May 2015 Issue
While itís not exactly a Cub clone, Groppoís new Trail kit shares some of the same DNA as Piperís classic.
There's a reason—actually a lot of reasons—why a Cub looks like a Cub. Any designer (other than Burt Rutan) who confronts a clean sheet wanting an airplane that's easy to build, practical to maintain and flyable with no nasty habits will put the basic strutted high-wing planform on the short list. Whether it's a tandem or side-by-side may be a toss-up, but to look right, the thing ought to have a tailwheel.
And that, in brief, describes why the Groppo Trail (www.groppotrail.com) looks like it does and why reiterations of the basic Cub concept remain a durable idea more than 80 years after the first E-2 appeared in a world then still dominated by biplanes. The Trail is the work of Nando Groppo, an Italian designer who has been involved in aircraft and component design since the 1970s.
The Trail—a Rotax-powered tandem taildragger with the option of a nosegear—has been making the rounds of the U.S. shows for about a year. Groppo will offer it as an E/A-B kit, an ELSA and an SLSA, and is just now setting up the mechanisms to export and ship the kit, which I got a look at last fall.
Like the Cub it resembles, the Trail is a simple airplane, both in systems and construction, and is a delight to fly. Where some LSA designers haven't seemed to pay much attention to how the airplane feels and handles, Nando Groppo has and it shows. Consistent with its European roots, the Trail is also one of a handful of light aircraft with a quick wing fold and trailering option. Whether that will prove popular in the U.S. is an unknown, but the option is there for builders who want their airplane to live in the garage next to the Mercedes. (Alright, the Jeep.)
Nando Groppo has been at the airplane business for a long time. Trained as an aeronautical engineer at Italy's Politecnio di Torino, Groppo worked in the aerospace industry through the 1970s before experimentation with Rogallo wings led him to form his own company. Following the trends of the day, Groppo designed ultralights whose basic features shaped his design philosophy in developing the Trail.
During the early 1980s, Europe was experiencing a wave of ultralight activity that persists yet today.
One of Groppo's first designs was the Gropino, an ultralight trike in the Quicksilver mold. (Groppo was an early Quicksilver dealer in Europe and later took on Zenith and Czech Aircraft Works as well.)
He branched into heavier ultralights with the Dui, whose resemblance to the Trail is unmistakable. Rather than the Rotax 912 found in the Trail, the Dui had a Rotax 503 and later an early Jabiru powerplant. The Dui had folding wings that pivoted into the vertical plane chordwise, so it could be trailered. About 30 of them were completed in Europe.
The Trail is the latest refinement in Groppo's line and the most numerous to date.
The first version of this model was built in 2005 and Groppo says about 112 have been produced with 75 flying in 11 countries, many of them kits. In an inteview last fall, Nando Groppo said some 37 kits are underway in Germany, France, the U.K. and Russia.
Most of these have been Rotax powered, although there are some Jabiru 2200 completions, too. As with the Cub paradigm in general, Groppo intended the Trail to have a utility role, thus many are used for towing gliders in Europe. There's also a float option for those interested in amphibious ops.
Although it can't be accurately called a Cub clone, the Trail's tandem taildragger design shares some of the same design points as the Piper classic.
The Trail is designed to be a quickbuild that requires neither extensive riveting/metalworking skills nor composite layup experience. With the exception of the provided fiberglass engine cowling, wingtips and empennage trim, the airplane is entirely metal.
The Trail is definitely a minimalist airplane. It's probably a stretch to call it a Cub clone, but it shares the basic idea.
The cabin is a welded cage of 4130 square-section chromoly tubing which, ŗ la Mooney, provides crashworthiness. That cage comes complete to the builder and provides a ready core to start construction. It even has the metal fuel lines from the wing tanks to the engine compartment tacked in place.
Aft of the cabin section, the airframe is conventional stressed-skin riveted aluminum construction over bulkheads and stringers.
Many of those rivets are pop rivets, which speeds and simplifies construction. There are a few bucked rivets at the trailing edge of the ailerons and flaps, for example, but most of the riveting is blind.
The wings are conventional aluminum skin over aluminum ribs with fuel stored in molded nylon tanks in the wingroots. The ribs are two-piece and riveted fore and aft to the spar web that comes pre-assembled from the factory.
The factory offers a quickbuild wing option for European customers, but it doesn't want to ship wings to the U.S., so builders will have to construct their own. Besides, Steve Bensinger, Groppo's first U.S. dealer, told me a quickbuild wing would bust the 51 percent limit.
While the European version of the aircraft has only 15 gallons of fuel capacity, the U.S. kit models will have 26 gallons, recognizing that U.S. pilots fly longer distances. (Or at least they want the option, bladder capacity notwithstanding.) From the two tanks in the wingroots, the fuel flows through the aforementioned metal fuselage tubes via a flexible line that runs through the cabin. The flexible line is necessary to allow the wings to fold, but as a crashworthiness element, it's none too comforting to have it just a few inches from your head. An armored hose would be a better option and Bensinger told me there's no reason a builder couldn't do that. (I would.)
At the tail is a heavy fabrication that ties the fuselage and empennage together and provides a beefy attach point for the tailwheel and an optional towing hook. This evidently makes the tail hell for strong because Nando Groppo delights in sitting on the horizontal stab for photos. Bensinger repeated the feat for my camera.
If there's a signature feature to Groppo's designs, it's folding wings. While there are hangars at European airports, there aren't many and they tend to rent for what a U.S. monthly mortgage payment might be. So trailering to and from the airport is popular in Europe and that requires folding wings.
The wings fold from a pivot point a third of the way back from the leading edge. To make this a single person job, a locking pin at the tip performs the final release, allowing the wing to be walked back and folded.
Bensinger says he isn't sure if kit builders or North American customers for the SLSA version will warm to trailering. "We're leaving it up to the buyer at this point. Because the tail doesn't fold yet, it's still a bit tricky to trailer," Bensinger said. Groppo is designing a folding tail which might complicate construction slightly for the benefit of reducing the airplane's width to the gear track—5 feet 7 inches. At that width, it will easily fit into one bay of a two-car garage or into a small shed.
It takes one person about five minutes to fold the wings, whose design is really quite well thought out.
The aileron push-tubes disconnect, and there's a removable pin to fasten each wing into the spar carry through. The flexible fuel lines remain attached. The wings rotate to the vertical—chordwise—and pivot toward the back, where a fixture secures them for towing.
Those fixtures will likely be options for the LSA Trail, as will floats, a full control set for the rear seat, a belly pod luggage compartment, and the parts to convert to trigear, which requires a few hours' work. In the kit version, rear brakes, controls, and a starter/flap control box are also options.
My view is that most U.S. builders will prefer to park their airplanes in an airport hangar rather than dragging them back and forth between home and the aerodrome. Hangars just aren't that expensive in the U.S. after you've dropped eighty grand building something.
Second, the nosewheel option. Think of what a Maule looks like with its optional nosewheel or what a Cub would look like on trigear. (Not for nothing do they call Tri-Pacers milk stools.) I'm not a tailwheel purist by any means, but yuck. The airplane just looks better dragging its tail.
Like other tandems, the Trail cockpit is narrow so the panel isn't generously large. In the SLSA version I flew, the steam gauge panel had a single AVmap display, a German-sourced radio/intercom and a Sandia STX-165 transponder. But to fit, those had to be placed on a sub-panel under the main panel.
The Trail's panel real estate is adequate, but not generous. In the demo model, to accommodate the AvMap display, the com radio and transponder were installed on a subpanel.
An additional option is the MGL Avionics Xtreme EMS, EFIS, and engine monitor pair, plus an iPad mini with ForeFlight for navigation. An E/A-B builder could install about anything from a Dynon suite to a Garmin G3X; there's certainly room to squeeze it in. But depending on other instrumentation, it may require the sub-panel.
While the space may be a little tight, the weight certainly isn't. The Trail is a relatively light airplane. In the SLSA version, its gross weight limit is 1300 pounds, not the usual 1320 pounds. Against an empty weight of just 720 pounds, that's a useful load of 580 pounds. That's a couple of 200-pounders, full fuel and an overnight bag. Not bad.
But don't get the idea that the Trail, despite the off-road pretensions of its name, will haul a bunch of stuff. While the luggage area behind the aft seat beats the Cub's canvas breadbox, it won't hold much volume. (The weight limit is 50 pounds.) If you had in mind a little outback camping at mountain airstrips, the optional belly pod might be the way to go. With that in mind, a turbocharged 914 Rotax might be a nice engine choice. That would make the airplane a stellar performer for mountain flying. (Groppo doesn't support that yet, but a builder could go that route.)
To ease ingress, the front seat pivots forward. The welded square section fuselage cage is visible in these photos.
Trail Flight Trial
It's no surprise that all of the Cub clones look similarly and fly similarly. How could they not? There's only so much you can do with 100 hp attached to a top-mounted wing with struts. So the Trail is perfectly competent in the company it keeps. But it does have a couple of nice qualities, which I'll get to in a moment.
First, getting in and out. The Trail solos from the front, so it's easy enough to do the butt-first cabin entry and swing your legs over the center stick, which is, thankfully, just the right height.
Getting into the rear is another matter. The seat is positioned just behind the cabin walls and would be difficult to get into if Groppo hadn't thoughtfully put the front seat on a pivot, so it swings easily out of the way. Once ingressed into either the front or the back, the cabin seems wider than other tandems I've been in, especially the front. It's definitely more commodious than a J-3.
Visibility from the front seat is excellent and not bad from the back, albeit the front-seat pilot blocks the view. From the front, no S-turns are required during taxi; the view is expansive. Even from the back, you can look around the front pilot without having to sashay the airplane much.
To accommodate the wing fold, the Trail's fuel lines are flexible and pass through the cockpit to metal fuel lines attached to the fuselage cage.
The Trail has a full-swiveling Matco tailwheel and Matco toe brakes, so ground handling should be crisp. In the version I flew, turn radius was somewhat hobbled because the wheel wouldn't break loose. It took a lot of brake and power to do tight taxi turns. That might take some tuning.
Compared to a Cub, or even Legend's version of it, the Trail's tail is a little slower to wake up. It might feel a little different solo, but just as you're wondering when it will come up, it does. From there on, it's just another Light Sport, with typical climb rates of about 750 fpm initial and 500 to 600 fpm after that. We easily got to the 1000-foot pattern altitude by the mid-downwind.
One thing I noticed—and liked—about the Trail is its control forces. In about half the Light Sport airplanes I fly, the control forces range from feather light to almost non-existent, with the Czech Sport Cruiser being the worst in this regard. Light control forces are not a good thing, necessarily. They invite overcontrol and, if the airplane is abused badly enough, actual structural damage. (A reader sent me a photo of a gaping hole in a Light Sport canopy, the result of a student who over pitched enough to float a fire extinguisher through the glass.)
The Trail proved a pleasant alternative. In roll, it's heavy enough to offer just the right amount of resistance—like a heavier airplane such as a Decathlon or a Diamond DA40. When I clamped a fish scale to the stick for an informal check of this, it revealed a pound of breakout (including friction) for roll and a little over two pounds for pitch; close to ideal. Someone more expert than I would have to refine and confirm the data, but it felt far more comfortable than say a Remos I once flew, in which the pitch force was so light I couldn't even measure it.
As a result, the Trail seems to go where you want it to with no encouragement to overpitch it. The stall is mild and doesn't seem to bite even if aggravated. When the pitch is disturbed, the airplane finds its trimmed airspeed in less than three cycles, which is not atypical of other LSAs.
The Trail has two-thirds span electric flaps deployed by a momentary switch in the cockpit, from either the front or rear. With two aboard, I didn't notice an appreciable pitch change during flap extension; that might be different while solo flying.
At this juncture, I could paste in the same performance paragraph I've written to describe every other Light Sport airplane with a 100-hp Rotax and a 1300-pound weight: About 100 mph on 4.5 to 5 gph.
That will vary with prop and engine. The airplane I flew had a two-blade wooden/composite prop, which Steve Bensinger said was overpitched a little. Coarser pitch may get a little more speed. Besides the Rotax 912, the airplane can also accommodate a Jabiru 2200 or a Sauer S 2200. Paired with other props, these may or may not improve cruise speed.
Landing anything with spring gear can be a piece of cake or a bounce fest, depending on the pilot's skill or lack thereof. The Trail has a single-piece aluminum spring that bolts to the outside of the belly. As taildraggers go, I thought the Trail was easier to land than most. Bensinger had suggested an approach speed of about 70 mph, but I found the airplane felt like it was being forced to fly that fast. So I let it settle back to where it wanted to be—about 60 mph indicated and 55 over the numbers. In a three-pointer, that resulted in a satisfying this-airplane-is-done-flying plop on the runway with no impulse to stab the brakes to get stopped. Wheelies take a defter touch, but not much. I used the same speed and added just a taste of power during the fly on and stuck it with a little forward pitch. It stayed stuck. Overall, I found the Trail a pleasure to fly and land and could have motored around the pattern all day.
Work in Progress
Compared to more established kit manufacturers, at least in the U.S., Groppo and the Trail is still a work in progress. While Groppo is prepared to ship what appears to be a complete, competent kit, the support structure is still in the construction phase.
But it looks like this is coming together rapidly. When I flew the Trail last fall, Steve Bensinger's Lone Palm Aero was the only U.S. dealer, and he hadn't yet completed his own Trail from a kit shipped to him by Groppo. Since then, two other U.S. dealers have joined the effort, one in Ohio, one in Maryland.
When I asked about support and warranty information, he said the details were still being worked out. During my research for this article, the factory was responsive, but for a builder with a burning question, there are time zone and language barriers to deal with. Bensinger says he's prepared to field any support questions, but again, the experience base isn't filled in much yet.
For experienced builders, this might not matter, given what appears to be a complete kit with good documentation and a design that isn't festooned with weird quirks. It's E/A-B building 101.
For a builder in need of a lot of support, it might be wise to delay purchase until Groppo has more kits fielded and a more mature support structure.
Paul Bertorelli is editorial director of Belvoir Media Group's aviation division. He flies his Cub in Florida.
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