February 2012 Issue
Kitfox Super Sport
A new American engine joins an American aircraft icon.
As often as this particular Kitfox seems to get new engines (this very airframe, now housing the Light Sport Aircraft-intended Lycoming O-233, once grasped the Rotec radial), you'd think something was up in Homedale. It's possible to imagine that this thrumming little shop on the western bank of the Snake River in Idaho has a huge machine extruding firewall-forward packages as fast as new engines can be found, like an overgrown Pez dispenser of internal combustion. A giant crane removes one powerplant from the airframe (still warm from a test flight), sets it aside, and grabs another. The propulsion package lands home with a thud. A complex quick-release system instantly marries the new engine to the Kitfox's simple airframe with a clack that would do coupling train cars proud.
Meanwhile, in some dark corner, Kitfox Aircraft owner John McBean cackles in delight, a countrified Dr. Evil in blue jeans and a flannel shirt. His machine is alive!
With the Lycoming O-233 on the nose, the Kitfox Series 7 Super Sport takes on a pert, compact appearance. Although Kitfox Aircraft had the older Lycoming O-235 as an optional engine for this airframe, making the 233 an ideal fit took a decent amount of work.
The gray goods: Lycoming's new O-233 is a refined version of the popular and enduring O-235. It makes 115 horsepower in this installation.
McBean only wishes he had such a machine. In fact, his penchant for sampling new and different engines on the front of the Kitfox represents a massive amount of additional work for his small staff. "But we have to try, don't we?" he asks in his best workboot-rhetorical tone. Like many manufacturers, Kitfox has to watch the bottom line carefully, so R&D projects using truly unusual engines or offbeat configurations just aren't part of the day to day. "We're open to trying a lot of things," says McBean, "but in the end we have to sell and support the design." Even if it's technically not the company's engine, Kitfox inevitably gets dragged into powerplant-related customer-assistance issues. Better, in this case, to go with what you know.
To speed development, Kitfox used an existing O-235 cowling as a template, hence the bump. It's likely this feature will disappear in the final cowling for the 233.
Which is why the Rotax 912S has become the default choice for the Kitfox Super Sport. The overwhelming majority of the kitbuilt S7s in the world have the Austrian engine, and all of the factory-built SLSAs do. But that didn't stop McBean from trying the Rotec seven-cylinder radial. (See "Kitfox with a Rotec" KITPLANES® March 2011, Page 8.) That airplane was a huge hit at AirVenture 2010 and caused many historically inclined pilots to stop and gawk. McBean admits the Rotec was a sentimental project, one not expected to threaten the sales of the Rotax Kitfox. But he was right that it drew attention to the airplane and to the company.
Now there's a Lycoming. A new Lycoming. OK, mostly new. Introduced in 2008 and finally released to the marketplace in early 2011, the O-233 is Lycoming's response to the Rotax 912 and a rejoinder to the Continental O-200-D Lightweight, both of which have proven to be popular LSA engines. (The Rotax much more so because it has a massive head start, particularly in LSA designs with extra-American roots.) For this project, Lycoming started with the long-running O-235 four-cylinder, air-cooled engine and ran it through an aggressive weight-reduction program. Jenny Craig for powerplants, only with CAD-CAM and an angle grinder in place of freeze-dried food and diet tips. (For more on this engine, see "Engine Update: Lycoming's Light-Sport ready O-233 arrives," Page 42.)
McBean approached Lycoming to be one of the early adopters of the 233 after the engine was introduced at Oshkosh. "I liked what I saw of the 233," he says, "and I'm always willing to try new things. Plus, I was eager to have an American-made engine." He's quick to praise the Rotax for its low weight and overall good reliability record, but you also catch a glint of a red, white and blue undershirt beneath his Cabela's flannel.
This would be a new relationship for Lycoming and Kitfox under the current ownership, but the airplane and the engine go way back. In the time of the Kitfox's rapid ascendancy, SkyStar Aircraft, which had purchased the company and the designs from Dan Denney, looked to expand the airplane's appeal. That desire resulted in the Kitfox Series 5, a significantly larger, beefier and more "grown up" Kitfox than the ones that started on two-stroke powerplants and a waif-like structure. The Series 5 was designed for the then-new Rotax four-strokes, sure, but it was also meant to take the small four-cylinder Continental and Lycoming engines. Many were built with the Continental O-200 and the Lycoming O-235, the latter an engine that could be readily found in the remainders bin.
Dual exhausts emerge ahead of a turned metal lower inset. A small lip on the outlet improves cooling, which was absolutely not an issue during the test flights.
Then and Now
It sure would have been nice if the O-233 had slipped right into the firewall- forward package designed for the O-235, but that was not the case. McBean and company decided to make some minor modifications this time around, taking advantage of some of the 233's intrinsic benefits. For example, with the Champion-built electronic ignition replacing magnetos, the back of the engine is much less crowded, especially so considering that few builders opt for a traditional instrument vacuum system. Even though the 233 was supposed to be much lighter than the 235, it still promised to be heavier than the Continental (by a little) and the Rotax (by a lot), so it made sense to move the engine rearward in the airframe. The 233's new layout made this alteration possible.
The propeller shown here, a first-test example from WhirlWind originally intended for the Continental O-200, has been replaced with a Catto prop with greater diameter. Kitfox is still testing to find the best prop for this airplane.
Lycoming has set aside the option of fuel injection for the ASTM-approved LSA engine, so the Kitfox wears a conventional carburetor and a slick NACA duct feeding it.
Originally, McBean wanted to move the engine aft 2 inches, but settled on 1.5 inches as the best compromise of weight placement and firewall access. Shifting an engine is not a trivial process. McBean had to create an all-new engine mount, have an entirely new exhaust system crafted (it's a conventional double-crossover system with shrouds for cabin and carburetor heat), rework the carburetor mounting system and airbox, and accommodate a lightweight starter and alternator. Oh, yes, plus do an entirely new set of rigid baffles. That, and create a new firewall-forward wiring harness and find room for the ignition coils on the cool side of the baffling. Trivial stuff, really.
Shortening a cowling is harder than it seems, but the Kitfox crew did a masterful job of keeping the sleek lines and flush oil access door.
Covering this engine is a cowling loosely based on the Kitfox/235's. "But, you know," McBean says, mentally reliving the process, "that's a compound curve all the way across the cowling, so slicing an inch and a half isn't just taking a bandsaw to it. Plus we had to adapt it to the new design fiberglass boot cowl that wasn't around when the first 235s were done." Every time you think these airplanes are modular, reality kicks you in the kneecap.
Lycoming, for its part, has been extremely supportive, says McBean. "We have a conference call every week," he says. "They want to know how the engine is performing, what kind of temperatures I'm seeing, everything. It's been a terrific relationship." Lycoming deferred to the Kitfox factory's expertise regarding the powerplant installation, though it did provide substantial documentation. While Lycoming believed that the engine would have been fine without an oil cooler, McBean learned otherwise; a compact cooler is now part of the firewall-forward package, nestled on the firewall ahead of the copilot's feet, fed cool air from the upper baffle area behind the No. 3 cylinder.
To simplify development, Kitfox kept the Cub-style landing gear on the O-233 airplane; one advantage is that it's slightly lighter than a normal one-piece, bent-aluminum gear.
Lighting the Sparkler
The version of the O-233 flying on the factory Kitfox isn't the most advanced. While it packs the electronic ignition, it doesn't have the fuel injection that Lycoming planned to offer (and does for the Experimental crowd). Even so, McBean confesses that the ignition arrived barely in time to make Oshkosh last year. Showing some real development savvy, Lycoming provided spares for the ignition system, appreciating that McBean would be short on time to fine-tune the installation before heading across the country. Rather than it being an admission that something might go wrong, this move by Lycoming was brilliant. Don't read it any other way.
This is the first effort at baffling for the O-233, which has a footprint almost exactly like the O-235. The inlet next to the starter gear ring provides air for the carb-heat system.
In the time since the airplane's return from AirVenture last summer, it's been flown almost daily in the quest to vet the engine, beat on the systems, and find the best propeller for overall performance. "It's been a great engine," McBean says. "We've worked it very hard. It hasn't burned any oil. It runs very well and has been very predictable. I've tested the 'mags' every two hours in flight and have never had a problem. The 'mag drop' is less than 100 rpm each side." This newfangled ignition system also has cured the engine's propensity for fouling plugs, at least as it used to as an O-235. (Raise your hand if, as a student pilot, you were ever stymied by a fouled-plug Cessna 152.)
Testing Ground in Use
I dropped in on the Kitfox factory in early August last year, with the crew still digging out from their trip to AirVenture. Mild weather in Homedale made for nearly ideal test conditions. It was a bit surprising to see the yellow- and-black Super Sport with a flat engine installed. The last time I saw this airframe it had the Rotec and the ring cowl. The new cowling looks great and fits snugly. You might notice the slight "cheeks" molded into the top cowl to clear the front cylinders, but these may not stay. "I'm not 100% sure we need them," says McBean. "Sometime before we release the final kit, we'll see if we can get rid of them." Otherwise, it's a conventional air-cooled installation, with modestly sized inlets, a single large outlet along the lower edge of the firewall and a NACA-style scoop for the carburetor some ways below the spinner.
Like all of the famous utility aircraft, the Kitfox moves the stabilizer's leading edge to adjust pitch trim. It's run through an electric motor that's ever so slightly too fast at cruise speeds. A blip will do ya.
For our flight, McBean was running a "gimme" prop. As in, gimme that prop standing on the wall, let's see if it fits. Actually, that's not quite it, but the closest to an ideal prop McBean had was a WhirlWind fixed-pitch, composite-blade beauty measuring 72 inches in diameter. It's actually intended for the Continental O-200, but the Lycoming's power and the Super Sport's expected speed range would be close enough to the prop's design point to perform the initial flights.
Other ongoing changes to the Super Sport are evident on N12KA. For example, the airplane retains the Cub-style steel-tube landing gear designed to look right with the Rotec. The criss-cross tubing under the belly and exposed shock units no doubt suck down a few miles per hour, but they're likely 5 pounds lighter than the massive Grove-made aluminum gear that's standard on the Series 7. This airplane also keeps the new smooth leading-edge treatment for the wings and the aforementioned fiberglass boot cowl—that's the piece between the back of the removable engine cowling and the doorposts. Finally, the same minimalist panel is aboard, with three white-faced gauges in front of the pilot and a Garmin GPSMAP 696 taking up most of the center stack. (Incidentally, McBean is working on a more comprehensive engine-monitoring system to help flight-testing move forward.)
Heated pitot? Not on this VFR-only Light Sport ship.
Turn the Key
Where the Rotec required a bit of finesse to start when cold and even the Rotax 912S asked for a certain process, the Lycoming lights off conventionally. Push the red knob in, pump the throttle, turn the key. It catches quickly and settles into a smooth, quiet idle. The runup is, likewise, straightforward, so by the time you've checked that the fuel is on (it's either on or off), elevator trim is set and flaperons are deflected to the first notch, you're just about ready to go.
Because the Lycoming packs 115 horsepower compared to the 912S's 100, the initial acceleration feels sprightly but not night-and-day different from the 912S iteration. That extra power is partially consumed by the additional weight of the Lycoming, and some of the potential thrust is squandered by the slightly too-small prop. (More on that in a minute.) Nevertheless, you can count to three and then raise the tail. I tended to over-rotate the nose down so that I was unintentionally holding the airplane on the ground. To its credit, the Kitfox tolerated this miscue without complaint.
Kitfox kept the panel unchanged from this ship's duty as the Rotec mule, but the panel will hold a large single-screen EFIS if you want. (A local Kitfox used in the training environment houses a Dynon SkyView system.)
Note to Rotax pilots: The red knob is called the mixture control. It adjusts the engine's fuel/air ratio. Learn it, love it.
The reclining seats are comfortable, while the ample baggage area behind can hold 150 pounds structurally.
In the climb we saw 500 fpm at 85 to 95 mph indicated. At closer to the best-rate speed of 65 mph, our climb rate increased to 750 fpm. Notice that these figures are lower than what the Rotax posts, according to Kitfox's data. We'd soon have a partial explanation. McBean and I leveled off at 4000 feet MSL (at our temperature that was 5600 feet density altitude), brought the throttle back until we saw 2800 rpm, then leaned to peak the rpm, which is theoretically the best-power mixture. By averaging two GPS-derived groundspeeds, one upwind and the other downwind, we witnessed a 125-mph true airspeed under these conditions. Pulling back to 2600 rpm reduced our TAS to 118 mph. It's worth noting that Kitfox claims 120 mph TAS nominally for the 100-hp version. That small prop helped high-speed cruise a bit at the expense of climb performance, the classic set of compromises laid bare.
Access to the Kitfox's cabin comes via twin top-hinged frames sheathed in 'glass.
In subsequent testing with a new Catto fixed-pitch prop, this one 74 inches in diameter (plus two from the WhirlWind), McBean reports typical cruise speeds of 122 to 123 mph true. There may be more speed to be had with fine-tuning of the cooling ducts and baffling, and it's likely that the Grove gear will give back some velocity. But until McBean has the full data-acquisition gear aboard, it's hard to know exactly where the engine is running along the fuel-mixture curve. So many variables, so little time.
The important fact is that Kitfoxes aren't about blazing speed, so a few miles per hour here and there aren't going to make or break a sale. Instead, the airplane is about comfortable low-speed handling, short takeoff and landing distances, and simple pleasures. In this sense, the Lycoming fits right in. Compared with the Rotax, which always feels busy, like it's just finished a triple espresso after a plate of tiramisu, the Lycoming is languid, chugging along with little apparent effort and commendably little vibration. (You might credit the composite prop for that feat.)
Specifications are manufacturer's estimates and are based on the configuration of the demonstrator aircraft. * Kitfox Aircraft has not completed full testing for the O-233 package and has not set final pricing for the specific kit components. The listed price is for the similar O-235 installation package, less engine. ** These performance figures are for the 100-hp Rotax version of the Super Sport.
Somewhat amazingly in an airplane significantly heftier than most of its kind—the O-233 Super Sport weighs 868 pounds empty, approximately 70 to 80 pounds more than one with the Rotax—handling is unblemished. As before, the full-span flaperons display their might to thick-handed pilots but settle down once you quit stirring the pot unnecessarily. The heavier Lycoming moves the Kitfox's empty center of gravity forward, so that helps with longitudinal stability, which is very good. Stick forces are on the light side in roll, moderate in pitch and again light in yaw. A hint of tail waggle sneaks in amid low-level turbulence, but it's just that…a hint. The hardest part of landing the Kitfox is, for me at least, pegging the correct pitch attitude in the roundout. It's a lively airplane with a fair bit of lift even at low speed, so it's easy to conclude a slight bounce with an amazing balloon ride. McBean prefers wheel landings, and I can see why.
It's fair to call the Lycoming O-233 Kitfox a work in progress. Lycoming continues to make small updates to the engine and systems, and McBean is chewing his way through prop choices. Until all the pieces are in place, it would be imprudent to drop performance figures into a brochure. Likewise, McBean is waiting until all the R&D is finished before finalizing the firewall-forward costs and specific components. But this much we know: The Lycoming O-233 lives and lives well. It hasn't quite met Lycoming's hopeful weight goals, but it runs like it should, is at its core a very well understood engine, and will likely have widespread support.
For Kitfox Aircraft's part, development will continue with the 233 until McBean is convinced it's as refined as it can be. And then…who knows? I thought I spied a tractor-trailer from Acme Aircraft Engines pulling up to the loading dock, but that could have been my imagination.
For more information, call 208/337-5111 or visit www.kitfoxaircraft.com.
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