Vertiflite May/June 2021

Toray has supplied thermoplastic prepreg for compression molded aerospace parts. (Toray Advanced Composites)

for the material system. Gattani explained, “Georgia Tech will utilize this information provided by Jaunt to develop an internal structural layout for a representative thermoplastic wingbox structure and establish a load envelope consisting of aerodynamic, propulsive and ground loads. This structure will be optimally sized using Georgia Tech’s computational tools and design allowables for the material system to obtain structural weight and performance.” The end deliverable to Jaunt will be a computer-aided design wingbox model, a finite-element model with material data and a report detailing performance comparisons and design methodologies. Jaunt and Georgia Tech in turn are collaborating with Triumph Aerospace Structures to integrate the company’s patented induction welding process into high-rate production. Triumph modeling will identify key manufacturing cost drivers. The structures supplier in Spokane, Washington, already produces thermoplastic parts for Boeing and other OEMs. “They hot press-form about 700 parts for the industry.” Peryea offered. “These parts are used to tie primary structure together. They’re secondary structural components. They’re also used to hang a lot of the aircraft systems. What the industry is doing from a technology development aspect is to make large structural, primary structural, components using a hot press forming technology.” Triumph has already fabricated a Journey wingbox from thermoplastic composites. We Have History Thermosetting composites already pay off throughout the aerospace industry with weight savings and fatigue and corrosion resistance.Thermoplastics have less history, but Howell noted, “Contrary to popular belief, thermoplastic composites have been used on aircraft for over 30 years.” Airbus uses thermoplastic shear clips between frames and stringers with Toray fibers pre-impregnated with polyphenylene sulfide (PPS) or polyetheretherketone (PEEK) resins. GKN Aerospace induction-welds the fiber-reinforced PPS rudder and elevator of the Gulfstream G650 business jet. Eddy currents in the conductive carbon fiber heat laminate plies from the inside and fuse mating parts without fasteners or adhesives. “This is

Thermoplastic airframe substructure for the Journey will be compression-molded from chopped-fiber composites. Wing skins, wing spars and tail booms will all be layed up by automated fiber placement. Thermoplastics make it possible for large sections of the Journey to be hot press formed to the required shape and welded or fused together using induction heating without fasteners. Eliminating fasteners helps cut the weight of thermoplastic assemblies 2–10% compared with thermoset structures. Jaunt has yet to finalize its material selections. “We’re still optimizing a couple of different materials that lend themselves to this type of manufacturing process,” said Peryea. Thermoplastic composites eliminate the costly refrigeration required with thermosets and lend themselves to faster, more automated processes. According to Jaunt chief engineer for aircraft certification Dr. Sanjay Gattani, “Typical thermoset composite cure cycles will not be able to support rate [production] at the affordability target.” The ROSA maker’s main objective during Phase I of the Air Force project is to model a thermoplastic composite wing structure and use advanced manufacturing techniques to achieve its low-cost commercial production targets. Jaunt worked with the Air Force to determine detailed mission and vehicle requirements subsequently used to develop a basic wingbox model and structural design criteria. Georgia Tech is under contract to Jaunt to design the internal structure for the thermoplastic composite wing and establish design allowables — stress, strain and stiffness values — The Jaunt production plan adopts a mix of thermoplastic processing techniques for the fuselage, tailboom and wing. (Jaunt Air Mobility)

May / June 2021

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