From 01515d09923f66fff330f08316c53c58f7adaaef Mon Sep 17 00:00:00 2001
From: Joshua Drake <joshua.ellis.drake@gmail.com>
Date: Fri, 1 Nov 2024 03:22:26 -0500
Subject: Added methodology from FAA pub.

---
 methodology.tex | 112 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 111 insertions(+), 1 deletion(-)

(limited to 'methodology.tex')

diff --git a/methodology.tex b/methodology.tex
index b6c8231..a55ff00 100644
--- a/methodology.tex
+++ b/methodology.tex
@@ -8,7 +8,117 @@
 \section{General Aircraft System}
 \section{Configuration One}
   \subsection{Data Acquisition}
+  The turboprop engine control unit
+(ECU) connects to a laptop-based program. This program outputs
+various metrics of the engine and can be used to record data visually.
+Unfortunately, the controller area network bus protocol used by the
+engine is proprietary and the manufacturer did not provide software
+to record data directly. Thus, all engine data was recorded from
+video capture of real-time graphical read-out, and figures were
+created during postprocessing.
+The main data acquisition system consists of three Arduino
+Megas. Two of the microcontrollers were utilized to record most of
+the sensor inputs. The third Arduino only measures voltage and was
+located inside the aircraft with the pilot. The two main boards utilize
+the printed circuit boards detailed in Fig. 9. The board was designed
+to accommodate the numerous sensors present on the aircraft,
+though this paper will focus on the power data because most of the
+recorded data was thermistor data and not particularly interesting.
+All the specifics of the relevant DAQ components are listed in
+Table 2.
+The locations of the hall effect current sensors can be seen in the
+main electrical system diagram shown in Fig. 5. The aircraft testbed
+consists of 2 LEM DHAB S-133 current sensors that can read up to
+750-A and are accurate to within 2% of the actual value. They are
+located after the generator and before the crowbar circuit. A third
+DHAB S-124 current sensor was also used before the battery, and it
+can read up to 500-A accurately. This sensor is slightly more
+accurate than the S-133 because it has a smaller current rating. The
+amount of power expended from the battery was not expected to
+exceed 300-A. These three sensors allow for current in the system to
+be fully accounted for and monitored. The current sensors are
+bidirectional and so can determine the direction electrical current is
+flowing. All power production (battery and generator) and power
+utilization (battery, wings, and crowbar) can be accurately measured
+in real-time.
+A voltage divider was utilized to reduce the 120-V to a 5-V range.
+This scaled range was then read by the analog port on an Arduino.
+For the voltage sensor, a separate dedicated Arduino was used to
+allow for an increased response rate and ease of electrical isolation.
   \subsection{Experimental Procedure}
+  Before hybrid-power testing
+commenced, the system went through a series of preliminary tests to
+reduce the technical risk of a full hybrid-power system test. These
+tests were important for informing the test matrix design. First, the
+turboprop engine was tested to ensure the engine was operating
+nominally, before adding the generator [18]. Next, a check run was
+performed using only the batteries, ensuring the power system and
+electric motors worked properly. The test confirmed that the data
+acquisition system and electric motors worked correctly. Before full
+system testing commenced, the generator was plugged into the
+power system and the engine was slowly brought up to speed to find
+the point where the generator voltage exceeded the battery voltage.
+During this testing, it was discovered that the generator had a k V of
+27 instead of the expected value of 23.
+The test procedure for the ground test rig consists of first charging
+and balancing the batteries. The batteries are then installed into the
+aircraft, with one battery connector left disconnected until just prior
+to the test. The aircraft strut is filled with air, the engine oil level is
+checked, and the brakes are checked. The aircraft is rolled out of its
+hanger and brought to an open field. The aircraft is then secured with
+a chain to the ground. The precharge circuit is then activated, and
+batteries are plugged into the main bus. The precharge circuit is then
+disabled. Two people then get into the aircraft, a pilot and a data
+recorder with a laptop. A third person records a video with a fire
+extinguisher on standby. The data recorder confirms that all sensors
+are working. Then the engine is started and brought to idle. Once the
+engine has reached operating temperature and is ready, the pilot
+designates the beginning of testing and brings up the throttle to the
+test point. The data recorder then brings up the electric motors to
+the respective test points. Finally, after the data have been recorded,
+the engine is brought down to idle and then turned off. The engine is
+cooled, the main power battery is disconnected, and the data are
+exported to the laptop hard drive.
+The test matrix was designed to accommodate the 27-k V value
+generator. If the voltage of the battery is higher than the output
+voltage of the generator, then no power is generated and the
+generator spins freely. This amounts to an all-electric configuration
+in practice if the generator is outputting below the battery voltage.
+The output voltage of the generator is around 111.1-V at the
+maximum power turbine shaft speed. The minimum battery voltage
+that was deemed safe is around 20% of the useful capacity.
+This meant that the cell voltage of the batteries was brought down
+to 3.81-V per cell. This brought the 28S battery to a total of 106.7-V,
+which meant that the generator would only be operating slightly
+above the battery voltage. The maximum voltage of the battery at
+4.2-V per cell is 117.6-V. This has practical advantages as it makes it
+difficult to overcharge the battery if the generator’s output voltage is
+less than the total maximum voltage of the battery. The net effect of
+the 27-k V generator was that the generator voltage would only
+exceed the battery voltage at full throttle. This meant that the full
+engine throttle test point was the only engine test point of interest.
+The maximum charging current of the battery specified by the
+manufacturer is 85-A and should not be exceeded. Based on this
+value and the known resistance values of the batteries, Eq. (2) was
+used to determine that a voltage difference of 7-V between the
+battery and generator would be needed to exceed the maximum
+current rating. However, the largest value that the generator could
+output was 111.1-V and the minimum battery voltage was 106.7,
+which lead to a maximum difference of 4.3-V, which is well below
+7-V. In practice, because the maximum RPM is not normally
+achieved under normal operation and there is a voltage drop across
+the rectifier the full 111.1-V, generator output will not be achieved.
+The test matrix in Table 3 was designed to operate at the full
+turboprop throttle position. The test procedure was developed to
+capture steady and transient data. The engine would be brought up to
+idle and then brought to full throttle. The low ESC throttle value was
+intended to be around 30-A per motor based on previous electric
+tests, with a medium value of around 80-A, and a high value intended
+to be around 150-A per motor. Both electric motors are brought up to
+a low value and then held for 5-s, before moving to the next value and
+holding it for 5-s as well. The result provided data at different
+relatively steady conditions, as well as the transient reaction of the
+electromechanical system to changes in the electrical load.
 \section{Configuration Two}
   \subsection{Data Acquisition}
-  \subsection{Experimental Procedure}
\ No newline at end of file
+  \subsection{Experimental Procedure}
-- 
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