January 2016 Issue
Stretching The Envelope
Flying the SuperSTOL Stretch XL with a 180-hp ULPower engine.
It was Editor Dye on the phone. “I have a Sun ’n Fun assignment for you. Just Aircraft will have an airplane there with a ULPower six-cylinder. Make arrangements to fly it, and write your impressions of both the engine and airframe.” My response, of course, was “Yes sir, I’ll get right on it.” I even kept a straight face, although inside I was grinning like a mule eating briars. Let’s see now, who to call first?
Early morning, a few weeks later; I’m standing on the green grass at Paradise City, Sun ’n Fun’s lightplane strip. In the ’80s and ’90s it was a beehive, but things got slow following the migration of most Light Sport vendors to the main flight line. Now people are returning, many to see the tall bush plane parked in front of the Just Aircraft tent. No one can miss it. It’s red, really red, with big balloon tires, long black legs, and a prop hub more than head high.
While the standard SuperSTOL is powered with a Rotax 912, this one mounts the new UL520i rated at 180 horsepower (see story in this issue). The ULPower installation manual says the 6-cylinder weighs about 250 pounds with all accessories: the exhaust, the oil cooler, the wiring looms, the coils and ECU, and even the oil. A Rotax 912 is roughly 100 pounds lighter, apples to apples, so to keep weight and balance within the acceptable range, the Stretch XL’s aft fuselage is 2 feet longer. Naturally, the cowl is a little longer too. The proportions are very pleasing, less stubby than the original, and less chunky than a Cub.
The lean look is entirely the result of the fuselage stretch, as the cockpit, wings, and tail feathers are identical to those proven on the standard SuperSTOL. The damped shock struts are slightly more robust, but they will be shared with the lighter Rotax-powered versions in future production. It’s a practical design choice that further toughens the original while maintaining a low parts count.
Comfortable seating for two. The long flap lever provides leverage, as it is pulled smartly during short takeoff.
Factory pilot Harrison Smith beckons toward the left seat. The doors are top-hinged and wide, so it’s easy to duck under them and climb aboard. The lift struts for the folding wings are behind the doors, and don’t interfere with cockpit access at all. I’m bubba-sized (6-2, 215), so it’s a pleasant surprise to find plenty of room. The seat adjusts fore and aft with a locking pin, and slides back far enough for full leg extension. Size 14 shoes have plenty of toe clearance, and the rudder pedal/brake pedal geometry is spot on. The doors bow out, adding elbowroom, and I have 3 or 4 inches of headroom to the skylight tubes. It fits, without control constraints. Score one for the big guys!
There are two short levers between the seats, in addition to the flap lever. One is trim, as you might expect, but the other is a tailwheel lock. The tailwheel is mounted on a long-travel swingarm with a shock, just like the maingear, and thus can’t be easily steered. So, it’s full swivel to taxi…or to spin around, tail high, doing the bush plane dance in the rocks. The tailwheel is locked for pavement or training, but doesn’t have to be, as there is plenty of rudder authority.
KIS principle at work; nothing extra here, and the analog airspeed only requires a glance at needle position for STOL ops.
Smith runs me through the start procedure. The UL520i has both electronic ignition and multiport electronic fuel injection, so there’s no setup or priming. This particular airplane was built with two of everything, so the drill is master on, main and crossover battery on, both ECU’s on, both injector drivers on, one fuel pump on, and then hit the start button. The actual start is like a car…a few rotations and it’s running. We set 1200 rpm and let it warm. The throttle is the only control, as the ECU controls mixture, there is no carb to ice, and this aircraft is fixed pitch. When wired for dual ECUs, the “mag check” consists of turning off one ECU at a time. If the engine stays running on one ECU, you’re good to go. Full throttle static rpm is 2800 with this particular custom-made Catto propeller.
Time for fun
As quickly as you can read this sentence, Smith goes to full throttle, pushes forward on the stick to raise the tail, pulls one notch of flaps, and rotates sharply to something past 45 degrees. The initial climb is helicopter-like, assuming you normally fly your helicopter while reclining with your feet higher than your head. Even when Smith relaxes the stick for a sustained climb at 50 knots IAS, the angle remains at an estimated 30 degrees or so, slats out.
Oh yeah, the leading edge slats. They swing outboard and forward on short arms, a mechanically robust arrangement, and just one of designer Troy Woodland’s many clever choices. The extension stops are rubber bumpers, which make a pleasing “thunk” to let the pilot know the slats are fully out in the breeze. Operation is entirely aerodynamic, with all extension and retraction in the speed range between 50 and 60. They’re not connected, and can deploy asymmetrically, which doesn’t seem to make any difference in control feel. Except for the thunk and a little motion in the corner of the pilot’s eye, there are no operational clues…if you don’t count the outrageous angle of attack they allow when extended.
We have a low overcast, with a storm brewing to the west. The Paradise City pattern is only 300 feet agl, so we can’t climb far anyway. Smith points the XL toward South Lakeland (X49), settles into cruise, and says, “Your airplane.” I take the controls and give the panel a scan. The UL520i feels and sounds just like an O-300 6-cylinder Continental, an engine I’ve always found to be very pleasant. Speed at 2500 rpm is 80 knots. The oil temperature is 214° F, which, given the short climb, seems a wee bit high to my Lycoming-trained mind (note: a subsequent inspection found a broken oil thermostat spring). On the other hand, CHT is low at 283° F. That doesn’t surprise me, given the huge cooling fin area I saw on the display engines.
I ask about stalls, and Smith just grins and says, “Go ahead.” I pull the power off, raise the nose, and wait. Other than slat extension, nothing happens. I raise the nose some more, then more again. Finally, at what seems like a ridiculous attitude for idle power, the nose bobs faintly. It’s not a stall in the conventional sense, but rather a big sink rate with the stick against the stop. There’s no tendency to fall off to the side. The airspeed is something less than 35 indicated.
Wing tanks fill a header tank hanging in the 32-cubic-foot baggage compartment, which in turn feeds the UL520’s electronic fuel injection. Recirculated fuel returns to the header.
At South Lakeland Smith shows me a short landing. It starts with power off, then hauling the nose up to kill speed and pop the slats, then extending the flaps and adjusting pitch to maintain 45 indicated. I can’t see over the nose, but it is possible to look around it on the side, and there’s a plentiful view of the rapidly rising green grass through the clear doors. At around 10 feet, Smith gives it a short burst of power, raises the nose to what seems like a ridiculous angle, stabilizes, and allows it to drop in tailwheel first. The big tires and the long-travel struts negate the impact nicely. It feels a lot like hitting a big bump while sitting in the air-ride seat of a Class A truck, or large agricultural tractor; just a comfortable smoosh into the hydraulic damping. Given the low stall speed (and no other choices), a terrain-trapped pilot might ride this one into the ground, upright and fully stalled, with a good chance of walking away.
I get one takeoff and landing before the weather dumps on us. We scoot back to Paradise City in the rain, narrowly missing two big orange flamingos scud-running toward Tampa. This time Smith sets up with power at 2000 rpm, assumes a steady nose-up attitude that looks like 25 degrees or so, and simply flies a normal approach into the ground at 45 with minimal flare, much like a Naval aviator arrives on a carrier. He pulls power at touchdown, applies moderate braking in the wet grass, and we roll maybe 200 feet.
LimoSTOL, Round Duex
Poor, poor me. The weather didn’t offer much opportunity to play in Lakeland, so it’s two weeks later and I’m in my RV-8, heading for Clemson, South Carolina. Smith will pick me up there, and we’ll fly the XL over to the Just Aircraft factory, on a wooded hill outside Walhalla. Ever been picked up in a limo? Well, I’m starting to think of the Stretch XL as the LimoSTOL. Rides good, and at my age it’s probably as much fun as a stretch Lincoln full of party girls.
We saddle up, and I try to duplicate Smith’s short field departure. It’s not difficult, but I’m a little slow as my right hand hunts for the flap lever. I don’t pull the nose up so much either; that will require a bit more familiarity. Climbing at 60 or 65 knots provides normal over-the-nose vision anyway. Other than the short roll and using the grass beside the runway, The Limo is perfectly comfortable in a conventional airport environment.
We check climb rate on the way over to Walhalla. Weight is a little over 1400 pounds, as this airplane is licensed E/A-B, not Light Sport. It’s a hot day too; density altitude is nearly 3000 feet when we start a climb at 1500 msl. Smith starts by pulling the nose to 50 knots, slats out, while I mind the stopwatch. Although the 5-minute maximum power is 180 hp at an electronically limited 3300 rpm, we set 2800, the max continuous rpm for the 520i, a fuzz under 170 hp at sea level and not much more than 155 with these conditions. We reach 3500 in 2:43, for a rate of 727 fpm. For contrast, Smith flew a repeat at 55 knots, with the leading edge slats in, and the result was 863 fpm. Although the gang on the FBO porch may not see these as bragging numbers, they’re actually quite respectable, and illustrate a point about climb rate vs climb angle. The Stretch XL is a low-speed airplane, and as such it doesn’t travel a great distance forward or upward in a given period of time. It can, however, fly an obstacle clearance angle pretty much like a cat climbing a screen door. It’s an airplane optimized for a particular mission.
I see that mission in all its glory when we reach the Just Aircraft plant. The, umm, runway is a bulldozed slash in the trees running straight up the hill to the plant’s parking lot. Smith does the same short field setup I saw back at X49, first getting slow, then using power to raise the nose a lot before landing like a fly on a wall. He then nonchalantly adds more power to taxi uphill to parking.
Troy Woodland, Smith, and I loaf on the front porch a while, talking about airplanes, the Stretch XL, and company history. After a plant tour (see sidebar), Woodland suggests a flying lunch. He hops into his personal short-body SuperSTOL (very light, and equipped with a modestly-pumped-up Rotax 912), does a warmup, then spins around, tail high, and disappears over the edge of the parking lot at full power. He quickly reappears, climbing steeply in a tight circle to stay over the clearing. Smith taxis to the edge, shoves in the throttle, and we too dive off what now seems like a cliff. We don’t roll far; given the UL520i’s 320 cubic inches (5254cc) and a gravity assist, we’re at flying speed in the blink of an eye.
Woodland’s lunch destination is the top of a rolling, grassy hill, at Chattooga Belle Farm, a pleasant 10-mile flight over the ridges. The manager retrieves us with a four-wheeler, and drops us at the farm restaurant. We dine outside, on a deck overlooking the vineyards, with the north Georgia mountains rising in the distance. This is Southern bush plane heaven…simply awesome.
Smith and I head for the Clemson airport after lunch. The afternoon is hot, the terrain is rolling, and at low altitude we should be wallowing and bouncing in the thermals, wishing we hadn’t eaten so much. The Stretch XL, however, displays very good manners in rough air. The wing is smaller than a Super Cub (147 square feet vs 178 square feet), so given a comparable load (here two guys and 12 gallons of gas), the XL’s wing is carrying about 11/2 pounds more per square foot. The ailerons also have less control system friction, so coordination is simply less work. There’s plenty of adverse yaw, but that’s expected to change. Woodland is already building wings with a new spoiler system intended to improve roll response at very low speeds. The spoilers are panels that pop up vertically from a slot at the crest of the airfoil, and by nature, they counter adverse yaw by providing drag on the wing opposite the downward deflected aileron.
Back on the ground, it is depressing to walk away. I really like the Stretch XL and the UL520i. They both seem to be products refined beyond what anyone has reason to expect, given they are relatively new designs. In each case their creators are serious men…and it shows.
Want more? Read Dave Prizio’s flight review of the standard SuperSTOL in our October 2013 issue.
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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