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Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects Figure 137: Buff-2B carrying empty water bottle payload 13.2.2.11 Flight Test #17 The purpose of flight test #17 was to load the aircraft with ½ the weight of the full bottle, in order to get the pilot comfortable flying with a heavier load. The payload consisted of 4.0 lbs of ballast placed in the external battery box, a payload designed for Buff-2B flights with the Lipo battery. The pilot felt this was necessary due to the extreme change in payload weight from the empty bottle (1.0 lbs) to full bottle (9.0 lbs) flight. Since the full bottle weighs more than the entire aircraft, it was important to test the CG shift and flight characteristics at a lower weight. No quantitative data was measured on this flight since it does not simulate any competition missions. The flight test was successful, and the pilot felt comfortable moving on to the full bottle payload. Unfortunately, some ground damage occurred after the flight. The full bottle flight was pushed back until the next flight test. 13.2.2.12 Flight Test #18 and #19 The purpose of flight test #18 was to fly the aircraft with the empty water bottle payload as a pilot warm up for the full bottle flight. After a successful landing on flight #18, the pilot was ready to attempt the full bottle flight. The goal of flight test #19 was to fly the aircraft with the full water bottle payload (9.0 lb payload weight). The two requirements that needed to be tested on this flight were the 100 ft takeoff requirement under full weight, and the average power draw at full weight. The pilot noticed steering issues during taxi tests before the flight. The weight of the full water bottle compressed the nose gear significantly, making it difficult to steer the aircraft. The pilot decided it would be safer to slowly accelerate rather than push to make the 100 ft takeoff 150
Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects distance and risk going off the runway and destroying the aircraft. The flight was not scrubbed because we could still gather the average battery power draw once airborne, and the pilot could still get experience flying at the maximum payload weight. The pilot was able to get airborne in 150 ft by slowly accelerating up to takeoff speed. Once airborne, the pilot did some maneuvering, flew one competition lap, and landed. The average power draw was 332 W, less than the 350 W of power draw. This was very significant because this proved that the aircraft could indeed make the four lap range with the full water bottle payload. A plot of power usage versus time is shown in Figure 138. 800 Power Usage 700 600 Power Usage (W) 500 400 300 200 100 0 0 20 40 60 80 100 120 140 160 Time (seconds) Figure 138: Power draw for full water bottle payload flight 13.2.2.13 Flight Test #20 The goal of flight test #20 was to fly the aircraft with what would be the best case single rocket asymmetric load; one rocket inboard on one wing, and no rockets on the other wing. This led to a lateral CG shift of 4.0”. On takeoff roll, there was a strong pull to the left (the side on which the asymmetric rocket was placed). The aircraft almost went off the runway, so the pilot applied full up elevator in order to lift off before going off the runway. The aircraft rolled more than 90°, stalled, and impacted the ground. The left wingtip was broken in half, along with damaged motor mounts and propellers. The cause of the accident was traced to the fact that the asymmetric load on one wingtip caused one of the main gear to compress significantly, causing the aircraft to pull to the left and almost go off the runway. The full up elevator applied in order to make the aircraft takeoff only exacerbated the turn and led to the stall. The pilot also regretted not using opposite aileron during 151
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