Solar Craft Flies Through Two Nights

An anonymous reader writes "A solar-powered, unmanned craft has flown for 54 hours — a record for both unmanned aerial vehicles and solar craft. None before has managed to store enough solar energy to fly through more than one night. There is also a video showing the 18m carbon fiber wing craft being launched."

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[stoolpigeon]

This BBC article has good info. [bbc.co.uk]
 
It should not be a surprise that the Global Hawk record did not stand. Look at the two craft. If a global hawk hit the zephyr it probably wouldn't even notice.

What constitutes Solar Power?

[mweier]

Obviously solar panels feed it to maintain energy stores; however since it must store this energy in a battery of some sort, is it required that the batteries be empty when launched? If not, what's to stop someone with a major pile of pre-charged solar-rechargeable batteries from tacking one solar panel on top & calling it a solar vehicle even if it could never fully charge those during use? Not accusing these folks of doing that but just curious about how they classify solar vehicles...

Re:An idea

[everphilski]

Depending on the time of year it wouldn't have to do that... you could have it do loops around the north or south pole at a much higher latitude and still get sunshine 24/7 (or damn near close) and not have to travel as fast as they would near the equator to keep up with the sun.

Re:What constitutes Solar Power?

[agingell]

The record in question actually has nothing to do with solar power. It is purely an endurance record for longest flight time under continuous power. The Global Hawk is actually powered by a turbojet engine and normal Jet A1 fuel.

Solar powered aircraft have been quite successful for some time for instance the Pathfinder and Helios aircraft by NASA the biggest issue is to get through the night on battery power. I believe the NASA aircraft had to resort to gliding and soaring which this aircraft does not.

A purely battery aircraft would fall out of the sky in a relatively short period of time, it would probably not even get to altitude before having to glide home.

Typically solar vehicles have to start races with the energy store empty however this is very unlikely in this case as they were just doing some tests. The flight tests all seem to end when there is an issue with the aircraft or the weather is not looking good. So it may well be the case that it would not be able to stay airborne indefinitely.

Talk about doing it the hard way

[Colin Smith]

Replace the wings with an envelope and you can stay up for weeks.

 

Re:An idea

[rleibman]

Speed of sound = 1225 km/h.

I am going to be pedantic and point out that the speed you give is at sea level, looking this up in wikipedia I read that the speed of sound in air is not heavily dependent on air pressure but more on temperature (it is slower as you go up since it gets colder).

At 29,000 the speed of sound is merely 1083 km/h.

Attaining altitude

[drwho]

Like many space and exotic aircraft, it must have to expend a lot of energy to get to its cruising altitude. Once that's done, conditions should become easier. Would it be considered 'cheating' to launch such a perpetual flying machine with an assistance device? That could be either disposable batteries that are jettisoned when discharged, or some chemcal rocket engine, or a jet engine, or have it launched from an aircraft.

Insolation is going to me much better at high altitudes. I just hope the photovoltaic cells are designed to take advantage of the increased amount of energy available in the UV spectrum. How about filling the free space in the wings with hydrogen? That might help lift a little, at least from the ground. However, there would have to be some way of dealing with the reduced pressure at operational altitude.

There's been a lot of interesting improvements in PV efficiency lately. However, most of these seem to only happen when the cell is operated at insolation far above normal. These are obtained by focusing the sunlight. Unfortunately, all of the technologies I know of which could do this are heavier than simply adding more, less efficient cells which operate at normal insolation or the slight improvement that high-atmosphere flight provides.