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Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects 12.0 Fabrication and Integration Author: Jarryd Allison Co-Authors: Mark Findley, Eric Hall 12.1 Interior Sub-Assembly Figure 106: Interior Landing Gear and Joiner Plate Assembly To begin building the aircraft multiple interior subsystems needed to be built in tandem in order to integrate these systems into the wing. The nose gear was started by first cutting a 10 inch section of aluminum T-bar. Once cut, all sharp edges were filed down and the end corners rounded to ease assimilation into the wing halves. A hole sized to fit the steering servo was cut into the aluminum bar, and to reduce weight, holes were drilled one inch apart long the shorter perpendicular section of the aluminum bar. The servo was set into the T-bar and secured by drilling holes into the aluminum bar at the appropriate locations. The COTS landing gear system (to include servo connection arm, hard plastic holders, and spar) was then installed into the aluminum bar by drilling holes into the aluminum which holds the spar holders via four small screws. The spar was then sent through the holders and held in place with the servo connection arm. The COTS landing gear was then attached to the servo and the system tested using the transmitter. The PIC microcontroller was built to attach to the receiver and control all avionics systems of the aircraft as well as the release mechanisms. Once the PIC was selected, code was written for the microcontroller and tested with the PIC on a breadboard. Once the breadboard prototype was completed, a circuit board was designed to house all of the necessary electronic components in a compact fashion, so it could easily be integrated into the plane. The components were soldered onto the circuit board and the microcontroller tested to ensure that all connections were secure. Each release mechanism consisted of a Trufire bow release trigger held in place using small sections of aluminum L-bar. To alter the triggers, the hand grip was removed on the band saw and the screws that hold the two halves of the system together also removed. The screw holes were then extended using a drill and the release trigger bolted to the aluminum holders. In the actual releasing part of the system, the spring was manipulated by installing a small screw into 124
Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects the release trigger directly behind the spring. This screw was then tied to a servo, and when pulled, activated the mechanism and released any stores that were attached to it. The centerline mount was built from a large sheet of plywood. Once cut, the plywood sheet was sanded smooth on all sides. Holes were cut into the mount to hold two release mechanisms and the servo in between which controlled both mechanisms. Great care was taken to ensure that the servo arm lay in the same plane as the release mechanism’s tops, so small balsa blocks were sized to raise the servo up to the necessary height. Making sure that the wiring remains long enough to thread through the wings, the servo was screwed into the balsa blocks and the release mechanisms into the plywood mount. The servo arm was then tied to each release system and the centerline mount tested with the centerline store. 12.2 Exterior Sub-Assembly Figure 107: Exterior Vertical and Main Gear Assembly The aircraft verticals were built by first removing the rudders using a bandsaw and carefully measuring the exact locations where the rudder is located. Once removed, the vertical and rudder were sheeted with balsa wood attached with Gorilla Glue © . When the glue set, the pieces were removed from their molds and any excess balsa removed. The verticals and rudders were then sanded to remove excess glue. At this point, the verticals were shaped to be easily fitted to the wingtip of the aircraft. Thus an airfoil hollow which stops halfway through the vertical was cut into the bottom of the vertical. This allowed the vertical to sit atop the wingtip snugly. Small balsa blocks were attached to the tops of the two pieces and sanded to a curved shape to improve aircraft aerodynamics. A cavity was created in the verticals to hold an interior-mounted servo which controls the rudder, and at the same time the rudders were monokoted. Holes were drilled into the rudder and small hinges glued into the holes, with like holes being drilled into the vertical. The vertical was then itself monokoted and the exposed rudder hinges glued into the vertical taking care not to cover the hinge with excess glue, which impinged on rudder movement. The servo was then attached to the rudder and the system tested. 125
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