Sunday, April 21, 2013

Flying without fuel is cool!

We got to see the Solar Impulse this weekend, and I must say it is truly inspirational.  This is the solar powered airplane that has already been able to fly for more than 24 hours straight.. meaning aside from the issues of keeping the pilot awake, they can stay up as long as they want.   They will be flying the plane from here to New York City starting next month.
The challenge of building a plane like this is to find just the right combination of strength, weight and power to stay aloft without using traditional fuel.  To do this, they created a plane with the wingspan of a Airbus 340 jumbo jet (over 60 meters), but the weight of a small car.  As you can imagine, some advanced materials were required to pull this off.  The fuselage is made of carbon fibre-honeycomb composite  that is essentially two thin carbon fiber layers with what looks like light weight cardboard between them.  Bix is holding a piece of it in the picture on the right.  It is incredibly light and sturdy.
The wings and the tail are covered on top with solar cells (I'm holding six cells in the picture on the left).  Actually, that isn't quite accurate.  I should say, the tops of the wings and tail are made of solar cells.  The surface of the wing is composed of these solar monocrystalline silicon cells that are a mere 150 microns thick so they can be light weight, flexible, generate a lot of power and provide the necessary structural integrity for these jumbo jet-sized wings.  The cells are efficient enough to generate four electric motors humming along while completely charging the batteries.  This allows them to run down the batteries over night and then recharge them without landing during the day.  

There are four main batteries corresponding to each of the four main engines onboard the Solar Impulse.  Each of these batteries weighs about 90 kg (~200 lbs) and make up about one quarter of the weight of the entire plane.

A part of an incredibly lightweight wing rib
The single seat cockpit of the Solar Impulse
The motors on the Solar Impulse are approximately 10 horsepower each, or about the same as the Wright Flyer had back in 1903.  These motors are able to pull the Solar Impulse to its 22 mph takeoff speed and ultimately to its cruising speed of about 40 mph.  During the day, the power produced by the solar panel is enough to fully charge the batteries while it drives the motors enough to allow the plane to climb.  In the evening when the sun goes down, they plan to have enough altitude to glide.  Over a 5 hour period they are able to lose only 7000 ft.  Unlike traditional gliders, they don't do this by seeking thermals.  The turbulents associated with these up currents in the air don't mix well with such a large and fragile ship as the Solar Impulse.

In 2015, they are hoping to circumnavigate the world without using a drop of fuel.  At 40 mph, you can see that this will take quite a bit of time.  Even though the airplane can fly continuously, there is no real autopilot or automatic way of flying the plane and it only has room for a single pilot, so the human becomes the limiting factor.  They will have to land regularly in order to allow the pilot to sleep.  As you might imagine crossing the ocean will be a significant challenge.  It will take about 5 days and nights to fly across the Atlantic ocean.  In order to stay awake for this period of time, both the pilots, Bertrand Piccard and Andre Borschberg have special techniques they will employ.  They believe that through self-hypnosis and meditation they will be able to fly continuously for over 100 without real sleep.  The ground crew person that we spoke with about this topic said that they will allow them to have 8 - 20 minute cat naps.

Bertrand Piccard and Andre Borschberg

Both Bertrand Piccard and Andre Borschberg were there when we visited.  Mr Piccard gave a rousing speech about the importance of taking risks and trying things.  He should know.  His father was the first person to go to the bottom of  the Challenger Deep, in the Mariana Trench.  Bertrand himself has piloted a balloon around the world.  My favorite part of his speech was when he talked about trying go around the world three times.  He said the failures were learning experiences and that a success is a situation where you tried one more time than the number of times you failed.  Cool!  Mr Borrschberg then talked about the technical details of the plane and its planned flight.

Solar Impulse Specs

63.40m (208 ft)
21.85m (72 ft)
6.40m (21 ft)
Take-off speed
35km/h (22mph)
Average speed
70km/h (43 mph)
Maximum altitude
8,500m (27,900 ft)
Solar cells
4 x 10hp electric engine
1,600kg (~3500 lbs)

"For success, it is only necessary to try one tome more than the number of times you fail"