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Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects Table 18: Calculating the Load on Each Strut Parameter Variable Value Units Length from main gear to CG l m 4.00 inches Length from nose gear to CG l n 7.50 inches Takeoff Weight W to 14.00 lbs Number of main gear struts n s 2 none Load on the nose gear strut P n 4.87 lbs Load on each main gear strut P m 4.57 lbs Percent of takeoff weight carried by the nose gear %W n 34.78 % Percent of takeoff weight carried by the main gear %W m 65.22 % 8.4.7 Main Gear Loading Analysis The strength of the main gear for the Buff-2 Bomber was determined by analyzing both a beam deflection and beam buckling case for the horizontal and vertical forces seen during landing. These forces were due to the friction between the wheel and the landing strip (calculated with a coefficient of friction 0.2 of to be 9lbs) and the impact force seen when the aircraft first touches down (found to be 54lbs), as Figure 66 clarifies. Note that the main gear struts are angled at 80°, increasing the overall length to 7.1 inches to preserve the 7 inches clearance of the aircraft. P N is the impact load normal to the runway, and P S is the frictional load applied due to rolling friction. This angle was done to extend the landing gear span while at the same time anchoring the gear to a thick portion of the wing to prevent the structure from tearing out during landing. Figure 66: Main Gear with Applied Loads Figure 67 shows the beam deflection case Free Body Diagram (FBD). 92
Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects Figure 67: Beam Deflection Analysis The maximum allowable deflection of the beam, set to 0.5in, allows the beam to be analyzed to determine the minimum radius of a number of materials, including the final selected Al 2024. Knowing the deflection as well as the supposed 3g maximum load on the landing gear (assuming heaviest aircraft weight of 14lbs), Equation 31 was twice integrated to solve for the required radius of the aluminum strut. The final solution is seen in Equation 32. These equations were obtained from Vable [28] . Equation 31: Second Order Moment Differential Equation Figure 68 shows the beam buckling case FBD. Equation 32: Minimum Radius for the Deflection Case Figure 68: Beam Buckling Case 93
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University of Colorado Design/Build
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PFR - Aerospace Engineering Sciences Senior Design Projects ...

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