Perhaps because it's outwardly a conventional-looking airplane, the Liberty probably hasn't gotten credit for its innovative features. In fact, in one regard, it is nothing short of a pioneer. The Liberty is the first production piston airplane with full authority digital engine control (FADEC).
As the guinea pig for fadec when it was being certified by the engine manufacturer, the XL2 went through teething pains with the technology, including nagging problems with rough idle. The problems are apparently solved. The fadec system on the Liberty I flew worked smoothly and flawlessly.
Why fadec? The benefits are compelling
For the past two decades pilots have been asking why our airplane engines couldn't have the same advanced features as automotive engines. As we've written about in these pages before, Teledyne Continental Motors (TCM) has invested millions in bringing us just that, with its lineup of fadec piston four- and six-cylinder engines. And the first to go into a production airplane is the IOF-240-B.
Fadec is a revolution in part because it takes care of all of the engine's parameters automatically, so the pilot doesn't have to. There is no mixture control in the XL2, just a throttle lever. And it's not just for convenience or ease of use. The fadec computer does an infinitely better job of monitoring power than any mere mortal could.
The fadec computer uses speed, temperature and pressure sensors to measure the health of each cylinder, as opposed to a mixture control, which throws more or less air/fuel at every cylinder all at once. In contrast, fadec meters the fuel and spark delivery of each one of the cylinders, so every one gets exactly the right spark and fuel flow for its needs.
Pilots use the throttle lever to set the desired phase of flight mode for the engine. The controller monitors the engine parameters and then sets the mixture and spark based on that phase of flight: start, idle, low power, low power cruise, high power cruise, max continuous power and takeoff (wide open throttle, or WOT). The concept of throttle detents is nothing new to pilots of jets, though it might take a while for light airplane fliers to get used to it. I do mean a "little" while, too, because it's an easy thing to get used to fast.
The biggest downside of fadec, some argue-and there aren't many critics-is that it's not a self-powered system, like the magneto-powered ignition systems in the current fleet. If you lose electrical power with fadec, the engine quits. To guard against this unlikely but unwelcome risk, the Liberty is outfitted with a pair of batteries, a main one powered by the alternator, and a backup unit, which is continuously charged by the main bus. If that main battery were to fail, the backup can provide up to an hour of power, so the idea is to get back on the ground soon and get it fixed. Of course, magnetos have their own mechanical and electrical failure modes, so it's hard to argue that there's any net loss with fadec.
The benefits of fadec are huge: better fuel economy (up to 15 percent better); longer engine life; high levels of reliability and redundancy, easy starting and smooth operation. There's also engine data logging, potentially reduced maintenance costs and, most apparent to the pilot, ease of operation. Sweet deal.
Liberty Aerospace Liberty XL2
The airplane flown for this report was equipped with a pair of Garmin navigators, a GNS 530 and a GNS 430, a Garmin Mode-C transponder, a Garmin GMA 340 audio panel, and a Vision Micro Systems engine instrumentation display system, as well as a pair of Garmin CDIs with glideslope indicators. All performance figures are from the manufacturer and unless otherwisenoted are for standard conditions.
|Typical Price $178, 318 Price as equipped $178,318
Engine Continental IOF-240, 125 hp, with FADEC
TBO 2,000 hours
Propeller Sensenich 2-blade, wood/fiberglass, fixed-pitch 69-inch diameter
Length 20.3 ft
Height 7.4. ft
Wingspan 28.8 ft
Wing area 112 sq ft
Wing loading 14.8 lbs/sq ft
Power loading 13.2 lbs/hp
Max takeoff weight 1,653 lbs
Empty weight 1,065 lbs (VFR airplane)
Useful load 588 lbs
Usable fuel (gallons) 28
Payload, full fuel 420 lbs
Max rate of climb 682 fpm
Never exceed 162 kias
Stall speed (landing) 39 kias
Max cruise 125 kias
Max no-wind range 500 nm (with VFR reserve)