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Solar Impulse - (update 231005)

According to the official website the design of the aircraft would be quite diffirent from the original. Instead of the curved wing there is now a straight one and the winglets are gone. The propellers are hinged under the wing and instead of pushing they now pulling the aircraft as in most conventional aircraft. The cockpit is also hinged with a pylon under the wing and as the new design is much more conventional, almost as basic as it could be.However that demands less techological risk and could result a lighter aircraft.

The first mockups are now under construction, here is the layout for the cokpit

for more information visit the official website:

Solar Impulse - presentation

Recently Global Flyer by Scaled/Virgin broke the record for a non-stop flight around the globe.However almost simultaneously with the conception of Global Flyer a maybe even more extreme project is started taking shape, the design of an aircraft tha could fly around the world using nothing else but the sun as a source of energy.

This effort is initiated by the Swiss federal Institute of Technology (EPFL) and the team of Bertrand Piccard.European Space Agency (ESA) is also contributing as a technical partner.Bertrand Piccard with Brian Jones flew around the world non-stop for a first time with a balloon in 1999.It was the last of 3 attempts, the first and the second had problems but the third was totally succesful.

The design of the aircraft isn't yet final, it will be mostly frozen at the end of 2005 according to the time schedule and the construction will began the year after.It will be a very big plane with a huge wingspan of about 70-80 meters (one of the biggest ever).It will be probably use two thrust propellers mounted in the rear horizontal stabilizer.There are a lot of challenges to face in the design process because apart from the weight limitation goal the wing should be studied for aeroelastic stability because of its very big size and because it also is housing the batteries. The reason for such a large wing apart from the flight profile is to maximise the area for the solar panels and also to minimise the induced drag.That is also why the solar impulse use very big winglets in the wingtips.

The inflight behaviour of such a strange aircraft will demand a lot of studying, simulations and tests. Solar impulse will take off autonomously and will climb at an altitude of 10-11km where the temperature is about -55C.At that altitude during the day there is uninterrupted sunlight because the aircraft is above the clouds.

According to the suggested flight profile the aircraft will gain continuously altitude during the day which in some amount will e lost during the night to save energy. In a way it will use altitude gain as an energy buffer like a virtual battery although altitude variations are restricted from flight control regulations to whom solar impulse must obey.

Energy management optimisation is part of the overhaul optimisation that needs to be done for such an extreme plane to accomplish a safe and succesfull flight.

ESA's technology transfer program is contributing in many areas of this project because there are a loto of problems that solar impulse is facing that are similar to those of the space program.The solar panels must be efficient, light and flexible (in most satellites they infold after the orbital deployment), the aircraft will use ultra light composite structures and the pressurized cabin should provide adequate conditions with the least possible resources for multiday flights by using similar methods and solutions with the International Space Station.

Battery efficiency is one of the most important (and restraining) factors for this project.Off the self Li-ion batteries that are avaliable today have specific capacity of about 200Wh/kg which is enough for a one pilot design aircraft only. For a 2 crew aircraft batteries of at least 300Wh/kg will be needed and they still are not avaliable.

The solar impulse project is now at the phase of conceptual design, at the end of 2007 the aircraft should be ready in order to fly for the first time the year after.At year 2009 long hauled flights should be possible firstly over a continent, then over the atlantic ocean and finally around the globe.

The around the globe flight will be accomplished with stops at every continent every 4-5 days because this is the calculated maximum amount of time the crew could fly the plane safel

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I.K.Erripis 100605

Aaerovironment's uninhabited vehicle Helios was the first solar aircraft to reach the altitude of 30.000ft

Virgin Global Flyer designed by Scaled Composites holds the record for the fastest non-stop around the world flight.

Companies that co-operate with ESA like EADS-Astrium have huge experience in constructing solar cell panels for satellites

Aircrafts manage to fly because the airflow around the wing creates a pressure diffirence up and below the wing.In the wingtip high pressure air masses from below the wing flows on top of it where the pressure is lower thus decreasing the lift.This negative factor is called induced drag and can be reduced by the aerodynamic optimisation of the wing and the use of special structures like winglets that reduce the flow from below to the upper surface of the wing without introducing significant amounts of drag.

ESA's experience from ISS will be very usefull in continious multiday flights

The distinguised solar car Nuna2 is using solar panels from ESA.

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