Solar Powered Airplane Literature Review

7/21/2019 Solar Powered Airplane Literature Review

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SOUTHERN ILLINOIS UNIVERSITY CARBONDALE

Solar-Powered Airplane

Literature Reiew

Senior Design Team 96

3/19/2009

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Solar-powered Airplane

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*+ ,ntroduction

Today, the vast majority of transportation vehicles around the world are powered by fossil

fuels. Moreover, this reality presents challenging problems to future generations. First, crude oil

and natural gas reserves are running out while the worlds demand is exponentially increasing.

Second, access to these resources will become more difficult to small companies and families as

gas or energy prices rise. astly, the extraction and production from fossil fuels results in a huge

environmental impact. !onsidering the three factors previously mentioned, it ma"es sense to

find other clean and sustainable ways to power our society.

The concept of creating an airplane that flies without using any fuel is not a new idea by

any means. #n the past three decades there have been many attempts to develop this type of

plane. Throughout the last thirty years, a common constraint was that technology could not meet

the re$uirements of the respective models. %owadays, present advances in nanotechnology,

composite materials and photovoltaic have significantly changed the scenario.

&athfinder, 'elios, Solar impulse, S"y(sailor and !enturion, just to name a few, are great

examples of solar(powered airplanes. These designs can be separated in two groups, manned or

unmanned. ) manned airplane needs to account for a larger number of factors such as extra

weight, si*e, power and security.

This literature research intends to study prior attempts in the incursion of the solar(

powered airplanes in order to understand the basics of this challenging concept. The literature

review describes subsystems such as solar panels, energy storage, type of motor and transmitters.

Furthermore, after the conclusion of this report, and based on the information collected from the

research, senior design team + will begin its own solar(powered airplane project.

-+ .istory of Solar Po$ered Flight

There have been several attempts in solar flight since the first ever solar powered model

too" flight on %ovember -, +/-. Solar &ower involves collecting energy from the sun0s rays and

using it for power or storing it for later use. oc"heed contracted )stroFlight, a 1nited States

21S3 company to research alternative fuel sources. Sunrise, as it was called, used just over 444


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solar cells yet only produced -54 watts of power. This would be enough to get its 6 lbs and 76 ft

wingspan to 64, 444 ft, which was a world record until the same company produced the Sunrise

## in +/5. Sunrise ## used --84 solar cells and delivered 44 watts of power. The succeeding

model was superior because it weighed just less than - lbs and could climb to an altitude of

/5,444 ft.

The next attempt would not be for another 5 years, when in +84 )ero9ironment a 1S

based company bac"ed by the :upont !orporation started to build the solar aircraft called The

;ossamer &enguin, a fragile and not very airworthy aircraft model. The name would later be

changed to 3.

1nli"e previous attempts, this prototype lac"ed the airplane model. ')S> was a simple

flying wing with a wingspan of +8 ft 274 m3. The main wing was made of carbon fiber

Styrofoam and =evlar which was covered by a thin Mylar plastic film. The overall result was a

light and extraordinarily strong material. There were + test flights done with the ')S>, but

after further review it was determined that the photovoltaic technology had not advanced enough

to continue.

Ten years later %)S) restarted its own ')S> project, naming it &athfinder.

&athfinder too" 7 years to perfect but was able to capture the altitude record for a propeller

driven aircraft at 84,64 ft. &athfinder was followed by an improved version called

&athfinder(&lus that had solar cells made of silicon, which improved efficiency by 5?. This

improvement was seen when power was boosted from /,544 watts in &athfinder to 6,544 watts

in &athfinder(&lus.

The !enturion project, later renamed 'elios, was larger than any previous attempt. #t

applied hybrid technology@ solar energy using photovoltaic cells by day and fuel cells by night.

AThe 'elios was designed to be the forerunner of high(altitude unmanned aerial vehicles that

could fly ultra(long duration environmental science or telecommunications relay missions,


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lasting wee"s or months without consumable fuels or emitting airborne pollutants< /*0. The

wingspan of 'elios was 6-/ ft and it used 6, 64 bi(facial solar cells to power it.

The first manned aerial vehicle powered by solar energy was developed by Solar Flight.

Bric Caymond, founder of the company, flew Sunsee"er # for the first time in +8. The concept

was further developed and Sunsee"er ## replaced the previous model in 6446. !urrently,

Sunsee"er ## is the only flying manned aerial vehicle in the world. >ther recent projects in

Burope are Dephyr, S"y(Sailor and Solar #mpulse. Dephyr was designed by EinetiE as a high

altitude platform for satellite communications. S"y(Sailor is a first prototype model in a project

aiming to develop a solar(powered aircraft able to conduct missions in Mars. Finally, Solar

#mpulse is an attempt to complete the first solar(powered flight around the world without any

stops. This incursion was initiated by ertrand &iccard, commander of the first non(stop round

the world balloon flight. &iccard and )ndre orschberg, !B> and co(founder of the project, will

pilot the airplane in hours intervals. The first flight of Solar #mpulse is scheduled in 644+.

The history in the solar powered airplane incursion is summari*ed by Table 6., which

compares the past attempts previously mentioned.

Table 6.G !haracteristics of various solar(powered airplanes

#odel YearSolarCell$

Ener%&'()

(ei%*t'l+$)

(in%$pan',t)

Altitude ',t)

Batter&

Control

Sunri$e I !./ !000 /10 "2 3" "04000N5A Re6ot

e

Sunri$e II !.1 //70 200 / 3" .14000N5A Re6ot

eSolarC*allen%er !70

!24!"7 "200 "00 /. !"4000

N5A Re6ote

HALSOL 8 !73 N5A N5A N5A 7 N5AN5A Re6ot

e

Pat*9nder !3Sili:o

n .4100 120 7 104100N5A Re6ot

ePat*9nder-

Plu$ !7

Sili:o

n !"4100 .00 !"! 704"0!

N5A Re6ot

e

Centurion !7Sili:o

n !"4100 !400 "02!00400

0N5A Re6ot

e

Helio$ !2"4!"

0 !"4100 "40/7 "/.!00400

0LiPo Re6ot

eSun$ee;er I !72 N5A N5A N5A N5A N5A NiCd PilotSun$ee;er II "00" N5A N5A N5A N5A N5A LiPo Pilot

SoLon% "001 .2 ""1 "1 !1


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S;&-Sailor "00/ "!2 0 "ne of the main challenges to overcome during the design of this project is to

achieve the perfect balance between total weight of the aircraft and solar power

generation. This relationship between the mass of the elements and the energy they can

store or transform is "nown aspower density. #n order to obtain enough power density to

fly the airplane during day and night, the most recent and efficient technologies must be

utili*ed. &roduction of light weight parts is possible than"s to the new advances in

composite materials and nanotechnology. #mportant brea"throughs in the latter, have

positively affected another determinant factor, energy efficiency. >ut of all the parts of

the airplane, the battery is the biggest weight contributor. Ta"ing S"y(sailor as an

example, the i&o battery accounted for --? of the total 6.5+5 "g of weight /-10. #n the

Soong model, the battery weight was -.75 "g out of a total mass of 4.8 "g /--0. Bric

Caymond /-30, a pioneer in this matter, stated that light weight batteries are the single

most important improvement that is needed. !urrently, lithium batteries are the best

option in the mar"et. !onsidering all previous aircraft projects, it is important to choose

the lightest materials available, while simultaneously meeting the model re$uirements at

the same time. The most problematic weight restraint is the battery of the plane.

1+- Si4e and Shape

The purpose and functionality of the airplane will significantly change the si*e of

the model. Many factors will determine the appropriate si*e of the aircraft. For example,


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if the plane is designed to be controlled by a pilot or fly for long periods of time 2day and

night3, a large wing surface area is re$uired for additional solar panels in order to account

for the extra weight or power needed, respectively. Solar #mpulse is a good example for a

large si*e airplane. The aircraft, with a wingspan of m /-50, is designed to be

controlled by a pilot and flight continuously around the world. >n the other hand,

unmanned airplanes designed for short flights do not need much power, therefore needing

less wing surface area for solar panels. )s a result, the aircraft model becomes smaller

and lighter. S"y(sailor, Dephyr and Soong are great examples for small airplane models

with a wingspan of 7.6 /-60, 6 /*0 and -./5 m /--0, respectively. >n another note, the

si*e of the airplane seems to determine the shape of the model. More specifically, the

shape of larger si*e aircrafts is similar to an actual airplane. #n contrast, the shape of

smaller si*e aircrafts is similar to gliders, ta"ing advantage of the aerodynamics and light

weight model in order to use less power. 'owever, projects developed by %)S) do not

follow this trend. &athfinder(plus, 'elios and !enturion are long flying wings with

multiple motors designed for long flights and high altitudes.

1+1 2ing design

) solar powered aircraft need wings that maximi*e both surface area and lift.

:esigns that have shown promise for solar flight include the flying wing, blended wing,

and conventional wing.

!onventional wings are what are found on most aircraft in the s"y. They provide

good stability since most of the weight falls along the planes center of gravity. )lthough

they are the most common design there is still room for improvement, as the wings do not

generate enough lift to carry very heavy loads in relation to total airplane weight.

)n improvement of this design first came with the flying wing. The flying wing

is defined as no visible fuselage or cargo area, only a large wing which houses the

payload. #t is theoretically the most fuel efficient aircraft in terms of aerodynamics and

structural weight due to the entire craft acting as an airfoil and generating lift. This is its

main advantage over other types of aircraft. 'owever, this comes at a price because what

is gained in improved lift is lost in the ability to control the aircraft as the giant wing with


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no rear tailfins has proven hard to stabili*e in the air. This has caused the emergence of

hybrid wings such as the (6 bomber as well as a modified design of the blended wing

/*-0.

The blended wing is an adaptation of the flying wing, but it has separate, visible

fuselage and cargo area which are blended into the rest of the large wing. Some

advantages of this design are increased fuel economy, as the whole aircraft is generating

lift and not only the wings. )nother important advantage is improved payload capability

due to the extra lift that is generated. The blended wing craft also has a heavier structural

weight ma"ing it a much more solid, rigid aircraft. >ne of the downfalls is that the cargo

area is more spread out so it is harder to maintain the majority of the weight along the

planes center of gravity. The blended wing is better suited for slower speed aircrafts

since the large front surface area of the giant wing and body create a much larger amount

of drag at high speeds than conventional aircraft /*10.

:rag, the only force other than gravity opposing the airborne plane, is created by

the aircraft physically moving through the air. #n order to maintain level flight aircraft

must maintain a balance between the lift and the drag. They are both determined by the

same e$uation, the only difference is the !oefficient of drag is used instead of !oefficient

of lift. The coefficient of drag can be approximated by the e$uation /*70

'3

This is then used to determine the power needed by the airplane to maintain level

flight using the following e$uation /*70

'3


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7+ Overall 8esign

!onsidering the design and construction of a solar(powered airplane, there is a number of

parts common to all past projects. These elements areG solar panels, battery, motor and a propeller.

The necessity of solar panels is evident, due to the purpose of the project. Solar panels lay on the

top surface of the wings in order to avoid sun bloc"age from other elements. The number of cells

will vary depending on the si*e of the airplane and the power is needed to maintain flight. Today,

solar panels made out of Silica are widely used because have a better efficiency. Cecent solar(

powered airplanes projects use maximum point power trac"ers 2M&&T3 to increase powerefficiency from the solar panels. The addition of M&&Ts is certainly beneficial considering their

light weight and positive effects on the overall efficiency of the solar cells. The power generated

by the solar cells is storage in batteries. )s previously mentioned, batteries are the heaviest part of

the plane. Today, i&o batteries have the best power to weight ratio, thus most of the previous

projects have selected them. Then the power flows from the batteries to the motor. #n some cases,

a :!I)! converter is used before the motor. 'owever, since the brushless :! motor is the most

popular choice, a converter is rarely necessary. Finally, the motor moves the propeller to begin

flight. Cegarding structure materials, carbon fiber is the number one choice due to its light weightand strength. =evlar is widely used for more strength and resistance too. :epending on the

purpose and function of the plane, other parts are added to the model. Some examples are

cameras, radios, altimeters, ;&S, sensor, etc. Figure -. and -.6show the electric system diagram

for the Solar #mpulse and S"y(Sailor, respectively. ) complete illustration of the S"y(Sailor

model, with its parts and location, is given in Figure -.7.


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Figure -.G Blectric system of Solar #mpulse /50

Figure -.6G Blectric and control system of the S"y(Sailor /-10


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Figure -.7G &arts and location of components of the S"y(Sailor /-10

9+ Solar :nergy

Solar energy is typically harnessed by two methodsG passive and active. ) passive solar

energy uses the sunrays directly to heat li$uid or gas, whereas an active system converts the suns

energy into electrical energy by using a photovoltaic semiconductor called a solar cell. The

passive solar system demands enough solar power density to ma"e it viable and it is most

effective during the daytime. The solar power density needed is calculated by

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Hhere tis the hour of the day using the 6- hour cloc",pma#is the maximum solar power

density of the day at t$2noontime in the e$uator3, %is the standard deviation of the normal

distribution function.

The highest efficiency solar cells were able to convert -4? of the available energy into

usable electrical power until recently when oeing created a solar cell able to attain -4./?

efficiency. This cell was developed using a uni$ue structure called a Amulti(junctionJ solar cell,


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which achieves a higher efficiency by capturing more of the solar spectrum. ) multi junction

solar cell is designed in layers such that every layer can obtain some part of the sunlight when it

passes through. These layers combined allow the cell to capture more of the solar spectrum and

convert it into electricity.

Figure 5.G &hotovoltaic cell

The total efficiency of the solar cell is calculated by

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&s power of sunrays reaching the solar cell

&out output electricity power consumed by the load

9 voltage

# current

K solar power density at the &9 surface

) area of the &9 cell facing the sun


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Table 5.G Solar &anel Specifications L7

>&o:era #odel (att$ A6p$ Volt$ (ei%*t 'l+$C !30?T !30 .C 71T 71 /


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A #ai6u6 Power Point Tra:;in% '#PPT) $&$te6 allow$ a PV

arra& to produ:e t*e 6ai6u6 power t*e& are :apa+le o,< It doe$ t*i$

+& ele:troni:all& ar&in% t*e ele:tri:al operatin% point [4]< T*e opti6al

#PPT te:*niue arie$ dependin% on appli:ation and ea$e o,

i6ple6entation.?%g

attery +5? 644

S>F! O4? 444

Flywheel +5? O54

Table /.GSummary of energy Storage options L8

>ne type of CF!S is the &lanar Solid >xide Fuel !ell 2S>F!3, which is currently

at TC 7. The S>F! wor"s by separating water molecules into hydrogen and oxygen

which is then used as fuel. The only byproduct from this process is heat, which can then

be recycled by the S>F!, ma"ing it a clean energy source. The efficiency of the S>F! is

low 2O4?3, but the energy density is 444 HN'I"g. This provides the possibility of

storing much more energy than a battery while still maintaining a relatively light weight

/30. Table 5. includes a summary of these results.

3+ #otor :fficiency

or t*e appli:ation o, a $olar powered airplane4 e:ien:& and

wei%*t are o, t*e ut6o$t i6portan:e $in:e a$ wei%*t in:rea$e$4 t*e

power reuire6ent$ in:rea$e< T*i$ 6ean$ 6ore $olar :ell$ and a+i%%er 6otor are needed4 and o,ten a $piral eJe:t o::ur$ 6a;in% t*e

proGe:t near i6po$$i+le< T*ere,ore4 t*e tar%et o, t*i$ reiew i$ to 9nd

t*e li%*te$t 6otor wit* t*e *i%*e$t e:ien:&

Solar Powered Airplane Literature Review

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