Paula J. Dempsey

Glenn Research Center, Cleveland, Ohio

Investigation of Sideband Index Response to

Prototype Gear Tooth Damage

NASA/TM—2013-216610

November 2013
NASA STI Program . . . in Profi le

Since its founding, NASA has been dedicated to the 

advancement of aeronautics and space science. The 

NASA Scientifi c and Technical Information (STI) 

program plays a key part in helping NASA maintain 

this important role.

The NASA STI Program operates under the auspices 

of the Agency Chief Information Offi cer. It collects, 

organizes, provides for archiving, and disseminates 

NASA’s STI. The NASA STI program provides access 

to the NASA Aeronautics and Space Database and 

its public interface, the NASA Technical Reports 

Server, thus providing one of the largest collections 

of aeronautical and space science STI in the world. 

Results are published in both non-NASA channels 

and by NASA in the NASA STI Report Series, which 

includes the following report types:

• TECHNICAL PUBLICATION. Reports of 

completed research or a major signifi cant phase 

of research that present the results of NASA 

programs and include extensive data or theoretical 

analysis. Includes compilations of signifi cant 

scientifi c and technical data and information 

deemed to be of continuing reference value. 

NASA counterpart of peer-reviewed formal 

professional papers but has less stringent 

limitations on manuscript length and extent of 

graphic presentations.

• TECHNICAL MEMORANDUM. Scientifi c 

and technical fi ndings that are preliminary or 

of specialized interest, e.g., quick release 

reports, working papers, and bibliographies that 

contain minimal annotation. Does not contain 

extensive analysis.

• CONTRACTOR REPORT. Scientifi c and 

technical fi ndings by NASA-sponsored 

contractors and grantees.

• CONFERENCE PUBLICATION. Collected 

papers from scientifi c and technical 

conferences, symposia, seminars, or other 

meetings sponsored or cosponsored by NASA.

• SPECIAL PUBLICATION. Scientifi c, 

technical, or historical information from 

NASA programs, projects, and missions, often 

concerned with subjects having substantial 

public interest.

• TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientifi c and 

technical material pertinent to NASA’s mission.

Specialized services also include creating custom 

thesauri, building customized databases, organizing 

and publishing research results.

For more information about the NASA STI 

program, see the following:

• Access the NASA STI program home page at 

http://www.sti.nasa.gov

• E-mail your question to help@sti.nasa.gov

• Fax your question to the NASA STI 

Information Desk at 443–757–5803

• Phone the NASA STI Information Desk at

 443–757–5802

• Write to:

 STI Information Desk

NASA Center for AeroSpace Information

 7115 Standard Drive

 Hanover, MD 21076–1320
Paula J. Dempsey

Glenn Research Center, Cleveland, Ohio

Investigation of Sideband Index Response to

Prototype Gear Tooth Damage

NASA/TM—2013-216610

November 2013

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
Acknowledgments

The author would like to thank the NASA Rotary Wing Project and Traci Stadtmueller and Paul Swindell of the FAA Technical 

Center for their assistance and support of this work.

Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5301 Shawnee Road

Alexandria, VA 22312

Available electronically at http://www.sti.nasa.gov

Trade names and trademarks are used in this report for identifi cation 

only. Their usage does not constitute an offi cial endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

This work was sponsored by the Fundamental Aeronautics Program 

at the NASA Glenn Research Center.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2013-216610 1 

Investigation of Sideband Index Response to 

Prototype Gear Tooth Damage 

Paula J. Dempsey 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

The objective of this analysis was to evaluate the ability of gear condition indicators (CI) to detect 

contact fatigue damage on spiral bevel gear teeth. Tests were performed in the NASA Glenn Spiral Bevel 

Gear Fatigue Rig on eight prototype gear sets (pinion/gear). Damage was initiated and progressed on the 

gear and pinion teeth. Vibration data was measured during damage progression at varying torque values 

while varying damage modes to the gear teeth were observed and documented with inspection photos. 

Sideband indexes (SI) and root mean square (RMS) CIs were calculated from the time synchronous 

averaged vibration data. Results found that both CIs respond differently to varying torque levels, damage 

levels and damage modes. 

Background 

Helicopter transmission health is important because helicopters depend on the power train for 

transmission of torque required for lift and flight maneuvering. Health Usage Monitoring Systems 

(HUMS) capable of predicting impending transmission component failure for “on-condition” 

maintenance have the potential to decrease operating and maintenance costs and increase safety and 

aircraft availability. “On-condition” refers to replacing time-based maintenance intervals with planned 

maintenance when HUMS “condition indicators” indicate decreased system performance. These HUMS 

“condition indicators” (CI) are typically vibration signatures or trends that develop when a fault occurs on 

a component and interacts with its operational environment. The CI must be correlated to a known failure 

mode to reliably detect the health of the system. 

A “seeded fault test,” in support of a rotorcraft condition based maintenance program (CBM), is an 

experiment in which a component is tested with a known fault while health monitoring data is collected. 

These tests are performed at operating conditions comparable to operating conditions the component 

would be exposed to while installed on the aircraft. Performance of seeded fault tests is one method used 

to provide evidence that a HUMS can replace current maintenance practices required for “on-condition” 

maintenance. 

Previous analyses were performed on rotorcraft spiral bevel gear condition indicator performance in 

support of the U.S. Army’s Condition-Based Maintenance (CBM) program (Refs. 1 and 2). CI performance was evaluated using helicopter datasets recorded when damage occurred on spiral bevel gear 

(pinion/gear) teeth. The type of damage was also tied to available Army Tear-Down Analyses in which 

tooth damage was documented through descriptions and photographs. The CI referred to as SI performed 

the best at detecting contact fatigue failure modes. 

The objective of this analysis was to gain a better understanding why gear vibration based CI trend 

with damage under some conditions and poorly for others. The focused objective was to evaluate the 

ability of the gear CI, sideband index, to detect contact fatigue damage on spiral bevel gear teeth of 

prototype gears. A second objective was to study the trends of the RMS CI as a function of the condition 

of the gears and operating conditions of the test rig. A third objective was to use the results of these tests 

to define analyses to be applied to tests of the gear final design. Tests were performed in the 

 
NASA/TM—2013-216610 2 

NASA Glenn Spiral Bevel Gear Fatigue Rig. The eight gear sets (pinion/gear) tested during four tests and 

evaluated within this analysis were prototypes of 42 newly designed spiral bevel gears. The results of 

these initial tests will be used to define analysis methods for the remaining 42 tests. 

Test Facility 

Tests were performed in the Spiral Bevel Gear Test Rig at NASA Glenn Research Center. A detailed 

description of this test facility can be found in References 3 and 4. The Spiral Bevel Gear Fatigue Rig is 

illustrated in Figure 1. In addition to developing gear health monitoring tools, the test facility has been 

used to study the effects of gear material, gear tooth design, and lubrication on the fatigue strength of 

gears. Two sets of spiral bevel gears are installed in the test rig and tested simultaneously. Facing the 

gearboxes per Figure 1, the left gear set (pinion/gear) is referenced as left and the right gear set 

(pinion/gear) is referenced as right within the paper. 

Figure 2 shows the cross-sectional view of the rig. The facility operates in a closed-loop arrangement 

where the load is locked into the loop via a split shaft and a thrust piston on the slave side of the rig. This 

forces a helical gear into mesh per Figure 2. Rotation is obtained using a drive motor connected through 

v-belts to the helical gear. The spiral bevel gears on the left side operate where the pinion drives the gear. 

The right side of the facility acts as a speed increaser where the gear drives the pinion. The concave side 

of the pinion is always in contact with the convex side of the gear on both the left and right side of the 

gearbox. Load and speed are monitored by torque and speed sensors. 

Data Acquisition and Instrumentation 

Vibration data was collected using accelerometers mounted on the left and right housing of the test 

rig. Further studies, outside the scope of this paper, are underway relating transfer paths between the gear 

mesh and accelerometer locations (Ref. 5). Data was collected at sample rates that provided sufficient 

vibration data for calculating time synchronous averaged data (TSA). TSA refers to techniques for 

averaging vibration signals over several revolutions of the shaft, in the time domain, to improve signal-tonoise ratio (Ref. 6). Using a once per revolution signal, the vibration signal is interpolated into a fixed 

number of points per shaft revolution. Signals synchronous with the shaft speed, will intensify relative to 

the non-periodic signals. 

Figure 1.—Spiral bevel gear fatigue rig. Figure 2.—Cross section of spiral bevel gear fatigue rig. 
NASA/TM—2013-216610 3 

Since helicopter gears generate vibration signals synchronous with speed, all helicopter gear 

condition indicators are calculated from TSA data. Gear vibration condition indicators are indexes 

calculated from vibration signal information. Many are based on statistical measurements of vibration 

energy. Signal processing techniques used to extract useful information to calculate a gear CI from the 

vibration signal are discussed in detail in Reference 7. Some gear CI’s are calculated from the time 

domain TSA signal, such as RMS. Some are calculated from the TSA converted to the frequency domain, 

such as SI. Some convert the TSA signal to the frequency domain, filter specific frequencies, convert it 

back to the time domain, then calculate a statistical parameter from this data with examples shown in 

References 6 to 8. 

Figure 3 illustrates the information used to calculate the TSA for the right gear and pinion. Using the 

sample rate of 200 KHz for 1 sec duration and the speed of both shafts, the number of TSA averages for 

each acquisition is determined. Each average consists of 1 revolution of the shaft. Each average is made 

up of the number of linearly interpolated points rounded down to a power of two. A power of two is used 

because it eases the future use of the Fast Fourier Transform (FFT) to transform the time domain signal 

for the time domain to the frequency domain. Per Figure 3, the top figure displays the right accelerometer 

data sampled for one second at 200,000 samples/second. The green and blue lines are pulses from the 

gear and pinion 1/rev signal measured for each shaft rotation during this one second period. Only the right 

accelerometer is plotted in the next figure with an expanded y-axis scale. The two lowest plots are the 

TSA signal calculated from the 1/rev and vibration data for the right gear and pinion. Pulses from the 41 

tooth gear and the 19 tooth pinion can easily be seen within these two plots. 

Figure 3.—Information used to calculate TSA. 

 
NASA/TM—2013-216610 4 

During these tests, three data acquisition systems were used. Vibration, oil debris, torque and speed 

data were collected once every minute with the NASA Glenn research data acquisition system, referred to 

as Mechanical Diagnostic System Software (MDSS). Vibration and speed data were collected from a 

second set of sensors with a helicopter Health Usage Monitoring System referred to as Modern Signal 

Processing Unit (MSPU). Operational parameters were collected with a third system referred to as 

Daytronic. These operational parameters included torque, speed, right and left gearbox oil inlet and outlet 

temperatures and oil system pressures. 

Turbine engine oil that meets DOD-L-87354 specifications is used in the test rig. Both gear sets are 

lubricated with oil jets pumped from an oil reservoir. The lubrication from the gearbox then exits the 

gearbox and flows through an inductance type in-line oil debris sensor then past a magnetic chip detector. 

A strainer and a three micron filter are located downstream of the oil debris (OD) sensor to capture any 

debris before returning to the sensor and gearbox. 

A non-contact rotary transformer shaft mounted torque sensor was used to measure torque during 

testing. Thermocouples were used to measure inlet and outlet oil temperatures. The inductance type oil 

debris sensor was used to measure the debris generated during fatigue damage to the gear teeth. For the 

sensor, the MDSS records the particle counts measured by the oil debris sensor, their approximate size 

and an approximate mass. The sensor measures the number of particles and their approximate size based 

on user defined particle size ranges or bins. Based on the bin configuration, the average particle size for 

each bin is used to calculate the cumulative mass for the experiment by assuming the average particle size 

as a diameter spherical in shape and multiplying it by the density of steel. Chip indications from the chip 

detector, when the gap was closed with debris, were also measured. 

For the MDSS system, accelerometers were installed on the right and left side of the test rig housing. 

Accelerometer frequency range is 0.7 to 20 KHz with a resonant frequency of 70 KHz. The MDSS 

accelerometers were mounted on the housing, radially and vertically with respect to the pinion, as shown 

in Figure 4. Facing the gearboxes, the left gear set (pinion/gear) and right gear set (pinion/gear) 

accelerometers were referenced as such in the MDSS system. Speed was measured with optical 

tachometers mounted on the left pinion shaft and right gear shaft to produce a separate once-per-rev tach 

pulse for the pinion and gears. Time synchronous averaging of the vibration data collected from the left 

and right accelerometer is performed in the MDSS system for the pinions via the pinion tach pulse and the 

gears via the gear tach pulse. 

For the MSPU system, accelerometers are also installed on the right and left side of the test rig. 

Accelerometer frequency range is 0.5 to 5 KHz with a resonant frequency of 26 KHz. A magnetic 

tachometer is installed on the right pinion and measures pinion pulses per tooth pass. This is used to 

calculate the TSA for both the pinion and the gear. The gear ratio is used to process the data at the correct 

speed for the gear. 

For the first test, the MSPU accelerometers were mounted on the housing, axially and horizontally 

with respect to the pinion. At completion of the test it was determined that this location had a poor 

response to the gear mesh vibration signatures through analysis of the TSA data. For the remaining three 

tests, the accelerometers were mounted on the housing, in close proximity to the MDSS accelerometers, 

radially and vertically with respect to the pinion, as shown in Figure 4. The TSA data had a good response 

to the gear mesh vibration and correlated well with the MDSS data at this location. The thrust and 

tangential forces at the mesh of the spiral bevel gear design were also calculated from the gear set 

operating conditions and found the tangential force in the radial direction significantly larger than the 

thrust force in the radial direction indicating a larger amplitude in the radial vertical orientation. This is 

illustrated in Figure 4. 
NASA/TM—2013-216610 5 

Figure 4.—Location of accelerometers. 
NASA/TM—2013-216610 6 

Test Gear Sets 

The gears tested were prototypes of gears designed and specified to represent a rotorcraft drive 

system gear mesh and fit within the space available in the spiral bevel gear fatigue rig gearboxes. The 

gears were made from a steel alloy CEVM 9310, carburized, hardened and ground. However, the eight 

gear sets tested differed from the final design in that they were not shot peened and the surface roughness 

varied. The surface roughness on the pinions tested ranged from 11 to 15 in. and the surface roughness 

on the gears tested ranged from 26 to 35 in. In addition, two of the sets tested, referred to as test 1, had 

pinion teeth slightly thicker than the final design due to incorrectly performing the final grind on the sets 

per the soft tooth finish. The other six sets tested also differed from the final design in that copper plating 

used for masking parts of the gear during carburization was not removed from the edge of the gear teeth 

and the edges were not broken to design specifications. 

The prototype gear sets tested have 6.4 in. diametral pitch, 20° pressure angle, 25° spiral angle, 

0.94 in. face width and 2.15 gear ratio. The gears have 41 teeth and the pinions have 19 teeth. The test 

gears were designed to operate at a gear speed of 3500 rpm and torque of 8000 in.-lbs, pinion speed of 

7553 rpm and torque of 3707 in.-lbs and 240 to 265 F inlet oil temperatures with an American Gear 

Manufacturers Association (AGMA) calculated contact stress of 237 ksi. 

Test Description 

For this study, eight gear sets were tested at a gear speed of 3500 rpm and pinion speed of 7553 rpm, 

except for the run-in of the test 1 gear set. Gear torque varied from 4000 to 8000 in.-lbs and pinion torque 

varied from 1854 to 3707 in.-lbs. At the start of each test, a run-in was performed for a minimum of 1 hr 

at 4000 in.-lbs gear torque/3500 rpm gear speed and 1854 in.-lbs pinion torque/7553 rpm pinion speed. 

Contact cycles accumulated at a rate of 210,000 per hour for the gear and 453,180 per hour for the pinion. 

At completion of the run-in, inspection photos were taken of the left and right gear and pinion teeth. 

Inspection photos were then taken throughout the test to document damage progression to the gear teeth. 

The failure modes to be investigated for this study were defined by class (contact fatigue), general 

mode (macro pitting) and degree (progressive) per American Gear Manufacturers Association (AGMA) 

standards for gear wear terminology outlined in Reference 9. However, additional failure modes were 

observed during each test. Using Reference 9 for tooth damage terminology, a numbering scheme per 

Reference 1 was developed to streamline the identification of gear damage. Table 1 illustrates this 

numbering scheme for the types of damage observed during these tests. Tables 2 to 5 summarize the 

observed failure modes observed on the gear teeth during each inspection interval. Note that the 3rd 

column in the tables labeled “MDSS Rdg (min)” is the time in operation of the rig in minutes. 

TABLE 1.—NUMBERING SCHEME FOR NOMENCLATURE 

OF GEAR FAILURE MODES (REF. 1) 

Class GeneralMode SpecificModeorDegree

2.0Scuffing 2.1Scuffing 2.1.1Mild

2.1.2Moderate

2.1.3Severe

4.0ContactFatigue 4.1SubcaseFatigue

4.2Micropitting

4.3Macropitting 4.3.1Initial

4.3.2Progressive

4.3.3Flake

4.3.4Spall

6.0Fracture 6.0Fracture
NASA/TM—2013-216610 7 

TABLE 2.—FAILURE MODES DURING TEST 1 

TABLE 3.—FAILURE MODES DURING TEST 2 

TABLE 4.—FAILURE MODES DURING TEST 3 

TABLE 5.—FAILURE MODES DURING TEST 4 

 

TestLWW9_RXX10 MDSS 

Date Rdg(Min) Torque GearLeft PinionLeft GearRight PinionRight

Start 12/14/2011 0 0 

Runin 12/14/2011 60 4000

Inspection 12/14/2011 186 4000

Inspection 12/14/2011 269 8000 4.2at,2.1.2at

Inspection 12/15/2012 553 8000 4.3.11t 4.2at 4.2at,2.1.2at

Inspection 12/20/2011 1862 8000 4.3.11t,4.3.41t,4.2at 4.2at,2.1.2at,6.0atet 4.2at,2.1.2at

Inspection 12/23/2011 4814 8000 4.3.43t 4.3.42t,4.2at 4.2at,2.1.2at,6.0atet 4.2at,2.1.2at*

Inspection 1/10/2012 6065 8000 4.3.45t,4.3.23t 4.3.42t,4.3.22t,4.2at 4.2at,4.3.1/4.3.419t,6.0atet 4.3.16t,4.3.2/4.3.43t*

Key:xt=numberofteeth;at=allteeth;et=edgesofteeth;*=addprecedingdamagetoinspectioninterval

MDSS 

Date Rdg(Min) Torque GearLeft PinionLeft GearRight PinionRight

Start 9/4/2012 0 0

Runin 9/4/2012 60 4000

Inspection 9/4/2012 108 4000

9/14/2012 202 4000

Inspection 9/14/2012 379 8000 6.0atet 4.22t 6.0atet,2.1.2at 4.2at,2.1.3at

9/18/2012 468 4000

Inspection 9/18/2012 559 8000 6.0atet 4.3.23t,4.3.42t 6.0atet,2.1.2at 4.2at,2.1.3at

9/19/2012 632 4000

Inspection 9/19/2012 662 8000 6.0atet 4.3.45t 6.0atet,2.1.2at 4.2at,2.1.3at

Key:xt=numberofteeth;at=allteeth;et=edgesofteeth

TestL0505R0606

MDSS 

Date Rdg(Min) Torque GearLeft PinionLeft GearRight PinionRight

Start 11/27/2012 0 4000

Runin 11/27/2012 69 4000

Inspection 11/27/2012 184 6000 6.0atet

11/28/2012 367 6000

Inspection 11/28/2012 520 8000 6.0atet 4.3.2at 6.0atet,2.1.2at 6.0atet,2.1.2at,4.3.41t

Inspection 11/29/2012 686 8000 6.0atet 4.3.2at,4.3.41t 6.0atet,2.1.2at 6.0atet,2.1.2at,4.3.45t,4.3.24t

Key:xt=numberofteeth;at=allteeth;et=edgesofteeth

TestL0701R0802

MDSS 

Date Rdg(Min) Torque GearLeft PinionLeft GearRight PinionRight

Start 12/4/2012 0 4000

Runin 12/4/2012 60 4000

Inspection12/5/2012 489 6000 6.0atet 6.0atet,2.1.2at 4.3.1at,2.1.2at

Inspection 12/6/2012 901 6000 6.0atet 6.0atet,4.3.1at 6.0atet,2.1.2at 4.3.1at,2.1.2at

Inspection 12/7/2012 1196 6000 6.0atet 6.0atet,4.3.1at 6.0atet,2.1.2at 4.3.1at,2.1.2at

Inspection 12/10/2012 1829 6000 6.0atet 6.0atet,4.3.1at 6.0atet,2.1.2at 4.3.1at,2.1.2at

Inspection 12/13/2012 4034 6000 6.0atet,4.3.45t,4.3.26t 6.0atet,4.3.1at 6.0atet,2.1.2at 4.3.1at,2.1.2at

Key:xt=numberofteeth;at=allteeth;et=edgesofteeth

TestL1103R1204
NASA/TM—2013-216610 8 

The tests ran until macro pitting/spalling (4.3.4) larger than one mm in diameter covered a significant 

area of two or more gear or pinion tooth surfaces. Definitions for pitting modes per Reference 9 are 

summarized as follows: 

 Initial—Pits less than 1 mm in diameter in localized areas removing high asperities. 

 Progressive—Pits in different shapes/sizes greater than 1 mm in diameter covering a large area of the 

tooth contact surface. 

 Flake—Pits that are shallow but cover large areas that consist of thin flakes. 

 Spalling—Progressive pitting where smaller pits combine to form irregular craters that cover an area 

of the tooth contact surface that exceeds progressive pitting. 

Since the focus for this analysis was CI performance when macro pitting/spalling was observed, this 

type of failure mode is highlighted in green in Tables 2 to 5. Other common failure modes observed for 

the four tests are also highlighted with the same color within each table. 

The reader should note that damage mode 6.0, fracture, was a failure mode observed due to the 

prototype gear design. In the prototype design, the edges of the teeth were not broken per design 

specifications and the copper masking was left on the edge of the teeth. This caused copper edges to 

fracture during testing. Since the oil debris sensor does not measure non-ferrous particles, this type of 

debris was not measured by the sensor. 

Due to the storage limitation of the MSPU system, data could only be recorded automatically every 

30 min during testing. Manual acquisitions were also performed periodically throughout the test. 

Sometimes, the system recorded the data for the pinion and did not record the data for the gear when 

manual acquisitions were performed due to storage and speed limitations. Since the timestamps and 

frequency of the data acquisition varied with both systems, the inspection intervals were used to correlate 

the time periods between both systems. Tables 6 to 9 list the MSPU reading that corresponds with the 

MDSS reading. Note the Index(in) refers to the pinion and the Index(out) refers to the gear. 

TABLE 6.—MSPU INDEXED TO MDSS FOR TEST 1 TABLE 7.—MSPU INDEXED TO MDSS FOR TEST 2 

 

TABLE 8.—MSPU INDEXED TO MDSS FOR TEST 3 TABLE 9.—MSPU INDEXED TO MDSS FOR TEST 4

 

LWW9_RXX10 MDSS

Date Rdg(Min) Index(in) Index(out) Torque

Start 12/14/2011 0 0

Runin 12/14/2011 60 1 1 4000

Inspection 12/14/2011 186 10 3 4000

Inspection 12/14/2011 269 17 10 8000

Inspection 12/15/2012 553 30 23 8000

Inspection 12/20/2011 1862 82 75 8000

Inspection 12/23/2011 4814 200 193 8000

Inspection 1/10/2012 6065 221 213 8000

MSPU MDSS

Date Rdg(Min) Index(in) Index(out) Torque

Start 9/4/2012 0 0

Runin 9/4/2012 60 10 10 4000

Inspection 9/4/2012 108 12 12 4000

9/14/2012 202 21 21 4000

Inspection 9/14/2012 379 32 32 8000

9/18/2012 468 40 40 4000

Inspection 9/18/2012 559 49 49 8000

9/19/2012 632 56 56 4000

Inspection 9/19/2012 662 59 59 8000

L0505R0606 MSPU
NASA/TM—2013-216610 9 

Analysis of Test Operational Conditions 

When detecting rotorcraft component damage, a data driven approach is traditionally used to identify 

damage within the transmission. Data from “healthy” transmission components are used to define healthy 

vibration signatures. Significant changes in these or signatures comparable to those historically measured 

on damaged components are used to indicate damage. A model based approach for assessment of CI 

response to damage has an advantage in that it does not require validation data from all types and modes 

of damage. Randall (Ref. 10) presented a model based on changes of the gear vibration signature caused 

by changes in the tooth profile caused by tooth wear or damage. He noted measuring gear mesh signatures 

at the same load due sensitivities of the signature to changes in the tooth profile caused by its deflection 

under load. To date, a model based approach has not been implemented. This is mainly due to the 

dynamic characteristics unique to each system, under varying operational conditions that can affect CI 

response (Ref. 11). 

Typically, within a helicopter HUMS system, the CI and operational data are acquired, stored, 

tracked, trended and monitored separately (Ref. 12). Limited work has been performed evaluating gear CI 

performance under varying load, speed and operational conditions (Refs. 13 to 17). Passing key 

information between both systems and integrating this information can improve the performance and 

reliability of both systems to indicate progression of damage and remaining time in operation. 

Operational parameters were collected during testing and are included within this discussion. Gear 

speed of 3500 rpm was maintained for each test. Torque was maintained at 3 levels: 4000, 6000, and 

8000 in.-lbs. Inlet oil temperatures ranged from 183 to 225 F, oil jet inlet temperatures ranged from 38 to 

79 psi. Often, the vibration signatures respond to significant changes in conditions. Although a complete 

data set of all the varying conditions was unavailable to statistically assess these differences a simple 

model will be applied to this dataset for future use when additional gear tests are completed. 

Table 10 provides a causal model that was presented in References 18 and 19 for use in the analysis 

of in-flight maneuvering effects on transmission vibration. Although our test rig does not simulate flight 

maneuvers, the framework can be applied to understand the affects inputs have on the measured outputs 

based on the internal response of the test gearbox to its inputs. These inputs are the test conditions that 

include torque, speed, oil temperatures and oil jet pressures. The internal response changes with these 

conditions when gear or pinion teeth are undamaged and is measured with the output sensors. When tooth 

damage occurs, the internal response will be affected causing changes in the output response. This 

response must differ from the undamaged gear output response and be reflected in the condition indicator. 

TABLE 10.—MODEL FOR CAUSAL RELATIONSHIPS (REFS. 18 AND 19) 
NASA/TM—2013-216610 10 

Several condition indicators exist to detect gear tooth damage. The referenced analysis (Refs. 18 and 

19) used the time domain CI, RMS of the time synchronous averaged vibration data (a), as the measured 

output of the internal response. 

   n

i i a

n 1

1 2 RMS (1) 

The RMS data from the left and right pinion and gear calculated for the four tests the will be plotted 

and discussed in conjunction with the sideband index in the following sections of this paper. 

Note that the accelerometers installed on the left side of the test rig were used to measure vibration 

for the pinion and gear installed on the left side of the gearbox. The accelerometers installed on the right 

side of the gearbox were used to measure vibration for the pinion and gear installed on the right side of 

the gearbox. The vibration data from the left accelerometer and the 1/rev signal on the pinion shaft were 

used to calculate left pinion CIs. The vibration data from the left accelerometer and the 1/rev signal on the 

gear shaft were used to calculate left gear CIs. The vibration data from the right accelerometer and the 

1/rev signal on the pinion shaft were used to calculate right pinion CIs. The vibration data from the right

accelerometer and the 1/rev signal on the gear shaft were used to calculate right gear CIs. 

As mentioned in the previous section, sideband index methods were studied in this work for use in 

detecting surface fatigue damage to spiral bevel gear teeth. Sideband index methods were selected for use 

in this study due to success at detecting damage to spiral bevel gear teeth in several helicopters (Refs. 1 

and 2) SI is a frequency domain based CI. The CI value is an average value of sideband amplitudes about 

the fundamental gear mesh frequency. The number of sidebands included in the calculation of the 

sideband CI can vary with different health monitoring systems. 

All gears generate a dominant gear mesh (GM) frequency in the vibration signature due to each tooth 

impacts against the gear it is driving as the pinion and gear mesh. The gear (or pinion) mesh frequency is 

equal to the number of gear teeth multiplied by its speed. Gear sets also produce pairs of equally spaced n 

sidebands on either side of the gear mesh equal to (n#teeth n) multiplied by speed. Certain types of gear 

tooth damage, such as pitting on several teeth, can affect the amplitude of the sidebands. Increases in 

sideband amplitudes are often used to calculate a gear condition indicator. 

Condition indicator (CI) SI was calculated for the left gear, left pinion, right gear and right pinion. 

For this CI, the time synchronous average data is converted to the frequency domain, then the amplitude 

of the average sidebands on either side of the gear mesh are trended. The MDSS system averages the 

amplitude of 1 sideband on either side of the gear or pinion mesh to calculate its SI CI. The MSPU 

system averages the amplitude of 3 sidebands on either side of the gear or pinion mesh to calculate its SI 

CI. For example, the pinion gear mesh is 19 time the rpm of the pinion. The MSPU system averages the 

amplitude of 3 sidebands (16	rpm, 17	rpm, 18	rpm, 20	rpm, 21	rpm, and 22	rpm) to calculate SI.

Figure 5 illustrates the steps required to calculate RMS and SI for each reading. RMS uses the 

interpolated TSA data per Figure 3 to calculate the RMS of the TSA. SI uses the TSA to calculate an 

FFT. Then the amplitudes of the FFT on either side of the gear mesh (GM) are used to calculate SI 

indexes. Note that the x-axis of the plot showing the FFT of the right gear is in shaft orders or multiples 

of shaft speed. For example, since the gear has 41 teeth, the gear mesh frequency (teeth x rpm) shows up 

at 41 shaft orders. 

 
NASA/TM—2013-216610 11 

Figure 5.—RMS and SI calculations. 

Experimental Data 

Summaries of each test will be discussed in the following sections that include plots of debris 

generated and gear torque measured during each test. Reference 20 contains a detailed analysis of the oil 

debris generated and operational parameters measured during these tests. Torque was measured in inchpounds and plotted in blue per the left y-axis. Debris generated was measured in milligrams and plotted in 

orange per the right y-axis. The x-axis was measured as the time of rig operation in minutes. The yellow 

triangles on the x-axis indicate the time when the gear and pinion teeth were inspected. During each test, 

RMS for the left and right pinion/gear set were plotted in volts. Multiplying the y-axis scale by 100 

converts volts to g’s. 

Sidebands were calculated and plotted in several different variations to determine if trends were 

observed with varying levels and types of tooth damage. The 3 individual sidebands for the left and right 

gear and pinion were calculated and plotted from vibration data collected on both the MDSS and MSPU 

systems. The average of 3 sidebands for the left and right gear and pinion were calculated and plotted 

from vibration data collected on both the MDSS and MSPU systems. The average of 1 sideband for the 

left and right gear and pinion were calculated and plotted from vibration data collected on both the MDSS 

and MSPU systems. The maximum 3 sideband for the left and right gear and pinion were also calculated 

and plotted from vibration data collected on both the MDSS and MSPU systems. 

Tables of mean and standard deviation values for individual sidebands for the left and right gear and 

pinion between inspection intervals and torque changes were also generated. Observations from the 

tabular and plotted data were included. Representative photos of gear and pinion teeth damage modes and 

their progression at the inspections intervals was provided in Appendix A. Plots of the MDSS and MSPU 

data of individual, average of 1 sideband, 3 sideband and maximum sideband will be included in 

Appendix B. Note that MSPU data will not be plotted for test 1 due to poor response of MSPU 

accelerometer for these tests. A summary of the operational data collected for each test averaged within 

each inspection period will be included in Appendix C. Only torque changes were plotted for this paper. 
NASA/TM—2013-216610 12 

Future study is warranted of the effect the other operational parameters listed in Appendix C have on CI 

response, but outside the scope of this paper. 

The purpose of plotting the data and generating the tables was to compare differences between 

sideband amplitudes for the gears, pinions, torque changes and failure modes. The hope going into this 

was that specific sidebands increased or decreased in values due to comparable operational and 

environmental conditions between tests. 

Test 1 

Figure 6 is a plot of debris generated and the torque during test 1. Figure 7 is a plot of RMS during 

test 1. Tooth damage photos for the gear and pinion during the inspection intervals can be found in 

Figures A.1.1 to A.1.5. 

For test 1, Figures A.1.1 to A.1.5 illustrate the progression of damage on the gear and pinion teeth. For 

the left pinion, macropitting was observed on one pinion tooth at reading 1862 and on two teeth at reading 

4814. For the left gear, macropitting was observed on three teeth at reading 4814 and five teeth at reading 

6065. Macropitting was also observed on the right gear and pinion at reading 6065, the end of the test. 

For test 1, per Figure 6, the rate of debris generation measured was 1.9 mg/hr at reading 1862, when 

spalling macropitting (4.3.4) was first observed on one left pinion tooth, although per Table 2, other types 

of damage occurred during this inspection interval on the right gear teeth. The rate decreased to 

0.4 mg/hr when macropitting was observed on all of the teeth. 

Figure 6.—Debris generated and torque during test 1. 
NASA/TM—2013-216610 13 

Figure 7.—RMS during test 1. 

Per Figure 7, RMS could not be used to isolate the pinion from the gear on the left and right side of 

the test rig. The left gear and pinion RMS values tracked each other very closely as did the right gear and 

pinion. Both responded to the restarts after inspections, but the right side was significantly more sensitive 

than the left. The left RMS values trended well with damage progression. 

Figures B.1.1, B.1.3, B.1.5, and B.1.7 are plots of the individual 3 sideband and the gear mesh for 

the 41 tooth gears and the 19 tooth pinions for left gear, right gear, left pinion, right pinion during the test. 

The left y-axis is scaled for the 3 sidebands. The right y-axis is scaled for the gear (Sig41) and pinion 

(SI19) meshes. The x-axis correlates to the time in operation of the test rig in minutes. The yellow 

triangles correlate to gear tooth inspections. 

Figures B.1.2, B.1.4, B.1.6, and B.1.8 are plots of the average 1 sidebands, average 3 sidebands 

and the maximum of the 3 sidebands for left gear, right gear, left pinion, right pinion during the test. The 

yellow triangles correlate to gear tooth inspections. 

Table 11 is a summary of the mean and standard deviation values for the individual sidebands 

between each inspection interval. The columns highlighted in blue are the gear and pinion meshes. The 

cells highlighted in red have the maximum values within that inspection interval. The cells highlighted in 

yellow have the next maximum values. The cells highlighted in green have the minimum values.
NASA/TM—2013-216610 14 

TABLE 11.—SUMMARY OF SIDEBANDS FOR TEST 1 

 

LWW9RXX10

LeftGearLeftGear

Torque Inspection SIgl38 SIgl39 SIgl40 SIgl41 SIgl42 SIgl43SIgl44 SIgl38 SIgl39 SIgl40 SIgl41 SIgl42 SIgl43SIgl44

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 1186 0.02 0.15 0.17 1.98 0.23 0.46 0.09 0.01 0.10 0.06 0.99 0.11 0.26 0.04

8000 187269 0.03 0.07 0.30 5.87 0.31 0.13 0.14 0.01 0.02 0.06 1.06 0.05 0.06 0.05

8000 270553 0.03 0.10 0.24 4.42 0.43 0.21 0.14 0.01 0.02 0.04 0.50 0.05 0.04 0.03

8000 5541862 0.06 0.05 0.11 4.00 0.19 0.16 0.07 0.01 0.02 0.02 0.18 0.09 0.04 0.02

8000 18634814 0.06 0.03 0.15 4.88 0.14 0.37 0.13 0.02 0.01 0.04 0.51 0.04 0.10 0.06

8000 48156065 0.05 0.05 0.06 6.61 0.26 0.63 0.18 0.01 0.02 0.03 0.36 0.08 0.07 0.03

LeftPinionLeftPinion

Torque Inspection SIpl16 SIpl17 SIpl18 SIpl19 SIpl20 SIpl21 SIpl22 SIpl16 SIpl17 SIpl18 SIpl19 SIpl20 SIpl21 SIpl22

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 1186 0.03 0.07 0.15 1.98 0.58 0.08 0.09 0.01 0.03 0.10 0.99 0.33 0.05 0.06

8000 187269 0.05 0.07 0.10 5.87 0.45 0.10 0.09 0.02 0.04 0.06 1.06 0.19 0.06 0.04

8000 270553 0.05 0.07 0.07 4.42 0.57 0.10 0.10 0.03 0.03 0.04 0.50 0.16 0.06 0.05

8000 5541862 0.08 0.07 0.08 4.00 0.42 0.12 0.09 0.04 0.03 0.04 0.18 0.12 0.05 0.04

8000 18634814 0.10 0.12 0.20 4.88 0.89 0.37 0.13 0.04 0.04 0.09 0.51 0.21 0.08 0.05

8000 48156065 0.15 0.22 0.32 6.61 1.30 0.44 0.12 0.04 0.04 0.05 0.36 0.14 0.08 0.05

LWW9RXX10

RightGearRightGear

Torque Inspection SIgr38 SIgr39 SIgr40 SIgr41 SIgr42 SIgr43SIgr44 SIgr38 SIgr39 SIgr40 SIgr41 SIgr42 SIgr43SIgr44

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 1186 0.06 0.24 0.10 3.03 0.23 0.17 0.10 0.02 0.14 0.03 1.37 0.06 0.11 0.04

8000 187269 0.05 0.06 0.11 4.38 0.14 0.09 0.10 0.02 0.03 0.03 0.88 0.06 0.03 0.04

8000 270553 0.04 0.08 0.08 3.59 0.11 0.11 0.13 0.01 0.03 0.03 0.32 0.04 0.03 0.03

8000 5541862 0.02 0.08 0.06 3.73 0.09 0.26 0.03 0.01 0.02 0.01 0.28 0.04 0.04 0.01

8000 18634814 0.06 0.06 0.12 6.12 0.31 0.46 0.08 0.01 0.02 0.03 0.61 0.11 0.06 0.05

8000 48156065 0.07 0.09 0.08 7.86 0.52 0.40 0.14 0.01 0.01 0.03 0.46 0.05 0.05 0.02

RightPinion

Torque Inspection SIpr16 SIpr17 SIpr18 SIpr19 SIpr20 SIpr21 SIpr22 SIpr16 SIpr17 SIpr18 SIpr19 SIpr20 SIpr21 SIpr22

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 1186 0.03 0.03 0.21 3.03 0.24 0.11 0.04 0.02 0.02 0.11 1.37 0.12 0.06 0.03

8000 187269 0.03 0.08 0.15 4.38 0.22 0.12 0.05 0.01 0.03 0.04 0.88 0.09 0.07 0.02

8000 270553 0.04 0.07 0.10 3.59 0.31 0.11 0.14 0.02 0.02 0.03 0.32 0.08 0.04 0.05

8000 5541862 0.05 0.11 0.13 3.73 0.28 0.12 0.04 0.02 0.03 0.06 0.28 0.07 0.05 0.02

8000 18634814 0.07 0.15 0.39 6.12 0.64 0.29 0.09 0.03 0.02 0.07 0.61 0.06 0.10 0.03

8000 48156065 0.11 0.14 0.43 7.86 0.57 0.38 0.09 0.02 0.01 0.04 0.46 0.07 0.05 0.02

StandardDeviations

StandardDeviations

Means

Means

RightPinionNASA/TM—2013-216610 15 

A summary of the response of the individual sidebands to damage between each inspection interval is 

listed below: 

1. Left gear: 

a. The +2 sideband (SI43) had the largest value when damage was observed on the gear 

teeth. 

b. The +2 sideband (SI43) trended well after gear damage progressed. 

c. The +2 sideband (SI43) had the largest value at lower torque. 

d. The +1 sideband (SI42) had the largest value when no damage was observed on the gear 

teeth. 

e. The +1 sideband (SI42) trended after gear damage progressed. 

2. Left pinion: 

a. The +1 sideband (SI20) had the largest value throughout the test. 

b. The +1 sideband (SI20) trended well after gear damage progressed to more than one 

tooth. 

c. The +1 sideband (SI20) had the largest value at lower torque. 

3. Right gear: 

a. The +2 sideband (SI43) had the largest value when damage was observed on the gear 

teeth. 

b. The +2 sideband (SI43) trended well after gear damage progressed until reading 4814, 

then dropped below 1 sideband (SI42). 

c. The –2 sideband (SI39) and had the largest value at lower torque. 

d. The +1 sideband (SI42) trended after gear damage progressed. 

4. Right pinion: 

a. The +1 sideband (SI20) had the largest value throughout the test. 

b. The +1 sideband (SI20) trended well after pinion damage progressed, but dropped 

slightly after reading 4814. 

c. The –1 sideband (SI18) trended well after pinion damage progressed, but dropped 

slightly after reading 4814. 

d. The +2 sideband (SI21) trended well after pinion damage progressed, but dropped 

slightly after reading 4814. 

e. The +1 sideband (SI20) had the largest value at lower torque. 

A summary of the response of the average of 3 sidebands, the average of 1 sideband and the 

maximum of the 3 sidebands is listed below: 

1. Left gear: 

a. The maximum sideband trended well after gear damage began and progressed to several 

teeth. 

b. The average +1 sideband did not trend well to damage progression. 

c. The average +3 sideband trended after gear damage progressed. 

2. Left pinion: 

a. The maximum sideband trended well after gear damage progressed to more than one 

tooth. 

b. The average +1 sideband trended after gear damage progressed to more than one tooth. 

c. The average +3 sideband trended after gear damage progressed to more than one tooth. 

3. Right gear: 

a. The maximum sideband trended well when gear damage began and progressed to several 

teeth, but decreased slightly at the last inspection interval (4814–6065). 

b. The average 1 sideband trended after gear damage progressed, but decreased slightly at 

last inspection interval (4814–6065). 
NASA/TM—2013-216610 16 

c. The average 3 sideband trended after gear damage progressed, but decreased slightly at 

last inspection interval (4814–6065). 

4. Right pinion: 

a. The maximum sideband trended well when gear damage progressed to several teeth, but 

decreased slightly at the last inspection interval (4814–6065). 

b. The average 1 sideband trended after gear damage progressed, but decreased slightly at 

last inspection interval (4814–6065). 

Test 2 

Figure 8 is a plot of debris generated and the torque during test 2. Figure 9 is a plot of RMS during 

test 2. Tooth damage photos for the gear and pinion during the inspection intervals can be found in 

Figure A.2.1. 

Figure 8.—Debris generated and torque during test 2. 

Figure 9.—RMS during test 2. 
NASA/TM—2013-216610 17 

For test 2, Figure A.2.1 illustrates the progression of damage to five left pinion teeth. The other 

photos are representative pictures of one left gear tooth, on right gear tooth and one pinion tooth. The 

damage to these gears did not change after the inspection at reading 379. For the left pinion, no 

macropitting was observed on the pinion teeth at reading 379, 6.32 hours into the test. At reading 559, 

9.32 hours into the test, 4.3.4 was observed on two pinion teeth. At reading 662, 11.03 hours into the test, 

4.3.4 was observed on five teeth. 

For test 2, per Figure 8, the rate of debris generation measured was at 8.96 mg/hr when progressive 

macropitting (4.3.2) was first observed on several teeth. The rate decreased to 3.75 mg/hr when the torque 

dropped to 4000 in.-lb. The debris generated then increased from 3.75 to 27.69 mg/hr when torque 

increased from 4000 to 8000 in.-lb, and spalling macropitting (4.3.4) was observed on five gear teeth. 

Per Figure 9, RMS could not be used to isolate the pinion from the gear on the left and right side of 

the test rig. The left gear and pinion tracked each other very closely as did the right gear and pinion. Both 

responded to the restarts after inspections, but the right side was significantly more sensitive than the left. 

The left and right side RMS values did not trend well with damage progression due to the varying torque 

levels throughout the test. Both increased in value with increases in torque. 

Figures B.2.1, B.2.5, B.2.9, and B.2.13 are plots of the individual 3 sideband and the gear mesh for 

the 41 tooth gears and the 19 tooth pinions for left gear, right gear, left pinion, right pinion during the test 

from the MDSS. The left y-axis is scaled for the 3 sidebands. The right y-axis is scaled for the gear 

(Sig41) and pinion (SI19) meshes. The x-axis correlates to the time in operation of the test rig in minutes. 

The yellow triangles correlate to gear tooth inspections. 

Figures B.2.2, B.2.6, B.2.10, and B.2.14 are plots of the individual 3 sideband and the gear mesh for 

the 41 tooth gears and the 19 tooth pinions for left gear, right gear, left pinion, right pinion during the test 

from the MSPU. The left y-axis is scaled for the 3 sidebands. The right y-axis is scaled for the gear 

(Sig41) and pinion (SI19) meshes. The yellow triangles correlate to gear tooth inspections per Table 7. 

Figures B.2.3, B.2.7, B.2.11, and B.2.15 are plots of the average 1 sidebands, average 3 sidebands 

and the maximum of the 3 sidebands for left gear, right gear, left pinion, right pinion during the test 

from the MDSS. The yellow triangles correlate to gear tooth inspections. 

Figures B.2.4, B.2.8, B.2.12, and B.2.16 are plots of the average 1 sidebands, average 3 sidebands 

and the maximum of the 3 sidebands for left gear, right gear, left pinion, right pinion during the test 

from the MSPU. The yellow triangles correlate to gear tooth inspections per Table 7. 

Table 12 is a summary of the mean and standard deviation values for the individual sidebands 

between each inspection interval. The columns highlighted in blue are the gear and pinion meshes. The 

cells highlighted in red have the maximum values within that inspection interval. The cells highlighted in 

yellow have the next maximum values. The cells highlighted in green have the minimum values. 

For test 2, Figure A.2.1, in Appendix A, illustrates the progression of damage to five left pinion teeth. 

The other photos are representative pictures of one left gear tooth, on right gear tooth and one pinion 

tooth. The damage to these gears did not change after the initial inspection. For the left pinion, no 

macropitting was observed on the pinion teeth 6 hr into the test. Nine hours into the test, 4.3.4 was 

observed on two pinion teeth. Eleven hours into the test, 4.3.4 was observed on five teeth.
NASA/TM—2013-216610 18 

TABLE 12.—SUMMARY OF SIDEBANDS FOR TEST 2 

 

Torque Inspection SIgl38 SIgl39 SIgl40 SIgl41 SIgl42 SIgl43SIgl44 SIgl38 SIgl39 SIgl40 SIgl41 SIgl42 SIgl43SIgl44

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 1108 0.08 0.14 0.25 2.91 0.20 0.31 0.34 0.03 0.07 0.05 0.67 0.04 0.17 0.04

4000 109202 0.08 0.06 0.11 1.49 0.24 0.44 0.40 0.02 0.03 0.03 0.40 0.11 0.10 0.11

8000 203379 0.03 0.04 0.28 3.99 0.13 0.48 0.12 0.01 0.01 0.02 0.52 0.04 0.03 0.05

4000 380468 0.07 0.07 0.23 1.96 0.32 0.54 0.38 0.02 0.02 0.05 0.43 0.09 0.10 0.11

8000 469559 0.01 0.04 0.30 3.30 0.31 0.41 0.09 0.01 0.01 0.01 0.22 0.02 0.03 0.02

4000 560632 0.10 0.07 0.17 1.61 0.39 0.55 0.38 0.02 0.01 0.03 0.26 0.06 0.03 0.08

8000 633662 0.01 0.04 0.31 3.80 0.34 0.34 0.07 0.01 0.01 0.06 0.56 0.06 0.06 0.02

Torque Inspection SIpl16 SIpl17 SIpl18 SIpl19 SIpl20 SIpl21 SIpl22 SIpl16 SIpl17 SIpl18 SIpl19 SIpl20 SIpl21 SIpl22

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 1108 0.03 0.13 0.27 2.91 0.39 0.33 0.06 0.01 0.04 0.07 0.67 0.12 0.09 0.02

4000 109202 0.02 0.14 0.25 1.49 0.29 0.27 0.04 0.01 0.06 0.08 0.40 0.08 0.06 0.01

8000 203379 0.09 0.15 0.10 3.99 0.21 0.25 0.03 0.03 0.03 0.03 0.51 0.03 0.03 0.01

4000 380468 0.07 0.08 0.21 1.96 0.44 0.28 0.03 0.01 0.03 0.06 0.43 0.09 0.07 0.01

8000 469559 0.13 0.17 0.26 3.30 0.12 0.14 0.05 0.02 0.01 0.04 0.22 0.05 0.04 0.01

4000 560632 0.10 0.11 0.27 1.61 0.35 0.29 0.03 0.01 0.02 0.06 0.26 0.06 0.02 0.01

8000 633662 0.19 0.13 0.21 3.81 0.05 0.31 0.08 0.05 0.02 0.04 0.56 0.03 0.06 0.02

Torque Inspection SIgr38 SIgr39 SIgr40 SIgr41 SIgr42 SIgr43SIgr44 SIgr38 SIgr39 SIgr40 SIgr41 SIgr42 SIgr43SIgr44

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 1108 0.09 0.11 0.16 4.36 0.06 0.46 0.27 0.02 0.03 0.04 0.85 0.04 0.04 0.08

4000 109202 0.14 0.05 0.12 4.18 0.11 0.28 0.21 0.04 0.03 0.04 0.99 0.07 0.09 0.07

8000 203379 0.05 0.07 0.33 13.65 0.44 0.15 0.14 0.01 0.02 0.04 0.96 0.05 0.05 0.02

4000 380468 0.09 0.13 0.13 5.45 0.22 0.35 0.24 0.02 0.03 0.04 1.57 0.08 0.11 0.09

8000 469559 0.02 0.09 0.21 6.80 0.30 0.12 0.08 0.01 0.01 0.02 0.79 0.05 0.03 0.01

4000 560632 0.15 0.17 0.07 3.64 0.14 0.37 0.19 0.02 0.02 0.02 0.24 0.02 0.05 0.05

8000 633662 0.02 0.08 0.23 6.85 0.24 0.12 0.07 0.01 0.01 0.04 1.25 0.05 0.03 0.02

Torque Inspection SIpl16 SIpl17 SIpl18 SIpl19 SIpl20 SIpl21 SIpl22 SIpl16 SIpl17 SIpl18 SIpl19 SIpl20 SIpl21 SIpl22

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 1108 0.04 0.16 0.22 4.36 0.19 0.20 0.03 0.01 0.03 0.05 0.85 0.04 0.06 0.01

4000 109202 0.03 0.15 0.18 4.18 0.20 0.18 0.02 0.01 0.03 0.04 0.99 0.10 0.04 0.01

8000 203379 0.05 0.08 0.19 13.65 0.20 0.27 0.03 0.02 0.01 0.03 0.96 0.05 0.02 0.01

4000 380468 0.02 0.17 0.23 5.45 0.20 0.20 0.10 0.01 0.03 0.05 1.57 0.06 0.04 0.02

8000 469559 0.04 0.12 0.16 6.80 0.29 0.16 0.21 0.01 0.01 0.04 0.79 0.05 0.03 0.05

4000 560632 0.02 0.10 0.24 3.64 0.07 0.19 0.22 0.01 0.02 0.02 0.24 0.03 0.03 0.02

8000 633662 0.05 0.09 0.17 6.85 0.31 0.18 0.21 0.02 0.02 0.03 1.25 0.06 0.04 0.03

RightGearRightGear

RightPinion RightPinion

LeftPinion LeftPinion

L0505R0606 Means StandardDeviations

Means StandardDeviations

LeftGearLeftGear

L0505R0606
NASA/TM—2013-216610 19 

A summary of the response of the individual sidebands to damage between each inspection interval is 

listed below: 

1. Left gear: 

a. The +2 sideband (SI43) had the largest value when damage was observed on the gear 

teeth. 

b. After damage was observed, the +2 sideband (SI43) increased with lower torque and 

decreased with higher torques. 

c. The +3 sideband (SI44) had the largest value when no damage was observed on the gear 

teeth during run-in. 

d. After damage was observed, the following increased with lower torque and decreased 

with higher torques: –3 (SI38), –2 (SI39), +1(SI42), +2(SI43) and +3(SI44). 

e. After damage was observed, the following increased with higher torque and decreased 

with lower torques: –1 (SI40), and gear mesh (SI41). 

2. Left pinion: 

a. The +1 sideband (SI20) and +2 sidebands (SI21) had the largest values during the test, 

but both did not trend well with damage. 

b. After damage was observed, the following increased with lower torque and decreased 

with higher torques: + (SI20) and +2 (SI21) 

c. The following did not indicate trends with torque changes: –1 (SI18) and +2 (SI22) 

d. After damage was observed, the following increased with higher torque and decreased 

with lower torques: –3 (SI16), –2 (SI17) and gear mesh (SI19). 

e. If you separate the trends into torque bands, the only sideband that trended with damage 

at 8000 in.-lbs torque was –3 (SI16). 

3. Right gear: 

a. The +1 sideband (SI42) and +2 sidebands (SI43) had the largest values during the test, 

but both did not trend well with damage. 

b. After damage was observed, the following increased with lower torque and decreased 

with higher torques: –3 (SI38) and +2 (SI43) and +3 SI44. 

c. The following did not indicate trends torque changes: –2(SI39) 

d. After damage was observed, the following increased with higher torque and decreased 

with lower torques: –1(SI40), +1(SI42) and gear mesh (SI41). 

e. If you separate the trends into torque bands, no sideband trended with damage at 

8000 in.-lbs torque. 

4. Right pinion: 

a. The –1 sideband (SI18), +1 sideband (SI20) and +2 sideband (SI21) had the largest 

values during the test, but did not trend well with damage. 

b. After damage was observed, the following increased with lower torque and decreased 

with higher torques: –1 (SI18). 

c. The following did not indicate trends with torque changes: –2(SI17), +2 (SI21) and 

+3(SI22) 

d. After damage was observed, the following increased with higher torque and decreased 

with lower torques: –3 (SI16), +1 (SI20) and gear mesh (SI19). 

e. If you separate the trends into torque bands, the only sideband that trended with damage 

at 8000 in.-lbs torque was +1 (SI20). 

 
NASA/TM—2013-216610 20 

A summary of the response of the average of +3 sidebands, the average of +1 sideband and the 

maximum of the +3 sidebands is listed below: 

1. Left gear: 

a. The maximum sideband, average 1 sideband and 3 sideband did not trend well with 

damage. 

b. The maximum sideband and 3 sideband increased with lower torque and decreased with 

higher torques. 

c. The +1 sideband did not trend with torque changes 

2. Left pinion: 

a. The maximum sideband, average 1 sideband and 3 sideband did not trend well with 

damage. 

b. The maximum sideband, 1 sideband and 3 sideband increased with lower torque and 

decreased with higher torques. 

3. Right gear: 

a. The maximum sideband, average + sideband and 3 sideband did not trend well with 

damage. 

b. The 1 sideband and 3 sideband increased with lower torque and decreased with higher 

torques. 

c. The maximum sideband did not trend with torque changes 

4. Right pinion: 

a. The maximum sideband, average 1 sideband and 3 sideband did not trend well with 

damage. 

b. The maximum sideband, 1 sideband and 3 sideband increased with higher torques and 

decreased with lower torques. 

Test 3 

Figure 10 is a plot of debris generated and the torque during test 3. Figure 11 is a plot of RMS during 

test 3. Tooth damage photos for the gear and pinion during the inspection intervals can be found in 

Figure A.3.1 to A.3.2. 

For test 3, Figures A.3.1 and A.3.2 illustrate the progression of damage to five right and left pinion 

teeth. No macropitting was observed on the pinion teeth at reading 184, 3.07 hr into the test. At reading 

482, 8.67 hr into the test, a pit was observed on a right pinion tooth. Several more pits were observed at 

reading 686, 11.43 hr into the test on the right pinion teeth and one pit on a left pinion tooth. 

For test 3, per Figure 10, the rate of debris generation measured increased when torque increased 

from 6,000 to 8,000 in.-lb. For this test, the torque was not decreased when the macropitting was 

observed on the teeth. The 6.37 mg/hr rate of debris generation when spalling macropitting (4.3.4) was 

observed at 8,000 in.-lb was higher than the 3.75 mg/hr rate of debris generation when spalling 

macropitting (4.3.4) was observed at 4,000 in.-lb for test 2. 

Per Figure 11, RMS could not be used to isolate the pinion from the gear on the left and right side of 

the test rig. The left gear and pinion tracked each other very closely as did the right gear and pinion. Both 

responded to the restarts after inspections, but the right side was significantly more sensitive than the left. 

The left and right side RMS values did not trend well with damage progression due to the varying torque 

levels throughout the test. The right side RMS values decreased when the torque increased from 6000 to 

8000 in.-lbs. At 8000 in.-lbs, the right side showed a slight increasing trend with damage. 

 
NASA/TM—2013-216610 21 

Figure 10.—Debris generated and torque during test 3. 

Figure 11.—RMS during test 3. 

Figures B.3.1, B.3.5, B.3.9, and B.3.13 are plots of the individual 3 sideband and the gear mesh for 

the 41 tooth gears and the 19 tooth pinions for left gear, right gear, left pinion, right pinion during the test 

from the MDSS. The left y-axis is scaled for the 3 sidebands. The right y-axis is scaled for the gear 

(Sig41) and pinion (SI19) meshes. The x-axis correlates to the time in operation of the test rig in minutes. 

The yellow triangles correlate to gear tooth inspections. 

Figures B.3.2, B.3.6, B.3.10, and B.3.14 are plots of the individual 3 sideband and the gear mesh for 

the 41 tooth gears and the 19 tooth pinions for left gear, right gear, left pinion, right pinion during the test 

from the MSPU. The left y-axis is scaled for the 3 sidebands. The right y-axis is scaled for the gear 

(Sig41) and pinion (SI19) meshes. The yellow triangles correlate to gear tooth inspections per Table 8. 
NASA/TM—2013-216610 22 

Figures B.3.3, B.3.7, B.3.11, and B.3.15 are plots of the average 1 sidebands, average 3 sidebands 

and the maximum of the 3 sidebands for left gear, right gear, left pinion, right pinion during the test 

from the MDSS. The yellow triangles correlate to gear tooth inspections. 

Figures B.3.4, B.3.8, B.3.12, and B.3.16 are plots of the average 1 sidebands, average 3 sidebands 

and the maximum of the 3 sidebands for left gear, right gear, left pinion, right pinion during the test 

from the MSPU. The yellow triangles correlate to gear tooth inspections per Table 8. 

Table 13 is a summary of the mean and standard deviation values for the individual sidebands 

between each inspection interval. The columns highlighted in blue are the gear and pinion meshes. The 

cells highlighted in red have the maximum values within that inspection interval. The cells highlighted in 

yellow have the next maximum values. The cells highlighted in green have the minimum values. 

For test 3, Figures A.3.1 and A.3.2 in Appendix A, illustrate the progression of damage to six right 

and left pinion teeth. No macro-pitting was observed on the pinion teeth 3 hr into the test. Eight hours into 

the test, a pit was observed on a right pinion tooth. Several more pits were observed 11 hr into the test on 

the right pinion teeth and one pit on a left pinion tooth. 

TABLE 13.—SUMMARY OF SIDEBANDS FOR TEST 3 

 

Torque Inspection SIgl38 SIgl39 SIgl40 SIgl41 SIgl42 SIgl43SIgl44 SIgl38 SIgl39 SIgl40 SIgl41 SIgl42 SIgl43SIgl44

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 169 0.12 0.11 0.05 2.20 0.29 0.30 0.42 0.02 0.01 0.02 0.11 0.09 0.03 0.05

6000 70184 0.06 0.12 0.15 3.50 0.33 0.17 0.13 0.01 0.03 0.01 0.45 0.03 0.08 0.03

6000 185367 0.06 0.08 0.15 3.66 0.35 0.12 0.09 0.01 0.02 0.02 0.23 0.04 0.08 0.02

8000 368520 0.03 0.06 0.19 3.74 0.26 0.14 0.06 0.01 0.01 0.02 0.06 0.02 0.01 0.01

8000 521686 0.03 0.12 0.14 4.61 0.39 0.26 0.11 0.01 0.04 0.05 0.48 0.07 0.03 0.03

Torque Inspection SIpl16 SIpl17 SIpl18 SIpl19 SIpl20 SIpl21 SIpl22 SIpl16 SIpl17 SIpl18 SIpl19 SIpl20 SIpl21 SIpl22

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 169 0.01 0.10 0.15 2.20 0.22 0.28 0.04 0.01 0.01 0.06 0.11 0.05 0.03 0.01

6000 70184 0.06 0.12 0.16 3.50 0.08 0.33 0.05 0.02 0.02 0.02 0.45 0.03 0.06 0.01

6000 185367 0.06 0.15 0.23 3.66 0.08 0.34 0.06 0.01 0.02 0.02 0.23 0.01 0.04 0.01

8000 368520 0.07 0.05 0.26 3.74 0.28 0.29 0.03 0.02 0.02 0.02 0.06 0.05 0.04 0.01

8000 521686 0.09 0.07 0.22 4.61 0.49 0.30 0.05 0.02 0.02 0.03 0.48 0.06 0.04 0.02

Torque Inspection SIgr38 SIgr39 SIgr40 SIgr41 SIgr42 SIgr43SIgr44 SIgr38 SIgr39 SIgr40 SIgr41 SIgr42 SIgr43SIgr44

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 169 0.16 0.05 0.10 4.10 0.13 0.28 0.22 0.02 0.02 0.02 0.21 0.03 0.04 0.04

6000 70184 0.04 0.31 0.09 7.20 0.12 0.53 0.05 0.01 0.07 0.03 0.68 0.03 0.20 0.03

6000 185367 0.05 0.34 0.10 7.40 0.15 0.55 0.04 0.02 0.08 0.03 0.83 0.04 0.18 0.02

8000 368520 0.01 0.15 0.18 5.05 0.29 0.22 0.05 0.01 0.01 0.02 0.68 0.03 0.02 0.01

8000 521686 0.02 0.16 0.20 5.40 0.26 0.22 0.04 0.01 0.03 0.04 0.51 0.06 0.05 0.01

Torque Inspection SIpl16 SIpl17 SIpl18 SIpl19 SIpl20 SIpl21 SIpl22 SIpl16 SIpl17 SIpl18 SIpl19 SIpl20 SIpl21 SIpl22

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 169 0.02 0.05 0.15 4.10 0.47 0.09 0.08 0.01 0.01 0.03 0.21 0.02 0.02 0.03

6000 70184 0.04 0.13 0.13 7.20 0.55 0.09 0.09 0.01 0.03 0.02 0.67 0.06 0.04 0.03

6000 185367 0.04 0.15 0.13 7.40 0.56 0.08 0.05 0.01 0.02 0.03 0.83 0.04 0.02 0.02

8000 368520 0.03 0.06 0.10 5.05 0.87 0.13 0.10 0.01 0.01 0.02 0.68 0.13 0.03 0.02

8000 521686 0.07 0.06 0.14 5.40 0.99 0.19 0.07 0.02 0.02 0.03 0.51 0.14 0.06 0.03

RightPinion RightPinion

L0701R0802 Means StandardDeviations

RightGearRightGear

L0701R0802

LeftPinion LeftPinion

Means StandardDeviations

LeftGearLeftGearNASA/TM—2013-216610 23 

A summary of the response of the individual sidebands to damage between each inspection interval is 

listed below: 

1. Left gear: 

a. The +1 sideband (SI42) had the largest value when damage was observed on the gear 

teeth, but did not trend upward between inspection interval 368-520. 

b. The +3 sideband (SI44) had the largest value when no damage was observed on the gear 

teeth during run-in. 

c. After damage was observed, the following increased with lower torque and decreased 

with higher torques: –3 (SI38) and +3(SI44). 

d. After damage was observed, the following increased with higher torque and decreased 

with lower torques: –1 (SI40), and gear mesh (SI41). 

e. The following did not indicate trends with torque changes: –2 (SI39), +1 (SI42) and +2 

(SI43). 

2. Left pinion: 

a. The +1 sideband (SI20) and +2 sidebands (SI21) had the largest values during the test 

and +1 sideband (SI20) trended well with damage. 

b. The following did not indicate trends with torque changes: –2 (SI17), +1(SI20), +2(SI21) 

and +2 (SI22). 

c. After damage was observed, the following increased with higher torque and decreased 

with lower torques: –3 (SI16), –1 (SI18) and gear mesh (SI19). 

d. If you separate the trends into torque bands, none trended with damage at 8000 in.-lbs 

torque. 

3. Right gear: 

a. The +1 sideband (SI42) and +2 sidebands (SI43) had the largest values during the test, 

but both did not trend well with damage. 

b. After damage was observed, the following increased with lower torque and decreased 

with higher torques: –3 (SI38). 

c. The following did not indicate trends with torque changes: –1(SI40), +1(SI42) and 

+3(SI44). 

d. The following were sensitive to torque changes but increased and decreased: –2(SI39), 

+2(SI43) and gear mesh (SI41). 

e. If you separate the trends into torque bands, no sideband trended with damage at 

8000 in.-lbs torque. 

4. Right pinion: 

a. The +1 sideband (SI20) had the largest values during the test and trended well with 

damage. 

b. None of the sidebands indicated significant trends with torque changes. 

c. If you separate the trends into torque bands, the following sideband trended with damage 

at 8000 in-lbs torque: –3 (SI16), +1 (SI20), +2(SI21). 

A summary of the response of the average of +3 sidebands, the average of +1 sideband and the 

maximum of the +3 sidebands is listed below: 

1. Left gear: 

a. The maximum sideband, average 1 sideband and 3 sideband did not trend well with 

damage. 

b. The maximum sideband increased with lower torque and decreased with higher torques. 

c. The 1 and 3 sideband did not trend with torque changes. 

 
NASA/TM—2013-216610 24 

2. Left pinion: 

a. The maximum sideband, average 1 sideband and 3 sideband did not trend well with 

damage from inspection interval 368–520. 

b. The maximum sideband, and 3 sideband trend well with damage from inspection 

interval 521-686. 

c. The 1 sideband increased with lower torque and decreased with higher torques. 

3. Right gear: 

a. The maximum sideband, and 3 sideband did not trend well with damage. 

b. The maximum sideband and 3 sideband increased and decreased with torque changes. 

c. The 1 sideband had the highest value when damage occurred. 

4. Right pinion: 

a. The maximum sideband, average 1 sideband and 3 sideband all trended with damage 

at 8000 in.-lbs. 

b. The maximum sideband slightly increased with higher torques and decreased with lower 

torques. 

Test 4 

Figure 12 is a plot of debris generated and the torque during test 4. Figure 13 is a plot of RMS during 

test 4. Tooth damage photos for the gear and pinion during the inspection intervals can be found in 

Figures A.4.1 to A.4.3. 

For test 4, Figures A.4.1 to A.4.3 illustrate no macropitting was observed on the pinion teeth at 

reading 1829, 30.48 hr into the test. At reading 4034, 67.23 hr into the test, several pits were observed on 

the left gear teeth and micropitting on both the left and right pinion teeth. The torque remained at 

6000 in.-lb during the test. 

For test 4, per Figure 12, the rate of debris generation measured was at 0.51 mg/hr rate of debris 

generation when spalling macropitting (4.3.4) was observed at 6000 in.-lb This rate was lower than the 

3.75 mg/hr rate of debris generation when spalling macropitting (4.3.4) was observed at 4000 in.-lb for 

test 2, and lower than the 6.37 mg/hr rate of debris generation when spalling macropitting (4.3.4) was 

observed at 8000 in.-lb for test 3. 

Per Figure 13, RMS could not be used to isolate the pinion from the gear on the left and right side of 

the test rig. The left gear and pinion tracked each other very closely as did the right gear and pinion. Both 

responded to the restarts after inspections, but the right side was significantly more sensitive than the left. 

The left and right side RMS values did not trend well with damage progression until after reading 1829, 

then showed and increasing trend with damage. Torque was held at 6000 in.-lbs during this time period. 

Figures B.4.1, B.4.5, B.4.9, and B.4.13 are plots of the individual 3 sideband and the gear mesh for 

the 41 tooth gears and the 19 tooth pinions for left gear, right gear, left pinion, right pinion during the test 

from the MDSS. The left y-axis is scaled for the 3 sidebands. The right y-axis is scaled for the gear 

(Sig41) and pinion (SI19) meshes. The x-axis correlates to the time in operation of the test rig in minutes. 

The yellow triangles correlate to gear tooth inspections. 

Figures B.4.2, B.4.6, B.4.10, and B.4.14 are plots of the individual 3 sideband and the gear mesh for 

the 41 tooth gears and the 19 tooth pinions for left gear, right gear, left pinion, right pinion during the test 

from the MSPU. The left y-axis is scaled for the 3 sidebands. The right y-axis is scaled for the gear 

(Sig41) and pinion (SI19) meshes. The yellow triangles correlate to gear tooth inspections per Table 9. 

Figures B.4.3, B.4.7, B.4.11, and B.4.15 are plots of the average 1 sidebands, average 3 sidebands 

and the maximum of the 3 sidebands for left gear, right gear, left pinion, right pinion during the test 

from the MDSS. The yellow triangles correlate to gear tooth inspections. 

Figures B.4.4, B.4.8, B.4.12, and B.4.16 are plots of the average 1 sidebands, average 3 sidebands 

and the maximum of the 3 sidebands for left gear, right gear, left pinion, right pinion during the test 

from the MSPU. The yellow triangles correlate to gear tooth inspections per Table 9. 
NASA/TM—2013-216610 25 

Figure 12.—Debris generated and torque during test 4. 

Figure 13.—RMS during test 4. 
NASA/TM—2013-216610 26 

Table 14 is a summary of the mean and standard deviation values for the individual sidebands 

between each inspection interval. The columns highlighted in blue are the gear and pinion meshes. The 

cells highlighted in red have the maximum values within that inspection interval. The cells highlighted in 

yellow have the next maximum values. The cells highlighted in green have the minimum values. 

For test 4, Figures A.4.1 to A.4.3, in Appendix A, illustrate no macropitting was observed on the 

pinion teeth 30 hr into the test. Sixty-seven hours into the test, several pits were observed on the left gear 

teeth and micropitting on both the left and right pinion teeth. The torque remained at 6000 in.-lb during 

the test. 

TABLE 14.—SUMMARY OF SIDEBAND FOR TEST 4 

 

Torque Inspection SIgl38 SIgl39 SIgl40 SIgl41 SIgl42 SIgl43SIgl44 SIgl38 SIgl39 SIgl40 SIgl41 SIgl42 SIgl43SIgl44

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 160 0.13 0.14 0.18 1.61 0.16 0.33 0.44 0.02 0.04 0.02 0.07 0.08 0.05 0.07

6000 61489 0.04 0.11 0.16 1.86 0.23 0.20 0.24 0.01 0.02 0.03 0.11 0.03 0.05 0.05

6000 490901 0.04 0.10 0.17 2.25 0.22 0.17 0.28 0.01 0.01 0.02 0.19 0.02 0.04 0.03

6000 9021196 0.04 0.09 0.14 2.53 0.23 0.16 0.26 0.01 0.03 0.03 0.21 0.02 0.06 0.04

6000 11971829 0.03 0.08 0.14 2.28 0.21 0.12 0.23 0.01 0.02 0.03 0.12 0.03 0.04 0.03

6000 18304034 0.04 0.07 0.09 2.65 0.16 0.11 0.20 0.01 0.01 0.02 0.28 0.04 0.04 0.03

Torque Inspection SIpl16 SIpl17 SIpl18 SIpl19 SIpl20 SIpl21 SIpl22 SIpl16 SIpl17 SIpl18 SIpl19 SIpl20 SIpl21 SIpl22

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 160 0.03 0.09 0.08 1.61 0.19 0.24 0.08 0.02 0.01 0.02 0.07 0.02 0.02 0.03

6000 61489 0.04 0.08 0.12 1.86 0.11 0.32 0.06 0.02 0.02 0.02 0.11 0.03 0.04 0.02

6000 490901 0.06 0.07 0.11 2.26 0.05 0.31 0.10 0.02 0.01 0.02 0.19 0.02 0.03 0.02

6000 9021196 0.04 0.11 0.10 2.53 0.05 0.32 0.18 0.03 0.01 0.01 0.21 0.04 0.03 0.04

6000 11971829 0.11 0.12 0.09 2.28 0.05 0.34 0.31 0.03 0.01 0.02 0.12 0.03 0.04 0.04

6000 18304034 0.13 0.12 0.23 2.65 0.15 0.33 0.25 0.03 0.02 0.04 0.28 0.02 0.05 0.06

Torque Inspection SIgr38 SIgr39 SIgr40 SIgr41 SIgr42 SIgr43SIgr44 SIgr38 SIgr39 SIgr40 SIgr41 SIgr42 SIgr43SIgr44

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 160 0.21 0.08 0.03 2.05 0.16 0.27 0.07 0.03 0.02 0.02 0.33 0.06 0.02 0.04

6000 61489 0.05 0.12 0.12 3.36 0.27 0.15 0.05 0.01 0.04 0.02 0.54 0.04 0.03 0.03

6000 490901 0.06 0.13 0.13 3.88 0.33 0.15 0.03 0.01 0.03 0.02 0.33 0.04 0.02 0.03

6000 9021196 0.06 0.11 0.12 3.69 0.37 0.12 0.05 0.01 0.03 0.03 0.33 0.04 0.02 0.03

6000 11971829 0.05 0.09 0.13 3.88 0.40 0.14 0.06 0.01 0.02 0.03 0.28 0.03 0.02 0.02

6000 18304034 0.07 0.08 0.12 3.54 0.47 0.17 0.08 0.01 0.01 0.02 0.50 0.03 0.03 0.02

Torque Inspection SIpl16 SIpl17 SIpl18 SIpl19 SIpl20 SIpl21 SIpl22 SIpl16 SIpl17 SIpl18 SIpl19 SIpl20 SIpl21 SIpl22

(inlb) Reading SB3 SB2 SB1 GM SB+1 SB+2 SB+3 SB3 SB2 SB1 GM SB+1 SB+2 SB+3

4000 160 0.03 0.05 0.20 2.05 0.40 0.07 0.14 0.01 0.01 0.02 0.33 0.04 0.03 0.05

6000 61489 0.04 0.05 0.41 3.36 0.70 0.13 0.15 0.01 0.02 0.04 0.54 0.08 0.05 0.03

6000 490901 0.04 0.05 0.44 3.88 0.78 0.21 0.21 0.01 0.02 0.04 0.32 0.11 0.04 0.03

6000 9021196 0.02 0.06 0.41 3.69 0.94 0.26 0.15 0.01 0.02 0.05 0.33 0.12 0.03 0.05

6000 11971829 0.05 0.06 0.45 3.88 0.98 0.27 0.10 0.02 0.01 0.03 0.28 0.09 0.03 0.06

6000 18304034 0.11 0.04 0.54 3.54 0.78 0.25 0.21 0.02 0.02 0.04 0.50 0.12 0.08 0.10

L1103R1204

LeftPinion LeftPinion

Means StandardDeviations

LeftGearLeftGear

RightPinion RightPinion

L1103R1204 Means StandardDeviations

RightGearRightGearNASA/TM—2013-216610 27 

A summary of the response of the individual sidebands to damage between each inspection interval is 

listed below: 

1. Left gear: 

a. The +3 sideband (SI44) had the largest value when damage was observed on the gear 

teeth. 

b. Since torque remained at 6000 in.-lbs after run-in, no effects due to torque changes could 

be evaluated for this test. 

c. None of the sidebands trended with damage at 6000 in.-lbs. Although the values 

increased as damage progressed at the end of the test for +1(SI42) and +2(SI43), these 

values were higher at the beginning of the test. 

2. Left pinion: 

a. The +2 sidebands (SI21) had the largest values during the test, but both did not trend well 

with damage. 

b. None of the sidebands trended with damage at 6000 in.-lbs. Although +3(SI22) increased 

when damage was first observed on the gear teeth, it dropped in value later in the test. 

3. Right gear: 

a. The +1 sideband (SI42) and +2 sidebands (SI43) had the largest values during the test. 

b. The +1 sideband (SI42) increased with damage. 

4. Right pinion: 

a. The +1 sideband (SI20) had the largest values during the test, increased with damage, 

decreased as the test progressed along with +2 (SI21). 

A summary of the response of the average of +3 sidebands, the average of +1 sideband and the 

maximum of the +3 sidebands is listed below: 

1. Left gear: 

a. The maximum sideband, average 1 sideband and 3 sideband did not trend well with 

damage. 

b. Although the values seem to increase at reading 3500 as damage these values were higher 

at the beginning of the test. 

2. Left pinion: 

a. The 3 sideband did trend with damage. 

3. Right gear: 

a. The maximum sideband, average +1 sideband and +3 sideband increased with damage 

until reading 3200, then decreased. 

4. Right pinion: 

a. The maximum sideband, average 1 sideband and 3 sideband increased with damage 

until inspection 1196, then decreased. 

Discussion of Results 

Many factors affect the gear CI’s ability to respond to tooth damage through vibration response. The 

response of the accelerometer to a specific fault can depend on the sensor specifications, the signal 

processing of the raw signal, mounting and its location. The CI method of calculation, operational 

conditions and type of failure mode can also affect its response. 

For these tests, accelerometer specifications, signal processing, mounting, location and structure 

remained the same for all four tests. Per table 10, the physical inputs {I} such as speed, temperatures and 

oil pressures remained within a small range for all tests once they reached steady-state conditions after 

restarting. Torque varied for several tests. The internal response {R} can change due to damage, but also 

type of failure mode and level of damage. Due to the design of our test rig, the internal response of the 
NASA/TM—2013-216610 28 

gear set on the left side may affect the right side. It was also found that the right and left side of our test rig 

responded differently to the varying levels of torque. The measured output {O}, vibration response from the 

left and right accelerometers then feeds into a CI calculation for the left gear, left pinion, right gear and right 

pinion. Each CI can respond differently to varying torque levels and varying levels of damage. 

Reviewing the RMS values for the four tests, several observations could be made. During test one, 

RMS values for all four components trended with damage when torque was maintained. RMS values for 

the right gear and pinion were significantly more sensitive to torque changes and shutdowns than the left 

for all four tests. During tests two and three, no RMS values trended with component damage, most likely 

due to varying torque levels throughout the test. During test four, RMS values for the left gear and pinion 

trended with component damage when torque was maintained. 

Individual sidebands, average and maximum sidebands responded differently for each test, torques, 

damage modes and components. In regards to torque changes, one interesting observation is that the 

amplitude changes with load, but not necessarily in a positive direction—lower torques produce higher 

amplitudes for some sidebands. 

Assessing whether a change in any particular condition indicator or sideband feature was due to only 

a change in damage level, a change in operating condition or some combination of both was a challenge 

since there are gaps in the data across all tests in regards to the different operating conditions. From what 

has been learned during this preliminary investigation, future tests are planned to determine the 

magnitude of these effects on the CI data collected. However, an initial investigation of the response of 

the different sideband indexes to damage modes will be presented. 

To perform the assessment required assigning a continuous monotonic increasing value to the 

different damage modes observed during each inspection interval. The values chosen for each test are 

listed in Table 15. The values were chosen based on the level of damage and the damage of the most 

interest for this study. A value of 0.1 was assigned to gear teeth broken in with no damage while a value 

of 5 indicates progressive macro-pitting on two or more gear teeth. Optimization of defining and 

assigning values to the damage modes for future tests is also planned. 

Damage values based on component tooth damage were generated for each reading for each test. 

Figure 14 is a plot of the damage values from Table 15 for test 1. An average damage value was also 

calculated for all 4 components for each reading. A fifth parameter, referred to as 4.3.2 Progressive, is a 

damage value when progressive pitting was observed on two or more teeth on any of the four 

components. For example, during test 1, this value was 0.1 until reading 1862. After this reading, the 

damage value remained at 5 for the rest of the test. Values were assigned and used to determine the 

sensitivity of the CI to this specific failure mode. Also note for tests 2 and 3, the torque changed within an 

inspection interval. Further work is required to optimize the values or classify and cluster them with 

additional information. 

Figure 14.—Damage values for test 1. 
NASA/TM—2013-216610 29 

TABLE 15.—ASSIGNED DAMAGE VALUES FOR DAMAGE MODES 

To assess the relationship between the different parameters, Pearson Correlation Coefficients (r) were 

calculated for the parameters. Correlations coefficients measure the strength and direction of the linear 

relationship between two parameters (Ref. 21). Correlation coefficients are calculated by dividing the 

covariance of the two variables by the product of their standard deviations. Its value ranges between 

–1 and +1. A perfect linear relationship between two parameters will have a correlation coefficient of 1 or 

–1. The focus for this analysis will be on r values greater than or equal to 0.8, indicating a CI response 

with a strong correlation to damage modes. A correlation matrix is generated for each test showing the 

linear relationship between CIs for the four components, torque, oil debris mass, and the six damage 

values calculated for the damage modes. Note that this method will only indicate linear relationships 

between parameters. 

One example of this analyses applied to test 1 will be presented. The left and right, gear and pinion, 

maximum and average 1 sideband indexes were calculated for comparison. Per review of the data in 

Table 11 the –3 sideband and the +3 sideband had the least response due to damage as compared to the 1 

and 2 sidebands. For this reason, the average 2 sidebands were calculated instead of the 3 for all four 

components for comparison using the correlation coefficients. The correlation tables for test 1 is shown in 

Table 16. 

 

Test1 Rdg(Min) Torque GearLeft PinionLeft GearRight PinionRight

Start 0 0 0.1 0.1 0.1 0.1

Runin 60 4000 0.1 0.1 0.1 0.1

Inspection 1186 4000 0.1 0.1 0.1 0.1

Inspection 187269 8000 0.1 0.1 0.1 3

Inspection 270553 8000 0.1 4 2 3

Inspection 5541862 8000 0.1 4 3.5 3

Inspection 18634814 8000 5 5 3.5 3

Inspection 48156065 8000 5 5 5 5

Test2 Rdg(Min) Torque GearLeft PinionLeft GearRight PinionRight

Start 0 0 0.1 0.1 0.1 0.1

Runin 60 4000 0.1 0.1 0.1 0.1

Inspection 1108 4000 0.1 0.1 0.1 0.1

202 4000 1 2 2 3

Inspection 109379 8000 1 2 2 3

468 4000 1 5 2 3

Inspection 380559 8000 1 5 2 3

632 4000 1 5 2 3

Inspection 560662 8000 1 5 2 3

Test3 Rdg(Min) Torque GearLeft PinionLeft GearRight PinionRight

Start 0 4000 0.1 0.1 0.1 0.1

Runin 69 4000 0.1 0.1 0.1 0.1

Inspection 69184 6000 1 0.1 0.1 0.1

367 6000 1 4 2 4

Inspection 185520 8000 1 4 2 4

Inspection 521686 8000 1 4 2 5

Test4 Rdg(Min) Torque GearLeft PinionLeft GearRight PinionRight

Start 0 4000 0.1 0.1 0.1 0.1

Runin 60 4000 0.1 0.1 0.1 0.1

Inspection61489 6000 1 0.1 2 4

Inspection 490901 6000 1 4 2 4

Inspection 9021196 6000 1 4 2 4

Inspection 11971829 6000 1 4 2 4

Inspection 18304034 6000 5 4 2 4
NASA/TM—2013-216610 30 

TABLE 16.—TEST 1 CORRELATION TABLE 
NASA/TM—2013-216610 31 

For test 1, 2 average sidebands for the left pinion, right gear and right pinion, 1 average sidebands 

for the right pinion and maximum sidebands for the right gear had a strong correlation to damage mode 

4.3.2. Average damage had a strong correlation to 2 average sidebands for the left and right pinion and 

the maximum sidebands for the right gear. Oil debris mass sensor also correlated to damage mode 4.3.2 

and average damage values. All 4 components had 4.3.2 damage at the end of the test. Note that no left 

gear sideband index values responded well to damage. One interesting observation was that a correlation 

coefficient value of 1 existed between the left pinion and right pinion maximum sideband values for all 

four tests. This indicates the coupling of the right and left pinion through their shafts in our test rig. Use 

of this CI to differentiate between the two components if only one had damage may be challenging. 

Results of the correlation coefficient analysis indicated strong linear correlations did not exist between 

several of the CIs measured during varying test conditions. However, non-linear correlations may exist 

between the CIs, damage modes and operating conditions that will require further analysis with different 

methods. Future test data will need to be generated that enables grouping the data into comparable torques 

and damage levels for comparison. 

Summary 

The purpose of this analysis was to evaluate the ability of gear CI to detect contact fatigue damage on 

spiral bevel gear teeth. Tests were performed in the NASA Glenn Spiral Bevel Gear Fatigue Rig on eight 

prototype gear sets during four damage progression tests. Vibration data was measured at varying torque, 

while varying modes and levels of tooth damage were observed. Due to the prototype gear design, failures 

modes in addition to contact fatigue occurred during testing. 

Gear condition indicator (CI) sideband index and individual sideband amplitudes were assessed to 

determine if they could detect contact fatigue damage on spiral bevel gear teeth. For these tests, 

individual, average and maximum sideband indexes (SI) responded differently for each test, torques, 

damage levels, damage modes and component. 

The performance of CI, RMS, was also evaluated for its ability to detect spiral bevel gear tooth 

damage. RMS values trended with damage progression when torque was maintained but did not trend 

well with damage progression at varying torque levels. It was also found that the RMS values for the right 

side of our test rig were significantly more sensitive to torque changes than the left side. 

Lessons learned during this preliminary investigation will be used to define the testing and analysis 

methods for future testing of forty-two final design gear sets. 

 

NASA/TM—2013-216610 33 

Appendix A.—Representative Photos of Gear and Pinion Teeth Damage 

Figure A.1.1.—Test 1 gear and pinion damage modes. 

Figure A.1.2.—Test 1 gear and pinion damage modes. 

Figure A.1.3.—Test 1 gear and pinion damage modes. 
NASA/TM—2013-216610 34 

Figure A.1.4.—Test 1 gear and pinion damage modes. 

Figure A.1.5.—Test 1 gear and pinion damage modes. 

Figure A.2.1.—Test 2 gear and pinion damage modes. 
NASA/TM—2013-216610 35 

Figure A.3.1.—Test 3 gear and pinion damage modes. 

Figure A.3.2.—Test 3 gear and pinion damage modes. 
NASA/TM—2013-216610 36 

Figure A.4.1.—Test 4 gear and pinion damage modes. Figure A.4.2.—Test 4 gear and pinion damage modes. 

Figure A.4.3.—Test 4 gear and pinion damage modes. 
NASA/TM—2013-216610 37 

Appendix B.—Plots of MDSS and MSPU Individual, Average of 

1 Sideband, 3 Sideband and Maximum Sideband 

Figure B.1.1.—Test 1 plot of left gear individual sidebands for MDSS. 

Figure B.1.2.—Test 1 plot of left gear average and maximum sidebands for MDSS. 

0 1000 2000 3000 4000 5000 6000 7000

0

0.5

1

Sidebands(g)

SIgl38

SIgl39

SIgl40

SIgl42

SIgl43

SIgl44

inspect

SIgl41

0 1000 2000 3000 4000 5000 6000 7000

0

5

10

Readings(minutes)

Gear Mesh 41t(g)

Gear Left

0 1000 2000 3000 4000 5000 6000 7000

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Readings(minutes)

Sidebands(g)

Gear Left

mean3SI

mean1SI

maxSI

inspect
NASA/TM—2013-216610 38 

Figure B.1.3.—Test 1 plot of left pinion individual sidebands for MDSS. 

Figure B.1.4.—Test 1 plot of left pinion average and maximum sidebands for MDSS. 

0 1000 2000 3000 4000 5000 6000 7000

0

0.5

1

1.5

2

Sidebands(g)

SIgl16

SIgl17

SIgl18

SIgl20

SIgl21

SIgl22

inspect

SIgl19

0 1000 2000 3000 4000 5000 6000 7000

0

2

4

6

8

Readings(minutes)

Pinion Mesh 19t(g)

Pinion Left

0 1000 2000 3000 4000 5000 6000 7000

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Readings(minutes)

Sidebands(g)

Pinion Left

mean3SI

mean1SI

maxSI

inspect
NASA/TM—2013-216610 39 

Figure B.1.5.—Test 1 plot of right gear individual sidebands for MDSS. 

Figure B.1.6.—Test 1 plot of right gear average and maximum sidebands for MDSS. 

0 1000 2000 3000 4000 5000 6000 7000

0

0.5

1

Sidebands(g)

SIgl38

SIgl39

SIgl40

SIgl42

SIgl43

SIgl44

inspect

SIgl41

0 1000 2000 3000 4000 5000 6000 7000

0

5

10

Readings(minutes)

Gear Mesh 41t(g)

Gear Right

0 1000 2000 3000 4000 5000 6000 7000

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Readings(minutes)

Sidebands(g)

Gear Right

mean3SI

mean1SI

maxSI

inspect
NASA/TM—2013-216610 40 

Figure B.1.7.—Test 1 plot of right pinion individual sidebands for MDSS. 

Figure B.1.8.—Test 1 plot of right pinion average and maximum sidebands for MDSS. 

0 1000 2000 3000 4000 5000 6000 7000

0

0.2

0.4

0.6

0.8

1

Sidebands(g)

SIgl16

SIgl17

SIgl18

SIgl20

SIgl21

SIgl22

inspect

SIgl19

0 1000 2000 3000 4000 5000 6000 7000

0

2

4

6

8

10

Readings(minutes)

Pinion Mesh 19t(g)

Pinion Right

0 1000 2000 3000 4000 5000 6000 7000

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Readings(minutes)

Sidebands(g)

Pinion Right

mean3SI

mean1SI

maxSI

inspect
NASA/TM—2013-216610 41 

Figure B.2.1.—Test 2 plot of left gear individual sidebands for MDSS. 

Figure B.2.2.—Test 2 plot of left gear individual sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.5

1

Sidebands(g)

SIgl38

SIgl39

SIgl40

SIgl42

SIgl43

SIgl44

inspect

SIgl41

0 100 200 300 400 500 600 700

0

5

10

Readings(minutes)

Gear Mesh 41t(g)

Gear Left

0 10 20 30 40 50 60

0

1

2

Sidebands(g)

SIgl38

SIgl39

SIgl40

SIgl42

SIgl43

SIgl44

inspect

torque

SIgl41

0 10 20 30 40 50 60

0

5

10

Readings

Gear Mesh 41t(g)

Gear Left
NASA/TM—2013-216610 42 

Figure B.2.3.—Test 2 plot of left gear average and maximum sidebands for MDSS. 

Figure B.2.4.—Test 2 plot of left gear average and maximum sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Readings(minutes)

Sidebands(g)

Gear Left

mean3SI

mean1SI

maxSI

inspect

0 10 20 30 40 50 60

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Readings(minutes)

Sidebands(g)

Gear Left

mean3SI

mean1SI

maxSI

inspect

torque
NASA/TM—2013-216610 43 

Figure B.2.5.—Test 2 plot of left pinion individual sidebands for MDSS. 

Figure B.2.6.—Test 2 plot of left pinion individual sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.5

1

Sidebands(g)

SIgl16

SIgl17

SIgl18

SIgl20

SIgl21

SIgl22

inspect

SIgl19

0 100 200 300 400 500 600 700

0

5

10

Readings(minutes)

Pinion Mesh 19t(g)

Pinion Left

0 10 20 30 40 50 60

0

0.2

0.4

0.6

0.8

1

Sidebands(g)

SIgl16

SIgl17

SIgl18

SIgl20

SIgl21

SIgl22

inspect

torque

SIgl19

0 10 20 30 40 50 60

0

2

4

6

8

10

Readings

Pinion Mesh 19t(g)

Pinion Left
NASA/TM—2013-216610 44 

Figure B.2.7.—Test 2 plot of left pinion average and maximum sidebands for MDSS. 

Figure B.2.8.—Test 2 plot of left pinion average and maximum sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Readings(minutes)

Sidebands(g)

Pinion Left

mean3SI

mean1SI

maxSI

inspect

0 10 20 30 40 50 60

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Readings(minutes)

Sidebands(g)

Pinion Left

mean3SI

mean1SI

maxSI

inspect

torque
NASA/TM—2013-216610 45 

Figure B.2.9.—Test 2 plot of right gear individual sidebands for MDSS. 

Figure B.2.10.—Test 2 plot of right gear individual sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.5

1

Sidebands(g)

SIgl38

SIgl39

SIgl40

SIgl42

SIgl43

SIgl44

inspect

SIgl41

0 100 200 300 400 500 600 700

0

10

20

Readings(minutes)

Gear Mesh 41t(g)

Gear Right

0 10 20 30 40 50 60

0

0.2

0.4

0.6

0.8

Sidebands(g)

SIgl38

SIgl39

SIgl40

SIgl42

SIgl43

SIgl44

inspect

torque

SIgl41

0 10 20 30 40 50 60

0

5

10

15

20

Readings

Gear Mesh 41t(g)

Gear Right
NASA/TM—2013-216610 46 

Figure B.2.11.—Test 2 plot of right gear average and maximum sidebands for MDSS. 

Figure B.2.12.—Test 2 plot of right gear average and maximum sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Readings(minutes)

Sidebands(g)

Gear Right

mean3SI

mean1SI

maxSI

inspect

0 10 20 30 40 50 60

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Readings(minutes)

Sidebands(g)

Gear Right

mean3SI

mean1SI

maxSI

inspect

torque
NASA/TM—2013-216610 47 

Figure B.2.13.—Test 2 plot of right pinion individual sidebands for MDSS. 

Figure B.2.14.—Test 2 plot of right pinion individual sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

Sidebands(g)

SIgl16

SIgl17

SIgl18

SIgl20

SIgl21

SIgl22

inspect

SIgl19

0 100 200 300 400 500 600 700

0

2

4

6

8

10

12

14

16

Readings(minutes)

Pinion Mesh 19t(g)

Pinion Right

0 10 20 30 40 50 60

0

0.2

0.4

0.6

0.8

Sidebands(g)

SIgl16

SIgl17

SIgl18

SIgl20

SIgl21

SIgl22

inspect

torque

SIgl19

0 10 20 30 40 50 60

0

5

10

15

20

Readings

Pinion Mesh 19t(g)

Pinion Right
NASA/TM—2013-216610 48 

Figure B.2.15.—Test 2 plot of right pinion average and maximum sidebands for MDSS. 

Figure B.2.16.—Test 2 plot of right pinion average and maximum sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

Readings(minutes)

Sidebands(g)

Pinion Right

mean3SI

mean1SI

maxSI

inspect

0 10 20 30 40 50 60

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Readings(minutes)

Sidebands(g)

Pinion Right

mean3SI

mean1SI

maxSI

inspect

torque
NASA/TM—2013-216610 49 

Figure B.3.1.—Test 3 plot of left gear individual sidebands for MDSS. 

Figure B.3.2.—Test 3 plot of left gear individual sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.5

1

Sidebands(g)

SIgl38

SIgl39

SIgl40

SIgl42

SIgl43

SIgl44

inspect

SIgl41

0 100 200 300 400 500 600 700

0

5

10

Readings(minutes)

Gear Mesh 41t(g)

Gear Left

0 5 10 15 20 25 30 35 40 45 50

0

0.5

1

Sidebands(g)

SIgl38

SIgl39

SIgl40

SIgl42

SIgl43

SIgl44

inspect

torque

SIgl41

0 5 10 15 20 25 30 35 40 45 50

0

10

20

Readings

Gear Mesh 41t(g)

Gear Left
NASA/TM—2013-216610 50 

Figure B.3.3.—Test 3 plot of left gear average and maximum sidebands for MDSS. 

Figure B.3.4.—Test 3 plot of left gear average and maximum sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Readings(minutes)

Sidebands(g)

Gear Left

mean3SI

mean1SI

maxSI

inspect

0 5 10 15 20 25 30 35 40 45 50

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Readings(minutes)

Sidebands(g)

Gear Left

mean3SI

mean1SI

maxSI

inspect

torque
NASA/TM—2013-216610 51 

Figure B.3.5.—Test 3 plot of left pinion individual sidebands for MDSS. 

Figure B.3.6.—Test 3 plot of left pinion individual sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.5

1

Sidebands(g)

SIgl16

SIgl17

SIgl18

SIgl20

SIgl21

SIgl22

inspect

SIgl19

0 100 200 300 400 500 600 700

0

5

10

Readings(minutes)

Pinion Mesh 19t(g)

Pinion Left

0 10 20 30 40 50 60

0

0.5

1

1.5

Sidebands(g)

SIgl16

SIgl17

SIgl18

SIgl20

SIgl21

SIgl22

inspect

torque

SIgl19

0 10 20 30 40 50 60

0

5

10

15

Readings

Pinion Mesh 19t(g)

Pinion Left
NASA/TM—2013-216610 52 

Figure B.3.7.—Test 3 plot of left pinion average and maximum sidebands for MDSS. 

Figure B.3.8.—Test 3 plot of left pinion average and maximum sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Readings(minutes)

Sidebands(g)

Pinion Left

mean3SI

mean1SI

maxSI

inspect

0 10 20 30 40 50 60

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Readings(minutes)

Sidebands(g)

Pinion Left

mean3SI

mean1SI

maxSI

inspect

torque
NASA/TM—2013-216610 53 

Figure B.3.9.—Test 3 plot of right gear individual sidebands for MDSS. 

Figure B.3.10.—Test 3 plot of right gear individual sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.5

1

Sidebands(g)

SIgl38

SIgl39

SIgl40

SIgl42

SIgl43

SIgl44

inspect

SIgl41

0 100 200 300 400 500 600 700

0

5

10

Readings(minutes)

Gear Mesh 41t(g)

Gear Right

0 5 10 15 20 25 30 35 40 45 50

0

0.5

1

1.5

Sidebands(g)

SIgl38

SIgl39

SIgl40

SIgl42

SIgl43

SIgl44

inspect

torque

SIgl41

0 5 10 15 20 25 30 35 40 45 50

0

5

10

15

Readings

Gear Mesh 41t(g)

Gear Right
NASA/TM—2013-216610 54 

Figure B.3.11.—Test 3 plot of right gear average and maximum sidebands for MDSS. 

Figure B.3.12.—Test 3 plot of right gear average and maximum sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Readings(minutes)

Sidebands(g)

Gear Right

mean3SI

mean1SI

maxSI

inspect

0 5 10 15 20 25 30 35 40 45 50

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Readings(minutes)

Sidebands(g)

Gear Right

mean3SI

mean1SI

maxSI

inspect

torque
NASA/TM—2013-216610 55 

Figure B.3.13.—Test 3 plot of right pinion individual sidebands for MDSS. 

Figure B.3.14.—Test 3 plot of right pinion individual sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

1

2

Sidebands(g)

SIgl16

SIgl17

SIgl18

SIgl20

SIgl21

SIgl22

inspect

SIgl19

0 100 200 300 400 500 600 700

0

5

10

Readings(minutes)

Pinion Mesh 19t(g)

Pinion Right

0 10 20 30 40 50 60

0

0.5

1

1.5

Sidebands(g)

SIgl16

SIgl17

SIgl18

SIgl20

SIgl21

SIgl22

inspect

torque

SIgl19

0 10 20 30 40 50 60

0

5

10

15

Readings

Pinion Mesh 19t(g)

Pinion Right
NASA/TM—2013-216610 56 

Figure B.3.15.—Test 3 plot of right pinion average and maximum sidebands for MDSS. 

Figure B.3.16.—Test 3 plot of right pinion average and maximum sidebands for MSPU. 

0 100 200 300 400 500 600 700

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Readings(minutes)

Sidebands(g)

Pinion Right

mean3SI

mean1SI

maxSI

inspect

0 10 20 30 40 50 60

0

0.5

1

1.5

Readings(minutes)

Sidebands(g)

Pinion Right

mean3SI

mean1SI

maxSI

inspect

torque
NASA/TM—2013-216610 57 

Figure B.4.1.—Test 4 plot of left gear individual sidebands for MDSS. 

Figure B.4.2.—Test 4 plot of left gear individual sidebands for MSPU. 

0 500 1000 1500 2000 2500 3000 3500 4000 4500

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Sidebands(g)

SIgl38

SIgl39

SIgl40

SIgl42

SIgl43

SIgl44

inspect

SIgl41

0 500 1000 1500 2000 2500 3000 3500 4000 4500

0

0.5

1

1.5

2

2.5

3

3.5

Readings(minutes)

Gear Mesh 41t(g)

Gear Left

0 20 40 60 80 100 120 140 160 180 200

0

0.5

1

Sidebands(g)

SIgl38

SIgl39

SIgl40

SIgl42

SIgl43

SIgl44

inspect

torque

SIgl41

0 20 40 60 80 100 120 140 160 180 200

0

5

10

Readings

Gear Mesh 41t(g)

Gear Left
NASA/TM—2013-216610 58 

Figure B.4.3.—Test 4 plot of left gear average and maximum sidebands for MDSS. 

Figure B.4.4.—Test 4 plot of left gear average and maximum sidebands for MSPU. 

0 500 1000 1500 2000 2500 3000 3500 4000 4500

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Readings(minutes)

Sidebands(g)

Gear Left

mean3SI

mean1SI

maxSI

inspect

0 20 40 60 80 100 120 140 160 180 200

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Readings(minutes)

Sidebands(g)

Gear Left

mean3SI

mean1SI

maxSI

inspect

torque
NASA/TM—2013-216610 59 

Figure B.4.5.—Test 4 plot of left pinion individual sidebands for MDSS. 

Figure B.4.6.—Test 4 plot of left pinion individual sidebands for MSPU. 

0 500 1000 1500 2000 2500 3000 3500 4000 4500

0

0.5

Sidebands(g)

SIgl16

SIgl17

SIgl18

SIgl20

SIgl21

SIgl22

inspect

SIgl19

0 500 1000 1500 2000 2500 3000 3500 4000 4500

0

5

Readings(minutes)

Pinion Mesh 19t(g)

Pinion Left

0 20 40 60 80 100 120 140 160 180 200

0

0.5

1

Sidebands(g)

SIgl16

SIgl17

SIgl18

SIgl20

SIgl21

SIgl22

inspect

torque

SIgl19

0 20 40 60 80 100 120 140 160 180 200

0

5

10

Readings

Pinion Mesh 19t(g)

Pinion Left
NASA/TM—2013-216610 60 

Figure B.4.7.—Test 4 plot of left pinion average and maximum sidebands for MDSS. 

Figure B.4.8.—Test 4 plot of left pinion average and maximum sidebands for MSPU. 

0 500 1000 1500 2000 2500 3000 3500 4000 4500

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Readings(minutes)

Sidebands(g)

Pinion Left

mean3SI

mean1SI

maxSI

inspect
NASA/TM—2013-216610 61 

Figure B.4.9.—Test 4 plot of right gear individual sidebands for MDSS. 

Figure B.4.10.—Test 4 plot of right gear individual sidebands for MSPU. 

0 500 1000 1500 2000 2500 3000 3500 4000 4500

0

1

Sidebands(g)

SIgl38

SIgl39

SIgl40

SIgl42

SIgl43

SIgl44

inspect

SIgl41

0 500 1000 1500 2000 2500 3000 3500 4000 4500

0

5

Readings(minutes)

Gear Mesh 41t(g)

Gear Right

0 20 40 60 80 100 120 140 160 180 200

0

0.2

0.4

0.6

0.8

Sidebands(g)

SIgl38

SIgl39

SIgl40

SIgl42

SIgl43

SIgl44

inspect

torque

SIgl41

0 20 40 60 80 100 120 140 160 180 200

1

2

3

4

5

Readings

Gear Mesh 41t(g)

Gear Right
NASA/TM—2013-216610 62 

Figure B.4.11.—Test 4 plot of right gear average and maximum sidebands for MDSS. 

Figure B.4.12.—Test 4 plot of right gear average and maximum sidebands for MSPU. 

0 500 1000 1500 2000 2500 3000 3500 4000 4500

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Readings(minutes)

Sidebands(g)

Gear Right

mean3SI

mean1SI

maxSI

inspect

0 20 40 60 80 100 120 140 160 180 200

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Readings(minutes)

Sidebands(g)

Gear Right

mean3SI

mean1SI

maxSI

inspect

torque
NASA/TM—2013-216610 63 

Figure B.4.13.—Test 4 plot of right pinion individual sidebands for MDSS. 

Figure B.4.14.—Test 4 plot of right pinion individual sidebands for MSPU. 

0 500 1000 1500 2000 2500 3000 3500 4000 4500

0

0.5

1

1.5

Sidebands(g)

SIgl16

SIgl17

SIgl18

SIgl20

SIgl21

SIgl22

inspect

SIgl19

0 500 1000 1500 2000 2500 3000 3500 4000 4500

0

2

4

6

Readings(minutes)

Pinion Mesh 19t(g)

Pinion Right

0 20 40 60 80 100 120 140 160 180 200

0

0.5

1

1.5

Sidebands(g)

SIgl16

SIgl17

SIgl18

SIgl20

SIgl21

SIgl22

inspect

torque

SIgl19

0 20 40 60 80 100 120 140 160 180 200

0

2

4

6

Readings

Pinion Mesh 19t(g)

Pinion Right
NASA/TM—2013-216610 64 

Figure B.4.15.—Test 4 plot of right pinion average and maximum sidebands for MDSS. 

Figure B.4.16.—Test 4 plot of right pinion average and maximum sidebands for MSPU. 

0 500 1000 1500 2000 2500 3000 3500 4000 4500

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Readings(minutes)

Sidebands(g)

Pinion Right

mean3SI

mean1SI

maxSI

inspect

0 20 40 60 80 100 120 140 160 180 200

0

0.5

1

1.5

Readings(minutes)

Sidebands(g)

Pinion Right

mean3SI

mean1SI

maxSI

inspect

torque
NASA/TM—2013-216610 65 

Appendix C.—Summary of Test Operational Data Averaged 

Within Each Inspection Period 

Table C.1: Daytronic Operational Parameters 

NAME MEASUREMENT DESCRIPTION 

LOI TC #2, LOI, Left side oil inlet 

LOO TC #3, LOO, Left side oil outlet 

Lchg LOI-LOO 

ROI TC #12, ROI, Right side oil inlet 

ROO TC #13, ROO, Right side oil outlet 

Rchg ROI-ROO 

Gear torque Gear torque 

Pinion torque Pinion torque 

Gear rpm Gear speed 

Pinion rpm Pinion speed 

Lpsi Left side oil inlet pressure 

Rpsi Right side oil inlet pressure 

Table C.2: Average Operational Parameter Values for Test 1 

Rdg(min) LOI LOO Lchg ROI ROO Rchg 

Gear 

torque 

Pinion 

torque 

Gear 

rpm 

Pinion 

rpm HP Lpsi Rpsi 

269 235 184 51 235 183 52 5079 2354 3063 6609 247 79 70 

553 247 201 45 247 197 49 7732 3583 3507 7567 430 67 60 

1862 245 195 50 245 194 52 7895 3659 3503 7559 439 63 54 

4814 246 205 41 246 201 45 7888 3655 3510 7573 439 71 63 

6065 250 203 47 250 200 50 7938 3679 3507 7568 442 62 55 

Table C.3: Average Operational Parameter Values for Test 2 

Rdg(min) LOI LOO Lchg ROI ROO Rchg 

Gear 

torque 

Pinion 

torque 

Gear 

rpm 

Pinion 

rpm HP Lpsi Rpsi 

108 248 207 41 248 206 42 3869 1793 3503 7560 215 61 58 

379 252 216 35 252 215 36 6439 2984 3469 7486 354 71 65 

559 262 210 53 263 210 53 5843 2708 3497 7545 324 42 38 

662 251 204 48 252 204 48 4927 2283 3502 7557 274 45 75 

Table C.4: Average Operational Parameter Values for Test 3 

Rdg(min) LOI LOO Lchg ROI ROO Rchg 

Gear 

torque Pinion torque 

Gear 

rpm 

Pinion 

rpm HP Lpsi Rpsi 

184 250 209 41 251 210 41 4917 2279 3501 7555 273 52 49 

520 255 219 36 256 221 35 6836 3168 3500 7553 380 52 55 

686 253 216 37 255 218 36 7834 3630 3501 7554 435 52 52 
NASA/TM—2013-216610 66 

Table C.5: Average Operational Parameter Values for Test 4 

Rdg(min) LOI LOO Lchg ROI ROO Rchg 

Gear 

torque 

Pinion 

torque 

Gear 

rpm 

Pinion 

rpm HP Lpsi Rpsi 

60 249 207 41 250 210 40 4986 2311 3500 7553 277 54 53 

489 254 218 36 255 220 35 5851 2712 3501 7554 325 54 53 

901 255 219 36 256 221 35 5808 2691 3501 7554 323 56 53 

1196 254 217 36 255 220 35 5827 2700 3501 7554 324 56 53 

1829 247 210 37 248 212 36 5950 2757 3501 7555 331 59 58 

4034 256 223 33 257 225 32 5954 2759 3500 7553 331 59 56 

References 

1. Delgado, Irebert; Dempsey, Paula; Antolick, Lance and Wade, Dan: Continued Evaluation of Gear 

Condition Indicator Performance on Rotorcraft Fleet. Airworthiness, CBM, and HUMS Specialists' 

Meeting, February 11-13, 2013, Huntsville, Alabama. 

2. Evaluation of Gear Condition Indicator Performance on Rotorcraft Fleet, Antolick, Lance; Branning, 

Jeremy; Dempsey, Paula; Wade, Daniel. 66th American Helicopter Society International Annual 

Forum 2010, Phoenix, AZ. 11-13 May 2010. 

3. Handschuh, R.F.: Thermal Behavior of Spiral Bevel Gears. NASA TM-106518, 1995. 

4. Handschuh, R.F.: Testing of Face-Milled Spiral Bevel Gears at High-Speed and Load. NASA/TM—

2001-210743, 2001. 

5. Feldman, J. and Larsen, C.: Bevel Gear Test Rig Transfer Path Measurements. Etegent Technologies 

Contract Report prepared for NASA Glenn Research Center. June 2013. 

6. Stewart, R.M. 1977. Some useful data analysis techniques for gearbox diagnostics. Machine Health 

Monitoring Group, Institute of Sound and Vibration Research, University of Southhampton, Report 

MHM/R/10/77, July 1977. 

7. Zakrajsek, J.J. 1989. An investigation of gear mesh failure prediction techniques. NASA TM– 

102340, AVSCOM TM 89–C-005. 

8. Zakrajsek, J.J., Handschuh, R.F., and Decker, H.J. 1994. Application of fault detection techniques to 

spiral bevel gear fatigue data. Proceedings of the 48th Meeting of the Mechanical Failures 

Prevention Group. Office of Naval Research, Arlington, Virginia, pp. 93–104. 

9. ANSI/AGMA 1010-E95. Appearance of Gear Teeth – Terminology of Wear and Failure. 

10. Randall, R.B., “A New Method of Modelling Gear Faults,” Journal of Mechanical Design, Vol. 104, 

pp. 259-267, April 1982. 

11. Manson, Graeme. Lecture 5 – Hierarchy of Damage Identification. University of Sheffield. 

Accessed 04/22/13. http://www.dynamics.group.shef.ac.uk/people/graeme/mec415/Lecture5.pdf. 

12. U.S. Army Aeronautical Design Standard for Condition Based Maintenance, ADS79 Handbook. 

August 2012. 

13. Dempsey, P.J. Zakrajsek, J.J., “Minimizing Load Effects on NA4 Gear Vibration Diagnostic 

Parameter,” NASA/TM—2001-210671, February 2001. 

14. Mosher, M.M., Pryor, Huff. E.M., “Evaluation of Standard Gear Metrics in Helicopter Flight 

Operation,” Proceedings of the 56th Meeting of the Society for Machinery Failure Prevention 

Technology, April 15–19, 2002, Virginia Beach, Virginia. 

15. Dempsey, P.J., Lewicki, D.G., and Le, D.D., Investigation of Current Methods to Identify Helicopter 

Gear Health. NASA/TM—2007-214664. Presented at the IEEE Aerospace Conference. Big Sky, 

Montana, March 3–10, 2007. 

16. Dempsey, P.J., Branning, J.S., Wade, D.R. and Bolander, N., Comparison of Test Stand and 

Helicopter Oil Cooler Bearing Condition Indicators. Proceedings of the American Helicopter 

Society 66th Annual Forum, Phoenix, Arizona, May 11-13, 2010. 
NASA/TM—2013-216610 67 

17. Dempsey, P.J., Mosher, M.M. and Huff, E.M., “Threshold Assessment of Gear Diagnostic Tools on 

Flight and Test Rig Data,” NASA/TM—2003-212220, February 2003a. 

18. Huff, E.M., Tumer, I.Y., Barszcz, E., Dzwonczyk, M., and McNames, J., An Analysis of 

Maneuvering Effects on Transmission Vibrations in an AH-1 Cobra Helicopter, J. of American 

Helicopter Society, Vol. 47, No. 1, 2002. 

19. Oza, N.C., Tumer, K., Tumer, I.Y. and Huff, E.M., Classification of Aircraft Maneuvers for Fault 

Detection, Proceedings of the 4th Intl Workshop on Multiple Classifier Systems, Guildford, Surrey, 

UK, June 11-13, 2003. 

20. Dempsey, P., Handschuh, R. and Delgado, I.: Integrating Condition Indicators and Usage 

Parameters for Improved Spiral Bevel Gear Health Monitoring. 66th American Helicopter Society 

International Annual Forum 2013, Phoenix, AZ. 21-23 May 2013. 

21. Triola, Mario. Elementary Statistics. 6th edition. Addison-Wesley 1995.