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NASA GLENN RESEARCH CENTER 170 2005 RESEARCH AND TECHNOLOGY
NASA has the goal of completely eliminating the harmful
emissions that areassociated with current aircraft propulsion
systems. An advanced electricdrive with electric power generated by
turbogenerators, or by fuel cells usinghydrogen, is an alternative
propulsion system for transport-sized aircraft thatmay help achieve
this goal. Another NASA goal is to develop specializedunmanned
aerial vehicles (UAV) to meet NASA science mission
objectives.Current propulsion technology limits the endurance and
range of UAVs. TheNASA Glenn Research Centers High Power Density
Motor (HPDM) develop-ment research team is interested in applying
its technology to high-altitude,long-endurance remotely operated
aircraft (HALE ROA) to enhance vehicleperformance (see the gure).
Consequently, a mission analysis of a HALEROA was conducted to
determine if HPDMs are a viable solution for thesepropulsion
challenges.
The mission analysis has four major parts: (1) mission
selection, (2) UAVselection, (3) matching the HPDM with mission
requirements and the UAVvehicle, and (4) mission analysis. Mission
selection involved examining sixNASA science missions that are
considered candidates for HALE ROA appli-cation. The hurricane
tracker mission was selected because it may benetthe most by using
a HPDM. This mission requires a UAV to y to a develop-ing tropical
cyclone and follow the system until it makes landfall. From birthto
landfall, a typical hurricane usually lasts 10 to 14 days, dening
the ightendurance requirement for this particular mission.
UAV selection was based on researchperformed on numerous current
UAVssuitable for this mission. The Global Hawkwas selected as the
best candidate. Cur-rently used by the U.S. military for
high-altitude reconnaissance, with its currentpropulsion system,
the Global Hawk canstay airborne for over 36 hr with regular-ity.
The aircraft is large enough, strongenough, and fast enough to y
in, over,and through strong hurricanes.
The current propulsion system, theAllison Rolls-Royce AE 3007H,
is amodied engine that allows the aircraft toclimb to altitudes of
65,000 ft. The engineproduces a maximum of 7600-lb thrust,rated at
takeoff, and the HPDM designused in the analysis can produce
upwardsof 1000 hp, providing enough thrust toallow the redesigned
aircraft to take off.
The mission analysis involved four phases of the ight prole:
takeoff, cruiseout to the storm, loiter over the stormuntil
landfall, and land after the storm hasmade landfall. From the
takeoff portion of the ight, the parameters that were most
important were the required horsepower,thrust, velocity, and
takeoff distance. For the cruise portion of the ight, the
aircraftcruising velocity was important since itdetermines how fast
the aircraft can reachthe storm system. For the loiter phase,when
the aircraft circles over or throughthe storm until it makes
landfall, the major factors that determine the aircrafts
per-formance are the cruise velocity and theendurance of the
aircraft.
The results of the study revealed that
the HPDM could not meet the minimum10-day endurance requirement
desiredfor hurricane tracking because of fuel-space limitations in
the current GlobalHawk design. The HPDM did, however,improve the
UAV endurance from 48to 130 hr, which is a very
signicantperformance improvement. If sufcient
Mission Analysis Conducted of a High-Altitude, Long-Endurance,
RemotelyOperated Aircraft With a High-Power-Density Electric
Motor
Cryogenic motor Ironless motor Tip drive motor Superconducting
motor
Advanced high-power-density electric motors, such as
superconducting motors,are being developed. These motors may
provide electric propulsion for futureHALE ROA used to support NASA
science missions, such as hurricane tracking.Flight mission
analyses have been conducted to determine the viability of
theseadvanced motors.
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RESEARCH AND TECHNOLOGY
NASA GLENN RESEARCH CENTER 171 2005 RESEARCH AND TECHNOLOGY
fuel space was available and the specic fuel consumption of the
fuel cellswas lowered, the proposed 240 hr could be reached. This
study shows thatHPDM technology could be viable for future aircraft
and UAV performing civilmissions like hurricane tracking. The
130-hr endurance shows that, based onthe assumptions and analysis
of this study, these motors will allow aircraft toy longer while
reducing harmful emissions.
Glenn contacts:Dr. Dexter Johnson,
2164336046,[email protected]; andDr. Gerald V. Brown,
2164336047,[email protected]
Author:Dr. Dexter Johnson
Headquarters program ofce:VSP
Programs/Projects:LEAP
In the design of future high-speed jet engines, whose operating
temperatureswill most likely exceed 400 C, the choice of a
lubricant and lubrication methodwill be of considerable concern.
Because of the thermal limits of conventionalliquid lubricants,
vapor/mist phase lubrication (VMPL) has received atten-tion over
the past decade as an alternative approach for
high-temperaturelubrication.
VMPL is a unique lubrication technology where a small quantity
of an organicliquid lubricant is either vaporized or misted into a
high-velocity stream of air.The air-lubricant stream is directed
toward bearings and/or gears. This tech-nology has substantial
potential for near-term use as an emergency backupsystem for
loss-of-oil situations in aircraft and couldserve, with further
renements, as the primary lubrica-tion system for advanced aircraft
of the future.
Nearly all previous work, including that by NASA andthe Air
Force, involving VMPL focused on the use of organophosphorous oils.
Although these oils adequately
lubricated bearings and gears, it was found that the oilsreacted
excessively with the bearing and gear surfaces,leading to
unacceptable wear rates and erratic tempera-ture spikes. Research
at the NASA Glenn ResearchCenter identied a thioether lubricant
that providesoutstanding lubrication with no detectable wear of
thebearing and gear components and elimination of thetemperature
spikes.
A series of tests were concluded thisyear that involved the
lubrication of aspur gearbox rig using the thioether as the
vapor/mist phase lubricant. Twospur gears were loaded against
eachother in excess of 1-GPa pressure toensure boundary lubricating
conditions,and they were operated at 10,000 rpm.The thioether was
delivered to the spur gears as a ne mist or fog at a rate of
only
Thioether Tested for the High-Temperature Vapor/Mist Phase
Lubrication ofBearings and Gears
Shop air (120 psi) Filter
Air-pressureregulator
Lubricant reservoir and mist system
Vent for vaporsSeparator
Test gearbox
Lubrication jets
Control valves
Thermocouple to recordgearbox ambient
temperature
Vapor/mist phase lubrication system.
