Piloted by Captain Piccard, the seasoned solar craft looks to set a fresh record

Today a solar plane embarked on what could be the first coast-to-coast trip ever by a piloted fuelless flier.  While the solar plane is landing at various destinations along the route, the multi-leg trek is expected to be the longest ever such trip.

I. Solar Impulse HB-SIA Flew High

With the cost of flight reaching all time highs due to a variety of factors -- passenger obesity, the cost of fossil fuels, and cuts in government subsidies, many are looking to alternative fuels and even solar as potential solutions to cut costs.  Bertrand Piccard and André Borschberg took that idea and flew with it, launching the Solar Impulse project.

While many scoffed at the pair's lofty dreams, they defied critics tasting their first success in 2010 when the Solar Impulse HB-SIA prototype took flight.  

That craft had a wingspan of Airbus A340, but weighed a mere 1,600 kg (3,527 lb) thanks to its carbon fiber body.  By contrast a lean Airbus A340 weighs nearly 100 times that with an empty takeoff weight of around 129,000 kg.  Powered by four 10 horsepower brushless DC motors, that initial prototype was able to accomplish the first piloted day-to-night flight without fuel.

Seventy lithium polymer battery accumulators (weighing 400 kg total) can store 96 kWh of charge from the 200 sq-m of solar cells on the wings and tail.

Solar Impusl
The Solar Impulse HB-SIA flying in its record-setting 2012 Europe-to-Africa flight.

In 2012, that prototype completed a multi-leg trek from Switzerland to Morocco.

II. Building the Second-Gen. Impulse

Meanwhile the team was hard at work on larger successor, the Solar Impulse HB-SIB, which entered construction in 2011.  The wingspan was bumped from 63.4 meters (208 ft) to 72 meters (236 ft), and the weight capacity was up to 2,400 kg (5,291 lb), about the weight of the average automobile.  That's an incredible design, considering the wingspan rivals that of the 500-ton Airbus A380.

Aside from more solar power via a wider wingspan, the new model also had a pressurized cockpit and advanced avionics for trans-continental/trans-oceanic flights.  The new model could cruise at an altitude of 12,000 m (39,000 ft) versus 8,500 m (27,900 ft) in the previous design.  

The higher altitude allowed the plane to tap into faster jet currents, which begin at around 33,000 ft.  These currents should allow the craft to travel faster and conserve battery.

Solar Impulse designer
Robert "Röbi" Fraefel is heading the design of the second-gen. solar flier.

Bayer AG's (ETR:BAYN) Material Sciences division helped build the craft with its patented nanotechnology.  Additionally the craft uses lighter carbon fibers, which claim to have the highest strength-vs-weight ratios ever witnessed.  The HB-SIB is able to fly in the rain for the first time.

The second-generation model quadruples the battery capacity, to around 384 kWh.

III. Maiden Voyage

The current test flight, the third major trek for the HB-SIA, will pave the way for a 2015 attempt with the HB-SIB to circumnavigate the globe in 20-25 days, with six stops (and an average time aloft of 3 to 4 days between stops).  

Solar Impulse leg 1
Leg 1 of the Solar Impulse's coast-to-coast trip is in progress.

The current flight will also have five legs, each about a day.  The first kicked off today in San Francisco, Calif.  The craft will land tomorrow in Phoenix, Ariz.  Then in mid-May, the ultra-lightweight plane will begin the second leg of its trip, taking off in Phoenix and landing in Dallas, Tex. Toward the end of May, the third leg between Dallas and St. Louis, Mo. will be traveled, followed by the fourth leg to Washington, D.C.  Finally, the trip will end with a flight to New York City in late June or early July.

Bertrand Piccard and André Borschberg will trade off piloting responsibilities during the various legs of the trip.  Captain Piccard is piloting the current first leg.  Between each leg the craft will be checked over to make sure it's not damaged in any way.

Bertrand Piccard
Captain Piccard, Solar Impulse co-founder is piloting the first leg. [Image Source: Meteo]

The cruising altitude for the trip will be 6,400 m (21,000 ft).  A similar trek is planned for 2014 using the under-construction HB-SIB, incorporating the lessons learned from this third test flight.

Sources: Google Maps [Live Flight Map], Solar Impulse [Live Stream]

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