08-10-2016, 10:06 AM
[attachment=72701]
Since its founding, NASA has been dedicated to the
advancement of aeronautics and space science. The
NASA Scientific and Technical Information (STI)
Program Office plays a key part in helping NASA
maintain this important role.
The NASA STI Program Office is operated by
Langley Research Center, the lead center for NASA’s
scientific and technical information. The NASA STI
Program Office provides access to the NASA STI
Database, the largest collection of aeronautical and
space science STI in the world. The Program Office is
also NASA’s institutional mechanism for
disseminating the results of its research and
development activities. These results are published by
NASA in the NASA STI Report Series, which
includes the following report types:
• TECHNICAL PUBLICATION. Reports of
completed research or a major significant phase
of research that present the results of NASA
programs and include extensive data or
theoretical analysis. Includes compilations of
significant scientific and technical data and
information deemed to be of continuing
reference value. NASA counterpart of peerreviewed
formal professional papers, but having
less stringent limitations on manuscript length
and extent of graphic presentations.
• TECHNICAL MEMORANDUM. Scientific
and technical findings 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. Scientific and
technical findings by NASA-sponsored
contractors and grantees.
CONFERENCE PUBLICATION. Collected
papers from scientific and technical
conferences, symposia, seminars, or other
meetings sponsored or co-sponsored by NASA.
• SPECIAL PUBLICATION. Scientific,
technical, or historical information from NASA
programs, projects, and missions, often
concerned with subjects having substantial
public interest.
• TECHNICAL TRANSLATION. Englishlanguage
translations of foreign scientific and
technical material pertinent to NASA’s mission.
Specialized services that complement the STI
Program Office’s diverse offerings include creating
custom thesauri, building customized databases,
organizing and publishing research results ... even
providing videos.
For more information about the NASA STI Program
Office, see the following:
• Access the NASA STI Program Home Page at
http://www.sti.nasa.gov
• E-mail your question via the Internet to
help[at]sti.nasa.gov
• Fax your question to the NASA STI Help Desk
at (301) 621-0134
• Phone the NASA STI Help Desk at
(301) 621-0390
• Write to:
NASA STI Help Desk
NASA Center for AeroSpace Information
7121 Standard Drive
Hanover, MD 21076-1320
Abstract
This is a final report on the research studies completed under NASA Grant NAG 1-03045,
“Development of Micro Air Vehicle Technology with In-Flight Adaptrive-Wing Structure.” This
project involved the development of variable-camber technology to achieve efficient design of
micro air vehicles. Specifically, it focused on the following topics:
1) Low Reynolds number wind tunnel testing of cambered-plate wings.
2) Theoretical performance analysis of micro air vehicles.
3) Design of a variable-camber MAV actuated by micro servos.
4) Test flights of a variable-camber MAV.
The results have been disseminated in the form of papers and seminar presentations and 2
master’s theses (see the list of publications). The grant also played an important role in the
organization of the 2004 International Micro Air Vehicle Competition hosted by the University
of Arizona on April 9-10, 2004.
Low Reynolds Number Wind Tunnel Testing of Cambered-Plate Wings
Four 9-inch micro air vehicle (MAV) wind tunnel models utilizing thin, cambered-plate airfoils
with cambers of 3, 6, 9, and 12% were tested in the Low Speed Wind Tunnel (LSWT, Figure 1)
at the University of Arizona (UA). Test velocities were 5 and 10 m/s, corresponding to Reynolds
Numbers (Re) of 4 6×10 and 5 1.2 1× 0 , respectively. Each model was tested for angle of attack,
α, ranging from approximately -10° to 32° (due to the slightly varying geometry of each model,
minimum and maximum angles of attack tested varied slightly).
Data recorded for each test consisted of the lift, drag, and pitching moment of the vehicle about
the ¼-chord point. With this raw wind tunnel data in hand, the lift, drag, and pitching moment
coefficients (CL, CD, and CM, respectively) were computed and plotted versus angle of attack.
These plots were later used in a theoretical performance analysis of a MAV.
1.1. Airfoil design for a variable camber wing
The latest airfoil that had been designed for MAV use by the UA is designated the S5010-
TOP24C [1] and is based upon the Selig 5010 flying wing airfoil. The airfoil is a thin, cambered- plate design with 6% camber and features a slight reflex in the trailing edge to reduce the
strength of the inherent, negative pitching moment. It was originally thought that the negative
pitching moment could easily be compensated for by a slight amount of up-elevator deflection on
an actual flying model. However, flight tests of MAVs implementing this airfoil proved
otherwise. The negative pitching moment could be compensated for but it took large up-elevator
deflections to do so. The result was increased drag and a substantially reduced endurance.
To remedy the situation, the reflex in the airfoil was increased using a trial-and-error approach.
A small amount of reflex was added and a flight test was performed to evaluate the flight
characteristics of the modified airfoil. After three successive reflex iterations (all completed
within two days), the proper amount of reflex was found. The result was an MAV that could
attain straight and level flight with minimal, if any, up-elevator deflection and substantially
increased endurance. The modified version of the airfoil is designated S5010-TOP24C-REF
(Figure 2) and has been successfully used on all flying MAVs developed at the UA since 2003.
Airfoils of 3, 6, 9 and 12% camber were employed in the study and the airfoil geometrical data is
presented in Table 1. All of the wind tunnel models tested were based upon the same S5010-
TOP24C-REF airfoil and represented, as close as possible, an accurate model based upon the
mechanics of an actual in-flight adaptive wing MAV. This means that if a 3% cambered-plate
wing was physically deformed to now have 6% camber, the 6% camber wind tunnel model wing
would realistically represent the 3% cambered wing that was deformed into 6% camber. Because
of this, all wind tunnel models had identical wetted areas (the true, wetted surface area of the top surface was 60 in2
for all models) and different projected areas. The difference in projected areas
is due to the decreased chord length seen when an increase in camber is induced.
The process of creating the different cambered airfoil shapes was fairly straightforward and done
using a JAVA-based program called JavaFoil [2]. In this program, airfoil coordinates are entered
and the geometry easily modified by simply entering new parameters (camber, chord, etc.). The
modified airfoil coordinates are then produced; they are easily copied and pasted into Microsoft
Excel for plotting and the subsequent printing of templates.
MAV wind tunnel model construction
In this section, the entire process used to construct a wind tunnel model is described in detail. It
includes the mold, wing, and fuselage construction process.
1.2.1. Mold construction
The physical construction of the MAV wind tunnel models started with the design and
construction of the molds for the different cambered wings. To construct a mold, a full-sized
paper template of the airfoil was created, printed, cut out, and then traced onto 1/64-inch birch
plywood. The airfoil shape was then cut out of the plywood, sanded smooth, and two holes were
drilled into it to aid in the subsequent foam mold cutting process (Figure 3). Two such plywood
templates were produced for each camber.
. Wing Construction
The wings of the MAV wind tunnel models are made from one sheet of 6 oz/yd2
bi-directional
carbon-fiber cloth laminated with epoxy resin and are constructed using the female airfoil mold.
Either the female or male mold could have been used, but the female mold was selected because
it results in a smooth surface on the top of the finished wing. The wing construction process
begins with the cutting of an approximately 10 10 × -inch sheet of the carbon fiber cloth. Also, a
piece of vacuum-bag plastic is affixed to the mold using spray adhesive so that the epoxy resin
does not stick to the foam, making the wing easy to remove from the mold when cured. With
these two steps complete, the epoxy resin and hardener are mixed and the piece of carbon-fiber
cloth is laid into the mold and laminated with the epoxy using a small plastic squeegee. Care is
taken at this time to remove any excess resin from the carbon cloth so that the wing is as thin,
smooth, and clean as possible when it has finished curing.
At this point a piece of porous “peel ply” is placed over the laminated (yet still uncured) wing
and paper towels are placed on top of the peel ply. With this system, any excess epoxy in the
wing is squeezed out through the peel ply during the vacuum-bagging process and is absorbed by
the paper towels, resulting in a thin, clean and lightweight wing (extremely important for an
actual flying model). Then the mold and laminated wing are wrapped in a layer of breather cloth
and placed into the vacuum bag. The breather cloth allows air to circulate over and around the
mold evenly so that an even pressure is applied to the wing in all places during the curing
process. With the wing and the mold in the bag, the vacuum pump is turned on and the ends of
the bag are sealed. The vacuum in the bag is set to approximately 6-7 lb/in2
and the wing is
allowed to cure at least 6 hours. At a vacuum setting of 6-7 lb/in2
, the wing is sufficiently and
evenly compressed into the mold and the foam mold is safe from crushing or deforming under
the pressure
Test procedure
After the MAV model was mounted in the tunnel, the pitch rod was placed in its “home”
position, that is, at it uppermost limit of travel. In this position, the MAV model was in its most
negative angle of attack. At this point the initial angle of attack was measured using a precision
bubble-level and recorded. At this point the test section was sealed up and the testing sequence
began.
At first tares were taken on all DAQ channels (zeroed) for a period of 10 seconds so that the
model weight and any other associated forces present in the equipment would not be associated
with forces produced by the model during testing. With the tares taken, the tunnel was started
and the tunnel velocity was brought up to the testing velocity of either 5 or 10 m/s depending
upon which test was being run at the time. When the tunnel velocity had stabilized, the data
acquisition process was initiated by clicking on a virtual LabView button designated for the data
taking process. During the data acquisition process, each channel was sampled at a rate of 1000
samples per second for a period of 10 seconds, and the forces were averaged and recorded. At
the end of the 10-second sampling period, the angle of attack of the model was increased by 1.3°,
corresponding to two “clicks” of the electronically-actuated pitch rod mechanism. The sampling
process was then repeated for each angle of attack until the pitch rod mechanism had reached the
limit of its travel. When the last measurement had taken place, the test was completed by
clicking on a virtual LabView button designated for the task, and at his point the data was
automatically written to a Microsoft Excel spreadsheet for later computations and analysis. It
should be noted that during the entire testing sequence the dynamic pressure was closely
monitored so that it could be kept extremely constant with the hand-operated fan RPM control
unit. This identical testing sequence was performed on each of the four different cambers at
velocities of both 5 and 10 m/s, corresponding to Reynolds Numbers of 6x104
and 1.2x105
,
respectively.
Since its founding, NASA has been dedicated to the
advancement of aeronautics and space science. The
NASA Scientific and Technical Information (STI)
Program Office plays a key part in helping NASA
maintain this important role.
The NASA STI Program Office is operated by
Langley Research Center, the lead center for NASA’s
scientific and technical information. The NASA STI
Program Office provides access to the NASA STI
Database, the largest collection of aeronautical and
space science STI in the world. The Program Office is
also NASA’s institutional mechanism for
disseminating the results of its research and
development activities. These results are published by
NASA in the NASA STI Report Series, which
includes the following report types:
• TECHNICAL PUBLICATION. Reports of
completed research or a major significant phase
of research that present the results of NASA
programs and include extensive data or
theoretical analysis. Includes compilations of
significant scientific and technical data and
information deemed to be of continuing
reference value. NASA counterpart of peerreviewed
formal professional papers, but having
less stringent limitations on manuscript length
and extent of graphic presentations.
• TECHNICAL MEMORANDUM. Scientific
and technical findings 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. Scientific and
technical findings by NASA-sponsored
contractors and grantees.
CONFERENCE PUBLICATION. Collected
papers from scientific and technical
conferences, symposia, seminars, or other
meetings sponsored or co-sponsored by NASA.
• SPECIAL PUBLICATION. Scientific,
technical, or historical information from NASA
programs, projects, and missions, often
concerned with subjects having substantial
public interest.
• TECHNICAL TRANSLATION. Englishlanguage
translations of foreign scientific and
technical material pertinent to NASA’s mission.
Specialized services that complement the STI
Program Office’s diverse offerings include creating
custom thesauri, building customized databases,
organizing and publishing research results ... even
providing videos.
For more information about the NASA STI Program
Office, see the following:
• Access the NASA STI Program Home Page at
http://www.sti.nasa.gov
• E-mail your question via the Internet to
help[at]sti.nasa.gov
• Fax your question to the NASA STI Help Desk
at (301) 621-0134
• Phone the NASA STI Help Desk at
(301) 621-0390
• Write to:
NASA STI Help Desk
NASA Center for AeroSpace Information
7121 Standard Drive
Hanover, MD 21076-1320
Abstract
This is a final report on the research studies completed under NASA Grant NAG 1-03045,
“Development of Micro Air Vehicle Technology with In-Flight Adaptrive-Wing Structure.” This
project involved the development of variable-camber technology to achieve efficient design of
micro air vehicles. Specifically, it focused on the following topics:
1) Low Reynolds number wind tunnel testing of cambered-plate wings.
2) Theoretical performance analysis of micro air vehicles.
3) Design of a variable-camber MAV actuated by micro servos.
4) Test flights of a variable-camber MAV.
The results have been disseminated in the form of papers and seminar presentations and 2
master’s theses (see the list of publications). The grant also played an important role in the
organization of the 2004 International Micro Air Vehicle Competition hosted by the University
of Arizona on April 9-10, 2004.
Low Reynolds Number Wind Tunnel Testing of Cambered-Plate Wings
Four 9-inch micro air vehicle (MAV) wind tunnel models utilizing thin, cambered-plate airfoils
with cambers of 3, 6, 9, and 12% were tested in the Low Speed Wind Tunnel (LSWT, Figure 1)
at the University of Arizona (UA). Test velocities were 5 and 10 m/s, corresponding to Reynolds
Numbers (Re) of 4 6×10 and 5 1.2 1× 0 , respectively. Each model was tested for angle of attack,
α, ranging from approximately -10° to 32° (due to the slightly varying geometry of each model,
minimum and maximum angles of attack tested varied slightly).
Data recorded for each test consisted of the lift, drag, and pitching moment of the vehicle about
the ¼-chord point. With this raw wind tunnel data in hand, the lift, drag, and pitching moment
coefficients (CL, CD, and CM, respectively) were computed and plotted versus angle of attack.
These plots were later used in a theoretical performance analysis of a MAV.
1.1. Airfoil design for a variable camber wing
The latest airfoil that had been designed for MAV use by the UA is designated the S5010-
TOP24C [1] and is based upon the Selig 5010 flying wing airfoil. The airfoil is a thin, cambered- plate design with 6% camber and features a slight reflex in the trailing edge to reduce the
strength of the inherent, negative pitching moment. It was originally thought that the negative
pitching moment could easily be compensated for by a slight amount of up-elevator deflection on
an actual flying model. However, flight tests of MAVs implementing this airfoil proved
otherwise. The negative pitching moment could be compensated for but it took large up-elevator
deflections to do so. The result was increased drag and a substantially reduced endurance.
To remedy the situation, the reflex in the airfoil was increased using a trial-and-error approach.
A small amount of reflex was added and a flight test was performed to evaluate the flight
characteristics of the modified airfoil. After three successive reflex iterations (all completed
within two days), the proper amount of reflex was found. The result was an MAV that could
attain straight and level flight with minimal, if any, up-elevator deflection and substantially
increased endurance. The modified version of the airfoil is designated S5010-TOP24C-REF
(Figure 2) and has been successfully used on all flying MAVs developed at the UA since 2003.
Airfoils of 3, 6, 9 and 12% camber were employed in the study and the airfoil geometrical data is
presented in Table 1. All of the wind tunnel models tested were based upon the same S5010-
TOP24C-REF airfoil and represented, as close as possible, an accurate model based upon the
mechanics of an actual in-flight adaptive wing MAV. This means that if a 3% cambered-plate
wing was physically deformed to now have 6% camber, the 6% camber wind tunnel model wing
would realistically represent the 3% cambered wing that was deformed into 6% camber. Because
of this, all wind tunnel models had identical wetted areas (the true, wetted surface area of the top surface was 60 in2
for all models) and different projected areas. The difference in projected areas
is due to the decreased chord length seen when an increase in camber is induced.
The process of creating the different cambered airfoil shapes was fairly straightforward and done
using a JAVA-based program called JavaFoil [2]. In this program, airfoil coordinates are entered
and the geometry easily modified by simply entering new parameters (camber, chord, etc.). The
modified airfoil coordinates are then produced; they are easily copied and pasted into Microsoft
Excel for plotting and the subsequent printing of templates.
MAV wind tunnel model construction
In this section, the entire process used to construct a wind tunnel model is described in detail. It
includes the mold, wing, and fuselage construction process.
1.2.1. Mold construction
The physical construction of the MAV wind tunnel models started with the design and
construction of the molds for the different cambered wings. To construct a mold, a full-sized
paper template of the airfoil was created, printed, cut out, and then traced onto 1/64-inch birch
plywood. The airfoil shape was then cut out of the plywood, sanded smooth, and two holes were
drilled into it to aid in the subsequent foam mold cutting process (Figure 3). Two such plywood
templates were produced for each camber.
. Wing Construction
The wings of the MAV wind tunnel models are made from one sheet of 6 oz/yd2
bi-directional
carbon-fiber cloth laminated with epoxy resin and are constructed using the female airfoil mold.
Either the female or male mold could have been used, but the female mold was selected because
it results in a smooth surface on the top of the finished wing. The wing construction process
begins with the cutting of an approximately 10 10 × -inch sheet of the carbon fiber cloth. Also, a
piece of vacuum-bag plastic is affixed to the mold using spray adhesive so that the epoxy resin
does not stick to the foam, making the wing easy to remove from the mold when cured. With
these two steps complete, the epoxy resin and hardener are mixed and the piece of carbon-fiber
cloth is laid into the mold and laminated with the epoxy using a small plastic squeegee. Care is
taken at this time to remove any excess resin from the carbon cloth so that the wing is as thin,
smooth, and clean as possible when it has finished curing.
At this point a piece of porous “peel ply” is placed over the laminated (yet still uncured) wing
and paper towels are placed on top of the peel ply. With this system, any excess epoxy in the
wing is squeezed out through the peel ply during the vacuum-bagging process and is absorbed by
the paper towels, resulting in a thin, clean and lightweight wing (extremely important for an
actual flying model). Then the mold and laminated wing are wrapped in a layer of breather cloth
and placed into the vacuum bag. The breather cloth allows air to circulate over and around the
mold evenly so that an even pressure is applied to the wing in all places during the curing
process. With the wing and the mold in the bag, the vacuum pump is turned on and the ends of
the bag are sealed. The vacuum in the bag is set to approximately 6-7 lb/in2
and the wing is
allowed to cure at least 6 hours. At a vacuum setting of 6-7 lb/in2
, the wing is sufficiently and
evenly compressed into the mold and the foam mold is safe from crushing or deforming under
the pressure
Test procedure
After the MAV model was mounted in the tunnel, the pitch rod was placed in its “home”
position, that is, at it uppermost limit of travel. In this position, the MAV model was in its most
negative angle of attack. At this point the initial angle of attack was measured using a precision
bubble-level and recorded. At this point the test section was sealed up and the testing sequence
began.
At first tares were taken on all DAQ channels (zeroed) for a period of 10 seconds so that the
model weight and any other associated forces present in the equipment would not be associated
with forces produced by the model during testing. With the tares taken, the tunnel was started
and the tunnel velocity was brought up to the testing velocity of either 5 or 10 m/s depending
upon which test was being run at the time. When the tunnel velocity had stabilized, the data
acquisition process was initiated by clicking on a virtual LabView button designated for the data
taking process. During the data acquisition process, each channel was sampled at a rate of 1000
samples per second for a period of 10 seconds, and the forces were averaged and recorded. At
the end of the 10-second sampling period, the angle of attack of the model was increased by 1.3°,
corresponding to two “clicks” of the electronically-actuated pitch rod mechanism. The sampling
process was then repeated for each angle of attack until the pitch rod mechanism had reached the
limit of its travel. When the last measurement had taken place, the test was completed by
clicking on a virtual LabView button designated for the task, and at his point the data was
automatically written to a Microsoft Excel spreadsheet for later computations and analysis. It
should be noted that during the entire testing sequence the dynamic pressure was closely
monitored so that it could be kept extremely constant with the hand-operated fan RPM control
unit. This identical testing sequence was performed on each of the four different cambers at
velocities of both 5 and 10 m/s, corresponding to Reynolds Numbers of 6x104
and 1.2x105
,
respectively.