Robert F. Handschuh, Joseph Polly, and Wilfredo Morales

Glenn Research Center, Cleveland, Ohio

Gear Mesh Loss-of-Lubrication 

Experiments and Analytical Simulation

NASA/TM—2011-217106

November 2011
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Robert F. Handschuh, Joseph Polly, and Wilfredo Morales

Glenn Research Center, Cleveland, Ohio

Gear Mesh Loss-of-Lubrication 

Experiments and Analytical Simulation

NASA/TM—2011-217106

November 2011

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

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Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2011-217106 1

Gear Mesh Loss-of-Lubrication Experiments and Analytical Simulation

Robert F. Handschuh, Joseph Polly,* and Wilfredo Morales

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Abstract

An experimental program to determine the loss-oflubrication characteristics of spur gears in an aerospace 

simulation test facility has been completed. Tests were 

conducted using two different emergency lubricant types: 

(1) an oil mist system (two different misted lubricants) and 

(2) a grease injection system (two different grease types). 

Tests were conducted using a NASA Glenn test facility 

normally used for conducting contact fatigue. Tests were run 

at rotational speeds up to 10000 rpm using two different gear 

designs and two different gear materials. For the tests 

conducted using an air-oil misting system, a minimum 

lubricant injection rate was determined to permit the gear 

mesh to operate without failure for at least 1 hr. The tests 

allowed an elevated steady state temperature to be established.

A basic 2–D heat transfer simulation has been developed to

investigate temperatures of a simulated gear as a function of 

frictional behavior. The friction (heat generation source) 

between the meshing surfaces is related to the position in the 

meshing cycle, the load applied, and the amount of lubricant 

in the contact. Experimental conditions will be compared to

those from the 2–D simulation.

Introduction*

The drive system used in rotorcraft applications has to pass 

a 30-minute loss-of-lubrication test prior to aircraft 

certification. This means that the drive system must continue 

to operate for 30 minute with the primary lubrication system 

inoperative (Ref. 1). When a new drive system is being 

qualified, this test is typically the last of an exhausted list of 

tests that need to be successfully passed during the 

certification process. This one test can drastically alter a drive 

system’s lubrication system configuration if a separate 

emergency lubrication system is necessary.

Gears are typically extremely susceptible to failure due to a 

starved lubrication condition. High-load, high-pitch line 

velocity, or the combination of both can cause the gears to 

heat to the point of failing, when the teeth bend back and fail 

to provide power transfer. Failure at the contact of gears can 

be summarized by Figure 1 (Ref. 2).

Preliminary studies conducted recently (Refs. 3 and 4) have 

made some initial attempts at evaluating the loss-oflubrication behavior of test hardware typically used at NASA 

 *

LERCIP Summer Intern

Glenn for contact fatigue studies. There has been some 

minimal progress made in these studies, however, duplicating 

the aerospace environment required modification of our 

contact fatigue test facilities to better mimic a rotorcraft drive 

system. These modifications will be mentioned later in this 

study.

All tests were run in a dry sump manner, where all 

lubrication is jet fed and gravity drained. This type of 

lubrication system results in efficient operation of the drive 

system. If the gears were to dip into the lubricant, the power 

loss would become quite large which is not representative of 

aerospace drive systems.

As can be seen in Figure 1, many combinations of rotational 

speed (sliding velocity) or load can push a design to failure 

even if the lubrication system is working correctly. Therefore, 

if conditions are borderline with respect to full fluid-film 

lubrication development, failure in a starved lubrication 

condition becomes even more of an issue.

The work discussed here describes the evolution of our test 

configuration from basic contact fatigue tests to tests

representative of an aerospace drive system. The current 

system consists of a shrouded spur gear pair with a lubricating 

jet and provisions for emergency lubrication systems. The 

front cover of the shroud is made from high temperature glass 

to permit operation to extremely high temperatures while 

providing visual access to the gears. Several design parameters 

were varied during testing. The lubricant, delivery method, 

gear design, and gear material were all parameters altered 

during testing. All of these effects will be discussed in this 

study.

Test Facility

The test facility used for conducting all loss-of-lubrication

simulation tests was the NASA Glenn Contact Fatigue Test 

Facility (Refs. 5 to 7). The facility is shown in the sketch 

contained in Figure 2. The facility is a torque regenerative test 

rig that locks torque in the loop via a rotating torque applier. 

The test gears have the same number of teeth on the driving 

and driven gears. Facility speed and torque can be varied if 

needed during a test. Two different test gear designs were 

utilized during the tests: the NASA contact fatigue test 

specimen (28 teeth) and a design version that had 42 teeth. 

The basic gear design information is contained in Table 1. The 

majority of the tests were conducted using the 42-tooth gear 

design.
NASA/TM—2011-217106 2

Figure 1.—Effects of speed and load on gear wear 

mechanisms.

Figure 2.—Cross-sectional sketch of the test gearbox used for 

loss of lubrication testing.

Figure 3.—Initial test gearbox arrangement during loss of 

lubricant testing.

TABLE 1.—BASIC GEAR DESIGN INFORMATION

28 tooth gear 42 tooth gear

Diametral pitch (1/in.) 8 12

Pressure angle (deg.) 20 25

Pitch diameter (in.) 3.5 3.5

Addendum (in.) 0.125 0.083

Whole depth (in.) 0.281 0.196

Chordal tooth thickness (in.) 0.191 0.128

Face width (in.) 0.25 0.25

Over the period of time the tests were conducted a number 

of changes to the gear cover, drainage, and shrouding were 

made to make the test arrangement emulate an aerospace 

(rotorcraft) transmission. These modifications could affect the 

outcome of the type of testing conducted in this study. A 

number of cover and shroud combinations were tested at the 

nominal 10,000 rpm speed that the facility is operated at 

during the loss-of-lubrication tests. The initial test facility 

arrangement is shown in Figure 3.

Initially there was no shrouding, and drainage from the 

gearbox was not optimal. A deepened sump and shrouds of 

different configurations were assessed experimentally. The 

current arrangement used for conducting the tests is shown in 

Figure 4. A thin, high-temperature glass cover enabled visual 

inspection of the test section during normal and loss of 

lubrication testing.

A schematic of the emergency oil mist lubrication system 

tested is shown in Figure 5. The system used shop air to pickup the lubricant supplied and formed an air-oil mist. The mist

was then injected radially inward toward the gear axis of 

rotation at two locations. These two locations were located 

approximately 30° at the out-of-mesh location. 

Figure 4.—Current test gearbox arrangement utilizing shrouds 

and improved lubricant drainage.
NASA/TM—2011-217106 3

Figure 5.—Sketch of current air-mist lubrication system.

Figure 6.—Photograph of post-test gear that failed during 

testing.

Testing Methodology

The majority of the loss-of-lubrication tests were performed 

for the shroud, oil mist system, and modified gearbox cover 

configurations as follows. After all system parameters were at 

steady state (including oil inlet/outlet temperatures, lubricant 

flow rate, and facility parameters), the test was initiated. To 

initiate the test the normal lubricating jet flow was terminated.

At this point the emergency lubrication system became

operational. Testing was continued until failure to transmit 

torque or impending failure was reached. An example of a test 

that was operated until impending failure is shown in Figure 6.

When operating in the loss of lubrication mode, several 

parameters, including temperature within the test gearbox 

were monitored. For the mist system, the air-flow rate and air 

supply pressures were monitored. For the test gears, the 

temperatures measured within the gearbox were from the fling 

off directly out of mesh location and at sites 180° from the 

meshing location. No instrumentation of the gears were used

during operation. 

Test Results

The test results from all loss of lubrication tests conducted 

with an emergency lubricant will now be discussed. Tables 2 

and 3 document the evolution of not only the test operation, 

but also includes changes to the shrouding, drainage, misting 

system, lubricant, and delivery method. Three series of tests 

were conducted with a total of 52 tests. The first series shown

in Table 2(a) are tests conducted in a lubrication-starved 

mode. No additional lubricant was used other than what was 

applied via syringe prior to testing. The next series, 

Table 2(b), was mainly vapor-mist lubrication during the loss 

of primary lubrication event. The third series (Table 3) was an 

investigation of injected grease as a possible solution for 

increasing loss-of-lubrication performance.

Vapor-Mist Test Results

A total of 46 tests (Table 2(a) and (b)) were conducted using 

just a small amount of lubricant (no normal lubricant delivery 

system) or variations of the mist-lubricant delivery. During 

these tests, many parameters were changed such as the 

gearbox cover, shrouding, mist delivery system, gear size, 

gear material, and the mist lubricant. Many of these test 

conditions were only run once. Some general observations are 

provided below.

Gear Material and Backlash

Two gear materials were tested: AISI 9310 and M50. M50 

was only used in five tests. The M50 and 9310 gears (8 

diametral pitch) had excessive backlash from their final 

grinding step in manufacturing. Increased backlash is 

important for reducing the chance that the gears could jam 

during loss of lubrication events due to thermal expansion. For 

the limited number of tests, M50 appeared to last longer 

during loss-of-lubrication than the AISI 9310 for similar 

conditions.
TABLE 2.—(a) LOSS OF LUBRICATION TEST RESULTS SUMMARY FOR LUBRICANT STARVED CONDITIONS

Test 

no.

Diametral 

pitch,

1/in

Material,

type

Serial 

no. 

left

Serial no.

right

Shroud,

Y/N

Backlash,

in.

Gearbox 

cover

Emergency 

lubricant 

type

Total emer. 

lube used 

during test,

ml

Flow 

rate,

ml/min

Speed,

rpm

Load 

pressure,

psi

Test tim

and c

1 12 9310 EG-20 EG-21 N 0.004 Original 1 0.8 0 10000 250 Failed at 2.1 min, applied 1 drop / 

2 12 9310 EG-52 EG-62 N 0.004 Original 1 5 0 10000 250 Failed at 2.8 min, 5 ml syringed on

3 12 9310 EG-44 EG-40 N 0.0035 Original 1 0.5 0 10000 250 Failed at 2.18 min, 0.5 ml syringed 

4 8 9310 #0060 #0024 N 0.018 Original 1 5 0 10000 250 5 ml syringed on teeth, ran 61 min 

5 8 9310 #0024 #0060 N 0.018 Original 1 0.5 0 10000 250 Failed at 9 min, 0.5 ml syringed on 

6 8 M-50 1-8-1F 1-7-7K N 0.009 Original 1 0.5 0 10000 250 Failed at 10.3 min, many teeth mel

(b) LOSS OF LUBRICATION TEST RESULTS FOR MISTED LUBRICATION

Test 

no.

Diametral 

pitch,

1/in

Material,

type

Serial no. 

left

Serial no. 

right

Shroud,

Y/N

Backlash,

in.

Gearbox 

cover

Air 

flow 

rate,

SCFM

Mister 

used

Mister 

air 

pressure,

psi

Emergency 

lubricant 

type

Total emer. 

lube used 

during test,

ml

Flow rate,

ml/min

Speed,

rpm

Load 

pressure,

psi

1 8 M-50 1-8-2K 1-7-1K N 0.014 Original 0.38 1 30 None 0 0 10000 250 No failure, ra

as 640 °F

2 8 M-50 1-8-2K 1-7-1K N 0.014 Original 0.38 1 30 None 0 0 10000 250 No failure aft

3 8 9310 #0058 #0075 N 0.009 Original 0.42 1 38 1 NR NR 10000 250 No failure, te

mister air pre

orifices out of 

4 12 9310 T-067 T-034 N 0.004 Original 0.43 1 40 1 NR NR 10000 250 Failed at 9 mi

5 12 9310 T-061 T-035 N 0.004 Original 0.38, 

0.33

1 30, 20 1 NR NR 10000 250 Failed at 48 m

(30 and 20 ps

6 8 9310 23 66 Y 0.015 Modified NR 1 NR 1 41 0.342 10000 250 No failure aft

7 8 9310 23 66 Y 0.015 Modified NR 1 NR None 0 0 10000 250 Failed at 20 m

8 8 9310 N0070 N0047 Y 0.0155 Modified NR 1 30 None 0 0 10000 250 Failed at 23.3 

9 12 9310 EG57 EG58 Y 0.005 Modified NR 1 50 None 0 0 10000 250 Failed at 8 mi

10 12 9310 EG50 EG56 Y 0.005 Modified 0 1 0 None 0 0 10000 250 Failed at 4.7 m

11 12 9310 EG48 EG43 Y 0.005 Modified 0.5 1 50 2 143 0.397 10000 250 No failure aft

backlash to st

12 12 9310 EG60 EG68 Y 0.005 Modified 0.5 1 50 1 259 0.682 10000 250 No failure aft

Tmax=281 °F

13 12 9310 EG53 EG04 Y 0.003 to 

0.0045

Modified 0.5 1 50 1 17 0.92 10000 250 Failed at 18.5 

14 12 9310 EG65 EG63 Y 0.005 Modified 0.5 1 50 2 61 2.65 10000 250 Failed at 23 m

15 12 9310 EG65 EG63 Y 0.005 Modified 0.5 1 50 2 18 3 10000 250 Failed at 6 mi

16 12 9310 EG48 EG43 Y 0.006 Modified 0.5 1 50 2 118 0.319 10000 250 No failure aft

17 12 9310 EG29 EG22 Y 0.005 Modified 0.5 1 50 1 88 0.978 10000 150 No failure aft

18 12 9310 EG29 EG22 Y 0.005 Modified 0.5 1 50 1 110 0.458 10000 150 No failure aft

19 12 9310 EG47 EG46 Y 0.005 Modified 0.5 1 50 1 150 0.568 5000 250 No failure aft

20 12 9310 EG47 EG46 Y 0.005 Modified 0.5 1 50 1 13 0.159 10000 150 Failed at 18 m

NASA/TM

—2011-217106 4 
Test 

no.

Diametral 

pitch,

1/in

Material,

type

Serial no. 

left

Serial no. 

right

Shroud,

Y/N

Backlash,

in.

Gearbox 

cover

Air 

flow 

rate,

SCFM

Mister 

used

Mister 

air 

pressure,

psi

Emergency 

lubricant 

type

Total emer. 

lube used 

during test,

ml

Flow rate,

ml/min

Speed,

rpm

Load 

pressure,

psi

21 12 9310 EG01 EG28 Y 0.005 Modified 0.5 1 50 None 0 0 5000 150 Failed at 7.75 

22 12 9310 EG13 EG15 Y 0.005 Modified 0.5 1 50 1 103 0.621 5000 250 No failure aft

23 12 9310 EG13 EG15 Y 0.005 Modified 0.5 1 50 1 200 0.563 7500, 

10000

250 No failure aft

24 12 9310 EG13 EG15 Y 0.005 Modified 2.4 2 23 1 18 0.3 10000 250 No failure aft

25 12 9310 EG13 EG15 Y 0.005 Modified 2.4 2 23 1 13 0.217 10000 250 No failure aft

26 12 9310 EG13 EG15 Y 0.005 Modified 2.4 2 23 1 20 0.333 10000 250 No failure aft

27 12 9310 EG13 EG15 Y 0.005 Modified 1.75 2 10 1 4 0.138 10000 250 Failed at 29 m

28 12 9310 EG12 EG10 Y 0.005 Modified 2.4 2 23 1 15 0.092 10000 250 No failure aft

29 12 9310 EG19 EG17 Y 0.005 Modified 3.3 1 50 1 1.06 0.133 10000 250 Failed at 8 mi

30 8 M-50 1-10-2F 1-7-4K Y 0.01 Modified 2 1 50 1 31.5 0.525 10000 250 No Failure aft

31 8 M-50 1-10-2F 1-7-4K Y 0.0125 Modified 3.3 1 50 1 8.52 0.142 10000 250 No failure aft

32 8 9310 33 32 Y 0.013 Modified 3.3 1 50 1 3.3 0.167 10000 250 Failed at 20 m

0.025 in.

33 12 9310 EDG14 EDG11 Y 0.005 Modified 2.2 1 50 2 16.5 0.275 10000 250 No failure aft

34 12 9310 EDG-14 EDG-11 Y 0.005 Modified 3.3 1 50 2 1.5 0.166 10000 250 Failed at 9 mi

35 12 9310 EAG-23 EAG-24 Y 0.005 Modified 3.3 1 50 2 0.444 0.0833 10000 150 Failed at 5.3 m

36 12 9310 EDG-006 EDG016Y 0.005 Modified 3.2 1 50 2 12 0.1 10000 150 No failure aft

37 12 9310 EG-76 EG-42 Y 0.005 Modified 1.1 3 45 1 40 0.666 10000 150 No failure aft

38 12 9310 EG-76 EG -42 Y 0.005 Modified 1.1 3 45 1 1 0.17 10000 150 Failed after 6 

39 12 9310 EG-64 EG-69 Y 0.005 Modified 1.1 3 45 1 36.5 0.61 10000 250 No failure aft

40 12 9310 EG-54 EG-55 Y 0.005 Modified 1.2 3 45 None 0 0 10000 150 Failure after 3 

Notes: Emergency lubricant 1, Reference 8, emergency lubricant 2, Reference 9. 

NR, not recorded. 

Gray shaded cells denote flow rate and amount not verified.

NASA/TM

—2011-217106 5
NASA/TM—2011-217106 6

TABLE 3.—LOSS OF LUBRICATION TEST RESULTS SUMMARY USING GREASE (AISI 9310 MATERIAL).

Test 

no.

Diametral

pitch,

1/in

Material,

type

Shroud,

Y/N 

Backlash,

in.

Gearbox 

cover

Emergency 

lube,

type

Initial lube 

on gears,

g

Grease 

injection 

rate,

g/pulse

Speed,

rpm

Load 

pressure,

psi

Time to failure or 

test stopped,

min

1 12 9310 Y 0.005 None 1 3.11 ----- 2500 and 5000 150 None

2 12 9310 Y 0.005 None 1 3.99 ----- 7500 150 9

3 12 9310 Y 0.005 Modified 1 3.16 0.16 7518 150 None

4 12 9310 Y 0.005 Modified 1 3.89 0.16 10000 150 ~4 

5 12 9310 Y 0.005 Modified 1 0 0.16 10000 150 30

6 12 9310 Y 0.005 Modified 2 0 0.35 10000 150 46 

Note: Lubricant 1, Reference 10, and lubricant 2, Reference 11

Gearbox Cover Modifications, Shrouds, and Mist Delivery

The original gearbox cover did not drain as well as needed 

for conducting this type of test. The flat-bottomed, gravity 

drained test gear cover allowed extra lubricant to stay within 

the vicinity of the rotating gears. The cover was changed and 

the residual lubricant in the testing zone was reduced.

Another modification to the test facility included the 

addition of shrouds. Several designs were fabricated and tested 

until the present system evolved. The final arrangement is 

shown in Figure 4. This shrouding arrangement, with a high 

temperature glass cover, permitted test observation.

Mist Delivery System

Three different commercially available mist systems were 

used during testing. All three provided an acceptable mist 

during operation. The control over the amount of lubricant per 

cubic foot of air was an issue as the need to adjust this amount 

was important to our test program. The minimum flow rate to 

achieve long-term operation in the loss of primary lubrication 

mode was dependent on the amount of lubricant being 

utilized. For this test system, the minimum level for the gears 

operating at 10000 rpm and approximately 70 N*m (630 

in.*lb) torque was approximately 0.3 ml/min (see Table 2(b)).

Flow rates less than this amount often resulted in failure of the 

components prior to 30 minute.

Speed, Load, and Liquid Lubricants

For most tests the speed was set to the maximum for the 

facility (10000 rpm). However, several tests were run at 

5000 rpm and different load levels. Tests ran with speed and 

load variation also experienced failure if emergency lubricant 

flow was too low or non-existent. Also, two different 

lubricants were used as vapor mist lubricants. Most of the tests 

used MIL-L-87354 (Ref. 8). Several tests were run using 

another high temperature lubricant (Ref. 9). No clear 

advantage was seen between the two lubricants tested. 1

Figure 7—Loss of lubrication data from test that failed after 

6 minute.

Example of Loss of Lubricant, Air-Oil Mist Tests

As an example of using a mist system, two tests will now be 

described. In one test the system failed after 6 minute of 

operation. The test data is shown in Figure 7. The flow rate of 

lubricant misted was 0.167 ml/min (Test no. 38, Table 2(b)). 

This test was halted as the temperature started to exponentially 

increase and the gears ended up operating such that a large 

amount of metal-to-metal contact was apparent. A photograph 

taken from a video of the test is shown in Figure 8. 

In the second test (Test no. 37, Table 2(b)) the mist 

lubricant rate was increased to 0.67 ml/min. In this test no 

failure resulted and the temperature reached a new steady state 

after the initial increase at the time when the primary 

lubrication system was shut down. The test results are shown 

in Figure 9. The test was ended after 1 hr of operation in this 

mode of lubrication and it is assumed that it would continue 

operation in this mode for some time, as evidenced by the 

temperature plots.
NASA/TM—2011-217106 7

Figure 8.—Photograph of gears in action during final seconds of operation.

Figure 9.—Loss of lubrication data from a test that was 

terminated after 1 hr of successful operation.

Grease Tests

As an alternative approach to improve gear performance, 

several tests were conducted to determine if a grease system 

might be better than using mist. It was thought that if the 

grease was injected in the correct location, operation in these 

extremely difficult situations might be better. A limited 

number of tests were run (six in total). The results are shown 

in Table 3. At first a completely closed gear shroud 

arrangement was tested as shown in Figures 10 and 11 (before 

and during the test respectfully). Test no. 1 from Table 3 was 

conducted to determine how well the gear would operate at 

high speed and at approximate 60 percent torque in a closed 

system. Test no. 2 indicated that higher speed and only a given 

amount of grease was not sufficient as the test failed at 

9 minute. The grease used in Tests 1 to 5 was hydrocarbonbased grease (Ref. 10). Test 6 used high-temperature, 

perfluoropolyether- (PFPE) based grease (Ref. 11). For tests 3 

and 4 grease was injected into a closed system after an initial 

amount was used prior to starting the test.

Figure 10.—Grease test—fully shrouded test before operation.

Figure 11.—Fully shrouded grease test just prior to 

shutdown (strobed photo).
NASA/TM—2011-217106 8

Tests 5 and 6 were conducted in a similar fashion as the 

vapor mist tests described earlier (see Fig. 12). Both of these 

tests were conducted at 10000 rpm, but the load was 

~60 percent of the full load that the facility could develop. 

For the grease tests conducted to date, the injection system 

provided a predetermined amount of grease in 1 minute

intervals after loss of the primary lubrication system occurred.

Both grease types were run at the same operational conditions.

The hydro-carbon based grease operated for 27 minute after 

the primary lubrication system was shut down. The teflonbased grease lasted for 46 minute. The post-test gears are 

shown in Figure 13 for the teflon-based grease.

Analytical Simulation and Results

A two-dimensional heat transfer simulation, as described in 

Reference 2, was used to model the loss-of-lubrication

condition. In this prior work, a 2–D finite difference mesh was 

used to develop a modeling method for spiral bevel gears.

Elements of this simple model are used in this paper to 

describe how an emergency lubrication condition can be 

modeled.

The model used is shown in Figure 14. Here, a 2–D 

rectangular region is used to simulate the actual spur gear 

tooth. The basic gear dimensions and number of teeth, speed, 

and load conditions were applied. The tooth whole depth was 

used as the height and the chordal thickness was used as the 

simulated tooth width. The finite difference mesh is shown in 

Figure 15. Several points within the finite difference mesh will 

be used for monitoring the temperature reached during normal 

and emergency lubrication conditions.

In Figure 14, the gear tooth is shown with a position varying 

heat flux applied. The heat flux was found from an analysis of 

the sliding and rolling losses as a function of meshing position 

(Refs. 12 and 13). The heat transfer coefficients were found 

from flat plates in forced convection conditions as described in 

References 2 and 14. In Figure 15, five locations of the model 

were followed for the results to be presented.

The model was run to a steady state condition at which time 

conditions were modified to reflect the loss-of-lubrication

condition. It was assumed that the load, speed, and ambient 

conditions remained the same during the loss-of-lubrication

period. In the model, at a predetermined number of 

“revolutions” the heat flux imposed at the surface was 

increased by a set amount. In the real event, the friction 

coefficient is changing from the fully-flooded contact to a 

mixed elastohydrodynamic condition to one of a starved, 

metal-to-metal condition.

As an example, the actual gears (12-pitch 42 teeth) used in 

the tests were modeled using this analysis. The gear design

parameters are shown in Table 1. The analytical results are 

shown for the following conditions: 10000 rpm, 70 N*m 

(630 in*lb) torque. The analysis was assumed to be at a steady 

state condition by 50000 revolutions of the pinion 

(approximately 300 sec). At this point the friction coefficient 

was increased by a factor of 10. 

Figure 12.—Photograph of test configuration with 

grease injection system.

Figure 13.—High temperature grease test, post-test 

condition with shrouding removed.

Figure 14.—Two-dimensional simulation model.
NASA/TM—2011-217106 9

Figure 15.—Simulated spur gear tooth finite difference mesh.

Figure 16.—Steady state temperatures until the heat flux was

increased 10X at 300 sec.

Figure 17.—Transient condition during simulated loss of 

lubrication conditions.

As shown in Figure 16, the temperature of the tooth 

increases rather quickly. Since the tooth pitch is rather fine, 

the difference in temperature at the five locations shown in 

Figure 15 is rather small during the loss-of-lubrication event 

or during normal operation. If during the loss-of-lubrication

period the time scale is changed to show three revolutions, the 

output is shown in Figure 17. The temperature is at its 

maximum at the surface the instant that the heat flux is 

imposed at the surface node. The cool down is due to the 

forced convection conditions for the rest of the tooth 

revolution.

This modeling technique can help with scaling the 

requirements for actual aviation applications. Enhancements to 

the modeling technique to improve its accuracy would allow it 

to then be used on other systems during the design stage.

Conclusions

Based on the results of the testing and analytical simulation 

described in this paper the following conclusions can be 

drawn:

1. An air-oil mist system was implemented in a simulated 

aerospace configuration such that loss-of-lubrication due 

to primary lubrication system failure was extended 

beyond the current 30-minute aircraft requirement.

Running tests without any emergency lubrication system 

in a shrouded gearbox led to failure within several 

minutes. 

2. Gear material and gear backlash may have some benefit 

in increasing loss-of-lubrication behavior, but this would 

need further verification through additional testing.

3. Grease injection was demonstrated to be a viable 

emergency lubrication system for our test facility. 

However this type of emergency system will require 

greater evolution to determine if it can be utilized in an 

aerospace environment.

4. A model has been developed that can provide some 

insight into loss-of-lubrication behavior. An analysis 

methodology is necessary to be able to scale test data 

collected to a high-speed main transmission system as 

found in rotorcraft.

References

1. ADS-50-PRF, “Aeronautical Design Standard, Rotorcraft 

Propulsion Performance and Qualification Requirements and 

Guidelines,” U.S. Army Aviation Troop Command, April 1996.

2. Handschuh, R., “Thermal Behavior of Spiral Bevel Gears,”

NASA TM–106518, ARL–TR–403, January 1995.

3. Morales, W. and Handschuh, R., “A Preliminary Study on the 

Vapor/Mist Phase Lubrication of a Spur Gearbox,” NASA TM1999-208833, February 1999.

4. Morales, W., Handschuh, R., and Krantz, T., “Feasibility Study 

of Vapor-Mist Phase Reaction Lubrication Using a Thioether 

Liquid,” NASA/TM—2007-215035, December 2007.
NASA/TM—2011-217106 10

5. Oswald, F., “Mechanical Components Branch Test Facilities and 

Capabilities,” NASA/TM—2004-212722, January 2004

6. Krantz, T. and Kahraman, A., “An Experimental Investigation of 

the Influence of the Lubricant Viscosity and Additives on Gear 

Wear,” NASA/TM—2005-213956, ARL–TR–3126, October 

2005.

7. Krantz, T., “The Influence of Roughness on Gear Surface 

Fatigue,” NASA/TM—2005-213958, October 2005.

8. Aeroshell Turbine Engine Oil 555, Product Data Sheet, Shell Oil 

Company, May 2008.

9. Santovac Fluids, LLC, MS-293 Advanced High Temperature 

Fluid Material Data Sheet.

10. Exxon Mobil, Material Data Sheet, Mobil Grease 28, March 

2006.

11. Dupont Krytox High Temperature (XHT) Grease, Material Data 

Sheet. 

12. Anderson, N., and Lowenthal, S., “Spur Gear System Efficiency 

at Part and Full Load,” NASA TP–1622, 

TR–79-46, February, 1980.

13. Hamrock, B., “Lubrication of Machine Elements,” NASA RP–

1126, August 1984.

14. Holman, J.: Heat Transfer, Fourth Edition, McGraw-Hill Book 

Company, 1976.

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4. TITLE AND SUBTITLE

Gear Mesh Loss-of-Lubrication Experiments and Analytical Simulation 

5a. CONTRACT NUMBER

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6. AUTHOR(S)

Handschuh, Robert, F.; Polly, Joseph; Morales, Wilfredo 

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WBS 877868.02.07.03.01.01.01 

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National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

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13. SUPPLEMENTARY NOTES

14. ABSTRACT

An experimental program to determine the loss-of-lubrication (LOL) characteristics of spur gears in an aerospace simulation test facility has 

been completed. Tests were conducted using two different emergency lubricant types: (1) an oil mist system (two different misted 

lubricants) and (2) a grease injection system (two different grease types). Tests were conducted using a NASA Glenn test facility normally 

used for conducting contact fatigue. Tests were run at rotational speeds up to 10000 rpm using two different gear designs and two different 

gear materials. For the tests conducted using an air-oil misting system, a minimum lubricant injection rate was determined to permit the gear 

mesh to operate without failure for at least 1 hr. The tests allowed an elevated steady state temperature to be established. A basic 2-D heat 

transfer simulation has been developed to investigate temperatures of a simulated gear as a function of frictional behavior. The friction (heat 

generation source) between the meshing surfaces is related to the position in the meshing cycle, the load applied, and the amount of 

lubricant in the contact. Experimental conditions will be compared to those from the 2-D simulation.

15. SUBJECT TERMS

Gears; Transmissions 

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