PFR - Aerospace Engineering Sciences Senior Design Projects ...

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Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects 8.0 Mechanical Design Elements Author: Shivali Bidaiah Co-Author: Ben Kemper, Mark Findley 8.1 Aerodynamics Mechanical Design Elements 8.1.1 Aircraft Geometry The analysis that was done on the effect of static margin with varying sweep angles and varying taper was used to determine the optimal geometry given the requirement for the aircraft to fit in the box. In order to have the most room along the wing for control surfaces, the span was chosen to be 68 inches. This satisfies the minimum wing span requirement of 60 inches. Figure 33 shows the aircraft geometry: Figure 33: Aircraft Geometry The analysis done showed that the static margin increased as the sweep angle increased between 20 and 25 degrees. The best possible configuration that meets the requirement to fit in a 4’x2’x2’ box is a leading edge sweep angle of 23 degrees and a taper ratio of 0.5. Because this project involves flight missions with asymmetric loading in the lateral direction, the addition of a vertical is necessary. The vertical is the equivalent of a vertical stabilizer and provides yaw control. Winglets were added to each wing tip to serve the purpose of a vertical stabilizer. The winglets were sized using the tail volume coefficient method. The tail volume coefficient method is based off of the sizing of past aircraft. This sizing is based off of the area of the wing, S w , the wing span, b, the area of the vertical tail, A vt , and the distance between the c. g. of the aircraft and the aerodynamic center of the vertical tail. The tail volume coefficient for most aircraft falls in the range of 0.03 to 0.06. A larger tail volume coefficient 60
Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects means that the aircraft will be more directionally stable. With the main geometry of the wing selected, the only parameter to determine is the sizing of the vertical tail. A tail volume coefficient of 0.04 was used giving the two vertical tails an area of 0.69 ft 2 . The vertical tails are shaped with a taper ratio of 0.5 and a straight trailing edge. This drove the vertical tails to be 13.25 inches tall. Table 6 summarizes the geometry of the aircraft. Table 6: Characteristics of Aircraft Geometry Parameter Value Leading Edge Sweep, Λ LE 23 degrees Quarter Chord Sweep, Λ c/4 19 degrees Trailing Edge Sweep, Λ TE 7.3 degrees Span, b 68” Wing Area, S 7.14 ft 2 Aspect Ratio, AR 4.5 Root Chord, c root 20.16” Tip Chord, c tip 10.08” Taper Ratio, λ 0.5 Winglet Height 13.25” Winglet Taper Ratio, λ v 0.5 Wing Area, S v 0.69 ft 2 8.1.2 Airfoil Selection and Aerodynamic Twist The airfoil chosen for the root of the aircraft was the HS602. This airfoil was chosen for the root primarily because it has a thickness to chord ratio of 10.21%. Because this aircraft does not have a fuselage, the wings will house the batteries, motor mounts, release mechanism mounts, the servos and the wiring. In order to ensure that these components will be housed in the wing, the root must have a reasonably thick airfoil. From a stability standpoint, it is ideal to have an airfoil with a moment coefficient of 0. Of all the airfoils analyzed, the airfoil that had the smallest moment coefficient was the HS520 airfoil (Figure 34). Since the HS520 has a thickness to chord percentage of only 8%, it is not the optimal choice for the root. In order to make a fair trade between the most desirable thickness to chord percentage that would house most of the components and the airfoil with the best moment coefficient, an aerodynamic twist was implemented into the design. The root section has the HS602 airfoil and the tip has the HS520 airfoil with a linear twist between the root and the tip of the wing. The winglets have the NACA 0010 airfoil; a symmetric airfoil with a 10% thickness to chord ratio. 61
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University of Colorado Design/Build
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