All-composite for on-demand operation

Adam Aircraft entered the VLJ market in late 2002 with the A700, a jet-powered derivative of its existing FAA-certified A500 twin-engine, turbocharged piston aircraft, an all-carbon composite design. The A700 has a larger cabin, longer overall length and is "beefier" to handle higher aerodynamic and crash loads created by higher cruise speed and altitude, says Pierre Harter, Adam's director of advanced structure. The high degree of commonality between the two planes is expected to make the A700's FAA type certification an easier process than for new jet manufacturers, because more than half the parts have already been certified for the A500. (A500 certification came in May 11, 2005.)

According to Harter, the A700 is made in a similar fashion as the A500 (see HPC July 2002, p. 33) using AGATE (Advanced General Aviation Technology Experiments) carbon fiber/epoxy Torayca prepregs manufactured by Toray Composites America Inc. (Tacoma, Wash.). As explained in previous HPC articles (for example, see "AGATE Methodology Proves Its Worth," HPC May 2003, p. 38), Toray has prequalified three prepreg systems, meaning that only limited additional qualification testing is needed on the part of a manufacturer to meet FAA requirements, thus saving considerable program time and cost.

Wings, tail and booms for the A700 are exactly the same shape as the A500 and are made on the same composite tools. Wing spars and skins for the jet are thicker and require more material. Wing skin layups start with a thin, solid laminate at the tip, and increase in thickness and complexity toward the root with the addition of core, typically aramid honeycomb supplied by Euro-Composites Corp. (Elkwood, Va.). Ply layup varies from 3/core/3 to 6/core/6, and is typically balanced and symmetrical with the majority of fibers oriented 0°/90° or ±45°, says Harter. The jet's wing skins incorporate a higher-density core, compared to the A500, to handle higher gust loads. As with the A500, parts are cured in a 50-ft (15.2m) long oven built by Gehnrich Oven Sales Co. (Ronkonkoma, N.Y.).

Because the A700's lightweight Williams FJ-33 jet engines each weigh about 300 lb (136 kg) less than a piston engine, the saved weight and center of gravity (CG) shift allows a larger fuselage — about 30 inches (76 cm) longer than the six-seat A500 — to accom- modate either two extra seats or a lavatory, explains Harter. The two engines have a higher fuel burn rate, however, so in addition to fuel tanks in the wings, a 135-gal capacity fuel pod has been added to the plane's belly. Robust composite skid plates have also been incorporated on the craft's underside. "In a crash scenario," Harter says, "the fuel has to remain contained, so the structure has been sized to meet those higher loads." The A700's weight figures aren't yet available from the company but, for comparison, the A500 has a gross weight (with fuel and passengers) of 7,000 lb (3,175 kg).

At $2.25 million (USD), the A700 has a 41,000 ft ceiling, 340-knot (391-mph) cruise speed and an 1,100-mile (1,770 km) maximum cruise range. Adam is squarely targeting the air taxi market and believes it has the "biggest potential" for VLJs, says Harter. A major air taxi operator has already preordered 75 A700s for its operation, although deliveries are dependent on certification, anticipated for late 2006.