August 2015
www.nzmanufacturer.co.nz
6 BUSINESS NEWS
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Emerald Foods: Powering through exporting challenges.
Helping businesses succeed through technical innovation.
DEVELOPMENTS
14
SOUTHMACH 2015 REVIEW
An astounding success for exhibitors and visitors.
IN FLIGHT The engineering of solar flight It’s weird enough that we drive around in machines powered by dead plants and animals from millions of years ago, but flying around in machines powered by sunbeams?! The latter part of this peculiar reality is the result of more than 10 years work, which saw the Solar Impulse aircraft circumnavigate the globe fuelled by nothing more than sunshine. While it is easy to label this project as a flight of fancy for engineers – a technical exercise to prove the possibilities without practical purpose – Solar Impulse has become all about proving people wrong. While practical outcomes are abundant (more on that later), the project has broken frontiers and is capturing the imagination of people young and old in much the same way as the early years of flight. Engineering is often seen more widely as safe, calculated and sanitised, and it is all too easy to forget about those inspiring engineering success stories from yesteryear. Solar Impulse along with Bloodhound SSC, but very few others, have taken the torch and are doing amazing things no one thought possible. And that is making everyone sit up and listen. “We see ourselves as pioneers but we also want to inspire,” said Marc Baumgarten, a lead engineer on the project. “We want to do something that people say ‘wow’ and capture that spirit of adventure by technical
knowhow like the space race did in the 1960s.” The biggest leap forward in solar flight has come in the last five years, as the team stepped up the capability of the originator, Solar Impulse 1. “There is a long history of flight, but some of the biggest developments have been in the last five years and are now flying in Solar Impulse 2,” added Baumgarten. The most striking change has been to the overall wingspan of Solar Impulse 2. Now, at over 70m, it is just 8m shy of the world’s largest airliner, the Airbus A380, and is actually greater than a Boeing 747-800. This shows the size of the project, and the aircraft itself. This is no flimsy small glider with batteries, it is a proper aeroplane. The top of the wing, fuselage and tail plane are covered in photovoltaic cells that trickle charge four large lithium-ion batteries (weighing 633kg), which power four large motors that turn propellers. It all provides enough propulsion to cruise at a normal 27,000ft (8,500m) and 87mph (140kph). But, at over 2,300kg, it is a wonder that Solar Impulse ever gets off the ground. And this was one of the biggest challenges for engineers: weight. “The plane needs a lot of batteries, and batteries are heavy,” explained Geri Piller, head of structural analysis at
Solar Impulse. “Yet the aeroplane gets only a small amount of energy from the solar cells, so it has to be really light overall.” The batteries are essential in providing enough power. Unable to be reduced, these are a deadweight that engineers have had to design around. Making everything lighter Solar Impulse 1 already used most of the obvious tricks of the trade in terms of reducing weight, with all the easy pickings exhausted. It meant that any further weight reduction was going to be a daunting challenge. “The challenge was huge as we had to make a large more powerful aircraft, but also make everything lighter and sturdier,” said Piller. The challenge was exemplified in the wingspan that needed to be increased nearly 10m. The increase, and corresponding greater surface area, was needed to go from 11,628
photovoltaic cells rating the aircraft at 45kW peak, to 17,248 photovoltaic cells and 66kW peak. In addition, the motors increased from 7.5kW to 13kW, and propellers from 3.5m to 4m. But perhaps the biggest weight gain came from the batteries, almost doubling output from 4 x 21kWh to 4 x 41kWh, adding an additional 183kg. It was clear that more than just good design was required, thorough analysis and simulation was needed. “We had to simulate to get the strongest lightest structure possible,” said Piller. “If we were not able to simulate and try all those different iterations and optimise the structure in such as a way that the whole structure become highly optimised, I don’t think we would have got off the ground.” The structural analysis team used Femap with NX Nastran software, from product lifecycle management (PLM)
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