SOLAR POWERED

AIRCRAFT

THE FUTURE HAS

ARRIVED

By

Sayan Mukherjee

B10023

PGP 1(2010-2012)

ABSTRACT

With ever increasing demand for aviation fuel to power our aeroplanes and its steep rising costs the time has come for us to find a more cost effective, efficient and ecofriendly way to power our aircrafts, thus solar powered aircrafts came into existence. The planes have photovoltaic cells on their wings which gather solar energy thereby recharging the batteries that powers its propellers. The planes are so designed that it can fly even during the night time and can stay in the air for as long as 26 hours.

Introduction and importance of solar powered aircrafts

Travelling by aeroplanes has been one of the most effective and efficient means of transportation, even now it is one of the most preferred means of transportation. Aviation fuel, the fuel which is used

in aeroplanes is a fossil fuel whose reserves are depleting at an extremely fast rate and also the emissions caused by such aeroplanes using aviation fuel is affecting our environment as well as our

ozone layer. So the time has come for us to power our aeroplanes using some other sources of energy and thus then emerged solar powered aeroplanes. One of the biggest advantage of using

solar powered aircrafts is that there would be no emissions and also over the years in the long run the cost of travelling by air would reduce drastically. Over a considerable period of time these aircrafts

have been modified and now these aeroplanes can fly around the world even without stopping once even during the night-time. These aircrafts have the capacity to stay in the air for as long as 26 hours. Thus if solar powered aircrafts are introduced on a large scale it will make our world a global village

making air travel eco-friendly and extremely cheap. Solar powered aircrafts can also play a pioneering role in the development of the economy in developing countries like India where air travel is still out of the bounds for the poorer sections of the society. Thus we can say that introduction of

solar powered aircrafts will usher in a revolution that might change the belief which the common man has about air travel.

What is the SOLAR IMPULSE project?

Solar Impulse is a European long-range solar powered plane project being undertaken at the institute École Polytechnique Fédérale de Lausanne(Switzerland). The project is pioneered by Bertrand Piccard, who is one of the main brains behind the project.

Piccard initiated the Solar Impulse project in 2003. Since then, the team has grown to a multi-disciplinary team of 50 specialists from six countries, assisted by about 100 outside advisers. The project is financed by private companies. The 3 main partners are Deutsche Bank, Omega SA and Solvay. Other partners include Bayer, MaterialScience, Altran and Swisscom .Supporters include Clarins, Semper, Toyota, BKW, STG. The EPFL, the European Space Agency (ESA) and Dassault provide additional technical expertise.

The aircraft made its first maiden flight on 3rd December 2009 it flew for 350 metres and about 1 metre above the ground. On 8th July 2010 the plane made its first overnight flight, the plane took off at 6:51am on 7th July from an airfield in Switzerland , it returned for landing the following morning at 9am local time.

The first aircraft built under this project is a one seater, capable of taking off under its own power and remaining airborne for 36 hours. This aircraft during its testing phase first flew for as long as 26 hours which included 9 hours of night flying on 7-8th July 2010. The aircraft is being modified further to go around the earth in 20 to 25 days time.

The solar impulse team is also planning to build a second aeroplane which will be complete by 2011, the plane will be having a special pressurized cockpit and advanced avionics to allow trans-oceanic and trans-continental flight. The solar impulse team hopes that round the world flight will be possible by 2012.

Vision of the solar impulse team

At each major premiere, the adventurers of the last century pushed back the limits of the impossible. today, human and technical enquiry must go on, with a view to improve the quality of life for humanity. By writing the next pages in the history of aviation with solar energy, as far as a flight around the world

without fuel or pollution is concerned, Solar Impulse's ambition is to contribute in the world of exploration and innovation to the cause of renewable energies. To demonstrate the importance of the new technologies in sustainable development, and of course, once again, to place dream and emotion

at the heart of scientific adventure.

How does a solar impulse aircraft actually look?

How does the solar impulse aircraft work?

The aircraft uses super-efficient solar cells and batteries to stay in the air after the Sun's rays had faded. The plane has 12,000 solar cells arranged on its wingspan which collected enough energy to power the plane for the flight. There are 11,628 monocrystalline silicon cells, each 150 microns thick, they have been selected for their lightness, flexibility and efficiency. At 22%, their energy efficiency

could have been higher, but the additional weight would have affected the aircraft during night flight.

Currently the major constraint of the project is storing energy in the lithium polymer batteries. At the present stage, the maximum energy density is 220 Wh/kg. The accumulators which are required for the night flight weigh 400 kg, equal to ¼ of the total weight of the aircraft. Success is therefore possible only by maximizing aerodynamic performance and optimizing the energy chain.

What were the sources of energy?

At midday, each m² of land surface receives an equivalent of 1,000 watts, or 1.3 horsepowerof light power. Over 24 hours this averages to 250 W/m². With 200m² of photovoltaic cells and 12% total efficiency of the propulsion chain, the aircraft‘s engines achieve on average of 8 HP or 6 KW –And it is this energy which is optimized from the solar panel to the propeller by the efforts of the entire team of solar impulse.

How does the propulsion system work?

Beneath the wings of the solar impulse plane are four gondolas, each containing a 10 HP motor, a lithium polymer battery set and a management system controlling charge/discharge and temperature. The thermal insulation had been designed to conserve the heat radiated by the batteries and to keep them functioning even at -40°C which the plane will encounter at 8,500 metres. Each engine is fitted with a reducer that limits the rotation of each 3.5 metre diameter, twin-bladed propeller within the range of 200-4,000 rpm.

What is the solar impulse aircraft made of?

With a 63.40 m wingspan and with the necessary rigidity, lightness and flight controllability and just 1,600 kg take-off weight is a challenge that had never before been met in aeronautics. Solar Impulse is built round a carbon fibre-honeycomb composite using a sandwich structure. The upper wing surface is covered with a skin of encapsulated solar cells, and the undersides of the wings with a high resistance flexible film. 120 carbon fibre ribs placed at 50 cm intervals profile these two layers and give the body its aerodynamic shape.

Some technical details

Wingspan 63.40 m

Length 21.85 m

Height 6.40 m

Motor power 4 x 10 HP electric engines

Solar cells 11,628 (10,748 on the wing,880 on the horizontal stabilizer)

Average flying speed 70 km/h

Maximum altitude 8,500 m (27,900 ft)

Weight 1,600 kg

Take-off speed 35 km/h

Pressurized air cabin

Advanced on board auto pilot system

Advanced inbuilt onboard computers to conserve power

Glimpses of the solar impulse aircraft in action

Taking off from airfield Payerne in Switzerland on 7th July 2010 at 6:51am

During its course in the night of 7th July 2010

Landing at Payerne in Switzerland at 9:00am on 8th July 2010

What is the economic potential of the project?

The project solar impulse has got tremendous economic potential. Some of its main partners include Omega, Deutsche bank and SOLVAY. Planes like the solar impulse are the planes of the future, like any Boeing or Airbus this plane can stay in the air for as long as 26 hours and even fly during the night time, the only major difference between the solar impulse plane and any other commercial plane is that it cannot carry too much weight. The research team of the solar impulse project is working hard to overcome this challenge they have also modified the aircraft in such a way that it can fly around the globe in 20-25 days.

According to Adrian Scott, a member of the research team, he says that once the plane is modified and made ready to carry heavy load and specially passengers this plane (solar impulse) will be one of the biggest competitors to Boeing and Airbus. He also added by saying that this plane(solar impulse) once fully modified and upgraded to the levels of any commercial plane will bring a revolution in the world of commercial jets as the solar impulse plane doesn’t require any aviation fuel to power itself

and can fly in the air simply by charging itself from the energy gained from the sun’s light. He also said that in the years to come most of the commercial planes will be solar powered as these planes are not

only fuel efficient but also have low maintenance costs. Thus we can say that the solar impulse project has got huge economic potential as in the years to come these are the planes which will

become commercial jets of the future.

Some of the main sponsors of the project

SOLVAY

Omega

Deutsche bank

Official partners

Bayer material science

Altran

Swisscom

Official suppliers

Victorinox

Solarmax

La semeuse

Hirslanden

Scientific partners

Dassault aviation

IATA

Current solar powered planes in existence

PATHFINDER

Pathfinder was developed by NASA in the year 1994 under the NASA’S ERAST program . It was named pathfinder because it was considered to be the pathfinder for future fleet of solar aircrafts

which could stay in the air for weeks or months on scientific sampling and imaging missions. A series of flights were planned to demonstrate that an extremely light and fragile aircraft structure with a very high aspect ratio (the ratio between the wingspan and the wing chord) can successfully take-off and land from an airport and can be flown to extremely high altitudes (between 50,000 feet (15,240.0 m) and 80,000 feet (24,384.0 m)) propelled by the power of the sun. In addition, the ERAST Project also

wanted to determine the feasibility of such a UAV for carrying instruments used in a variety of scientific studies.

Aircraft description of the pathfinder

Pathfinder was powered by eight electric motors — later reduced to six — which were first powered by batteries. It had a wing span of 98.4 feet (30.0 m). Two underwing pods contain the landing gear, batteries, instrumentation system, and flight control computer. In the year 1994 when the aircraft was taken in the ERAST project of NASA solar cells were added to the entire upper surface of the wing.

The solar arrays provided power to the aircraft's electric motors, avionics, communications and other electronic systems. Pathfinder also had a backup battery system which could provide power between two to five hours to allow limited-duration flight after dark. Pathfinder flew at an airspeed of 15miles per hour.

Future modifications of the pathfinder

In 1998 pathfinder was further modified to pathfinder plus. The new pathfinder had a longer wingspan. The center section of the pathfinder was topped by more efficient solar cells which could convert 19%

of the solar energy to electric energy which was useful to power the craft’s motors, avionics and communication system, the power was further boosted by the 14% efficiency older solar arrays that covered most of the surface of the mid- and outer wing panels from the original Pathfinder. Maximum

potential power was boosted from about 7,500 watts on Pathfinder to about 12,500 watts on Pathfinder-Plus. The number of electric motors was increased to eight, and the motors used were

more powerful units, designed for the follow-on aircraft. All these enabled the pathfinder plus to fly at an altitude of 80,201 feet.

Centurion

Centurion was also built under the ERAST project, it was designed to fly at an altitude of 100000 feet,

it was a third generation aircraft in the series. The ERAST program managers had decided that an aircraft based on the Pathfinder/Pathfinder Plus concept would be the lowest risk approach of

achieving the altitude goal. The full-size Centurion's maiden flight took place at Rogers Dry Lake on November 10, 1998.

What the aircraft looks like

The design of Centurion resulted in an aircraft that looked very much like the Pathfinder, but with a much longer wingspan of 206 feet (62.8 m). Although the Centurion shape resembled the Pathfinder,

the structure was designed to be stronger and capable of carrying numerous payloads (up to 600 pounds (272.2 kg)) more efficiently. Its wing incorporated a redesigned high-altitude airfoil and the span was increased to 206 feet (62.79 m). The number of motors was increased to 14 and the

number of underwing pods to carry batteries, flight control system components, ballast, and landing gear we increased to four.

Helios Prototype

The Centurion was modified into the Helios Prototype configuration by adding a sixth 41 feet (12.5 m) wing section and a fifth landing gear and systems pod, becoming the fourth configuration in the series

of solar-powered flying wing demonstrator aircraft developed by AeroVironment under the ERAST project. The larger wing on the Helios Prototype accommodated more solar arrays to provide

adequate power for the sun-powered development flights that followed. The aircraft's maiden flight was on September 8, 1999. The ERAST program had two goals when developing the Helios

Prototype: 1) sustained flight at altitudes near 100,000 feet (30,480.0 m) and 2) endurance of at least 24 hours, including at least 14 of those hours above 50,000 feet (15,240.0 m).

How the aircraft actually looked like

The Helios Prototype was an ultra-lightweight flying wing aircraft with a wingspan of 247 feet (75.3 m), longer than the wingspans of the U.S. Air Force C-5 military transport (222 feet (67.7 m) or the Boeing

747. The electrically powered Helios was constructed mostly of composite materials such as carbon

fibre, graphite epoxy, Kevlar, styrofoam, and a thin, transparent plastic skin. The main tubular wing spar is made of carbon fibre. The spar, was thicker on the top and bottom to absorb the constant

bending motions that occur during flight, was wrapped with Nomex and Kevlar for additional strength. The wing ribs are also made of epoxy and carbon fiber. Shaped styrofoam is used for the wing's

leading edge and a durable clear plastic film covered the entire wing.

Crash of the Helios prototype

Helios with very high wing dihedral just before breaking up

Helios disintegrated as it fell towards the Pacific

Wreckage of Helios in the Pacific

On June 26, 2003, the Helios Prototype broke up and fell into the Pacific Ocean about ten miles west of the Hawaiian Island Kauai during a remotely piloted systems checkout flight in preparation for an endurance test scheduled for the next month. After a delayed take off, due to the failure of the winds to shift as predicted, Helios spent more time than expected flying through a zone of low-level turbulence on the lee side of Kauai, because it was climbing slower than normal, since it had to contend with cloud shadows and the resultant reduction in solar power.

As the aircraft climbed through 2,800 feet (853.4 m), according to the subsequent mishap investigation report, "At about 30 minutes into the flight, the aircraft encountered turbulence and morphed into an unexpected, persistent, high dihedral configuration. As a result of the persistent high dihedral, the aircraft became unstable in a very divergent pitch mode in which the airspeed excursions from the nominal flight speed about doubled every cycle of the oscillation. The aircraft’s design airspeed was subsequently exceeded and the resulting high dynamic pressures caused the wing leading edge secondary structure on the outer wing panels to fail and the solar cells and skin on the upper surface of the wing to rip off.

CHALLENGES FACED BY THE SOLAR IMPULSE TEAM

Some of the challenges or hurdles faced by the solar impulse team were to ensure that the aircraft actually had enough power even during the night time to stay airborne moreover unlike other solar

powered aircrafts this was much heavier as it was not a UAV and had a cockpit and pilot inside it so they had to actually make the plane as light as possible by removing all unwanted things in the

aircraft. The aerodynamics of the plane had to be flawless and left no margin of error such that with minimum amount of power the plane could produce maximum speed also when faced with a

turbulence the plane would remain stable and not increase its speed to extreme high levels unlike Helios which would cause the aircraft to disintegrate and crash.

One of the biggest challenges which the solar impulse team is currently facing is that in order to make solar planes a reality such that it can be compared to any commercial plane of Boeing or Airbus, the solar impulse plane must be able to carry a large number of passengers. Currently the solar impulse

plane is able to carry only one pilot so the plane requires some significant modifications which will enable it to carry large number of passengers. The solar impulse plane also needs to increase its

cruise speed from 70 km/h to a minimum of 600 km/h in order to be at par with any other commercial plane. The solar impulse team is facing a major hurdle while modifying the plane to enable it to fly

around the world and that is the design and the kind of material with which the plane must be properly built, they have to make the plane light but at the same time they cannot use materials that are

extremely light such that in case the plane faces a turbulence and its speed increases then unlike Helios this plane shouldn’t fall apart so for this reason they are building the entire structure of the

plane with carbon fibre.

Speed of the aircraft is also a very big problem while cruising around the world, since the speed of the solar impulse aircraft is less so it will be requiring a minimum of 20-25 days to fly around the world this

means more food and drinking materials have to be loaded in the aircraft thereby further increasing the weight of the plane. So for this reason only the solar impulse team has decided to break the

journey into five legs of two to three days each.

While going around the globe the plane will cruise at just under 30 mph at sea level to minimize the drag . The custom-designed 12-ft.-dia. propellers will turn at a slow 500 rpm to maximize efficiency.

While a tortoise-like pace saves energy, it introduces several problems. One is adverse yaw. When a plane banks into a turn, the aileron on the outside wing causes the wing to generate more lift than its

counterpart on the inside wing. More lift equals more drag, which tends to pull the nose away from the direction of the turn. The usual solution is to use the plane's rudder to push the nose around into the

turn. But Solar Impulse's huge wing-span and low airspeed will greatly magnify the adverse yaw problem, perhaps so much that the rudder won't be sufficient to overcome it. So now the solar impulse team has developed a special rudder which is modified specially for the solar impulse plane such that

it can actually control the aircraft while turning even if the yaw effect is severe.

THE SOLAR IMPULSE TEAM MODIFYING THE SOLAR IMPULSE AIRCRAFT

THE SOLAR IMPULSE TEAM

Summary, Conclusion and Way forward

The solar impulse aircraft is the aircraft of the future being dependent on solar energy and creating no pollution or harm to the environment it is definitely the technology or invention we are looking forward

as it has the capacity to bring a revolution in the world of air travel by making it cheaper and more effective. The solar impulse plane having a wing span of 63.4m , length 21.85m and height of 6.4m and weighs only 1600 kg being made completely of carbon fibre which is light yet extremely sturdy this aircraft has the capacity to fly for straight 26 hours at a stretch and is currently being modified to

fly around the world. The aircraft has four 10hp motors and 11628 solar cells which charge the batteries during the daytime, the plane also has a highly advanced onboard computer which helps it to

conserve maximum amount of energy possible and its state of the art auto pilot system which helps the pilots a lot while flying during night time. Each engine is fitted with a reducer that limits the rotation

of each 3.5 metre diameter, twin-bladed propeller within the range of 200-4,000 rpm.

There are several other solar powered aircrafts in existence like pathfinder which built under NASA’s ERAST program in the year 1994, then there was another solar powered aircraft named centurion which was also built under NASA’s ERAST program and which could fly upto a altitude of 100000

feet. The same centurion aircraft was further modified and made better by adding a sixth 41 feet wing section and a fifth landing gear and system pod and was named HELIOS. On June 26th 2003 the

Helios prototype while doing a checkout flight over the pacific ocean faced extreme turbulence and crashed into the ocean after breaking up. All these solar powered aircrafts invented by NASA were

highly different from the solar impulse aircraft as all of them were a remotely controlled UAV whereas the solar impulse aircraft like any other normal aircraft has a cockpit and is capable of carrying one

person(pilot) throughout its flight.

The solar impulse team was also facing certain problems or challenges even while building the aircraft they had to make the aircraft as light as possible thus for this reason they had to remove all unwanted weights but they had to also keep in mind that they should build the aircraft with such a material which

was lightweight and yet strong enough to withstand a turbulence, so they finally built the aircraft completely with carbon fibre. The solar impulse team is also working hard to enable the solar impulse plane to carry a large number of passengers like any commercial aircraft, to make the aircraft capable enough to fly around the earth in 15-20 days. Cruising at a speed of 70km/h is also a challenge for the

The solar impulse team celebrating the success of their project

Bertrand Piccard celebrating immediately after landing at

solar impulse team as the slow pace of the aircraft will pose several problems for it when it goes for its journey around the world specially the aircraft might face the yaw problem.

Inspite of so many challenges challenges and hurdles faced by the solar impulse team they have overcome most of them and that’s why on 7th July 2010 the plane took off from Payerne, Switzerland at 6:51am flew for 26 hours straight and landed on 8th July at 9:00am. So we can say that the solar

impulse aircraft is the aircraft of the future and soon in the years to come they will be the planes which will fly in the sky carrying passengers around the world.

References

www.bbc.co.uk

www.solarimpulse.com

www.fiddlersgreen.net

www.plastemart.com

www.businessgreen.com

www.banking-on-green.com

www.ubergizmo.com

www.economist.com

www.popsci.com

www.spacemart.com

www.telegraph.co.uk

www.solvay.com

www.iata.org