AN AIRPLANE

The gigantic dimensions of this ultra-lightweight revolutionary airplane - capable of flying day and night without fuel - are its trademark feature. To build it, the whole team had to push back the frontiers of knowledge in materials science, energy management and the man-machine interface. Every one of its take-offs, propelled silently by its four electric motors, inspires us to consider using clean, new technologies to free our society, little by little, from dependence on fossil energy. 

DRIVER OF PROGRESS

Aviation has always been an outstanding agent of progress and innovation.

It transformed the 20th Century, and set whole generations dreaming. Today, the world faces major challenges, and aviation must continue to show the way forward. The aim of Bertrand Piccard and André Borschberg is not to revolutionize the aviation industry – it would be stupid and pretentious to even attempt this – but instead to use the power of this airborne symbol to help change people’s minds about renewable energies. In the present context, people are put off by the sheer scale of the problems. Instead, they should be encouraged, because technological solutions exist that can create jobs and open new markets whilst also protecting the environment.

Aviation, for its part, must clearly change to survive, given the constant rise in the price of kerosene and CO2 taxes. But it is obvious that, unlike Solar Impulse, airliners’ engines are not about to start functioning without fuel.  The solar airplane simply demonstrates that “less can mean more”.

Solar Impulse has started to fulfill the good-citizenship role for which it was designed. The solar airplane provokes discussions amongst the highest political and economic authorities about technological solutions currently available to help them achieve the world’s agreed CO2 reduction targets. And it also allows them to tackle the problem of resistance to change, which risks locking us for too long into the dangerous and costly consequences of old habits. It is with the aim of promoting such processes of change that Europe is using Solar Impulse, to give an example of what clean technology is capable of achieving. Hence the patronage of the Presidents of the European Parliament and the Council of Europe, as well as the European Commission.

 

“Our airplane is not designed to carry passengers, but to carry a message.”  Bertrand Piccard

“From the very start of the project, we understood that our primary goal was to save energy.” André Borschberg

MORE CONTENT ABOUT THE AIRPLANE

With its huge wingspan equal to that of an Airbus A340, and its proportionally tiny weight – that of an average car - the HB-SIA prototype presents physical and aerodynamic features never seen before.

Discover Solar Impulse Prototype

Solar Impulse 2 was designed with one goal in mind: rise up to the challenges of a round-the-world flight. Now is the final construction phase, and the airplane will soon be unveiled to the public.

Learn more about Solar Impulse 2

Discover the major steps: from Bertrand Piccard's family adventure, the first round-the-world balloon flight, starting the project with André Borschberg ... to the First Round-the-World Solar Flight in 2015.

Read the story of Solar Impulse

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Critical Design Review

How to be sure that we have thought of everything in terms of safety, how to ensure that we do all the necessary tests, how to avoid pitfalls in the development of a brand new plane?

This is what the CDR - Critical Design Review - is meant to achieve. Last week we brought together some of the best engineers from ...

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How to be sure that we have thought of everything in terms of safety, how to ensure that we do all the necessary tests, how to avoid pitfalls in the development of a brand new plane?

This is what the CDR - Critical Design Review - is meant to achieve. Last week we brought together some of the best engineers from Dassault, a Partner of Solar Impulse, and other leading aerospace companies. The group was comprised of experts from a variety of disciplines such as structural analysis, aerodynamics, flight mechanics, electrical systems and avionics.
We exposed , showcased and explained all our designs, calculations and tests and then answered and responded to a flood of questions from an impressive external team of highly competent engineers who have many years of experiences.
Going through such an exercise means taking the risk of being criticized. But just as important, this is a unique opportunity to learn, to improve, to challenge and especially to avoid the potentially serious consequences of errors and failures.
Two days of passionate and exciting work, to refocus on new developments for this second plane, such as the " Stability Augmentation System", which would allow the pilot to rest during the flights over the Pacific Ocean - that will last several days and nights.

One more important step towards the end of the construction of HB -SIB scheduled for February 2014 !

Solar (Lego) Land

As Solar Impulse engineers slowly conclude most of the testing, many parts are laying scattered around the immense Dübendorf hangar. This is when, in the Making of process, the assembly of the solar airplane begins. Just like with Legos, the Production ...

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As Solar Impulse engineers slowly conclude most of the testing, many parts are laying scattered around the immense Dübendorf hangar. This is when, in the Making of process, the assembly of the solar airplane begins. Just like with Legos, the Production and Workshop team, responsible for building the solar airplane, take the finished pieces and put them all together. Of course, there are some slight differences between a construction game and Solar Impulse. Our solar airplane is much larger, the parts don’t connect so easily and the people assembling the plane have long passed the days of fiddling around with brightly colored plastic cubes (well, I guess that’s just an assumption…)

Led by Martin Meyer, Production and Workshop is a team of seven. With additional support from partnering companies Décision (6 people), Ruppert Composite GmbH (2 people) and Sportec AG (1 person), they follow the blueprints and technical drawings of the design engineers and proceed to bring the two-dimensional sketches to life. They’re an extremely heterogeneous team consisting of carpenters, composite specialists, mold makers, mechanics and even a gardener not to mention a design engineer, Martin. This diversity is crucial in such a versatile team.

They’re not only responsible for assembling the solar airplane, they’re also responsible for building prototypes, like the human size wooden cockpit; or smaller parts that are too complicated to outsource, such as the iPad holder that will be integrated into HB-SIB’s cockpit or the solar panels. These “little” projects can actually amount to 80 orders a month!  But the most important requirement to integrate Martin’s team is to be an ingenious and diligent handyman (and prove you were a Lego fan in your childhood).

Larger parts are outsourced to our suppliers as we don’t have the infrastructure or human resources to follow. If the assembly requires gluing, like the ribs to the wing spar, the part might be retested afterwards to ensure the bonding process was successful.

Martin has become leader of this team less than a year ago as he was previously part of the design team. “As a design engineer, I had to be more creative in terms of finding a good solution to a technical issue. Now it’s more about organizing the work and dispatching it to people depending on their capabilities. But having design experience helps me detect where the problem is when it arises.”

I guess that a multi-colored, Lego-like solar plane could be an amusing sight, but would be too attractive for birds and bees – but why not a toy model? I’m sure if Lego made a miniature HB-SIB, their target consumers wouldn’t only be kids…   

 

Photo (left to right): Jürg Birkenstock (Ruppert Composite GmbH), Peter Schindler, Simon Wyss, Martin Meyer, Stefan Stadelmann, Rolf Meier (Sportec AG), Jakob Reck (Trainee), Daniel Kober, David Fankhauser (Ruppert Composite GmbH)

Keeping the airplane balanced

Have you ever started feeling tense when, during a flight, your drink starts shaking so much that it’s about to spill and, in a moment of panic, you glance out of the window to check the state of the wings? All sorts of scenarios rush through your mind and you pray the aeronautical engineers weren’t distracted when ...

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Have you ever started feeling tense when, during a flight, your drink starts shaking so much that it’s about to spill and, in a moment of panic, you glance out of the window to check the state of the wings? All sorts of scenarios rush through your mind and you pray the aeronautical engineers weren’t distracted when building the plane.

Solar Impulse might not carry 300+ passengers, but the forces the solar plane has to withstand are proportionally the same as a commercial one: it’s physics. At Solar Impulse, the man that ensures the wings don’t collapse when strained in turbulence is our Loads Engineer, Richard Leblois. He calculates the main load pattern (the force the wings have to withstand during flight) for every single aircraft component.

Richard is present throughout the making of process. During the design phase he virtually attributes the loads to every part, via special software. Once the engineers agree on a part’s final blueprint, it’s sent into production. Let’s take the backbone of HB-SIB’s wing as an example, the wing spar: an ultra-light yet very large (over 70 meters long!) carbon fiber box. Once the wing spar is delivered, Richard works with the analysis team to simplify the tests while ensuring that the wing spar goes through all the necessary steps to be declared flight-ready. This means that real-world situations must be simulated with an intricate game of weights, test jigs and forces. Richard calculates those variables and subsequently helps develop the jigs.

Unlike other engineers on the team, Richard only gets the confirmation that his calculations were correct once he sees the plane in flight. Think of your shaking drink… Just kidding! That’s what test flights are for.

Richard has a critical role second role as the weight and balance calculator where his responsibility is to track the aircraft’s mass and center of gravity to guarantee aircraft stability. That’s when Richard laughs and says: “I basically create my own destiny: if I define the loads too high at the beginning of the process, the part will be too heavy and could become an issue for me later during the Weight and Balance assessment.”

But rest assured, when you see how far up the wings are bent during the structural tests, you would never again panic. You would simply proceed to sip you drink, relaxed, and try to enjoy the turbulent flight.

Testing of the new wing spar

Pushing the limits is a tough job, but it’s a necessity when innovation is the ultimate goal. The problem is that it’s hard to know ahead of time where the limit is. Solar Impulse crossed that thin line last year, on July 5th, 2012, during the structural test of HB-SIB’s wing spar – the central part ...

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Pushing the limits is a tough job, but it’s a necessity when innovation is the ultimate goal. The problem is that it’s hard to know ahead of time where the limit is. Solar Impulse crossed that thin line last year, on July 5th, 2012, during the structural test of HB-SIB’s wing spar – the central part of the second solar airplane’s wings. We got too close to the edge and fell overboard: i.e. the wing spar broke. Only by persevering and learning from one’s mistakes can innovation happen. In fact, this is the attitude that made it possible to build the first solar airplane able to fly day and night with the wingspan of a Jumbo Jet, the weight of a small car and an almost limitless endurance.

The new wing spar was delivered July 19th, 2013 in Dübendorf. The engineers had no time to lose and immediately began preparations for the upcoming tests of this very large and bulky part (over 70 meters in length). The first one, a torsion test and also the most difficult one, took place on Monday August 5th. Solar Impulse engineers decided to start with the one that had caused the first spar to break in order to instantly know whether the new structure would be able to handle the load. Nothing in the configuration of the test was changed. In fact, the analysis done after last year’s incident proved that the load cases, test jigs and overall setup were indeed correct.

The maximum load for the torsion test was of 4.9 tons of lead. However, the weight is applied in a way that half the load goes upward and the other half, downward consequently twisting the part. The tension in the hangar was high as the engineers looked on, in silence, secretly hoping no strange sounds would be heard.

 

The test was a complete success, to everybody’s relief. The structure of the wing spar hasn’t changed to the naked eye, but the pieces that made the cracking noise during last year’s incident, the bulk heads – small, square carbon fiber plates placed inside the spar to keep the structure from deforming – are now more numerous, adding an additional 2 kilos to the overall structure.

On August 8th, the second test – bending – took place. The wing spar is placed upside down and the weight is either focused on the inner section, the outer section (both along the x-axis, i.e. in the direction of flight) or on the z-axis (i.e. vertically). These are three separate tests to verify different flight and wind scenarios. For the bending test, a maximum of 3.5 tons are placed on the spar, basically bending the wings upwards.

The weight used for the tests is much less than what was used for HB-SIA, the first prototype solar aircraft. This is because, firstly, Solar Impulse engineers know more about load cases and what to expect from these lightweight structures and, secondly and most importantly, because the HB-SIB motor gondolas will be placed in a different position than the first plane, modifying the load requirements.

This series of tests will be completed by the end of August from which point the “dressing” of the wing will start. Solar panels, ribs, fabric and motor gondolas will be added to the structure bringing the solar wings slowly to life…

HB-SIB is ready to land

While the logistics of the final leg of the Across America mission –Washington D.C. to New York City - are being finalized, Solar Impulse engineers are advancing the construction of the second solar plane, HB-SIB.

On Thursday June 27th, ...

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While the logistics of the final leg of the Across America mission –Washington D.C. to New York City - are being finalized, Solar Impulse engineers are advancing the construction of the second solar plane, HB-SIB.

On Thursday June 27th, they did one of the landing gear tests to check the structure’s solidity at the time of landing. This first test was a dynamic one, meant to verify the reactivity of the landing gear during a hard landing.

Inside the landing gear structure there is a thing called a “crash element” which is made out of aluminum honeycomb: very light but also extremely resistant. This part is supposed to handle an impact of up to 4.3 tons and, during a tough landing, it is designed to collapse in a structured way at a defined force to avoid damaging other parts of the plane.

RTEmagicC_landing_gear_2.jpg.jpg

Solar Impulse engineers set up a pretty ingenious jig to simulate this scenario. The landing gear was placed on the ground horizontally while a crate filled with 2 tons of lead was hung on a cable next to it. During the test, the crate is pulled back and released causing an impact of the lead with the landing gear. The crash element takes the shock while also releasing a certain amount of force to avoid collapse.

The crash element is already delivered with the proper force it needs to be collapsed. The test is therefore mostly designed to check the landing gear structure and how it reacts to dynamic loads. The engineers simply verify the resulting g-loading (stress) caused by the adjusted crash load to understand how much friction occurs inside the landing gear (friction inside the crash element’s cylinder can cause higher g-loadings before it collapse).

A similar test will be done again (ultimate load), but the force will be applied statically and this time up to 6 tons. 


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