Engineering Design
(Press and hold to move 3D object)
I designed and manufactured a small aircraft that was rubber band powered for my cornerstone of engineering class. The wing ribs were 3d printed out of an ultralight plastic. The structure was carbon fiber tubing and achieved the goal of being extremely light. This project involved iterative design and prototyping with constraints being time, weight, and ability to 3D print with a filament that is extremely difficult to print with.
First, I began by researching wing profiles. I knew that the air speed would be low and so I wanted wing profiles for low velocity, low thrust glide vehicles. The wing profile eventually used was from an unpowered glider and is perfect for minimizing parasitic drag while maximizing lift. The first iteration of this wing profile did not work as intended when installed on the wing spar. The original design has a wing rib every 20mm and bridges the gap with a shrink film that covers the entire wing like a skin and makes it more aerodynamic. This idea failed when the 3D printed ribs weakened and deformed while the heat film was being applied. One of the many lessons learned was that 3D printing filament takes high temperature to melt into a liquid but does not take a lot of heat to weaken.
The second iteration used the 3D printed wing ribs as the skin itself, by extruding them in 200mm lengths. With four of these, the whole wing was assembled, and printer paper was used to bridge the gaps between. Below are some photos of the final iteration. A few small, but necessary pieces were also 3D printed but with a traditional PLA filament. These pieces attached the carbon fiber wing spar to the wooden dowel that made up the body of the plane. On the front, an adapter was printed to attach the propeller (provided by professor) to the wooden dowel. At the rear, the stationary rudder, and elevator were glued to a 3D printed adapter that also served to hold the rubber underneath. Finally, at the trailing edge of the wing, attached to the wooden dowel body, was a fixture that held the wings stationary from rotation about the wing spar. 12 of these trailing edge pieces were printed, all at different heights, to test which angle of attack for the wings was best, to maximize lift on the vehicle but not induce a stall (when the wing can no longer provide lift because the angle of attack, and the air separates from the upper surface). It was required to laser cut one pieces of the plane, and I chose that to be the rudder because it only needs to be within certain specifications in two dimensions, the third being width, could just be sanded down to make more aerodynamic.
The end result was visually appealing, but when test flying, we found the thrust provided by the rubber band propeller to be too weak for the wings to generate enough lift to stay aloft. Even with a throw the plane fell out of the sky. Due to the limitations of this project, no further iterations were made, but many lessons were learned.