Thursday, July 1, 2004
This two-seater is certified and ready to roll!
The Liberty XL2’s new wing is primarily the brainchild of Don Dykins, an airfoil expert with experience dating all the way back to the early Airbus and the Mach 2.0 Concorde. The Liberty settles for more like Mach .20, still excellent efficiency considering the horsepower. It seems practically every new aircraft design touts its natural laminar-flow wing, but Dykins’ airfoil may be closer to that ideal, keeping the airflow attached to the surface for a greater percentage of the chord. Dykins’ wing also features three sets of vortex generators on the outboard wing to improve aileron response at high angles of attack. If performance is any indicator, Dykins obviously must have done several things right.
For power, Liberty chose the IOF-240B Continental, a relatively new-generation engine rated for 125 hp at 2,800 rpm. As the name implies, the little Continental is injected, essentially the same mill used by Diamond Aircraft on the C1. Liberty opted for the Powerlink FADEC (Full Authority Digital Engine Controls) version, however, featuring a computerized electronic ignition system.
FADEC monitors all aspects of engine operation several times a second—throttle setting, rpm, density altitude, CHT, EGT, fuel pressure, temperature and pressure—and adjusts mixture and mag timing for all stages of flight, takeoff, climb, cruise and descent. By definition an all-electric system, the Continental’s FADEC relies on the alternator and two batteries for redundancy. Accordingly, the Liberty center console couldn’t be much simpler. Although it also houses fuel selector, trim, flaps, alternate air and brakes, the whole idea was to make engine operation as idiot-proof as possible. There’s only a throttle lever for power control—push forward to go, pull back to stop.
Engine health reads out through a Vision Microsystems VM1000 that serves as an EICAS, airline speak for Engine Instrument and Crew Alerting System. The system reads power in percentage and warns if any parameter approaches tolerance limits.
Most pilots argue you can never have enough power, but with only 1,653 pounds to lift, the Liberty makes do very nicely with 125 hp. Grumman-American’s Lynx, Piper’s Tomahawk, Cessna’s venerable 152 and the Beech Skipper lifted roughly the same weight with 108, 108, 112 and 115 hp, respectively, so the Liberty, with an average 10% more horsepower, enjoys a definite advantage in power loading. In combination with the 112-square-foot, NLF wing, the XL2 offers considerably better performance than the older airplanes, proof that the glass-is-half-empty pessimists are mostly half-wits.
One obvious advantage of the small wing is less drag, and that translates directly to more speed. In fact, you’re unlikely to find anything in production aircraft ranks that will cruise alongside the XL2 on the same horsepower. Back in the bad ol’ days of general aviation, we used to measure an efficient design by 1 mph/hp. In other words, any airplane that could score 150 mph on 150 hp was considered efficient. These days, the XL2 produces more like one knot per horsepower. In fact, it does even better, considering that the 132-knot cruise spec demands only 75% of 125 hp or 93 hp.
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