Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.
Issue link: http://experimenter.epubxp.com/i/134623
it nearly 3 inches wider than a Cessna 172. It's actually the same width as that of a late model Cessna 182, but optional bulged doors add even more shoulder width. "Besides the removing of the slats," Sebastien said, "the most obvious visual change is that we replaced the fat wheels and tires with 5.00-by-5 and wheelpants; that alone produced around a 7-mph increase in cruise speed. However, if a builder wants, he can go with larger wheels and tires." Because Zenith envisioned the CruZer as a cruiser, weight wasn't as much of an issue, so they gave up a few pounds in the engine compartment in favor of some bigger, more traditional engines. At the same time, they designed the firewall forward with enough flexibility that a builder could use state-of-the-art engines as they appear on the market. As displayed A direct drive, thoroughly traditional engine, the 130-hp ULPower UL350iS incorporates the latest in electronic ignition and FADEC control. ULPower's UL350iS Engine bustion, less friction, and lighter components. This appears to be the route ULPower has gone in designing a vaguely old-fashioned engine for the new millennium. ULPower's approach to building an airplane engine is to not invent a new wheel but to improve upon a proven, traditional one. Its UL350iS is totally traditional in layout—four-cylinder opposed (it also has a six-cylinder version) and direct drive, which is a major departure from some current approaches to getting power out of small packages. Its little 172-pound package gets its maximum power (130 hp) at 3300 rpm, which works against swinging a larger diameter, more efficient prop. However, the horsepower/ torque curves appear to cross at 120 hp and about 2650 rpm, which is a sweet spot for a bigger prop. It should be noted that ULPower's literature contradicts itself a little in that the curves show the foregoing, but their spec tables say the torque peaks at 2400. This, however, is misleading because the torque curve is marvelously flat from about 2350 rpm to about 2600 rpm. It's not perfectly flat, but close enough for government work. The torque probably does peak at 2400 rpm, but it tapers off only slightly to 2600 rpm. Not enough to worry about. So a bigger prop will work just fine at a number of different rpms and the thrust/horsepower will benefit. Traditional done modern By far, the biggest problem in getting power out of small displacement engines is…well…they're small and an engine is basically nothing more than an air pump. You suck air in, give it more energy via fuel and heat, and spit it back out again. In the process, it converts some of that energy to rotary motion through a series of monkey-motion machinery that hasn't changed in a century or two and isn't likely to. To oversimplify: the more air that's pumped through, the more power that is generated. There are only two ways to increase power output: Either turn the engine faster so more air/fuel is cycled through or increase the size of the pump. Bigger pumps are heavier. Faster turning pumps run into the propeller tip speed limitation; the diameter/efficiency of the prop comes down when the rpm goes past a certain point and pretty much hits an efficiency wall at 0.92 to 0.95 Mach. There is, however, one other part of the equation that can be worked for more power: Overall efficiency of the compressor can be improved in the form of better airflow, more efficient com- Photography by Budd Davisson The engine has left things like mixture controls and magnetos in the dust, has gone completely electronic in all areas, and is FADEC controlled. Outwardly it appears to be a very well-produced package, and Sebastien said it runs as good as it looks. Being direct drive and totally electronic, it is a simple, straightforward piece of propulsion with very little to go wrong. However, only time will tell if it will escape the unpredictable demons that seem attracted to aircraft engines in general. For more information, e-mail Info@ulpower.net or visit www.ULPower.net. EAA Experimenter 17