PFR - Aerospace Engineering Sciences Senior Design Projects ...

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Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects 8.4.9 Motor Mount The motor and propulsion systems were designed to attach to the foam wing. A mounting system that integrates into the wing was designed in order to accomplish this. This mounting system consists of four major components. The motor is the first component and attaches directly into the motor pylon, the second component, as shown in Figure 71. Simple M2.6 machine screws and aluminum strap are used to secure the main motor body to the pylon. A motor pylon was required in order to maintain necessary propeller clearance on a swept wing. The motor pylon is to be made from 0.02 inch 2024 aluminum sheet formed such that it was 6.5 inches long and 1.2 inches in width. Figure 71: Motor and Motor Pylon System The motor and pylon assembly then integrates into the third component which is a balsa hard mount that is installed into the wing structure. The wing itself makes the fourth and final component of the motor mounting system. In addition to accommodating the motor, the aluminum pylon in the airflow also acts as an effective heat sink for both the attached motor and speed controller. The integration of the motor pylon into the balsa hard mount and into the wing itself is shown in Figure 72. This balsa insert was designed to distribute the propulsion system’s load into a large surface area of the wing foam-core and balsa skin. The motor pylon requires a hard point to bolt onto because the foam does not provide adequate structural support. The pylon and balsa insert are bolted together using four light ¼ inch nylon bolts through the holes seen in Figure 72. Lastly, the balsa insert is glued into a slot cut from the wing before the wing is sheeted with the balsa skin. Wire access to the motor is provided by a tunnel bored through the foam and balsa to the pylon. 96
Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects Figure 72: Motor Mount System Integrated into the Wing 8.4.10 Motor Mount Loading Analysis To ensure that the motor mount is capable of supporting the stresses encountered in flight, a loading analysis was done using COSMOSWorks. The wing and balsa attachment was determined to be strong enough due to the use of both glue and the wing skin to hold the balsa insert in place. A stress analysis of the motor on the pylon was done to assure the design of the pylon was structurally sufficient. A static load of 6 pounds was applied from the motor to the pylon, with the nylon bolts serving as the only restraint. The 6 pound load is the highest expected thrust from any propeller configuration with the motor. The results of the COSMOSWorks analysis can be seen in Figure 73. A maximum stress of 18.7 ksi was located at the nylon bolt holes shown in close-up within Figure 74. However the yield stress of aluminum 2024 is 58 ksi, which creates a minimum 3.1 safety factor in the pylon design. A strain analysis was also done on the entire motor pylon assembly, shown in Figure 75, and it was confirmed that all strain deflections were negligible in magnitude. 97
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