Characterization and Analysis of the 

UEL 1100 Oil Pump 

by Logan P. Riley and Albert K. Owen 

ARL-TR-4520 June 2009 

Approved for public release; distribution unlimited.
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Army Research Laboratory 

NASA Glenn Research Center, Cleveland, OH 44133 

ARL-TR-4520 June 2009 

Characterization and Analysis of the 

UEL 1100 Oil Pump 

Logan P. Riley and Albert K. Owen 

Vehicle Technology Directorate, ARL 

Approved for public release; distribution unlimited. 
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Characterization and Analysis of the UEL 1100 Oil Pump 

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6. AUTHOR(S) 

Logan P. Riley and Albert K. Owen 

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US Army Research Laboratory Vehicle Technology Directorate 

NASA Glenn Research Center 

Cleveland, OH 44133 

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13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

The U.S. Army’s Shadow unmanned aerial vehicle (UAV) is an indispensable tool in modern military intelligence acquisition. 

The Shadow is powered by one UEL 1100 engine, a single-rotor Wankel engine. However, at high-altitude, low-temperature 

conditions, engine operation may be compromised due to insufficient oil delivery to the engine. To develop a better 

understanding of the engine system’s oil delivery, we have evaluated the performance of the oil pump. Testing consisted of 

measuring oil pumping capability at various temperatures and speeds, and with different grades of oil. 

15. SUBJECT TERMS

UEL Oil System, Lubrication 

16. SECURITY CLASSIFICATION OF: 

19a. NAME OF RESPONSIBLE PERSON

Albert K. Owen 

a. REPORT 

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UU 

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(216) 433-5895 

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Prescribed by ANSI Std. Z39.18 
iii

Contents 

List of Figures iv

Acknowledgments v

1. Background 1

2. Oil Types 1

3. Oil Pump 1

4. Test Configurations 3

5. Test Procedures 7

6. Preliminary Testing 7

7. Ice Testing 9

8. Conclusions 12

List of Symbols, Abbreviations, and Acronyms 13

Distribution List 14 
iv

List of Figures 

Figure 1. Oil pump showing oil outlets. .........................................................................................2 

Figure 2. Configuration 1................................................................................................................3 

Figure 3. Initial trials used this configuration.................................................................................4 

Figure 4. Graduated cylinders collect the oil from their respective lines. ......................................4 

Figure 5. Configuration 2 (side)......................................................................................................5 

Figure 6. Top view of “cold” configuration....................................................................................5 

Figure 7. A schematic top view of “cold” rig layout. .....................................................................6 

Figure 8. Air in lines at cold temperatures....................................................................................10 

Figure 9. Comparison of the three oils tested in this analysis (0W-40, 15W-40, and MIL23699). .....................................................................................................................................11 

Figure 10. Test of field oil (15-40W) vs. temperature..................................................................12 
v

Acknowledgments 

The researchers and the staff of the Vehicle Test Directorate (VTD) thank the Program 

Management Staff, Unmanned Aircraft System (UAS), for their support of this work, including 

providing the necessary oil pumps; and Mr. Daniel J Groner and the U.S. Army Aviation 

Engineering Directorate (AMRDEC). 
vi

INTENTIONALLY LEFT BLANK. 
1

1. Background 

The UEL 1100 series rotary engines (UEL 1100 and UEL 1101) power the U.S. Army Shadow 

unmanned aerial vehicle (UAV). This vehicle has been used in situations where it has 

experienced operational difficulties due to extremely cold conditions (~ –20 oF). The Aviation 

Engineering Directorate (AED) of the U.S. Army Aviation and Missile Research, Development, 

and Engineering Center (AMRDEC) tasked the U.S. Army Research Laboratory’s (ARL) 

Vehicle Technology Directorate (VTD) to provide experimental data to aid in evaluating 

potential solutions to this problem. 

In order to facilitate the development of an adequate solution, oil pumps for the engine used on 

the UAV underwent extensive laboratory evaluation at VTD. The focus of this research was on 

the characterization of the pump’s performance with various oils and the collection of data to 

help determine the most appropriate solution to the observed field problem. 

In characterizing the pump, we examined several variables to define the pump performance. 

Pump speed, head pressure, exit back pressure, temperatures of the oil, the oil intake line, the oil 

pump, and the type of oil were all factors considered and tested. This analysis, however, 

primarily focused on the different weight oils and the effect of temperature on the oil and oil 

pump. As the tests progressed, however, interest in not only the temperature of the pump, but of 

the feed line and oil reservoir, developed. 

2. Oil Types 

Three oil types were considered in this initial analysis: an 0W-40 automotive oil, a 15W-40 

automotive oil, and a turbine oil meeting specification MIL-23699. The 15W-40 is currently in 

use in the field. We chose the other two oils for their respective viscosity properties. These 

three oils were tested to assess changes in pump performance with the different viscosity oils. 

3. Oil Pump 

The five pumps provided for this study are identified in table 1. Of the five pumps, four were 

field tested. These pumps, numbered two through five, were screened in a 15-min field test, 

which looked for pumps that did not meet the minimum requirement of pumping 50 mL in 
2

15 min (200 mL/hr). Pumps two and three were tested at VTD and showed comparable results 

for the typical flow rates. Pump four, one of the pumps that failed the screen, was also evaluated 

during this project. 

Table 1. Oil pumps evaluated. 

Pump # Pump S/N Field Test 

1 FT73-2440 n/a 

2 FT73-6353 pass 

3 FT73-6383 pass 

4 FT73-6350 fail 

5 FT73-6356 fail 

Figure 1 is a picture of the oil pump. There is one inlet port and four outlet ports (labeled 1 

through 4). Outlet ports 1 and 2 feed the shaft bearings and ports 3 and 4 feed the rotator seals. 

Figure 1. Oil pump showing oil outlets. 

To better understand the operation of the pump and to provide information for a computational 

simulation analysis of pump operation and a further exploration of pump performance using 

other oils, one of the pumps was disassembled. This disassembly confirmed that the internal 

pump mechanism is geared down at an 11-to-1 ratio. Thus, for every 11 turns of the pump drive 

shaft, the cylinder that pumps the oil rotates once. 

Exit Port 3 

Exit Port 1 

Exit Port 4 

Exit Port 2 

Oil Inlet Port 
3

4. Test Configurations 

The pumps were tested using one of two rig configurations. The first configuration provided test 

data to analyze how speed and head pressure affected flow. However, a key focus of this study 

was to investigate the influence of temperature on different viscosity oils. Therefore, the first 

configuration, shown in figure 2, was later altered to create a rig that allowed for the temperature 

to be lowered using dry ice. 

Figure 2. Configuration 1. 

The milling machine sits at the left, as shown in figures 2, 3, and 4, with its spindle rotated 90o to 

horizontal. The milling machine was used to drive the pump. In the center is a metal box to 

which the pump is mounted. At the right sits a 1.5 qt capacity oil tank and a set of four 

graduated cylinders for collecting the oil, shown in figure 4. This UEL engine uses a total loss 

oil system. Thus, in the field, oil is not returned to the oil tank and recirculated. However, in this 

study of the pump, oil was reused. 
4

Figure 3. Initial trials used this configuration. 

Figure 4. Graduated cylinders collect the oil from their respective lines. 

The second configuration of the test rig, as shown in figures 5, 6, and 7, was used for testing the 

oils and pump at different temperatures. More specifically, oil and oil pump performance below 

0 oC was studied using this configuration. It features a typical beverage cooler set on the milling 

machine bed with the pump and oil tank mounted within. The pump is driven by a milling 

machine shaft with a flexible coupling as in the first configuration. 
5

Figure 5. Configuration 2 (side). 

Figure 6. Top view of “cold” configuration. 
6

Figure 7. A schematic top view of “cold” rig layout. 

Initially, one thermocouple measured the temperature of the oil within the reservoir, and another 

measured the air temperature inside the cooler, which was assumed to be indicative of the 

approximate supply line temperature. A third thermocouple was added to measure the 

temperature of the oil in the supply line and the air temperature thermocouple was moved 

adjacent to the pump to display its approximate temperature. The oil reservoir temperature 

continued to be monitored. 

The test configuration was cooled using dry ice. In order to effectively regulate the temperature 

of the oil, foam insulation was added to the partition around the oil tank to aid in cooling the oil 

reservoir and insulation was placed around the output lines to keep them warmer. The oil in the 

long 1/8-in plastic tubing on the output lines repeatedly froze during the initial testing, making 

the insulation around the output lines necessary to effectively measure oil flow. Clearly, in the 

operation configurations, the output from the pump will go directly into the engine. 
7

5. Test Procedures 

For each experiment, or test condition, 30 min of data was typically collected. Table 2 is a 

representative sample test matrix. For the initial experiments, three 10-min tests were conducted 

under each condition. As the study progressed, the experiments were refined so by the end of 

testing, one uniform 30-min test was conducted for each trial. 

During these tests, measurements were made every 5 min to record the volume of oil pumped, 

and the temperatures of the oil in the tank, the supply line, and pump. The chart in table 2 shows 

the average temperature. 

Table 2. Sample test matrix. 

Trial Configuration 

Pump 

No. 

Oil 

Type 

Temperature 

Oil 

(K) a

Temperature 

Air 

(K) a

Temperature 

Line 

(K) a

Duration 

(min.) 

22 2 3 0W-40 Ambient Ambient Ambient 30 

23 2 3 0W-40 Ambient Ambient Ambient 30 

24 2 3 0W-40 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 30 

25 2 3 0W-40 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 30 

26 2 3 Turbine Ambient Ambient Ambient 30 

27 2 3 Turbine Ambient Ambient Ambient 30 

28 2 3 Turbine 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 30 

29 2 3 Turbine 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 30 

30 2 3 Turbine 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 30 

31 2 3 Turbine 244 (–20 °F) 255 (–20 °F) 244 (–20 °F) 30 

32 2 3 15W-40 Ambient Ambient Ambient 30 

33 2 3 15W-40 Ambient Ambient Ambient 30 

34 2 3 15W-40 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 30 

35 2 3 15W-40 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 30 a

Temperatures vary. 

During “cold” tests, dry ice was added to the insulated tank compartment and to the bed of the 

cooler. Once the oil in the tank was at the desired temperature, tests were conducted. As 

necessary, ice was moved or removed to keep the temperatures constant. A small handheld 

electric fan was to regulate the temperature of the system. 

6. Preliminary Testing 

While most of the tests took a quantitative approach, a few qualitative analyses, like that of the 

preliminary testing of the pump, or preliminary testing of the “cold” rig were also conducted. 
8

Following the preliminary test, we conducted a series of three 10-min trials tests in which 

variables like head pressure and speed were investigated. 

Preliminary tests and all ambient temperature tests were typically measured at 

approximately 295 K. 

Under the first configuration, the pump designated number one was tested by running it up to 

speed in small increments. Results of this part speed testing showed that the pump flow is nonexistent or extremely low (>50 mL/hr). A minimum pump speed of 3600 rpm was required to 

move oil through each of the lines. However, ports 1 and 2 moved oil (if intermittently) even at 

low rpms. Port 1 pumps roughly the same amount of oil as port 2; likewise, port 3 moves the 

same amount as port 4. Only at full speed do ports 3 and 4 provide oil; however, they move far 

less oil than ports 1 and 2. Table 3 provides these results with no flow in port 4 until the pump 

speed was set to 3000 rpm. Indeed, at that speed, the flow in all ports was intermittent and port 4 

flow was characterized as weak. 

Table 3. Oil flow in preliminary test. 

Pump 1 Flow 

Time Elapsed RPM Port 1 Port 2 Port 3 Port 4 

0–5 min 1000 Y Y R R 

10 min 2000 Y Y Y R 

15 min 3000 LG LG LG Y 

20 min 4000 G G G G 

25 min 0 LG R LG R 

Chart Color Definitions 

Flow Rate 

Continuous Flow G Green 

Moderate/Intermittent LG Light Green 

Weak/Intermittent Y Yellow 

None R Red 

Ports 1 and 2 are believed to send oil to the engine bearings while ports 3 and 4 provide 

lubrication for the seals. 

Oil flowing from the lines leading from the pump was collected into four graduated cylinder (one 

for each line) and, during these tests, we observed that having the collection cylinders below the 

pump (thus reducing exit back pressure) caused a number of side effects. In the first line, it 

significantly increased the number of air bubbles present in the lines, while the second line 

continued to have a smooth continuous flow. Flow in the third line was significantly reduced 

and no flow was observed in the fourth line. It must be noted that air found in the lines of this 

pump is not indicative of the other pumps and was found to be anomalous behavior at warm 

temperatures. Seals within the pump may be related to the appearance of air in the outlet lines. 
9

The cylinders were placed roughly level with the pump apparatus so that the pump had to pump 

slightly uphill to the collection cylinders. This kept a small back pressure on the pump allowing 

for more uniform flow. This test was done only with this pump. 

Initial findings indicate that head pressure and back pressure, though they have an effect on the 

quality of the flow, do not typically show significant changes in the amount of oil pumped. 

However, head pressure cannot be expected to change significantly even if the oil reservoir in the 

aircraft were to be moved (up or down), unless the aircraft executes an unusual maneuver during 

flight. 

Back pressure, though, is important in keeping oil flowing through all of the lines. Low back 

pressure caused the lines of the first pump to show large increases in the number of air pockets or 

caused some lines to cease functioning entirely. Although the reason back pressure is required is 

not known, back pressure is important to oil delivery to the engine. 

Thus, these parameters were largely ignored in the later part of the analysis, and the remainder of 

the study centered on effect of oil on flow rates. Testing showed that the maximum output by 

any of the pumps under ambient conditions (~295 K) was 300 mL/hr. This served as a point of 

comparison during the other tests. 

7. Ice Testing 

The initial “cold” analysis, given in table 4, followed a similar format to that of the preliminary 

test of the pump. 

Table 4. Preliminary ice testing, pump 2, 30 June 2008. 

Temperature 

(K) Port 1 Port 2 Port 3 Port 4 

255 G G G G 

250 LG LG LG LG 

244 Y Y Y Y 

239 R R R R 

Chart Color Definitions 

Flow rate 

Nominal G Green 

Moderate LG Light Green 

Weak Y Yellow 

None R Red 
10

As the oil approaches 244 K (–20 °F) overall output drops considerably, and below this 

temperature, oil flow ceases entirely. Data from subsequent testing are provided in table 5. 

Table 5. Temperature analysis matrix. 

Oil Type 

Temperature 

Oil 

(K) a

Temperature 

Air 

(K) a

Temperature 

Line 

(K) a

Pump 

(RPM) 

Duration 

(min) 

Average Oil Flow 

(mL/h) 

0W-40 Ambient Ambient Ambient 4000 30 288.00 

0W-40 Ambient Ambient Ambient 4000 30 312.00 

0W-40 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 4000 30 72.00 

0W-40 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 4000 30 36.00 

Turbine Ambient Ambient Ambient 4000 30 300.00 

Turbine Ambient Ambient Ambient 4000 30 300.00 

Turbine 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 4000 30 24.00 

Turbine 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 4000 30 36.00 

Turbine 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 4000 30 36.00 

Turbine 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 4000 30 36.00 

15W-40 Ambient Ambient Ambient 4000 30 312.00 

15W-40 Ambient Ambient Ambient 4000 30 300.00 

15W-40 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 4000 30 48.00 

15W-40 244 (–20 °F) 244 (–20 °F) 244 (–20 °F) 4000 30 48.00 a

Temperatures vary. 

Also of note, of the three pumps tested under conditions around 244 K, air appeared in the output 

lines of all three pumps. Figure 8 is indicative of the extent that air appeared in the oil output 

lines. During these cold tests 90–95% of the length of the output lines contained air. As the oil 

warmed the volume of air in the lines decreased. It is hypothesized that seals within the pump do 

not react well at cold temperatures, thereby allowing air to be introduced into the system. 

Figure 8. Air in lines at cold temperatures. 
11

At 244 K, all of the oils became very thick, almost solid substances. After thawing, sediment in 

the oils was also observed. Extreme temperature changes may bring the heavier elements in the 

oil out of solution. 

Most importantly, in monitoring the temperature of the oil and the pump, the pump was found to 

generate a considerable amount of heat, even at cold temperatures. Notice in figure 8 that the 

pump temperature remained at roughly 290 K even at air and oil temperatures of 244 K. Even at 

this low air temperature, the pump will continue to pump air. This indicates that pump 

temperature, while it may affect output by a few milliliters, does not inhibit the flow of oil. This 

implies the temperature of the oil governs the oil flow rates. 

The pump has been observed to attain a maximum temperature of 315 K (110 oF) at ambient 

temperatures. 

Figure 9 shows a comparison of the three oils tested in this analysis (0W-40, 15W-40, and 

MIL-23699). The comparison of the warm and cold tests in figure 9 show that changing the oils 

did not affect flow in the pump significantly. In this plot, each oil was tested for 30 min with the 

flow rate measured every 5 min (tests 1 through 5). 

Oil Flow Comparison

0

50

100

150

200

250

300

350

02468

Test

Flow (mL/Hr)

0W-40

15W-40

Turbine

At Ambient Temperature

At 244 K

Figure 9. Comparison of the three oils tested in this analysis (0W-40, 15W-40, and MIL-23699). 

Figure 10 show a plot of the effects of oil temperature on flow rate for the current oil using the 

15W-40 oil. As the oil temperature decreases, the oil flow decreases significantly. 
12

15W-40 Oil Flow vs Temperature

0

50

100

150

200

250

300

350

400

240 250 260 270 280 290 300

Temperature (K)

Oil Flow (mL/hr)

Air/Line Temperature Oil Temperature

At stable 245K

oil flow is typically 

50 ml/hr or less

As pump warms

output increases.

Particularly after

cold conditions

Figure 10. Test of field oil (15-40W) vs. temperature. 

8. Conclusions 

In this project, several important factors and characteristics regarding the oil pump used on the 

Shadow UEL 1101 engine have been determined. First, it appears that different oil viscosities do 

not have a significant influence over the oil flow. In addition, since the pump warms itself 

significantly during operation, pump temperature is not significant factor, as originally thought. 

While fluctuations in pump temperature may influence the flow, it generates considerable heat 

while running, and will continue to pump, albeit with a significant amount of air in the lines at 

cold temperatures. Air bubbles in the exit flow lines present a huge loss of oil flow. The air in 

the output lines is likely related to seals within the pump and should be considered for future 

analysis of the pump. Also, operating speed plays a significant factor in performance. A very 

slight reduction in pump speed will stop oil flows to one or possibly two output lines. 

Furthermore, there exist some instances in which pump performance appears to drop off after 

20 min, suggesting longer pump screenings may be needed. 

Overall, the pump is typically ineffective in terms of oil delivery during very cold weather 

operation; thus, an alternative positive displacement pump may be the only effective solution to 

addressing the oil delivery concerns of the Shadow engine. 
13

List of Symbols, Abbreviations, and Acronyms 

AED Aviation Engineering directorate 

AMRDEC Aviation and Missile Research, development, and Engineering Center 

ARL U.S. Army Research Laboratory 

UAV unmanned aerial vehicle 

VTD Vehicle Technology Directroate 
14

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