PFR - Aerospace Engineering Sciences Senior Design Projects ...

Project Final Report – CUDBF April 30 th , 2009
ASEN 4028: Aerospace Senior Projects
In order to isolate the cause of the motor failure, the propulsion system was bench tested on the
ground after the flight. It was determined that there were no issues with the motors, speed
controllers, or wiring. The problem was determined to be a receiver issue. The receiver used on
this flight was a 72 MHz receiver instead of a 2.4 GHz receiver, which will be used at
competition. During bench testing, there was significant interference noticed with the 72 MHz
receiver. The possible cause of the crash was suspected to be from the faulty receiver which
caused the motor to cut out in flight. The 72 MHz receiver was replaced with the 2.4 GHz
receiver. There were no receiver issues after replacing the receiver.
13.2.2.4 Flight Test #5
Flight test #5 was another flight dedicated to getting the pilot used to flying the aircraft. During
this flight, the aircraft experienced servo travel on the right elevator. The right elevator was
deflected up about 20° while the pilot commanded neutral elevator. The red arrow shown in
Figure 125 shows the deflection experienced in flight. The pilot aborted landing twice before
being able to force the aircraft on the ground during the third attempt. After the flight, it was
determined that the servo travel occurred because the servo was over-torqued.
Figure 125: Elevator servo travel experienced on flight test #5
During analysis, the worst case scenario torque calculated for the elevator servo was 92 oz/in.
This would only occur at the aircraft top speed of 70 mph, and a full control surface deflection of
25°. However, it was determined that the pilot would never use full control deflection at top
speed. Therefore, a lower torque servo was used in order to save weight. The servo torque of
48.6 oz/in was used since it still allows for 20° of deflection at 60 mph. However, this torque
proved to be insufficient through flight testing. Therefore, the next size up in servos was chosen,
providing 66.7oz/in of torque. This allows for full 25° elevator deflection at up to 60 mph, and
up to 20° of elevator deflection at the top speed of 70 mph.
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