# Design, Manufacturing, and Flight Testing of an Experimental Flying Wing UAV
## 6 Flight Test  
The experimental flying wing UAV consists of a propulsion system, flight control and navigation system, battery pack, main and secondary structural modules, control surface actuators, and a ground control station. The propulsion system consists of an AXi 4130/20 kv305 electric brushless motor and a \(15.5\times 12\) four-blade propellers. Pixhawk 4 (PX4), a low-cost autopilot software, is used as the flight control and navigation system [20]. PX4 has an IMU module (gyroscopes and accelerometers), magnetometer (compass), barometer, GPS module, power system, and various interfaces (e.g., PWM, general-purpose serial ports, I2C, SPI buses, CANBuses, R/C input). It can handle all flight control and navigation requirements of the experimental flying wing UAV. PX4 has a weight of \(15.5\) g, dimensions of \(44\times 84\times 12\) mm, and operating temperature of \(-40\)\({}^{\circ}\)C to \(85\)\({}^{\circ}\)C. The battery pack is 1.6 kg, and then the total weight of the experimental flying wing UAV is 8.62 kg. The total weight of the actual UAV exceeds the original design weight of 6.5 kg. If the payload is not loaded, the cruising speed increases to 20.3 m/s, and this requires a power of 77 W.  
According to flight test guidelines [21], the flight test is conducted without the payload. The flight test consists of two phases. The first phase involves remote control by a pilot R/C direct command in the planned flight condition. Flight in the first phase is observed and evaluated by a pilot. The first phase of the flight test clarifies the basic performance. The second phase involves remote control governed by PX4 without a pilot R/C direct command; the flight attitude is determined by PX4 using the gyroscopes and accelerometers to analyze the aircraft's dynamic characteristics. Flight tests are performed to measure and evaluate the UAV's characteristics during flight and to verify that these characteristics are as desired. Proper preparations and inspections help ensure that the UAV is ready to fly and contribute toward an efficient, productive, and safe flight test program. Before the first flight test, the flight plan must be reviewed carefully. When all flight preparations and inspections were completed and the weather was within acceptable limitations, the first flight test was performed at 2 pm on 29 May 2018, in New Taipei City. It followed a typical airfield traffic pattern, that is, a standard path followed by an aircraft when taking off or landing while maintaining visual contact with the airfield. Such patterns are used at airfields for air safety. Owing to the use of a consistent flight pattern, pilots will know from where to expect other air traffic and be able to see and avoid it. When pilots fly under visual flight rules (VFRs), the airfield traffic pattern is vital in keeping things orderly and safe. Figure 14 shows a typical airfield traffic pattern [22]. Figure 13: (**a**) Main structural modules (left and right wings) and secondary structural modules (wing tip) and (**b**) experimental flying wing UAV. The battery pack was charged fully at first, and then, the primary control test was performed. This test is an important inspection for the UAV. The primary control of the flying wing UAV involves the throttle and the elevons to control the pitch and roll. These main control commands are transmitted by a remote controller. When the throttle command is tested, the aircraft must be firmly fixed on the ground to avoid injury to people. Control surface commands are transmitted to the servo system that consists of servo and control surfaces, and every control surface must move smoothly. According to the flight plan, the flying wing UAV was positioned at the start of the runway. Its direction of flight was into the wind, and the throttle command was set to the maximum. The airplane accelerated along the ground, and we tried to keep it going in a straight line along the runway at all times. Owing to the risk, the first flight test was not attempted in crosswind.