The document outlines a research project to design and test advanced wing structures for unmanned aerial vehicles that are lighter yet able to withstand greater loads. Various wing design options and materials will be considered and prototypes will be manufactured and tested to evaluate their strength, weight, production cost, and feasibility. The goals are to develop a wing design that meets criteria for the annual AIAA Student Design Build Fly competition and can be modified for future competitive aircraft designs.

1. Advanced Aircraft Wing Structural
Design and Fabrication
By Laliphat (Mai) Kositchaimongkol, Saho King, Richard Cheng,
Don Raveen Solanga Arachchige, and Ryan Razo
Faculty Advisor: Professor Robert H. Liebeck
Graduate Student Advisor: Colin A. Sledge

2. Advanced Aircraft Wing Structural Design and Fabrication 2
Table of Contents
Introduction………………………………………………………………………………………. 3
Background………………………………………………………………………………………. 3
Methods and Preliminary Experimentation on the Wing……….……………………………….. 5
Proposed Work……………………………………………………………….……..………….... 6
Various Structural Designs and Materials Table………………………………………..……….. 7
Criteria Table…………………………………………………………………………………….. 8
Applications..…………………………………………………………………………………….. 9
Student Specific Responsibility……….………………………………………………………......9
Source of Project Cost…………………………………………………………………………...11
Timeline………………………………………………………………………………………….12
References………………………………………………………………………………………..13

3. Advanced Aircraft Wing Structural Design and Fabrication 3
Introduction:
Unmanned Aerial Vehicles (UAVs) are becoming increasingly prominent in various commercial
and military applications. The combination of being able to remotely pilot a UAV along with a
generally faster manufacturing process as opposed to a traditional manned aircraft has captured
the interest of many aerospace companies and organizations. UAVs are already being used for
aerial reconnaissance, search and rescue, crop dusting, disaster effects management, and even
monitoring air pollution. To accomplish these tasks even more efficiently in the future, a great
deal of improvements to structural components needs to be researched.
One of the most essential components of an airplane is the wing, as it generates lift during flight
and must support the weight of the aircraft in straight and level flight, and higher loads in
accelerated flight, such as a turn. The weight of the plane directly affects the loads experienced
by the plane, and thus determines how much lift is required. For these reasons, the wings need to
stay light while also being strong enough to resist the loads.
Different structural designs and construction methods affect an aircraft's weight and robustness.
Wings are a substantial part of the weight, and its strength is important for reasons previously
mentioned. The advantages and disadvantages of different wing structural designs and
construction methods on UAVs and small remotely piloted aircraft will be researched. By
analyzing these differences, more informed decisions will be made in the future when designing
structures for specific tasks.
Background:
One relevant application from this research is designing and building remotely piloted electric
airplanes for the annual international AIAA Student Design Build Fly (DBF) competition. The
UCI DBF team has competed in this competition for the past ten years and has placed within the
top two against one hundred schools for the past four years. With different mission criteria each
year, competing teams design their own remotely piloted airplane and then fly a number of
missions with a variety of payloads. Weight is a critical metric in aircraft design. In the Design
Build Fly competition, for example, the scoring system used makes weight paramount, as the
weight always divides the score. The wing weight is a substantial contributor to the overall
weight and the necessity of a lightweight structure with reliable performance is crucial to the
success of the project. Because some of the missions are speed oriented, torsional and bending
strength are critical to mission success. Consequently, designing a wing that can meet the proper
criteria and can be quickly redesigned and built is of the utmost importance.

4. Advanced Aircraft Wing Structural Design and Fabrication 4
Figure 2. A computer-aided design (CAD) of the
balsa wing that was used in the 2015 DBF
competition. It shows the leading edge, ribs, spar,
and heat shrink wrap.
Over the past three years, the UCI DBF team has changed the wing structural design and
manufacturing methods from using foam to balsa wood in order to make the wing lighter. In one
of the previous structures, the foam wings contained a spar composed of foam wrapped in carbon
fiber. This wing provided bending and torsional strength due to the rigidity of the foam and the
carbon fiber spar, however it was heavy. While this design was functional, a major disadvantage
was its weight. In a competition where weight plays a critical role, the team decided to explore
different avenues. Currently, the wings are
comprised of balsa wood ribs, a balsa
wood spar with a square cross-section, and
a foam trailing edge with a fiberglass skin.
These wing components are covered with a
lightweight plastic film that shrinks when
heat is applied. This lightweight skin is
responsible for a portion of the torsional
rigidity. While this design is lightweight,
it is not as torsionally rigid as some of the
previous wing structures. The torsional rigidity of the wing is an important parameter in terms of
aeroelasticity. Aileron reversal can be a limiting criterion for high speed flight. The aileron is a
control surface on the trailing edge of the wing that controls the roll of the aircraft when
deflected. Once deflected, the torsional moment of the wing, about the spar, changes and a wing
that is compliant will twist. Aileron deflection increases the coefficient of lift for the given angle
of attack, while the compliance of the wing
will generally lower the angle of attack. At
the aileron reversal speed, the increase in
the angle of attack due to the flap
deflection is negated by the twist of the
wing caused by the increase in the torsional
moment due to this same deflection. At
velocities above the aileron reversal speed,
the deflection of the trailing edge flaps will
have an opposite rolling effect due to the
torsional deflection, which can lead to a
total loss in control.
Figure 1. The foam wing (top) that the UCI DBF team
manufactured and used in the 2012 competition. The
current balsa wing structure (bottom) used on the UCI
DBF airplane in the 2015 competition.

5. Advanced Aircraft Wing Structural Design and Fabrication 5
Figure 3. Detailed image of the components that
make up a wing.
Methods and Preliminary Experimentation on the Wing:
In the past, there have been issues with torsional rigidity which has led to investigations of a
wing made up of a molded composite leading edge and a balsa structure. The major challenges
with using composites for the leading edge include the difficulty of controlling the weight and
producing the proper stiffness. The first attempt of a molded leading edge used two layers of
carbon veil with a single layer of fiberglass. The second attempt had a single layer of kevlar with
an additional piece on the root of the wing, but resulted in considerable buckling in the leading
edge due to a lack of stiffness. A carbon fiber rod was implanted in the spar to resolve the
bending and torsional issues. A general consensus was reached that a wing with a molded kevlar
leading edge would not be as stiff and as light as the balsa wing, unless the wing design was
changed as well. These results have shown that further research will be worthwhile.
The core components of a wing include a
thin skin stiffened by a combination of ribs
and a spar. The skin is the outer surface of
a wing, typically made of lightweight
composite materials or heat shrink wrap.
The inner skeleton of the wing consists of
the ribs, which provide strength and
rigidity. The ribs also provide the airfoil
shape. At the core of the wing is the spar,
which extends along the span of the wing
and is designed to carry the bending
loads, as well as a portion of the torsional
loads, and transfer them to the rest of the airplane.
In flight, a wing’s structure must be able to withstand various loads, mainly bending and torsion.
The wing can be thought of as a cantilever beam with a distributed load because it is attached at
one end and free at the other. Bending moments at any particular section of a wing are produced
by the span-wise lift load. These loads put compression on top of the wing and tension on the
bottom of the wing. Putting a carbon tube along the spar has been shown to add strength and help
the wing to resist some of the bending forces; however, it is uncertain if torsional strength was
gained. A wing’s torsional strength can be evaluated through deflection, the angle the wing is
displaced under a load.

6. Advanced Aircraft Wing Structural Design and Fabrication 6
Figure 5. The airfoil used to shape the wing.
Proposed Work: Advanced Aircraft Wing Structural Design and Fabrication
The main objective for this summer research project is to design a wing that is lighter, yet able to
withstand more force as, if not more than, the current wing. This means the wing will have to be
able to support the same load factor of 6.5G, where 1G is equivalent to 7.5 lbs. It will also need
to have an accurate airfoil shape, a smooth leading edge, and be able to withstand at least the
same amount of torque (refer to criteria table). In addition to performing well, it will also have to
be easy and relatively cost effective to manufacture.
The first design will consist of a molded leading edge integrated with a redesigned spar which
will reduce the overall weight of the structure as well as add more torsional stiffness. The second
design will have a closed D section molded leading edge integrated with the spar that will
provide much more rigidity and torsional strength to the wing. The third design will contain a
foam leading edge with a balsa wing which will make use of the foam’s rigidity. The three
designs will be narrowed down to one final design after the properties of both the materials and
the structures have been analyzed based on knowledge of previously constructed designs and
relevant resources. The final design will be manufactured, and based on its structural
deficiencies, redesigns will be made for a second prototype to be constructed along with a third
prototype following this basis. After conducting extensive analyses, the prototype that meets all
or most of the criteria will be further analyzed for the final report.

7. Advanced Aircraft Wing Structural Design and Fabrication 7
Various Structural Designs and Materials
Options Advantages Disadvantages
LeadingEdge
Balsa
Unidirectional grain
provides a specific
direction for the internal
structural strength
Provides more strength in
the grain direction
Molded
Allow us to pick the
directions of the fibers of
materials
Hard to control the weight
of the resin in the molded
part
Foam Stiff tendencies Heavy
SparDesign
I-beam
Lighter and lower cost of
materials, good at resisting
bending
Does not provide torsional
strength to the wing
Solid Square
Fastest manufacturing
process. Flat face allows
easy attachment of ribs
Very heavy
Hollow Square Block
Fast manufacturing
process. Provides more
torsional strength that I-
beam
Heavier than I-beam
Tapered
Combining different spar
structures can make it
lighter
Complicated
manufacturing process
Carbon Tube
Good in bending and
torsion, lower
manufacturing time
Expensive, heavy
RibDesign
Thickness
Thicker makes the wing
stronger
Greater thickness
increases weight
Spacing
Increasing spacing
decreases weight
Wing skin warps with
increased spacing, doesn't
keep airfoil shape
Holes
Increasing the size of the
holes lightens weight
Increasing size of the
holes weakens the ribs

8. Advanced Aircraft Wing Structural Design and Fabrication 8
Criteria
Criteria
Objectives
Light Weight Torsional Strength Consistent Airfoil and
Leading Edge Shape
Load Factor plus Safety
Factor
• Negative G
• Positive G
Efficient
Manufacturing
Goals
Lighter than 7
oz.
An angle of
deflection
less than the angle
of deflection on the
benchmark wing
• Whole wing’s shape is
consistent with the airfoil
• Leading edge holds its
shape; doesn’t buckle
nor warp
• Positive G
6.5 G (48.75 lbs total)
• Negative G
1 to 3 G
• Manufacture parts
time-efficiently and
cost-efficiently
Specification
Weight
• Aileron reversal
speed
• Angular deflection
• Torsional stiffness
• Airfoil has an error
within 1/8th of an inch,
based on developer
specifications in all
directions
• 1G = 7.5lbs
• Bank Angle over
60 degrees
• Pull-up Maneuver
• Time (hours/days)
Less than 7 days for
manufacturing
process
• Number of people
required
The bending loads will be accounted for in the flexure formula from Mechanics of Materials by
R.C. Hibbeler. This equation will relate the stress distribution in the wing to the internal resultant
bending moment, which is the result of the lift loads:
where, = the maximum normal stress in the member, which occurs at a point on the cross-
sectional area furthest away from the neutral axis
M = the resultant internal moment, which is calculated about the neutral axis of the
cross section.
c = the perpendicular distance from the neutral axis which is on the centroid of the
cross-sectional area to a point farthest away from the neutral axis. This is where
acts.
I = the moment of inertia of the cross-sectional area about the neutral axis.
The failure strength, or the amount of stress that the wing can endure before breaking, can be
varied by changing the material of the leading edge. “M” is dependent on the lift of the load on
the spar. “c” is the function of the thickness of the spar, the distance from the neutral axis. Since
the wing structures will heavily rely on adhesive bonds between the components, the overall

9. Advanced Aircraft Wing Structural Design and Fabrication 9
rigidity of, and hence success of the wings, will be closely related to the strength of the glue
bonds, more research will also be conducted analyzing the strengths of different glue bonds.
Applications:
Since aircraft are controlled through a combination of thrust and lift, the mechanical parts
producing these two forces are expected to be reliable to the pilot. However to push an aircraft to
its limits, these two components must also be durable, lightweight, and emerge from a
thoroughly thought out design. In this project, a wide variety of wing structures will be studied to
create different prototypes, which will then be analyzed for strength, weight, production cost,
and manufacturing feasibility. The UCI DBF team takes all of these criteria into serious
consideration for every part that goes into a plane; as the budget and time for completion is
limited, and the scoring for the yearly competition is based heavily on overall weight and
performance in flight. In the past there have been difficulties with developing substantial
torsional strength in the balsa wings; these problems in wing failure can be largely attributed to
insufficient testing and research conducted on wing structure designs. This research will ensure
that a wing that has been thoroughly tested for varying types of loads can be used and modified
for competitive planes in the future.
Student Specific Responsibility:
Chief Engineer: Laliphat (Mai) Kositchaimongkol
As the chief engineer of this project, my responsibilities include researching various wing
structural designs and fabrication methods, designing and finalizing all of the upcoming
prototypes, evaluating the disadvantages and advantages of each prototype and manufacturing
procedures, validating the quality of each prototype compared to the criteria, and collaborating
with all of the team members and Professor Liebeck. Additionally, I will be responsible for
debriefing the team weekly and updating Professor Liebeck on our progress. In order to follow
our progress, I will be supervising the progress of each of the team members and documenting
the structural designs, fabrication, structural deficiencies, and quality of the prototypes.
Testing Engineer: Don Raveen Solanga Arachchige
I will be responsible for testing the various aspects of the wings to validate the analytical models
we use to design the wing. The testing procedures will be done after building a test stand to hold
the wing firmly in place. I will be doing a bending test by loading sandbags on the wing to
simulate the G forces the wing will experience during flight, a torsional test on the wing to see
how much it will twist while in flight, and also be testing the buckling of the material on the
leading edge of the wing. The results will be used to analyze to our theoretical data we had
calculated and to select materials that complement each other and build a better wing than the
previous.

10. Advanced Aircraft Wing Structural Design and Fabrication 10
Structural Design Engineers: Saho King and Richard Cheng
We will be responsible for researching the advantages and disadvantages of the materials in
consideration. With this, we will collaborate with the chief engineer to develop the various wing
designs. Then, we will evaluate their structural integrity based on calculations. If the analysis
shows the structure is unstable, we will rework with the chief engineer on modifications. If the
analysis shows the structure is stable, we will communicate with the rest of the team to illustrate
the specifics of the design. We will collaborate with the manufacturing engineer on the methods
of production to minimize manufacturing errors that may affect the design. Furthermore, we will
be responsible for creating the computer-aided design (CAD) of each of the designs so we can
conduct analysis on them before manufacturing.
Manufacturing Engineer: Ryan Razo
I will be responsible for researching the proper ways to manufacture the structures that we will
be assembling as well as leading my team through the manufacturing processes. During the
research portion of my job, collaboration with the chief engineer will be essential; this research
will take into account other structural wing designs that have been constructed for past DBF
competitions, as well as searching other resources to see how other structures may be assembled.
In extension to this I will ensure that my team is using machinery properly and is equipped with
the proper safety equipment while working with hazardous materials such as carbon fiber,
acetone, and resin. My job will also consist of cutting any foam needed for the project on the
computer numerical control (CNC) machine and preparing it for assembly by both dry and wet
sanding the foam. As the materials may not come in the desired dimensions or quality, I will be
checking materials for acceptable quality as well as cutting them to the required sizes. After each
day, I shall document the daily progress and check that our work has been constructed properly.

11. Advanced Aircraft Wing Structural Design and Fabrication 11
Source of Project Cost
ITEMS QUANTITY UNIT
MATERIAL
COST ($)
SAFETY
Gloves 1.0 box of 200 $10.00
Safety Goggles 5.0 goggle $32.50
Dust Mask 1.0 box of 50 $6.00
Protective Suit 5.0 suit $48.25
Pumice Hand Soap 1.0 1/2 litter $20.00
Subtotal $116.75
TOOLS
Epoxy Spreader 5.0 spreader $10.00
Popsicle Sticks 1.0 box of 100 $4.00
Plastic Cups 2.0 cup $4.00
Kevlar Scissor 1.0 scissor $50.00
Scissor 2.0 scissor $20.00
Subtotal $88.00
MATERIALS
Balsa Wood 60.0 sheet of 4" x 36" $200.00
Fiberglass 1.0 roll of 38" x 15' $65.95
Wax Paper 1.0 box of 11.9" x 75' $5.00
Kevlar 10.0 roll of 39.37" x 24" $169.50
Carbon Rods 4.0
2 m rod with 0.010"
dia.
$30.00
Carbon Fiber 1.0 roll of 0.787" x 25" $29.95
Epoxy Resin 1.0 gallon $101.00
Epoxy Hardener 1.0 27.5oz can $55.00
Cyanoacrylate Super Glue (fast curing) 3.0 2oz bottle $30.00
Cyanoacrylate Super Glue (slow curing) 3.0 2oz bottle $30.00
Foam 1.0 block of 3"x24"x96" $16.35
Vacuum Bag 1.0 roll $30.00
Vacuum Bag Sealant Tape 4.0 roll $80.00
Masking Tape 2.0 roll of 0.94" x 180.3' $6.00
Freezer Paper 1.0 roll of 18" x 50' $5.00
Brushes 5.0 1" brush $5.00
Acetone 1.0 gallon $16.77
Paper Towel 6.0 roll $30.00
Heat Shrink Wrap (Microlite) 4.0 roll $55.96
Sealing Iron and Heat Gun 1.0 set $32.95
Subtotal $994.43
Subtotals $1,142.25

12. Advanced Aircraft Wing Structural Design and Fabrication 12
Timeline: Summer 2015
Task
Week1-Week2
Develop the testing criteria
Research different materials and their advantages and disadvantages
Calculate the strength of the benchmark balsa wing
Manufacture the benchmark balsa wing and document the procedure
Test the benchmark wing
Collect and analyze data
Week3-Week5
Research and develop three prototypes of different structural designs
Calculate and predict the strength, advantages, and disadvantages of each prototype
Finalize the design and select the best prototype to build
Manufacture prototype one and document the procedure
Test prototype one
Collect and analyze data
Week6-Week7
Redesign prototype one based on its structure deficiencies
Finalize the design of prototype two
Calculate and predict the strength of this prototype
Manufacture prototype two and document the procedure
Test prototype two
Collect and analyze data
Week8-Week9
Redesign prototype two based on its structural deficiencies
Finalize the design of prototype three
Calculate and predict the strength of this prototype
Manufacture prototype three and document the procedure
Test prototype three
Collect and analyze data
Week10
Compile and compare data
Document the advantages and disadvantages of each procedure
Determine which prototype met all the stated criteria

13. Advanced Aircraft Wing Structural Design and Fabrication 13
References:
Abbott, Ira H. & Von Doenhoff, Albert E., Theory of Wing Sections, 1st ed., Dover Publications,
Inc., New York, 1959.
Anderson, John D. Jr., The Airplane: A History of Its Technology, the American Institute of
Aeronautics and Astronautics, Inc., Reston, Virginia, 2002.
Anderson, John D. Jr., Aircraft Performance and Design, the McGraw-Hill Companies, Inc.,
1999.
Hibbeler, R.C. , Mechanics of Materials, 8th ed., Prentice Hall, Upper Saddle River, NJ, 2011.
“Major Components (Part One) Fuselage and Wings.” FlightLearnings. Accessed May 1, 2014.
http://www.flightlearnings.com/2011/03/15/major-components-part-one-fuselage-and-wings/.
Megson, T.H.G. , An Introduction to Aircraft Structural Analysis, Elsevier, India, 2010.
Schaufele, Roger D. , The Elements of Aircraft Preliminary Design, Aries Publications, Santa
Ana, CA, 2007.
Wright, Jan R. & Cooper, Jonathan E. , Introduction to Aircraft Aeroelasticity and Loads, John
Wiley & Sons, Ltd, 2007.