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M A Y 2 0 1 4 | 6 1 FEATURE / PLANT TOUR Skillen points out that the most effcient airfoil is elliptical, like a Spitfre. "This is exactly the top profle of the KittyHawk," he adds. At full scale, the plane will measure 26 ft/8m in length with a span of 22.5 ft/7m and a body height of 4 ft/1.25m, offering signifcantly more usable internal vol- ume than other aircraft of similar gross weight. (Empty weight will be ~750 lb/340 kg, using 100- to 125-hp engines). "It will offer a 7-ft/2m cockpit width, which is Assembly of the VX-1 KittyHawk blended wing body Ribs were bonded to the bottom skin (left), and then the top skin — with openings for payload access — was bonded onto this assembly; the silver cleco clamps show the drilled holes where fasteners will be installed. The photo at right shows the VX-1 KittyHawk airframe readied to receive its payload access cover. S I D E S T O R Y A UAV fueled by CNG? Originally developed for manned fight in light aviation, the VX-1 KittyHawk has received more recent attention as a long-range, fuel-effcient unmanned aerial vehicle (UAV). "There is noth- ing like it fying today," claims Bob Skillen, the founder and chief engineer at VX Aerospace (Morgantown, N.C.). The plan for both markets is to power the VX-1 KittyHawk with compressed natural gas (CNG). Skillen relates that Aviat Aircraft (Avton, Wyo.) generated a lot of press for its Husky CNG-fueled model at the EAA AirVenture 2013 show in Oshkosh, Wis. "The tank hung below the belly, and the aircraft achieved 80 to 90 mph, burning only 8 to 9 gal/hr," Skillen recalls. "A full-scale KittyHawk can accommodate CNG tanks without any aero- dynamic compromise or cockpit modifcations." CNG is currently one-third the cost of aviation fuel, which the U.S. government would like to see phased out anyway, he points out, because it contains lead. With CNG at $2/gal, Skillen projects the KittyHawk can fy two occupants at 140 mph/225 kmh with a fuel cost of $.08/mile. "Currently, most light aircraft have a fuel cost of $.20 to $.30/mile," he notes, "So the KittyHawk would reduce that by a factor of three, but also cut emissions by up to 40 percent." close to completion. The wing tooling is next in line. Limited rate production of 20 aircraft per year is planned using a team of 20 employees. First in flight The VX-1KittyHawk strikes a marked con- trast with the Falcon. Its blended wing body features wings that are smoothly blended into an airfoil-shaped fuselage, achieving a 50 percent greater lift-to- drag ratio than conventional designs. machining unit by Diversifed Machine Systems (DMS, Colorado Springs, Colo.), which cut precision masters (top photo, p. 58) from 38-lb/ft 3 (0.6-g/cm 3 ) RAKU- TOOL plastic board supplied by Rampf Tooling (Grafenberg, Germany). Pattern surfaces were prepped and sealed with Chemlease (Chem-Trend, Howell, Mich.) and then polished and coated with Chemlease again in preparation for lami- nate lay up (bottom photo, p. 58). VX Aero uses recycled carbon fber mat (photo, p. 58) from Materials Inno- vation Technology Recycled Carbon Fi- ber (MIT RCF, Fletcher, N.C.) as the tool- ing bulk layers to build thickness quickly and cheaply (less than $2.00/ft 2 ), inter- spersed with 3K carbon fber plain weave fabric (about $5.00/ft 2 ). This dry laminate is then infused with 350°F/180°C-cure PT5712 epoxy tooling resin from PTM&W; Industries (Santa Fe Springs, Calif.), postcured at 25°F over T g for 18 hours and then surface coated. The Falcon's fuselage tools were made using LTM318-1B glass fber/epoxy OOA tooling prepreg from Cytec Aerospace Materials (Tempe, Ariz.) to match the fnal part materials. "Everybody loves vinyl ester surface coats because they are hard, not prone to air leaks and have less water ingres- sion," notes Skillen, "But they are not compatible with epoxy matrix resins." VX Aerospace achieves a vinyl ester (VE) surface coat by using 1799-006 vinyl ester primer from Hawkeye Industries (Bloom- ington, Calif.). Skillen says the resulting tools are void-free with very high gloss surfaces (see middle photo. p. 58). By the end of 2013, VX Aerospace had completed masters for the Falcon's hori- zontal tail and all of the fuselage com- ponents. Tooling from those masters is Source (both photos): VX Aerospace 0514HPC IM PlantTour-OK.indd 61 4/22/2014 4:00:36 PM