VaxSCinator

• Wing ribs were 3D printed using Onyx carbon fiber filament while the aft spar was fabricated using 1/8 inch plywood laser-cut to shape. Components of the wing were attached using a combination of cyanoacrylate glue and epoxy, with fiberglass/epoxy tape added on structural areas such as the attachment between servo mounting ribs and spars. Following mission parameters, the wing was divided between a center section and two outer sections which were manufactured and assembled separately. 

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• Styrofoam female molds for each fiberglass wing skin were cut using a hotwire tool guided over plywood templates, laser cut to the shape of the chosen airfoil. Molds were prepared by adding a thin layer of epoxy on their surfaces, which allowed for sanding to achieve a smooth surface finish. They were then treated with parting wax and PVA release film to further fix surface imperfections. The wing skins were manufactured by performing wet layups on the molds with one ply of fiberglass with respect to the spanwise direction to provide additional torsional strength. 

In-house fabrication of tube spars was selected due to long lead times and limited designable parameters of store-bought tubes. A cylindrical core made from 3-lb/ft3 (48-kg/m3) Styrofoam, was hotwired with circular plywood templates laser cut to the desired inner tube diameter. The spar was divided between a center and two outer sections with an internal diameter of 1 in. (2.5 cm) and 1.5 in. (3.8 cm), respectively. A combination of unidirectional and bi-directional twill weave carbon fiber, with 5.7-oz/yd2 (0.19 kg/m2) densities for both, was laid up on the foam core using a rolling method to ensure proper adherence between the plies. The tube was then wrapped in peel ply to absorb excess epoxy and left to cure for 12 hours. A 3D-printed clamp was used to obtain a circular surface without wrinkling for the overlapping portion.

Female molds were 3D printed in six separate sections and attached with epoxy. Each mold was prepared with the same method as the wing skin molds, coated with a thin layer of epoxy to fill in grooves from printing, sanded, and treated with parting wax and PVA release film. Balsa and fiberglass strips were laid up over the carbon skin of the bottom fuselage shell along the wing and tail areas for additional reinforcement. A plywood hardpoint was embedded into the nose.

Two carbon fiber pieces were laid up and placed over and under a Nomex honeycomb core to make the fuselage sandwich panel. Once cured, the panel was trimmed to the shape of the fuselage and epoxied to the sides of the fuselage with carbon fiber tape at the edges. The 3D printed Onyx adapters for the tail boom were epoxied onto the sandwich panel with fiberglass tape. Lastly, a hole was made on the side of the fiberglass boom for the button clip to secure it to the adapters in the fuselage.

The main bow gear was manufactured using 23 plies of unidirectional fiberglass wrapped with two plies of fiberglass. Slow-curing epoxy resin was applied after each layer and then sealed in a vacuum bag for 12 hours. Each side of the bow gear had a hole drilled through it to fit an axle to hold a 3.0-in. wheel. The wheels and axles were secured in place using collars and hex nuts. The total weight of the gear was 0.49 lbs. The fiberglass gear was integrated into the aircraft using a plywood slot that had been epoxied onto the fuselage to secure it in yaw. It was also kept in place using a single nylon bolt designed to shear off in case the aircraft sustained maximum 3G landing loads. This bolt is located on the centerline of the gear 0.9 in. from the back of the bow. The tailwheel was integrated using a square carbon fiber tube with plywood slabs that slides onto the boom in between the tail attachments. Attached to the tube is an axle onto which a 1-in.wheel is placed on.

1/2 by 1/2 by 6 in. steel bars were used for the weight increments and 1/8-in. plywood sheets were used for the shell. The plywood sheets were first sized for the minimum dimensions and weighed, so the remaining weight required for steel is found. Smaller increments of steel were made using a metal bandsaw, the rest of the space was filled in with plywood pieces, and the entire package is wrapped in duct tape. There were still slight shifts of the steel, so expanding spray foam was applied through a small hole drilled through the plywood shell to fill up any remaining space on the inside. Velcro was adhered to the bottom side of the package, and matching Velcro is adhered to the correct position on the Nomex honeycomb sandwich panel in the fuselage. The L-shaped wooden guide pieces are made using 1/8-in. plywood and connected using Cyanoacrylate, before being epoxied to the fuselage plate.

The antenna adapter was designed using CAD and 3D-printed using an Ender S1 printer with PLA filament, with 0.08 in. (2 mm) wall thickness and 10% infill. A rough semicircle cutout was added to the PVC antenna using a Dremel and refined with sandpaper to match the adapter. Once the antenna fit into the adapter snuggly, a 0.12 in. (3 mm) hole was drilled into the antenna while it was fully seated in the adapter to ensure the holes lined up. Lastly, a nut was placed inside the adapter and a plywood insert with a 0.12-in. (3-mm) hole was epoxied next to it to prevent the nut from slipping back out.

1/4 in. plywood sheets and metal brackets were cut with a bandsaw. 1/8 in. holes were drilled through the plywood sheets and metal brackets, which were then riveted together. 1 in. wide strips of 1/8 in. plywood were cut and attached to the box walls using wood glue to provide additional rigidity.

The Ground Mission test rig consists of the load platform, stands, and the winch. Beams of wood were cut to construct a 51 x 39 in. platform frame, reinforced by two sets of beams through the middle of the frame. The reinforcement beams were placed 1 in. apart to fit 3/4 in. round steel bars which served as lifting hardpoints for the chains. Six 350-lb rated caster wheels were secured to the bottom of the frame for mobility, and 3/4 in. plywood was secured to the top of the frame for a level surface to load the 60 lb concrete bag weights. A 2 by 4 by 3 bag loading configuration was chosen to minimize the overall height of the Ground Mission test rig, allowing for a variable load capacity of 1,440 lbs. The complete structure has a maximum test capacity of 2,100 lbs. The platform connects to the aircraft via a series of chains and straps. Four chains connect the platform to the lower winch hook. The winch is then connected to the center of a 1.5 in. diameter aluminum rod, which is connected to the straps hanging from the aircraft tube spars.