UROP Proposal Advanced Aircraft Wing Structural Design and Fabrication

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

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


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.


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.


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.


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.


Various Structural Designs and Materials

Options Advantages Disadvantages

Lea

din

g E

dge

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

Sp

ar

Des

ign

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

Rib

Des

ign

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


Criteria

Criteria

Ob

ject

ives

Light Weight Torsional Strength Consistent Airfoil and

Leading Edge Shape

Load Factor plus Safety

Factor

• Negative G

• Positive G

Efficient

Manufacturing

Go

als

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

Sp

ecif

icati

on

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


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.


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.


Source of Project Cost

ITEMS QUANTITY UNIT MATERIAL

COST ($)

SA

FE

TY

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

TO

OL

S

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

MA

TE

RIA

LS

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


Timeline: Summer 2015

Task

Wee

k 1

- W

eek

2 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

Wee

k 3

- W

eek

5 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


Wee

k 6

-Wee

k 7

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


Wee

k 8

- W

eek

9 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


Wee

k 1

0

Compile and compare data

Document the advantages and disadvantages of each procedure

Determine which prototype met all the stated criteria


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.

Documents

UROP Proposal Advanced Aircraft Wing Structural Design and Fabrication