The Spectrum 33 may be light, but its also surprisingly roomy

EBACE Convention News » 2006
November 29, 2006, 11:04 AM

The recently unveiled Spectrum 33 business jet can be categorized as “very light” in terms of weight and yet its cabin is roomier than that of a Cessna Citation CJ2, which would not be categorized in the very light jet (VLJ) class. The new airplane’s composite airframe and its additional electric systems are no strangers to this paradox. The first prototype built by U.S. start-up company Spectrum Aeronautical made its maiden flight in January.

“Roughly speaking, the aircraft’s airframe is 20 percent lighter than a similar one made of aluminum alloys,” Austin Blue, Spectrum Aeronautical’s vice president, told EBACE Convention News. In November, the California-based firm said the jet (which has a 7,300-pound maximum takeoff weight) has a fuselage weighing a mere 309 pounds, complete with integrated window and door frames. The Spectrum’s single-piece, 42-foot-span wing weighs just 305 pounds. Its total empty weight is 3,620 pounds.

The company and its partner, Rocky Mountains Composites (RMC), use a technology dubbed FibeX, which Blue said is “very similar to fiber placement but somewhat cheaper.” Although few details are available, it is clear that the process is unusual. The carbon fiber-based material is not a prepreg (pre-impregnated with epoxy resin) and no autoclave is needed to cure the structure. “We do not principally use fiber-placement machines, but our own FibeX material instead,” Blue added. The automated machine can wind up a complete fuselage in five hours. Blue asserted the Spectrum’s 33 composite material is similar to that employed on the in-development Boeing 787 widebody airliner.

Linden Blue, Austin’s father and the CEO of Spectrum Aeronautical, is known to many as the father of the Beech Starship, the first all-composite pressurized aircraft to be certified by the U.S. Federal Aviation Administration. However, the type of composites materials used today are very different from those used on the Starship, although they are also based on carbon fiber and epoxy resin. For example, the Spectrum 33’s stiffened monocoque structure has no honeycomb core. The aircraft’s design was launched in 1998.

Asked about manufacturing costs, Blue acknowledged that composites remain more expensive than aluminum. “But we do not focus on production costs; we rather try to bring operating costs down,” he explained. A lighter airframe directly translates into a reduced fuel burn. And the higher performance of composites, notably in terms of damage resistance, should not be forgotten.

The innovative Spectrum 33 also features a number of electric–rather than hydraulic or pneumatic–control systems. “For example, flap actuators and landing gear actuators are electric; the only place for hydraulics are the brakes,” Blue explained. The company intends to use a resistive de-icing system, he added.

Conventional window shades may be replaced with electrically dimmable windows (the Boeing 787 also will feature such equipment). On the Spectrum 33, bleed air will still be used for cabin pressurization. Engines will also provide more electric power than usual and are thus fitted with bigger generators, Blue said.

According to Blue, electric systems bring a combination of advantages, including weight and cost savings and increased reliability. He claimed that “half of unscheduled maintenance on airliners has to do with hydraulics.” He added that progress in the reliability of electric motors is now making hydraulics replacement possible.

Blue is keen on comparing the Spectrum 33 to the Boeing 787. The latter arguably contains the greatest electric content of all existing and in-development civil airplanes. Boeing is taking full advantage of recent progress in the reliability of high-power electronic components, the manufacturer reports. Power distribution will be easier thanks to this new architecture, it claims, and a weight advantage should be found, as hydraulic and air tubings are gone. Safety should be improved, too, as the risk of hydraulic leak and subsequent fire is suppressed. Last, but not least, no pneumatic power means bleedless engines. This translates into better compressor efficiency and thus lower fuel burn, the larger electric power production capabilities installed notwithstanding.

In spite of these claimed benefits, Spectrum is among the very few business jet manufacturers to go ahead with more electric architecture. Eclipse Aviation and, to a lesser extent, Embraer are going down the electric road. But well-established manufacturers such as Dassault, Gulfstream and Raytheon have recently expressed reluctance to drop conventional hydraulic and pneumatic systems.

The Spectrum 33 can seat one pilot and six to nine passengers. It is powered by two Williams FJ33-4 turbofan engines, providing 1,568 pounds of thrust each.

The new jet is priced at $3.65 million and is pegged to enter into service in 2008. Spectrum Aeronautical and RMC employ a total of 70 persons, 20 of whom are involved in the Spectrum 33’s design.   

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