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Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects 12” propeller without any additional landing gear size and weight. Propeller sizes up to 14” in diameter were tested incase additional thrust was needed, since the takeoff incidence angle allows for propellers of up to 14”. A motor was run at 800W, the maximum theoretical power that could be delivered by the battery pack to each motor (20V and 40 amps per motor, or 80 amps total). Table 25: Static Thrust Test Results Propeller Diameter (in) Propeller Pitch Maximum Thrust (lb) 12 6 5.37 12 12 4.30 13 6.5 5.06 13 10 4.78 14 7 5.87 14 12 4.65 This test confirms the expected result that higher diameter propellers as well as lower pitch propellers produce more static thrust than lower diameter and higher pitch propellers. In order to get the required thrust of 8.0lbs of static thrust at 1200W, each motor must produce 5.33 lbs of thrust at 800W. Therefore, this test confirms that the only usable propellers are 12in x 6 and 14in x 7 propellers. 13.1.2.2 Battery Endurance Testing In order to determine aircraft endurance, the battery pack was discharged on the ground in a mission profile similar to the aircraft when in flight. It was determined that mission two, described in 2.2, would require the most battery endurance since the aircraft will be carrying the weight of the full water bottle load for four laps. In order to simulate this mission, the battery was first discharged at full power for ten seconds to simulate takeoff. The power was then cut in half for an additional ten seconds to simulate climb, and then reduced to cruise power until the battery pack voltage dropped below 0.9V per cell. The battery pack used in this test can be seen in Figure 112. Figure 112: Competition Battery Packs 132
Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects The cruise power was estimated to be 350W. Assuming an average battery pack voltage of 1.0V per cell (24.0V) during the discharge, an approximate amp draw of 15 amps was required to generate 350W of power. While the batteries are designed to hold 1500mah of power, the batteries cannot discharge this amount when discharged under such high amp draw (10C). Therefore, it was assumed that only 1000mah of actual usable power could be drawn from the battery pack before the power would drop off below a usable level. The rest would be dissipated as heat from the internal resistance of the battery cells. With an average amp draw of 15 amps and 1000mah of usable power, the calculated endurance of the battery pack at cruise speed would be 4:00. The plots in Figure 113 show the battery pack voltage and power consumption as a function of time. 34 Battery Voltage 1200 Power Usage 32 30 1000 Battery Voltage (V) 28 26 24 22 Power Usage (W) 800 600 400 20 18 200 16 0 50 100 150 200 250 300 350 400 Time (seconds) 0 0 50 100 150 200 250 300 350 400 Time (seconds) Figure 113: Battery Voltage and Power Over Time The results of the test indicate that the battery pack voltage dropped below 0.9 V/cell at 4 minutes 10 seconds into the test, and then the power dropped below the 350 W required for cruise flight. This was slightly higher than the 4 minutes predicted because the battery pack provided about 1050 mah of usable power, above the 1000 mah used in the initial assumptions. Based upon the assumption of one minute per lap, this test verifies that the Buff-2 Bomber can in fact fly four laps in cruise with the heaviest payload configuration. The battery pack continues to provide sufficient power to sustain a slow descent until 4 minutes 30 seconds into the test, when the power drops below 200W. This extra power margin was designed to be used as reserve power during flight. 13.1.3 Structures Subsystem Verification and Validation A whiffle tree test was performed to determine whether or not the Buff-2 Bomber wing can sustain the expected loads seen in flight. The wing was loaded using a whiffle tree system and mounted upside down to simulate lift in flight. A right wing half was built according to normal construction spec in order to correctly determine the actual strength of the wing. The wing half 133
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PFR - Aerospace Engineering Sciences Senior Design Projects ...

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