Powertrain

Payload capacity plays a critical role in determining its flight range and endurance. We designed the aircraft to be capable of flying with a 0.5 kg payload for extended periods. Our 8kg AUW aircraft utilizes four KV320 brushless motors paired with 22-inch bi-blade carbon fiber propellers. Two bladed propellers with a 6.6” pitch were selected to operate efficiently in low free-stream velocity conditions. This propulsion system provides almost 5kg of thrust per motor, as shown in Figure 6, giving us a total thrust to weight ratio of almost two to one. This propulsion configuration gives us more flexibility in the mechanical design of our aircraft and allows for larger payloads in the future.

Assembly and Integration

Structural components were 3D printed from PPA-CF and ASA for strength and heat resistance. The carbon fiber arms were cut to length and epoxied to the motor and arm mounts to form the main frame (Figure 9). The central pod plates originally used carbon fiber but we accidentally ordered uniaxial weave and quickly discovered that our parts snapped laterally after we waterjet them. We pivoted to aluminum since it was the best alternative we had on hand. After verifying fit and alignment, motors, ESCs, and landing gear were installed, with wiring routed internally through the arms. The assembled prototype (Figure 10) was tested for structural integrity, vibration isolation, and electrical continuity before inserting the avionics stack.

Testing

Weeks of flight testing was conducted to ensure safe aircraft operation and mission capabilties. I led all flight efforts and piloted from full acro mode to operating missions.

Competition

Placed 3rd in mission demonstration and design review. 

Participating institutions included: Cornell, IIT-Bombay, Cal Poly SLO, Cal State LA, San Diego State and CSU Bakersfield.

Failures and Lessons Learned

During the waypoint navigation mission, we decided to push the envelope and command 10 m/s aircraft velocity. There was also a unit conversion issue in the mission planning that caused the aircraft to go to 100m instead of 100 ft. These factors caused the autopilot to initiate an emergency RTL due to critical thrust loss. When the aircraft came home, it was also having GPS issues, which caused a slow spiral down. After the first impact, which reported 10 g from the FC accelerometer, the aircraft bounced 20ft into the air, so I switched to ACRO mode and landed it safely. I disarmed the aircraft, and one of the arms fell limp onto the ground. This clearly meant that the first impact broke the arm, and the thrust force kept it intact for the secondary landing. 

We were able to fix the arm and avionics box with epoxy and JB Weld. One of our transmission cables was also sheared in half so we had to solder the coaxial cable together during the competition. Our team flew two more missions and finished third.