## 2 Materials and Methods  
A static, ground test stand was designed and assembled to test the turboelectric system's capabilities and potential safety concerns, specifically during transient, dynamic loading. This bench test stand utilized an aluminum optical breadboard attached to a steel rolling table for ease of mobility and modularity. A 20 kW-rated electric motor, driving a three-blade, 28 in. propeller, and two separate five kW-rated electric ducted fans (EDFs) were chosen as the applied electric loads during the experiments. Electric motors pose a danger risk more severe than that of piston engines, as stated in [20]: \"Model aircraft electric motors can be more dangerous than gas engines of the same power class because the propeller does not slow down readily when a body part is hit; rather, the motor just pulls more current from the battery (source) as it attempts to retain the RPM\". The 20 kW motor and corresponding propeller were housed within a wire-mesh assembly to ensure foreign objects could not impact the blades to help prevent injury during testing. The ground test stand provides a portable testbed that can be utilized for differing ranges of turboelectric systems, with a maximum overall power loading capability of 23 to 28 kW. A photo of this system can be seen in Figure 4.  
Multiple temperature sensors were installed to monitor the thermal performance at critical locations on the test setup. Voltage and current produced by the generator were monitored and logged to provide real-time power production values of each system. The power produced was calculated using voltage and current values measured by the Mauch Power Module in Table 1. This power module was placed inline between the turboelectric system and the electric load (motor). This hall effect sensor package designed to monitor voltage and current data can be seen in Figure 5. Power was calculated from the measured voltage and current values. Turbine throttle data and turbine fuel consumption rate were also observed in real-time to help ensure the turbine was not operating in a dangerous regime (e.g., operating at too high of a voltage). \[V_{Pack}=N_{Series}*V_{Cell} \tag{4}\]  
Figure 4: A photo of the bench test stand with the K-60 TP-based system installed, showing the available electric loads of the 28 in. propeller motor and two additional five kW EDFs. For a battery pack to achieve total voltages higher than the 4.2 V maximum of the individual cells, the cells can be placed in series to add their corresponding voltages together in total, as shown in Equation (4) [20]. For example, a 12S battery pack has 12 individual Lithium polymer (Li-Po) cells tied together in series, hence the \"S\". This 12S battery pack adds the twelve 3.7 V cells together to create a 44.4 V nominal battery pack. Suppose the battery assembly voltage is monitored with disregard to individual cells. In that case, it is a potential hazard that an individual cell could under or overvolt while the battery pack appears to be within a tolerable voltage window altogether. For this reason, it is necessary to ensure that each cell of the Li-Po battery packs used in the turboelectric system maintains an acceptable voltage. Li-Po batteries present potential safety hazards if any under or overvoltage is experienced for extended periods. General characteristics of a select number of battery chemistries can be found in Table 2--Specific energy of different battery chemistries [20]. A battery augmentation system was developed to aid with the performance of the turbine and system response time. A battery package can add power in conjunction with the turbogenerator output and respond to desired power inputs more quickly than the turbine is physically able to. A battery management system (BMS) was used to monitor the voltages of the individual cells of the batteries. The battery's charge capacity, instantaneous charge/discharge rates, and voltages for each battery cell were tracked by the BMS to ensure the battery system would not be damaged.