R. Handschuh

Glenn Research Center, Cleveland, Ohio

C. Kilmain, R. Ehinger, and E. Sinusas

Bell Helicopter Textron Inc., Fort Worth, Texas 

Gear Design Effects on the Performance 

of High Speed Helical Gear Trains as 

Used in Aerospace Drive Systems

NASA/TM—2013-217897

June 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
R. Handschuh

Glenn Research Center, Cleveland, Ohio

C. Kilmain, R. Ehinger, and E. Sinusas

Bell Helicopter Textron Inc., Fort Worth, Texas 

Gear Design Effects on the Performance 

of High Speed Helical Gear Trains as 

Used in Aerospace Drive Systems

NASA/TM—2013-217897

June 2013

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

69th Annual Forum and Technology Display (Forum 69)

sponsored by the American Helicopter Society (AHS)

Phoenix, Arizona, May 21–23, 2013
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

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2013-217897 1

Gear Design Effects on the Performance of High Speed Helical

Gear Trains as Used in Aerospace Drive Systems

R. Handschuh

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

C. Kilmain, R. Ehinger, and E. Sinusas

Bell Helicopter Textron Inc.

Fort Worth, Texas 76101

Abstract

The performance of high-speed helical gear trains is of 

particular importance for tiltrotor aircraft drive systems. These 

drive systems are used to provide speed reduction/torque 

multiplication from the gas turbine output shaft and provide the 

necessary offset between these parallel shafts in the aircraft. 

Four different design configurations have been tested in the 

NASA Glenn Research Center, High Speed Helical Gear Train 

Test Facility. The design configurations included the current 

aircraft design, current design with isotropic superfinished gear 

surfaces, double helical design (inward and outward pumping), 

increased pitch (finer teeth), and an increased helix angle. All 

designs were tested at multiple input shaft speeds (up to 15,000 

rpm) and applied power (up to 5,000 hp). Also two lubrication, 

system-related, variables were tested: oil inlet temperature (160 

to 250 °F) and lubricating jet pressure (60 to 80 psig). 

Experimental data recorded from these tests included power loss 

of the helical system under study, the temperature increase of 

the lubricant from inlet to outlet of the drive system and fling 

off temperatures (radially and axially). Also, all gear systems 

were tested with and without shrouds around the gears. The 

empirical data resulting from this study will be useful to the 

design of future helical gear train systems anticipated for next 

generation rotorcraft drive systems.

Introduction

Rotorcraft drive systems are critical to the high efficiency 

and lightweight requirements of the propulsion system. 

Tiltrotor aircraft, as currently designed, utilize the drive 

system as a means to fly even when one engine is inoperative 

through the use of shafting and other gearboxes to connect the 

two rotors together. A sketch of the entire propulsion system is 

shown in Figure 1 and a close up of the wing tipped nacelle 

propulsion system is shown in further detail in Figure 2 (Ref. 1).

Also in a tiltrotor aircraft, the entire propulsion system is 

required to tilt from the vertical position (helicopter mode) to 

that of the horizontal position (forward flight—airplane 

mode). The unique capabilities allow this aircraft to fly at a 

high rate of speed in the airplane mode and land vertically, 

greatly enhancing the aircraft’s usefulness in fulfilling a 

number of military missions. 

The drive system contained within the prop-rotor gearbox 

connects the parallel shafts of the gas turbine engine to that of 

the propeller via a gear train of helical gears. The gear train 

operates at high rotational speeds that result in high pitch line 

velocity of the gears that can affect the overall drive system 

performance through an increase in windage power losses. It 

is of the utmost importance for drive system efficiency to 

make the transition from the gas turbine engine to the 

propeller with the minimum amount of power loss. High 

power loss is absorbed by the lubricant or expelled through the 

gearbox housing in the form of heat. Therefore improved 

performance of the gearbox can result in more power available 

to the rotor, increased load capacity, or extended range.

The objective of this study is to experimentally determine 

how operating conditions, gear design, and gear shrouding can 

influence the performance of high-speed helical gear trains as 

used in a tiltrotor aircraft.

Test Facility, Test Hardware, and Test 

Method

Test Facility

The test facility used in this study is the High Speed Helical 

Gear Train Test Facility located at NASA Glenn Research 

Center (Ref. 2). The test facility arrangement is shown in 

Figure 3 and a sketch of the key test system components is 

shown in Figure 4. 
NASA/TM—2013-217897 2

Figure 1.—Tilt rotor propulsion system components (Ref. 1).

Figure 2.—Propulsion system components that reside within the aircraft 

nacelle. Tilt axis gearbox (TAGB), and prop-rotor gearbox (PRGB).

Figure 3.—Test facility arrangement.
NASA/TM—2013-217897 3

Figure 4.—Sketch of test facility primary components.

Referring to Figure 3 for the discussion, the facility operates 

as a closed-loop test facility. Power is circulated from the test 

gearbox to the slave gearbox and then returns to complete the 

torque loop. A rotating torque actuator in the slave gearbox 

provides an adjustable loop torque while the drive motor must 

provide for all of the gear, bearing, and windage losses. With 

the current components, up to 5,000 hp can be circulated 

around the test to the slave gearbox loop. The high-speed 

shaft, simulating the power turbine shaft, can be rotated to 

15,000 rpm. Most of the test conditions that will be reported in 

this paper have to do with the hover and forward flight speed 

conditions. The drive system input shaft rotates at 15,000 and 

12,500 rpm, respectively at these conditions. Both gearboxes 

have separate lubrication systems that include supply and 

scavenge pumps, filters (3 μm), heaters, heat exchangers, etc. 

The test and slave gearboxes operate in a dry sump mode

where the lubricant that is jet fed to the gears and bearings is 

removed immediately after lubricating and cooling via the 

scavenge pumps. For all the data presented in this report, the 

slave gearbox operating conditions were constant, at ~160 °F 

lubricant inlet temperature, and ~80 psi jet pressure. 

Test Hardware

The gearing components used in the test program included 

four different gear designs. There is the baseline (currently 

used aircraft design), baseline with isotropic superfinishing 

(ISF), double helical, fine pitch, and increased helix angle 

designs. The design information for all four cases are provided 

in Table 1. The same gear material, Pyrowear 53, was used in 

all gearing components and all were manufactured with the 

same surface finish and gear quality. A photograph of the 

input gear designs is shown in Figure 5. The gearing 

components are shown during their installation into the 

gearbox housing as shown in Figure 6 (baseline design).

TABLE 1.—BASIC GEAR DESIGN INFORMATION

Baseline 

design

Double 

helical 

design

Fine pitch 

design

Increased 

helix angle 

design

Number of teeth, input 

and 2nd idler/1st and 

3rd idler/ bull gear

50/51/139 50/51/139 70/73/196 50/51/139

Normal module, mm, 

(diametral pitch, (1/in.))

3.033 

(8.375)

2.540 

(10.000)

2.142 

(11.858)

2.9136 

(8.7177)

Face Width, mm (in.) 66.68 

(2.625) 78.23 (3.08) 66.68 (2.625)

66.68 

(2.625)

Normal pressure angle, 

deg. 20 20 20 20

Transverse helix angle 

at pitch diameter, deg. 12 35 12 20

Test Method

The test facility was operated at all conditions long enough 

to establish steady state conditions. This typically took ~ 5 

min to attain once the first test condition was reached. An 

example of this will be presented later in this paper. Data 

taken was stored remotely for playback if needed. The rate of 

data acquisition for all tests was 0.5 or 1.0 Hz.
NASA/TM—2013-217897 4

Figure 5.—Photograph of input gear designs. Baseline, baseline 

+ ISF, double helical, fine pitch, and increased helix angle.

Figure 6.—Baseline test hardware during installation.

Figure 7.—Rake probes (a) and array probe (b).

Test Gearbox Instrumentation

The test facility provided for five operational condition 

measurements: drive motor power, drive motor speed, test 

system loop power, lubricant pressure and all the facility 

temperatures. Drive motor power to the facility is monitored 

via a commercially available torquemeter. Loop power is 

measured using a torque-bridge-telemetry system attached to 

the Bull Gear connect shaft between the test and slave 

gearboxes. A plethora of thermocouples monitor the lubricant, 

gearbox housing, bearings, and fling-off temperatures. Flingoff temperatures are found via two different probe types.

Rake and array thermocouple probes were designed and 

fabricated to indicate the lubricant temperature radially flung 

off and axially pumped respectively (Ref. 3). The two 

different probe types are shown in Figure 7. The rake probes 

had five thermocouples across the face width of the gear (six 

for double helical design) and the array probe had nine 

thermocouples in a 25.4- by 25.4-mm (1- by 1-in.) substrate. 

Both probes were located very close to the mesh position of 

the gears. The rake and array probes were located within the 

test gearbox as shown in Figure 8.

Test Data

Test Operation

Test operation was conducted in the following manner. First 

the rotational speed and applied load were established and 

then the temperatures of the facility were allowed to come to 

steady state once the oil inlet and outlet temperatures 

stabilized. An example of a typical time history of a test is 

shown in Figure 9 for the conditions given in Table 2 (Ref. 4). 

In the data to be presented, values from all important variables 

will be presented at a steady state operating point.

TABLE 2.—CONDITIONS FOR FIGURE 9. GEARS

WERE BASELINE DESIGN, SUPERFINISHED,

AND 160 °F OIL INLET TEMPERATURE

Condition Input shaft 

speed 

(krpm)

Lower 

power

(hp)

Temperature 

increase across 

gearbox

(°F)

Drive 

motor 

power

(hp)

A Warm up

B 12.5 1,379 50.6 138.0

C 12.5 2,801 55.1 149.2

D 12.5 4,170 59.7 160.1

E 15.0 1,657 73.8 201.9

F 15.0 3,366 79.1 213.2

G 15.0 4,986 83.0 225.1
NASA/TM—2013-217897 5

Figure 8.—Locations of the rake (a) and array (b) probes in the test gearbox.

Figure 9.—Temperature data at mid-face of rake and at array probe center 

for all sensor locations (conditions shown in Table 2, one scan = 2 sec, 

160 °F oil inlet temperature) super-finished baseline design test results.
NASA/TM—2013-217897 6

Spin Loss Data

In order to understand the drive system losses, experimental 

tests were conducted to full speed (except in some unshrouded 

cases) at approximately 10 percent of the full torque of the 

facility. The data generated was for the various gear designs, 

with and without shrouding. The test gearbox (top cover 

removed) with the shrouding installed is shown in Figure 10(a) 

and shrouding removed in (b).

The results from the shrouded and unshrouded tests are 

shown in Figure 11(a) and (b), respectively. The shrouded 

gear tests were run at ~ 160 °F lubricant inlet temperature. The 

unshrouded gear tests were run for most of the gear designs at 

two lubricant inlet temperatures (~160 and 200 °F). 

The non-linear increase in drive motor power requirement 

for these tests resembles the windage power loss curves 

generated in Reference 5. The data plotted in all the curves 

here, and those to come later with respect to “drive motor 

power”, refer to the entire test system (test and slave 

gearboxes). As shown in Figure 11(b), for the high helix angle 

gear design, the facility could not stably run at the 12,500 and 

15,000 rpm conditions in the unshrouded case. This is an 

indication of the windage from the gears interrupting the 

scavenging of lubricant from the test gearbox. 

A comparison of the double helical—outward pumping

design, is shown in Figure 12. The data indicates the effect of 

having the shrouds installed. The drive system power 

requirement difference is a direct measurement of the shroud 

effectiveness at a given speed and torque combination. Note 

that rotational speed change is far more important than the 

level of applied load, meaning that the windage part of the 

losses is dominating the drive motor power requirements.

Gear Design Effects

An indication of how the different gear designs affect the 

performance for the same operating conditions for all four 

designs will be addressed in this section. In Figure 13 the 

design effect is shown at 160 °F lubricant inlet temperature 

and in Figure 14 at 250 °F lubricant inlet temperature as a 

function of applied bull gear torque at two different rotational 

speeds. Both figures were for shrouded gears. 

It is apparent from these two figures that the rotational 

speed had the largest effect on the results for a given design. 

Higher lubricant inlet temperature reduced the power 

requirement, and the baseline or high helix angle designs 

produced the largest power requirements. The fine pitch 

design produced the lowest power requirements for all 

conditions shown. This result must be tempered with the fact 

that the test and slave gearboxes had this type of gearing, 

therefore the power savings of an individual gearbox would be 

similar to that of the double helical gear design that were 

operated in the outward pumping arrangement.

As an example of how the lubricant inlet temperature affects 

the power loss of a given configuration is shown in Figure 15. 

In this figure the drive motor power is plotted versus bull gear 

shaft torque for two input shaft speeds for the baseline design. 

Higher lubricant inlet temperature reduces the power loss of 

the gear train at all speed and load conditions. For the baseline 

design this resulted in a ~10 hp reduction in power loss by 

increasing the lubricant inlet temperature from 160 to 250 °F.

Figure 10.—Test gearbox with the shrouding installed and 

removed. (a) Shrouding installed (baseline). (b) Shrouding 

removed (double helical inward pumping).
NASA/TM—2013-217897 7

Figure 11.—Spin loss data for (a) shrouded and (b) unshrouded conditions.
NASA/TM—2013-217897 8

Figure 12.—Effect of shrouding on drive motor power. Double 

helical gears, outward pumping 200 °F oil inlet temperature.

Figure 13.—Effect of gear design shrouded on drive motor 

power, 160 °F lubricant inlet temperature. 

Figure 14.—Effect of gear design (shrouded) on drive motor 

power, 250 °F lubricant inlet temperature.

Figure 15.—Lubricant inlet temperature effects on drive motor 

power required (gears shrouded). 
NASA/TM—2013-217897 9

Lubrication Jet Pressure Tests

Three lubricant jet pressure (flow rate) conditions are shown 

for the two speed conditions and one level of applied load 

(~33 percent of full torque). The drive motor power required is 

shown in Figure 16 and the lubricant temperature increase 

across the gearbox (exit temperature minus inlet temperature) 

is shown in Figure 17. In either figure the lower symbol for a 

given design is the 12,500 rpm data and upper symbol is the 

15,000 rpm data. As would be expected, higher flow rate of 

lubricant reduced the temperature change, but higher jet 

pressure (flow) increase the power loss for all conditions. The 

fine pitch design had the lowest drive motor required (note 

fine pitch gears were installed in both the test and slave 

gearbox) and minimum temperature increase for any rotational 

speed or loop torque requirement.

Internal Gearbox Instrumentation

The final comparison to be made in this paper is how the 

instrumentation inside the gearbox, fling off temperatures, 

were affected by gear designs and operation conditions. As 

described earlier, rake probes (radial) and array probes 

(axially) will be used to generate the data discussed here. The 

data presented was the maximum from any of the three rake 

probes or the four array thermocouple sensors. Generally 

speaking, the highest temperature locations were those at the 

idler gear positions. 

An example of the rake probe data is shown in Figure 18. 

The lubricant inlet temperature for this data was 200 °F. Six 

different test configurations are shown all with the gears 

shrouded. As with all the other data presented in this study, the 

fine pitch gear design performed the best and rotational speed 

was a larger factor than applied load on the results. The fling 

off temperature from the rake probes could be in excess of 

125 °F higher than the lubricant inlet temperature. 

An example of the array probe data is shown in Figure 19. 

This data was also taken at the same inlet lubricant 

temperatures as the data from Figure 18. This data requires a 

little more explanation than the rake data. The array probe data 

is influenced by the axially pumped air-lubricant mixture due 

to the helical gear meshing action. For the single helical gear 

designs, the air-lubricant mixture expended from the ends of 

the teeth impinge directly on the array sensor. Therefore the 

single helical gear design data is clustered at a higher 

temperature than either of the double helical results. The 

outward pumping helical gears have approximately one-half of 

the face width before the air lubricant mixture impinges on the 

array sensor. The distance that the air-lubricant mixture is 

pumped in a single helical gear is the complete face width. 

Therefore single helical results would be expected to have a 

higher axially pumped measured temperature.

Figure 16.—Lubricant pressure effects on drive motor power 

requirements. Shrouded gears, ~19,000 in.*lb torque, 200 °F 

oil inlet temperature.

Figure 17.—Lubricant pressure effects on temperature increase 

across the test gearbox, 200 °F oil inlet temperature.
NASA/TM—2013-217897 10

Figure 18.—Rake probe lubricant fling-off data, maximum for a

given speed and load condition, 200 °F oil inlet temperature.

Figure 19.—Array probe fling-off data, maximum values for a 

given speed and load, 200 °F oil inlet temperature. (Note: 

Data at higher symbol is at 15,000 rpm and lower symbol 

12,500 rpm.)

Conclusions

Based on the results attained in this study the following 

conclusions can be made:

1. High-speed gearing benefits from the use of shrouding 

when the pitch line velocity exceeds ~ 15,000 ft/min. At 

conditions above this pitch line speed, the windage 

losses can dominate those from other sources (gear 

meshing and bearing losses).

2. Gear design characteristics can also impact the drive 

system power losses. For the tests conducted in this 

study, the fine pitch gear design had the least power loss 

and lowest temperature increase of the lubricant across 

the gearbox.

3. Lubricant inlet temperature changes indicated that 

higher inlet temperature required less drive motor power 

for identical conditions for all designs.

4. Lubricant jet pressure (flow) affects the power loss and 

temperature change from the inlet to exit of the gearbox. 

Lower flow resulted in less power required, but resulted 

in an increase in temperature across the gearbox. 

5. Special rake and array probes indicated that the 

temperature of the lubricant that is flung off radially and 

pumped axially far exceeds the bulk flow temperature 

exiting the gearbox. The temperature rise can exceed 

125 °F radially (rake probe) and 165 °F axially (array 

probe) depending on the speed, load, and other 

conditions applied.

References

1. Kilmain, C., Murray, R., and Huffman, C.: V-22 Drive 

System Description and Design Technologies, American 

Helicopter Society 51st Annual Forum, May 1995.

2. Handschuh, R. and Kilmain, C.: Preliminary Investigation 

of the Thermal Behavior of High-Speed Helical Gear 

Trains, NASA/TM—2002-211336, ARL-TR-2661, 

March 2002.

3. Handschuh, R. and Kilmain, C.: Experimental Study of 

the Influence of Speed and Load on Thermal Behavior of 

High-Speed Helical Gear Trains, NASA/TM—2005-

213632, ARL-TR-3488, July 2005.

4. Handschuh, R. Kilmain, C., and Ehinger, R.: Operational 

Condition and Superfinishing Effect on High-Speed 

Helical Gearing Performance, NASA/TM-2007—214696, 

ARL-TR-4099, June 2007.

5. Handschuh, R. and Hurrell, M.: Initial Experiments of 

High-Speed Drive System Windage Losses, NASA/TM—

2011-216925, November 2011.

REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the 

data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this 

burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. 

Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB 

control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

01-06-2013 

2. REPORT TYPE

Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Gear Design Effects on the Performance of High Speed Helical Gear Trains as Used in 

Aerospace Drive Systems 

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Handschuh, R.; Kilmain, C.; Ehinger, R.; Sinusas, E. 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

WBS 380046.02.03.02.02.01 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

8. PERFORMING ORGANIZATION

 REPORT NUMBER

E-18652-1 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

10. SPONSORING/MONITOR'S

 ACRONYM(S)

NASA 

11. SPONSORING/MONITORING

 REPORT NUMBER

NASA/TM-2013-217897 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Category: 37 

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

This publication is available from the NASA Center for AeroSpace Information, 443-757-5802

13. SUPPLEMENTARY NOTES

14. ABSTRACT

The performance of high-speed helical gear trains is of particular importance for tiltrotor aircraft drive systems. These drive systems are 

used to provide speed reduction / torque multiplication from the gas turbine output shaft and provide the necessary offset between these 

parallel shafts in the aircraft. Four different design configurations have been tested in the NASA Glenn Research Center, High Speed Helical 

Gear Train Test Facility. The design configurations included the current aircraft design, current design with isotropic superfinished gear 

surfaces, double helical design (inward and outward pumping), increased pitch (finer teeth), and an increased helix angle. All designs were 

tested at multiple input shaft speeds (up to 15,000 rpm) and applied power (up to 5,000 hp). Also two lubrication, system-related, variables 

were tested: oil inlet temperature (160 to 250 °F) and lubricating jet pressure (60 to 80 psig). Experimental data recorded from these tests 

included power loss of the helical system under study, the temperature increase of the lubricant from inlet to outlet of the drive system and 

fling off temperatures (radially and axially). Also, all gear systems were tested with and without shrouds around the gears. The empirical 

data resulting from this study will be useful to the design of future helical gear train systems anticipated for next generation rotorcraft drive 

systems. 

15. SUBJECT TERMS

High speed gearing; Aerospace drive systems; Helical gear 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

 ABSTRACT

UU 

18. NUMBER

 OF 

 PAGES

18 

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email:help@sti.nasa.gov) 

a. REPORT

U 

b. ABSTRACT

U 

c. THIS 

PAGE

U 

19b. TELEPHONE NUMBER (include area code)

443-757-5802 

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. Z39-18