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Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects The cause of the crash was due to a weakened nose gear servo from previous flight test crashes. This resulted in the aircraft unable to steer on takeoff, resulting in a slow takeoff and subsequent stall. Two major lessons were learned from this flight test. The first is that all aircraft components should be carefully inspected before every flight. A flight test checklist was created in order to verify that critical systems are checked before flight. The flight test checklist created is shown in Figure 132. Another major lesson learned was to “Fix the problem, not compensate for it.” This lesson was applied throughout the rest of the project. Figure 132: Flight test checklist 13.2.2.8 Flight Test #10 The purpose of flight test #10 was to assess the general flying qualities of the new aircraft, the Buff-2B. In addition, this flight test would be the first flight test utilizing the NiMH battery pack. A series of events contributed to a crash on landing. First, the transmitter used for previous flight tests was under recall. The transmitter that was substituted for this flight did not have the dual rate control surface deflections programmed into it. Dual rate control surface deflections allow the pilot to have full control surface deflection for takeoff and landing, and then limit deflection once airborne in order to avoid over-controlling. Since the aircraft was not carrying any payload, the pilot decided it would be better to select the limited control surface deflections, assuming he would still have sufficient control for takeoff and landing. Another issue was that the ailerons on the first aircraft had been trimmed slightly up for some additional nose up control. The ailerons could not be digitally trimmed up on the transmitter being used. Finally, a wire on the battery 146
Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects pack was frayed during loading. This meant that the battery pack could not deliver full power during flight. A picture of the damaged battery pack is show in Figure 133. The green box shows an intact wire, while the red box shows the frayed wire. Figure 133: Frayed wire on NiMH battery pack The aircraft approached nose low on landing, the pilot lacked full control surface authority, the usual nose up trim, and was unable to provide full power for a go around. This resulted in the aircraft striking the ground extremely hard and nose gear first. Fortunately, only minor damage was suffered. The propellers and motor mounts required replacement, and additional screws needed to be replaced on a wingtip hinge. Despite hitting the ground nose gear first, there was absolutely no damage to the nose gear. This hard impact proved that the nose gear design is effective at withstanding hard nose gear first landings and proved to be a vast improvement from the original design. 13.2.2.9 Flight Test #11 and 12 The purpose of flight test 11 and 12 was to get the Buff-2B airborne following the crash. Flight test 11 utilized a LiPo battery. This allowed the pilot to assess the aircraft handling qualities without introducing any propulsion battery issues into the mix. After a successful landing, the LiPo battery was replaced with the repaired NiMH battery pack. The goal of flight test 12 was to test the aircraft handling characteristics of the Buff-2B with the NiMH battery pack. The pilot reported he had sufficient power throughout the flight. This confirmed that the frayed battery wire caused the lack of power on flight test 10. After these successful flight tests, the aircraft was cleared to start flying actual competition missions. A picture of the Buff-2B airborne during flight test #12 is shown in Figure 134. 147
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University of Colorado Design/Build
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