Plane & Pilot
Monday, January 26, 2009

Liberty XL2 Vanguard: The Soul Of A Tiger

The FADEC-equipped two-seater makes training and cruising fun again


The Vanguard XL2 avionics panel comes standard with a Garmin 430 and SL 40; it can be upgraded to include the Aspen Evolution Pro PFD and Garmin 530.

The Smile Factor
The Liberty XL2 Vanguard Edition is a refreshing and different airplane. It’s a well-mannered trainer for FBO fleets. With its advanced avionics and the low pilot workload offered by FADEC, the aircraft excels as an IFR platform. The quiet, spacious, auto-like cabin and 500 nm range (or five hours for people with super-bladders) make it an ideal cross-country machine. The miserly fuel consumption and uncomplicated maintenance make it easy on the wallet, and the aircrat’s looks are difficult to beat.

Back at Santa Monica, as we pulled into the FBO, the line guys smiled, did some good-natured goofing as we followed them to a parking spot and looked over the XL2 like it had come down from space. The camera-ship crew came over to brief the photo flight. The first thing they all did when they saw the XL2 was predictable: They smiled.

The Facts On FADEC
An important engine-man
agement technology in aviation

One of the most innovative things about the Liberty XL2 is that it’s the only FAA-certified single-engine piston production aircraft equipped with full authority digital engine control (FADEC). Teledyne Continental Motors (TCM) has put millions of dollars into FADEC technology, and the IOF-240-B engine is the first one on a production airplane.

FADEC is revolutionary in the aviation world. It’s a technology that takes care of all the engine’s operating parameters automatically. It’s not static technology. FADEC constantly monitors multiple aspects of engine performance and adjusts them without intervention from the pilot. Because FADEC is a computer, it monitors faster and better than any human pilot ever could.

The most obvious result is that there’s no mixture control on the XL2. That means no more having to deal with leaning the mixture as you climb or when you operate from high-altitude airports. Multiple sensors monitor things like prop rpm, temperature and pressure. FADEC uses these values to adjust the operation of the engine, including the fuel-air mixture and spark timing. It does so in each individual cylinder and on every stroke of the engine. By contrast, a mixture control adjusts only the fuel-air mixture and applies it to all cylinders in the same amount.

FADEC also uses the concept of “phase of flight” to adjust both spark and fuel flow. The “phase” is set by the pilot through the throttle. By setting the throttle at a certain position, the pilot initiates start, idle, low-power cruise, high-power cruise or other modes of flight. For example, takeoff is labeled on the throttle as “WOT” (wide open throttle). When the pilot advances the throttle to that position, FADEC recognizes that phase and knows what to do. The computer adjusts the engine to get the highest performance from each individual cylinder for the takeoff task.

The benefits of FADEC are obvious: With a computer controlling the engine, it’s possible to get unheard-of performance. That’s how the XL2 manages fuel consumption of 4.8 to 5.5 gph at speeds that match a Cessna 172. FADEC has the potential of increasing engine life due to its micromanaging of cylinder health. Another huge plus is that FADEC decreases a pilot’s workload in a dramatic way. Not having controls for mixture, prop and carb heat allows the pilot to concentrate on other duties.

Detractors of FADEC point to the fact that losing the electrical system means the engine stops. While that’s true, Liberty has answered that complaint with characteristic ingenuity. The XL2 is equipped with two batteries. The main one runs off the alternator. The second, a backup battery, is constantly charged by the main bus. If the entire electrical system fails, then the backup battery kicks in with one hour of charge—more than enough time to land.

FADEC seems to be the future of aviation. It’s a technology that has been proven in automobiles for decades now. Liberty is, once again, a pioneer here. The XL2, with its FADEC-controlled performance has opened a lot of eyes in the aviation world. As Teledyne Continental and other engine manufacturers embrace FADEC, it will be interesting to see the realm of cockpit-performance management change forever.

Labels: Piston Singles


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