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\chapter[RESULTS]{RESULTS}
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\section{Configuration One}
\subsection{Turboprop Engine Data}
Figure 11 shows the power
turbine shaft torque output and rotational speed throughout the test
run. The impact of the power generator can be seen in the mechanical
system data. The turboprop was taken to full throttle and left there
for the duration of the electrical system testing. The turboprop
maintains a specific shaft speed at each throttle setting and so should
not change throughout the run. The decrease in RPM around the 355-s
mark was caused by the load of the generator slowing it down. After
5-s, the engine control unit brought the turboprop back to the intended
speed. However, it can be seen that the engine was now producing
more torque at that same RPM, and thus more power.
The turboprop is rated for a peak shaft speed of 2158-RPM, which
was used in the design of the generator system. The peak value
measured during testing was 2136-RPM. So, the generator was
spinning at 2990-RPM and the design speed for the generator is
3000-RPM, so it was operating nominally. The peak power
produced by the turboprop was about 150-kW. The nominal max
continuous output of the engine is 160-kW, but the engine can
temporarily boost to 180-kW for takeoff. This means that
throughout testing, the maximum power rating of the engine was
never exceeded. The engine performed well, and no otherwise
unexpected phenomenon happened to the engine throughout testing.
\begin{figure}[h]
	\centering
	\includegraphics[width=\textwidth]{img/test1prop.png}
	\caption{\label{test1prop}Turboprop Shaft Torque and Speed}
\end{figure}
\subsection{Electrical System Performance}
Figure 12 shows the
voltage of the central bus and the current flow from the generator and
battery. The ESC throttle positions are labeled in the figure. The
voltage data contain some noise caused by the electrical output of
the generator. The cause of the noise being something else, such as
the vibration of the instrumentation, is unlikely because it only
appears when the generator hits the designed speed and exceeds the
voltage of the battery. The Arduino and probes that measure the
main bus voltage are also not located on the engine, further
increasing the notion that the noise is caused by the generator
creating a noisy DC signal.\\
Figure 13 shows the total electrical and mechanical power during
the same period as Fig. 12, allowing for direct comparison. The
trends for the voltage data are quite clear. The battery begins at
106.5-V and ends at 105.9-V. Under peak load at around 365-s, the
minimum operating voltage of 100-V is achieved. From left to right,
the changes in ESC throttle position can be seen. Starting from the
left the battery begins charging at 14.4-A. The two ESCs are then
commanded to start at the expected nearly 15-A current draw, but the
left ESC failed to engage properly.\\
Surprisingly, the medium throttle position on the right ESC was
achieved by drawing ~75-A, but the amount of current from the
generator saw only a minor increase. Instead, the difference was
almost entirely picked up by the battery. This can also be seen in the
power data. There is a small bump in generator power at the ESC
medium point, but the power decreases slightly and is picked up by
the battery. The mechanical data show a drop in rotational speed at
about the same time the medium throttle point was engaged.
Whenever the load was increased, it slowed down the rotational
speed (and thus voltage) of the generator preventing it from picking
up the difference. The generator was slowed down from the near
constant ~2990-RPM to 2904-RPM, which would have reduced the
output voltage by 3-V. Because the output voltage of the generator is
so close to the battery voltage, this decrease in voltage significantly
impacted the current output. The battery responded to the increased
load almost instantly but based on the power/RPM data, it took ~5-s
for the turboprop ECU to adequately react to the increase in
mechanical load.\\
Once the high ESC throttle position was reached, a significant
amount of current ~150-A total was discharged. The voltage then
dropped by several volts and the amount of current from the
generator increased significantly to its maximum of 39-A. At this
point, around 4-kW was being extracted from the turboprop using
the generator, while about 13-kW of power came from the battery.\\
Afterward, the second medium throttle position was hit. The total
current was ~40-A compared to the previous 75-A. The reason for
the significant difference may have been an error made by the
operator, who may have missed the target ESC throttle positions.
The power data, however, provides evidence that the total power
output of the propeller was continuously decreasing despite the
operator holding the throttle steady for each position. The simple
explanation may be that the inertia of the propeller and electric
motor is quite large. The electric motor did not require as much
power because it was slowing down instead of speeding up. The final
observation is that the resting current output of the generator
recharging the battery is slightly higher than at the beginning of the
run. This is because the voltage difference between the generator
and battery increased since the battery discharged some of its power.
\begin{figure}[h]
	\centering
	\includegraphics[width=\textwidth]{img/test1electric.png}
	\caption{\label{test1electric}Voltage and Current Data}
\end{figure}
\begin{figure}[h]
	\centering
	\includegraphics[width=\textwidth]{img/test1power.png}
	\caption{\label{test1power}Mechanical versus Electrical Power}
\end{figure}
\subsection{Electronic Speed Controller Failure}
After the main test was completed, the left ESC that had failed to
start properly was investigated. The ESC and electric motor had
previously been successfully tested during an all-electric check-out
test run. The electric motor was again tested on battery power to
figure out what was wrong. During this attempt at starting the motor,
the ESC saw a significant in-rush current as shown in Fig. 14. This
caused spontaneous failure and the rupturing of the capacitors inside
the ESC creating a minor fire. The current draw during failure shown
in Fig. 14 is an underestimate. The sensor used to monitor the battery
current maxes out slightly over 500-A, so the instantaneous
maximum values may have been higher than 550-A.\\
The electrical data during the failure were of particular interest.
During previous testing, an ESC had desoldered its connection point
with its main power wire, which had removed the ESC load from the
main bus. In this case, the ESC shorted, causing a substantial
unexpected load of 46-kW of electrical power on the central bus.
This caused significant strain on the battery, whose maximum rated
current was around 350-A. Had this event occurred during full
system testing, then it could have damaged the turboprop engine or
the battery.\\
The acquisition rate of the current sensor data is slow compared to
the failure causing steep step changes. However, it appears that as
the failed system was failing, the minimum of the oscillating current
expenditure creeps up from around 20-A (at 423-s) to about 50-A
(428-s). This gave rise to clear recommendations for the handling of
electrical failure modes.
\section{Configuration Two}