that's the rigid section behind the removable cowling that surrounds the fuselage cage and supports the windshield), saving about 15 pounds in empty weight. Any pound you can save when the maximum weight is set by decree benefits useful load. On that front, RANS has also bumped the maximum-gross weight of the S-7S to 1320 pounds, the LSA-legal maximum, a gain of 20 pounds from the old gross. According to RANS, this raised limit applies to the S-7S, some S-7s and the Sport Wing S-6.
Optional carbon-fiber wingtips shod with simple LED strobe/navigation lights keep the S-7S straightforward, light and modern.
Some of that newfound capacity can go into fuel. With the latest version of the S-7S, RANS has bumped total fuel capacity from 18 to 26 gallons in roto-molded plastic tanks. These tanks slip into the wing from the root end. The difference with the new tank is that it more closely follows the contour of the airfoil; it doesn't have to penetrate much farther into the wingspan (from the root side) to accommodate the extra fuel. Actually lighter than the old tanks, the new high-capacity models use the same sight gauges at the root and have the same fitting locations as the smaller tanks. Schlitter, when asked why the airplane didn't have the fuel capacity before if the space was available, said, "Heck, we thought 18 gallons was plenty of fuel! But the builders want more, and we were able to give it to them." Also new with the greater tankage are flush fuel caps. Even with the new tanks full, you still have 436 pounds for the cabin—based on the typical empty weight of 732 pounds.
Over time, the S-7's tail has seen updates—including being mounted on a longer tailboom—all in the name of improved stability and utility. Both rudder and elevator are mass and aerodynamically balanced. A full-width electric trimtab is on the other elevator.
Structure, Systems, Synergy
Behind the cowl lives the ever-popular Rotax 912S.
The S-7S carries classic RANS design features. Chrome-moly steel tubes make up the fuselage structure, while the wings use tubular spars and (now) fully CNC-machined, one-piece ribs. These replace the multi-piece assembled ribs used before; they're simpler, lighter and stronger. This structure supports conventional fabric. That airfoil started out as a NACA 2412 but was modified by Schlitter to have a slight bulge on the bottom surface, only 3/8 inch tall, centered at about mid-chord. You might almost think it's a Cub-style flat-bottom airfoil if you didn't look carefully. Schlitter felt the cambered lower surface gave better handling and reduced drag. As a result of the docile nature of the airfoil, the wing has little twist or washout—the typical twisting of the wing so that the outboard sections have a lower angle of attack than the inboard sections. This trick ensures that the roots stall first, preserving roll control in stall and near-stall conditions.
Revised ailerons place the hinge line well behind the wing's trailing edge for reduced roll effort.
RANS builders have become accustomed to tweaking their instrument panels and instrument placement to accommodate the forward tilt of the traditional S-7 panel. The tilt exists to improve visibility over the nose and to the sides, but it complicates life in this new world of all-glass panels. So now the company will offer a vertical panel in all current S-7LS SLSA models and S-7S kits. (The S-7LS photographed for this story was built before the vertical panel became standard.)
Fuel gauges? Sure, always in sight, never need batteries.
A dedicated, 10-cubic-foot baggage compartment carries up to 50 pounds.
In other respects, the S-7S is a fairly conventional tandem-seat taildragger. Curved sticks come up from the spine for both front and rear pilots—solo is from the front—and there are conventional toe brakes front and rear. Both seats slide on tracks to make pilots of all sizes happy. These adjustments have to be done on the ground; they're not in-flight accessible. The S-7S is meant to be flown right hand on the stick, so the throttle lever is on the left sidewall, the other engine controls on the left side of the panel and the flap handle down on the left-side cockpit floor, just below your knee.
As mentioned, I caught up with the latest S-7S at Sebring in January. Demo pilot Jana Morenz walked me through the abbreviated start-up procedure. It's typical Rotax 912: a bit of choke to get it started then a minute or two of watching the idle speed before the engine settled down. After bringing the avionics online, the centerpiece of which is the Dynon FlightDEK-D180 EFIS/engine monitor, we trundled out toward the runway. The first impressions were that the airplane sits nearly flat in the three-point stance, but that was mostly an illusion from the low cowling, high seating position and forward-canted instrument panel. In fact, visibility all the way around is exceptional. We taxied out with both of the top-hinged doors open. The entire area above the pilot is a plexiglass pane, so it takes relatively little bank angle to be able to look into turns. Even though the cabin width of 30 inches doesn't seem huge, the impression is that the front office is as roomy as you'd want.
Dual Matco brakes respond to your toes on the small, U-shaped pedals. It's easy to drag a brake on landing until you get the hang of it.
Weather at Sebring was clear, light winds, temperature in the high 70s. With two of us aboard and half fuel, our estimated gross weight was just under 1200 pounds. The initial takeoff acceleration is quick, though certainly not startling. As soon as the throttle is full forward, you can lift the tail. At about the time you're wondering if the pitch attitude is right, the S-7S is flying. Centerline tracking was very good, with moderate rudder effort required and little tendency to over-correct or otherwise stymie the occasional taildragger pilot. In fact, the only odd thing you notice is the tendency to over-pitch slightly for the climb, purely an artifact of the excellent over-the-nose visibility. After an hour in the airplane, I'd worked out what the picture needed to be and had no trouble nailing level-offs from a climb or descent.
The latest design from RANS, the S-19, may not seem so related to the S-7S, but they share a simple design ethos.
Twin flip-up doors can remain open in flight.
The S-7S places the Rotax's radiator at the cowling outlet to keep the front half slim.
Heading straight to the south of Sebring at 65 mph indicated airspeed (IAS), the under-gross S-7S climbed at 1200 fpm on full throttle. At once you notice the benefits of the new ailerons. Where the previous S-7S felt light in pitch and a tad ponderous in roll (actually, that's unfair; it was just the high stick forces that made it feel less than sprightly), this new machine is well balanced. All the forces are on the light side, by design, says Schlitter, but they're appropriate for the intended mission of the airplane. Even though you can load it up with IFR-ready gear, this is really a fun, see-the-scenery kind of airplane.
Continuing the climb, the rate tapered to 850 fpm through 1500 feet as I let the nose drop, but our climb through 3000 feet MSL continued at that pace or slightly better. Clear of the Sebring area, we started maneuvering. The first impression when making large or rapid turns is that the airplane wants a fair bit of lead rudder to keep the ball in the center. It's not an annoying trait as much as it is just something you must learn to live with. Schlitter later told me that he had installed fairly stiff rudder-return springs to help with yaw stability. The breakout force for the rudder is higher than in some airplanes, but not out of the ordinary for taildraggers.
A "bush" tailwheel is an option on both kitbuilt and SLSA versions.
Once this is understood, the S-7S flies wonderfully. As mentioned, those new ailerons bring roll forces more into line with pitch effort, so it's much easier to peg a roll angle without inadvertently affecting pitch and, in general, the control harmony feels good. After the initial rudder input to begin the turn, you can release pressure and trim the slip angle with fairly small movements of your feet. Describing it is more work than doing it.
We tried a couple of speed runs to see how this utility airplane performs. One test, at 5300 rpm, showed 104 mph TAS at just under 3000 feet density altitude. Another run at 4800 rpm yielded a true airspeed of 94 mph as calculated by the Dynon. We ran a back-and-forth run to compare TAS to an average groundspeed on the GPS and proved that the pitot-static calibration was right on. RANS claims a top cruise speed of 110 mph TAS, which seems perfectly reasonable at a more speed-friendly altitude. Bear in mind that the LS demonstrator had the 100-horsepower Rotax 912S and a three-blade, 72-inch Warp Drive prop; different props will have an impact on cruise and climb performance. The S-7S's speed is competitive with other high-wing utility taildraggers—including the Kitfox Super Sport Model 7 and the Just Aircraft Highlander—and well ahead of the Cub-style airplanes with 100 hp. (The Cubs have about 178 square feet of wing, while the RANS has 147 and the Kitfox 132.)
The standard wheel fitting is a 6.00x6, but these 8.00x6 tires are an option.
During the usual flight-test maneuvers, the S-7S proved to have excellent pitch stability and a healthy tendency to remain at trimmed airspeed. In the stick-free test, where you pitch up from a trimmed airspeed and let the airplane recover on its own, the S-7S returned to level flight after three long-period cycles. This means the airplane wants to return to trimmed airspeed but won't snap right to it. Overall, the pitch and roll control systems felt like they had little friction, the forces built up naturally from on center, and it was simple to select and hold a bank or pitch angle at any airspeed from approach to high-speed cruise. The controls stiffened slightly at high speed, but not uncomfortably so.
Slow flight and stalls were, as the hackneyed flight-test phrase goes, nonevents. In fact, the hardest aspect was finding the flap lever under your knee and wrestling the flaps into one of the two deployed settings. Pitch change with flap extension was moderate and the effect on speed quickly noticeable. With flaps fully out and power off, the nose seemed relatively level. There was a mild shudder in the airframe and the stick began to go soft just at the stall. Despite having so little washout, the airplane maintained good roll authority into the pre-stall region.
Rubber, Meet Road
Specifications are manufacturer's estimates and are based on the configuration of the demonstrator aircraft.
Flying a new or revised model at a trade show can be tricky because you might have to fit into a line of other demo ships and arriving customers. That happened to us at Sebring; with a slightly rushed downwind and a premature dive across the base leg, I found myself a bit high and fast turning final. No problem. A big, long slip shed the altitude quickly, and I was surprised to find that the airplane snapped back to the desired 65-mph approach speed like it knew what it was doing. With full flaps, the picture over the nose remained full of detail, and I had to remind myself to resist the temptation to fill the view with cowling in the roundout.
I needn't have worried. The S-7S pitches smoothly into a three-point attitude and loses speed in a predictable way. The wheels touched down just about when I expected them to. The only surprise was that I'd allowed my right foot to slide up on the pedal, so we landed with a touch of brake applied. (This even after Morenz had warned me to keep my big toes off the brakes!) The tire protested momentarily before I realized what was happening. A quick, small tug on the stick to keep the nose where it was and a small movement off the brake pedal were all we needed. The S-7S showed no tendency at that moment to dart for the weeds.
The Designer's Mind
After the flight, I spent a good half hour with Schlitter in the RANS booth, discussing the design and how it compared to other similar designs I'd flown. He was genuinely interested in how the new ailerons worked and if I thought they were an improvement. He peppered me with questions about other competitive aircraft, and I could see his mind working. Later, I ran into Schlitter at Sun 'n Fun, and he talked openly about the other changes and minor updates he'd like to make to the S-7S, about the challenge of installing the new Rotax 912iS—a program the company has not yet begun but that Schlitter thinks is inevitable—and about how seemingly minor changes can make an airplane. "We want to keep things interesting," he said. "There are always things we can do better, ways to make the kit easier to build or take weight out of the airplane." All good things, because even in a time when many companies are pulling back on developments, it's still true that if you aren't moving ahead, you run the risk of falling behind.
For more information, contact RANS Designs at 785/625-6346 or visit www.rans.com.
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