-by Ken Ibold
A few miles down the road from where NASA fits the space shuttle for flight is an assembly plant of much more modest proportions: the final put-together hangar of the Liberty XL-2.
Liberty Aerospace is positioning the XL-2 as a two-seat touring airplane, suitable for single pilots and empty-nesters who want to travel at reasonable speeds with low operating costs. The companys unusual strategy-which matches the somewhat unusual airplane-hinges on success in two areas. It needs to build the right airplane for that mission but it also needs to be right that the market for an airplane tailored to such a mission is big enough in the first place.
The answer on both accounts, in our view, is a solid perhaps, but dont count on it. In a soft market, niches within niches may be increasingly difficult to find, in our estimation.
The XL-2 owes its existence to the Europa line of experimental aircraft introduced more than a decade ago. The mid-wing, two-seat airplane was originally designed with a single main landing gear that retracted into a center console between the seats.
The monowheel is augmented by a tailwheel and small retractable outrigger wheels on the wings. Europa later created a tricycle gear version of the airplane and its this version that bears the most family resemblance to the Liberty XL-2.
In 1997, Liberty commissioned the Europa designers to engineer the XL-2 with certification in mind. Their charge was to use advanced materials and manufacturing techniques to produce an affordable and technically advanced aircraft that incorporated proven aircraft design and had good all around performance.
The prototype was unveiled in 2000 and featured a 100-HP Rotax engine, tubular steel welded chassis, Dowty carbon-fiber fixed-pitch propeller and a 48-inch-wide carbon-fiber fuselage. The chassis and the fuselage made it into the final version; the Rotax and the prop did not.
Replacing the Rotax is a 125-HP Continental IOF-240 engine, which features the full authority digital control or FADEC system developed by Aerosance for Continental. Essentially, the PowerLink FADEC system replaces the magnetos with electronic ignition and uses a computer to monitor and optimize mixture and spark timing. While it sounds revolutionary in aircraft engines, its been common on automobiles for decades.
The upshot of FADEC is that power control consists of throttle forward to make more noise, throttle back to make less. The computer takes care of the rest, at least in theory. In addition to the engine change, the prop evolved from the exotic composite Dowty to a wooden Sensenich. Although cost was part of the picture, the company says they experienced some delamination problems with the composite prop.
Getting the XL-2 into its certification prototype stage, where it is now, has been a long road. Over the past three years, the designs evolution has been matched by the change in its target market, as well. The companys promotional materials from two and three years ago tout the airplane as a low-cost trainer la the Diamond Katana/Eclipse in addition to a personal aircraft.
The current plan, however, is to market it as a touring airplane. Both the demonstrator and the conforming prototype are chock-full of avionics, including the Apollo MX-20 moving map, something you dont often see in a two-placer.
Liberty has adopted an unusual design strategy for the XL-2. The airplane is based on a rolling chassis made of steel tubing. To this is affixed the engine and fixed landing gear and the cabin and fuselage is mounted to the frame with titanium supports. The fuselage is carbon fiber composite, incorporating the smooth, sweeping lines so common among homebuilts and such airplanes as the Cirrus and Diamond models.
One advantage of the chassis is immediately obvious. A single belly pan mounted to the chassis drops off easily and opens up virtually all of the systems for inspection, including the pushrods that move the control surfaces. In addition, the chassis helps improve the airplanes crashworthiness and spreads landing gear loads better than a semi-monocoque design.
The pushrod controls are connected to a central junction under the center console and control sticks emerge for each seat. The result is a sort of hybrid control that works like a stick but moves something like a yoke. When banking right, for example, the stick at the left seat rises and the stick at the right seat descends. While it sounds somewhat awkward, in practice it works easily and intuitively.
At first glance, the wings look like a set of constant-chord Hershey Bar wings right off a Cherokee. In fact, they do taper slightly but the 7-to-1 aspect ratio and 112 square-feet of wing area prove that this is not your fathers Cherokee. The wings are conventional aluminum rib-and-sheet construction and are also flush-riveted to give them a clean look that matches the composite fuselage.
The wings mount to the rolling chassis individually rather than to a spar carry-through. The leading edge of the wing starts at about the front of the gull-wing doors and the trailing edge is just aft of the rear of the door. The wings carry no fuel and have electric slotted flaps that are infinitely adjustable.
The fully castering nosewheel means that steering on the ground is by differential braking, which is actuated by finger levers on the center console rather than toe brakes. The rudder is nominally effective even at taxi speed and supplies good authority on the runway, which eases transition to brakes.
The tail includes an all-flying stabilator with electric trim. Although not fitted to either the prototype or the conforming airplane, the company has produced molds for a ventral fin that will mount under the tail to improve low-speed handling. The need for this, at this point, is theoretical and is only experimental at the moment. The cabin also reflects the unique design standard the team chose to pursue. At 48 inches, its wider than a Bonanza and on par with a Saratoga. The gull-wing doors on each side provide good access to the cabin-with what we consider two significant limitations. Entry to the cabin is easy on a nice day but sloppy in foul weather. The standard drill for climbing into the airplane is awkward at best. The door release is on the fuselage aft of the door, yet the airplane is intended to be boarded from the leading edge of the wing.
At the leading edge, you sit on the wing, slide yourself back until you can stand on the wing, then step into the cockpit. Do it in the rain or when the airplane has been sitting outside for a few days and we guess youll reconsider the wisdom of this arrangement. In addition, we think it less than prudent to design an entry for passengers to routinely pass between the wing and the propeller. Its just not a good idea, in our view.
Liberty says they plan to offer an optional step in front of the wing that will preclude the sit/slide maneuver and as of press time, theyre also considering a behind-the-wing entry method of some kind. We think a more conventional step onto the wing trailing edge makes more sense for both convenience and safety and we would like to see that incorporated into the airplane.
Climbing into the cabin is similar to a Socata Tobago/Trinidad. The door swings comfortably out of the way overhead. Its possible to be seated without stepping on the seat, but we think many passengers will do it anyway.
Speaking of the seats, theyre molded into the fuselage and cushions are Velcrod in place. The rudder pedals are adjustable to accommodate different size pilots via a manual crank under the panel, but those who are short of torso have little recourse other than to get thicker cushions-which Liberty doesnt offer at this point.
Thats a shame, too. Because while the stock leather-upholstered cushions in the demonstrator were pretty comfy at first, they started feeling hard after only a short flight.
Once inside the cabin, its easy to forget youre in a two-seat, 1100-pound airplane. The center console neatly divides the cockpit into mine and yours, and its wide enough that two occupants dont get in each others way much.
The panel is ergonomically refined, with the center avionics stack canted toward the left seat. The gyros are electric, as the airplane has no vacuum system, but an HSI is not offered in any of the avionics packages.
Engine instrumentation is excellent. The Vision MicroSystems VM-1000 panel monitors RPM, percent power, voltage, amperage, manifold pressure, fuel pressure, oil temperature and oil pressure, along with displaying EGT and CHT for all four cylinders.
With the VM-1000 displaying RPM and percent power in digital form, the precision of power settings is limited only by the friction built into the single-lever power control.
There is an unfamiliar annunciator, along with adjacent Power A and Power B toggle switches, tied to the FADEC electronics. The switches supply power to the computer and electronic ignition. Power A is main power and is on for normal flight. Power B is a back-up battery that powers only the FADEC. Its also on for normal flight, but part of the preflight check involves ensuring the battery is on-line.
With electronic ignition, electric gyros, digital instrumentation and a full avionics suite, we were somewhat surprised to find a 60-amp, 14-volt electrical system. A higher capacity alternator or a 28-volt system would give more leeway for future growth as well as accommodate owners who plug multiple gizmos into the power outlet that used to be called the cigarette lighter socket.
Behind the seats, nestled into the steel chassis, is the airplanes 28-gallon polyethylene fuel tank. The fuel tank forms the base of the seatbacks, with storage areas molded on top to form the headrests. Although some may question the wisdom of putting the fuel so close to the occupants-were among them-Liberty designers say its well protected from impact by the steel chassis. While we agree that a wheels-first impact or cartwheeling arrival seems unlikely to break the tank free or puncture it, we also think that its never a good idea to put fuel inside the cabin.
The baggage area behind the seats will accommodate 100 pounds, but getting big bags into the space may be a problem for some. Because the seatbacks are a molded part of the carbon-fiber fuselage, they cant swing forward. Loading baggage, then, requires navigating the bag around the headrests/storage areas. The space is generous, and to make full use of it wed like to see an external baggage door.
After boarding the XL-2 in the unconventional manner outlined above and settling into the seats, it doesnt take long to run into yet another surprise. With the four-point harness fastened, you reach up to close the gull-wing door and come away with nothing but a handful of air. From a sitting position, you cant reach the door sill to pull it closed.
Grab the door from a point near the hinges and you can manage to close it enough to reach the handle molded into the sill and pull it shut. An inopportune gust at this point and you can count on pinched fingers-or worse.
Liberty says its considering installing some kind of pull-down strap, but offers no details on where, how or when. The door latches easily in place, with latch pins in the front and aft of the door. This design, coupled with the light construction of the door, allows the door to bulge outward slightly in the center, inducing wind noise in flight. A third latch may be added, or at the very least the door may be stiffened, the company says.
A conventional preflight checklist is complicated only slightly by the FADEC, and starting is somewhat simpler given the fact that the ignition computer takes a large part of the guesswork out of priming/ignition/mixture dance.
While starting is perhaps slightly more complex than the car-like ease advertised, its unquestionably simpler than other fuel-injected aircraft engines from Lycoming and Continental.
The engine fired within a couple of blades and then we ran into another surprise. For such a small engine, the little Continental vibrated. A lot. Liberty says it and Continental are working on some software tweaks that should smooth out the engine, but for now, extending an index finger from the stick while at cruise power shakes the fingertip more than a half an inch back and forth.
Taxiing with the finger brakes was surprisingly easy, especially considering that the rudder began to show effectiveness even at a fast taxi speed. We could do a serviceable job of taxiing within about 30 seconds and dont consider this kind of braking to be an issue.
The airplane taxies easily because of the light weight and the combination of brakes and rudder effectiveness. In most airplanes, steering by differential braking poses the most problems during the initial takeoff run and in the final stages of the landing roll. We found the XL-2 better than average in this regime because the positive rudder control extends down to almost a walking speed.
Setting a notch of flaps for takeoff is more work than it should be because the flap indicator on the center console of the demonstrator is marked with ticks, but the settings that correspond to the standard flap positions are not marked.
For that, you have to look at the left wing, where the trailing edge of the wing and the leading edge of the flaps are marked with tape. Look for that to be corrected in the production model.
Set power, check the gauges and takeoff is conventional in all respects. Initial climb is not bad for an airplane hanging on 125 HP, but hardly stellar. On initial climb, pitching the airplane to an attitude that allowed reasonable visibility over the nose resulted in 400 to 500 FPM at our test weight of about 1500 pounds-nearly 150 pounds under max- at about 80 knots. Pitching to a Vy of 65 knots to try for the manufacturers claimed 1150 FPM resulted in an extremely nose-high attitude that seemed imprudent in the trainer-laden airspace around us.
The wind conditions during our test flight were 12 to 14 knots, with gusts to nearly 20 knots at times. With a wing loading of 14.8 pounds per square foot-12 percent higher than a Skyhawk-we bounced around a bit. But the airplane remained light on the controls and displayed good stability.
We conducted a variety of maneuvers and concluded that control forces are pleasantly light and balanced in roll and pitch. We felt the rudder was perhaps a bit too light, but close enough that we hesitate to list this as a fault. The pitch trim, however, proved to be a real pain in the stick.
The airplane is equipped with electric trim only-no manual trim wheel-and the motor is geared entirely too fast. We couldnt trim it for hands-off flight; the best we could do was get it close for minimum pressure on the stick. Liberty demo pilot Jason Livingston admitted he cant trim it for hands off either and said the company is planning to reduce the trim speed.
In cruise, the airplane showed an average estimated true airspeed (based on GPS groundspeed) of 110 knots at 3000 feet with the VM-1000 showing 75 percent power over a two-way speed run measured by the on-board GPS. The manufacturer claims 132 knots at 75 percent at critical altitude, which it does not define in its literature. Thats typically about 8000 feet in a non-turbo single. We were not able to test that claim.
Stalls are similar to other sport aircraft. They include a sharp break and demand attention to the ball to keep the wings level. The nose drop was normal for a sport airplane at about 20 to 30 degrees, although Piper pilots may find them a bit shocking at first. Releasing the back pressure was enough to break the stall even before the power came up.
The visibility was excellent all around, which took some of the sting out of pattern work. With the wind 90 degrees to the runway at 12 to 14 knots and the airplane crabbed seriously into the wind, the view down final was great. The airplane displayed no bad habits during the flare and touchdown, but did demonstrate a remarkable desire to weathervane into the wind as we slowed below about 30 knots.
Liberty expects to sell about 50 to 70 airplanes per year and says it has orders for 70 on the books already. Much of the manufacturing work is farmed out and the companys new Melbourne facility will only need about 45 production workers to handle assembly. Just when that will happen remains up in the air.
In January, the company expected to get its type certificate in April, with the production certificate coming six months or more after that. Deliveries in late 2003 are possible, but thats what they said about 2002 as well.
Such delays seem to be the norm in aviation, especially for new models. Both Cirrus and Lancair saw their schedules slip repeatedly as the airplane moved from prototype to customer.
It remains to be seen whether Liberty will complicate its production certification by extensive farming out of manufacturing. In January, the company was considering contracting with a company in Romania to produce the fuselage halves. Given the FAAs track record in certifying composites, that remains a huge question mark.
Liberty also is entering a market where Diamond Aircraft has staked something of a claim to the two-seat traveling owner market with the Diamond DA20-C1 Eclipse. Although the Diamond does not incorporate FADEC, it does share many of the same capabilities and limitations of the XL-2.
Diamond has sold about 170 of the Continental-powered DA20 since the Eclipse was launched in 1998 and many of those have gone to flight schools. In other words, the market for a two-place, relatively slow cruiser may be sharply limited.
Libertys current sales focus appears to be bypassing flight schools altogether, meaning it must carve a new-airplane niche that does not appear to exist at this point.
Liberty says thats because an airplane focused on the two-seat touring market has not yet been available, but the Diamond falls pretty close to the Liberty.
Were sure that many buyers who might be interested in that mission have opted instead for a Skyhawk or other conventional airplane due to the notion that the backseat may someday come in handy.
Libertys quest to design a frugal touring airplane is clearly European in origin. The high cost of fuel in Europe puts a premium on low fuel consumption. Diamond also shows this European bias.
In the U.S., however, we suspect anyone planning to drop $150,000 on a new airplane wont pay much attention to the $20 an hour increase in operating cost between a Liberty or Diamond and a tried-and-true Skyhawk, which carries more.
Also With This Article
Click here to view “Libertys Daunting Market Challenge.”
Click here to view “Checklist.”
Liberty Aerospace Inc.
1401 General Aviation Drive
Melbourne, FL 32935
-Ken Ibold is editor of Aviation Safety magazine.