PFR - Aerospace Engineering Sciences Senior Design Projects ...

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Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects From this equation, it was possible to determine a parameter’s influence on the total flight score by creating nominal values for each of the parameters and taking the partial derivative with respect to that particular design parameter. These nominal values are based on heuristics and are listed as follows: • 6 lb aircraft • 10 lb container • 2 lb transmitter • 14 lb payload • 10 sec load time • 30 sec assembly time • 120 sec flight time An example of this partial derivative of the flight score with respect to aircraft weight is shown in the following equation. Equation 7: Partial Derivative of the Flight Score with Respect to Aircraft Weight It was determined from the mission score sensitivity analysis that the assembly time of the aircraft was most sensitive to the overall score, followed by the load time, the aircraft weight and lastly the flight time. The results of the analysis can be seen in Table 2, and allowed the design to focus on maximizing the factors that most affect total overall score. Table 2: Mission Score Sensitivity Results Parameter Assembly Time Load Time Aircraft Weight Flight Time Percent Change -7.50 % -3.67 % -1.88 % -0.0488 % Order of Importance 1 st 2 nd 3 rd 4 th It is important to note that the drag of the aircraft was not counted for as a separate factor simply because the aircraft drag and weight are so closely related. More drag implies more thrust is needed for the aircraft to complete its mission. More thrust entails more batteries which in turn increase the overall system weight. 26
Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects 3.2 Aircraft Configuration For this mission, the payload cannot be contained within the airplane. Because of this all configurations that have a fuselage were not considered as possible design solutions simply because a fuselage is unneeded and unused weight and space. Additionally, configurations that have multi-wing designs were eliminated since they add weight and are unnecessary for this mission. Possible design alternatives were thus narrowed down to three configurations: flying wing, conventional without a fuselage, and canard without a fuselage. The canard and conventional designs without a fuselage indicate that a boom replaces the fuselage which connect the nose and tail sections. 3.2.1 (System Option #1) Flying Wing Pros: The absence of a tail provides a lighter airframe than other configurations. The lack of excess control surfaces creates less drag. Due to the absence of a tail, the aircraft is easier to compact and requires less pieces to construct (increases ground mission score). Cons: A large effort must be put into the aerodynamic design in order to make this aircraft stable. Longitudinally, the aircraft can easily become unstable. Although some sources exist, less literature is available on designing a flying wing aircraft. 3.2.2 (System Option #2) Canard Pros: The canard surface at the front of the aircraft provides positive lift, decreasing the lift required by the wing. The canard increases lifting efficiency as opposed to decreasing. The presence of a canard decreases the time required to design the aircraft to be longitudinally stable. Cons: The canard construction increases the weight of the aircraft. This added weight makes the canard’s wing slightly bigger than the flying wing. The canard surface creates more pieces for the aircraft assembly time. 3.2.3 (System Option #3) Conventional Pros: The conventional aircraft requires the least amount of design time and experience to design. The tail provides longitudinal stability. Cons: The tail introduces two negative factors: weight and negative lift. The excess weight from the tail requires a bigger wing to compensate; increasing the weight. The tail’s negative lift also increases the size of the wing. This leads to decreased efficiency compared to the other designs. The tail creates more pieces for the aircraft assembly time. 3.3 Comparison of System Options To increase the project’s overall competition score, the aircraft must be lightweight, have low drag, and be assembled from the aircraft container as quickly as possible. The aircraft’s weight and wing area were estimated and aspect ratios were used to determine the drag effects on the 27
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