# Integration and Flight Test of a 7 kW Turboelectric Vertical Take-Off and Landing Unmanned Aircraft
## 4 Results
### Power Data  
As expected, idle voltage was lower at the end of the flight than at the beginning because of energy drained from the battery. Figure 5 shows two significant spikes of around 336 A and 390 A at around 486 s and 566 s, respectively. These spikes are due to the pilot rapidly gaining altitude after pulling out of an unintentional dive. The timing of the spikes was unexpected. The expected maximum case was during takeoff, but this was only around 240 A at the 460 s mark. Thus, the unexpected maximum occurrence was around 48% larger than at takeoff, and the most critical electric load case was during a dive recovery. It is recommended that future VTOL aircraft be designed around these dive recovery power requirements for power delivery.  
The main power batteries utilized in this study were 65 12,000 mAh Graphene LiPo batteries, which had a discharge rating of 15C continuous and 30C burst [18]. This equates to a maximum current rating of 180 A continuous and 360 A burst. Based on the current data below, the batteries were sized adequately to handle the 240 A  
Figure 5: Current over the course of the flight.  
distributed electric motors. Without the turbogenerator the maximum load case of 390 A would have exceeded the maximum current rating of the batteries.  
Figure 6 shows voltage data over that same period. The voltage data acts as an inverse to the current data of Figure 5. Whenever a large amount of current was demanded by the motors, the system voltage dropped accordingly. The authors did not anticipate the amount of voltage fluctuation. The expected peak voltage of slightly more than 48 V for a 12S system was experienced at the beginning of the data, before takeoff began. The ending voltage was around 45 V. The average voltage of the dataset is 41 V, and the mean deviation is around 2 V. The system transiently experienced a voltage dip to almost 34 V. This is almost 25% less than even the final voltage. The turbine normally keeps up the system voltage by increasing the throttle. This large voltage sag means that the turbine engine's power output had already been exceeded and further strain was being placed on the batteries. Thus, a maximum load case with a 25% drop in voltage from the expected no load voltage is a good starting point for similar future aircraft. The power required during a pull-out could be found and thus the expected amperage of the system in that pullout could be estimated.  
Furthermore, the voltage drop itself is of critical importance to the designers of electric hybrid aircraft, and especially UAVs. For hybrid vehicles, it is desirable to minimize the size (and thus capacity) of the battery system. This means future vehicles will experience similar substantial voltage drops. Several electronic speed controllers (ESCs) and battery management systems (BMSs) have built in protections to prevent the battery from being fully drained. Both systems often utilize a voltage cutoff point, in which any voltage below a certain threshold causes the system to think the batteries are empty. These systems do not have a sensor for the current load being placed on the batteries and will instead shut off if a lower voltage is achieved. This can cause an unintentional forced landing if the power is cutoff during a critical phase of flight, like a pull-up. Therefore, future designers should remove these voltage cutoffs until data for their aircraft configuration have been tested.  
By multiplying voltage and current, the maximum instantaneous power being used by the vehicle was determined to be about 14 kW. This is consistent with the maximum estimate that was used to size the electronics (15 kW to 20 kW). However, because of the strain placed on the electrical system, the voltage drop plays a key role. To meet the power demand, the system current must rise even further, because of the lowered voltage. Thus, despite the power load being lower than expected, the maximum current case of 390 A was only just below the designed load case of 400 A [18].  
Figure 6: Voltage over the course of the flight.