PFR - Aerospace Engineering Sciences Senior Design Projects ...

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Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects Figure 34: The Tip Airfoil (HS520) 8.1.3 Aircraft Incidence Angle By definition, the incidence angle on a fixed-wing aircraft is the angle between the chord line of the wing root where the wing is mounted to the fuselage and the longitudinal axis of the fuselage. However, on this aircraft, due to the absence of a fuselage, the incidence angle is the angle of attack. A slight incidence angle is necessary to ensure the necessary takeoff rotation needed during takeoff. To determine the angle of incidence necessary, the takeoff distance was estimated using Equation 14 S LO 2 1.44W = ρgC T L max Equation 14: Takeoff Distance Equation The maximum lift coefficient in the takeoff distance equation corresponds to the angle of attack or in this case, the incidence angle necessary to meet the takeoff distance requirement. From the coefficient of lift vs. angle of attack curve for the airfoil selected, at an angle of attack of 0, the corresponding Cl is ~0.1, and at the stall angle of attack of 13º, the Cl is ~1.4. The lift coefficient needed to meet the takeoff distance requirement of 100 ft is ~0.7, which corresponds to an incidence angle of 5 degrees. As a result, a 5 degree incidence angle was implemented into the design to achieve the rotation and ground roll necessary on takeoff. 8.1.4 Control Surface Sizing For this airplane, conventional control surfaces (ailerons, elevators and rudders) were chosen. The aileron sizing was driven by the requirement to fit the airplane in the box. The ailerons were sized based on the location of the fold on the wings. It is ideal to use the least number of servos possible in order to reduce weight. In order to eliminate the weight of an additional servo, it is desirable to limit the length of the aileron by the location of the fold. Figure 35 shows the location of the fold and the aileron size based on the fold: 62
Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects Figure 35: Location of the Fold on the Wing The percentage of the chord for the control surfaces is important to ensure that the control surfaces produce the necessary control authority. An upper bound on the chord percentage is about 30% because flow separation occurs on the wing for larger percentages. The ailerons were sized to 15” from the wingtip and 30% along the chord. The rudders were sized so that maximum possible control could be achieved. The rudder was sized to be the entire length of the vertical with a 0.25” clearance so it would not interfere with the ailerons. The rudder is 13” long along the winglets and 30% along the chord. Since pitch control is a concern for flying wing configurations, it is important to ensure that maximum pitch control is available. The elevator was sized by the ailerons. The elevator is located between the ailerons, inside of the fold along the wing. The elevator has a constant chord percentage of 15%. Figure 36 shows the three control surfaces employed by this design: Figure 36: Control Surfaces on the Aircraft 63
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University of Colorado Design/Build
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