Development work continued on the DarkAero 1 prototype in September. The remaining wing shear webs were installed, and the center section of the wing was closed out. Ground testing continued to characterize the wing root rib angular deflection under load. DarkAero team members attended the Composites and Advanced Materials Expo, and interviews continued with the aim of hiring additional technicians and engineers.

Center Wing Section 
The remaining sandwich panel shear webs were installed in the center section of the wing, followed by installation of the center section upper wing skin. This infused carbon fiber part is bonded to the left and right upper wing skins across a large stepped lap joint that is designed to transmit in-plane loads through the upper wing skins while minimizing peel stresses. The assembly of upper wing skins forms a bonded primary structure in the aircraft with no additional mechanical fasteners. DarkAero bonding procedures developed over the past several years help ensure integrity of this bonded joint during assembly. The center section of the wing also forms a portion of the seat bottom. The contour of the seat bottom is partially established by a 3D-contoured foam segment bonded on top of the center section upper wing skin. This foam core was installed and laminated over with several plies of carbon fiber. Additional carbon fiber plies were added to the far-forward and far-aft faces of the center section shear webs to provide impact protection from accidental kicks during pilot ingress and egress.

Through the process of modifying the center section of the wing and adding multi-pi joints, the original foam cores in the lower wing skin were removed to provide additional bonding area and ply drop off distance for the base flanges of the mulit-pi joints. The foam cores in the lower wing skin are required to locally stiffen the skin and prevent it from buckling away from the center section structures under high loading conditions. These foam core segments were installed again and covered with carbon fiber to complete the wing center section close out. 

The entire modification of the wing center section was co-cured at elevated temperatures as a complete assembly to more thoroughly cure the composite components and bonded joints and also maximize the resulting mechanical, thermal, and chemical properties of the new structures. After curing, the wing was fastened to the stand for testing. 

Testing
Lift loads bend the wings, which results in angular deflection in the wing root ribs where the wing attaches to the fuselage. Measuring this angular deflection allows the same deflection to be applied to the fuselage wing attach lugs during respective proof load testing. This helps ensure ground testing is closely representative of flight loading conditions. Testing was set up to characterize and quantify the angular deflection per g of the wing root ribs. This involved mounting the wing to the original wing proof load test stand and loading it with weight to simulate aerodynamic loads while taking precise measurements at specific locations.

Measurements were taken at a range of simulated positive and negative g loads to obtain angular deflection numbers. Starting with initial DarkAero pi joint manufacturing, strength characterization, and wing center section structural design, it has taken several weeks to obtain these measurements. Obtaining this data is an exciting milestone to have complete, and it is now checked off the Milestones section of the website. A bonus outcome of the test was measurement of the wing bending stiffness with the new multi-pi joints and center section structures. Although not a previous concern, the wing tip deflection per g was decreased by over 25% with the implementation of the new center section structures.

CAMX
Last month, DarkAero team members attended CAMX, the Composites and Advanced Materials Expo, in Orlando, FL. This show is held annually, and represents the largest composites conference in North America. Attending CAMX gave the opportunity to connect with suppliers, explore new manufacturing equipment, and gather insights that will allow further expansion of composite manufacturing capabilities at DarkAero. 

Of particular interest to DarkAero was the Autometrix CNC fabric cutting table on display at the show. This machine is capable of accurately cutting intricate shapes from prepreg and dry fabric at a rapid pace. A similar unit was recently purchased by DarkAero, and it will be delivered and commissioned in early October. This equipment addition will significantly accelerate the preparation of composite ply kits. Instead of relying on tedious manual cutting, the CNC cutter will produce precise, repeatable patterns at a much faster pace. This will reduce variability, increase accuracy, and free up time to focus on more challenging manufacturing processes. The addition of this piece of equipment highlights DarkAero’s continued expansion of composite manufacturing capabilities.

Courses
Session 26 of the DarkAero Aerospace Composites Course will be held on October 2-3. This session is nearly full, but the following session scheduled for January 29-30 still has more open available seats. 

The course material has been continuously refined over the past four years, and covers both the theoretical and hands-on aspects of aerospace composite materials and manufacturing. Live demos of wet layup, vacuum bagging, infusion, and prepreg allow students to gain experience in a broad range of manufacturing processes so the right process can be selected for their application. Fiber reinforcements including carbon, glass, aramid, and boron fibers are discussed, as well as approachable methods for selecting fabric weave types, resin systems, core materials, and adhesives. Reserve your spot in the next session using the link below:

Sign up for the DarkAero Aerospace Composites Course!

DarkAero Careers
The DarkAero team is continuing to grow, and DarkAero is hiring! We're continually looking for Manufacturing Technician and Manufacturing Engineer applicants. Open positions on the DarkAero Careers page also include Test Engineer, Propulsion Engineer, Operations Specialist, Quality Assurance Technician, Welder, and Machinist. Candidates with a strong work ethic, hands-on skills, and a desire to work on challenging projects are an ideal fit for the team. Visit darkaero.com/careers to apply!

Looking Ahead
Wing attach lug test fixture components will be machined in early October, allowing testing on the wing-to-fuselage interface to continue. The team will be using the angular deflection numbers collected during testing last month to drive these efforts. Installation of the new Autometrix cutting table will proceed, and more interviews are planned for both technician and engineering candidates.