Prototype to Production

“We are applying modern CFRP technology to make the traditional performance of blended wing body aircraft even better,” says Skillen. The aircraft’s structurally efficient shape eliminates the need for high-strength spars. Thus, the airframe is essentially hollow. Beyond its top skin, bottom skin and four ribs that make up the body, the only other parts required are vertical fins and flight control surfaces. Skillen asserts that this makes the KittyHawk easy and cost-effective to manufacture.


Such a design, however, requires large, unsupported, high stiffness-to-weight structural panels. “This is the sweet spot for CFRP construction,” Skillen claims, noting that, here, “CPLY furthers the weight savings possible, with skins that are significantly lighter than if using 3K plain-weave fabric.” He adds that C-PLY speeds the layup, with two plies applied at once, and results in laminates with a more homogeneous fiber distribution throughout, which increases fracture toughness compared to conventional unidirectional materials.


Tooling for the 1:4 scale aircraft was directly CNC-machined from plastic tooling board because it is temporary and, therefore, can be designed for short life and low cost. Layup of the 1:4 scale aircraft structures used six layers (12 plies total) of C-PLY, again with a 150-g/m2 weight and 0.006-inch thickness per two-ply layer (left photo, p. 59). Parts were then infused (right photo, p. 59) using PTM&W’s 2712 epoxy resin. Demolded parts were then assembled. First, ribs were bonded to the bottom skin; then the top skin which includes openings for payload access was bonded to this assembly (see photos, p. 61). The payload access cover was then attached with mechanical fasteners.


The first finished airframe (see p. 56) was displayed by Chomarat at JEC 2014 (March 11-13, Paris, France). A second 1:4 scale aircraft, assembled in March, was delivered to NCSU for flight testing.


Skillen anticipates full-scale aircraft production will likely use C-PLY pre-pregged with Cytec’s Cycom MTM45-1 OOA prepreg resin. However, the final decision, prepreg vs. infusion, will be made based on the customer’s production volume. (Several potential customers, are awaiting flight test results before making commitments.) Parts can be layed up quickly using C-PLY.


Skillen estimates the VX-1 KittyHawk will use 6,000 ft2/557m2 of C-PLY per plane. “We could design and make this aircraft with traditional carbon fiber roll goods,” Skillen admits, “but the efficiency and performance C-PLY delivers gives a small company like us a real competitive advantage.”