All Grown Up

The Titan-powered SuperSTOL Stretch XL.

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Really, it was only a matter of time. First there was the Highlander, a nice little two-place side-by-side. In the hands of the “We land wherever we want” crowd, it quickly grew longer legs, big tires, and a rapacious appetite for little grass strips out behind the barn. When Just Aircraft’s Troy Woodland swapped the wood-ribbed wing for an aluminum structure with automatic slats, the available angle of attack became so great that the next evolution was a damped landing gear with 21 inches of stroke. The new bird, introduced at Oshkosh in 2012, became the SuperSTOL.

A standard Rotax-powered SuperSTOL is something like a 4-stroke dirt bike on steroids. In the hands of an expert, it leaps into the air as if launched off a jump, returns to earth near vertically, then pivots tail-high and leaps skyward again in a burst of noise and dust. Like the bike, this sort of fun can keep a pilot engrossed all afternoon, grinning like a madman.

Titan 340 with prototype twin plenums and Lightspeed ignition.

Contrast the original SuperSTOL with the de facto king of the off-airport world, the Super Cub. To some traditionalists, it somehow seemed a bit too small, too busy, perhaps even immature. None of these things are entirely true of course. The airframe is a bit smaller, with 5 feet less wingspan and 3 feet less length, but the baggage area is arguably larger, and the side-by-side seating is both roomy and ergonomically correct. Although a recent design, the SuperSTOL is also a product of long evolution reaching back to roots in the Idaho kit-aircraft industry, much as today’s Cub clones all have roots in Lock Haven. So why the perception? Frantic antics aside, the key was the Rotax humming at 5800 rpm. To the old-school crowd, it just wasn’t right, and never would be. Forget the 912’s well-earned reputation for reliability; they wanted a traditional 2700 rpm, large displacement, air-cooled engine.

CMG Titan 340 with P-Mag ignition.

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Woodland and partner Gary Schmitt like to have fun, but they are also sober men of business. They had watched the price of the 912 rise every year, until it was approaching Lycoming dollars. They knew competitors (those Cubs again) were trending toward more and more power, and even at an equal price, Rotax was not in a position to deliver 180, or even 160, hp anytime soon. And Woodland knew (in his heart, if not in hard statistical evidence) that there were a lot of dusty Lycoming O-320 core engines in hangars and shops. Combine a reasonably priced kit with a home-overhauled 320, and the result could be very affordable.

The new model was called the SuperSTOL Stretch XL. Park the standard and XL models together, and the difference is obvious. Although they share the same wing, tail, and landing gear, the XL fuselage carries a longer cowl to enclose larger engines, and is extended about two feet behind the cabin for balance. The visual transformation is significant; the XL presents as a large airplane, yet manages to appear leaner at the same time. The long gear legs and 29-inch flotation tires seem to be in proper proportion, too. Overall, the impression is more 4×4 than bike, a serious machine for serious play.

The KIS principle at work; GPS, radio, engine monitor, and an ELT head.

Speak softly and swing a bigger Catto.

The first public example was built for a European client, the bright red Stretch XL reviewed in the January 2016 issue of KITPLANES. Reflecting the customer’s Euro preference (and Woodland’s willingness to try new things), it mounted a ULPower 520i six-cylinder, rated at 180 horsepower. I found both the airframe and engine delightful to fly. Could traditional power make it better? The answer would require another trip to Walhalla, South Carolina, to fly the latest Stretch. It’s good work if you can get it.

Big Blue

The Just Aircraft demo and test mule, N223JA, is painted an attractive medium blue, with the silver belly seen on most SuperSTOLs. Although it looks great with any primary color, the silver is not strictly a decorative pick. It’s actually Poly Fiber’s Poly-Spray, normally used under a top coat; the color is UV-blocking aluminum powder. Bare Poly-Spray is a practical choice for an off-airport airplane, as it makes fabric repair easy when sticks and stones poke holes in the belly. No topcoat also saves a little weight.

N223JA’s powerplant is a Continental Motors Group (CMG) Titan OX-340. It’s the current darling of the off-airport clan, shared (with various accessory

differences) by the popular Carbon Cub and the new Super Legend HP. Stroking adds little mass, thus the X-340 weighs roughly the same as a similar 320 from Lycoming, Superior, or Titan. However, using the OX-340 bumps available horsepower to 180, which translates directly to increased climb rate.

Early prototype cowl inlets.

Catto supplied two of their famous wood/composite propellers, an 80×50-inch pitch (also shared with the Cubs) and an 86×35-inch pitch, which factory pilot Harrison Smith frankly calls “the show prop.” The 80×50 is the all-around performer, and results in excellent climb while still turning in efficient cruise speeds. The 86×35 maximizes STOL performance, something that often draws involuntary expletives from first-time passengers. Customers may pick either, and many will buy both.

Development required the Just Aircraft crew to spend some time on cooling experiments. The problem with any high-power STOL aircraft is the very low airspeed used for maximum performance. A short burst at VX is no great challenge, but extended climbs at best rate speed can be another story. The 340-powered Stretch has a VY of 68 mph (59 knots) at 1550 pounds. Aircraft velocity that low means the available dynamic pressure to drive cooling flow is little more than 2 inches H2O near sea level, and even that measly figure drops to 1.7 inches at 10,000 feet. As a rough rule of thumb, an engine like the 340 requires about 2 pounds of cooling air per second to keep CHTs below limits; with standard-wrap baffles, delivering that mass flow requires 5 to 6 inches of pressure drop across the cylinder fins. Clearly it can’t be done with aircraft velocity alone, so much of the necessary pressure must stem from high-velocity propeller outflow, and the inlets must capture it effectively.

Horizontal stabilizer tip fences.

The inlets you see in these photos were in place last spring at Sun ‘n Fun. They fed individual plenums over each cylinder bank, while air for the oil cooler entered via a NACA duct on the right side. By Oshkosh, the inlets had grown, as had the exit area, but CHT would still reach 440F when asked for maximum performance. The latest cowl (installed on a customer airplane, not shown here) nearly doubles the original inlet area. It also incorporates conventional flap baffle seals around a single large plenum volume, and feeds the oil cooler from behind the #4 cylinder. The new cowl is holding CHTs at a typical 400F or so, which Titan considers to be entirely satisfactory.

Roomy cabin offers plenty of legroom.

Leading edge slats extend automatically.

Sharp-eyed SuperSTOL fans will notice two experiments at the tail. The horizontal stabilizer is now an inverted airfoil, rather than the slab stabilizer previously used. In addition, small fences have been added to the tips of the HS. Smith reports subtle differences in cruise speed and handling, all of them good, so the changes are expected to be seen in regular production.

Mister Manners

Is it a better airplane? Heck, yes. Let’s go fly.

Entry is easy; big doors open upward, and the strut attach points are out of the way, aft of the door. The seats are easily adjustable, the doors bow outward for elbow room, and the pedal angles work. I’m a bit more than 6 feet 2 inches tall, top 220 pounds stark naked, and come factory-equipped with size 14 shoes. Even so, there is plenty of room in every dimension.

The carbureted OX-340 is dirt simple to operate; prime or pump, ignitions on, and crank. Idle, taxi, and run-up are conventional. The fun starts when the throttle goes in. Although it can be flown like any normal taildragger, a full yee-haw departure requires nothing more than a rapid application of WOT and a tug on the flap handle…one thousand one, one thousand two, and it’s airborne. Pick a pitch angle somewhere between mild and wild, depending on desired view out the windshield. I’d usually be a bit shy about the maximum, while Smith constantly encouraged more pull.

As you might already guess, the slow-turning OX-340 and its 80-inch prop outclimbs the Belgian six-cylinder, which spins a 76-inch Catto at a higher rpm. The European also has a 5-minute power limitation, while the Titan has none, unless (of course) the airframe is licensed Light Sport. To its credit, the six-cylinder is smoother, while the four is more harsh, a natural result of physical mechanics (a flat six has no free inertias or free moments; reciprocating forces don’t result in vibratory block motion). Regardless, the old-school motor quickly fades from notice. For anyone raised on Brand C, P, B, or M, it just feels normal.

The ailerons can now be teamed with a spoiler system.

Practically all late-model SuperSTOLs (both short and long) are equipped with a roll spoiler system to augment the ailerons at low speed. The spoilers work very well indeed, providing positive roll control with the airplane in a fully stalled condition. Actually it’s not really stalled, as the extended leading edge slats largely maintain attached flow over the wing. Power off, nose up, the airplane merely settles into a sink rate, typically between 800 and 850 feet per minute depending on temperature and weight. While sinking, stick fully aft, Smith even applied a bunch of aileron and then held the aircraft upright with a boot-full of opposite rudder…stalled, while sideways, in full control.

The spoilers are not just for the freak show. They’re located at the crest of the airfoil, and deploy straight up through slots in the wing surface. Ailerons and spoilers are linked so that each spoiler extends progressively when its companion aileron is deflected upward. In this way, it both kills lift and adds drag, nicely offsetting the lifting drag of the opposing downward-deflected aileron. The result is limited adverse yaw and less pedal requirement. The entire roll system exhibits little friction. When combined with the longer XL fuselage, it’s very pleasant to fly, even on the bumpy days.

Since we were out having a good time, it was only natural that we visit the land-like-a-fly-on-the-wall hillside airstrip at the Just Aircraft plant. Smith handled that one, but careful observation says success mostly requires aim and timing, because the actual vertical speed at impact doesn’t matter very much. The damped, long-stroke gear soaks it up. Earlier, back at the Clemson airport for a gas stop, Smith had grinned and said, “Watch this,” then proceeded to put the stick in his lap and drop it in from about 10 feet up. It didn’t even bounce.

So there you have it. The original SuperSTOL is great fun, and it’s really hard to knock any Rotax 9-series. Most of the airframe features are shared with the XL; there is nothing lost by choosing the smaller of the siblings. That said, for an old-school guy, the familiarity of Lycoming-style engines brings a certain comfort level to the game…and there are a lot of ways to play. Lycoming, Continental, and Superior all offer suitable power. There are good custom shop rebuilds, used-but-serviceable salvage motors, and a frugal builder can always team up with his local A&P for an educational field overhaul. The Stretch XL offers choices…and all of them are good.

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Dan Horton
Dan Horton says he is "just a homebuilder". He has been a pilot more than 30 years and currently flies a custom RV-8.

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