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Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects transmitter was set so the microcontroller was disarmed. A power source was used for the transmitter, so the transmitter would not lose power during testing and provide false results. The setup of this experiment is shown in Figure 121. Figure 121: PIC testing The PIC was programmed such that if it got past the arming routine and starts to read the control surface signals, an LED would turn on. After 90 minutes of testing, no false signals were read by the microcontroller. To ensure communication between the transmitter and the PIC was still working, the arming/disarming switch was flipped at the end of the test. When the switch was moved to the “arm” position at the end of the test, the LED turned on, confirming no communication loss, indicating that the PIC was programmed correctly for the test. With the results of these two tests, it was determined that the microcontroller was indeed safe to use for competition. 13.2 System Verification and Validation 13.2.1Wingtip Lift Test Before any flight testing can be completed, had to be lifted off the ground by the wingtips. This test simulates a 2.5g load at the root of the wing, and is demonstrated to the judges upon technical inspection at competition. This test demonstrates that the aircraft’s structure is flight worthy. Each model of the Buff-2 successfully passed the wingtip lift test. 13.2.2 System Flight Testing 13.2.2.1 Flight Test #1 The purpose of flight test #1 was to assess the general aerodynamic flying qualities and test the proof-of-concept of the flying wing design with the aerodynamic prototype, Buff-2A. As a safety precaution for the first flight, the aircraft was initially ballasted with weight in order to increase the static margin to 10% to ensure the aircraft was stable. The goal was to have the pilot takeoff, fly for no more than two minutes, and land the aircraft. The purpose of this flight test was purely to get qualitative data on aircraft handling characteristics from the pilot. 138
Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects The first flight of the aerodynamic prototype was a success. The pilot reported that the aircraft was indeed stable, and the decision was made to remove the ballast to return the aircraft to its normal static margin of 5%. A long ground roll was noticed on takeoff. This was attributed to an analysis error made early on in the year. The relationship between the Cl in the takeoff distance equation and aircraft incidence angle was not recognized, which resulted in a lower aircraft Cl than predicted during initial analysis. To account for this lack of lift, an incidence angle of 5° was added in order to increase the takeoff C L to 0.6 in order to make the 100 ft takeoff requirement. More about this change can be found in section 8.1.3. Pictures from the first flight are shown in Figure 122. Figure 122: Pictures of Buff-2A flight test #1 13.2.2.2 Flight Test #2 and #4 The purpose of these flight tests were to gather more qualitative data on aircraft handling and to accustom the pilot to the aircraft before riskier tests were undertaken. Both of these flight tests had successful takeoffs and airborne maneuvering portions. However, both of these flight tests ended with the nose gear breaking on landing. The main reason for the nose gear failure was that the aircraft was designed to sustain normal main-gear-first landings of up to 4.0 g’s. However, the nose gear was not designed to sustain the loads encountered by fast nose-gear-first landings. The reason for the nose-gear-first landings was due to the pilot still getting accustomed to landing the aircraft. The Buff-2 Bomber was designed with a relatively small wing and high stall speed in order to reduce aircraft size, fit in the box, and reduces overall weight. However, these design decisions indicate that the aircraft must land at a relatively high speed (25 mph when empty) and the pilot needed some practice flying the aircraft in order to make purely main-gearfirst landings. The nose gear failures that occurred during these two flight tests led to a redesign of the nose gear shown in section 8.48. Pictures of the nose gear failure upon landing are shown in Figure 123. 139
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PFR - Aerospace Engineering Sciences Senior Design Projects ...

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